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The following is an archived discussion of a featured article nomination. Please do not modify it. Subsequent comments should be made on the article's talk page or in Wikipedia talk:Featured article candidates. No further edits should be made to this page.

The article was promoted by Laser brain 16:55, 8 February 2011 [1].

Rhodocene

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Rhodocene (edit | talk | history | protect | delete | links | watch | logs | views)

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Nominator(s): EdChem (talk) 13:50, 4 January 2011 (UTC)[reply]

I am nominating this for featured article because I would like to see more featured content relating to chemistry, because I am proud of the work I have done on this article to date, and because it is already a GA and would like to improve it further. This is my first FA nomination, so apologies in advance for whatever I get wrong. I recognise that my writing is overly technical at time, and welcome advice on areas needing further explanation / clarification. I also recognise that the images / structures could be redrawn to be sharper, but do not presently have access to the software to do the job. EdChem (talk) 13:50, 4 January 2011 (UTC)[reply]

Comments by Sasata (talk) 18:40, 4 January 2011 (UTC)[reply]

  • Hi EdChem. This is pretty hardcore stuff. I've taken organic chem at the graduate level, but I suspect it's going to take me a while to work through this article. At first glance, I think the lead needs to be made friendlier. Given this is a highly technical subject, it might be a good idea to target the lead for someone who's taken a first-year university chemistry class, and leave the nitty gritty details and jargon for the main article body.
  • Keep in mind the following policy: "A Wikipedia article should not be presented on the assumption that the reader is well versed in the topic's field. Introductory language in the lead and initial sections of the article should be written in plain terms and concepts that can be understood by any literate reader of Wikipedia without any knowledge in the given field before advancing to more detailed explanations of the topic" Sasata (talk) 07:08, 5 January 2011 (UTC)[reply]
  • My initial overall question is (reading the lead): so what? Why is this compound important? What's it used for?
  • if possible, avoid making consecutive (side-by-side) wikilinks (says the MoS); in the lead there are four in the first four sentences.
  • redox is linked twice (once as redox, once as reduction, which leads to redox). More later.
Thanks for your comments, Sasata. I have started reworking the lede in hopes of making it more accesible, though I think the WP:NOT goal of "can be understood by any literate reader of Wikipedia without any knowledge in the given field" is unrealistic given most college chemistry students study for at least two years before encountering organometallic chemistry. I am willing to work on improvements but this is a specialised area.
On "why", it's hard to answer without OR. It's too unstable for many applications though it is chemically interesting as a metallocene. There are oodles of applications for half-sandwich rhodocene species in catalysis, but that isn't strictly relevant. Theoretically, a substituted rhodocene of sufficient stability (like octaphenylrhodocene) could be a useful catalyst for a one-electron redox process, though there are others that already exist, and stating this would be getting a little speculative (as opposed to source-based).
I think your last two points have been addressed (in the lede) in my recent redraft. EdChem (talk) 16:09, 5 January 2011 (UTC)[reply]
I have added some comparison material on cobaltocene as a one-electron reducing agent, and also expanded on bonding in organometallic chemistry - rhodocene was a part of the investigations that allowed ferrocene to be figured out, opening up the metallocenes and leading to the '73 Nobel Prize in Chemistry. EdChem (talk) 21:12, 8 January 2011 (UTC)[reply]
  • several German-language source titles need a umlaut in "uber"
  • ref #7 (Zeise) should indicate German language (to be consistent with others)
  • ref 11 missing a year
  • refs 19 & 20 should show the German title
  • publisher location for refs 22, 23, 24, 35, 36?
  • page #'s for ref 29, 35, 36?
    • References 35 and 36 are used to support a general statement about research using metallopharmaceuticals, and the entire books are relevant; no specific page is being referenced. As for ref 29, I will need to check up on which chapter describes the oxidation states of rhodium in typical compounds and the eclipsed conformation of ruthenocene, though this information would be covered in any comprehensive textbook of inorganic chemistry. EdChem (talk) 03:24, 26 January 2011 (UTC) I have replaced reference 29 with a specialist text on precious metal chemistry where I was able to locate page numbers via google books. I have also replaced the reference for eclipsed ruthenocene with a ref already used which has page numbers. EdChem (talk) 01:32, 28 January 2011 (UTC)[reply]
  • isn't ref 33 ("Kolle" 1991) actually in German? And please check the spelling of the authors, there may be some umlauts required
  • Anything worth adding from these sources?
Title: OBSERVATION OF RHODOCENIUM AND SUBSTITUTED-RHODOCENIUM IONS AND THEIR NEUTRAL COUNTERPARTS BY MASS-SPECTROMETRY
Author(s): ZAGOREVSKII, DV; HOLMES, JL
Source: ORGANOMETALLICS Volume: 11 Issue: 10 Pages: 3224-3227 Published: OCT 1992
Title: ELECTROCHEMICAL REDUCTION PATHWAYS OF THE RHODOCENIUM ION - DIMERIZATION AND REDUCTION OF RHODOCENE
Author(s): ELMURR, N; SHEATS, JE; GEIGER, WE, et al.
Source: INORGANIC CHEMISTRY Volume: 18 Issue: 6 Pages: 1443-1446 Published: 1979

Support—I think the article is very good, and meets the FA criteria. Sasata (talk) 17:55, 28 January 2011 (UTC)[reply]

Query - Who is this article aimed at? Fasach Nua (talk) 21:01, 4 January 2011 (UTC)[reply]

Disambig/External Link check - no dabs or dead external links. --PresN 00:45, 5 January 2011 (UTC)[reply]

Thanks. EdChem (talk) 21:12, 8 January 2011 (UTC)[reply]

Comments by Canada Hky (talk) 03:28, 5 January 2011 (UTC)[reply]

  • I did the GA review on this article. As an analytical chemist, I always wondered when that graduate level organometallic class was going to come in handy, and I think this might be the moment. I can't foresee anything else.  :)
  • I'd like to see some of the application stuff, brief as it might be, in the lead. I don't think its possible to get organometallic chemistry down to the level of the average first year chem class, but "why" is always a good question to answer, even if it is just to say that they are mainly used for research.
  • More to come, after I get through everything.
I have added some of the application information to the lede, and also expanded the material in the body of the text. EdChem (talk) 07:45, 8 January 2011 (UTC)[reply]

Comments by SmartSE (talk) 15:47, 6 January 2011 (UTC)[reply]

  • Can you mention what an organometallic compound is in the first sentence, rather than in the second paragraph? I'd never heard of them before reading the article and it should be made clear what the article is about ASAP.
  • Similarly an explanation of paramagnetic and diamagnetic in the lead would also be useful.
  • "liquid nitrogen temperatures" why not just say -200°C (or whatever it is)?
  • Maybe explain that ferrocene is the same as rhodocene but with iron instead of rhodium.
  • Changing "Cyclopentadienyl" to something more wordy, e.g. two rings of five carbon atoms and five hydrogen atoms might be useful.
  • Is there anywhere metallopharmaceutical could be directed to? If not maybe just write pharmaceuticals containing metals or something similar.
  • Would it be possible to make the illustrations as .svgs? They look a lot better than .pngs as they aren't grainy. If you can't DIY, then Edgar181 may well be able to help out. (I'm not sure if this is an FAC criteria or not and it may well not be).
  • Could you add a diagram of ferrocene to the history section?
  • I'll try to come back and give it another read if you like, as a scientific but relatively chemically incompetent reader.
  • I am concerned about trying to define 'organometallic compound' in the first sentence, because I think that the first sentence should focus solely on the definition of 'rhodocene'.
  • I have added diagrams to the history section.
  • Thinking about response to other comments, more to come later. EdChem (talk) 07:45, 8 January 2011 (UTC)[reply]
  • The terms 'paramagnetic' and 'diamagnetic' are not easily defined in a few words for readers not familiar with chemistry, and the key point being made in the lede in this section is that rhodocene exists in a monomeric form at very low temperatures and in gas phase, but in a dimeric form in between. The electron count information will point to paramagnetism of the radical for experienced chemists, and the terms do not add much for readers unfamiliar with the concepts anyway. So, I have redrafted the lede to emphasise the key point and removed the terms that could be confusing, leaving them only in the body text where they are wiki-linked to articles which explain the concepts in detail. EdChem (talk) 08:35, 8 January 2011 (UTC)[reply]
  • On 'metallopharmaceutical', Boghog has created a stub with this title following my seeking a suitable article at Wikipedia talk:WikiProject Pharmacology. I have added some general books on the topic as other reading, and have then added references on metallopharmaceuticals and rhodium in medicine to the relevant rhodocene section. This includes noting that compounds incorporating the isotope in question (103mRh) have been proposed elsewhere for use in small tumour radiotherapy. EdChem (talk) 11:42, 8 January 2011 (UTC)[reply]
  • Following on from the comment below from Hchc2009 and the suggestions above, I have worked the definition of organometallic compound into the first paragraph, and removed it from the lede sentence. I have also noted the analogue between ferrocene and rhodocene in the first paragraph.
  • The reason for using "liquid nitrogen temperatures" as I think this is more evocative of really cold than an actual number - scientists will know what −196 °C is like but I think most non-scientist readers would have no real picture in their mind of what −196 °C is like (as opposed to, say, −96 °C). So, I chose an expression I think is evocative for a non-expert reader. I would be interested in the views of others as to which is more useful in the context of the article introduction. EdChem (talk) 12:26, 8 January 2011 (UTC)[reply]
  • Thanks for making the changes, the lead is looking a lot better now. I think it might be useful to say (-196°C) after liquid nitrogen, so that a reader doesn't have to click that link to find out how cold it is. I agree that this allows those who already know how cold liquid N is to know, but if you don't know about that, it is more confusing than a standard temperature. SmartSE (talk) 19:54, 8 January 2011 (UTC)[reply]

Comments

  • The only concern is the PhD thesis - how long is it and should we have page numbers if it's longer than about 50 pages? Also, is it cited by other reliable sources or has it been ignored? Or better yet, did the author expand his thesis afterwards and get the revised paper published elsewhere? It's not a huge concern, but generally theses are not cited a lot in wikipedia, and it'll need to fulfill the "high quality" part of the FAC requirements.
  • Need to note that current ref 1 (Federman) needs a subscription to access it.
Otherwise, sources look okay, links checked out with the link checker tool. I ran the article through Coren's tool and Earwig's tool and nothing showed up in regards to plagiarism with those tools. Ealdgyth - Talk 18:05, 7 January 2011 (UTC)[reply]
Regarding the He thesis, I have added a link to the library record, which is here. The thesis is described as 271 leaves, which I guess makes it 271 pages. I can look for page numbers of the actual syntheses and note the characterisation data provided (which, I'd guess, would be IR, melting point, NMR, MS). I don't know of it being cited elsewhere or published, but I do happen to know of its existence. The data that backs it establishes that the syntheses were completed successfully and the chemistry of the syntheses is quite typical of these systems, so I do not doubt the veracity of the statements made. USyd is an internationally known research university, they do not hand out PhD's without proper examination by suitable experts, so I believe the information is reliable and to omit it when its existence is known and verifiable would be to decrease the completeness of the coverage. If the area were one where publications are common then its inclusion could be a case of undue weight, but it is not and I think this is a case where a thesis from a reputable institution is a suitable source. EdChem (talk) 07:45, 8 January 2011 (UTC)[reply]
I have removed the url from the Federman ref (currently ref 1) as it links to the same place as the existing doi link, so it was redundant. EdChem (talk) 07:49, 8 January 2011 (UTC)[reply]
I'm going to leave the stuff about the PhD thesis out for others to satisfy themselves, but I'm fine with it being a reliable source. Ealdgyth - Talk 14:50, 8 January 2011 (UTC)[reply]

Comments

  • I came to this article without a chemistry background, and thought the writing was generally clear and accessible. A lot of it was relatively technical, but it was clear and relatively easy to work through. Nicely done.
  • I think some more work still needs to be done on the first paragraph of the lede. In particular, I'm not sure it entirely complies with the MOS requirement that "Where uncommon terms are essential to describing the subject, they should be placed in context, briefly defined, and linked. The subject should be placed in a context with which many readers could be expected to be familiar.... Readers should not be dropped into the middle of the subject from the first word; they should be eased into it." I think this is really important for the first paragraph of the lede, which will confuse an awful lot of readers.
  • To demonstrate what I mean... Having read the article, if I had to explain the topic to someone else, I'd probably start off with something like this:

e.g. "Rhodocene is a chemical compound containing rhodium, carbon and hydrogen atoms, with the formula [Rh(C5H5)2]. Rhodecene is classed as an organometallic compound because it contains both metal and carbon atoms. Within a rhodocene molecule, a rhodium atom is "sandwiched" between two parallel rings containing carbon and hydrogen atoms; these rings are called cyclopentadienyl complexes. This molecular structure is typical of the subset of organometallic compounds called metallocenes to which rodocene belongs. Rhodocene has several interesting characteristics..."

  • ...I've probably made some errors in that (!), but it gives a sense of what I could draw from the lead as a non specialist, and where I think the article needs to give a typical reader a leg up - referring back to phrases like "chemical", "atom" etc. that a non-scientific reader is more likely to recognise.
  • Incidentally, there's a extra blank line in the "history" section I think.
  • Hchc2009 (talk) 10:40, 8 January 2011 (UTC)[reply]
Thanks for your comments, I'll try a draft along the lines you suggest and see how it comes out. Incidentally, though you are correct that your draft includes a few errors, I am grateful for your draft as it shows me where a non-expert might misinterpret what I have written. EdChem (talk) 11:42, 8 January 2011 (UTC)[reply]
Cheers! Hchc2009 (talk) 12:07, 8 January 2011 (UTC)[reply]
May I ask that you have a look at the version now? Thanks. EdChem (talk) 12:26, 8 January 2011 (UTC)[reply]
  • Of course. I think the opening reads better, and I can also see where I previously misunderstood it (which is good!).
  • One final thought. On the final sentence of the first paragraph, can I check that I'm getting the meaning right?
  • Repeating the same exercise as above: "At relatively high and very low temperatures, rhodocene takes the form of a gas, [Rh(C5H5)2], a 19-valence electron, highly reactive radical. At room temperature, however, pairs of rhodocene molecules combine to form a (more stable?) 18-valence electron ansa-metallocene structure, [Rh(C5H5)2]2."
  • What I most wanted to confirm was that I understood the use of the term gas phase (i.e. that this means it is a gas - I'd clicked on the link, and that was the conclusion I drew); that the gas state applied to the low temperature state as well, and that I'd understood the dimerising verb properly! There's a link you could give to ansa-metallocene perhaps. Hchc2009 (talk) 12:50, 8 January 2011 (UTC)[reply]
  • No, gas-phase does not apply to below liquid nitrogen temperatures. What it means (in practice) is that it dimerise unless it is really really cold, or it is in gas-phase where the molecules are well separated. In liquid nitrogen it is almost certainly a solid. EdChem (talk) 13:32, 8 January 2011 (UTC) PS: Thanks for the link to ansa-metallocene, I had not noticed the creation of this article.  :)[reply]
Thanks. My advice would be to expand the "dimerises" verb in that first paragraph (e.g. perhaps "however, at room temperature, pairs of rhodecene molecules combine, or dimerise, to form..."), as it is crucial to understanding that bit of the paragraph (even if a reader doesn't understand what a radical is, for example, they can sort of understand that its a quality or attribute of rhodocene of some sort; because dimerise is the key verb in that part of the paragraph, though, it will really throw a reader off track if they don't know what it means, and I'm guessing most won't). Support, by the way! Hchc2009 (talk) 18:19, 8 January 2011 (UTC)[reply]
I've further tweaked the language in that part of the lede. EdChem (talk) 21:12, 8 January 2011 (UTC)[reply]
On Why

I have made a series of changes to the lede and history section of the article, and think that the question of why / who cares is now more clearly addressed. In describing the history of the compound and of organometallics, I have highlighted two compounds (Zeise's salt and nickel tetracarbonyl) that could not be explained by existing bonding models until a new model was postulated in the early 1950s. Ferrocene was discovered around the same time, and also posed a problem for bonding models. Investigations of rhodocene, cobaltocene and other metallocenes led to understanding of this new class of compounds, which ultimately led to the 1973 Nobel Prize for Wilkinson and Fischer. Rhodocene has turned out to be much less stable than cobaltocene, and so has not been used in applications that cobaltocene has, but at lesat one rhodocene derivative have been investigated for use in medical applications. Rhodocene also shows some interesting behaviour (dimerisation and protonation) described in the structure section that is not common in metallocene systems, making it of intellectual interest to those who have an interest in organometallic chemistry. I have not added anything on half-sandwich rhodium complexes as catalysts because it is not strictly relevant to the rhodocene article, though there has been a lot of research on the subject. I hope these reasons now come across to readers in the redrafted version. Thanks. EdChem (talk) 19:33, 9 January 2011 (UTC)[reply]

Question Is this used for anything? Is it present in anything? Is it related to anything that is present in anything? Anything? Although my questions and comments are always ignored, because I'm not part of the in-crowd here, I am tired of FAs on the main page that leave me fighting to figure out what it is, or tell me that it's something it isn't (at least this article might not have the latter problem). I will repeat this comment, possibly, when the gobbly goop is on the main page, and I expect to be ignored then also. --Kleopatra (talk) 15:29, 11 January 2011 (UTC)[reply]

Kleopatra, I welcome any and all comment, so thanks for stopping by. Just FYI, this is my first FA nomination and I think I have commented on maybe one other FA nom in the past, so I'm not part of the in-crowd... I don't even know who the DYK in-crowd is. To try to answer your question... when ferrocene was reported in 1951, it was another of the real puzzles offered by organometallic chemistry. The composition C10H10Fe was easily confirmed but made little sense it terms of the developed knowledge of bonding, especially in light of its remarkable stability. Even when the Dewar-Chatt-Duncanson model was proposed it still did not explain ferrocene. Consequently, intense work began to establish (a) what ferrocene was and (b) what produced its observed properties. This work included structural studies (like X-ray structures), derivatising reactions (demonstrating the aromatic behaviour was similar to benzene) and the synthesis of analogues with other metals, including cobaltocene and rhodocene. Both cobaltocene and rhodocene turned out to be unstable (rhodocene very extremely so) but both had high stability +1 cations - which points strongly to the importance of the 18-electron structure. Understanding metallocenes, which this was all part of, was the reason for the award of the 1973 Nobel Prize in Chemistry. Rhodocene might seem of low importance now, but it was all part of the picture that explained ferrocene, and that was a landmark addition to chemistry. Cobaltocene has gone on to be a useful one-electron reducing agent, but rhodocene has turned out to be way too unstable for this application, and even derivatised rhodocenes have yet to demonstrate sufficient stability. As the article states, one biomedical application has been reported, which was the radioactive ruthenocyl-haloperidol system that decays to a rhodocene system and was investigated for anti-tumour applications. On its own that application would be a "who cares?" but it is relevant to the discussion of the rhodocene system. Rhodocene itself also demonstrates some unusual structural behaviour (dimerisation and redox protonation) to attain 18-electron structures, which of at least of intellectual interest to organometallic chemistry (I think). The one-pot synthesis with 20 new carbon-carbon bonds is something not seen frequently in chemistry either, and it is a lovely illustration of the ability of a metal centre to influence the acidity of ligands. Ordinary pentamethylcyclopentadienyl anions are not vulnerable to deprotonation, yet coordinated to a rhodium centre each of the five methyl groups can be deprotonated twice to make pentaisopropylcyclopentadienyl ligands. Yes, this is specialised material. No, it isn't going to matter a damn to the everyday person walking along the street. Does that mean that it is unworthy of an article or of FA status? I don't think so. Maybe it should never go on the main page - that's not for me to decide, nor is it the topic of discussion now. I would welcome suggestions as to how to make some of the above clearer in the article, if you think that is necessary, or any other improvements that can be made. Thanks. EdChem (talk) 16:04, 11 January 2011 (UTC)[reply]
I will read this in depth later, but, really, if you were going to tell me one paragraph of information, me, a non-chemist, something about this, wouldn't you say why it was discovered, why it was worked on (hopefully would reveal information about something else), how it turned out to be unstable and not particularly useful, but that it might have a specific application, and it's this type of chemical molecule, then go on and on about its chemical properties, the most important and unique ones first, its placement in its class well emphasized? --Kleopatra (talk) 16:24, 11 January 2011 (UTC)[reply]

Round two from SmartSE (talk) 21:51, 23 January 2011 (UTC)[reply]

  • Should it say "the chemical formula" in the first sentence?
  • I find the 18-electron valence etc. in the lead a bit heavy. Could it be simplified just to say it is a monomer at low and high temperatures and a dimer at RTP? Alternatively you could explain a bit more about what the valences mean.
  • In the lead, would "unable to rationalise their formation" be better as "unable to explain their formation"?
  • You say that some compounds have potential medical uses, but it isn't clear why the binding to different tissues is useful, does the ref mention this?
    • Binding to different tissues is useful for targeting tumours in different organs. For example, iodide binds in large quantities in the thyroid, which makes it ideal for targetting thyroid tumours. However, it is virtually useless for other tumours because a susbstantial dose of radiation will be given to the thyroid whether there is a tumour there or not. Suppose the idea of the haloperidol species was to accumulate in the brain - in that case, binding to lung but not brain tissue would be unhelpful. Alternatively, if the goal was to target lung cancer then binding lung cells but not brain cells is helpful. Studies like these often start by just observing what binds where and going on from there. I am not sure what you feel I should add to clarify on biomedical applications. Should I add something like "(potentially useful for targeting tumours in the lungs)" into the lede? EdChem (talk) 03:06, 28 January 2011 (UTC)[reply]
      • Yea, that's the sort of thing I was meaning, I happen to have some idea of why it might be useful, but readers may not. Does the paper mention it though or not? I saw that the abstract doesn't, but I'd imagine that the full version would. Thanks for the reminder btw. SmartSE (talk) 14:28, 28 January 2011 (UTC)[reply]
        • Sorry, I didn't mean to waste your time with unnecessary explanations. As far as I can see, the article mentions the benefits of the short half-life and the ease of separation, and notes concerns that the gamma ray is low energy, but does not explicitly note the benefits of organ specificity. EdChem (talk) 15:14, 28 January 2011 (UTC)[reply]
  • That's all from me for now. It's a great deal better than it was before - well done!

Further comments from Canada Hky (talk) 16:07, 24 January 2011 (UTC)[reply]

I got away from this for a while, but have a few more comments. I think the article is very close to being as accessible as possible to the layman. While it is a noble goal, even a principle of Wikipedia to make articles accessible, I think it needs to be acknowledged that subjects which people study individually for years in graduate school just may not reach that level. I think the lead as it is written now makes it clear to a layman what they need to know about rhodocene - what it is, what its used for, and that it isn't an everyday subject.

  • In "History" - "The space-filling model of the anion of Zeise's salt (image at left)[21] clearly shows that it is an organometallic species as there is direct bonding between the platinum metal centre" the "as there is" seems a bit off. Possibly, "...(image at left) shows direct bonding between the metal centre (platinum) and carbon (ethylene ligand) characteristic of an organometallic species..." Or maybe I am completely wrong. Just something to consider.
  • Just to clarify - have you written out the element name in all cases when discussing oxidation states?
  • In "Synthesis" - you use "Cp" in the chemical formula - good for me, but as a non-standard abbreviation in a chemical formula, it might cause troubles, or confusion. Why not just use C5H5? Similarly - the link the Methyl for the first use of Me is good, but I missed it in the formula the first couple times through. Why not define it off to the side similar to M = Ni...?
    • As far as I can see, Cp only appears in the text as CpMgBr immediately following the name cyclopentadienylmagnesium bromide. I have wiki-linked the Cp to cyclopentadienyl. The article names in the refs include the use of Cp so I see having it in the article somewhere as useful, but will change it to C5H5MgBr if you prefer. I have used Me for methyl in numerous places, mostly as C5Me5 (or Cp*) ligands because it emphasises the cyclopentadienyl rings, also seen in the C5Ph5 and C5iPr5 systems. Using formulae like C5{CH(CH3)2}5 or C5(C6H5)5 are more likely to be confusing, in my opinion. EdChem (talk) 00:52, 26 January 2011 (UTC)[reply]
      • The single usage of "Cp" was one of the reasons why the abbreviation seemed unnecessary. You've called it cyclopentadienyl when you named it, the chemical formula should then show the chemical formula. I suppose you could define Cp = C5H5, but with the single usage, it would be better to just be explicit. I need to think about about the Me usage a bit more. Canada Hky (talk) 03:52, 26 January 2011 (UTC)[reply]
        • I have changed CpMgBr to C5H5MgBr, as requested. EdChem (talk) 04:13, 26 January 2011 (UTC)[reply]
          • Good on that one, as far as the Me - I wasn't meaning to suggest removing it, rather defining it in the text the first time it appears, similar to any other non-standard (unfortunately, organic chem is non-standard to the masses) abbreviation.
  • I'm not sure how to work it in, perhaps the link the hapticity is good enough, but the "eta" symbol just kind of appears. If it could be introduced in the section along with hapticity, I think the next few sentences would be clearer.

Support - After those comments have been addressed, and reading through the responses to other's concerns, I really like how this article has progressed, and think it meets all the criteria. To comment on the referencing issue regarding a Ph.D. thesis, I would think it's a reliable source. It is nice to know someone reads them after they get put on a shelf in the library. Canada Hky (talk) 01:57, 28 January 2011 (UTC)[reply]

Support by Ruhrfisch comments Seems very well done to me (but I am familiar with the subject, so I cannot easily comment on its accessibility to an interested lay person). I am reading through the article and making nit-picky comments and suggestions as I go - leaning toward support, but need to read the whole article carefully.

  • In the Lead, should the formula of ferrocene follow its first mention (currently given after the second mention)? Might make the analogous structure clearer to give the formula right away
  • Similarly, would it help to add the formula [Rh(C5H5)2]+ after the unipositive cations statement in the lead?
  • Cobaltocene should be linked on first mention in the lead (now linked on second mention)
  • In History I would explicitly say that [Ni(CO)4] is metal carboyl in ...the model was expanded over time to cover systems like metal carbonyls where π backbonding is important.[24] perhaps something like ...the model was expanded over time to cover systems like metal carbonyls (including [Ni(CO)4]) where π backbonding is important.[24]
  • Why not name the lead author in the X-ray structure of ferrocene? Using just "the third group" seems short shrift.
  • I would say here that both have 18 valence electrons This observation is not unexpected given that the cobalticinium cation and ferrocene are isoelectronic, although the bonding was not understood at the time. and not just that they are isoelectronic.
  • In Structure I would explicitly mention the rhodicinium cation in the first sentence, so something like ...this explains the unusually high stability observed for ferrocene[9] and for the cobalticinium [and rhodicinium] cation[s].
  • Would it help to give the valence electron count for the dimeric form in the first paragraph (currently in the second paragraph)?
  • Would it help to briefly explain the differing hapticities of the ligands - all 5 carbons in the planar Cp ring coordinated to the Rh, vs only 4 in the cyclopentadiene ligand?
  • I am not sure most readers would get that (η4-Cyclopentadiene)(η5-cyclopentadienyl)rhodium(I) in the last sentence of this section is the compound whose formmula is given in the preceding sentence.
  • In Synthesis "with only 30 seconds of microwaving" seems a bit colloquial in the reaction yield exceeds 60% with only 30 seconds of microwaving.[31] how about something like the reaction yield exceeds 60% after only 30 seconds in the microwave oven.[31]?
  • In Substituted rhodocenes and rhodicinium salts, would it help to somehow identify 1,2-dimethoxyethane as the solvent at the end of the first paragraph?
  • Needs a ref: These reactions demonstrate that the acidity of the methyl hydrogens .... and the resulting carbanion undergoing nucleophilic substitution with methyl iodide to form a new carbon-carbon bond.
  • Also needs a ref and its redox couple is sufficiently well behaved that it may be used as an internal standard in cyclic voltammetry. (I am not asking for a ref for the following sentence that no substitued rhodocene has yet been used in a similar way, though if you have one, please do add it.
  • In Use of a rhodocene derivative in biomedical research, There has also been substantial research using metallocene derivatives of ruthenium[37] and iron[38] as metallopharmaceuticals. is the second sentence in a row to start "There has [also] been..." so could it be tweaked, perhaps to something like A substantial body of research has examined using metallocene derivatives of ruthenium[37] and iron[38] as metallopharmaceuticals.
  • Shouldn't it be "rhodicinium" not "rhodocenium" in ...and rapidly oxidises to the expected cationic rhodocenium-haloperidol species.[19]?
    • Wait, never mind. But I think that rhodocenium should be explained in some way, even though it is only mentioned twice.
  • Wikilink half life?
  • Why are some isotopes in the format superscript number preceding element symbol, while others are element name hyphen number (too lazy to format it, but copy and pasted an example is Beta- and gamma-emiting radionuclides used medically include iodine-131, iron-59, and calcium-47, and 103mRh has been proposed for use in radiotherapy for small tumours.[18]
  • General comment - per WP:HEAD the headers should avoid repeating the name of the article if at all possible. Not sure how to do this with "Substituted rhodocenes and rhodicinium salts", but could "Use of a rhodocene derivative in biomedical research" be made simpler? Perhaps "Use of a derivative in biomedical research" or even "Biomedical use of a derivative"? Your call.
  • I just re-read the lead and it is fairly technical, but as noted above, I am not the best judge of its accessibility for someone who is not familiar with the subject.

Overall very nicely done - I am very close to supporting, but would like to see the responses to my other points first. I also made a few copyedits - please revert if I made things worse or introduced American English into a British English article. Ruhrfisch ><>°° 02:18, 26 January 2011 (UTC)[reply]

Oppose until some points are solved. It reads well, but I think the article misses on some key issues:

  • rhodicinium needs some explanation for non-experts
  • [(η5-C5H5)Rh(η4-C5H6)], the "protonated rhodocene"[3] that forms when the monomeric form of rhodocene is generated in solution makes no sense. shouldn't it be hydrogenated rhodocene? and what kind of solution? protic?
    • Butting in - at the risk of telling Nergaal things s/he already knows, here is how I understand it. The cyclopentadienyl ligand, C5H5-, is an anion which has 6 pi electrons (so it is aromatic, like benzene with its 6 pi electrons). When it becomes "protonated" it really only gains a proton (H+) to become neutral cyclopentadiene, C5H6. I tend to think of hydrogenated as adding either molecular hygdrogen (like H2 across a double bond in an alkene) or a hydrogen atom (with its one electron). Ruhrfisch ><>°° 02:05, 6 February 2011 (UTC)[reply]
      • The picture shows an H• addition, not H+. If it was H+, then it would have been [CpRh(C5H6)]+, a cation.
        • I may be wrong, but let me try to explain my understanding in more detail. I assume by "the picture" you mean File:Protonated rhodocene.svg, which shows the compound which results from two reactions, a protonation and a reduction. The word "protonated" appears in the article only three times - once in the caption of the image of the protonated rhodocene, and twice in the adjoining paragraph. This paragraph mentions aqueous solution and it makes sense to me that the proton could come from water. Since monomeric Rhodocene is a 19 electron compound, protonation would initially make a cation, and the resulting change to an eta-4, 4 electron donor cyclopentadiene ligand would reduce the electron count by 2, to 17. The Rh then gains an electron to reach the stable 18 electron count (and adding a negative electron to a cation makes a neutral compound). The article says Acting as a 4-electron donor, the formation of cyclopentadiene has reduced the electron count of the species by 2, and an 18-valence electron species is not formed until the rhodium centre gains one electron to become a rhodium(I) structure.[4] I have not looked at the original article, but can if you want. I hope EdChem weighs in here soon to clarify things. Agreed that these sentences could be clearer. Thanks, Ruhrfisch ><>°° 04:25, 6 February 2011 (UTC)[reply]
          • doi:10.1021/om00053a Nergaal (talk) 10:21, 6 February 2011 (UTC)[reply]
          • doi:10.1039/JR9590003753 call it bis-Cp rhodium hydride. Nergaal (talk) 10:27, 6 February 2011 (UTC)[reply]
          • NB: I have sent a copy of the paper in German to Ruhrfisch and await his input. EdChem (talk) 18:17, 6 February 2011 (UTC)[reply]
  • the intro should make a clearer distinction between the monomer and the dimer (i.e. the compound is stable as a dimer only at room temperature, and the radicalic monomer only at low or high temp)
  • are the 10 Rh-C bonds in the monomer exactly equal in the crystal structure? how long are they?
    • I have added data on a crystal structure of a substituted rhodocenium salt showing the Rh-C bonds are essentially equal and average about 2.17 Å. I don't know of any crystal structure of the monomer itself. An image of the crystal structure for the cation in question is being prepared by Edgar181, and should be added to the article within a day. EdChem (talk) 18:17, 6 February 2011 (UTC)[reply]
    • I have also provided data on the octaphenylrhodocene crystal structure, with comparisons. EdChem (talk) 20:50, 6 February 2011 (UTC)[reply]
  • what is the redox couple of Rc+/Rc? how does that compare to the cobaltocenium/cobaltocene one?
  • the article compares the compound to ferrocene in detail, but tends to ignore comparisons to cobaltocene, and says absolutely nothing about iridocene (is the latter known?)
    • Iridocenium salts are reported along with the rhodoceniums, with broadly similar properties - I will add some comments to that effect. EdChem (talk) 06:58, 6 February 2011 (UTC)[reply]
    • I have added a paragraph on iridoceniums at the end of the speciation section. EdChem (talk) 09:26, 6 February 2011 (UTC)[reply]
      • do they say anything about its redox potential? Nergaal (talk) 10:01, 6 February 2011 (UTC)[reply]
        • The paper that reported the −1.53 V reduction reports that the iridocenium to iridocene reduction could not be detected. Other papers (such as El Murr) compare cobaltocene and rhodocene but not iridocene. I still want to see if I can find the iridocenium / iridocene redox couple. EdChem (talk) 18:17, 6 February 2011 (UTC)[reply]
          • Looked again - still haven't got the iridocenium / iridocene couple, but I have added the pentamethyliridocenium / pentamethyliridocene and decamethyliridocenium / decamethyliridocene couples, which I think illustrate the point sufficiently.
  • the article completely lacks a physical properties section. melting point? color? solubility?
  • is the structure of the dimer correct? I would have thought that the fused Cp's have the H in the "endo" position (i.e. H is inside, the other Cp on the outside)

Nergaal (talk) 09:31, 29 January 2011 (UTC)[reply]

  • Looks exellent to me on a surface reading; interested to see you and Nergaal work through those points. Compounds and bonds should take an en dash rather than a hyphen, shouldn't they? rhodium–carbon bonds; a rhodocenyl–haloperidol compound; metal–carbon bonds, etc. Tony (talk) 11:41, 2 February 2011 (UTC)[reply]
Apologies for my slow response, but there are a few things going on for me here. The first is that my time over the last two weeks has been limited and stressed by the unexpected surgery on my dog, followed by an unanticipated diagnosis of stage 5 malignant lymphoma (unanticipated as the vet's comments had not even canvassed the possibility of lymphoma). One consequence of this has been my dealing more3 with what is easy rather than what is hard. On the questions relating to protonation, the source is in German, which I do not speak. It is some years since I originally went through this literature and at that time a colleague was a German speaker. So, trying to answer the question is challenging. My recollection is that protonation was the term used by the authors, but I have yet to confirm this recollection/ I agree that the reaction is clearly more than a protonation, but I concur with Ruhrfisch's concerns about the use of "hydrogenation". Some redrafting of the section is clearly needed to address the concerns raised, but I am as yet unsure of a clearer wording that I am confident is backed by sources. Ruhrfisch's comments sound reasonable (and presuming an oxidation of the solvent to allow the reduction of the metal centre) but I want the content to be source-based (as do we all, I'm sure). Regarding Nergaal's other comments, I have found a recent(ish) paper with a crystal structure of a substituted rhodocenium cation and redox data, and plan to add info to the article to addres other concerns. I have requested Edgar181 to draw me a diagram to accompany the text (see Edgar's talk). So, there is activity, albeit slower than I would prefer. EdChem (talk) 06:51, 6 February 2011 (UTC)[reply]
I am very sorry about uour dog. My posts above on protonation were based solely on trying to make sense of what is in the Wikipedia article. I do not have access to that issue of The Journal of Organometallic Chemistry, but do read and speak German fairly well. My email is enabled so if someone who has the journal emailed me, I could email back and the journal article could be sent to me, I could read the relevant part and provide a rough translation on the talk page here or for the article. Ruhrfisch ><>°° 13:53, 6 February 2011 (UTC)[reply]
Thanks. I have emailed you. EdChem (talk) 14:18, 6 February 2011 (UTC)[reply]
I have read the whole article and given a rough translation of the relevant paragraph at Wikipedia talk:Featured article candidates/Rhodocene/archive1. Will be away from my computer for the next several hours for a certain American football game ;-) Ruhrfisch ><>°° 22:30, 6 February 2011 (UTC)[reply]
Thank you, Ruhrfisch - very helpful... I have made some redrafts based on the new information, see what you think.  :) EdChem (talk) 23:44, 6 February 2011 (UTC)[reply]
You are very welcome - it looks good to me. I fixed a typo in the caption and tweaked the changed text to make it a bit clearer that Fischer et al. published no information to support their reduction followed by protonation theory (before it sounded a bit like no information had ever been published on it). The synthesis of the mixed-hapticity ligand Rh complex sounds pretty straightforward, so it seems likely to me that someone has made it again since 1966. Ruhrfisch ><>°° 02:47, 7 February 2011 (UTC)[reply]

OK, Update... I have made all the significant changes that came up in investigating Nergaal's comments, including adding a new application. What is left (as far as I am aware, and providing no further suggestions are made (which they can be, of course)) is:

  • the image of the crystal structure of the 1,2,3-tri-tert-butylrhodocenium cation has yet to be added - Edgar181 has offered to make this image
  • I added two new images in the added application section that need to be vectorised - I have made a request for this to be done
  • I am looking forward to feedback on the changes relating to "protonated" rhodocene from Nergaal, plus any comments on the added sections (new application, cation structure, comparisons to iridocene system, added redox data).

Here's hoping we are now on the final stretch.  :) EdChem (talk) 04:28, 7 February 2011 (UTC)[reply]

    • The article looks good now as far as I am concerned. There are probably a few more tweaks that could be made from an inorganic chemistry perspective, but the article is good enough to deserve to become an FA. The only minor tweak I would still like to see (unless it I missed it) some sort of experimental evidence for the monomer having a five-fold rotation symmetry axis (either D5h or D5d). It is not surprising that the substituted versions, or the cations do that; the simple monomer (which the article is about) might not quite be (and instead be Cs), and if that is the case, it should be in. Nergaal (talk) 17:23, 7 February 2011 (UTC)[reply]
      • The same Fischer et al. paper I translated above addresses this. On page 562, second paragraph, it says that the monomer produced by reduction of the rhodocenium PF6 salt with alkali metal is brown-black when collected on a liquid-nitrogen-cooled cold finger (it sublimes there). If allowed to warm up, it becomes the yellow dimer in less than 5 minutes, but if the reaction is done in a special small quartz reaction chamber and the monomer is transferred cold to an ESR (EPR), then ESR proves it is a paramagnetic, monomeric "dicyclopentadienylrhodium(II)". The sample shows 2 g factors. The compound has a high order symmetry axis (so Cn with n > 2) with a plane of symmetry (mirror plane, sigma) perpendicular to it, so thus it is a genuine "sandwich" structure. Ruhrfisch ><>°° 19:32, 7 February 2011 (UTC)[reply]


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