Field of Science

A history of metallocenes: Bringing on the hashish

Following on the heels of the comprehensive article on metal-catalyzed reactions noted by Derek, here's another one by Helmut Werner specifically about the history of ferrocene and other metallocenes. It's got lots of interesting trivia about priorities, personalities and chemical developments. The article traces early priority disputes in the discovery of ferrocene followed by an account of the rush to explore other metal-organic systems.

It's hard for us today to imagine the shock that was felt on witnessing the existence of the first sandwich compound, a complex of iron sandwiched between two cyclopentadienyl rings. Before ferrocene the division of chemistry into inorganic (especially metallic) and organic compounds was assumed to be virtually set in stone, and this was one of those classic developments that shatters the mirror between two realms. The world of transition metal-mediated chemistry that the discovery inaugurated completely transformed the academic and industrial practice of chemistry, led to several Nobel Prizes and turned out to be one of the most beneficial scientific developments of the latter half of the twentieth century. 

The novelty of the new compound is best captured by what must surely be the most memorable reply sent by a journal editor to a submitting author, this one being from Marshall Gates (the editor of JACS) to R. B. Woodward:

"We have dispatched your communication to the printer but I cannot help feeling that you have been at the hashish again. 'Remarkable' seems a pallid word with which to describe this substance"

Perhaps the most extraordinary part of the story is the candid and rather dramatic note from Woodward to the Nobel committee lamenting his exclusion from the 1973 Nobel Prize awarded to Geoffrey Wilkinson and Ernst Fischer.

"The notice in The Times of London (October 24, p. 5) of the award of this year's Nobel Prize in Chemistry leaves me no choice but to let you know, most respectfully, that you have - inadvertently, I am sure - committed a grave injustice"

Woodward went on to rather pointedly emphasize his individual contributions to the discovery, making it sound like he had done Wilkinson at least a minor favor by putting his own name last on the manuscript. 

"The problem is that there were two seminal ideas in this field-first the proposal of the unusual and hitherto unknown sandwich structure, and second, the prediction that such structures would display unusual, "aromatic" characteristics. Both of these concepts were simply, completely, and entirely mine, and mine alone. Indeed, when I, as a gesture to a friend and junior colleague interested in organo-metallic  chemistry, invited Professor Wilkinson to join me and my colleagues in the simple experiments which verified my structure proposal, his initial reaction to my views was close to derision . . . . But in the event, he had second thoughts about his initial scoffing view of my structural proposal and its consequences, and all together we published the initial seminal communication that was written by me. The decision to place my name last in the roster of authors was made, by me alone, again as a courtesy to a junior staff colleague of independent status".

Interestingly, his recollection almost completely differs from that of Wilkinson's who stated in a 1975 review that he thought of the structure right away while Woodward immediately started thinking about its reactions. It's intriguing - and probably futile - to psychoanalyze the reasons for this very public expression of disappointment, especially coming from one who was not exactly known for publicly airing his personal feelings (for instance, his Cope Award lecture is the only time Woodward really provided personal biographical details). By 1973 Woodward had already won the Nobel Prize, and while he was always known to be extraordinarily ambitious, he must have known that his place in chemical history had already been secured; at that point he had even published the landmark papers on the Woodward-Hoffmann rules. Perhaps he sincerely felt that he deserved a share of the prize; nevertheless, it's a little curious that such a towering figure in the field made it a point to convey his disappointment at not winning a prize so publicly and strongly. Whatever the reason, Woodward's note makes it clear that scientists - both famous ones and otherwise - are keen to stake their priority. They are after all human.

To be fair to the prize committee, the award was given for the more general field of organometallic chemistry that the discovery of ferrocene launched rather than for the structure of ferrocene itself. Even at the beginning Wilkinson had been more interested in the new structural class of metallocenes while Woodward had been more interested in the kind of reactions the novel compounds would undergo. After the initial finding, while Wilkinson immersed himself in investigating the interactions of other metals with similar organic systems, Woodward went back to his life's love; the chemistry of natural products. Thus, it seems sensible in retrospect to have the prize given to Wilkinson and Fischer if the purpose had been to honor a new field of chemistry. Woodward died in 1979, and I am not familiar with his later thoughts on the subject if he had any. But of course, his place in the annals of science had long been assured, and ferrocene has turned into little more than an interesting historical footnote in his list of superlative achievements.

Note: The quotes by Woodward come from an article by Thomas Zydowsky from the Northeastern Section of the ACS that I had noted in the mailing list 2001. Time flies.

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