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Storable Sources of Atomic Fe-, Nb-, Ta- and other Wonders of Transition Metal Chemistry

Recent research from the group of Professor John E Ellis.

In recent years, we have prepared the first examples of homoleptic polycyclic aromatic hydrocarbon, or polyarene, complexed metal anions, in which the polyarene ligands often undergo facile and complete displacement by good acceptor ligands, such as CO, PF3, P(OR)3, CNR, olefins and potentially many others. Thus, these unprecedented polyarenemetalates function as previously almost inaccessible transition metal atomic anions for use in conventional inorganic/organometallic syntheses. Compounds of this type are now known only for the elements, Ti, Zr, Hf, V, Nb, Ta, Fe and Co, all of which have been originally prepared in this laboratory. So there is a considerable amount of exciting exploratory research remaining to be carried out in this relatively new area of chemistry!

Very recently, graduate students William Brennessel, Robert Jilek, and Victor Sussman, working in the laboratory of Professor John Ellis, prepared dark red bis(anthracene)ferrate(1-), 1, the first homoleptic polyarene complex of iron and bright orange bis(naphthalene)bis(trimethylphosphane)niobate(1-), 2, an unprecedented niobium naphthalene complex, respectively, and examined their reactions with 1,3-butadiene, an important hydrocarbon in industry, organic synthesis, and organometallic chemistry. In these experiments the butadiene rapidly displaced all ligands from highly air-sensitive 1 and 2 to afford good yields of the first isolable and structurally characterized anionic homoleptic butadiene metal complexes: the 17-electron pink-red [Fe(C4H6)2]-, 3, and the 18-electron colorless [Nb(C4H6)3]-,4. Thus, in these reactions 1 and 2 function as sources of atomic Fe- and Nb-, respectively. Amazingly, 3, 4, and the analogous tantalum complex prepared in this study, [Ta(C4H6)3]-, are precedented by only two other well-defined homoleptic 1,3-butadiene transition metal complexes, the 18-electron neutral species, M(C4H6)3, M = Mo, W. Syntheses of the latter compounds represented a significant early triumph of the now classic metal vapor synthesis (MVS) method, which has greatly contributed to our fundamental understanding of inorganic and organometallic chemistry through the discovery of new classes of "textbook" molecules. Interestingly, prior attempts to obtain homoleptic butadiene complexes of Fe, Nb or Ta by the MVS route failed, so in this regard the syntheses of 3, 4, and [Ta(C4H6)3]- represent a significant new advance in our polyarenemetalate research, which is generously supported by the National Science Foundation. Also see the “Research News” report of 27 March 2007 describing recent results from the laboratory of Professor Doreen G. Leopold on an amazing benzeneniobate(1-), another formally Nb(I-) complex, which may be regarded as an extraordinarily electron deficient relative of 2.

A graphic depicting the syntheses and structures of the niobium and tantalum complexes is shown below. This artwork was prepared by Dr. Victor Sussman, who now is a research scientist at the Dow Chemical Company.


The iron chemistry has recently been published: “Bis(1,2,3,4-h4-anthracene)ferrate(1-): A Paramagnetic Homoleptic Polyarene Transition-Metal Anion,” Brennessel, W. W.; Jilek, R. E.; Ellis, J. E. Angew. Chem. Int. Ed. 2007, 46, 6132-6136 ( The niobium and tantalum chemistry will soon appear online: “From Storable Sources of Atomic Nb- and Ta- to Isolable Anionic Tris(1,3-butadiene)metal Complexes: [M(h4-C4H6)3]-, M = Nb, Ta,” Sussman, V. J.; Ellis, J. E. Angew. Chem. Int. Ed. ( This article was selected as a “Very Important Paper,” a status achieved by less than 5% of the communications published in Angewandte Chemie.


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