44049-AC3
All-Inorganic Metallocenes and Related Transition Metal Derivatives of the Heavier Group 15 Elements
44049-AC3 All-Inorganic Metallocenes and Related Transition Metal Derivatives of the Heavier Group 15 Elements.
John E. Ellis, Chemistry, Department of Chemistry, University of Minnesota, Minneapolis MN 55455
A unique "all-inorganic" metallocene, [Ti(h-P5)2]2-, was obtained via reaction of elemental phosphorus with a naphthalene stabilized synthon for Ti2-.1 This result and computational studies suggesting that related species should be stable for other d-block elements, at least as individual, isolated molecules, led to the present study. Although we have obtained P-31 NMR data to indicate that zirconium and hafnium may form possibly analogous species, all attempts to characterize these substances by single-crystal X-ray crystallography have been unsuccessful to date. Separation of these products from polyphosphide by-products, especially P162-, has been problematic also. However, considerable progress has been achieved in the synthesis and structural characterization of homoleptic polyarenemetalates, which appear to be the most promising precursors for the general preparative routes to other types of carbon-free metallocenes. Our most important recent success in this regard is described in an article just accepted for publication (on August 13, 2008) entitled, "Structurally Distinct Homoleptic Anthracene Complexes, [M(C14H10)3]2-, M = Ti, Zr, Hf: Tris(arene) Complexes for a Triad of Transition Metals."2 This paper was accorded "VIP" status by Angewandte Chemie, a category achieved by less than 5% of communications published in this journal. Therein unprecedented examples of tris(arene) complexes for a triad of transition metals were described for the first time. The hafnium anthracene complex, along with the naphthalene analog, are of interest as previously unknown examples of hydrocarbon stabilized negative-valent hafnium, Hf(II-) and promise to be important precursors for studies on low-valent hafnium chemistry, which remains very poorly explored (see TOC). The homoleptic anthracenetitanate(2-), and analogous naphthalene complex also reported, are unique examples of tris(arene)metal complexes for 3d-elements and are also the only known 16-electron homoleptic arene complexes to contain arenes of different hapticities within the same molecule. Interestingly, the previously unreported tris(naphthalene)titanate(2-) is the precursor to the long known [Ti(CO)6]2- 3 and the recently reported [Ti(P5)2]2-.1 Related research involving previously funded PRF projects have been published on the first homoleptic butadienemetalates of early transition metals, [M(h-C4H6)3]-, M = Nb, Ta (See Nugget),4 unprecedented examples of titanium polyisocyanide complexes,5 and an unusual reaction of [PPN]+ or [N(PPh3)2]+ with a transition metal complex, in which two of the phenyl groups on one of the triphenylphosphane units have undergone ortho-metallation. In toto, the reaction described in this article is without precedent.6
(1) Urnezius, E.; Brennessel, W. W.; Cramer, C. J.; Ellis, J. E.; Schleyer, P. V. R. Science 2002, 95, 832; (2) Jilek, R. E.; Jang, M.; Smolensky, E. D.; Ellis, J. E. Angew. Chem. Int. Ed.2008, 47, DOI: 10.1002/anie200802780; (3) Chi, K.-M.; Frerichs, S. R.; Philson, S. B.; Ellis, J. E. J. Am. Chem. Soc. 1988, 110, 303; (4) Sussman, V. J.; Ellis, J. E. Angew. Chem. Int. Ed. 2008, 47, 484; (5) Allen, J. M.; Ellis, J. E. J. Organometal. Chem. 2008, 693, 1536; (6) Sussman, V. J.; Ellis, J. E. Chem. Commun. 2008, DOI: 10.139/b811320c.
