Richard D. Ernst
Professor (b. 1951)
Office# HEB
Department of Chemistry, U of U
Salt Lake City, UT 84112-0850
Phone : (801) 581 - 8639
E-Mail : ernst@chem.utah.edu

Field of Interest : Inorganic Chemistry

Education

Table of Contents

Research Interest

Research efforts have been geared to a number of general areas in inorganic chemistry. Our most intensive efforts are being applied to the synthesis, chemical studies and structural characterization of transition metal complexes containing allyl or pentadienyl ligands. The pentadienyl ligands in particular seem interesting as they can be considered to be opened cyclopentadienyl ligands. One might therefore expect that a large area of chemistry would exist wherein pentadienyl ligand replaces its more familiar cyclic counterpart. A likely advantage of such a ligand would be its expected greater ability to exist in monohapto (I) and trihapto (II) bonding configurations as well as pentahapto (III). The ability of a coordinated ligand (see Figure 1) to undergo such isomerizations can be very beneficial chemically as well as catalytically, as a facile mechanism then becomes available for either bringing on additional ligands or getting rid of old ones. For these reasons one can expect metal pentadienyl complexes to be chemically very reactive. Further, since h5- bound pentadienyl is in essence a greater chelate than allyl, a wide variety of metal-pentadienyl complexes should possess reasonable thermal stabilities. Thus, a major goal of our work in this area is to investigate both the physical natures and chemical reactivities of these systems and hopefully correlate the two types of information.
To date, we have prepared and characterized various bis(pentadienyl) compounds for a variety of transition metals (Ti, V, Cr, Fe, Ru, Os, Zr, Hf, Nb, Mo, W) and have amply demonstrated the fact that both thermal stability and chemical reactivity are present in these systems. In fact, while the M-C bond distances for our Cr, Fe, and Ru compounds are reasonably comparable to those of the corresponding metallocenes, the V-C distance in bis(2,4-dimethylpentadienyl)vanadium is 2.21 , compared to 2.28 for vanadocene. Further, bis(2,4-dimethylpendatienyl)titanium is quite stable thermally relative to various titanocenes. Clearly in some cases our open metallocenes are more stable than the metallocenes themselves. Besides these indications of stability, our compounds are characterized by very high reactivities. Thus, some of our compounds react readily with H2, CO, PF3, CO2 and compounds are also very active catalytically in a number of chemical transformations.
We are at present extending these results to a number of systems which seem to offer the most promising chemistry. Among these may be included the half-open metallocenes,Ó which we have now prepared for Cr, Fe, Co+, Ru, Os, and in other forms such as ligand adducts for Ti, V, Mn, and Zr. Especially noteworthy have been the half-open tianocenes, which react with a wide variety of unsaturated organic molecules (ketones, imines, nitriles, isonitriles, and alkynes), yielding a variety of products in which coupling to the pentadienyl ligand takes place. When diynes are used, fused ring complexes result, which may find applications in organic synthesis (see Figure 2).
Other efforts have focused on metal complexes of open fulvalene ligands, in order to assess the degree of metal-metal communication through such bridging species. We have been able to prepare and characterize complexes of vanadium, cobalt, and ruthenium, and a variety of physical methods are being used to examine these compounds.
We commonly employ a number of techniques for characterization of these compounds, including nuclear magnetic resonance, electron spin resonance, infrared and mass spectroscopy as well as magnetic susceptibility and X-ray diffraction measurements.

Selected Publications

R.D. Ernst, J.W. Freeman, L. Stahl, D.R. Wilson, A.M. Arif, B. Nuber and M.L. Ziegler, Longer but Stronger Bonds: Structures of PF3, P(OEt)3, and PMe3 Adducts of an Open Titanocene, J. Am. Chem. Soc. 117, 5075 (1995).

J.T. Spencer and R.D. Ernst, Chemical Vapor Deposition Process Employing Metal Pentadienyl Complexes, U.S. Patent 5,352,488 (1994).

L. Stahl, W. Trakarnpruk, J.W. Freeman, A.M. Arif and R.D. Ernst, Synthesis, Structure, and Binding of the Open Titanocene-Cage Phosphite Complex Ti(2,4-C7H11)2[P(OCH2)3CC2H5]: Further Implications for Phosphite Cone Angles, Inorg. Chem. 34, 1810 (1995).

W. Trakarnpruk, A.M. Arif and R.D. Ernst, Reactions of [Ru(C5Me5)Cl]4 with Enones and Enals: Ru(C5Me5) as a Carboxophile, Organometallics 13, 2423 (1994).

T.E. Waldman, L. Stahl, D.R. Wilson, A.M. Arif, J.P. Hutchinson and R.D. Ernst, Phosphine Adducts of the Open Metallocenes of Zirconium, Hafnium, Niobium, and Molybdenum: Syntheses, Structures, and Reactions with Carbon Monoxide, Organometallics 12, 1543 (1993).

T.E. Waldman, A.M. Wilson, A.L. Rheingold, E. Melendez and R.D. Ernst, Half-Open Titanocene Chemistry: Coupling Reactions of Pentadienyl Ligands with Carbon-Nitrogen and Carbon-Oxygen Multiple Bonds, Organometallics 11, 3201 (1992).

A.M. Wilson, T.E. Waldman, A.L. Rheingold and R.D. Ernst, Ring Fusion and Polycyclic Ring constructions via Half-Open Titanocenes, J. Am. Chem. Soc. 114, 6252 (1992).

J.W. Freeman, N.C. Hallinan, A.M. Arif, R.W. Gedridge, R.D. Ernst and F. Basolo, Syntheses, Characterization, Structual, and Kinetic Studies of Half-Open Chromocenes and Their Ligand Adducts, J. Am. Chem. Soc. 113, 6509 (1991).

E. Melendez, A.M. Arif, M.L. Ziegler and R.D. Ernst, Pentadienyl, A More Reactive and More Strongly Bound Ligand than Cyclopentadienyl, Ang. Chem. Intl. Ed. Engl. 27, 1099 (1988).

E-mail me at ernst@chem.utah.edu

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