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Inorganic Chemistry Use of ligand design to control the reactivity of main-group and transition metal organometallic and coordination complexes; investigation of steric effects on the reactivity and magnetic properties of metal complexes; synthesis of precursors to materials with desirable electronic/optical properties; computational investigation of bonding and structure in inorganic systems. Molecular chemistry of the main-group metals: Our group has been developing ligand-based approaches to manipulating the structure and reactivity of main-group metals. Use of sterically bulky allyl ligands in catalysis and the study of non-covalent interactions: The compact size of the allyl anion ([C3H5]-) means that its transition metal complexes are often coordinatively unsaturated and prone to facile decomposition. Symmetryeffects on the magnetic properties of transition metal complexes:There is considerable interest in the synthesis of transition metal compounds whose magnetic properties can be influenced by external agents. In the case of spin-crossover complexes, transitions between high- and low-spin states can be induced by temperature, pressure, and light, and the effective control of such transitions could ultimately lead to applications in switching devices, magnetic storage, and photonic systems. Metallocene-based complexes have been attractive in this regard, and variations in the metals, their oxidation states, and ring substituents have led to species displaying spin-crossover behavior, molecular ferromagnetism, and ferromagnetic/antiferromagnetic exchange. We have been studying bis(indenyl)metal complexes, which are relatives of metallocenes, but whose ligand conformations are sensitive to orbital occupancies. Monomeric (1-RC9H6)2Cr (R = t-Bu, SiMe3) are staggered, high-spin complexes with 4 unpaired electrons. When additional bulk is added to the ligands (e.g., (1,3-R2C9H5)2Cr; R = t-Bu, SiMe3), however, rotation to a gauche (near 90)conformation is forced upon the molecule. Owing to increased metal-ligand orbital mixing, maintenance of the high-spin state is no longer possible, Selected Publications Johns AM, Chmely SC, Hanusa TP. Solution Interaction of Potassium and Calcium Bis(trimethylsilyl)amides; Preparation of Ca[N(SiMe3)(2)](2) from Dibenzylcalcium. Inorganic Chemistry. 2009, 48 (4): 1380-1384. Chmely SC, Carlson CN, Hanusa TP, Rheingold AL. Classical versus Bridged Allyl Ligands in Magnesium Complexes: The Role of Solvent. Journal of the American Chemical Society. 2009, 131 (18): 6344-+. Meredith MB, Crisp JA, Brady ED, Hanusa TP, Yee GT, Pink M, Brennessel WW, Young VG. Tunable Spin-Crossover Behavior in Polymethylated Bis(indenyl)chromium(II) Complexes: The Significance of Benzo-Ring Substitution. Organometallics. 2008, 27 (21): 5464-5473. Brady ED, ChmelySC, JayaratneKC, HanusaTP, Young VG, Jr. s-Block Metal Complexes of the Bis(tetramethylcyclopentadienyl) Phosphonium Diylide [Me(t-Bu)P(C5Me4)2]–. Organometallics. 2008, 27 (7): 1612-1616. Quisenberry KT, Gren CK, White RE, Hanusa TP, Brennessel WW. Trimethylsilylated allyl complexes of the heavy alkali metals, M[1,3-(SiMe3)(2)C3H3](thf)(n) (M = K, Cs). Organometallics. 2007, 26 (17): 4354-4356. White RE, Hanusa TP, Kucera BE. Compositional variations in monomeric trimethylsilylated allyl lanthanide complexes. Journal of Organometallic Chemistry. 2007, 692 (16): 3479-3485. Gren CK, Hanusa TP, Rheingold AL. Threefold cation-pi bonding in trimethylsilylated allyl complexes. Organometallics. 2007, 26 (7): 1643-1649. Meredith MB, Crisp JA, Brady ED, Hanusa TP, Yee GT, Brooks NR, Kucera BE, Young VG. High-spin and spin-crossover behavior in monomethylated bis(indenyl) chromium(II) complexes. Organometallics. 2006, 25 (21): 4945-4952. White RE, Hanusa TP. Prediction of Y-89 NMR chemical shifts in organometallic complexes with density functional theory. Organometallics. 2006, 25 (23): 5621-5630. White RE, Hanusa TP, Kucera BE. Generation of dimethylsilylene and allylidene holmium complexes from trimethylsilylated allyl ligands. Journal of the American Chemical Society. 2006, 128 (30): 9622-9623. White RE, Carlson CN, Veauthier JM, Simpson CK, Thompson JD, Scott BL, Hanusa TP, John KD. Observation of internal electron transfer in bulky allyl ytterbium complexes with substituted terpyridine ligands. Inorganic Chemistry. 2006, 45 (17): 7004-7009. Gren CK, Hanusa TP, Brennessel WW. Allyl complexes of heavy group 13 elements: Structure and bonding in [1,3-(SiMe3)(2)C3H3](3)Ga. Polyhedron. 2006, 25 (2): 286-292. Crisp JA, Meredith MB, Hanusa TP, Wang GB, Brennessel WW, Yee GT. Bis(1,2,3-trimethylindenyl)iron(III) 2,3-dicyanonaphtho-1,4-quinonide, a non-metallocene, charge-transfer salt metamagnet with complementary donor-acceptor geometries. Inorganic Chemistry. 2005, 44 (2): 172-174. Simpson CK, White RE, Carlson CN, Wrobleski DA, Kuehl CJ, Croce TA, Steele IM, Scott BL, Young VG, Hanusa TP, Sattelberger AP, John KD. The role of alkali metal cations in MMA polymerization initiated by neutral and anionic allyl lanthanide complexes. Organometallics. 2005, 24 (15): 3685-3691. Crisp JA, Meredith MB, Hanusa TP, Wang GB, Brennessel WW, Yee GT. Bis(1,2,3-trimethylindenyl)iron(III) 2,3-dicyanonaphtho-1,4-quinonide, a non-metallocene, charge-transfer salt metamagnet with complementary donor-acceptor geometries. Inorganic Chemistry. 2005, 44 (2): 172-174. Quisenberry KT, Smith JD, Voehler M, Stec DF, Hanusa TP, Brennessel WW. Trimethylsilylated allyl complexes of nickel the stabilized bis(pi-allyl)nickel complex [eta(3)-1,3,(SiMe3)(2)C3H3](2)Ni and its mono(pi-allyl)NiX (X = Br, I) derivatives. Journal of the American Chemical Society. 2005, 127 (12): 4376-4387. Carlson CN, Hanusa TP, Brennessel WW. Metal allyl complexes with bulky ligands: Stabilization of homoleptic thorium compounds, [(SiMe3)(n)C3H5-n](4)Th (n=1, 2). Journal of the American Chemical Society. 2004, 126 (34): 10550-10551. Smith JD, Quisenberry KT, Hanusa TP, Brennessel WW. Bis[1,3-bis(trimethylsilyl)alyl]cobalt(II), a stable electron-deficient allyl complex. Acta Crystallographica Section C-Crystal Structure Communications. 2004, 60: 507-508. Carlson CN, Smith JD, Hanusa TP, Brennessel WW, Young VG. Homoleptic allyl complexes of chromium with trimethylsilylated ligands. Formation and molecular structure of {[1-SiMe3)C3H4](2)Cr}(2), [1,3-(SiMe3)(2)C3H3](2)Cr, and [1,1 ',3-(SiMe3)(3)C3H2](2)Cr. Journal of Organometallic Chemistry. 2003, 683 (1): 191-199. Kuehl CJ, Simpson CK, John KD, Sattelberger AP, Carlson CN, Hanusa TP. Monomeric f-element chemistry with sterically encumbered allyl ligands. Journal of Organometallic Chemistry. 2003, 683 (1): 149-154. Smith JD, Hanusa TP. Trends in the structures and energetics of the group 14 metallocenes (C5H5)(2)M (M = Si-Pb): A density functional theory study. Organometallics. 2002, 21 (7): 1518. Hanusa TP. New developments in the cyclopentadienyl chemistry of the alkaline-ear. Organometallics. 2002, 21 (13): 2559-2571. Brady ED, Overby JS, Meredith MB, Mussman AB, Cohn MA, Hanusa TP, Yee GT, Pink M. Spin-state alteration from sterically enforced ligand rotation in bis(indenyl)chromium(II) complexes. Journal of the American Chemical Society. 2002, 124 (32): 9556-9566. Specialties
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Vanderbilt University Department of Chemistry |
Professor of Chemistry
The synthesis of volatile and/or liquid compounds that could be useful for the preparation of thin films of metal oxides and halides by chemical vapor deposition (CVD) methods is of particular interest. We have used large, sterically demanding cyclopentadienyl ligands to turn poly- or oligomeric compounds of the heavier alkaline-metals (Ca, Sr, Ba) into monomeric species, often dramatically lowering their sublimation temperatures or melting points. Aluminum alkoxides and alkyls are being designed to deposit stochiometrically precise films of alumina on silicon wafers for microelectronics applications.
We have used sterically bulky substituents (e.g., SiMe3) to produce pi-allyl transition metal compounds that have no unsubstituted analogues, such as the extremely electron deficient 12- and 14-electron species [1,3-(SiMe3)2C3H3]2Cr and [1,3-(SiMe3)2C3H3]2Fe. We are synthesizing new bis- and tris(allyl) metal complexes of the transition metals, and lanthanides and examining the way that the double bonds of allyl ligands can engage in cation-pi interactions. These non-covalent interactions are important in biological systems, but commonly involve aromatic rings. We are examining non-aromatic cation-pi interactions such as that between K+
and the molecules adopt low-spin configurations with 2 unpaired electrons. This indicates that both steric bulk and electronic effects brought about by selective substitution of the indenyl ligand can be used to tailor the magnetic properties of the compounds, making them suitable as tunable sources of variable spin molecules. The spin state changes also suggest that there may be useful variations in the reactivity of the complexes, a possibility we are investigating.