Synthesis, Characterization and Reactivity of Ru(II) and Rh(I) Hydrocarbyl and Hydride Complexes

by Lee, John

Abstract (Summary)
The hydroarylation of multiple bonds is the addition of an aromatic C-H bond across a C=X (X = C, N or O) bond to produce new C-C bonds. Our group has been studying Ru(II) complexes of the type TpRu(L)(NCMe)R {Tp = hydridotris(pyrazolyl)borate; L = CO, PMe3, P(N-pyrrolyl)3 and P(OCH2)CEt; R = Me or Ph} for the catalytic hydroarylation of non-functionalized olefins. Insertion of the C=X (X = heteroatom) bond into a metal-aryl bond is a key step in catalytic hydroarylation reactions. Herein, insertion reactions of substrates that possess C-X multiple bonds into the Ru-Ph bond of TpRu(L)(NCMe)Ph (L = CO or PMe3) complexes have been explored. The results of these efforts have increased understanding of factors that control the insertion process. For example, the reaction of TpRu(CO)(NCMe)Ph with either N,NÎ-di-n-hexylcarbodiimide or N,NÎ-di-phenylcarbodiimide produces the amidinate complexes TpRu(CO){N,N-(R)NC(Ph)N(R)}(R = n-hexyl or phenyl). Heating TpRu(CO)(NCMe)Ph in the presence of t-butylisonitrile followed by addition of trimethylphosphine results in an equilibrium between TpRu(CO)(CNtBu)Ph and TpRu(CO){C(Ph)=N(tBu)}(PMe3). Heating TpRu(CO)(NCMe)Ph in the presence of aldehydes results in the decarbonylation of the organic to produce TpRu(CO)2Ar (Ar = phenyl or p-tolyl) and benzene. DFT calculations were carried out to further delineate the thermodynamics and kinetics for C-X multiple bond insertion reactions involving complexes of the type TpRu(L)(NCMe)Ph. In addition, we have studied the possibility of the inter- and intramolecular hydroarylation of isonitriles catalyzed by TpRu(L)(NCMe)Ph complexes. In addition, efforts have been directed to Ru(II) complexes supported by sterically demanding N-heterocyclic carbene (NHC) ligands. For example, the novel 4-coordinate Ru(II) hydride complex [(IMes)2Ru(H)(CO)][BAr'4] {IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene; Ar' = 3,5-(CF3)-C6H3} has been prepared and studied. Both experimental and theoretical studies are consistent with a monomeric, diamagnetic 4-coordinate Ru(II) complex that possesses see-saw geometry without agostic interactions. Attempts to grow X-ray quality crystals under a variety of conditions resulted in the formation of [(IMes)2Ru(H)(CO)(N2)][BAr'4] as determined by X-ray crystallography and confirmed by variable temperature NMR studies. Furthermore, the reaction of [(IMes)2Ru(H)(CO)][BAr'4] with t-butylisonitrile produces [(IMes)2Ru(H)(CO)(CNtBu)2][BAr'4], which has been isolated and fully characterized including X-ray crystallography. [(IMes)2Ru(H)(CO)][BAr'4] reacts with D2 rapidly to produce [(IMes)2Ru(D)(CO)][BAr'4], and catalyzes the hydrogenation of olefins, aldehydes and ketones. Attempts to use [(IMes)2Ru(H)(CO)][BAr'4] for the catalytic addition of a benzene C-H across ethylene resulted in 1.5 turnovers of styrene. Studies of catalytic hydroarylation of olefins have been extended to d8 square planar catalyst precursors. In particular Rh(I) complexes of the type (tbubpy)Rh(L)R (tbubpy = 4,4'-di-tert-butyl-2,2'-bipyridyl; L = neutral 2-electron donor; R = Me or Ph) have been prepared as candidates for olefin hydroarylation and/or oxidative olefin hydroarylation. Initial results for the preparation of (tbubpy)Rh(NCMe)R are discussed.
Bibliographical Information:

Advisor:Paul A. Maggard; Elon Ison; T. Brent Gunnoe; Christian Melander

School:North Carolina State University

School Location:USA - North Carolina

Source Type:Master's Thesis



Date of Publication:06/27/2008

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