Intramolecular Hydrogen Transfer Reactions Catalyzed by Pentamethylcyclopentadienyl Rhodium and Cobalt Olefin Complexes: Mechanistic Studies.

The mechanism of intramolecular transfer dehydrogenation catalyzed by [CpM(VTMS)] (, M=Rh, , M=Co, Cp* = CMe, VTMS = vinyltrimethylsilane) complexes has been studied using vinyl silane protected alcohols as substrates. Deuterium-labeled substrates have been synthesized and the regioselectivity of H/D transfers investigated using H and H NMR spectroscopy. The labeling studies establish a regioselective pathway consisting of alkene directed α C-H activation, 2,1 alkene insertion, and finally β-hydride elimination to give silyl enol ether products.

Activation of sp3 C-H bonds with cobalt(I): catalytic synthesis of enamines.

C-H bond activation has been extensively studied with (Cp*)M(L)n (M = Ir, Rh), but cobalt, the third member of this triad, has not previously been shown to activate sp3 C-H bonds. Further, practical functionalization of the metal alkyl products of oxidative addition has not been fully explored. Toward these ends, we have developed catalytic dehydrogenation of alkyl amines with a Co(I) catalyst.

ansa-Zirconocene ester enolates: synthesis, structure, reaction with organo-lewis acids, and application to polymerization of methacrylates.

The synthesis, structural characterization, and abstraction chemistry of ansa-zirconocene ester enolate complexes relevant to the isospecific polymerization of methacrylates are reported. Reactions of rac-(EBI)ZrMe(OTf) and rac-(EBI)Zr(OTf)(2) [EBI = C(2)H(4)(Ind)(2)] with 1 and 2 equiv of lithium isopropylisobutyrate in toluene produce the first examples of ansa-zirconocene mono- and diester enolate complexes: rac-(EBI)ZrMe[OC(O(i)Pr)=CMe(2)] (1) and rac-(EBI)Zr[OC(O(i)Pr)=CMe(2)](2) (2) in 89% and 50% isolated yields, respectively. The reaction of 1 with B(C(6)F(5))(3) was investigated in six different organic solvents; in THF at ambient temperature, this reaction cleanly produces the isolable cationic ansa-zirconocene ester enolate complex rac-(EBI)Zr(+)(THF)[OC(O(i)Pr)=CMe(2)][MeB(C(6)F(5))(3)](-) (3) in quantitative yield.

Isotactic-b-syndiotactic stereoblock poly(methyl methacrylate) by chiral metallocene/Lewis acid hybrid catalysts.

Stereoblock polymerization with chiral ansa-metallocene/strong Lewis acid hybrid catalysts capable of switching stereospecificity of the methyl methacrylate polymerization produces the highly stereoregular isotactic-b-syndiotactic stereoblock poly(methyl methacrylate).