ABSTRACT
Generated in situ from air-stable cobalt precursors or readily synthesized using NaHBEt3, (PPh3)3CoH(N2) was found to be an effective catalyst for the hydroboration of alkenes. Unlike previous base-metal catalysts for alkene isomerization-hydroboration which favor the incorporation of boron at terminal positions, (PPh3)3CoH(N2) promotes boron incorporation adjacent to π-systems even in substrates where the alkene is at a remote position, enabling a unique route to 1,1-diboron compounds from α,ω-dienes.
ABSTRACT
Knowledge of exactly how metal complexes react with molecular oxygen is still limited and this has hampered efforts to develop catalysts for oxidation reactions using O2 as the oxidant and/or oxygen-atom source. A better understanding of the reactions of different types of metal complexes with O2 will be of great utility in rational catalyst development. Reactions between molecular oxygen and Pd(0-II) and Pt(0-IV) complexes are reviewed here.
ABSTRACT
The addition of carbon dioxide to ((tBu)PNP)CoH [(tBu)PNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine] resulted in rapid insertion into the Co-H bond to form the corresponding κ(1)-formate complex, which has been structurally characterized. Treatment of ((tBu)PNP)CoH with PhSiH3 resulted in oxidative addition to form trans-((tBu)PNP)CoH2(SiH2Ph), which undergoes rapid exchange with excess free silane. With 0.5 mol % ((tBu)PNP)CoH, the catalytic hydrosilylation of CO2 with PhSiH3 to a mixture of oligomers containing silyl formate, bis(silyl)acetyl, and silyl ether subunits has been observed.
ABSTRACT
The thermolyses of ((tBu)P(O)N)PtMe2 (, (tBu)P(O)N = (di-tert-butylphosphinito)pyridine) and ((tBu)P(N-H)N)PtMe2 (, (tBu)P(N-H)N = (di-tert-butylphosphino)-2-aminopyridine) in benzene-d6 were investigated. With ((tBu)P(O)N)PtMe2, the product of a rollover cyclometalation of the pyridyl ring was observed in 80% yield along with formation of CH4. In contrast, thermolysis of ((tBu)P(N-H)N)PtMe2 resulted in competing rollover cyclometalation and intermolecular benzene C-H activation with production of a mixture of CH4 and CH3D.
ABSTRACT
[Pd(P(Ar)(tBu)2)2] (1, Ar=naphthyl) reacts with molecular oxygen to form Pd(II) hydroxide dimers in which the naphthyl ring is cyclometalated and one equivalent of phosphine per palladium atom is released. This reaction involves the cleavage of both C-H and O-O bonds, two transformations central to catalytic aerobic oxidizations of hydrocarbons. Observations at low temperature suggest the initial formation of a superoxo complex, which then generates a peroxo complex prior to the C-H activation step. A transition state for energetically viable C-H activation across a Pd-peroxo bond was located computationally.