Highly efficient monophosphine platinum catalysts for alkyne diboration

Automated parallel screening using a series of in situ generated platinum(0 ) phosphine complexes has allowed the identification of improved catalysts for the diboration of alkynes using bis(pinacolato)diboron (B-2(pin)(2), pi n=OCMe2CMe2O). A selection of phosphines were added to [Pt(NBE)(3)] (NBE=no rbornene), which contains only labile mono-olefin ligands, and the activity of the resulting solutions as catalysts for the diboration of 4-CF3C6H4C=C C6H4CF3-4' 1 by B-2(pin)(2) was investigated by in situ GC-MS and/or NMR sp ectroscopy. This allowed the optimum phosphine:platinum stoichiometry to be identified as 1:1, and the large differences in catalyst activity dependin g on the nature of the phosphine to be quantified. The best phosphines empl oyed in the study, PCy3 and PPh2(o-Tol) (o-Tol=C6H4Me-o), give activities o rders of magnitude greater than the worst, such as P(C6F5)(3) and PBu3t. Th e monophosphine catalysts function much more efficiently than previous cata lysts for a range of alkynes allowing diborations to be performed at ambien t temperatures. The diboration of strained cyclic alkenes and some vinyl- a nd allyl-arenes proceeded well, although the catalysts were inactive for ot her olefinic systems examined. As a result of these studies, the isolable a nd stable compound [Pt(PCy3)(eta (2)-C2H4)(2)] was identified as an excelle nt catalyst for alkyne diboration even at room temperature.