Platinum-catalysed 1,4-diboration of 1,3-dienes

The chiral diborane(4) compounds B-2[R,R-O2CH(CO2Me)CH(CO2Me)](2), B-2(S-O2CH2CHPh)(2), B-2(R,R-O2CHPhCHPh)(2) and B-2(O2C20H12)(2) (O2C20H12 = 1,7'-bi-2-naphtholate) have been synthesized. All four compounds have been characterised by X-ray crystallography, the latter as a racemate. The B-B bond oxidative-addition reactions of the first three compounds with [Pt(PPh3)(2)(eta-C2H4)] resulted in the platinum(II) bis(boryl) complexes cis-[Pt(PPh3)(2){B[R,R-O2CH(CO2Me)CH(CO2Me)}(2)], cis-[Pt(PPh3)(2){B(S-O2CH2CHPh)}(2)] and cis-[Pt(PPh3)(2){B(R,R-O2CHPhCHPh)}(2)]; the former two were also characterised by X-ray crystallography. The platinum-catalysed diborations of a range of prochiral 1,3-dienes with the compounds B-2[R,R-O2CH(CO2Me)CH(CO2Me)](2), B-2(S-O2CH2CHPh)(2) and B-2(R,R-O2CHPhCHPh)(2) were studied. Although these reactions were clean and quantitative, observed product d.e.s (measured by H-1 NMR spectroscopy) were low or non-existent indicating that chirality transfer from the diborane(4) diolate groups to the diene diboration product is not efficient in these cases.