Conversion of trans-diboran(4)yl platinum complexes into their cis-bisboryl analogues.

The diboran(4)yl trans-[(iPr3 P)2 Pt(Br){B(NMe2 )B(NMe2 )Br}] (1) is readily converted into its cis-bisboryl analogues 2 and 3 by reaction with the chelating bisphosphines 1,2-bis(dicyclohexylphosphino)ethane (dcpe) and 1,1-bis(dicyclohexylphosphino)methane (dcpm), respectively. A plausible mechanism of this transformation consists of a sequence of reductive diborane(4) elimination and subsequent reoxidative addition of its BB bond to the low-valent platinum centers. Thus, the forced cis configuration of the phosphine ligands induces a change in the preferred reaction site of the diborane(4) with respect to oxidative addition. The reactions proceed with high selectivities, and the cis-bisboryl complexes 2 and 3 were isolated in moderate yields (55 and 46 %). Moreover, their identity was clearly verified by NMR spectroscopy and X-ray diffraction studies.