Platinum(0)-Catalyzed Diboration of Alkynylboronates and Alkynylphosphonates with Bis(pinacolato)diborane(4):  Molecular Structures of [((Me₄C₂O₂)B)(C₆H₅)CC(P(O)(OC₂H₅)₂)(B(O₂C₂Me₄))] and [((Me₄C₂O₂)B)(C₄H₉)CC(B(O₂C₂Me₄))₂]

The platinum(0)-catalyzed diboration addition reaction of bis(pinacolato)diborane(4) [(Me 4 C 2 O 2 )BB(O 2 C 2 Me 4 ), 1 ] with various 1-alkynylphosphonates and 1-alkynylboronates 3a − d gave the desired novel cis -1,2-diboronated vinylphosphonate and trisboronated alkene products 5a, 5b and 5c, 5d respectively, in high yields. No detectable amount of the desired trisboronated alkene products 5c and 5d were isolated when the alkynylboronate was immediately added to a toluene solution of the catalyst and bis(pinacolato)diborane(4) followed by stirring overnight at 80 °C. Under these conditions, cis -1,2-diboronated alkenes 6c and 6d were obtained in 100% conversion yields. Only after changing the reaction conditions were 5c and 5d obtained in high yields. The structure and configuration of the new compounds have been fully characterized by 1 H, 13 C, 31 P, and 11 B NMR, GCMS, elemental analysis, and single-crystal X-ray structure determination. The structure of 5d was found to be fully isomorphous to that of 5c, with the C 6 H 5 ring located in place (and similarly disordered about the 2-fold symmetry axis) of the C 4 H 9 residue; therefore the results of the diffraction analysis, crystal data, and details of the structure determination of 5d are not included.