Synthesis and Reactions ofcis-Silyl(boryl)platinum(II) Complexes

Four kinds of silyl(boryl)platinum(II) complexes, 2a − 2d, have been prepared by oxidative addition of silylboranes to platinum(0) complexes, in situ generated from Pt(cod) 2 and 2 molar quantity of tertiary phosphine ligands (L) in Et 2 O: cis -Pt(SiMe 2 Ph)(BX 2 )L 2 (X 2 = −OCMe 2 CMe 2 O− (pin), L = PMe 3 ( 2a ), PMe 2 Ph ( 2b ), PEt 3 ( 2c ); X 2 = −NMeCH 2 CH 2 NMe− (dmeda), L = PMe 3 ( 2d )). Complexes 2a − 2c undergo selective insertion of phenylacetylene into the Pt−B bond at room temperature in CD 2 Cl 2, giving cis -Pt{C(Ph) CH(Bpin)}(SiMe 2 Ph)L 2 (L = PMe 3 ( 3a ), PMe 2 Ph ( 3c ), PEt 3 ( 3c )), respectively, while 2d is inactive toward insertion. The X-ray structure of 3b has been determined. Kinetic study using 2a indicates the mechanism involving prior dissociation of L, followed by insertion of phenylacetylene into the Pt−B bond. The insertion complexes 3a − 3c undergo C−Si reductive elimination to give ( Z )-α-silyl-β-borylstyrene. The reactivity decreases in the order 3c ≫ 3b > 3a .