A new synthesis and the molecular structure of trimethyl(silylmethylene)phosphorane in the gas phase, determined by electron diffraction

Trimethyl(silylmethylene)phosphorane ( 1 ) has been prepared in a reaction of H 3 SiCH 2 CH 2 Cl and (CH 3 ) 3 PCH 2 in a molar ratio 1:2. C 2 H 4 is evolved in a β‐elimination process, followed by formation of [(CH 3 ) 4 P] + Cl − in a transylidation step. — The molecular structure of (CH 3 ) 3 PCHSiH 3 in the gas phase has been determined by electron diffraction. Principal bond lengths ( r a ) are: PC = 180.7(8), P = C = 165.3(11), SiC = 185.2(20) pm. The angles between the PC(methyl) bonds are 103.4(13)° and the SiCP angle is 123.4(8)°, consistent with a planar configuration of the methylene carbon atom. The molecule adopts a conformation in which the SiC bond is twisted 25° from a position in which it eclipses one PC bond, but there is a large amplitude torsional vibration about the PC bond.