Synthesis and crystal structures of chloro(trimethylphosphine)tris(trimethylsilylmethyl)molybdenum(IV) and Di-µ-chloro-bis[bis(carbonyl)trimethylphosphine(1—2-η-trimethylsilylmethylcarbonyl)molybdenum(II)]

Abstract

Tetrachlorobis(tetrahydrofuran)molybdenum and bis(trimethylsilylmethyl)magnesium react in the presence of trimethylphosphine to give a five-co-ordinate molybdenum(IV) alkyl MoCl(CH₂SiMe₃)₃(PMe₃), which upon carbonylation at room temperature and pressure yields [MoCl(1–2-η-COCH₂SiMe₃)(CO)₂(PMe₃)]₂. l.r. and ¹H n.m.r. data for the latter complex suggest the presence of an η²-acyl linkage, a result later confirmed by an X-ray crystal-structure determination. The crystal structures of MoCl(CH₂SiMe₃)₃(PMe₃) and [MoCl(COR)(CO)₂-(PMe₃)]₂ have been determined from three-dimensional X-ray diffraction data collected by counter methods. The former crystallizes in the monoclinic space group P2₁/n with a= 10.400(5), b= 19.029(7), c= 12.849(5)Å, β= 91.74(4)°, and Z= 4 for D_c= 1.23 g cm^–3. The final R value was 0.033 for 2 198 independent observed reflections. Electron deficiency at the metal centre of this five-co-ordinate molybdenum compound is the apparent cause of the very short molybdenum–carbon σ-bond length of 2.110(16)Å. [MoCl(COR)(CO)₂(PMe₃)]₂ crystallizes in the monoclinic space group P2₁/c with a= 8.415(3), b= 10.484(3), c= 19.229(5)Å, β= 90.62(2)°, and Z= 2 for D_c= 1.48 g cm^–3. A final R value of 0.020 was obtained based on 2 579 independent observed reflections. The molecule exists as a chlorine-bridged dimer with an η²-acyl linkage. The molybdenum–carbon(acyl) bond length is 2.023(3)Å and the molybdenum–oxygen(acyl) distance is 2.292(2)Å.