Organoimido complexes of tungsten(IV) containing π-olefin ligands. The X-ray crystal structure of dichloro(2-methylpropene)(phenylimido)bis-(trimethylphosphine)tungsten(IV), [WCl2(NPh)(Me2CCH2)(PMe3)2]

Abstract

Reduction of [WCl₃(NPh)(PMe₃)₂] in benzene with Na–Hg amalgam under ethylene gave [WCl₂(NPh)(CH₂CH₂)(PMe₃)₂](1) for which i.r. and n.m.r. spectral data indicated cis-chloro and trans-phosphine ligands. Similar complexes were prepared from propene, cis- and trans-but-2-ene, and 2-methylpropene. The complex [WCl₂(NPh)(MeCHCH₂)(PMe₃)₂](2) forms two isomers in which the olefin methyl groups lie either above or below the equatorial co-ordination plane. The reduction reaction with trans-but-2-ene and 2-methylpropene also produces [{WCl₂(NPh)(PMe₃)₂}₂](5)(16 and 19%, respectively). 2-Methylbut-2-ene and 2,3-dimethylbut-2-ene do not form identifiable π-olefin complexes but complex (5) is produced in 27 and 70% yield, respectively. The n.m.r. spectra of [WCl₂(NPh)(MeCHCH₂)(PMe₃)₂](2), [WCl₂(NPh)(trans-MeCHCHMe)(PMe₃)₂](4), and [WCl₂(NPh)(Me₂CCH₂)(PMe₃)₂](6) show non-equivalent trans-phosphine ligands. The ¹J(PW) values [e.g. 243.7 and 228.8 Hz for (6)] suggest small differences in the W–P bond lengths. The structure of (6) was determined by X-ray crystallography. The complex has a distorted octahedral geometry with trans-phosphines, cis-chloro ligands, and mutually cis orientated phenylimido and 2-methylpropene ligands. The W–P bond lengths are significantly different at 2.564(5) and 2.522(6)Å, the longer of the two lying adjacent to the two methyl groups of the Me₂CCH₂ ligand. The W–C bond lengths are 2.25(2) and 2.30(2)Å and the olefinic C–C bond length is 1.45(3)Å. The W–C–CH₃ bond angles are 110.9(14) and 118.1 (15)° and the upper and lower methyl groups incline away to different extents from the CC bond [CH₃–C–C bond angles 113(2) and 124(2)°].