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)(Me2CCH2)(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)°].