ORGANOIMIDO COMPLEXES OF TUNGSTEN(IV) CONTAINING PI-ACCEPTOR LIGANDS

Reaction of PhCCPh with [WCl2(NR)(PMe3)3] gives the cis-dichloro-trans- phosphine complexes [WCl2(NR)(PhCCPh)(PMe3)2] [R = Ph (1), R = CHMe2 (3)] in which the π-acceptor acetylene ligand lies cis to the imido function. For 1 v(CC) is at 1760 cm-1 and for 3, 1740 cm-1. Me3SiCCSiMe3 and PhCCPh do not replace phosphine ligands from [WCl2(NPh)(PMe3)3] or [WCl2(NPh)(PMePh2)3]. Reaction of PhCCPh with [WCl2(NPh)(PMe2Ph)3] gives [WCl2(NPh)(PhCCPh)(PMe2Ph)2] (2). Alkyl substituted acetylenes do not react cleanly with [WCl2(NPh)(PMe3)3] but HCCH gives [WCl2(NPh)(HCCH)(PMe3)2] (4). Reaction of PhCCH with [WCl2(NR)(PMe3)3] gives [WCl2(NR)(PhCCH)(PMe3)2] [R = Ph (5), R = CHMe2 (6)]. The phenylacetylene ligand gives rise to asymmetry in 5 and 6 leading to AB system 31P{1H} NMR spectra. Different values of 1J(PW) for the two phosphine ligands in both complexes indicate small differences in WP bonding. The acetylenic protons and carbons in the 1H and 13C{1H} NMR spectra of the phenylacetylene complexes couple differently to the two phosphines. For 5 3J(HP) cis and trans = 5.90 and 17.26 Hz, 2J(C[H]P) cis and trans = 5.29 and 21.99 Hz and 2J(C[Ph]P) cis and trans = 4.88 and 15.63 Hz. The 13C{1H} NMR acetylenic carbon resonance positions in complexes 1, 3, 5 and 6 suggest that an isopropylimido ligand is a better π-donor than a phenylimido ligand, allowing more metal-acetylene π-back donation. Reduction of [WCl3(NPh)(PMe3)2] with Na/Hg amalgam under CO gives [WCl2(NPh)(CO)(PMe3)2] (7) for which v(CO) at 1925 cm-1 indicates considerable π- backbonding. © 1990.