D(2) COMPLEXES OF TUNGSTEN-CONTAINING P-TOLUONITRILE AS A 4-ELECTRON OR 2-ELECTRON DONOR AND OXIDATIVE ADDITION GIVING THE 2-ELECTRON DONORACYLIMIDO LIGAND NCOC6H4ME-4

Reaction of benzonitrile with WCl6 in the presence of CCl2CCl2 gave th e complex [{WCl4(NCPh)}(x)] of undetermined structure which does not s how equivalent chemistry to the d(0) complexes [{WCl4(PhC2Ph)}(2)] and [{WCl4(NPh)}(2)]. The complex [WCl2(eta(2)-NCC6H4Me-4)(PMe3)(3)] 1 ca n be prepared by reduction of [WCl4(PMe3)(3)] with 2 equivalents of Na /Hg amalgam in the presence of p-toluonitrile. The nitrile carbon in t he C-13-{H-1} NMR spectrum appears at delta 232.2 consistent with a fo ur-electron donor nitrile ligand. Reaction of [WCl2(NC6H3Pr2i-2,6)(PMe 3)(3)] with purified p-toluonitriIe in refluxing toluene or reduction of [WCl3(NC6H3Pr2i-2,6)(PMe3)(2)] in benzene with 1 equivalent of Na/H g amalgam in the presence of p-toluonitrile led to [WCl2(NC6H3Pr2i-2,6 )(eta(2)-NCC6H4Me-4)(PMe3)(2)] 2 as shown by H-1, C-13-{H-1} and P-31- {H-1} NMR spectroscopy. The position of the nitrile carbon in the C-13 -{H-1} NMR spectrum (delta 178.9) is consistent with a two-electron do nor nitrile ligand. Reaction of [WCl2(NC6H3Pr2i-2,6)(PMe3)(3)] with un purified p-toluonitrile gave [WCl2(NC6H3Pr2i-2,6)(NCOC6H4Me-4)(OPMe3) (PMe3)] 3 in addition to 2. A crystal structure determination showed c is orientated imido and acylimido ligands [W-N 1.769(5) and 1.823(6) A ngstrom, W-N-C 174.5(5) and 158.9(5)degrees], cis-chloro ligands and a cis orientation of the PMe3 and OPMe3 ligands. The bond lengths and a ngles about the NCOPh function are not significantly different to thos e of a variety of uncomplexed organic amide groups. Hartree-Fock and d ensity-functional calculation performed on the model complex [WCl2(NMe )(NCOH)(OPH3)(PH3)] 4 showed structural parameters in good agreement w ith those of 3 when the phenyl groups were removed. Pm NBO (natural bo nd orbital) analysis of the W-NMe bond generated one sigma and two pi bonds between nitrogen s and p atomic orbitals (AOs) and tungsten d AO s. The nitrogen of the NCOH ligand binds to tungsten via one sigma and one pi bond. In contrast to the NMe ligand, the NBO analysis located a nitrogen 'lone pair' orbital on the NCOH ligand which overlaps somew hat with the C-O pi orbitals (11% for carbon, 5% for oxygen) and with tungsten (8%). The structural and theoretical studies indicate the NMe ligand nitrogen atom dominates the pi donation.