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DOI: 10.1039/A702839C (Paper) Reference Section for: J. Chem. Soc., Dalton Trans., 1997, 3311-3318

d2 Complexes of tungsten containing p-toluonitrile as a four- or two-electron donor and oxidative addition giving the two-electron donor acylimido ligand NCOC6H4Me-4

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Alastair J. Nielson, Patricia A. Hunt, Clifton E. F. Rickard and Peter Schwerdtfeger

Abstract

Reaction of benzonitrile with WCl6 in the presence of CCl2CCl2 gave the complex [{WCl4(NCPh)}x] of undetermined structure which does not show equivalent chemistry to the d0 complexes [{WCl4(PhC2Ph)}2] and [{WCl4(NPh)}2]. The complex [WCl2(η2-NCC6H4Me-4) (PMe3)3] 1 can 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 the 13C-{1H} NMR spectrum appears at δ 232.2 consistent with a four-electron donor nitrile ligand. Reaction of [WCl2(NC6H3Pri2- 2,6)(PMe3)3] with purified p-toluonitrile in refluxing toluene or reduction of [WCl3(NC6H3Pri2- 2,6)(PMe3)2] in benzene with 1 equivalent of Na/Hg amalgam in the presence of p-toluonitrile led to [WCl2(NC6H3Pri2- 2,6)(η2-NCC6H4Me-4)(PMe3 )2] 2 as shown by 1H, 13C-{1H} and 31P-{1H} NMR spectroscopy. The position of the nitrile carbon in the 13C-{1H} NMR spectrum (δ 178.9) is consistent with a two-electron donor nitrile ligand. Reaction of [WCl2(NC6H3Pri2- 2,6)(PMe3)3] with unpurified p-toluonitrile gave [WCl2(NC6H3Pri2- 2,6)(NCOC6H4Me-4)(OPMe3)(PMe3 )] 3 in addition to 2. A crystal structure determination showed cis orientated imido and acylimido ligands [W–N 1.769(5) and 1.823(6) Å, W–N–C 174.5(5) and 158.9(5)°], cis-chloro ligands and a cis orientation of the PMe3 and OPMe3 ligands. The bond lengths and angles about the NCOPh function are not significantly different to those of a variety of uncomplexed organic amide groups. Hartree–Fock and density-functional calculations performed on the model complex [WCl2(NMe)(NCOH)(OPH3)(PH3)] 4 showed structural parameters in good agreement with those of 3 when the phenyl groups were removed. An NBO (natural bond orbital) analysis of the W–NMe bond generated one σ and two π bonds between nitrogen s and p atomic orbitals (AOs) and tungsten d AOs. The nitrogen of the NCOH ligand binds to tungsten via one σ and one π bond. In contrast to the NMe ligand, the NBO analysis located a nitrogen ‘lone pair’ orbital on the NCOH ligand which overlaps somewhat with the C–O π orbitals (11% for carbon, 5% for oxygen) and with tungsten (8%). The structural and theoretical studies indicate the NMe ligand nitrogen atom dominates the π donation.

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