Synthesis and characterisation of binuclear and trinuclear organoimido complexes of tungsten-(VI) and -(V) and a binuclear tungsten(V) oxoanion. X-Ray crystal structures of [{WCl4(NEt)}2], [P(CH2Ph)Ph3][W3Cl7(NBut)3(µ-NPh)3], [P(CH2Ph)Ph3][W2Cl7(NR)2](R = Et or Ph), and [P(CH2Ph)Ph3][W2O2Cl7]

Abstract

The X-ray crystal structure of [{WCl₄(NEt)}₂] has been determined and shows the molecule to be binuclear with asymmetric chlorine bridges and linear ethylimido groups having a W–N distance of 1.69(1)Å. Binuclear, mixed organoimido compounds [{WCl₂(NBu^t)(µ-NR)(NH₂Bu^t)}₂](R = Ph or C₆H₄Me-p) with asymmetric NR bridges have been converted to the trinuclear anions [W₃Cl₇(NBu^t)₃(µ-NR)₃]^–. The X-ray crystal structure of [W₃Cl₇(NBu^t)₃(µ-NPh)₃]^– shows it to contain terminal, linear NBu^t groups with an average W–N distance of 1.70 Å, almost symmetrical bridging NPh groups with an average W–N distance of 2.00 Å, and a triply bridging chlorine. Carbon-13 and ¹H n.m.r. spectra of this anion show that rotation of the phenyl rings in the µ-NPh groups is restricted. Reduction of [WXCl₄] with 1 equivalent of sodium amalgam in the presence of chloride ions gave the distorted confacial bioctahedral tungsten(V) anions [W₂X₂Cl₇]^–(X = NEt, NPh, or O). X-Ray crystal structures of all three anions have been determined and show the π-bonding ligands to be terminal with average W–N distances of 1.69 (X = NEt) and 1.72 Å(X = NPh) and an average W–O distance of 1.67 Å. The W–W distances in the three anions are 2.839(4)(X = NEt), 2.835(4)(X = NPh), and 2.849(1)Å(X = O).