Alkyl cyanides (RCN, R = Me, Et, and n-Pr) react with molybdenum(v) chloride, tungsten(v1) and tungsten(v) chloride, and tungsten(v) bromide, with reduction of the metal to the quadrivalent state and the formation of complexes MX,, ZRCN. These complexes have been characterised as 6-coordinate complexes, and the results of spectroscopic and magnetic susceptibility studies are discussed on the basis of an octahedral model. The use of these complexes as starting materials for the preparation of a large number of other complexes of quadrivalent molybdenum and tungsten is discussed. ALKYL cyanides are known k 2 to react with the chlorides and bromides of quadrivalent titanium and zirconium to give compounds of the general formula MX4,2RCN. The analogous vanadium compounds VC14,2RCN can be prepared if the reactants are well diluted with an inert ~o l v e n t ,~.~ but excess of alkyl cyanide brings about reduction of vanadium to the tervalent state with the formation of the compounds VC1,,3RCN. These compounds, their bromo analogues, and the corresponding compounds of tervalent titanium, have been prepared directly by the reaction of the alkyl cyanides with the appropriate t~ihalide.~ The pentachloride and pentabromide of niobium and tantalum are not reduced by alkyl cyanides, however, even when the reactants are heated in a sealed tube to 150°, but simple 1 : 1 adducts MX,,RCN have been isolated and ~haracterised.~ In this Paper we report on the reactions of alkyl cyanides with molybdenum(v) chloride, tungsten(v1) and tungsten(v) chloride, and tungsten(v) bromide. These reactions were carried out with considerable excess of alkyl cyanide, and in every case a dark brown solid was obtained which analysed to MX,, 2RCN (cf. Table 2). All the compounds showed some solubility in the parent alkyl cyanide, and measurement of the conductance of the solutions (cf. Table 3) indicated that the compounds behaved essentially as non-electrolytes, the measured values of the molar conductivity in every case being less than 10, as compared to values of around 150 for typical 1 : 1 electrolytes. Unfortunately, only the n-propyl cyanide compounds were sufficiently soluble in solvents such as benzene for molecular weight measurements to be made but, in these cases at least, the compounds were monomeric. We propose accordingly that the compounds be considered as simple 6x0-ordinate complexes. It is worth noting that, whereas the molybdenum and tungsten
