Improved synthesis of the heteronuclear phosphido Mo–W complex CO4Moμ-PMe22WCO4 and its use as MOCVD precursor

The heteronuclear complex (1) has been prepared by thermal cyclization of the linear dimer [(CO)5MoPMe2PMe2W(CO)5]. An improved yield in 1, with respect to the literature, has been obtained with a different synthetic route to the linear complex and with a better separation, by flash chromatography, of 1 from its homonuclear Mo–Mo and W–W congeners. The conditions of thermal cyclization are rather critical and in one case the major product was the phosphine complex [M(μ-PMe2)(CO)3(PMe3)]2 (M=Mo and W in 1/4 ratio: monoclinic, space group P21/n, a=9.568(1), b=9.305(1), c=15.009(2) Å, β=102.3(1)°, Z=2, R=0.035, Rw=0.036). Complex 1 is a convenient MOCVD precursor and sublimes at low temperatures, ⩽85 °C, to give thin films of mixed MoO3/WO3 oxides or Mo/W alloys, depending on the deposition conditions.