Improved synthesis of the heteronuclear phosphido Mo-W complex [CO)(4)Mo(mu-PMe2)(2)W(CO)(4)] and its use as MOCVD precursor

The heteronuclear complex [(Co)(4)Mo(mu -PMe2)(2)W(CO)(4)] (1) has been pre pared by thermal cyclization of the linear dimer [(CO)(5)MoPMe2PMe2W(CO)(5) ]. An improved yield in 1, with respect to the literature, has been obtaine d 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(mu -PMe2)(CO)(3) (PMe3)](2) (M = Mo and W in 1/4 ratio: monoclinic, space group P2(1)/n, a = 9.568(1), b = 9.305(1), c = 15.009(2) Angstrom, beta = 102.3(1)degrees, Z = 2, R = 0.035, R-w = 0.036). Complex 1 is a convenient MOCVD precursor and sublimes at low temperatures, less than or equal to 85 degreesC, to give t hin films of mixed MoO3/WO3 oxides or Mo/W alloys, depending on the deposit ion conditions. (C) 2001 Elsevier Science B.V. All rights reserved.