Improved synthesis of the heteronuclear phosphido Mo-w complex [(CO)_4Mo(#mu#-PMe_2)_2W(CO)_4] and its use as MOCVD precursor

摘要

The heteronuclear complex [(CO)_4Mo(#mu#-PMe_2)_2W(CO)_4] (1) has been prepared by thermal cyclization of the linear dimer [(CO)_5MoPMe_2PMe_2W(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 between 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#-PMe_2)(CO)_3(PMe_3)]_2 (M=Mo and W in 1/4 ratio: monoclinic, space group P2_1, a=9.568(1), b=9.305(1), c=15.009(2) A, #beta#=102.1(1)deg, Z=2, R=0.035, R_w=0.036). Complex 1 is a convenient MOCVD precursor and sublimes at low temperatures, <=85deg C, to give thin filsm of mixed MoO_3/WO_3 oxides or Mo/W alloys, depending on the deposition conditions.