INVESTIGATIONS ON THE SYNTHESIS AND STABILITY OF ETA(3)-BONDED CYCLOHEPTADIENYL COMPLEXES OF MOLYBDENUM

The trihapto bonded cycloheptadienyl complexes [MoX(CO)(2)L-2(eta(3)-C 7H9)] (X = Cl, L-2 = Ph2PCH2CH2PPh2 (dppe) 1, L-2 = Ph2PCH2PPh2 (dppm) 2; X = NCO, L-2 = dppe 3) have been synthesised by reaction of [Mo(CO )(2)L-2(eta(5)-C7H9)][BF4] with LiCl or KNCO in acetone. Spectroscopic investigations indicate that 1-3 possess an asymmetric structure with one end of the bidentate phosphine ligand located trans to the C7H9 r ing. In solution in acetonitrile [Mo(CO)(2)L-2(eta(5)-C7H9)](+) may ex ist in equilibrium with the adducts [Mo(CO)(2)(NCMe)L-2(eta(3)-C7H9)]( +) with the composition of any mixture temperature and L-2 dependent. Variable temperature P-31-NMR studies on [Mo(CO)(2)(dppe)(eta(5)-C7H9) ][BF4] in CD3CN reveal that the proportion of [Mo(CO)(2)(NCMe)(dppe)(e ta(3)-C7H9)](+) present is increased as the temperature is lowered. Th e new complexes [Mo(CO)(2)L-2(eta(5)-C7H9)][BF4] (L-2 = Me2PCH2CH2PMe2 (dmpe) 4 or 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) 5) ha ve been prepared, the latter as an isomer mixture. Complex 4 remains u nchanged in acetonitrile but infrared and variable temperature P-31-NM R studies on 5 in acetonitrile establish the partial formation of [Mo( CO)(2)(NCMe)(triphos)(eta(3)-C7H9)](+). (C) 1997 Elsevier Science S.A.