Investigations on the synthesis and stability of ν3-bonded cycloheptadienyl complexes of molybdenum

Abstract

The trihapto bonded cycloheptadienyl complexes [MoX(CO) 2L 2( η 3-C 7 H 9)] (X  Cl, L 2 = Ph 2PCH 2PPh 2 (dppe) 1, L 2  Ph Ph 2PCH 2PPh 2 (dppm) 2; X  NCO, L 2 = dppe 3) have been synthesised by reaction of [Mo(CO) 2L 2( η 5-C 7H 9)][BF 4] with LiCl or KNCO in acetone. Spectroscopic investigations indicate that 1–3 possess an asymmetric structure with one end of the bidentatephosphine ligand located trans to the C 7H 9 ring. In solution in acetonitrile [Mo(CO) 2L 2( η 5-C 7H 9)] + may exists in equilibrium with the adducts [Mo(CO) 2(NCMe)L 2( η 3-C 7H 9)] + with the composition of any mixture temperature and L 2 dependent. Variable temperature 31P-NMR studies on [Mo(CO) 2(dppe)( η 5-C 7H 9)][BF 4] in CD 3CN reveal that the proportion of [Mo(CO) 2(NCMe)(dppe)( η 3-C 7H 9)] + present is increased as the temperature is lowered. The new complexes [Mo(CO) 2L 2( η 5-C 7H 9)[BF 4] (L 2  Me ePCH 2CH 2PMe 2 (dmpe) 4 or 1,1,1- tris(diphenylphosphinomethyl)ethane (triphos) 5) have been prepared, the latter as an isomer mixture. Complex 4 remains unchanged in acetonitrile but infrared and variable temperature 31P-NMRstudies on 5 in acetonitrile establish the partial formation of [Mo(CO) 2(NCMe)(triphos)( η 3-C 7H 9)] +.