REACTIONS OF A CATIONIC MOLYBDENUM COMPLEX WITH OLEFINS .2. OLIGOMERIZATION OF 1,1-DISUBSTITUTED OLEFINS

The oligomerization of 2-methylpropene and of other terminal disubstituted olefins in dichloromethane solution was catalyzed by [(CPMO)2(S2CH2)(mu-S)(mu-SR)]OTf, where R = H, 1, or CMe3, 2. Oligomers of 2-methylpropene of the formula (C4H8)n, where n = 2-8, were detected, and the major C-8 and C-12 isomers have been identified. The distribution of oligomers was consistent with a carbocationic coupling mechanism. Molybdenum products isolated from the 2-methylpropene coupling reaction were found by mass spectrometry to have the formula [(CPMO)2(S2CH2)(mu-S)(mu-S(C4H8)nH)]+, where n = 1-3. The role of the molybdenum catalysts as proton donors and as carbenium ion donors has been investigated, and a mechanism for oligomerization has been proposed which also takes into account the known stoichiometric reactions of 1 and 2 with olefins.