Synthesis of bifunctional imido alkylidene bispyrrolide complexes of molybdenum and their conversion into bifunctional imido alkylidene diolate complexes that can be employed as ROMP initiators

Abstract

Addition of four equivalents of lithium 2,5-dimethylpyrrolide to a solution of [Mo(NAr)(OR(F6))(2)(CHC(5)H(4))](2)Fe (OR(F6)=OCMe(CF(3))(2)) in dichloromethane led to [Mo(NAr)(Me(2)Pyr)(2)(CHC(5)H(4))](2)Fe (2; Me(2)Pyr=2,5-dimethylpyrrolide) and lithium hexafluoro-tert-butoxide, which crystallizes out upon cooling the reaction mixture to -35 degrees C. Attempts to prepare parent pyrrolide complexes analogous to 2 resulted in the formation of a mixture of two products. The one that could be isolated contains one equivalent of lithium pyrrolide per molybdenum, that is [Mo(NAr)(Pyr)(3)(CHC(5)H(4))](2)FeLi(2) (3). The X-ray structure obtained shows it to be a dimer of dimers in which each lithium atom is bound to three pyrrolides. Addition of four equivalents of lithium 2,5-dimethylpyrrolide to [Mo(NAr)(OR(F6))(2)](2)(DME)(2)(CH-1,4-C(6)H(4)CH) (1 b) in cold DME produced [Mo(NAr)(Me(2)Pyr)(2)](2)(CH-1,4-C(6)H(4)CH) (4) in good yield, in which the bridging alkylidene is derived from 1,4-divinylbenzene. Three equivalents of (S)-H(2)[Biphen] are required for a clean reaction with 3 to form [Mo(NAr)(Biphen)(CHC(5)H(4))](2)Fe (5) (H(2)[Biphen]=3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diol), Li(2)[Biphen], and two equivalents of pyrrole. Reactions involving 4 with the chiral diols are the best behaved. Brown [Mo(NAr)(Benz(2)Bitet)](2)(CH-1,4-C(6)H(4)CH) (6) can be isolated upon addition of (R)-H(2)[Benz(2)Bitet] (H(2)[Benz(2)Bitet]=(3,3'-dibenzhydryl-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2,2'-diol) to 4, while addition of (R)-H(2)[Mes(2)Bitet] (H(2)[Mes(2)Bitet]=3,3'-dimesityl-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2,2'-diol) to 4 yields [Mo(NAr)(Mes(2)Bitet)](2)(CH-1,4-C(6)H(4)CH) (7). Compounds 5, 6, and 7 were employed as initiators for the polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD) and 2,3-bis(trifluoromethyl)norbornadiene (NBDF6).