title: 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).
authors.affiliation: Department of Chemistry 6-331, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Gabert
authors.forename: Richard R
authors.initials: RR
authors.lastname: Schrock
authors.forename: Peter
authors.initials: P
authors.lastname: Müller