Pseudo-Halide and Nitrate Derivatives of Grubbs and Grubbs–Hoveyda Initiators: Some Structural Features Related to the Alternating Ring-Opening Metathesis Copolymerization of Norborn-2-ene with Cyclic Olefins

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Abstract

A series of novel Ru–alkylidene-based initiators, in which both chloride ligands were replaced by pseudo-halides or by nitrate, i.e., [Ru(NCO)2(IMesH2)(C5H5N)(CHC6H5)] (1b), [Ru(CF3SO3)2(IMesH2)(C5H5N)(CHC6H5)] (1c), [Ru(NCO)(CF3SO3)(IMesH2)(C5H5N)(CHC6H5)] (1d), [Ru(CF3SO3)(CF3CO2)(IMesH2)(C5H5N)(CHC6H5)] (1e), [Ru(NCS)2(IMesH2)(C5H5N)(CHC6H5)] (1f), [Ru(NO3)2(IMesH2)(CH-2-(2-PrO)-C6H4)] (2d), and [Ru((CF2)3(CO2)2)(IMesH2)(CH-2-(2-PrO)(C6H4)] (2f) (IMesH2 = 1,3-dimesitylimidazolin-2-ylidene), have been prepared. The novel initiators and those of the general formula [RuX2(L)n(NHC)(CHPh)] and [RuX2(NHC)(CH-2-(2-PrO)-C6H4)] (X = Cl, C6F5COO; NHC = IMesH2, 1,3-dimesitylpyrimidin-2-ylidene, 1,3-dimesityldiazepin-2-ylidene, 1-mesityl-3-(2-phenylethyl)imidazolin-2-ylidene, 1-mesityl-3-adamantylimidiazolin-2-ylidene; L = PCy3, pyridine, n = 1, 2) were investigated for their propensity to copolymerize NBE with cyclopentene (CPE) and cis-cyclooctene (COE), respectively, in an alternating way. Alternating copolymers, that is, poly(NBE-alt-CPE)n and poly(NBE-alt-COE)n containing up to 55 and 40% alternating diads, respectively, were obtained. Moreover, initiator 4b turned out to be a highly efficient initiator for the homopolymerization of cyclopentene (CPE), allowing for the synthesis of high-molecular-weight poly(CPE). Some fundamental effects of the nature of the pseudo-halide ligand on the extent of alternating copolymerization of NBE with CPE or COE are presented. Finally, the effects of the ring size of the N-heterocyclic carbene on the configuration of the double bonds in the final polymer are addressed.

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