Ru−Alkylidene Metathesis Catalysts Based on 1,3-Dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidenes: Synthesis, Structure, and Activity

Novel 1,3-dimesityl-4,5,6,7-tetrahydro-[1,3]-diazepin-2-ylidene-coordinated Ru−alkylidene complexes RuCl2(1,3-dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene)(CH-2-(2-PrO)C6H4) (2) and Ru(CF3COO)2(1,3-dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene)(CH-2-(2-PrO)C6H4) (3) were synthesized from the first-generation Grubbs−Hoveyda catalyst, [RuCl2(PCy3)(CH-2-(2-PrO)C6H4)] (1). The single-crystal X-ray structure of 3 was determined. Compound 2 showed excellent reactivity in ring-opening metathesis polymerization (ROMP) of cis-cycloocta-1,5-diene (COD), yielding polymers with a high trans-content of 80%. Compound 3 is also an active initiator for ROMP; however, a low trans-content of only 14% was found for poly-COD prepared by this initiator. Both 2 and 3 turned out to be good catalysts for cross-metathesis (CM), while both compounds showed only moderate activity in ring-closing metathesis (RCM). Finally, 3 is also a good polymerization catalyst for the regioselective cyclopolymerization of dipropargyl diethyl malonate (DEDPM), resulting in poly-DEDPM virtually solely based on five-membered repeat units.