Olefin Metathesis and Stereoselective Ring-Opening Metathesis Polymerization with Neutral and Cationic Molybdenum(VI) Imido and Tungsten(VI) Oxo Alkylidene Complexes Containing N-Chelating N-Heterocyclic Carbenes

Neutral and cationic molybdenum(VI) imido and tungsten(VI) oxo alkylidene complexes containing an N-chelating N-heterocyclic carbene, Mo(N-2,6-Me2-C6H3)I(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph) (Mo1), Mo(N-2-tBu-C6H4)I(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph) (Mo2), Mo(N-2,6-Me2-C6H3)(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)(L)B(ArF)4 (Mo3: L = none, Mo4: L = CH3CN), Mo(N-2-tBu-C6H4)(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)B(ArF)4 (Mo5), W(O)(B(C6F5)3)Cl(1-methyl-3′-(2-N-(2,6-iPr2-C6H4)-1-C6H4)imidazol-2-ylidene)(CHCMe2Ph) (W1), and W(O)(1-methyl-3′-(2-N-(2,6-iPr2-C6H4)-1-C6H4)imidazol-2-ylidene)(CHCMe2Ph)B(ArF)4 (W2) have been prepared. Catalysts Mo2, Mo4, W1, and W2 were characterized by single-crystal X-ray analysis. Catalysts Mo4 and W2 were benchmarked in homo-, cross-, ring-closing metathesis (RCM) as well as in ring-opening cross-metathesis (ROCM) reactions. In the ring-opening metathesis polymerization (ROMP) of endo,exo-2,3-dicarbomethoxynorborn-5-ene (DCMNBE), methyl-N-(S)-(−)-α-methylbenzyl-2-azabicyclo2.2.1hept-5-ene-3-carboxylate, exo-N-(R)-(+)-α-methylbenzyl-5-norbornene-2,3-dicarboximide, and 2,3-bis((menthyloxy)carbonyl)norbornadiene Mo4 and W2 offered access to trans-isotactic and cis-syndiotactic polymers, respectively.