Abstract
The origin of hydroxyl group tolerance in neutral and especially cationic molybdenum imido alkylidene N‐heterocyclic carbene (NHC) complexes has been investigated. A wide range of catalysts was prepared and tested. Most cationic complexes can be handled in air without difficulty and display an unprecedented stability towards water and alcohols. NHC complexes were successfully used with substrates containing the hydroxyl functionality in acyclic diene metathesis polymerization, homo‐, cross and ring‐opening cross metathesis reactions. The catalysts remain active even in 2‐PrOH and are applicable in ring‐opening metathesis polymerization and alkene homometathesis using alcohols as solvent. The use of weakly basic bidentate, hemilabile anionic ligands such as triflate or pentafluorobenzoate and weakly basic aromatic imido ligands in combination with a sterically demanding 1,3‐dimesitylimidazol‐2‐ylidene NHC ligand was found essential for reactive and yet robust catalysts.
Highlights
Olefin metathesis catalysts based on high-oxidation state molybdenum or tungsten alkylidene species, usually referred to as “Schrock catalysts”, have been under development for decades and are a cornerstone for a vast number of regio- and stereoselective transformations today.[1]
We were interested in the question, whether the reported tolerance towards hydroxyl groups and general reactivity would be retained under more harsh conditions and employed the previously reported[4a] neutral pentacoordinate complex Mo(N-2,6-Me2-C6H3)(CHCMe2Ph)(IMesH2)(OTf)2 (1, IMesH2 = 1,3-dimesitylimidazolin-2-ylidene, OTf = CF3SO3) in the acyclic diene metathesis (ADMET) polymerization of 6hydroxy-1,10-undecadiene (M1)[6] and diphenylbis(pent-4-en1-yl)silane (M2) at 80 8C and 20 mbar,[7] resulting in the formation of high molecular weight poly-M1 (Mn = 11 000 g molÀ1, = 2.0, 16 % trans) and poly-M2 (Mn = 433 000 g molÀ1, = 1.8, 77 % trans), both in 95 % isolated yield
We extended the concept of functional grouptolerant Mo-imido alkylidene Nheterocyclic carbene (NHC) complexes
Summary
Olefin metathesis catalysts based on high-oxidation state molybdenum or tungsten alkylidene species, usually referred to as “Schrock catalysts”, have been under development for decades and are a cornerstone for a vast number of regio- and stereoselective transformations today.[1] their inherent oxophilicity and sensitivity to air and moisture limits the user-friendliness that competing ruthenium alkylidenes can offer in many cases.
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