Group-6 Imido Activation by a Ring-Strained Alkyne

Abstract

Treatment of M(NAr)2(Cl)2(DME), where Ar = 2,6-diisopropylphenyl, with cyclooctyne results in the formation of M(C8H12C8H12NAr)(Cl)2(NAr), where M = Mo (1) and W (2). The complexes have metrical and spectroscopic parameters that are most consistent with an alkylidene-imine formulation with some participation by the alkyl-amido resonance form. Thermolysis of metallacycles 1 and 2 generates a pyrrole elimination product, with the tungsten derivative being more thermally stable. In addition, the metallacycle is quite hydrolytically stable. Addition of 50% H2SO4 to a toluene solution of 2 protolytically cleaves all the ligands on the metal except those associated with the metallacycle, which are retained in the oxo product [W(O)(μ-O)(C8H12C8H12NAr)]2 (3). The metallacycles 1−3 will polymerize norbornene in the presence of AlCl3. Compounds 1−3 and the pyrrole were characterized by X-ray diffraction.