Fundamental Studies of Molybdenum and Tungsten Methylidene and Metallacyclobutane Complexes

Addition of ethylene to Mo(NAr)(CHCMe2Ph)(OHIPT)(Pyr) (NAr = N-2,6-i-Pr2C6H3, OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3, Pyr = NC4H4) led to the trigonal bipyramidal metallacyclobutane complex, Mo(NAr)(C3H6)(OHIPT)(Pyr), in which the imido and aryloxide ligands occupy axial positions. Mo(NAr)(C3H6)(OHIPT)(Pyr) loses ethylene to give isolable Mo(NAr)(CH2)(OHIPT)(Pyr). W(NAr)(CH2)(OTPP)(Me2Pyr) (OTPP = O-2,3,5,6-Ph4C6H, Me2Pyr = 2,5-Me2NC4H2) was prepared similarly. Single crystal X-ray studies of Mo(NAr)(CH2)(OHIPT)(Pyr) and W(NAr)(CH2)(OTPP)(Me2Pyr) show that they are monomers that contain an η-pyrrolide ligand and a methylidene ligand in which the M-C-Hanti angle is smaller than the M-C-Hsyn angle, consistent with an agostic interaction between CHanti and the metal. Attempts to prepare analogous Mo(NAd)(CH2)(OHIPT)(Pyr) (Ad = 1-adamantyl) yielded only the ethylene complex, Mo(NAd)(C2H4)(OHIPT)(Pyr). W(NAr)(CH2)(OTPP)(Me2Pyr) (Ar = 2-t-BuC6H4) was isolated upon loss of ethylene from W(NAr)(C3H6)(OTPP)(Me2Pyr),