Monoaryloxide Pyrrolide (MAP) Imido Alkylidene Complexes of Molybdenum and Tungsten That Contain 2,6-Bis(2,5-R[subscript 2]-pyrrolyl)phenoxide (R = i-Pr, Ph) Ligands and an Unsubstituted Metallacyclobutane on Its Way to Losing Ethylene

摘要

We report the synthesis of Mo and W MAP complexes that contain O-2,6-(2,5-R[subscript 2]-pyrrolyl)[subscript 2]C[subscript 6]H[subscript 3] (2,6-dipyrrolylphenoxide or ODPP[superscript R]) ligands in which R = i-Pr, Ph. W(NAr)(CH-t-Bu)(Pyr)(ODPP[superscript Ph]) (4a; Ar = 2,6-disopropylphenyl, Pyr = pyrrolide) reacts readily with ethylene to yield a metallacyclobutane complex, W(NAr)(C[subscript 3]H[subscript 6])(Pyr)(ODPP[superscript Ph]) (5). The structure of 5 in the solid state shows that it is approximately a square pyramid with the WC[subscript 4] ring spanning apical and basal positions. This SP′ structure, which has never been observed as an actual intermediate, must now be regarded as an integral feature of the metathesis reaction.