Abstract
We report the synthesis of Mo and W MAP complexes that contain O-2,6-(2,5-R(2)-pyrrolyl)(2)C(6)H(3) (2,6-dipyrrolylphenoxide or ODPP(R)) ligands in which R = i-Pr, Ph. W(NAr)(CH-t-Bu)(Pyr)(ODPP(Ph)) (4a; Ar = 2,6-disopropylphenyl, Pyr = pyrrolide) reacts readily with ethylene to yield a metallacyclobutane complex, W(NAr)(C(3)H(6))(Pyr)(ODPP(Ph)) (5). The structure of 5 in the solid state shows that it is approximately a square pyramid with the WC(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.