Monoaryloxide Pyrrolide (MAP) Imido Alkylidene Complexes of Molybdenum and Tungsten That Contain 2,6-Bis(2,5‑R₂‑pyrrolyl)phenoxide (R = i‑Pr, Ph) Ligands and an Unsubstituted Metallacyclobutane on Its Way to Losing Ethylene

We report the synthesis of Mo and W MAP complexes that contain O-2,6-(2,5-R₂-pyrrolyl)₂C₆H₃ (2,6-dipyrrolylphenoxide or ODPP^R) ligands in which R = i-Pr, Ph. W­(NAr)­(CH-t-Bu)­(Pyr)­(ODPP^Ph) (<b>4a</b>; Ar = 2,6-disopropylphenyl, Pyr = pyrrolide) reacts readily with ethylene to yield a metallacyclobutane complex, W­(NAr)­(C₃H₆)­(Pyr)­(ODPP^Ph) (<b>5</b>). The structure of <b>5</b> in the solid state shows that it is approximately a square pyramid with the WC₄ 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