Synthesis and Reactivity of Molybdenum Imido Diamido Metallacyclopentenes and Metallacyclopentadienes and the Mechanism of Ethylene Exchange with Metallacyclopentane Complexes

In this paper the reactivity of the previously reported metallacyclopentane complex [Mo(NPh)(o-(Me3SiN)2C6H4)(CH2)4] (1) is reported. Complex 1 reacts with acetylenes via ethylene exchange to form novel
Mo imido metallacyclopentene complexes, [Mo(NPh)(o-(Me3SiN)2C6H4)(CRCR‘(CH2)2)4] (R = Ph, R‘
= H, 4a; R = H, R‘ = Ph, 4b; R, R‘ = CO2Et, 4c). The kinetics of the formation of 4c from 1, in the
presence of excess diethyl acetylenedicarboxylate (DEAC), was examined. The activation parameters
for the formation of 4c were found to be ΔH⧧ = 20.5(2.3) kcal mol-1 and ΔS⧧ = −14.8(6.6) cal (mol
K)-1. The metallacyclopentadiene complex [(NPh)Mo(C(Ph)CHCHC(Ph)){o-(Me3SiN)2C6H4}] (7) was
synthesized by the oxidative coupling of two phenylacetylene molecules. Compound 7 is active as a
catalyst for the cyclotrimerization of phenylacetylene. X-ray crystal structures of 1, 4b, and 7 are reported.