A study of the reaction between Mo 2(OCH 2CMe 3) 6(μ-η 1,η 2-NCNR 2) compounds (R = Me and Et) and 2-butyne

Abstract

The compound Mo 2(ONp) 6(μ-η 1,η 2-NCNEt 2) reacts with MeCCMe (2 equiv.) in hydrocarbon solvents at ca 0°C to give Mo 2(ONP) 6(μ-C 4Me 4)(NCNEt 2), I, which is shown to be structurally related to the previously characterized compound Mo 2(ONp) 6(μ-C 4H 4)py obtained in the reaction between Mo 2(ONp) 6 and HCCH (2 equiv.) in the presence of pyridine (py = pyridine and Np = neopentyl). Compound I is unstable in hydrocarbon solutions at room temperature. It rapidly and reversibly loses NCNEt 2 and addition of py or PMe 3 leads to the compounds Mo 2(ONp) 6(μ-C 4Me 4)L, where L = py or PMe 3. Compound I also reacts by CC and NH bond formation to give Mo 2(ONp) 6(μ-C 4Me 3CH 2C(NEt 2)NH), II. A mechanism for the conversion of I to II is proposed to involve (i) initial dissociation of NCNEt 2, (ii) CH bond cleavage of a β-CMe group and (iii) insertion of the CN moiety into the MoH bond with CC bond formation. Rate studies show that the conversion of I to II is suppressed by the addition of excess py or PMe 3 supporting the view that initial dissociation of NCNEt 2 is required in a rapid pre-equilibrium step. The new compounds I and II have been characterized by elemental analyses, IR spectroscopy, 1H and 13C NMR spectroscopy and single crystal X-ray studies.