Carbon–nitrogen bond cleavage in 1-dimethylaminobut-2-yne and derived ligands in triruthenium and triosmium clusters

Abstract

Dodecacarbonyltriruthenium reacts in refluxing cyclohexane with 1-dimethylaminobut-2-yne (MeC CCH2NMe2) to give good yields of the isomers [Ru3H(CO)9(µ3-MeCCCHNMe2)](1) and [Ru3H(CO)9-(µ3-MeCCHCNMe2)](2) which are related in stoicheiometry (although perhaps not in structure) to known complexes containing µ3-allenyl (R1CCCHR2) or diosmium-substituted µ3-allyl (R1CCHCR2) ligands. The osmium analogue of complex (1) is obtained similarly from [Os3(CO)12] but [Os3(CO)10-(MeCN)2] reacts at room temperature with the alkyne giving [Os3H(CO)9(µ3-MeCCCH2)] by C–N bond cleavage. Rotation about the C–N bond in complex (1) in chloroform solution is restricted but the rate is accelerated by the addition of small amounts of CF3CO2H while, in neat CF3CO2H, compound (1) is protonated to give [Ru3H2(CO)9(MeCCCHNMe2)]+ for which the rotation barrier is much higher. Neutralisation of acidic solutions of complex (1) gives up to 15% of the but-2-ynal compound [Ru3H2(CO)9(µ3-MeC2CHO)] by hydrolysis. Compound (1) is converted totally into (2) in refluxing hexane but in the presence of H2 hydrogenolysis of the C–N bond also occurs to give the compounds [Ru3H2(CO)9(µ3-MeC2Me)], [Ru3H(CO)9(µ3-MeCCCH2)] and [Ru3H(CO)9(µ3-MeCCHCH)].