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

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 (R¹C=C=CHR²) 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-MeC=C=CH₂)] 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-MeC ₂CHO)] 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-MeC ₂Me)], [Ru₃H(CO)₉(μ₃-MeC=C=CH₂)] and [Ru₃H(CO)₉(μ₃-MeCCHCH)].