Reactions of HC.tplbond.CCMe2NHCOR alkynes with M3(CO)12 carbonyl (M = Ru, R = C6H9, Ph; M = Os, R = C6H9). Synthesis and crystal structure of Ru4(CO)11(HC.tplbond.CCMe2NHCOC6H9), a butterfly cluster showing an interaction between a wingtip metal and the amide CO