Synthesis, structure, and isomerisation of triruthenium and triosmium clusters derived from 3-dimethylaminoprop-1-yne; X-ray crystal structure of [Ru3–H(CO)9(Me2N+C–CCH2)]
Both [Ru3(CO)12] and [Os3(CO)12] react with 3-dimethylaminoprop-1-yne (HCCCH2NMe2) to give fairly low yields of the compounds [M3H(CO)9(Me2NCCCH2)](M = Ru or Os), apparently derived by oxidative addition with cleavage of the terminal C–H bond and a 1,3 shift of the NMe2 group. Crystals of [Ru3H(CO)9(Me2NCCCH2)] are monoclinic, space group P21/n with Z= 4 and cell dimensions a= 13.067(2), b= 10.398(2), c= 15.544(2)Å, and β= 112.78(2)° the X-ray structure was refined to R= 0.019 8 for 3 138 observed reflections. The µ3 ligand is not bound like the µ3-allenyl ligand in [Ru3H(CO)9(µ3-EtCCCHMe)] but extensive π donation from the NMe2 group modifies the ligand-to-metal bonding and makes a zwitterionic description [Ru3–H(CO)9(Me2N+C–CCH2)] more realistic. In spite of the different bonding, the terminal CH2 protons of the triruthenium compound exchange (n.m.r. coalescence), corresponding to the methyl exchange previously observed for [Ru3H(CO)9-(µ3-MeCCCMe2)]. The triruthenium compound much less readily undergoes a hydrogen-atom shift observed generally for compounds of type [Ru3H(CO)9(R1CCCHR2)], being stable up to at least 140 °C. However, a PPh3-catalysed shift is observed at 55 °C to give [Ru3H(CO)9(Me2NCCHCH)] as well as the substitution product [Ru3H(CO)8(PPh3)(Me2NCCCH2)].