A NEW ALLENYL BONDING MODE IN BINUCLEAR COMPLEXES - CHARACTERIZATION AND MOLECULAR-STRUCTURES OF -PPH(2))(MU-ETA(1)-ETA(2)(BETA-GAMMA)-C(PH)=C=CH2) (M=RU, OS)

The binuclear allenyl complexes -PPh(2))(mu-eta(1):eta(beta,gamma)(2)- C(Ph)=C=CH2) (1a, M = Ru; 2a, M = Os), obtained from the mu-eta(1):eta (2)-acetylides M(2)(CO)(6)(mu-PPh(2))(mu-eta(1):eta(2)-C=CPh) via reac tion with diazomethane, have unprecedented structures in which C-alpha is sigma-bonded to one metal site while the C-beta-C-gamma double bon d is coordinated to the second metal. Previously only mu-eta(1):eta(al pha,beta)(2) and mu-eta(alpha,beta)(2):eta(alpha,beta,gamma)(3) bondin g modes: were known for the allenyl ligand on dinuclear centers. React ion of 1a with Ph(2)PCH(2)PPh(2) affords )(mu-DPPM)[mu-eta(2),eta(3)-P (Ph(2))C(O)C(Ph)CCH2] (6), containing a novel allenyl-carbonyl-phosphi do ligand.