SELF-ACTIVATION OF A CLUSTER-BOUND ALKYNE TOWARD CARBON-CARBON BOND-FORMING REACTIONS

The methanol-catalyzed elimination of Cl- from the ''activated'' anion ic species [PPN][Ru-3-(mu-Cl)(mu-PhCCPh)(CO)(9)] (1) in the presence o f bis(diphenylphosphino)methene (dppm) constitutes a rational high-yie ld route (>90%) to either the unique unsaturated 46-e (alkyne)-triruth enium cluster, Ru-3(mu-PhCCPh)(CO)(7)(dppm) (2), or its 48-e CO adduct , Ru-3(rho-PhCCPh)- (3). Whereas the CO-induced conversion of 2 into 3 is complete within few seconds at 25 degrees C under 1 atm of CO, the reverse transformation takes 1 h at 80 degrees C. The X-ray structure analysis of 2 is reported, revealing a. perpendicular conformation of the alkyne relative to the metal triangle. The high reactivity of 2 i s substantiated by a high chemical reactivity toward 2-e donors. Its r eaction with 1 equiv of dppm (25 degrees C, 3h) leads to the bis-dppm- substituted complex, Ru-3(mu-PhCCPh)(CO)(6)(dppm)(2) (4) (53% yield). Reaction of 2 with hydrogen gas (1 atm, 25 degrees C, 10 min) yields t he dihydrido species, Ru-3(mu-H)(2)(mu-PhCCPh)- (CO)(7)(dppm) (5) (89% yield) existing as a mixture of two isomer differing in the orientati on of the alkyne relative to the edge-bridging dppm ligand. Complex 2 reacts with a terminal alkyne like phenylacetylene under mild conditio ns to afford a, mixture of the ''fly-over'' type compound Ru-3{mu-HCC( Ph)C(O)(Ph)CCPh}(dppm)(CO)(6) (6) (57% yield) and the diruthena-cyclop entadiene derivative Ru-2{mu-HCC(Ph)(Ph)CCPh}(mu-dppm)(CO)(4) (7) (20% yield). The structure of 6 reveals the occurrence of a disymmetric ed ge-bridging dialkenyl ketone ligand HC=C(Ph)C(O)(Ph)C=CPh, resulting f rom regioselective coupling between the two alkynes and a carbonyl gro up. The formal unsaturation of 6 is masked by a weak interaction betwe en the terminal C-Ph bond of the organic chain and one of the metal ce nters, Facile loss Of this interaction is induced by mild thermolysis of 6. As a consequence, free rotation of the organic moiety around the metal-metal edge brings the opposite end of the organic chain (i.e., the C-H bond) close to the opposite face, thereby favoring CH activati on to convert the alkenyl end into vinylidene. This leads to quantitat ive formation of the vinylidene alkenyl ketone derivative, Ru-3(mu-H){ mu-CC(Ph)C(O)(Ph)CCPh}(dppm)(CO)(6) (8) (94% yield). The X-ray structu re of 8 is reported. Unsuccessful attempts to release the organic moie ty from the cluster core are described. The reaction of a THF solution of 6 with CO in a reactor [P(CO) = 10 atm, T = 80 degrees C] leads to the new binuclear ''fly-over'' species Ru-2{mu-HCC(Ph)C-(O)(Ph)CCPh}( CO)(6) (9a), thereby indicating that elimination of the edge-bridging dppm and cluster fragmentation are more favorable than elimination fre e ketone from the intact cluster. The X-ray structure of Ru-2{mu-HCC(C 3H7)C(O)(Ph)CCPh}(CO)(6) (9b) (resulting from the coupling between dip henylacetylene and 1-pentyne) is reported.