SYNTHESIS, COORDINATION BEHAVIOR AND THER MOLYSIS OF ALKYNYL-FUNCTIONALIZED TRANSITION-METAL COMPLEXES - CRYSTAL-STRUCTURE OF (MO-2(ETA(5)-C5H5)(2)(CO)(4)[(MU(4)-ETA(2 2/2/2)-ME(3)SIC-C-C-CSIME(3))CO-2(CO)(6)])/

The synthesis and reaction behaviour of [M(eta(5)-C5H5)(CO)(3)(C=CSiMe (3))] (4: M=Mo; 5: M=W) is discussed. The synthesis of compounds 4 and 5 can be achieved by the reaction of [M(eta(5)-C5H5)(CO)(3)Cl](1: M=M o; 2: M=W) with LiC=CSiMe(3)) (3). Compounds 4 and 5 react with Co-2(C O)(8) (6) to yield H5)(CO)(3)[(mu-eta(2:2:1)-C=CSiMe(3))Co-2(CO)(6)]} (7: M=Mo; 8: M=W). In 7 and 8 the Me(3)SiC=C unit is eta(2)-coordinate d to a Co-2(CO)(6) moiety. The use of the dinuclear compound [Mo(eta(5 )-C5H5)(Co>(3)](2) (9), instead of Co-2(CO)(8) (6), results in the for mation of -C5H5)(2)(CO)(4)(mu-eta(2:2)-Me(3)SiC=C-CSiMe(3))] (11), as well as (eta(5)-C5H5)(3)(CO)(7)(mu-eta(2:2:1)-C=CSiMe(3))] (10); compo und 11 is isostructural with 7 and 8. The reaction sequence for the fo rmation of 11 is discussed. 11 is also formed by heating 4 in toluene. Compound 11 contains a non-coordinated Me(3)SiC=C building block and therefore reacts with Co-2(CO)(8) (6) to afford )-eta(2:2:2:2)-Me(3)Si C=C-C=CSiMe(3))Co-2(CO)(6)]} In 12, one C-2 building block of the 1,3- butadiyne Me(3)SiC=C-C=CSiMe(3) is eta(2)-coordinated to a Mo-2(eta(5) -C5H5)(2)(CO)(4) moiety and the other one to a Co-2(CO)(6) fragment. H owever, if [W(eta(5)-C5H5)(CO)(3)(C=CSiMe(3))] (5) is reacted with [W( eta(5)-C5H5)(CO)(3)](2) (13), the compound (CO)(8)(mu(4)-eta(2:2:2:2)- Me(3)SiC=C-C=CSiMe(3))] (14) is formed. In 14 each trimethylsilylethyn yl building block of the 1,3-butadiyne Me(3)SiC=C-C=CSiMe(3) (15) is e ta(2)-coordinated to a W-2(eta(5)-C5H5)(2)(CO)(4) fragment. The synthe sis of complex 14 may also be achieved by the reaction of Me(3)SiC=C-C =CSiMe(3) (15) with [W(eta(5)-C5H5)(CO)(3)](2) (13). The reaction of [ Mo(eta(5)-C5H5)(CO)(3)](2) (9) with the silyl-bridged 1,4-diynes RC=C- SiR'R''-C=CR (16a: R=H, R'=R''=Me; 16b: R=Ph, R'=H, R''=Me' 16c: R=Ph, R'=CH=CH2, R''=C=CPh) results in the formation of (5)-C5H5)(2)(CO)(4) (mu-eta(2:2)-RC=C-SiR'R''-C=CR] (17a: R=H, R'=R''=Me; 17b: R=Ph, R'=H, R''=Me; 17c: R=Ph, R'=CH=CH2, R''=C=CPh) in significantly better yiel ds. Compounds 17a-17c contain a non-coordinated RC=C group adjacent to a sterically hindered molybda-carbon-tetrahedrane unit. All compounds synthesized have been characterized by analytical and spectroscopic d ata (IR, H-1-, C-13-NMR, MS). In addition, compound -eta(2:2::2:2)-Me( 3)SiC=C-C=CSiMe(3))Co-2(CO)(6)]} (12) was characterized by X-ray struc ture analysis.