Reactions of Diphosphine-Stabilized Tetracobalt Carbonyl Clusters with −Si(OR)3-Functionalized Alkynes

Short-bite ligand cluster stabilization is achieved in the tetrahedral clusters [Co4(μ-CO)3 (CO)7(μ-dppy)] (1a−c), obtained in high yields by reactions of [Co4(CO)12] with 1 equiv of the diphosphine ligands dppy, Ph2PCH2PPh2 (dppm), Ph2PNHPPh2 (dppa), or (Ph2P)2N(CH2)3Si(OEt)3 (dppaSi), respectively. The structure of 1a has been determined by X-ray diffraction, and the P atoms occupy axial positions on the basal face, transoid to a Co−Co bond. Clusters 1a−c were reacted with phenylacetylene to afford the corresponding butterfly clusters [Co4(μ-CO)2(CO)6(μ-dppy)(μ4-η2-PhC2H)] (2a−c) by insertion of the alkyne into a Co−Co bond of the precursor. This was established by an X-ray diffraction study of [Co4(μ-CO)2(CO)6(μ-dppm)(μ4-η2-PhC2H)] (2a). In an alternative synthetic procedure, the alkyne cluster [Co4(CO)10(μ4-η2-PhC2H)] (3), prepared from [Co4(CO)12] and phenylacetylene, was reacted with the diphosphines dppy. This led in good yields to butterfly clusters, isomeric with 2a−c in terms of the position of the bridging carbonyls, as revealed by an X-ray diffraction study of the dppa derivative 2‘b·0.5CH2Cl2. To obtain suitable cluster precursors to sol−gel materials, we have reacted 1a,b with the new trialkoxysilyl alkyne PhC⋮CC(O)NH(CH2)3Si(OMe)3 (L 1 ) and isolated the corresponding functionalized butterfly clusters [Co4(μ-CO)2(CO)6(μ-dppy){μ4-η2-PhC2C(O)NH(CH2)3Si(OMe)3}] (4a,b), respectively. Similar reactions between 1a,b and the alkyne HC⋮CCH2NHC(O)NH(CH2)3Si(OEt)3 (L 2 ) afforded the related clusters [Co4(μ-CO)2(CO)6(μ-dppy){μ4-η2-HC2CH2NHC(O)NH(CH2)3Si(OEt)3}] (5a,b). The cluster [Co4(μ-CO)2(CO)6(μ-dppm){μ4-η2-HC2(CH2)2OC(O)NH(CH2)3Si(OEt)3}] (6a) was obtained by reaction of 1a with HC⋮C(CH2)2OC(O)NH(CH2)3Si(OEt)3 (L 3 ). Reaction of [Co4(CO)12] with L 1 led to the formation of the dinuclear complex [Co2(CO)6{μ-η2-PhC2C(O)NH(CH2)3Si(OMe)3}] (7), which was also prepared by reaction of [Co2(CO)8] with L 1 . Reaction of 1a with dppaSi afforded the mixed-diphosphine cluster [Co4(μ-CO)3(CO)5(μ-dppm)(μ-dppaSi)] (8), which was characterized by X-ray diffraction. In the course of attempts at linking two molecules of 2a with 1,4-diodobenzene under Sonogashira conditions, the dinuclear complex [Co2(CO)4(μ-dppm){μ-η2-PhC2H}] (9) was isolated instead. Reaction of 1,4-bis(trimethylsilyl)butadiyne (L 4 ) with [Co4(CO)12] afforded the known complex [{Co2(CO)6(μ2-η2-Me3SiC2-)}2] (10) and with 1a yielded the desired product [Co4(CO)8(μ-dppm)(μ4-η2-Me3SiC2C⋮CSiMe3)] (