Reactions of diphosphine-stabilized tetracobalt carbonyl clusters with -Si(OR)3-functionalized alkynes

Short-bite ligand cluster stabilization is achieved in the tetrahedral clusters [Co-4(mu-CO)(3)(CO)(7)(mu-dppy)] (1a-c), obtained in high yields by reactions Of [Co-4(CO)(12)] with 1 equiv of the diphosphine ligands dppy, Ph2PCH2PPh2 (dppm), Ph2PNHPPh2 (dppa), or (Ph2P)(2)-N(CH2)(3)Si(OEt)(3) (dppaSi), respectively. The structure of la 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 la-c were reacted with phenylacetylene to afford the corresponding butterfly clusters [Co-4(mu-Co)2(CO)(6)(mu-dppy)(mu(4)-eta(2)-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 [Co-4(eta-CO)(2)(CO)(6)(mu-dppm)(mu(4)-eta(2)-PhC2H)] (2a). In an alternative synthetic procedure, the alkyne cluster [Co-4(CO)(10)(mu(4)-eta(2)-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.0.5CH(2)Cl(2). To obtain suitable cluster precursors to sol-gel materials, we have reacted 1a,b with the new trialkoxysilyl alkyne PhCdropCC(O)NH(CH2)(3)-Si(OMe)(3) (L-1) and isolated the corresponding functionalized butterfly clusters [Co-4(mu-CO)(2)-(CO)(6)(mu-dppy) {mu(4)-eta(2)-PhC2C(O)NH(CH2)(3)Si(OMe)(3)}] (4a,b), respectively. Similar reactions between la,b and the alkyne HCdropCCH(2)NHC(O)NH(CH2)(3)Si(OEt)(3) (L-2) afforded the related clusters [Co-4(mu-CO)(2)(CO)(6)(mu-dppy){mu(4)-eta(2)-HC2CH2NHC(O)NH(CH2)(3)Si(OEt)(3)}] (5a,b). The cluster [Co-4(mu-CO)(2)(CO)(6)(mu-dppm){mu(4)-eta(2)-HC2(CH2)(2)OC(O)NH(CH2)(3)Si(OEt)(3)}] (6a) was obtained by reaction of la with HCdropC(CH2)(2)OC(O)NH(CH2)(3)Si(OEt)(3) (L-3). Reaction Of [Co-4(CO)(12)] with L-1 led to the formation of the dinuclear complex [Co-2(CO)(6){mu-eta(2)-PhC2C(O)NH-(CH2)(3)Si(OMe)(3)}] (7), which was also prepared by reaction Of [Co-2(CO)(8)] with L-1. Reaction of la with dppaSi afforded the mixed-diphosphine cluster [Co-4(mu-CO)(3)(CO)(5)(mu-dppm)(mu-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 [Co-2(CO)(4)(mu-dppm){mu-eta(2)-PhC2H}] (9) was isolated instead. Reaction of 1,4-bis-(trimethylsilyl)butadiyne (L 4) with [Co-4(CO)(12)] afforded the known complex [{Co-2(CO)(6)(mu(2)-eta(2)-Me3SiC2-)}(2)] (10) and with la yielded the desired product [Co-4(CO)(8)(mu-dppm)(mu(4)-eta(2)-Me(3)SiC(2)CdropCSiMe(3))] (12), in addition to the known complex [Co-2(CO)(4)(mu-dppm)(mu-eta(2)Me(3)SiC(2)CdropCSiMe(3))] (13). Proto-desilylation of 12 using TBAF/THF-H2O occurred unexpectedly at the cluster core-bound alkyne carbon to afford [Co-4(mu-CO)(2)(CO)(6)(mu-dppm)(mu(4)-eta(2)-HC2-CdropCSiMe(3))] (16), instead of the anticipated cluster [Co-4(mu-CO)(2)(CO)(6)(mu-dppm)(mu(4)-eta(2)-Me(3)SiC(2)CdropCH)]. The crystal structure of 16 has been determined by X-ray diffraction.