ON THE CHEMISTRY OF GALLIUM, PART-12 - THE TRIS(TRIMETHYLSILYL)SILYLGALLIUM GROUP AS A BUILDING-BLOCK IN GALLIUM-IRON CLUSTERS

Reaction of [(Ga(Cl)Si(SiMe3)(3)](4)] with the iron carbonylates Na2Fe (CO)(4), Na2Fe2(CO)(8), and Na2Fe3(CO)(11) affords derivatives of Fe-2 (CO)(9), in which either all, two, or one of the bridging CO ligands a re replaced by the gallanediyl fragment GaSi(SiMe3)(3). The Ga-Fe bond length in these compounds is 238 pm. This is shorter than the Ga-Fe s ingle-bond length in bicyclic [(CO)(4)FeGa3(OH)(4)(Si(SiMe3)(3)](3)] ( d(Ga-Fe)=248.7 pm) or in [{(CO)(3)Fe}(2)(GaSi(SiMe3)(3)](2)Cl](-) (d(G a-Fe)=245 pm). The latter is the chloride adduct of the Fe-2(CO)(9) de rivative with two bridging CO ligands substituted by GaSi(SiMe3)(3). T he description of these gallanediyl derivatives as CO analogues is sup ported by density functional calculations on gallane-substituted iron carbonyls. In the reactions mentioned above higher gallium-iron cluste rs with trigonal bipyramidal frameworks, which consist of two gallium and three iron atoms, are also formed. These are namely the anionic [{ (Me3Si)(3)SiGa}(2)Fe-3(CO)(9)H](-) and [{(Me3Si)(3)SiGa}(2)Fe-3(CO)(9) GaFe(CO)(4)](-) clusters, which can be described according to Wade's r ules as close-clusters. The latter exhibits a gallium atom coordinated by three iron atoms: two Fe(CO)(3) groups and a Fe(CO)(4) fragment. T he Ga-Fe(CO)(4) bond may be compared with a metal-carbene bond.