PENTAMETHYLCYCLOPENTADIENYLGALLIUM (CP-ASTERISK-GA) - ALTERNATIVE SYNTHESIS AND APPLICATION AS A TERMINAL AND BRIDGING LIGAND IN THE CHEMISTRY OF CHROMIUM, IRON, COBALT, AND NICKEL

An alternative synthetic route to eta(5)-pentamethylcyclopentadienylga llium (Me5C5Ga, CpGa, 1) via reductive dehalogenation of (pentamethyl cyclopentadienyl)diiodogallane (CpGaI2, 2) is reported. In addition, the behavior of compound 1 as a ligand in transition metal chemistry i s examined. In the reaction of 1 with CT(CO)(5)(C8H14) (C8H14 = ciscyc looctene), Fe-2(CO)(9), Fe(CO)(3)CHT (CHT = cycloheptatriene), Co-2(CO )(8), and Ni(CO)(4) the new complexes Cr(CpGa)(CO)(5) (3), Fe(Cp*Ga)( CO)(4) (4), Fe-2(mu-CpGa)(3)(CO)(6) (5), CO2(mu-Cp*Ga)(2)(CO)(6) (6), and Ni-4(mu-CpGa)(4)(CO)(6) (8), respectively, were obtained. They w ere characterized by analytical and spectroscopic methods; solid-state structures were determined by X-ray diffraction analysis. In the reac tion of 1 with Ni(CO)(4), the complex Ni(CpGa)-(CO)(3) (7) is an inte rmediate, which was characterized by IR and NMR data. The eta(5)-bondi ng mode within the CpGa ligand is maintained, apart from one Cp*Ga un it in 5 which exhibits eta(3)/eta(1)-bonding. The cone angle of eta(5) -CpGa is 112 degrees, as determined on the basis of structural data o f 3 and 4. Concerning the sigma-donor/pi-acceptor properties, 1 is cla ssified as a predominant electron donor.