Pentamethylcyclopentadienylgallium (Cp*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)-pentamethylcyclopentadienylgallium (Me5C5Ga, Cp*Ga, 1) via reductive dehalogenation of (pentamethylcyclopentadienyl)diiodogallane (Cp*GaI2, 2) is reported. In addition, the behavior of compound 1 as a ligand in transition metal chemistry is examined. In the reaction of 1 with CT(CO)(5)(C8H14) (C8H14 = ciscyclooctene), Fe-2(CO)(9), Fe(CO)(3)CHT (CHT = cycloheptatriene), Co-2(CO)(8), and Ni(CO)(4) the new complexes Cr(Cp*Ga)(CO)(5) (3), Fe(Cp*Ga)(CO)(4) (4), Fe-2(mu-Cp*Ga)(3)(CO)(6) (5), CO2(mu-Cp*Ga)(2)(CO)(6) (6), and Ni-4(mu-Cp*Ga)(4)(CO)(6) (8), respectively, were obtained. They were characterized by analytical and spectroscopic methods; solid-state structures were determined by X-ray diffraction analysis. In the reaction of 1 with Ni(CO)(4), the complex Ni(Cp*Ga)-(CO)(3) (7) is an intermediate, which was characterized by IR and NMR data. The eta(5)-bonding mode within the Cp*Ga ligand is maintained, apart from one Cp*Ga unit in 5 which exhibits eta(3)/eta(1)-bonding. The cone angle of eta(5)-Cp*Ga is 112 degrees, as determined on the basis of structural data of 3 and 4. Concerning the sigma-donor/pi-acceptor properties, 1 is classified as a predominant electron donor.