Pentamethylcyclopentadienylgallium (Cp*Ga): Alternative Synthesis and Application as a Terminal and Bridging Ligand in the Chemistry of Chromium, Iron, Cobalt, and Nickel

Abstract

An alternative synthetic route to η 5 -pentamethylcyclopentadienylgallium (Me 5 C 5 Ga, Cp*Ga, 1 ) via reductive dehalogenation of (pentamethylcyclopentadienyl)diiodogallane (Cp*GaI 2, 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 Cr(CO) 5 (C 8 H 14 ) (C 8 H 14 = cis -cyclooctene), 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 (μ-Cp*Ga) 3 (CO) 6 ( 5 ), Co 2 (μ-Cp*Ga) 2 (CO) 6 ( 6 ), and Ni 4 (μ-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 η 5 -bonding mode within the Cp*Ga ligand is maintained, apart from one Cp*Ga unit in 5 which exhibits η 3 /η 1 -bonding. The cone angle of η 5 -Cp*Ga is 112°, as determined on the basis of structural data of 3 and 4 . Concerning the σ-donor/π-acceptor properties, 1 is classified as a predominant electron donor.