Highly Reduced Organometallics. 32. Cyclopentadienyl- and Pentamethylcyclopentadienyl-Substituted Heptacarbonyls of Zerovalent Titanium, Zirconium, and Hafnium, [(C₅R₅)M(CO)₄]⁻, and Derivatives Thereof

Reduction of (C₅R₅)MCl₃ (R = H, Me; M = Ti, Zr, Hf) by alkali-metal naphthalenides at low temperature followed by carbonylation at atmospheric pressure provided 40–75% isolated yields of [(C₅R₅)Ti(CO)₄]⁻ as Et₄N⁺ salts and 15–40% isolated yields of the corresponding zirconium and hafnium salts. Also, [(C₅Me₅)Hf(CO)₄]⁻was isolated in 40–50% yields as pure [K(cryptand 2.2.2)]⁺ or [K(15-crown-5)₂]⁺ salts. Except for unsolvated Na[(C₅H₅)Ti(CO)₄], which proved to be explosive at room temperature, the other compounds were quite thermally stable materials and were easily handled in the absence of oxygen and moisture. Interactions of the carbonyltitanates and -zirconates with Ph₃SnCl and Ph₃PAuCl provided what are believed to be the first series of heterobimetallic complexes to contain tin and gold atoms bound to Ti(II) and Zr(II). Although the zirconium complexes (C₅R₅)Zr(CO)₄E (E = SnPh₃, AuPPh₃) proved to be too thermally unstable for isolation, their spectral properties were very similar to those of the significantly more robust titanium analogs. Reaction of [(C₅Me₅)Ti(CO)₄]⁻ with I₂ provided the very thermally unstable (C₅Me₅)Ti(CO)₄I, which in turn gave a more stable dmpe derivative, (C₅Me₅)Ti(CO)₂(dmpe)I (dmpe = 1,2-bis(dimethylphosphino)ethane). The IR and NMR spectral properties of the latter substance are compared to those of (C₅Me₅)Zr(CO)₂(dmpe)Cl and (C₅-Me₅)Hf(CO)₂(dmpe)Cl, which are believed to have quite similar half-sandwich molecular structures. The divalent Zr and Hf carbonyl chlorides were obtained by the reductive carbonylation of the corresponding (C₅Me₅)MCl₃ in the presence of dmpe. Of the three halocarbonyl–dmpe complexes described herein, only the hafnium complex was sufficiently robust to be isolated as a pure substance.