Highly Reduced Organometallics. 33. Carbonyl Hydrides of Titanium and Corresponding Carbonyltitanates

John E Ellis, Beatrice Kelsey Stein, Scott R. Frerichs

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Photopromoted substitution reactions of [(C5R5)Ti(CO)4] (R = H, Me) with organophosphines have been examined for the first time and provided new zerovalent titanium carbonyls of the general formula [(C5R5)Ti(CO)3(PR3)] Disubstituted phosphine derivatives of the formula [(C5R5)Ti(CO)2(dmpe)] were obtained by the alkali metal naphthalenide promoted reductive cleavages of titanocene dicarbonyls (C5R5)2Ti(CO)2 (R = H, Me) in the presence of dmpe, i.e., 1,2-bis(dimethylphosphino)ethane. The reductively promoted substitution reaction of (C5Me5)2Ti(CO)2 appears to be the first report of such a reaction involving a bis(pentamethylcyclopentadienyl)metal complex although corresponding reactions involving bis(cyclopentadienyl)metal complexes are well-known. Spectral studies on alkali metal salts of [(C5R5)Ti(CO)2(dmpe)] established that the cations interacted strongly with the carbonyl oxygens of the anions and promoted anion decomposition. Alkali metal complexants substantially reduced this site-specific ion-pairing interaction and dramatically improved the thermal stability of the anions in solution and in the solid state. Protonation of the carbonyltitanates provided the first examples of carbonyl hydrides of titanium. While hydrides of the monophosphine derivatives (C5R5)Ti(CO)3(PR′3)H (R′ = Me, Ph) were found to be thermally unstable, the corresponding dmpe derivatives (C5R5)Ti(CO)2(dmpe)H were isolated as pure substances at room temperature. These anions and hydrides have been characterized in solution by IR, 1H NMR, and 13C NMR spectroscopy. The carbonyl 13C chemical shifts of these carbonyltitanates are of particular interest in that they represent the most downfield values (δ 300–320) observed to date for coordinated terminal carbonyl groups in metal carbonyls.

Original languageEnglish (US)
Pages (from-to)4066-4075
Number of pages10
JournalJournal of the American Chemical Society
Volume115
Issue number10
DOIs
StatePublished - May 1 1993

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