Highly Reduced Organometallics. 20. The First General Synthetic Route to Zerovalent Titanium Carbonyls. Synthesis and Properties of Ti(CO)5(Me2PCH2CH2PMe2)

Kai Ming Chi, Scott R. Frerichs, Beatrice Kelsey Stein, David W. Blackburn, John E. Ellis

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Abstract

Synthetic procedures developed in this study provide the first general route to zerovalent titanium carbonyls and should facilitate future investigations in this relatively unexplored area of organotitanium chemistry. Sodium naphthalenide reductions of TiCl4(THF)2(THF = tetrahydrofuran), in the presence of 2.1-2.3 equiv of Me2PCH2CH2PMe2 (dmpe) in THF at-70 to-80 °C under argon, followed by carbonylation at atmospheric pressure provide 70-80% isolated yields of the previously known but relatively inaccessible Ti(CO)3(dmpe)2. Under a carbon monoxide atmosphere at room temperature within 3 h, the latter is partially converted to Ti(CO)5(dmpe), the initial example of a pentacarbonyltitanium species. Addition of about 2 equiv of BH3•THF to the Ti(CO)3(dmpe)2/Ti(CO)5(dmpe) mixture under a CO atmosphere in THF binds free dmpe as dmpe•2BH3 and causes disappearance of all Ti(CO)3(dmpe)2, thereby allowing the isolation of substantially pure Ti(CO)5(dmpe). The latter is a bright red crystalline material that decomposes within hours at room temperature and has been characterized by infrared, 13C, 31P, and 1H NMR spectroscopy. Unlike Ti(CO)3(dmpe)2, the pentacarbonyl compound is quite reactive toward a variety of main group nucleophiles and thereby represents the first accessible synthetic equivalent of the unknown Ti(CO)7. Its reactions with 1, 1, 1-tris(dimethylphosphinomethyl)ethane (trmpe), sodium cyclopentadienide, sodium indenide, and potassium hydrotris(1-pyrazolyl)borate ((HB(Pz)3)-) result in the loss of dmpe and provide 70-80% isolated yields of Ti(CO)4(trmpe), C5H5Ti(CO)4-, C9H7Ti(CO)4-, and [HB(Pz)3]Ti(CO)4-. The trmpe derivative is a rare example of a neutral tetracarbonyl of titanium and is one of the most thermally stable organophosphine derivatives of Ti(CO)7 presently known. Thermally robust tetraethylammonium salts of the carbonyl anions were obtained and include the initial indenyl and organonitrogen derivatives of zerovalent titanium. Treatment of Ti(CO)5(dmpe) with Ph3ENa, where E = Ge and Sn, results in the retention of dmpe and formation of Ti(CO)4(dmpe)(Ph3E)-. These were isolated as Ph4As+ salts and are formal derivatives of the presently unknown Ti(CO)62-.

Original languageEnglish (US)
Pages (from-to)163-171
Number of pages9
JournalJournal of the American Chemical Society
Volume110
Issue number1
DOIs
StatePublished - Jan 1988

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