[12129-51-0]  · C12H10O2Ti  · Dicarbonylbis(cyclopentadienyl)titanium  · (MW 234.09)

(deoxygenates sulfoxides;3 forms alkenes by reductive coupling of aromatic aldehydes;4a reduces alkynes5)

Physical Data: mp 90 °C (dec), subl 40-80 °C/0.001 mmHg.1a

Solubility: sol most common organic solvents; reacts with CHCl3 and CH2Cl2.

Analysis of Reagent Purity: IR, NMR.2

Preparative Method: reduction of Dichlorobis(cyclopentadienyl)titanium with Magnesium Amalgam under CO atmosphere.2

Purification: recrystallization from toluene or sublimation at 40-80 °C/0.001 mmHg.

Handling, Storage, and Precautions: pyrophoric; store and handle under an inert atmosphere.1a Use in a fume hood.

Deoxygenation of Sulfoxides.

Sulfoxides are readily deoxygenated by dicarbonylbis(cyclopentadienyl)titanium to form sulfides in high yield.3 It is noteworthy that this deoxygenation is not accompanied by byproducts that sometimes result from Pummerer rearrangement in other methods. A range of alkyl and aryl sulfoxides are reduced in yields which are generally higher than 80% (see eq 1, for example).

Reductive Coupling of Aromatic Aldehydes.

Reductive coupling of aromatic aldehydes forms stilbene derivatives in good yields (eq 2).4a These reactions apparently proceed through the intermediacy of pinacol derivatives which are often observed as byproducts of the reaction, especially at short reaction times, and in the presence of substoichiometric quantities of dicarbonylbis(cyclopentadienyl)titanium. Related reductive dimerizations have also been reported for diethyl ketomalonate,4b N,N-di-p-tolylcarbodiimide,4b and carbon disulfide.4c

Reduction of Alkynes.

Terminal alkynes are hydrogenated to terminal alkenes using dicarbonylbis(cyclopentadienyl)titanium as the catalyst. Aryl alkynes are reduced to the corresponding ethane derivatives under the same conditions (Table 1).5a A more potent catalyst is obtained by treating Cp2Ti(CO)2 with Diphenylacetylene. The resulting p-acetylene complex rapidly and completely reduces diphenylacetylene, styrene, trans-stilbene, 1-octene, and 1,4-diphenylbutadiene to the corresponding ethane derivatives.5b

Stoichiometric alkyne reductions have also been reported. Low yields of cis alkenes are obtained by treatment of internal alkynes with Cp2Ti(CO)2 in wet hexane followed by cleavage of the resulting complex with HCl in CH2Cl2.5c The reaction of several unsaturated diacids with Cp2Ti(CO)2 gave the corresponding saturated carboxylate complexes in fair to excellent yields, rather than the expected unsaturated complexes.5d

1. (a) Dictionary of Organometallic Compounds; Macintyre, J. E., Ed.; Chapman & Hall: London, 1988; 4th Suppl., p 239. (b) Bottrill, M.; Gavens, P. D.; McMeeking, J. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 3, pp 285-291. (c) Sneeden, R. P. A. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 8, p 28. (d) Tkatchenko, I. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 8, p 219. (e) Pez, G. P.; Armor, J. N. Adv. Organomet. Chem. 1981, 19, 1. (f) Sikora, D. J.; Macomber, D. W.; Rausch, M. D. Adv. Organomet. Chem. 1986, 25, 317.
2. Sikora, D. J.; Moriarty, K. J.; Rausch, M. D. Inorg. Synth. 1990, 28, 248.
3. Chen, T. L.; Shaver, A.; Chan, T. H. JOM 1989, 367, C5.
4. (a) Chen, T. L.; Chan, T. H.; Shaver, A. JOM 1984, 268, C1. (b) Pasquali, M.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. JACS 1979, 101, 4740. (c) Harris, H. A.; Rae, A. D.; Dahl, L. F. JACS 1987, 109, 4739.
5. (a) Sonogashira, K.; Hagihara, N. BCJ 1966, 39, 1178. (b) Fachinetti, G.; Floriani, C. CC 1974, 66. (c) Demerseman, B.; Dixneuf, P. H. CC 1981, 665. (d) Corbin, D. R.; Atwood, J. L.; Stucky, G. D. IC 1986, 25, 98.

Thomas E. Snead

Emory University, Atlanta, GA, USA

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