19-Electron Intermediates in the Ligand Substitution of CpW(CO)3 • with a Lewis Base

• Published in: Journal of the American Chemical Society Vol. 128; no. 10; pp. 3152 - 3153
• Main Authors: Cahoon, James F, Kling, Matthias F, Sawyer, Karma R, Frei, Heinz, Harris, Charles B
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.03.2006
• Subjects: Chemistry; Exact sciences and technology; Free radicals chemistry; Organic chemistry; Reactivity and mechanisms; Ligand substitution; Tertiary phosphine; Transition metal Carbonyl Complexes; Tungsten Organic compounds; Experimental study; Phosphorus Organic compounds; Infrared spectrometry; Organic free radical; Reaction mechanism; Kinetic parameter; Rate constant; Molecule radical reaction; Tungsten Carbonyl Complexes
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja058258i

The photochemical reactions of [CpW(CO)3]2 with the Lewis base P(OMe)3 are examined on the nanosecond and microsecond time scales using step-scan FTIR spectroscopy. Photolysis at 532 nm produces the 17-electron (17e) radicals CpW(CO)3 •, which are in equilibrium with the 19-electron (19e) radicals CpW(CO)3P(OMe)3 • on the nanosecond time scale. The reactions of the 19e radical are directly observed for the first time; the major reaction pathway is spontaneous loss of a carbonyl to form the 17e species CpW(CO)2P(OMe)3 •, with a barrier of 7.6 ± 0.3 kcal/mol for this process. The minor reaction pathway (<20%) at this concentration of P(OMe)3 (85 mM) is disproportionation to form the products CpW(CO)3P(OMe)3 + and CpW(CO)3 -. On the microsecond time scale, the 17e radicals CpW(CO)2P(OMe)3 • dimerize to form the ligand substitution product [CpW(CO)2P(OMe)3]2. These results indicate that the 19e species is a stable intermediate rather than transition state in the ligand substitution reaction, and this type of reactivity is likely to be typical of 17e organometallic radicals which undergo associative substitution mechanisms.