Relative Importance of Dissociative Loss of Carbon Monoxide and Formation of Benzyl Radicals from Photoexcitation of (η5-C5R5)Fe(CO)2(η1-CH2C6H5) and Evidence for Reaction of Carbon Monoxide with 17-Electron Radicals

Article abstract of DOI:10.1021/ja00295a023

Near-UV irradiation of (η⁵-C5R5)Fe(CO)2(η¹-CH2C6H5) (R=H, Me) yields both loss of CO and CH2C6H5 radicals as primary photoprocesses, though the loss of CO dominates the excited-state chemistry.At 77 K in a rigid alkane matrix the only detectable photoreaction is loss of CO to form (η⁵-C5R5)Fe(CO)(η³-CH2C6H5).In fluid alkane solution at 298 K the dominant metal-containing photoproduct is (η⁵-C5R5)2Fe2(CO)4, unless the solution is actively purged with a stream of an inert gas such as Ar or N2.When the solution is purged with Ar there are two main products: (η⁵-C5R5)Fe(CO)(η³-CH2C6H5) (90-95percent) and (η⁵-C5R5)2Fe2(CO)4 (5-10percent).The 366-nm quantum efficiency for CO loss is ca. 0.5, and that for CH2C6H5 loss is ca. 0.05.When (η⁵-C5R5)Fe(CO)2(η¹-CH2C6H5) is irradiated under 2 atm of CO in alkane solution at 298 K (η⁴-C5R5(CH2C6H5))Fe(CO)3 is formed in good chemical yield (>50percent).X-ray crystallography establishes (η⁴-C5Me5(CH2C6H5))Fe(CO)3 to have the CH2C6H5 group in an exo position.The formation of (η⁴-C5R5(CH2C6H5))Fe(CO)3 occurs via light-induced loss of a CH2C6H5 radical from (η⁵-C5R5)Fe(CO)2(η¹-CH2C6H5) followed by reaction of (η⁵-C5R5)Fe(CO)2 with CO to form (C5R5)Fe(CO)3 that then couples with a CH2C6H5 radical to give the exo isomer of (η⁴-C5R5(CH2C6H5))Fe(CO)3.