Photochemistry of (.eta.5-C5H5)Rh(CO)2 in phosphine solutions: evidence for an associative photosubstitution mechanism

Abstract

Over the past few years there has been much interest in the photochemistry of (i/5-C5R5)ML2 and (r)5-C5R5)ML(H)2 ( = Rh, Ir; R = H, CH3; L = CO, PR3, olefin) complexes leading to intermolecular activation of hydrocarbon C-H bonds.1 Extensive matrix isolation, flash photolysis, and low-temperature solution studies have been performed on these systems, and they indicate that their C-H activation and photosubstitutional reactions proceed initially via ligand dissociation to yield a 16electron species.2 Recently, theoretical models of methane C-H

A model study on the photodecarbonyl reaction of (η5-C5H5)M(CO)2 (M = Co, Rh, Ir)

“…5. According to some availably experimental observations, 23,29,30 Harris and coworkers reported that the irradiation of light to Rh-S 0 -Rea is 295 nm (¼ 96.9 kcal mol À1 ).…”

“…Indeed, this nding has been conrmed by the experimental observations, in which the photodecarbonyl reaction of Rh-S 0 -Rea nally occurs a singlet 16-electron organometallic h 5 -CpRh(CO) species. 23,29,30 Subsequently, Rh-S 0 -Int interacts with Si(H)Me 3 to form a singlet precursor complex (Rh-S 0 -Cpx), whose energy is Fig. 6 Energy profiles for the photo-oxidative-addition reactions for h 5 -CpIr(CO) 2 (Ir-S 0 -Rea).…”

“…In spite of the fact that the photochemical behavior of h 5 -CpIr(CO) 2 (Ir-S 0 -Rea) has been experimentally reported elsewhere, unlike its cobalt and rhodium counterparts, [24][25][26][27][28][29] the photodecarbonyl mechanism of Ir-S 0 -Rea has not been investigated neither experimentally nor theoretically. [30][31][32][33][34] In this work, the same computational method (MP2-CAS) is used to theoretically investigate the potential energy surfaces of h 5 -CpIr(CO) 2 for its photochemical oxidative reaction.…”

“…The above theoretical conclusions have previously been veried by some experimental ndings. [24][25][26][27][28][29][30][31][32][33][34][35][36] (2) On the other hand, aer the CO-photoextrusions of h 5 -CpRh(CO) 2 (Rh-S 0 -Rea) and h 5 -CpIr(CO) 2 (Ir-S 0 -Rea), our theoretical ndings demonstrate that their half-sandwich monocarbonyl intermediates (Rh-S 0 -Int and Ir-S 0 -Int) should still proceed on the singlet energy surfaces. In other words, the conical intersection plays a central role in determining the mechanisms of their photochemical oxidative addition reactions with alkylsilanes.…”

“…Nevertheless, most of the E-H bond insertion reactions by CpML 2 organometallic compounds are heavily focused on their thermodynamical aspects, with a few discussions of their initially photochemical aspects. Indeed, to our knowledge, there has been little mechanistic study regarding the photolysis of the CpML 2 complex, [24][25][26][27][28][29][30][31][32][33][34][35][36] much less related theoretical research. In addition to the limitations of the spectroscopic instruments, there are many fundamental questions about the photolysis of CpML 2 in hydrosilane solution that need to be answered.…”