Photochemical intermediates of trans-Rh(CO)L2Cl where L = PMe3, PBu3, and i-Pr2HN and cis-Rh(CO2)(i-Pr2HN)Cl in frozen organic glasses

The Nujol glass matrix photolyses of Rh(CO)(PMe₃)₂Cl (1), Rh(CO)(PBu₃)₂Cl (2), Rh(CO)₂ (i-Pr₂HN)Cl (3), and Rh(CO)(i-Pr₂HN)₂Cl (4), have been examined. Phototolysis of 1 (λ_irr > 400 nm) and 2 (350 <λ_irr <400 nm) give new species, A, with carbonyl stretching bands slightly the parents bands. In the case of 1 this species appears to give rise to a second product, C, upon either extended photolysis or annealing. High-energy photolysis of 1, 2, and 4, result in loss of CO and formation of an IR silent species, RhL₂Cl. In the case of 1 a new carbonyl species, B, is observed upon high-energy photolysis or annealing of a matrix containing CO and Rh(PMe₃)₂Cl. B may be converted to 1 by either back potholysis or annealing. Compound 3 undergoes photochemical CO-loss to form tow isomeric photoproducts. Comparison of the carbonyl stretching frequencies of phosphine and ammine derivatives and photoproducts made it possible to eliminate PR₃ loss as the source of A. DFT calculations suggest that A may be a non-planar, triplet excited state of 1 or 2. DFT calculations also support the assignment of B to cis-Rh(CO)(PMe₃)₂Cl.