Orthometalation of Tp*Rh(PPh₃)₂:  Implications for Catalytic Reactivity

In the course of our studies of the catalytic reactivity of Tp*Rh(PPh₃)₂ (1), we noted considerable decomposition of 1 in reactions conducted in 1,2-dicholoroethane (DCE) requiring extended reaction times (>12 h). Because this decomposition could have significant implications for the catalytic utility of 1, we have undertaken a study of the decomposition process. We herein report that 1 undergoes facile, irreversible orthometalation of a PPh₃ ligand at room temperature in slightly polar solvents, such as THF and 1,2-dichloroethane. In comparison, orthometalation is virtually undetectable in PhCH₃ at room temperature. Fortunately, 1 shows catalytic activity for hydrothiolation and hydrophosphinylation in low-polarity solvents. Accordingly, reactions using 1 (and potentially related complexes) should be conducted in nonpolar solvents or solvent mixtures whenever possible.