Kinetic‐Mechanistic and Solid‐State Study of the Oxidative Addition and Migratory Insertion of Iodomethane to [Rhodium(<i>S</i>,<i>O</i>‐<i>BdiPT</i> or <i>N</i>,<i>O‐ox</i>)(CO)(PR¹R²R³)] Complexes

Abstract

Rhodium(I) carbonyl complexes containing bidentate X , O ‐Bid [ S , O ‐ BdiPT or N , O ‐ ox; S , O ‐ BdiPT H = N ‐benzoyl‐ N′ , N′ ‐(diphenyl)thiourea; N , O ‐ ox H = 8‐hydroxyquinoline] ligands of the form [Rh( X , O ‐Bid)(CO)(PR 1 R 2 R 3 )] (R 1 , R 2 , R 3 = Ph or Cy) bearing different phosphine ligands, were investigated, the structural characterization of four example complexes is described and an extensive spectroscopic kinetic‐mechanistic study of the oxidative addition of iodomethane thereto is discussed. Reaction with iodomethane led to Rh III ‐acyl species as secondary (final) products, whereas the primary Rh III ‐alkyl complexes, although rapidly formed, were only observed as intermediates, in small quantities for S,O‐BdiPT (large S–Rh–O bite angle of 90–91°) but in significant amounts for N , O‐ox complexes (less steric with a smaller N–Rh–O bite angle of 79–80°). Overall, almost an order‐of‐magnitude difference in rate constants was observed for the S,O‐BdiPT complexes, with the PPh 2 Cy‐ and PPhCy 2 ‐bearing complexes showing the largest variation. In both the S,O ‐ BdiPT and N , O‐ox ligand systems an associative activation is inferred from the large negative Δ S ≠ values. The relative reactivity of Rh I ‐ X,O ‐Bid complexes, where X = O, S or N , follows a surprising similar reactivity relationship when stepwise varying the PPh 3 , PPh 2 Cy, PPhCy 2 and PCy 3 tertiary phosphine ligands, suggesting a systematic behavior by the PR 3 ligands, independent of the X,O ‐Bid ligand at the Rh I metal center.