Addition of aldehydes and acyl chlorides to [Rh(PiPr3)2Cl]2. Thermodynamics and molecular and crystal structures of Rh(PiPr3)2ClX[C(O)Ph] (X = H, Cl)

Article abstract of DOI:10.1021/om00010a065

Addition of aldehyde (ECHO; R = n-octyl, Ph, p-Tol, p-MeOC₆H₄, p-CF₃C₆H₄) to [Rh(PⁱPr₃)₂Cl]₂ (1) results in rapid addition of the aldehyde C-H bond to yield Rh(PⁱPr₃)₂-ClH[C(O)R] (2-R). 2-Ph was isolated, and a single-crystal X-ray diffraction study reveals a trigonal-bipyramidal structure with a small H-Rh-C(acyl) angle of 85(4)°. Enthalpies of addition to 1 were measured by solution calorimetry (R, ΔH/(kcal/mol)): octyl, -15.2 ± 0.3; Ph, -10.8 ± 0.4; p-Tol, -10.6 ± 0.4; p-CF₃C₆H₄, -12.7 ± 0.4; p-MeOC₆H₄, -10.5 ± 0.3. Electron-withdrawing para substituents on the aromatic aldehydes favor addition. Addition of nonanal is more favorable than addition of benzaldehydes, probably due to steric effects, particularly the close hydride-phenyl contact found in 2-Ph. 1 reacts with acyl chlorides (RC(O)Cl, R = octyl, Ph) rapidly to give Rh(PPr₃)₂Cl₂[C(O)R] (3-R). 3-Ph possesses a square-pyramidal structure. The enthalpies of addition were also measured calorimetrically (R, ΔH/(kcal/mol)): octyl, -24.6 ± 0.3; Ph, -21.7 ± 0.3. Relative to the addition of acyl chlorides, the exothermicity of aldehyde addition is greater than would be expected on the basis of thermodynamic data for related late-transition-metal complexes.