ADDITION OF ALDEHYDES AND ACYL CHLORIDES TO [RH(P(I)PR3)(2)CL](2) - THERMODYNAMICS AND MOLECULAR AND CRYSTAL-STRUCTURES OF RH(P(I)PR3)(2)CIX[C(O)PH] (X=H, CL)

Addition of aldehyde (RCHO; R = n-octyl, Ph, p-Tol, p-MeOC(6)H(4), p-C F3C6H4) to [Rh((PPr3)-Pr-i)(2)Cl](2) (1) results in rapid addition of the aldehyde C-H bond to yield Rh((PPr3)-Pr-i)(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)degrees. Enthalpies of addition to 1 were measured by solution calo rimetry (R, Delta H/(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-MeOC(6)H(4), -10 .5 +/- 0.3. Electron-withdrawing para substituents on the aromatic ald ehydes favor addition. Addition of nonanal is more favorable than addi tion of benzaldehydes, probably due to steric effects, particularly th e close hydride-phenyl contact found in 2-Ph. 1 reacts with acyl chlor ides (RC(O)Cl, R = octyl, Ph) rapidly to give Rh((PPr3)-Pr-i)(2)Cl-2[C (O)R] (3-R). 3-Ph possesses a square-pyramidal structure. The enthalpi es of addition were also measured calorimetrically (R, Delta H/(kcal/m ol)): octyl, -24.6 +/- 0.3; Ph, -21.7 +/- 0.3. Relative to the additio n 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.