Inorganic Chemistry, Vol.58, No.1, 557-566, 2019
Coordination or Oxidative Addition? Activation of N-H with [Tp ' Rh(PMe3)]
A thermal reaction of amines, anilines, and amides with Tp'Rh(PMe3)(CH3)H (1, Tp' = tris(3,5-dimethyl-pyrazolyl)borate) is described in this report. No N-H bond cleavage was observed for reactions between ammonia or unsubstituted aliphatic amines with the reactive fragment [Tp'Rh(PMe3)]. Instead, amine coordination products (kappa(2)-Tp')-Rh(PMe3)((NHRR2)-R-1) (R-1 = H, R-2 = H, Pr-n, Pr-i, octyl; R-1 = R-2 = Et; R-1, R-2: pyrrolidine) were observed, and the crystal structure of (kappa(2)-Tp')Rh(PMe3)-((NH2Pr)-Pr-i) is reported. No coordination products were observed when 1 was reacted with 1,1,1,3,3,3-hexafluoropropan-2-amine, anilines, and amides. Instead, the oxidative addition products (kappa(3)Tp')Rh(PMe3)(NHR)H (R = CH(CF3)(2), C6H5, 3,5-dimethylbenzyl, C6F5, C(O)CH3, C(O)CF3) were observed. Both Rh-1-N coordination products (kappa(2)-Tp')Rh(PMe3)(NH2CH2CF3) and Rh-III N-H addition products (kappa(3)-Tp')Rh(PMe3)(NHCH2CF3) H were generated when 1 was reacted with 2,2,2-trifluoroethylamine. Coordination products dissociate ammonia and amines in benzene much faster than oxidative addition products eliminate anilines and amides. The relative metal-nitrogen bond energies were studied using established kinetic techniques. Analysis of the relationship between the relative M-N bond strengths and N-H bond strengths showed a linear correlation with a slope = RM-N/N-H of 0.91 (10), indicating that the Rh-N bond strength varies in direct proportion to the N-H bond strength.