77535-62-7Relevant academic research and scientific papers
Use of Ligand Steric Properties to Control the Thermodynamics and Kinetics of Oxidative Addition and Reductive Elimination with Pincer-Ligated Rh Complexes
Gu, Shunyan,Nielsen, Robert J.,Taylor, Kathleen H.,Fortman, George C.,Chen, Junqi,Dickie, Diane A.,Goddard, William A.,Gunnoe, T. Brent
, p. 1917 - 1933 (2020)
Oxidative addition and reductive elimination reactions are central steps in many catalytic processes, and controlling the energetics of reaction intermediates is key to enabling efficient catalysis. A series of oxidative addition and reductive elimination reactions using (RPNP)RhX complexes (R = tert-butyl, isopropyl, mesityl, phenyl; X = Cl, I) was studied to deduce the effect of the size of the phosphine substituents. Using (RPNP)RhCl as the starting material, oxidative addition of MeI was observed to produce (RPNP)Rh(Me)(I)Cl, which was followed by reductive elimination of MeCl to form (RPNP)RhI. The thermodynamics and kinetics vary with the identity of the substituent R on phosphorus of the PNP ligand. The presence of large steric bulk (e.g., R = tert-butyl, mesityl) on the phosphine favors Rh(I) in comparison to the presence of two smaller substituents (e.g., R = isopropyl, phenyl). An Eyring plot for the oxidative addition of MeI to (tBuPNP)RhCl in THF-d8 is consistent with a polar two-step reaction pathway, and the formation of [(tBuPNP)Rh(Me)I]I is also consistent with this mechanism. DFT calculations show that the steric bulk affects the reaction energies of addition reactions which generate six-coordinate complexes by tens of kcal mol-1. The ligand steric bulk is calculated to have a reduced effect (a few kcal mol-1) on SN2 addition barriers, which only require access to one side of the square plane.
Synthesis and characterization of organorhodium(I) complexes with the tridentate ligand 2,6-bis(diphenylphosphanylmethyl)pyridine [Rh(PNP)R] (R = CH3, C6H5) and their reactivity toward ethylene and protic acids
Hahn, Christine,Spiegler, Michael,Herdtweck, Eberhardt,Taube, Rudolf
, p. 1425 - 1432 (2008/10/08)
The organorhodium(I) complexes [Rh(PNP)R] [PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine, R = CH3 (3a), C6H5 (3b)] were synthesized from [Rh(PNP)(C2H4)IBF4 (1a) and LiR and characterized by 31P-, 1H-, and 13C-NMR spectroscopy and EI mass spectrometry. In a THF solution saturated with ethylene 3a and 3b form the five-coordinate ethylene organorhodium(I) complexes [Rh(PNP)R(C2H4)] (5a, b). The stable monohydridorhodium(III) complex [Rh(PNP)ClH-(CH3CN)]SO3CF3 (7) was obtained by the reaction of [Rh(PNP)Cl] with HSO3CF3 in a solution of THF/acetonitrile and characterized by X-ray crystallography. In a THF solution the organorhodium(I) complexes 3a, b react upon the addition of either HSO3CF3 or HNMe3Cl with the immediate release of the respective hydrocarbon HR.
Synthesis of 2,6-bis(diphenylphosphinomethyl) pyridine-monoligand-rhodium(I) complexes [Rh(PNP)L]X with L = pyridine, CH3CN, DMSO and X = CF3SO3, BF4 from the corresponding ethylene complex and comparison of the structures to the piperidine complex (L = piperidine, X = BF4)
Hahn, Christine,Sieler, Joachim,Taube, Rudolf
, p. 1183 - 1193 (2008/10/09)
Investigation of the coordination conditions at the 2,6-bis(diphenylphosphinomethyl)pyridine-rhodium(I) fragment [Rh(PNP)]+ by X-ray crystallography showed a square planar geometry of the neutral chloro and the cationic piperidine complexes, [Rh(PNP)Cl] (1) and [Rh(PNP)(pip)]BF4 (2). New cationic rhodium(I) complexes [Rh(PNP)L]X (L = pyridine, X = SO3CF3 3; L = CH3CN, X = SO3CF3 4a, X = BF4 4b; L = DMSO, X = SO3CF3 5) have been synthesized from the ethylene complexes [Rh(PNP)(C2H4)]X by substitution of the ethylene by the ligand L (L = py, CH3CN, or DMSO). The complexes 3-5 were characterized by IR spectroscopy, 1H-, 13C-, and 31P-NMR spectroscopy and X-ray crystallography. The influence of the ligands on the structure of the complexes was investigated. The cis influence was determined by measurement of the coupling constant JP-Rh and the average length of the Rh - P bonds and the trans influence by the length of the Rh - N(1) bond.
