Structural and dynamic properties of propane coordinated to TpRh(CNR) from a confrontation between theory and experiment

被引:30
作者
Clot, Eric
Eisenstein, Odile [1 ]
Jones, William D.
机构
[1] Univ Montpellier 2, CNRS, UMR 5253, Inst Charles Gerhardt, F-34095 Montpellier 5, France
[2] Univ Montpellier I, Ecole Natl Super Chim Montpellier, F-34006 Montpellier, France
[3] Univ Rochester, Dept Chem, Rochester, NY 14627 USA
关键词
density functional theory; hydrocarbon activation; rhodium; selectivity;
D O I
10.1073/pnas.0609454104
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Density functional calculations with the B3PW91 functional have been carried out on the TpRh(CNMe) species [Tp = HB(pyrazolyl)(3)] as a model for Tp'Rh(CNCH2CMe3) [Tp' = HB(3,5-dimethylpyrazolyl)(3)] in interaction with propane. Two sigma, complexes have been found as minima coordinated through either a methyl or a methylene C-H bond, the former being more stable. The approach of the alkane to TpRh(CNMe) has been studied. Although no transition state could be located, study of this path reveals the key importance of the partial decoordination of one pyrazole ring. The full coordination of the alkane can only be achieved when the metal is essentially in a square pyramid coordination with one of the three pyrazole groups only weakly interacting with Rh. The main reaction of the methyl or complex is oxidative addition, leading to the n-propyl hydride complex. In contrast, two reactions are found for the methylene sigma complex: (i) oxidative addition to give the isopropyl complex and (h) exchange between the secondary and primary C-H bonds to convert the methylene complex of propane into a methyl complex of propane. This latter reaction has a much lower barrier than the oxidative addition at the methylene C-H bond. The results account well for most of the experimental results obtained from kinetic studies. Steric factors are found to control the energy barriers between these various processes, disfavoring any process that brings the central carbon into close proximity to Rh.
引用
收藏
页码:6939 / 6944
页数:6
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