Mechanism and thermodynamics of alkane and arene carbon-hydrogen bond activation in (C/sub 5/Me/sub 5/)Rh(PMe/sub 3/)(R)H
The complexes (C/sub 5/Me/sub 5/)Rh(PMe/sub 3/)(R)X(R=Me(CH/sub 3/),Ph-)Phenyl), p-tolyl,3,4-C/sub 6/H/sub 3/Me/sub 2/, 2,5-C6H/sub 3/Me2, and C=CH=CHgreater than or equal to-CH/sub 2/-CH/sub 2/;X=Br) react with hydride doners Li(HB(sec-Bu/sub 3/ (butyl)) or Na/sup +/(H/sub 2/Al(OCH/sub 2/CH/sub 2/CH/sub 2/OCH/sub 3/)/sub 2/)-to produce (C/sub 5/Me5)Rh(PMe/sub 3/)(R)H. The complexes with R=alkyl or R=vinyl are unstable, undergoing rapid reductive elimination at 25/sup 0/C, but can be observed by /sub 1/H NMR below -20/sup 0/C. (C/sub 5/Me/sub 5/)Rh(PMe/sub 3/)(CH/sub 3/)H undergoes first-order reductive elimination with k=(6.38 +/-0.10) X 10/sup -5/ s/sup -1/ at -17/sup 0/C. In contrast, (c/sub 5/Me/sub 5/)Rh(PMe/sub 3/)(C/sub 6/H/sub 5/)h undergoes a more complicated first-order process in C/sub 6/D/sub 6/, producing C/sub 6/H/sub 6/ and (C/sub 5/Me/sub 5/)Rh(PMe/sub 3/)(C/sub 6/D/sub 5/)D with the overall activation parameters delta H/sup +/=30.5 +/- 0.8 kcal/mol and ..delta..S/sup +/=14.9+/- 2.5 eu. The alkyl and aryl hydride complexes can also be generated by photochemical extrusion of H/sub 2/ from (C/sub 5/Me/sub 5/)Rh(PMe/sub 3/)H/sub 2/ in the presence of alkane or arene solvent. In a competition experiment, a 5.4:1 selectivity for benzene over cyclopentane was exhibited at -35/sup 0/C. Irradiation in toluene solvent at -45/sup 0/C produced products in which activation of all possible C-H bonds of toulene was observed 57% meta, 36% para, 7% ortho, and <1% benzyl. Thermodynamically controlled competition between activation of benzene and tolune, m-xylene, o-xylene, or p-xylene showed preferences for benzene of 2.7, 12.1, 7.6, and 58.6. The aryl complexes (C/sub 5/Me/sub 5/)Rh(PMe/sub 3/)(aryl)H were found to be in rapid equilibrium with their ..nu../sup 2/-arene derivatives at temperatures above -15/sup 0/C. Mechanistic studies revealed a (1,2)-shift pathway around the ring with ..delta..H/sup +/ =16.3 +/- 0.2 kcal/mol and ..delta..S/sup +/ =-6.3 +/- 8 eu for derivative with R=2,5-C/sub 6/H/sub 3/Me/sub 2/.
- OSTI ID:
- 6139429
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 106:6; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
Similar Records
Reactions of (C sub 5 Me sub 5 )Rh(PMe sub 3 )(R)H with electrophiles. Insertion of unsaturated molecules into activated carbon-hydrogen bonds
Selectivity in the activation of fluorinated aromatic hydrocarbons by [(C[sub 5]H[sub 5])Rh(PMe[sub 3])] and [(C[sub 5]Me[sub 5])Rh(PMe[sub 3])]
Related Subjects
400201 -- Chemical & Physicochemical Properties
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACTIVATION ENERGY
ALKANES
ALKENES
ALKYLATED AROMATICS
AROMATICS
BENZENE
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPARATIVE EVALUATIONS
COMPLEXES
CYCLOALKENES
DATA
DECOMPOSITION
DEUTERIUM COMPOUNDS
ENERGY
EXPERIMENTAL DATA
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
INFORMATION
ISOMERIZATION
KINETICS
LOW TEMPERATURE
MEDIUM TEMPERATURE
NMR SPECTRA
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
ORGANIC SOLVENTS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
RHODIUM COMPLEXES
RHODIUM COMPOUNDS
RHODIUM HYDRIDES
SOLVENTS
SPECTRA
STABILITY
SYNTHESIS
TEMPERATURE DEPENDENCE
TOLUENE
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
XYLENES