Showing papers by "William D. Jones published in 1984"

The mechanism and thermodynamics of alkane and arene carbon-hydrogen bond activation in (C5Me5)Rh(PMe3)(R)H

Abstract: 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%more » 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/.« less

Preparation and conformational dynamics of (C5Me5)Rh(PR'3)RX. Hindered rotation about rhodium-phosphorus and rhodium-carbon bonds

Abstract: Etude de l'influence des substituants en para du coordinat aryl sur la rotation des liaisons Rh-P et Rh-C, a partir des spectres RMN 1 H, 31 P, 13 C. Etude structurale de [C 5 (CH 3 ) 5 ] Rh[P(CH 3 ) 3 ] [C 6 H 5 Br]

The mechanism and thermodynamics of alkane and arene carbon-hydrogen bond activation in (c5me5)rh(pme3)(r)h

Abstract: 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%more » 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/.« less