Abstract
The aryl-PC type ligand 3, benzyl(di-tert-butyl)phosphane, reacts with [Rh(coe)2(solv)n]BF4 (coe = cyclooctene, solv = solvent), producing the C-H activated complexes 4a-c (solv = (a) acetone, (b) THF, (c) methanol). Complexes 4a-c undergo reversible arene C-H activation (observed by NMR spin saturation transfer experiments, SST) and H/D exchange into the hydride and aryl ortho-H with ROD (R = D, Me). They also promote catalytic H/D exchange into the vinylic C-H bond of olefins, with deuterated methanol or water utilized as D-donors. Unexpectedly, complex 2, based on the benzyl-PC type ligand 1 (analogous to 3), di-tert-butyl(2,4,6-trimethylbenzyl)phosphane, shows a very different reversible C-H activation pattern as observed by SST. It is not active in H/D exchange with ROD and in catalytic H/D exchange with olefins. To clarify our observations regarding C-H activation/reductive elimination in both PC-Rh systems, density functional theory (DFT) calculations were performed. Both nucleophilic (oxidative addition) and electrophilic (H/D exchange) C-H activation proceed through η2-C,H agostic intermediates. In the aryl-PC system the agostic interaction causes C-H bond acidity sufficient for the H/D exchange with water or methanol, which is not the case in the benzyl PC-Rh system. In the latter system the C-H coordination pattern of the methyl controls the reversible C-H oxidative addition leading to energetically different C-H activation processes, in accordance with the experimental observations.
| Original language | English |
|---|---|
| Pages (from-to) | 11041-11050 |
| Number of pages | 10 |
| Journal | Journal of the American Chemical Society |
| Volume | 125 |
| Issue number | 36 |
| DOIs | |
| Publication status | Published - Sep 10 2003 |
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Cite this
Aromatic vs aliphatic C-H bond activation by rhodium(I) as a function of agostic interactions : Catalytic H/D exchange between olefins and methanol or water. / Rybtchinski, Boris; Cohen, Revital; Ben-David, Yehoshoa; Martin, Jan M L; Milstein, David.
In: Journal of the American Chemical Society, Vol. 125, No. 36, 10.09.2003, p. 11041-11050.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Aromatic vs aliphatic C-H bond activation by rhodium(I) as a function of agostic interactions
T2 - Catalytic H/D exchange between olefins and methanol or water
AU - Rybtchinski, Boris
AU - Cohen, Revital
AU - Ben-David, Yehoshoa
AU - Martin, Jan M L
AU - Milstein, David
PY - 2003/9/10
Y1 - 2003/9/10
N2 - The aryl-PC type ligand 3, benzyl(di-tert-butyl)phosphane, reacts with [Rh(coe)2(solv)n]BF4 (coe = cyclooctene, solv = solvent), producing the C-H activated complexes 4a-c (solv = (a) acetone, (b) THF, (c) methanol). Complexes 4a-c undergo reversible arene C-H activation (observed by NMR spin saturation transfer experiments, SST) and H/D exchange into the hydride and aryl ortho-H with ROD (R = D, Me). They also promote catalytic H/D exchange into the vinylic C-H bond of olefins, with deuterated methanol or water utilized as D-donors. Unexpectedly, complex 2, based on the benzyl-PC type ligand 1 (analogous to 3), di-tert-butyl(2,4,6-trimethylbenzyl)phosphane, shows a very different reversible C-H activation pattern as observed by SST. It is not active in H/D exchange with ROD and in catalytic H/D exchange with olefins. To clarify our observations regarding C-H activation/reductive elimination in both PC-Rh systems, density functional theory (DFT) calculations were performed. Both nucleophilic (oxidative addition) and electrophilic (H/D exchange) C-H activation proceed through η2-C,H agostic intermediates. In the aryl-PC system the agostic interaction causes C-H bond acidity sufficient for the H/D exchange with water or methanol, which is not the case in the benzyl PC-Rh system. In the latter system the C-H coordination pattern of the methyl controls the reversible C-H oxidative addition leading to energetically different C-H activation processes, in accordance with the experimental observations.
AB - The aryl-PC type ligand 3, benzyl(di-tert-butyl)phosphane, reacts with [Rh(coe)2(solv)n]BF4 (coe = cyclooctene, solv = solvent), producing the C-H activated complexes 4a-c (solv = (a) acetone, (b) THF, (c) methanol). Complexes 4a-c undergo reversible arene C-H activation (observed by NMR spin saturation transfer experiments, SST) and H/D exchange into the hydride and aryl ortho-H with ROD (R = D, Me). They also promote catalytic H/D exchange into the vinylic C-H bond of olefins, with deuterated methanol or water utilized as D-donors. Unexpectedly, complex 2, based on the benzyl-PC type ligand 1 (analogous to 3), di-tert-butyl(2,4,6-trimethylbenzyl)phosphane, shows a very different reversible C-H activation pattern as observed by SST. It is not active in H/D exchange with ROD and in catalytic H/D exchange with olefins. To clarify our observations regarding C-H activation/reductive elimination in both PC-Rh systems, density functional theory (DFT) calculations were performed. Both nucleophilic (oxidative addition) and electrophilic (H/D exchange) C-H activation proceed through η2-C,H agostic intermediates. In the aryl-PC system the agostic interaction causes C-H bond acidity sufficient for the H/D exchange with water or methanol, which is not the case in the benzyl PC-Rh system. In the latter system the C-H coordination pattern of the methyl controls the reversible C-H oxidative addition leading to energetically different C-H activation processes, in accordance with the experimental observations.
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U2 - 10.1021/ja029197g
DO - 10.1021/ja029197g
M3 - Article
C2 - 12952486
AN - SCOPUS:0042232830
VL - 125
SP - 11041
EP - 11050
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 36
ER -