C-H Activations at Iridium(I) Square-Planar Complexes Promoted by a Fifth Ligand
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- 作者：Marta Martí ; n ; Olga Torres ; Enrique Oñ ; ate ; Eduardo Sola ; and Luis A. Oro
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：December 28, 2005
- 年：2005
- 卷：127
- 期：51
- 页码：18074 - 18084
- 全文大小：418K
- 年卷期：v.127,no.51(December 28, 2005)
- ISSN：1520-5126
文摘
In the presence of ligands such as acetonitrile, ethylene, or propylene, the Ir(I) complex [Ir(1,2,5,6-
-C8H12)(NCMe)(PMe3)]BF4 (1) transforms into the Ir(III) derivatives [Ir(1-
-4,5,6--C8H12)(NCMe)(L)(PMe3)]BF4 (L = NCMe, 2; 2-C2H4, 3; 2-C3H6, 4), respectively, through a sequence of C-H oxidative additionand insertion elementary steps. The rate of this transformation depends on the nature of L and, in the caseof NCMe, the pseudo-first-order rate constants display a dependence upon ligand concentration suggestingthe formation of five-coordinate reaction intermediates. A similar reaction between 1 and vinyl acetate affordsthe Ir(III) complex [Ir(1--4,5,6--C8H12){-O-2-OC(Me)OC2H3}(PMe3)]BF4 (7) via the isolable five-coordinateIr(I) compound [Ir(1,2,5,6--C8H12){-O-2-OC(Me)OC2H3}(PMe3)]BF4 (6). DFT (B3LYP) calculations in modelcomplexes show that reactions initiated by acetonitrile or ethylene five-coordinate adducts involve C-Hoxidative addition transition states of lower energy than that found in the absence of these ligands. Keyspecies in these ligand-assisted transformations are the distorted (nonsquare-planar) intermediatespreceding the intramolecular C-H oxidative addition step, which are generated after release of onecyclooctadiene double bond from the five-coordinate species. The feasibility of this mechanism is alsoinvestigated for complexes [IrCl(L)(PiPr3)2] (L = 2-C2H4, 27; 2-C3H6, 28). In the presence of NCMe, thesecomplexes afford the C-H activation products [IrClH(CH=CHR)(NCMe)(PiPr3)2] (R = H, 29; Me, 30) viathe common cyclometalated intermediate [IrClH{-P,C-P(iPr)2CH(CH3)CH2}(NCMe)(PiPr3)] (31). The mosteffective C-H oxidative addition mechanism seems to involve three-coordinate intermediates generatedby photochemical release of the alkene ligand. However, in the absence of light, the reaction rates displaydependences upon NCMe concentration again indicating the intermediacy of five-coordinate acetonitrileadducts.
-C8H12)(NCMe)(PMe3)]BF4 (1) transforms into the Ir(III) derivatives [Ir(1--4,5,6--C8H12)(NCMe)(L)(PMe3)]BF4 (L = NCMe, 2; 2-C2H4, 3; 2-C3H6, 4), respectively, through a sequence of C-H oxidative additionand insertion elementary steps. The rate of this transformation depends on the nature of L and, in the caseof NCMe, the pseudo-first-order rate constants display a dependence upon ligand concentration suggestingthe formation of five-coordinate reaction intermediates. A similar reaction between 1 and vinyl acetate affordsthe Ir(III) complex [Ir(1--4,5,6--C8H12){-O-2-OC(Me)OC2H3}(PMe3)]BF4 (7) via the isolable five-coordinateIr(I) compound [Ir(1,2,5,6--C8H12){-O-2-OC(Me)OC2H3}(PMe3)]BF4 (6). DFT (B3LYP) calculations in modelcomplexes show that reactions initiated by acetonitrile or ethylene five-coordinate adducts involve C-Hoxidative addition transition states of lower energy than that found in the absence of these ligands. Keyspecies in these ligand-assisted transformations are the distorted (nonsquare-planar) intermediatespreceding the intramolecular C-H oxidative addition step, which are generated after release of onecyclooctadiene double bond from the five-coordinate species. The feasibility of this mechanism is alsoinvestigated for complexes [IrCl(L)(PiPr3)2] (L = 2-C2H4, 27; 2-C3H6, 28). In the presence of NCMe, thesecomplexes afford the C-H activation products [IrClH(CH=CHR)(NCMe)(PiPr3)2] (R = H, 29; Me, 30) viathe common cyclometalated intermediate [IrClH{-P,C-P(iPr)2CH(CH3)CH2}(NCMe)(PiPr3)] (31). The mosteffective C-H oxidative addition mechanism seems to involve three-coordinate intermediates generatedby photochemical release of the alkene ligand. However, in the absence of light, the reaction rates displaydependences upon NCMe concentration again indicating the intermediacy of five-coordinate acetonitrileadducts.