Methyl iodide oxidative addition to monocarbonylphosphine [Rh((C4H3S)COCHCOR)(CO)(PPh3)] complexes utilizing UV/vis and IR spectrophotometry and NMR spectroscopy to identify reaction intermediates: R=C6H5 or C4H3S
摘要:
The chemical kinetics, studied by UV/vis and IR, of the oxidative addition of CH3I to [Rh((C4H3S) COCHCOR)(CO)(PPh3)], with R = C6H5 (Ph) or C4H3S, consists of three definite reaction steps and involves isomers of two distinctly different classes of a Rh-III-alkyl and two distinctly different classes of a Rh-III-acyl species according to the following reaction scheme:Rh-1+CH3 I[reversible arrow(K1,k1)(k-1){Rh-III-alkyl1]reversible arrow(K2,k2)(k-2)[Rh-III-acyl1]}reversible arrow(k3)(k-3)[R-III-alkyl2]reversible arrow(k4)(k-4) [Rh-III-acyl2]The molecular formulas of all the Rh-III-alkyl and Rh-III-acyl species are [Rh((C4H3S) COCHCOR)(CH3)(CO)(PPh3)(I)] and [Rh((C4H3S) COCHCOR)(COCH3)(PPh3)(I)] respectively, but the geometry is different due to different co-ordination positions of the ligands. The equilibrium K-2 was fast enough to be maintained during the Rh-I depletion in the first reaction step and during the Rh-III-alkyl2 formation in the second reaction step. A H-1 and P-31 NMR study of the oxidative addition of CH3I to the different isomers of [Rh((C4H3S) COCHCOC6H5)(CO)(PPh3)], containing an unsymmetrical beta-diketonato ligand, reveals the existence of at least two structural isomers for each reaction intermediate according to the following reaction scheme:[GRAPHICS]The observed rate of formation and depletion of the two Rh I isomers of the [Rh((C4H3S) COCHCO(C6H5))(CO)(PPh3)] complex, as well as the different isomers of each reaction intermediate, are the same, contrary to what was previously found for the formation of the alkyl2 isomers when R = CF3. All reaction intermediates are identified spectroscopically. (C) 2007 Elsevier B. V. All rights reserved.
Methyl iodide oxidative addition to monocarbonylphosphine [Rh((C4H3S)COCHCOR)(CO)(PPh3)] complexes utilizing UV/vis and IR spectrophotometry and NMR spectroscopy to identify reaction intermediates: R=C6H5 or C4H3S
摘要:
The chemical kinetics, studied by UV/vis and IR, of the oxidative addition of CH3I to [Rh((C4H3S) COCHCOR)(CO)(PPh3)], with R = C6H5 (Ph) or C4H3S, consists of three definite reaction steps and involves isomers of two distinctly different classes of a Rh-III-alkyl and two distinctly different classes of a Rh-III-acyl species according to the following reaction scheme:Rh-1+CH3 I[reversible arrow(K1,k1)(k-1){Rh-III-alkyl1]reversible arrow(K2,k2)(k-2)[Rh-III-acyl1]}reversible arrow(k3)(k-3)[R-III-alkyl2]reversible arrow(k4)(k-4) [Rh-III-acyl2]The molecular formulas of all the Rh-III-alkyl and Rh-III-acyl species are [Rh((C4H3S) COCHCOR)(CH3)(CO)(PPh3)(I)] and [Rh((C4H3S) COCHCOR)(COCH3)(PPh3)(I)] respectively, but the geometry is different due to different co-ordination positions of the ligands. The equilibrium K-2 was fast enough to be maintained during the Rh-I depletion in the first reaction step and during the Rh-III-alkyl2 formation in the second reaction step. A H-1 and P-31 NMR study of the oxidative addition of CH3I to the different isomers of [Rh((C4H3S) COCHCOC6H5)(CO)(PPh3)], containing an unsymmetrical beta-diketonato ligand, reveals the existence of at least two structural isomers for each reaction intermediate according to the following reaction scheme:[GRAPHICS]The observed rate of formation and depletion of the two Rh I isomers of the [Rh((C4H3S) COCHCO(C6H5))(CO)(PPh3)] complex, as well as the different isomers of each reaction intermediate, are the same, contrary to what was previously found for the formation of the alkyl2 isomers when R = CF3. All reaction intermediates are identified spectroscopically. (C) 2007 Elsevier B. V. All rights reserved.
Stereochemistry of the reaction products of the oxidative addition reaction of methyl iodide to [Rh((C4H3S)COCHCOR)(CO)(PPh3)]: A NMR and computational study. R=CF3, C6H5, C4H3S
作者:Marrigje M. Conradie、Jeanet Conradie
DOI:10.1016/j.ica.2008.04.046
日期:2009.1
A NMR study of the reaction mixture of the square planar [Rh((C4H3S) COCHCOR)(CO)(PPh3)] complex and CH3I, where R = CF3, C6H5 or C4H3S, revealed that two types of alkyl and one (R = CF3) or two (R = C6H5 or C4H3S) types of acyl species exist in the system. Two isomers of each species with an unsymmetrical beta-diketonato ligand were observed. H-1-H-1 NOESY NMR unambiguously showed that the PPh3 group is in the apical position in the more stable Rh-III-alkyl product. Theoretical computations of the equilibrium geometry of the possible reaction products, consistent with experimental observations, revealed that the. first alkyl product results from trans addition to Rh-I and that the second thermodynamic alkyl product adopts an octahedral geometry with the PPh3 group and the iodide above and below the square planar plane. Theoretical computations also revealed that the thermodynamic acyl product adopts a square-pyramidal geometry with the COCH3 group in the apical position. (C) 2008 Elsevier B.V. All rights reserved.