Methyl iodide oxidative addition to monocarbonylphosphine [Rh((C 4 H 3 S)COCHCOR)(CO)(PPh 3 )] complexes utilizing UV/vis and IR spectrophotometry and NMR spectroscopy to identify reaction intermediates: R = C 6 H 5 or C 4 H 3 S Marrigje M. Conradie, Jeanet Conradie * Department of Chemistry, University of the Free State, Bloemfontein, Free State 9301, South Africa Received 4 September 2007; received in revised form 25 October 2007; accepted 26 October 2007 Available online 4 December 2007 Abstract The chemical kinetics, studied by UV/vis and IR, of the oxidative addition of CH 3 I to [Rh((C 4 H 3 S)COCHCOR)(CO)(PPh 3 )], with R=C 6 H 5 (Ph) or C 4 H 3 S, 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: { } k -1 K 1 , k 1 Rh I +CH 3 I[ Rh III -alkyl1] [Rh III -acyl1] K 2 , k 2 k -2 k 3 k -3 [Rh III -alkyl2] k 4 k -4 [Rh III -acyl2] The molecular formulas of all the Rh III –alkyl and Rh III –acyl species are [Rh((C 4 H 3 S)COCHCOR)(CH 3 )(CO)(PPh 3 )(I)] and [Rh((C 4 H 3 S)COCHCOR)(COCH 3 )(PPh 3 )(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 1 H and 31 P NMR study of the oxidative addition of CH 3 I to the different isomers of [Rh((C 4 H 3 S)COCHCOC 6 H 5 )(CO)(PPh 3 )], containing an unsymmetrical b-diketonato ligand, reveals the existence of at least two structural isomers for each reaction intermediate according to the following reaction scheme: k -1 K 1 , k 1 Rh I -A Rh I -B + CH 3 I [Rh III -alkyl1A] [Rh III -acyl1A] K 2 , k 2 k -2 [Rh III -alkyl1B] [Rh III -acyl1B] K c1 K c2 K c3 [Rh III -alkyl2A] [Rh III -alkyl2B] K c4 k 3 k -3 k 4 k -4 [Rh III -acyl2A] [Rh III -acyl2B] K c5 The observed rate of formation and depletion of the two Rh I isomers of the [Rh((C 4 H 3 S)COCHCO(C 6 H 5 ))(CO)(PPh 3 )] 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 = CF 3 . All reaction intermediates are identified spectroscopically. Ó 2007 Elsevier B.V. All rights reserved. Keywords: b-Diketonate; Thienyl; Rhodium; Oxidative addition; NMR; Carbonyl; Phosphine 1. Introduction The interaction of square planar rhodium(I) complexes with methyl iodide keeps drawing attention as a simple 0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2007.10.052 * Corresponding author. Tel.: +27 51 4012194; fax: +27 51 4446384. E-mail address: conradj.sci@ufs.ac.za (J. Conradie). www.elsevier.com/locate/ica Available online at www.sciencedirect.com Inorganica Chimica Acta 361 (2008) 2285–2295