Key factors determining the course of methyl iodide oxidative addition to diamidonaphthalene-bridged diiridium(I) and dirhodium(I) complexes

The course of methyl iodide oxidative addition to various nucleophilic comp lexes, [Ir-2(mu -1,8-(NH)(2)naphth)(CO)(2)(PiPr(3))(2)] (1), [IrRh(mu -1,8- (NH)(2)naphth)(CO)(2)(PiPr(3))(2)] (2), and [Rh-2(mu -1,8-(NH)(2)naphth)(CO )(2)(PR3)(2)] (R = iPr, 3; Ph, 4; p-tolyl, 5; Me, 6), has been investigated . The CH3I addition to complex 1 readily affords the diiridium(II) complex [Ir-2(mu -1,8-(NH)(2)naphth)I(CH3) (CO)(2)(PiPr(3))(2)] (7), which undergoe s slow rearrangement to give a thermodynamically stable stereoisomer, 8. Th e reaction of the Ir-Rh complex 2 gives the ionic compound [IrRh-(mu -1,8-( NH)(2)naphth)(CH3)(CO)(2)(PiPr(3))(2)]I (10). The dirhodium compounds, 3-5, undergo one-center additions to yield acyl complexes of the formula [Rh-2( mu -1,8-(NH)(2)naphth)I(COCH3)(CO)(PR3)(2)] (R = iPr, 12; Ph, 13; p-tolyl, 14). The structure of 12 has been determined by X-ray diffraction. Further reactions of these Rh(III)-Rh(I) acyl derivatives with CH3I are productive only for the p-tolylphosphine derivative, which affords the bis-acyl comple x [Rh-2(mu -1,8-(NH)(2)naphth)(CH3CO)(2)I-2(P(p-tolyl)(3))(2)] (15). The re action of the PMe3 derivative, 6, allows the isolation of the bis-methyl co mplex [Rh-2(mu -1, 8-(NH)(2)naphth)(mu -I)(CH3)(2)(CO)(2)(PMe3)(2)]I (16a) which emanates from a double one-center addition. Upon reaction with methyl triflate, the starting materials, 1, 2, 3, and 6, give the isostructural c ationic methyl complexes 9, 11, 17, and 18, respectively. The behavior of t hese cationic methyl compounds toward CH3I, CH3OSO2CF3, and tetrabutylamoni um iodide is consistent with the rot of these species as intermediates in t he S(N)2 addition of CH3I, Compounds 18 and 17 react with an excess of meth yl triflate to give [Rh-2(mu -1,8-(NH)(2)naphth)(mu -OSO2CF3)(CH3)(2)(CO)(2 )(PMe3)(2)][CF3SO3](19) and [Rh-2(mu -1,8-(NH)(2)naphth)(OSO2CF3)(COCH3)(CH 3)(CO)(PiPr(3))(2)] [CF3SO3] (20), respectively. Upon treatment with aceton itrile, complexes 17 and 18 give the isostructural cationic acyl complexes [Rh-2(mu -1,8-(NH)(2)naphth)(COCH3)(NCCH3)(CO)(PR3)(2)][CF3SO3] (R = iPr, 2 1; Me, 22). A kinetic study of the reaction leading to 21 shows that format ion of these complexes involves a slow insertion step followed by the fast coordination of the acetonitrile. The variety of reactions found in this sy stem can be rationalized in terms of three alternative reaction pathways, w hich are determined by the effectiveness of the interactions between the tw o metal centers of the dinuclear complex and by the steric constraints due to the phosphine ligands.