The course of methyl iodide oxidative addition to various nucleophilic complexes, [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 undergoes slow rearrangement to give a thermodynamically stable stereoisomer, 8. The 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 complex [Rh-2(mu -1,8-(NH)(2)naphth)(CH3CO)(2)I-2(P(p-tolyl)(3))(2)] (15). The reaction of the PMe3 derivative, 6, allows the isolation of the bis-methyl complex [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 cationic methyl complexes 9, 11, 17, and 18, respectively. The behavior of these cationic methyl compounds toward CH3I, CH3OSO2CF3, and tetrabutylamonium iodide is consistent with the rot of these species as intermediates in the S(N)2 addition of CH3I, Compounds 18 and 17 react with an excess of methyl 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)(CH3)(CO)(PiPr(3))(2)] [CF3SO3] (20), respectively. Upon treatment with acetonitrile, 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, 21; Me, 22). A kinetic study of the reaction leading to 21 shows that formation of these complexes involves a slow insertion step followed by the fast coordination of the acetonitrile. The variety of reactions found in this system can be rationalized in terms of three alternative reaction pathways, which are determined by the effectiveness of the interactions between the two metal centers of the dinuclear complex and by the steric constraints due to the phosphine ligands.