Co-operativity effects between adjacent metal sites—kinetics of methyl iodide addition to pyrazolyl-bridged iridium dimers: argument for a concerted mechanism in the reversible two-fragment, two-centre oxidative addition to the cyclo-octa-1,5-diene di-iridium(I) complex [Ir(COD)(µ-pz)]₂

Abstract

Addition of Me1 occurs irreversibly to [Ir(CO)2(p-pz)12 [(I), pzH = pyrazole] in two kinetically distinguishable steps (AM, ASS respectively 32 k 2, 40 k 5 kJ mol-l, -152 k 8, -157 k 16 J mol-l K-l); by contrast Me1 and [Ir(C0D)(p-pz)l2 [ ( Z ) , COD = cyclo-octa-1,5-diene]) enter into equilibrium, AG0298 = -5 k 2 kJ mol-1, with AM = 89 k 4 kJ mol-1, A S = 40 k 15 J mol-1 K-1 for the forward reaction, in striking contrast with activation parameters for related reactions including that of (1) and interpretable together with lack of any kinetic salt or solvent dependence as evidence for a concerted mechanism.

Kinetic and Mechanistic Aspects of Sulfur Recovery from Pd2I2(μ-S)(μ-dpm)2Using I2and Structures of Pd(II) Complexes with the Chelated Monosulfide of dpm

“…The activation parameters Δ H I ⧧ = 32 kJ mol -1 and Δ S I ⧧ = −91 J mol -1 K -1 are typical of those seen for addition at either one or two metal centers ,,, and are comparable to values reported for halogenation of the complexes M 2 (CO) 8 L 2 (M = Mn, Re; L = reactions for which ionic halide intermediates were favored …”

Pyrazolyl-Bridged Iridium Dimers. 16.1 The Atropisomeric (C2) System [Ir(CO)(PPh3)(μ-pz)]2. Synthesis of Homologous Diastereomeric Complexes That Undergo Slow Stereomutation by Ring Inversion of the Bridging Framework: Mechanistic Implications for Bimetallic Substrate Activation

“…The role of mononuclear rhodium(I) complexes (d 8 ) in olefin hydrogenation and hydroformylation has become a paradigm in this context because detailed kinetics data are available to decipher the progression of molecular steps that combine to close the catalytic cycle. Similar studies on related systems support a coherent mechanistic view of oxidative addition mediated at a single metal site. , In contrast, how corresponding two-center chemistry operates is still very poorly defined, despite the implicit significance of binuclear substrate activation as a model for cooperative intermetallic effects . It is particularly difficult to rule out mononuclear character concealed in a dimer fragmentation/activation/recombination sequence.…”

Oxidative-Addition Reactions of Diiodine to Dinuclear Rhodium Pyrazolate Complexes

“…Significant differences on the reactivity of [{M(μ-Pz)(CO) 2 } 2 ] (M = Rh, Ir) complexes toward MeI have been observed. Thus, the rhodium(I) complex does not react with MeI, most probably because the rhodium centers are not basic enough to promote the oxidative-addition reaction, which is more favored for the iridium(I) compound to give the diiridium (II) complex [{Ir(μ-Pz)(CO) 2 } 2 (Me)(I)]. Moreover, [{Rh(μ-Pz)(CO)(P{OPh} 3 )} 2 ] does react with MeI to give the dirhodium(III) complex [{Rh(μ-Pz)(Me)(CO)(P{OPh} 3 )} 2 (μ-I)]I ( 25 ).…”