Cooperative Bimetallic Effects on New Iridium(III) Pyrazolate Complexes:  Hydrogen−Hydrogen, Carbon−Hydrogen, and Carbon−Chlorine Bond Activations

Abstract

The reaction of fac-[IrH2(NCCH3)3(PiPr3)]BF4 (1) with potassium pyrazolate gave the binuclear 34-electron complex [Ir2(μ-H)(μ-Pz)2H3(NCCH3)(PiPr3)2] (2). The structure of 2 was determined by X-ray diffraction. An electrostatic potential calculation located three terminal hydride ligands and one hydride bridging both iridium centers. The feasibility of this arrangement was studied by EHMO calculations. The spectroscopic data for 2 show that the complex is rigid in solution on the NMR time scale. In solution, the acetonitrile ligand of 2 dissociates. The activation parameters for this dissociation process in toluene-d 8 are ΔH ⧧ = 20.9 ± 0.6 kcal mol-1 and ΔS ⧧ = 2.5 ± 1.3 e.u. Reaction of 2 with various Lewis bases (L) gives the substitution products [Ir2(μ-H)(μ-Pz)2H3(L)(PiPr3)2] (L = C2H4 (3), CO (4), HPz (5)). The reaction of complex 5 with C2H4 yields the ethyl derivative [Ir2(μ-H)(μ-Pz)2(C2H5)H2(HPz)(PiPr3)2] (6); this reaction is reversible. Complexes 2 and 3 react with CHCl3 to give CH2Cl2 and the compounds [Ir2(μ-H)(μ-Pz)2H2(Cl)(L)(PiPr3)2] (L = NCCH3 (7), C2H4 (8)). In the 1H NMR spectra of 2 − 6, the signal of the bridging hydride ligand shows two very different J HP couplings; in contrast, for the chloride complexes 7 and 8, two equal J HP couplings are observed. NOE and T 1 measurements lead to the conclusion that in complexes 2 − 6 the hydride bridges the iridium centers in a nonsymmetric fashion, whereas for 7 and 8 the bridge is symmetrical. This structural feature largely influences the reactivity. Compounds 2 and 3 undergo H/D exchange under a D2 atmosphere. Analysis of the isotopomeric mixtures of 2 reveals downfield isotopic shifts in the 31P{1H} NMR spectrum. Downfield as well as high-field shifts are found for the hydride signals in the 1H NMR spectrum of partially deuterated 2. Further reaction of 3 with H2 gave ethane and the dihydrogen complex [Ir2(μ-H)(μ-Pz)2H3(η2-H2)(PiPr3)2] (9). Under a deficiency of H2, in toluene-d 8 solution, 9 undergoes H/D scrambling with the participation of the solvent. It has also been found that under H2 complex 3 catalyzes the hydrogenation of cyclohexene.

Binuclear Oxidative Addition of Hydrogen in Diamidonaphthalene‐Bridged Diiridium Complexes

“…As in other cases where an asymmetric bridging hydride has been found, [11,19] the asymmetry can be attributed to the different trans influences of the ligands trans to the bridge. The structural parameters of the acetone ligand of 4 are similar to those found in the mononuclear complex [IrH 2 (Me 2 CO) 2 (PPh 3 ) 2 ]BF 4 , [21] the previously sole example of an (acetone)Ir III complex determined by X-ray diffraction.…”

“…However, the same investigations proposed that these additions could be more favorable in d 7 ± d 7 species, as suggested by the calculations on iron(i) models. Due to the importance of oxidative additions in homogeneous catalysis [10] and following our interest in the catalytic applications of binuclear complexes, [11] the present work focuses on the study of concerted oxidative additions in binuclear iridium complexes. From the variety of possible reactions and reactants, we have restricted ourselves to simple processes, such as protonations, oxidations, and additions of hydrogen, which can model the behavior of other small molecules of interest in homogeneous catalysis.…”

“…(2)]. [11,19] A weak band in the IR spectrum at 2253 cm À1 can be attributed to the terminal hydride, whereas the carbonyl stretching frequencies at 2076 and 2056 cm À1 agree with an Ir III ± Ir III complex. [20] The triflate ligand of 3 can be substituted by weak Lewis bases, such as acetone or acetonitrile, to give the solvato complexes Figure 1 shows the structure of the cation of 4, as determined by X-ray diffraction and Table 1 lists the relevant distances and angles.…”

“…[11] The different rates of deuteration of the two hydrido ligands suggest that, for complexes 4 and 5, the terminal hydrides are kinetically more acidic than the bridging ones. In contrast to this, treatment of complexes 3 ± 5 with one equivalent of triethylamine yielded the terminal hydrido complex 2.…”

Activation of CCl and CH Bonds by Ligated S22− Ions: Conversion of Organic Chlorides into Organosulfur Compounds in cis‐[(IrCp*)2(μ‐CH2)2(μ‐S2R)]+

“…As a result, various investigators are engaged in the activation of carbon-chlorine bonds using chemical, microbial, or thermal methods for converting organic halides into either less toxic or industrially useful materials. [1][2][3][4][5][6][7] The activation of C À Cl bonds by chemical methods essentially involves reactions at a metal surface [2] or oxidative addition at the metal center of complexes. [3,4,7] Thiolate anions S n 2À (n = 1, 2, 3) can convert alkyl chloride into dialkyl oligosulfane by activation of the CÀCl bond.…”