The interaction of a cyclo-octa-1,5-diene-iridium complex with molecular hydrogen (original) (raw)
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Organometallics, 1999
The trisacetonitrile complexes [IrClH(P i Pr 3 )(NCCH 3 ) 3 ]BF 4 (1) and [IrH 2 (P i Pr 3 )(NCCH 3 ) 3 ]-BF 4 (2) have been prepared in one-pot reactions with high yields by reaction of the iridium-(I) dimers [Ir(µ-Cl)(coe) 2 ] 2 and [Ir(µ-OMe)(cod) 2 ] 2 with the phosphonium salt [HP i Pr 3 ]BF 4 . The rates of exchange between free acetonitrile and the labile acetonitrile ligands of complexes 1 and 2 have been measured by NMR spectroscopy. This kinetic study has shown that both complexes readily dissociate one acetonitrile ligand trans to hydride, giving rise to fluxional five-coordinate intermediates. Substitution products 3-7 have been obtained by treatment of complexes 1 and 2 with CO and PMe 3 . The structures determined for 3-7 can be rationalized on the basis of the steric requirements of the ligands, indicating that the products are formed by thermodynamic control. Ethene inserts reversibly into the Ir-H bond of 1 to give the compound [IrCl(Et)(P i Pr 3 )(NCCH 3 ) 3 ]BF 4 (8), which has been used for the preparation of the stable ethyliridium(III) complexes [IrCl(Et)(P i Pr 3 )(Py) 2 (NCCH 3 )]BF 4 (9) and [Ir(η 2 -O 2 CCH 3 )Cl(Et)(P i Pr 3 )(NCCH 3 ) 3 ] (10), respectively. The molecular structure of 10 has been determined by X-ray crystallography. The reaction of 2 with ethene, at low temperature, results in the sequential formation of the ethene complex [IrH 2 (
Ligand exchange reactions of iridium hydrido formyl compounds
Organometallics, 1987
Facile halide, CO, and PMe, substitution for the iodide ligand of IrH(CHO)I(PMe3)3 (la) has been observed. The evidence supports a conventional dissociative mechanism for the substitution reaction: an acetonitrile-solvated 16-electron hydrido formyl compound has been detected following treatment of compound la with silver ion, and mechanisms involving mobile hydrogen atoms have been ruled out by isotope labeling studies.
Vinylic C−H Bond Activation and Hydrogenation Reactions of Tp‘Ir(C2H4)(L) Complexes
Inorganic Chemistry, 1998
The substitution of one of the ethylene ligands of the complexes Tp′Ir(C 2 H 4) 2 (Tp′) Tp Me 2, 1*; Tp′) Tp, 1) by soft donors such as tertiary phosphines or carbon monoxide is a facile reaction that gives the corresponding Tp′Ir(C 2 H 4)(L) adducts. Spectroscopic studies support their formulation as five-coordinate, 18-electron species that possess a distorted trigonal bipyramidal geometry. This proposal has been confirmed by a single-crystal X-ray study carried out with the PMe 2 Ph complex Tp Me 2Ir(C 2 H 4)(PMe 2 Ph) (3b*). Related hydride derivatives of Ir(III) can be obtained either by hydrogenation of the Ir(I) adducts (in general, this gives Tp′IrH 2 (L) compounds) or by thermal activation of one of the C-H bonds of the coordinated C 2 H 4 ligand of the Tp Me 2Ir(C 2 H 4)(L) compounds. All these reactions can be understood by invoking the participation of transient, 16-electron (η 2-Tp′)Ir intermediates, but the thermodynamics of the [Ir](C 2 H 4) to [Ir]H(CHdCH 2) conversion does not require an overall change in the coordination mode of the Tp′ ligand.
Organometallics, 1982
crystal was mounted on the goniometer head with its long dimension nearly parallel to the phi axis of the diffractometer. A total of 8327 independent reflections having 2@MoK& 55' (the equivalent of 1.0 limiting Cu Ka spheres) were measured in two concentric shells of increasing 28, each of which contained approximately 4150 reflections. A scanning rate of 6'/min was used for all others. Each of these 1.1' wide scans were divided into 19 equal (time) intervals, and those 13 contiguous intervals which had the highest single accumulated count at their midpoint were used to calculate the net intensity from scanning. Background counta, each lasting for one-fourth the total time used for the net scan (13/19 of the total scan time), were measured at u settings 1.1' above and below the calculated Kn doublet value for each reflection. Since $ scans for several intense reflections confirmed the anticipated absence of variable absorption for this sample, the intensities were reduced without absorption corrections to relative squared amplitudes, Fd2, by meana of appropriate Lorentz and polarization corrections. The structure was solved by using the "heavy-atom" technique. Unitweighted full-matrix least-squares refinement which utilized anisotropic thermal parameters for all 39 crystallographically independent nonhydrogen atoms converged to R1 (unweighted, based on flu = 0.046 and Rz (weighted, based on flu = 0.057 for 3482 independent reflections having 28-< 4 3 ' and I > 3a(Z). A difference Fourier synthesis at this point permitted the location of all 59 hydrogen atoms in the asymmetric unit. All additional least-squares cycles for 1 refined hydrogen atoms with isotropic thermal parameters and nonhydrogen atoms with anisotropic thermal parameters. Unit-weighted cycles gave R1 = 0.023 and R2 = 0.025 with 3482 reflections. Similar unit-weighted refinement cycles with the more complete (2@MoKa < 55') data set gave R1 = 0.028 and Rz = 0.029 for 6133 reflections. The final cycles of empirically ~eighted'~ full-matrix least-squares refinement with (48) The R values are defined as Rl = xIIFoI-~F c~~/~~F o~ and Rz = {xw(pol-. pc1)2/FylFo12f/z, where w is the weight given each reflection. The function mmmlzed I xw(lFol-I(IFc1)2, where K is the scale factor. 98 independent atoms gave R1 = 0.028 and R2 = 0.034 for 6133 independent reflections having 2 @ h m < 55' and I > 3a(I). Since a careful comparison of final Fo and F, values22 indicated the absence of extinction effeds, extinction corrections were not made. All structure factor calculations employed recent tabulations of atomic form factorsub and anomalous dispersion corrections4Bc to the scattering factors of the Rh and P atoms. All calculations were performed on a Data General Eclipse 5-2 0 computer with 65K of 16-bit words, a floating point processor for 32-and 64-bit arithmetic and versions of the Nicolet E-XTL interactive crystallographic software package as modified at Crystalytics Co. Acknowledgment. This research was supported by the National Science Foundation. E.L.M. is indebted t o the Miller Institute for Basic Research in Science for a grant in the form of a Miller Professorship. R.R.B. is the recipient of a National Science Foundation Graduate Fellowship (197S1982). The rhodium chloride was furnished on a loan grant through the generosity of Johnson Matthey, Inc. We thank R. Hoffmann for helpful suggestions.
Organometallics, 1998
The reaction of fac-[IrH 2 (NCCH 3) 3 (P i Pr 3)]BF 4 (1) with potassium pyrazolate gave the binuclear 34-electron complex [Ir 2 (µ-H)(µ-Pz) 2 H 3 (NCCH 3)(P i Pr 3) 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 ∆H q) 20.9 (0.6 kcal mol-1 and ∆S q) 2.5 (1.3 e.u. Reaction of 2 with various Lewis bases (L) gives the substitution products [Ir 2 (µ-H)(µ-Pz) 2 H 3 (L)(P i Pr 3) 2 ] (L) C 2 H 4 (3), CO (4), HPz (5)). The reaction of complex 5 with C 2 H 4 yields the ethyl derivative [Ir 2 (µ-H)(µ-Pz) 2 (C 2 H 5)H 2 (HPz)(P i Pr 3) 2 ] (6); this reaction is reversible. Complexes 2 and 3 react with CHCl 3 to give CH 2 Cl 2 and the compounds [Ir 2 (µ-H)(µ-Pz) 2 H 2 (Cl)(L)(P i Pr 3) 2 ] (L) NCCH 3 (7), C 2 H 4 (8)). In the 1 H 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 D 2 atmosphere. Analysis of the isotopomeric mixtures of 2 reveals downfield isotopic shifts in the 31 P{ 1 H} NMR spectrum. Downfield as well as high-field shifts are found for the hydride signals in the 1 H NMR spectrum of partially deuterated 2. Further reaction of 3 with H 2 gave ethane and the dihydrogen complex [Ir 2 (µ-H)(µ-Pz) 2 H 3 (η 2-H 2)(P i Pr 3) 2 ] (9). Under a deficiency of H 2 , in toluened 8 solution, 9 undergoes H/D scrambling with the participation of the solvent. It has also been found that under H 2 complex 3 catalyzes the hydrogenation of cyclohexene.
Organometallics, 2009
We report the synthesis of the pincer-cyclometalated (NNC t-Bu )Ir(III) dihydroxo pyridyl complex 6, which catalyzes hydrogen-deuterium (H/D) exchange between water and benzene in the presence of base (TOF = ∼6 Â 10 -3 s -1 at 190°C). Experimental and density functional theory (B3LYP) studies suggest that H/D exchange occurs through loss of pyridine followed by benzene coordination and C-H bond activation by a heterolytic substitution mechanism to give a phenyl aquo complex, which may dimerize. Exchange of H 2 O for D 2 O followed by the microscopic reverse of CH activation leads to deuterium incorporation into benzene. Synthesis of the μ-hydroxo phenyl dinuclear complex [(NNC t-Bu )Ir(Ph)(μ-OH)] 2 (9) also catalyzes H/D exchange with a turnover frequency (TOF = ∼7 Â 10 -3 s -1 at 190°C) similar to that for 6.
Journal of the …, 1993
IrHC12P2 (P = PiPr3) reacts rapidly with H2 at 25 OC to set up an equilibrium where Hz binds trans to the original hydride ligand (trans-2). A second slower reaction forms IrH(H2)C12P2 (cis-2), where the cis disposition of the chlorides, and also H cis to Hz, was established by neutron diffraction. This molecule (unlike trans-2), shows rapid site exchange between coordinated H and Hz. cis-2 can be induced to lose HCl to form Ir(H)2ClP2 (3). The structure of Ir(H)ZCl(PtBu2Ph)2, an analog of 3, was shown by neutron diffraction to have a planar HzIrCl in a Y shape, with C1 at the base of the Y and a H-Ir-H angle of only 73'. ECP ab initio calculations of IrHzCl(PH& show that the Y shape with a H-Ir-H angle close to the experimental value has the minimum energy. They also show that the trans-2 isomer of IrH(H2)Clz(PH3)2 is less stable than the cis-2 isomer by 10.3 kcal/mol. The Ir-Hz interaction is stronger in cis-2. The rotational barrier has been calculated in the two isomers as 2.3 (trans) and 6.5 (cis) kcal/mol. In agreement with the experimental structure, the H-H bond is found to eclipse preferentially the Ir-H bond in cis-2. The calculations also show that the Ir-H2 bond dissociation energy is greatkr in cis-2. It thus appears that the binding ability of a metal fragment not only depends on its ligands but is also linked in a subtle way to its stereochemistry. The J(HD) value for coordinated Hz in cis-2 is 12 f 3 Hz. The implication of this small value and of a Tl,i,(200 MHz) of 38 ms is an H/H distance of 1.07-1.35 A, which compares to the neutron diffraction distance of 1.11(3) A. The Ir-H distances of cis-2 are unprecedented in that the hydride-Ir distance (1.584( 13) A) is not shorter than the distances to the H2 hydrogens (1.537(19) and 1.550(17) A). One of the H2 hydrogens interacts with chloride of an adjacent molecule to give an infinite hydrogen-bonded polymer. An inelastic neutron scattering spectroscopic study on solid IrHCl~(Hz)(PiPr3)2 sets a lower limit on the rotational barrier of the Ir(Hz) unit of 2.0 kcal/mol. Ab initio calculations on IrHCl2(Hz)(PH3)2 yield a H-H distance in these two isomers of 0.81 and 1.4 A, respectively, showing that the moiety IrHClz(PH3)z with chlorides mutually cis is a much stronger reducing agent than that with chlorides trans (and thus H trans to Hz). Crystallographic data: For cis-2 (at 15K), a = 13.008(4) A, b = 11.296 (4) A, c = 16.095(4) A in space group Pna2l (2 = 4). For Ir(H)zC1(PtBu2Ph)2 (at 15K), a = 8.236(2) A, b = 17.024(6) A, c = 20.528(10) A, j 3 = 96.27(4)' in space group P21/c ( Z = 4).