19472-16-3Relevant academic research and scientific papers
Photochemical pump and NMR probe to monitor the formation and kinetics of hyperpolarized metal dihydrides
Procacci, Barbara,Aguiar, Pedro M.,Halse, Meghan E.,Perutz, Robin N.,Duckett, Simon B.
, p. 7087 - 7093 (2016/11/23)
On reaction of IrI(CO)(PPh3)21with para-hydrogen(p-H2),Ir(H)2I(CO)(PPh3)22 is formed which exhibits strongly enhanced 1H NMR signals for its hydride resonances. Complex 2 also shows similar enhancement of its NMR spectra when it is irradiated under p-H2. We report the use of this photochemical reactivity to measure the kinetics of H2 addition by laser-synchronized reactions in conjunction with NMR. The single laser pulse promotes the reductive elimination of H2 from Ir(H)2I(CO)(PPh3)22 in C6D6 solution to form the 16-electron precursor 1, back reaction with p-H2 then reforms 2 in a well-defined nuclear spin-state. The build up of this product can be followed by incrementing a precisely controlled delay (τ), in millisecond steps, between the laser and the NMR pulse. The resulting signal vs. time profile shows a dependence on p-H2 pressure. The plot of kobs against p-H2 pressure is linear and yields the second order rate constant, k2, for H2 addition to 1 of (3.26 ± 0.42) × 102 M?1 s?1. Validation was achieved by transient-UV-vis absorption spectroscopy which gives k2 of (3.06 ± 0.40) × 102 M?1 s?1. Furthermore, irradiation of a C6D6 solution of 2 with multiple laser shots, in conjunction with p-H2 derived hyperpolarization, allows the detection and characterisation of two minor reaction products, 2a and 3, which are produced in such low yields that they are not detected without hyperpolarization. Complex 2a is a configurational isomer of 2, while 3 is formed by substitution of CO by PPh3
Reactivity patterns and catalytic chemistry of iridium polyhydride complexes
Goldman, Alan S.,Halpern, Jack
, p. 237 - 253 (2007/10/02)
(1, P=PPri3) reacts autocatalytically with CF3COOR (R=CH2CF3) in cyclo-C6D12 at 60 deg C according to: 1 + CF3COOR -> (2) + ROH (4) (eq.1).The rate-law, -d/dt=k1/21/2-1/2 (k=1.25*10-4 M-1/2 sec-1), is consistent with the mechanism, 1 + 2 2 (5) + 4 (rapid equilibrium); 5 + CF3COOR -> > (6) (rate determining); 6 -> 2 + CF3CHO; 5 + CF3CHO -> 2. 2 reacts rapidly with H2 (25 deg C, 1 atm) according to: 2 + 2H2 -> 1 + 4 (eq.2).Although the combination of reactions 1 and 2 constitute a catalytic cycle for the hydrogenation of CF3COOR (CF3COOR + 2H2 -> 2 (4), catalyzed by 1), such catalytic hydrogenation does not occur, presumably because H2 suppresses reaction by rapidly converting the catalytic intermediates, 2 and 5, to 1.However, 1 was found to be effective as a catalyst or catalyst precursor for transfer hydrogenation, e.g.CH2=CHC(CH3)3 + (CH3)2CHOH -> CH3CH2C(CH3)3 + (CH3)2C=O.While not directly detected, IrH3P2 could be trapped at low temperatures by N2 to yield the complexes and which are related through the labile equilibrium, + N2 2 (Keq ca. 1.5 at 35 deg C).
Alkyl halide transfer from palladium(IV) to platinum(II) and a study of reactivity, selectivity, and mechanism in this and related reactions
Aye, Khin-Than,Canty, Allan J.,Crespo, Margarita,Puddephatt, Richard J.,Scott, John D.,Watson, Andrew A.
, p. 1518 - 1522 (2008/10/08)
Kinetic studies of the oxidative addition of MeI or PhCH2Br to [MMe2(L2)] (M = Pd or Pt, L2 = 2,2′-bipyridine or 1,10-phenanthroline) indicate that the reactions occur by the SN2 mechanism, and the reactions occur 7-22 times faster when M = Pt over Pd and 1.2-2.2 times faster when L2 = phen over bpy. Reductive elimination from [PdBrMe2(CH2Ph)(L2)] in the solid state occurs to give both Me-Me and PhCH2Me, and there is a preference for methyl group loss. Thermochemical studies indicate that CH3-CH3 loss gives ΔH = -108 ± 4 kJ mol-1 but PhCH2-CH3 loss gives ΔH = -48 ± 12 kJ mol-1, indicating a relatively strong PhCH2-Pd bond. The complexes [PdIMe3(L2)] or [PdBrMe2(CH2Ph)(L2)] react rapidly with [PtMe2(L2)] by alkyl halide transfer. Kinetic studies have shown that the major route involves loss of halide from palladium(IV) in a preequilibrium step, followed by SN2 attack by [PtMe2(L2)] on an alkyl group of [PdMe3(L2)]+ or [PdMe2(CH2Ph)(L2)]+. In the latter case, benzyl group transfer is preferred over methyl group transfer.
Novel Halogen Exchange Reactions between Halosilanes and Rh(I) or Ir(I) Complexes
Yamashita, Hiroshi,Kobayashi, Toshi-aki,Hayashi, Teruyuki,Tanaka, Masato
, p. 471 - 474 (2007/10/02)
Vaska-type complexes such as MCl(CO)L2 (M=Rh or Ir, L= tertiary phosphine) or the Wilkinson complex RhCl(PPh3)3 underwent halogen exchange reactions with halosilanes Me3SiX (X=Br, I) to give MX(CO)L2 or RhX(PPh3)3 respectively with the formation of Me3SiC
FORMATION OF CARBON-CARBON BONDS ON DI(ORGANO)IRIDIUM COMPLEXES, RR'Ir(CO)(PPH3)2X (R,R' = Me, Ph, CH2Ph, C(O)CH3; X = Cl, I) AND THE CRYSTAL STRUCTURE OF cis,cis,trans-
Churchill, Melvyn Rowen,Fettinger, James C.,Janik, Thomas S.,Rees, Wayne M.,Thompson, Jeffrey S.,et al.
, p. 233 - 246 (2007/10/02)
The reactions of RX with trans-R'Ir(CO)(PPh3)2 are reported.Addition of CH3C(O)Cl to trans-CH3Ir(CO)(PPh3)2 leads to acetone; addition of CH3I to trans-PhIr(CO)(PPh3)2 leads to toluene; and addition of CH3I to trans-C6H5CH2Ir(CO)(PPh3)2 leads to ethylbenzene.Reaction of C2H5Br with trans-CH3Ir(CO)(PPh3)2 leads to CH4 and C2H4.The addition of CH3I to trans-CH3Ir(CO)(PPh3)2 leads to Ir(CH3)2Ir(CO)(PPh3)2I from which Ir(CH3)2(CO)2(PPh3)2(1+) and Ir(CH3)2(CO)(PPh3)2(1+) can be prepared.These dimethyl complexes do not undergo reductive elimination of ethane, acetone or diacetyl under a variety of conditions (CH4 and C2H6 are formed at decomposition).Thus for these complexes the charge, the presence of a free coordination site and the cis stereochemistry do not facilitate reductive elimination reactions.To ascertain that no structural features were preventing reductive elimination from the dimethyl complex we have examined the structure of cis,cis,trans-.This crystallizes in the centrosymmetric triclinic space group P (C1i; No. 2) with a 11.708(2), b 11.738(2), c 14.702(2) Angstroem, α 87.544(13), β 79.181(14), γ 76.963(15)deg, V 1933.4(6) Angstroem3 and D(calc'd) 1.64 g cm-3 for mol. wt. 951.9 and Z = 2.X-ray diffraction data (Mo-Kα, 2θ 4.5-50.0deg) were collected with a Syntex P21 automated four-circle diffractometer and the structure was refined to R 3.5percent for all 6835 reflections (R 2.9percent for those 6133 reflections with F0 > 6?(F0)).The central d6 iridium(III) ion has a slightly distorted octahedral stereochemistry, with Ir-CO 1.943(5) and 1.956(5) Angstroem, Ir-CH3 2.152(5) and 2.155(5) Angstroem and Ir-PPh3 2.391(1) and 2.400(1) Angstroem; interligand angles include OC-Ir-CO 102.09(20), CH3-Ir-CH3 89.70(19) and PPh3-Ir-PPh3 174.68(4)deg.
