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Organometallics 40(11), 1751 - 1757 (2021). doi:10.1021/acs.organomet.1c00216, Platinum hydride species catalyze a number of interesting organic reactions. However, their reactions typically involve the use of high loadings of noble metal and are difficult to recycle, making them somewhat unsustainable. We have synthesized surface-immobilized Pt–H species via oxidative addition of surface OH groups to Pt(P$^t$Bu$_3$)$_2$ (1), a rarely used immobilization technique in surface organometallic chemistry. The hydride species thus made were characterized by infrared, magic-angle spinning nuclear magnetic resonance, and X-ray absorption spectroscopies and catalyzed both olefin isomerization and cycloisomerization of a 1,6 enyne (5) with a high selectivity and low Pt loading., Published by ACS Publ., Washington, DC

The influence of nuclearity and charge of chiral Rh diene complexes on the activity and enantioselectivity in catalytic asymmetric 1,2-additions of organoboron reagents to N-tosylimines and 1,4-add...

We synthesized isolated Cr(III) sites on SiO2-Al2O3 and Al2O3 by grafting and subsequent controlled thermal treatment of Cr(OSi(OtBu)3)3(THF)2 and Cr(Al(OiPr)4)3 on alumina. CrOx/Al2O3 was obtained from incipient wetness impregnation of Al2O3 with CrO3 in H2O followed by calcination as carried out for the synthesis of industrial Cr based dehydrogenation catalysts. These materials were characterized by IR EPR XAS and by the adsorption of the probe molecules CO and pyridine and the results were compared to previously reported isolated Cr(III)/SiO2. All of these materials were active in propane dehydrogenation at 550 °C where higher TOFs were obtained for Cr(III)/SiO2 Al2O3 and Cr(III)/Al2O3 than for CrOx/Al2O3 and Cr(III)/SiO2. For mechanistic studies the reverse reaction propene hydrogenation was studied. Here the order of reactivity was opposite that of dehydrogenation with CrOx/Al2O3 and Cr(III)/SiO2 being more active in hydrogenation than Cr(III)/SiO2 Al2O3 and Cr(III)/Al2O3. Kinetic analysis and labeling studies with D2 showed that the rate law is in all cases first order in H2 partial pressure but had different dependence on propene partial pressure from catalyst to catalyst. We found small normal kinetic isotope effects of 1 = KIE = 2 activation enthalpies up to 40 kJ mol–1 and large negative activation entropies between -100 and -194 J K–1 mol–1 for the different Cr catalysts. We also performed parahydrogen induced polarization (PHIP) experiments which showed that H2 addition to propene proceeds at least in part via a pairwise mechanism. The experimental data for propene hydrogenation suggests adsorption/desorption pre equilibria of H2 (or D2) and propene followed by H2 activation and insertion of propene. DFT computations for propane dehydrogenation and propene hydrogenation on Cr(III) on a periodic alumina model show that a mechanism involving X–H activation (X = R H) is energetically feasible with activation enthalpies and entropies that are comparable to the experimentally determined values.

Several different pKa values for the complex (η5-C5H5)Fe(CO)2H (FpH) in acetonitrile are present in the literature, ranging over 7 orders of magnitude. As a result, the energy of its Fe–H bond is also in dispute, making it difficult to predict the reactivity of this complex. The pKa, bond dissociation enthalpy, bond dissociation free energy, and hydricity of FpH have been measured. The pKa values of analogous group 8 hydrides have been determined, and the energies of the M–H bonds and the hydricity of FpH have been established.