An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The predictive ability of density functional theory is fundamental to its usefulness in chemical applications. Recent work has compared solution-phase enthalpies of activation for metal-ligand bond dissociation to enthalpies of reaction for bond dissociation, and the present work continues those comparisons for 43 density functional methods. The results for ligand dissociation enthalpies of 30 metal-ligand complexes tested in this work reveal significant inadequacies of some functionals as well as challenges from the dispersion corrections to some functionals. The analysis presented here demonstrates the excellent performance of a recent density functional, M11plus, which contains nonlocal rung-3.5 correlation. We also find a good agreement between theory and experiment for some functionals without empirical dispersion corrections such as M06, r2SCAN, M06-L, and revM11, as well as good performance for some functionals with added dispersion corrections such as ωB97X-D (which always has a correction) and BLYP, B3LYP, CAM-B3LYP, and PBE0 when the optional dispersion corrections are added.
The synthesis, spectroscopic, and X-ray structural studies of acrylic acid complexes of iron and ruthenium tetracarbonyls are reported. In addition, the deprotonated η2-olefin bound acrylic acid derivative of iron as well as its alkylated species were fully characterized by X-ray crystallography. Kinetic data were determined for the replacement of acrylic acid, acrylate, and methylacrylate for the group 8 metal carbonyls by triphenylphosphine. These processes were found to be first-order in the concentration of metal complex with the rates for dissociative loss of the olefinic ligands from ruthenium being much faster than their iron analogues. However, the ruthenium derivatives afforded formation of primarily mono-phosphine metal tetracarbonyls, whereas the iron complexes led largely to trans-di-phosphine tricarbonyls. This difference in behavior was ascribed to a more stable spin crossover species 3Fe(CO)4 which undergoes rapid CO loss to afford the bis phosphine derivative. The activation enthalpies for dissociative loss of the deprotonated η2-bound acrylic acid ligand were found to be larger than their corresponding values in the protonated derivatives. For example, for dissociative loss of the protonated and deprotonated acrylic acid derivatives of iron(0) the ΔH⧧ values determined were 28.0 ± 1.2 and 34.1 ± 1.5 kcal·mol–1, respectively. Density functional theory (DFT) computations of the bond dissociation energies (BDEs) in these acrylic acids and closely related complexes were in good agreement with enthalpies of activation for these ligand substitution reactions, supportive of a dissociative mechanism for olefin displacement. Processes related to catalytic production of acrylic acid from CO2 and ethylene are considered.
Milstein and co-workers have reported that the pincer complexes trans-[Ru(H)2(PNN)(CO)] catalyze the unprecedented homogeneous hydrogenation of dimethyl carbonate to methanol. A mechanism for this reaction was proposed on the basis of (i) carbonyl group insertion into one of the Ru–H bonds to produce the six-coordinate trans-[Ru(OCH(OMe)2)(H)(PNN)(CO)] intermediate and (ii) a metal–ligand cooperative transformation, involving proton transfer from the phosphine arm of the PNN ligand to a methoxy group of the Ru-coordinated [OCH(OMe)2]− anion along with cleavage of a C–OMe bond, to produce methanol and an O-bound methyl formate complex of the dearomatized square-pyramidal form of the catalyst, [Ru(H)(PNN)(CO)]. We investigate herein the possibility of an alternative reaction pathway proceeding as (i) an outer-sphere hydride transfer from [Ru(H)2(PNN)(CO)] to the carbonyl of dimethyl carbonate to give an ion pair of the cationic metal fragment and the [OCH(OMe)2]− anion in which the C–H bond is facing the metal center, (ii) reorientation of the [OCH(OMe)2]− anion within the intact ion pair to coordinate a methoxy group to the metal, and (iii) C–OMe bond cleavage (methoxide abstraction by the cationic ruthenium center) to yield methyl formate and trans-[Ru(H)(OMe)(PNN)(CO)]. Using DFT calculations applied at the M06 and ωB97X-D levels with a polarizable continuum representing THF as solvent, we calculate the energy profile of this pathway to be significantly lower than the metal–ligand cooperative pathway. The analogous pathway is also favored for the reaction of [Ru(H)2(PNN)(CO)] with methyl formate. The new mechanism corresponds to a direct metathesis transformation in which a hydride and an alkoxide are exchanged between a metal center and a carbonyl group via an outer sphere ion pair formation and reorientation of the alkoxide anion. The calculations also indicate that the metathesis can proceed indirectly via outer sphere ion pair mediated carbonyl insertion of dimethyl carbonate and methyl formate to give [Ru(H)(OCH(OMe)2)(PNN)(CO)] and [Ru(H)(OCH2OMe)(PNN)(CO)], respectively, as intermediates, followed by ion pair mediated deinsertion of methyl formate or formaldehyde. Inclusion of one methanol molecule as an explicit H-bond donor solvent does not change the main conclusions of the study.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
We applied a test set of ligand dissociation enthalpies derived entirely from a unified experimental approach to evaluate the efficacy of various methods for modeling organometallic chemistry.
The dissociative displacement of the THF solvent molecule from LRe(CO)2−THF (L = Tp, Tp*, Cp*) and of MenTHF (n = 1, 2) from TpRe(CO)2−MenTHF by acetonitrile is studied. While the reactivity of the Re−THF bond depends on the electronic properties of the ancillary ligands (Tp, Tp*, Cp*) attached to the metal center, the lability of the Re−MenTHF bond is primarily influenced by the steric demands of the departing solvent.
Photolysis of CpMn(CO)3 in a hexane/water biphasic system has been shown to generate hydrogen peroxide and hydrogen in 40−50% yield. Photolysis of the title compound results in loss of a CO ligand followed by coordination of a water molecule. The initially formed CpMn(CO)2(H2O) intermediate was detected using time-resolved IR spectroscopy. The cyclopentadiene (CpH) monomer is generated as the major product, formed by the transfer of an H atom from the coordinated H2O solvent to the Cp ring. A simple mechanism for H2 generation is proposed on the basis of deuteration studies which demonstrate the production of D2 and CpD upon photolysis of CpMn(CO)3 in a hexane/D2O biphasic system.
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