A Theoretical Insight into the Ability of Group 6 ML₅ Metal Fragments to Break the H−H Bond

Abstract

The interaction between H2 and M(CO) n (PH3)5 - n (M = Cr, Mo, W; n = 0, 3, 5) metal fragments has been studied by means of CCSD(T)//B3LYP calculations. Three steps in the dihydrogen addition path that starting from the ML5 and H2 separated fragments leads to a stable dihydride have been considered: (i) dihydrogen coordination; (ii) cleavage of the H−H bond in a dihydrogen-like structure, leading to a PB1 cis-dihydride; (iii) reorganization of the pentagonal bipyramidal cis-dihydride formed to a more stable PB2 dihydride structure. From the thermodynamic results and the energy profiles for the oxidative addition the nine complexes under study can be classified in three groups: (i) only dihydrogen observable; M(CO)5H2 (M = Cr, Mo, W); and M(CO)3(PH3)2H2 (M = Cr, Mo); (ii) equilibrium between dihydrogen and PB2 dihydride: W(CO)3(PH3)2H2 and M(PH3)5H2 (M = Cr, Mo); (iii) only dihydride observable; W(PH3)5H2. The different behavior for dihydrogen addition is related to the energetics of the M−H2 and M−H bonds and to the singlet−triplet separation in the ML5 fragment.

Evaluation of the Thermodynamic Properties of H2 Binding in Solid State Dihydrogen Complexes [M(η2-H2)(CO)dppe2][BArF24] (M = Mn, Tc, Re): An Experimental and First Principles Study

“…30, 31 To obtain thermal corrections to the energy and normal mode frequencies, the Hessian matrix for each fragment was calculated at the B3LYP/LANL2DZ-ECP level of theory using seminumerical methods, with contributions from positive and negative displacements of 0.01 bohr. Vibrational analysis in the rigid rotor approximation was performed to obtain partition functions and normal modes of the fragments, q tot , at 1 atm pressure.…”

Hydrogen Bonding and Proton Transfer to the Trihydride Complex [Cp*MoH3(dppe)]: IR, NMR, and Theoretical Investigations

“…-ion pair. As in previous studies of dihydrogen Ǟ dihydride interconversions, [37] we have chosen the H-H distance as a reaction coordinate for the H-H bond breaking. This distance varies from 0.884 Å in the dihydrogen structure to 1.812 Å in the tetrahydride.…”

Stereoisomerism of bis(σ‐Zincane) Complexes: Evidence for an Intramolecular Pathway

“…The isomerisation mechanism was approached by first considering the parent bis(dihydrogen) complexes as models for 2 – 4 . Spectroscopic evidence has been presented for [M(CO) 5 (η 2 ‐H 2 )] (M=Cr, Mo, W), whereas complexes for the form [Cr(CO) 4 (η 2 ‐H 2 ) 2 ] have been generated in dihydrogen‐containing matrices or in liquid xenon solution . DFT calculations revealed three minima, trans , cis‐1 and cis‐2 (Figure ).…”

“…[49,50] Monitoring the isomerisation of 3a/3b in the presence of an externall igand, HBpin, revealed no incorporation of the borane in to the product (HBpin = pinacolborane). The isomerisation mechanism was approached by first considering the parentb is(dihydrogen) complexes as modelsf or 2-4.S pectroscopic evidence has been presented for [M(CO) 5 (h 2 -H 2 )] (M = Cr, Mo, W), [51][52][53][54] whereas complexes for the form [Cr(CO) 4 (h 2 -H 2 ) 2 ] have been generated in dihydrogen-containing matrices or in liquid xenon solution. [55,56] DFT calculations revealed three minima, trans, cis-1 and cis-2 (Figure 4).…”