C−H Bond Activation of Methane Promoted by (η⁵-Phospholyl)Rh(CO)₂:  A Theoretical Perspective

Abstract

Quantum mechanical calculations at the MP4(SDQ)//MP2 were carried out to evaluate, a priori, the reactivity of [(η 5 -phospholyl)Rh(CO) 2 ] toward C-H bond activation of methane. The compound [(η 5 -phospholyl)Rh(CO) 2 ] is an analogue of [(Cp)Rh(CO) 2 ], which is well known to activate alkanes of moderate sizes. Our results show that compound [(η 5 -phospholyl)Rh-(CO) 2 ] has a singlet ground state, with the lowest triplet state lying 55.1 kcal/mol above it. The calculation of the electronic spectrum of this compound revealed that the MLCT charge transfer band (M f CO) that leads to CO dissociation occurs at much higher energy (5.28 and 5.54 eV) than the value for the parent Cp compound. The methane substrate interacts with the monocarbonyl compound, generated after CO dissociation, forming a η 2 adduct, which is stabilized by 11.7 kcal/mol. The C-H bond activation of methane proceeds through a three-center transition state with a small activation enthalpy of 6.1 kcal/mol, relative to the η 2 adduct intermediate. Comparisons with the [(Cp)Rh(CO) 2 ] analogue are made and discussed. The results presented in this work suggest that the compound [(η 5 -phospholyl)-Rh(CO) 2 ] can be used to activate the C-H bond of alkanes.

Steric and Electronic Analyses of Ligand Effects on the Stability of σ-Methane Coordination Complexes: A DFT Study

“…We discuss this interaction in more detail in Section . In general, the calculated distances for the metal-methane interaction in 2 agree well with those of other σ-methane complexes. ,,,,− In the final part of the reaction coordinate, the dissociation of methane from 2 produces the dissociated state 3 , in which the metal center and the methane molecule no longer interact.…”

C—H Bond Activation in Transition Metal Species from a Computational Perspective

“…23 Recently, Xavier et al have studied at the MP4(SDQ)//MP2 level the CsH activation of methane promoted by (η 5 -phospholyl)Rh(CO) 2 and compared it with CpRh(CO) 2 . 66 The work by Su and Chu on the reaction between CpM(PH 3 ) (M ) Rh, Ir) and propane is the first attempt to address computationally the important aspect of selectivity in CsH activation. 67 Alkanes are very poor Lewis bases, and the only MOs available for σ-donation are σ CH 2 and π CH 2 (Figure 2).…”

“…Following the publication of the work of Bergman and Jones, several computational studies have examined CH activation by CpML, – and they are described in detail in the review by Niu and Hall . Recently, Xavier et al have studied at the MP4(SDQ)//MP2 level the CH activation of methane promoted by (η 5 -phospholyl)Rh(CO) 2 and compared it with CpRh(CO) 2 …”

Consequences of Surface Oxophilicity of Ni, Ni-Co, and Co Clusters on Methane Activation

“…Reaction of methane and carbon dioxide is an attractive route for producing a CO–H 2 mixture as a chemical precursor for commodity chemical and liquid fuel synthesis. The reaction involves an initial methane activation on transition metals [clusters: Ni, − Pd, , Pt, , Rh, ,− Ir, ,, and Ru; , surfaces: Ni(111), − Rh(111), Ru(1120), and Co(111)] and transition metal complexes [Au­(HSO 4 ) 3 , Pt II -NHC (N-heterocyclic carbenes), Pd 0 -NHC, Pd­(PH 3 ) 2 , and (η 5 -phospholyl)­Rh­(CO) 2 ], examined extensively with rate and isotopic assessments, ,,,− spectroscopic studies, ,− and first-principle density functional theory (DFT) calculations. ,,− ,− On transition metal surfaces [Ni(111), − Rh(111), Ru(1120), Co(111), and Pd clusters , ], the initial methane activation is the kinetically relevant step, catalyzed by a metal atom via an oxidative addition pathway mechanistically analogous to those undergone by homogeneous catalytic complexes [Au­(HSO 4 ) 3 , Pd II -NHC, and Pd­(PH 3 ) 2 ]. The oxidative addition step involves metal atom (*) insertion into the C–H bond via a late, three-center (H 3 C···*···H) ⧧ transition state, during which the metal atom donates its electron density into the C–H antibonding orbital (σ C–H *) .…”