C−S and C−H Bond Activation of Thiophene by Cp*Rh(PMe₃):  A DFT Theoretical Investigation

Abstract

A theoretical analysis of the C-S and C-H bond-activation pathways involving thiophene and Cp*Rh(PMe 3 ) is presented in which B3LYP density-functional theory is utilized. In addition to the traditional pathway which connects the η 2 -coordinated intermediate with the C-H bond activation products, a new pathway is discussed which connects the η 1 S-bound intermediate with these products. Calculations are performed in the basis of molecular orbitals of the interacting fragments for the reactive η 1 -and η 2 -coordinated intermediates to examine the orbital interactions and density transfer between the fragments. The calculated binding energy of the η 1 -coordinated intermediate is 15.5 kcal/mol weaker than that for the η 2 -coordinated intermediate due to the increased energy separation and reduced density transfer between the molecular orbitals of the interacting fragments. The structure of the transition state connecting the η 1 -coordinated intermediate with the C-S bondactivated product involves the strong overlap of the HOMO of the metal fragment with the LUMO of thiophene which results in the close proximity of the distal carbons on thiophene with the methyl groups of the Cp* ligand. Substitution of bulky groups at the 3 and 4 positions on thiophene may result in a significant steric component to the C-S activation barrier. Substitution of bulky groups on all carbons results in a significant thermodynamic component to the instability of the ring-opened product. Preliminary results indicate that the lack of reactivity toward C-S bond activation in Cp*Re(CO) 2 is due to the participation of the electron withdrawing carbonyl groups in the transfer of density between the interacting fragments.

C–S Bond Activation and Partial Hydrogenation of Thiophene by a Dinuclear Trihydride Platinum Complex

“…[56,57] However, theoretical analyses of HDS mechanisms using organometallic reagents are still scarce, [43,44] and in general have focused on investigating the nature and energetics of the interactions between T and single-metal organometallic complexes. [58][59][60][61][62][63][64] In this section we present a complete computational study of the reaction mechanism of I with T using DFT methods.…”

“…[34] Although no intermediates were detected in this reaction, the use of selectively deuterated reagents and theoretical calculations made it possible to propose the corresponding mechanism. [42][43][44] In terms of mono-and dinuclear transition-metal complexes, the only example of a complete desulfurization of thiophene to butadiene was achieved by means of a dinuclear polyhydride iridium complex in the presence of a hydrogen acceptor compound. [45] Several intermediate species identified by NMR showed how the activation of the second C-S bond is subsequent to the hydrogenation of the thiophenic chain.…”

Computational QM/MM study on the structure and energetics of species involved in the activation of the C–H and C–S bonds of thiophene by Cp*RhPMe3

“…This basis set is very similar in quality to that of Sargent and Titus in their previous computational study. 42 We did not add an additional set of p functions on the Rh because preliminary calculations showed it had little effect on the results.…”

“…38,39 Of particular interest is the case of rhodium complexes of the Cp*(Me 3 P)Rh, 30,31,33,40 and Tp*(R 3 P)Rh, 36 types. In particular, the experimental study by Dong and coworkers 40 and, later, the theoretical study by Sargent and coworkers 41,42 Calculations are increasingly useful tools in transition metal chemistry. 43,44 Although this reaction could be calculated with an accurate quantum mechanical (QM) method, 42 the size of the systems involved in these processes still poses a challenge to current computational resources, especially if sulfur-containing molecules larger than thiophene are to be considered.…”

“…In particular, the experimental study by Dong and coworkers 40 and, later, the theoretical study by Sargent and coworkers 41,42 Calculations are increasingly useful tools in transition metal chemistry. 43,44 Although this reaction could be calculated with an accurate quantum mechanical (QM) method, 42 the size of the systems involved in these processes still poses a challenge to current computational resources, especially if sulfur-containing molecules larger than thiophene are to be considered. Because of this, the application of hybrid QM/MM methods, in which a region of the system is treated with a more affordable molecular mechanics (MM) description, looks attractive.…”