Insights on the Reactivity of Terminal Phosphanido Metal Complexes toward Activated Alkynes from Theoretical Computations

Abstract

Herein we present a theoretical study on the reaction of [Re(PPh) (CO)(phen)] (phen = 1,10-phenanthroline) and [Re(PPh) (CO)(bipy)] (bipy = 2,2'-bipyridine) toward methyl propiolate. In agreement with experimental results for the phen ligand, the coupling of the substituted acetylenic carbon with the nonsubstituted ortho carbon of the phen ligand is the preferred route from both kinetic and thermodynamic viewpoints with a Gibbs energy barrier of 18.8 kcal/mol and an exoergicity of 11.1 kcal/mol. There are other two routes, the insertion of the acetylenic fragment into the P-Re bond and the coupling between the substituted acetylenic carbon and a carbonyl ligand in cis disposition, which are kinetically less favorable than the preferred route (by 2.8 and 1.9 kcal/mol, respectively). Compared with phen, the bipy ligand shows less electrophilic character and also less π electron delocalization due to the absence of the fused ring between the two pyridine rings. As a consequence, the route involving the coupling with a carbonyl ligand starts to be kinetically competitive, whereas the product of the attack to bipy is still the most stable and would be the one mainly obtained after spending enough time to reach thermal equilibrium.

Addition of Re‐Bonded Nucleophilic Ligands to Activated Alkynes: A Theoretical Rationalization

“…The reactive process involving the PPh2 ligand had been previously investigated from a theoretical point of view. [61] The reaction mechanism found is closely related to that shown in Scheme 2 (see below) and confirms the product experimentally found. However, the results of this single study are not enough to rationalize the formation of different products when PPh2 is replaced by OH, OMe or NHpTol.…”

“…In general, DLPNO-CCSD(T) energies are more accurate than B3LYP ones using at least a triple-zeta quality basis set. [67] For comparison purposes, the single-point energy of the species containing the PPh2 ligand, previously investigated at the PCM-B3LYP/6-311+G(2d,p) (LANL2TZ+f for Re)//PCM-B3LYP/6-31+G(d,p) (LANL2DZ for Re) level, [61] was also recomputed at the CPCM-DLPNO-CCSD(T)/def2-TZVPP//PCM-B3LYP/6-31+G(d,p) (LANL2DZ for Re) one (Tables S1-S4 in the Supporting Information). For brevity, henceforth in this work, the levels of theory PCM-B3LYP/6-31+G(d,p) (LANL2DZ for Re) and CPCM-DLPNO-CCSD(T)/def2-TZVPP//PCM-B3LYP/6-31+G(d,p) (LANL2DZ for Re) will be denoted as B3LYP and DLPNO-CCSD(T), respectively.…”

Influence of the Nucleophilic Ligand on the Reactivity of Carbonyl Rhenium(I) Complexes towards Methyl Propiolate: A Computational Chemistry Perspective

“…As just mentioned in the Introduction section, experimental studies on the reactivity of the complexes [ReY(CO) 3 (N-N)] (Y = NH p Tol, OH, OMe, PPh 2 ; N-N = bipy and/or phen) towards activated alkynes (HMAD and/or DMAD) have shown the formation of three types of products (see Scheme 1 ) [ 48 , 51 , 52 , 53 , 54 ]. Theoretical investigations using the bipy ligand and the HMAD activated alkyne have not only corroborated the formation of such products, but also shown all the species involved in the reaction mechanisms leading to the P cco / P ccoh , P ccb , and P ins products [ 57 , 58 ]. Looking at the reaction mechanisms involved, three different patterns of potential energy surfaces (PES) were found [ 58 ].…”

“…Based on our previous theoretical studies on the reactions of [ReY(CO) 3 (bipy)] (Y = NH p Tol, OH, OMe, PPh 2 ) complexes towards HMAD [ 57 , 58 ] and for comparison purposes, the present research was carried out using the levels of theory PCM-B3LYP/6-31+G(d, p)-LANL2DZ and CPCM-DLPNO-CCSD(T)/def2-TZVPP//PCM-B3LYP/6-31+G(d, p)-LANL2DZ for obtaining molecular geometries and energies, respectively (see Computational Chemistry Details in the Supporting Information for a more detailed description). For brevity, the levels of theory PCM-B3LYP/6-31+G(d, p)-LANL2DZ and CPCM-DLPNO-CCSD(T)/def2-TZVPP//PCM-B3LYP/6-31+G(d, p)-LANL2DZ have been denoted as B3LYP and DLPNO-CCSD(T), respectively.…”

“…Our theoretical investigations on the reaction between the complexes [ReY(CO) 3 (bipy)] (Y = NH p Tol, OH, OMe, PPh 2 ) and HMAD uncovered that the reaction rate is, on the whole, controlled by the first stage of the reaction mechanism, that is, the nucleophilic attack of the Y ligand on the non-substituted alkyne carbon [ 57 , 58 ]. Nonetheless, the subtle balance between kinetics and thermodynamics of the formation step of the plausible products determines the type of product formed.…”