Gas-Phase Ligand Exchange in a Square-Planar Rhodium(I) Complex Proceeding by Dissociative Exchange:  ESI FT-ICR MS and DFT Evidence

Abstract

Although the kinetics of square-planar d8 ligand-substitution reactions have been explored extensively in solution, no such studies of gas-phase systems have been reported. Measurement of gas-phase ligand exchange offers the advantage that the exchange mechanism is readily determined in the absence of solvent effects. The complex trans-Rh(PPh3)2CO(4-picoline)+ substitutes pyridine for its 4-picoline ligand readily in the gas phase but also loses CO during the reaction. The double-resonance experiments show that its primary substitution pathway proceeds dissociatively, unlike almost all solution ligand substitutions for Pt(II) and Pd(II). The density functional calculations reveal that the bond energies of Rh-4-picoline, Rh-pyridine, and Rh−CO are similar enough that CO loss might be expected. In support of the dissociative mechanism, the calculations also show five-coordinate intermediates for the associative pathway to be relatively high in energy.

One‐Step Dispersion of Cellulose Nanofibers by Mechanochemical Esterification in an Organic Solvent

“…Ligand substitutions at rhodium( I ) centers have been observed to follow both associative22–25 and dissociative26, 27 mechanisms. Complexes 4 a – c can be viewed as arrested intermediates in an associative substitution process involving PCP type complexes.…”

Electrospray mass spectrometric studies of nickel(II)-thiosemicarbazones complexes: Intra-complex proton transfer in the gas phase ligand exchange reactions

“…The mass difference (9 Da) of the two product ions is just equal to that of the two ESI solvent molecules. Therefore, the two product ions at m/z 299 and m/z 308 were ascribed to [Ni 2+ exchange reactions of metal complexes have been reported in the EI triple quadrupole [36], the quadrupole ion trap [37] and the ESI FT-ICR mass spectrometer [38]. The coordinative unsaturated metal complexes [26][27][28], some organic ions [39,40], and even halide anions [41] have been documented to undergo the gas-phase ion-molecule reactions with ESI solvent molecules to form adduct species in ion trap.…”

π‐Accepting‐Pincer Rhodium Complexes: An Unusual Coordination Mode of PCP‐Type Systems

“…[19,20] Interestingly, X-ray diffraction studies revealed square-pyramidal geometries with trans-disposed amine donors, rather than trigonal-bipyramidal geometries, for these complexes. [21] Ligand substitutions at rhodium(i) centers have been observed to follow both associative [22][23][24][25] and dissociative [26,27] mechanisms. Complexes 4 a-c can be viewed as arrested intermediates in an associative substitution process involving PCP type complexes.…”