Formation and Structure of Rh⁽⁰⁾ Complexes of Phosphinine-Containing Macrocycles:  EPR and DFT Investigations

Abstract

Electrochemical and chemical reductions of Rh(I) complexes of L P4 (a macrocycle containing four phosphinine rings) and of L P2S2 (a macrocycle containing two phosphinine rings and two thiophene rings) lead, in liquid solution, to EPR spectra exhibiting large hyperfine couplings with 31P nuclei. An additional coupling (27 MHz) with 103Rh is detected, in the liquid state, for the spectrum obtained with [L P2S2 Rh (0) ]; moreover, resolved 31P hyperfine structure is observed in the frozen solution spectrum of this latter complex. DFT calculations performed on Rh(I) complexes of model macrocycles L‘ P4 and L‘ P2S2 indicate that, in these systems, the metal coordination is planar and that one-electron reduction induces a small tetrahedral distortion. The calculated couplings, especially the dipolar tensors predicted for [L‘ P2S2 Rh (0) ], are consistent with the experimental results. Although the unpaired electron is mostly delocalized on the ligands, the replacement of two phosphinines by two thiophenes tends to increase the rhodium spin density (ρRh =0.35 for [L‘ P2S2 Rh (0) ]). It is shown that coordination to Rh as well as one-electron reduction of the resulting complex provoke appreciable changes in the geometry of the macrocycle.

Paramagnetic (Alkene)Rh and (Alkene)Ir Complexes: Metal or Ligand Radicals?

“…According to DFT calculations (supported by EPR property calculations) these latter species are best described as ligand radicals. [31] …”

Tetrathiafulvalene–phosphine-based iron and ruthenium carbonyl complexes: Electrochemical and EPR studies

“…15,16 Due to the large atomic hyperfine constants 17 of 31 P, EPR is a very efficient method of determining the localization of the unpaired electron in the reduction or oxidation compounds of transition metal complexes of organophosphorus ligands. 18,19 We, therefore, decided to investigate by EPR the oxidation behavior of the iron and of the ruthenium complexes of the redox active chelating diphosphine 3,4-dimethyl-3 0 ,4 0 -bis-(diphenylphosphino)-tetrathiafulvalene (P2).…”

The σ‐donating and π‐accepting properties of ortho‐Si(CH3)3 phosphinine macrocycles

“…More recently, the synthesis of the silacalix[n]phosphinines, a novel class of macrocycle phosphinines that represent the first sp 2 -based phosphorus macrocycles was reported [9]. Additionally, metal complexes of the silacalix[n]phosphinines have been synthesized and studied both experimentally and theoretically [10].…”

“…Thus this specific property can be exploited in catalysis [2] and for the stabilization of highly reduced transition-metal species [10]. Nevertheless, in some cases it would be desirable to have phosphinine derivatives in which the -donating properties were improved.…”