Structural, 103Rh NMR and DFT Studies of a Bis(phosphane)RhIII–Porphyrin Derivative

Abstract

AbstractThe synthesis and characterisation of a novel bis(phosphane)rhodium(III)–porphyrin, [Rh(TPP)(PEtPh2)2]SbF6 (compound 1; TPP = dianion of 5,10,15,20‐tetraphenylporphyrin) is described. The X‐ray structure of the bis(dichloromethane) solvate of the complex has a moderately ruffled porphyrin core conformation, which is primarily determined by the relative orientations of the axial phosphane ligands and their steric interaction with the porphyrin phenyl rings. The mean Rh–N and Rh–P bond lengths for 1 are 2.036(5) and 2.401(3) Å, respectively. The mean absolute perpendicular displacements of the porphyrin α‐, β‐ and meso‐carbon atoms from the 24‐atom porphyrin mean plane measure 0.15(3), 0.11(8) and 0.27(2) Å, respectively. The 103Rh NMR chemical shifts of 1, determined by means of indirect detection through polarisation transfer from 31P, were δ = 2480, 2558 and 2590 ppm at 213, 300 and 333 K, respectively. The 31P chemical shifts measured δ = 10.68, 10.79 and 10.84 ppm at the same temperatures. Ruffled and planar porphyrin conformations are possible for 1 and were modelled by using DFT simulations at the PBE1PBE/3‐21G** level of theory with the cation [Rh(TPP)(PEtPh2)2]+. Accurate structural parameters (calculated bond lengths and out‐of‐plane porphyrin core atom displacements within 2 % and 0.02 Å of the experimental values, respectively) and moderately accurate 103Rh isotropic shielding tensors (δRhcalcd. within 13 % of δRhexp. at 0 K using the GIAO method) were calculated with this hybrid functional and relatively small all‐electron basis set. The DFT simulations indicate unusually high fractional electron populations for the formally antibonding 4d and 4d orbitals of both the ruffled and planar conformers of [Rh(TPP)(PEtPh2)2]+, consistent with the relatively low energies of these metal‐character orbitals that are evidently well‐mixed with ligand orbitals.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)