Coordinatively Unsaturated [RhCp*Rf₂] (Cp* = C₅Me₅; Rf = C₆F₃Cl₂-3,5), General Precursor to Cp*-Diaryl and Cp*-Halo-Aryl Rh^III Complexes. Observing and Testing the Effect of Cp* as Electronic Buffer

Abstract

The pentacoordinated [RhCp*Rf 2 ] (Rf = C 6 F 3 Cl 2-3,5) and the octahedral (µ-Cl) 2 [RhCp*Rf] 2 , obtained by stoichiometric rearrangement with (µ-Cl) 2 [RhCp*Cl] 2 , are general precursors of [RhCp*RfXL] (X = Rf, Cl; L = ligand) complexes, which were studied by NMR (L dissociation and fluxional processes) and X-ray diffraction (structural effects affecting the Rh-Cp* distances) techniques. The Rh-Cp*centroid distance decreases markedly for identical L in the order [RhCp*Rf 2 L] > [RhCp*RfClL] > [RhCp*Cl 2 L], and are further influenced regularly within each family by the trans influence of L (longer distances for higher trans influence of L). The structural effects observed reveal a remarkable capability of Cp* to act as an electron-density buffer, which attenuates the Rh electron density variations induced by the substituents in front of Cp* by releasing towards Rh or polarizing towards Cp*, at demand, electron density of the Rh-Cp* bonds. This buffer-effect explains the easy L dissociation from [RhCp*Rf 2 L] and the accessibility to formally 16e pentacoordinated [RhCp*Rf 2 ]. 16e CO I − AsPh 3 PPh 3 L trans influence 18e complexes Rh-Cp* centroid Distance (Å)

Expanding the Concepts Trans Influence and Back-Donation: Hybrid and Side Donations in [Cp*MIII(L)XY] (M = Rh, Ir) Complexes with CO, CN–, and CNR Ligands. A Window to Cis Influence

“…As for ligands involving back-donation from M (the isoelectronic CO and CNXylyl), complexes 3a and 4a had been reported in our previous study . The iridium analogues, 3b and 4b , reported herein, have been obtained quantitatively by the reaction of 2b with the π-acceptor ligands CO or CNXylyl.…”

“…These syntheses are depicted in Scheme . Because the chemistry of the Cp*Ir complexes in this work is so similar to the one we previously reported for Cp*Rh, we comment on it only very briefly. Details are given in the Supporting Information (SI).…”

“…The crystalline structures of 3b and 6b are shown in Figure . The analogous 6a and 7a had been previously reported …”

“…In fact, by changing the Cp* centroid –M distance, the Cp*M interaction attenuates the influence of the other ligands on the rhodium­(III) electron density. We named this remarkable feature the electronic buffer effect of Cp* …”

Análisis de los procesos de intercambio arilo/haluro en AuIII y revisión de los conceptos retrodonación e influencia trans en sistemas MIIICp*

“…Gráfica distancias Rh-Cp*centroide. 4 Teniendo en cuenta estos precedentes, la primera parte de esta tesis se centra en primer lugar en el análisis teórico de la combinación de Cp* con ligandos π aceptores (Figura 1, derecha), usando tanto Rh III como Ir III como centros metálicos, y su posible interacción. Además, usando las geometrías optimizadas computacionalmente de algunos de estos complejos, se pretende racionalizar las diferencias en las distancias C-C y M-C (C = carbono del Cp*) tratando de predecir los patrones de asimetría observados.…”