Cationic Two-Coordinate Complexes of Pd(I) and Pt(I) Have Longer Metal-Ligand Bonds Than Their Neutral Counterparts
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2016 Elsevier Inc. One-electron oxidation of known (tBu3P)2M (1, M= Pd; 2, M= Pt) with [Ph3C][HCB11Cl11] leads to two-coordinate, monovalent cations of the formula [(tBu3P)2M][HCB11Cl11] (3, M= Pd; 4, M= Pt), which also possess linear geometry but with elongated MP bonds. Spectroscopic and computational studies consistently show that the unpaired electron of the d9 configuration of 3 and 4 belongs to largely non-bonding orbitals: the s/dz2 hybrid for Pd and the degenerate dx2-y2/dxy pair for Pt. We show that molecular-orbital-based arguments alone are incapable of predicting or rationalizing the observed MP bond lengthening on oxidation; correct prediction and rationalization are achieved only by inclusion of electrostatic and Pauli effects. This emphasizes the dangers of interpreting any perturbative changes in bond metrics solely on the basis of energies and occupancies of molecular orbitals; the inclusion of electrostatic and Pauli components is essential to providing a more complete picture.