Solution and Solid‐State Ligand K‐Edge XAS Studies of PdCl2 Diphosphine Complexes with Phenyl and Cyclohexyl Substituents

Abstract

Listen

Translate article

Here we report P K‐edge X‐ray absorption spectroscopy (XAS), density functional theory (DFT), and time‐dependent density functional theory (TDDFT) studies of [R2P(CH2)nPR2]PdCl2, where R = phenyl or cyclohexyl and n = 1–3. P K‐edge XAS data were collected on room temperature CH2Cl2 solutions of [Ph2P(CH2)nPPh2]PdCl2, where n = 1 (dppm; 1), 2 (dppe; 2), or 3 (dppp; 3) to determine if solid‐state variations in covalent Pd–P bonding reported previously (Inorg. Chem. 2015, 54, 5646) were present in solution. A flow cell was used to overcome challenges associated with photon‐induced decomposition, which often occurs rapidly in solution during ligand K‐edge XAS data collection at room temperature. While the solid‐state data for 2 revealed a 10 % increase in P 1s→Pd‐P σ* transition intensity compared to 1 and 3, no statistical difference in Pd–P covalency was observed for 1–3 in solution. In contrast, solid‐state P K‐edge XAS data collected on [Cy2P(CH2)nPCy2]PdCl2, where n = 1 (dcpm; 4), 2 (dcpe; 5), or 3 (dcpp; 6), matched the trend in P 1s→Pd–P σ* transition intensity for solids of 1–3 despite exchanging the phenyl substituents for cyclohexyl. DFT and TDDFT calculations conducted on 4–6 corroborated the experimental data. Collectively, the solid‐state XAS and DFT results suggest that changes in the diphosphine backbone have the same relative effect on Pd–P σ covalency regardless of the substituents attached to phosphorus.