Synthesis and Characterisation of {PdNO}10 Pincer Complexes

The synthesis and characterisation of two square planar {PdNO}¹⁰ pincer complexes of the form [Pd(pincer)(NO)]⁺ (pincer = 2,6-(tBu₂PCH₂)₂C₅H₃N, 1; 2,6-(tBu₂PO)₂C₅H₃N, 2) are reported. These complexes are readily isolated by phosphine substitution of T-shaped [Pd(PtBu₃)₂(NO)]⁺ 3 in THF and the bent nitrosyl coordination mode observed in 3 is retained, as evidenced by X-ray diffraction (∠PdNO ∼ 120°), IR spectroscopy and analysis of isotopically enriched samples by ¹⁵N NMR spectroscopy. Effective oxidation states of Pd⁰/NO⁺ are calculated for 1–3 and nitrosyl coordination is principally attributed to metal-centred σ-bonding, with supplementary π-backbonding. Computational analysis, however, indicates that the Pd−NO bonds in 1 and 2 have greater Pd^I/NO^• character and σ-bonding is more prominent than in 3. These differences in bonding are manifested experimentally in more red-shifted nitrosyl stretching frequencies and the propensity of 1 and 2 to react with dichloromethane to afford palladium(II) chloride derivatives.