On the appearance of nitrite anion in [PdX(OAc)L2] and [Pd(X)(C^N)L] syntheses (X = OAc or NO2): photocrystallographic identification of metastable Pd(η1-ONO)(C^N)PPh3

Abstract

Pd3(OAc)5NO2, an impurity in “Pd(OAc)2” {formally Pd3(OAc)6}, emerges as a serious issue in the synthesis of pure PdII complexes derived from Pd(OAc)2, for example in our C–H activation precatalyst, Pd(OAc)2(pip)2 (pip = piperidine). A previous proposal that nitrite anion can be formed by oxidation of CH3CN by metallic Pd and air, leading to cyclo(ortho)palladated complexes containing nitrite anion, e.g. Pd(NO2)(C^N)L (C^N = papaverine; L = CH3CN or DMSO) can be explained by Pd3(OAc)5NO2 acting as the nitrite source. Finally, photocrystallographic metastable linkage isomerisation and complete conversion to an oxygen-bound nitrito complex Pd(η1-ONO)(C^N)PPh3 has been observed

Facile Hydrolysis and Alcoholysis of Palladium Acetate

“…When considering the mechanisms associated with a synthetic or catalytic process, for instance the transformation of a pre‐catalyst into an active species, it is critically important to be confident of the integrity of the starting material. Palladium(II) acetate is a ubiquitous precursor in an extremely wide range of synthetic and catalytic transformations, yet we show herein that in very many cases what is assumed to be palladium acetate is in fact not 1. This is because palladium acetate is highly sensitive to moisture in solution, reacting readily with low concentrations of water in a range of common organic solvents, including solvents that have been “dried” over calcium hydride, to give the structurally characterized complex [Pd 3 (μ 2 ‐OH)(OAc) 5 ] ( 1 ) 2.…”

Redox‐Active NOxLigands in Palladium‐Mediated Processes

“…Linkage isomerization involving M‐NO 2 is well established for transition metals,38 the effect of which in terms of applied homogeneous catalysis processes has not been investigated to a great extent. With regard to stoichiometry, my group presented the first well‐characterized “PdNO 2 ”→“PdONO” linkage isomerization39 for a Pd II complex, namely palladacycle 32 , formed by cyclopalladation of the natural product papaverine,40 in the solid‐state41 (Scheme ). The linkage isomerization process can either be thermally or photochemically induced, and results in the “ONO” group being endo to the Pd center (as shown in 32 ′) 42.…”

Steady‐State and Pseudo‐Steady‐State Photocrystallographic Studies on Linkage Isomers of [Ni(Et4dien)(η2‐O,ON)(η1‐NO2)]: Identification of a New Linkage Isomer

“…We have subsequently developed these methodologies to produce series of nickel(II) and palladium(II) nitrite complexes that readily exhibit high levels of nitro–nitrito conversion in the single crystal 5d. f, g High conversion levels have also been achieved in nitrosyl linkage isomer systems; in 2009 Cormary et al. reported 92 % excitation to the η 1 ‐ON isomer (MS1) in the complex [RuCl(NO)py 4 ](PF 6 ) ⋅ 1/2H 2 O (py=pyridine) 9.…”