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

Pd 3(OAc) 5NO 2, an impurity in "Pd(OAc) 2" {formally Pd 3(OAc) 6}, emerges as a serious issue in the synthesis of pure Pd II 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 CH 3CN by metallic Pd and air, leading to cyclo(ortho)palladated complexes containing nitrite anion, e.g. Pd(NO 2)(C∧N)L (C∧N = papaverine; L = CH 3CN or DMSO) can be explained by Pd 3(OAc) 5NO 2 acting as the nitrite source. Finally, photocrystallographic metastable linkage isomerisation and complete conversion to an oxygen-bound nitrito complex Pd(η 1-ONO)(C∧N)PPh 3 has been observed.