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

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) (CN) L (CN = 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) (CN) PPh3 has been observed.