Organometallic Zwitterions:  Arylpalladium(II) (Pincer) Complexes with a Tethered Sulfato Group as para-Substituent

Arylpalladium (NCN-pincer) complexes [NBu4][O3SO(CH2) n SiMe2NCNPdCl] (n = 3 (1a) and n = 6 (1b)) with a tethered sulfato group as para-substituent were synthesized. These novel complexes combine an anionic sulfato group and a neutral NCN−Pd−Cl group in one molecule. Furthermore, 1a,b were converted into their corresponding cationic Pd-aqua complexes 9a,b, which bear both separated anionic sites and Pd cationic sites stabilized by counterions. These mixed, zwitterionic salts can be isolated devoid of counterions to give the pure unimolecular zwitterions [O3SO(CH2) n SiMe2NCNPd(OH2)] (n = 3 (2a) and n = 6 (2b)) that aggregate in order to stabilize their ionic sites. The crystal structure of HO(CH2)6SiMe2NCNPdCl (8b) was revealed and used to study the effect of the tether group on the type of aggregate that is formed. The crystal structure of 8b comprises a dimeric structure, which is formed via noncovalent interactions, i.e., O−H···Cl−Pd hydrogen bonds.