Tin(II) cations stabilized by non-symmetric N,N',O-chelating ligands: synthesis and stability.

A series of novel non-symmetric neutral N,N',O-chelating ligands derived from the α-iminopyridine 2-(C(R 1 )N(C 6 H 3 -2,6-iPr 2 ))-6-(R 2 R 3 PO)C 5 H 3 N (L1: R 1 = H, R 2 = R 3 = Ph; L2: R 1 = Me, R 2 = R 3 = Ph; L3: R 1 = H; R 2 = Ph, R 3 = EtO; L4: R 1 = Me, R 2 = Ph, R 3 = EtO; L5: R 1 = H, R 2 = R 3 = iPrO; L6: R1 = Me, R 2 = R 3 = iPrO) were synthesized. Ligands L1-6 were reacted with SnCl 2 and Sn(OTf) 2 with the aim of studying the influence of different R 2 R 3 PO functional groups on the Lewis base mediated ionization of SnCl 2 and Sn(OTf) 2 . While all ligands L1-6 provided the corresponding ionic tin(II) complexes [L1-6 → SnCl] + [SnCl 3 ] - (1-6), only ligands L1, L4 and L6 were able to stabilize tin(II) dications [L1,4,6 → Sn(H 2 O)][OTf] 2 (7-9). The auto-ionized compounds [L3-6 → SnCl] + [SnCl 3 ] - possessing ethylphenyl phosphinate and diisopropylphosphite substituents undergo elimination of EtCl and iPrCl, respectively, yielding compounds 10-13. These can either be interpreted as neutral tin(II)phosphinate chloride (10, 11) and tin(II)phosphonate chloride (12, 13), respectively, containing Sn-O and Sn-Cl bonds, and a PO → SnCl 2 interaction, or as zwitterionic compounds, where the positive charge of the central tin atom is compensated by an [OSnCl 2 ] - anion. Finally, DFT studies were performed to better understand the steric and electronic properties of the ligands L1-6 as well as the nature of the bonds in the resulting products, with a particular focus on complexes 10-13.