Activation of imines by platinum(II) to give aminoalkyl complexes: Scope and limitations of the reaction

Reaction of an excess of the ligand 1,2-C2H4(N=CH-2-C5H4N)(2) (1), 1,2-C2H4 (N=CH-2-C-9-H6N)(2) (2), or 1,3-C3H6(N=CH-2-C5H4N)(2) (3) with [Pt2Me4(mu-S Me2)(2)] gives the following platinum(II) complexes that contain a free imi ne functional group: [PtMe2{C2H4(N=CH-2-C-5-H4N)(N=CH-2-C5H4N)}] (4), [PtMe 2{C2H4(N=CH-2-C9H6N)(N=CH-2-C9H6N)} (5), or [PtMe2-{C3H6(N=CH-2-C5H4N)(N=CH -2-C5H4N)}] (6) (C5H4N = pyridyl, C9H6N = quinolyl). The reaction of comple xes 4-6 with excess CF3CO2H or HCl gave aminoalkylplatinum(IV) products, an d it is suggested that the reactions occur by protonation of the free imine nitrogen atom followed by oxidative addition of the transient iminium grou p so formed. The products were formed as a mixture of isomers whose structu res were deduced from their spectroscopic properties and, for the complexes [PtMe2{C2H4(N=CH-2-C5H4N)(NH2CH-2-C5H4NH)}(O-2-CCF3)][O2CCF3](2) (7a) [PtM e2{C2H4(N=CH-2-C5H4N)(NH2CH-2-C5H4NH)}Cl][Cl](2) (8a), and [PtMe2n{C3H6(N=C H-2- C5H4N)(NH2-CH-2-C5H4N)Cl][Cl] (14a), by X-ray structure determinations . The reaction of 5 with an equimolar amount of CF3CO2H gave [PtMe2{C2H4(N= CH-2-C9H6N)(NHCH-2-C9H6V)}][CF3CO2] (9), which was shown by X-ray structure determination to contain a four-membered azametallacyclobutane ring. Attem pts to effect the intermolecular protonation/metalation of imines by platin um(II) were unsuccessful, since reactions of [PtMe2(bu(2)bpy)] (bu(2)bpy = 4,4'-di-fert-butylbipyridine) with N-benzylidenemethylamine or N-benzyliden eaniline and CF3CO2H led only to protonolysis of the methylplatinum bonds.