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-SMe2)(2)] gives the following platinum(II) complexes that contain a free imine functional group: [PtMe2{C2H4(N=CH-2-C-5-H4N)(N=CH-2-C5H4N)}] (4), [PtMe2{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 complexes 4-6 with excess CF3CO2H or HCl gave aminoalkylplatinum(IV) products, and it is suggested that the reactions occur by protonation of the free imine nitrogen atom followed by oxidative addition of the transient iminium group so formed. The products were formed as a mixture of isomers whose structures 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) [PtMe2{C2H4(N=CH-2-C5H4N)(NH2CH-2-C5H4NH)}Cl][Cl](2) (8a), and [PtMe2n{C3H6(N=CH-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. Attempts to effect the intermolecular protonation/metalation of imines by platinum(II) were unsuccessful, since reactions of [PtMe2(bu(2)bpy)] (bu(2)bpy = 4,4'-di-fert-butylbipyridine) with N-benzylidenemethylamine or N-benzylideneaniline and CF3CO2H led only to protonolysis of the methylplatinum bonds.