Synthesis and characterization of diacetyl platinum(II) complexes with two primary and secondary amine ligands

[Pt(COMe)2(bpy)] (2; bpy = 2,2′-bipyridine) and [Pt(COMe)2{H(Me)dmg}] (5; H(Me)dmg = MeO–NC(Me)–C(Me)N–OH) were found to react with primary and secondary amines yielding diacetyl platinum(II) complexes with two monodendate amine ligands [Pt(COMe)2(NH2R)2] (R = Bn, 3a; CH2CH2Ph, 3b; Et, 3c; i-Pr, 3d; CH2CHCH2, 3e; Cy, 3f; Bn = benzyl, Cy = cyclohexyl) and [Pt(COMe)2(NHR2)2] (R = Me, 6a; Et, 6b), respectively. The equilibrium of these ligand exchange reactions was investigated by NMR experiments and DFT calculations showing that complex 5 is the more preferable starting complex and a large excess of the amine has to be used. The sterically demanding diisopropylamine was found to react with 5 yielding a thermally highly unstable dinuclear bis(acetyl) bridged complex [{Pt(COMe){NH(i-Pr)2}}2(μ-COMe)2] (7). Analogous reactions with ethylenediamine derivatives resulted in the formation of [Pt(COMe)2(N^N)] (N^N = ethylenediamine, en, 8a; N,N′-dimethylethylenediamine, 8b; N,N-dimethylethylenediamine, 8c; N,N,N′,N′-tetramethylethylenediamine, TMEDA, 8d). All complexes were fully characterized by microanalysis/high-resolution ESI mass spectrometry, by NMR (1H, 13C, 195Pt) and IR spectroscopies as well as by single-crystal X-ray diffraction measurements (3a/3d). Due to the high trans influence of the acetyl ligands, the Pt–N bonds were found to be relatively long (2.164(2)–2.182(3) Å). The resulting weak coordination of the amines gave rise to a decomposition of complexes 3 under CO extrusion yielding carbonyl–methyl complexes.

Diacetyl platinum complexes [Pt(COMe)2(N^N)] (N^N = bpy, MeO–NC(Me)–C(Me)=N–OH) were found to react with primary and secondary amines yielding diacetylbis(amine)platinum(II) complexes and a dinuclear bis(acetyl) bridged complex [{Pt(COMe){NH(i-Pr)2}}2(μ-COMe)2], respectively. NMR spectroscopic measurements and DFT calculations give an insight into which factors affect these unusual ligand substitution reactions.Figure optionsDownload as PowerPoint slideHighlights
► Diacetyl platinum(II) complexes bearing two monodentate amine ligands NH2R/NHR2.
► A highly reactive dinuclear bis(acetyl) bridged platinum complex.
► Position of the equilibrium for a substitution of 2,2′-bipyridine by monodentate amines.
► The influence of the substituent R on reaction course examined by DFT calculations.