Reactions of platinum(iv)-bound nitriles with isomeric nitroanilines: addition vs. substitution

Abstract

The platinum(IV) complex trans-[PtCl₄(EtCN)₂] reacts smoothly and under mild conditions with isomeric o-, m- and p-nitroanilines (NAs) yielding two different types of products depending on the NA isomer, viz. the nitroaniline complexes cis/trans-[PtCl₄(NA)₂] (cis/trans-1–3) and the amidine species trans-[PtCl₄{NHC(Et)NHC₆H₄NO₂-m}(EtCN)] (4), trans-[PtCl₄{NHC(Et)NHC₆H₄NO₂-m}₂] (5) and trans-[PtCl₄{NHC(Et)NHC₆H₄NO₂-p}(EtCN)] (6). Complexes 4 and 5 undergo cyclometalation, furnishing mer-[PtCl₃{NHC(Et)NHC₆H₃NO₂-m}(EtCN)] (7) and mer-[PtCl₃{NHC(Et)NHC₆H₄NO₂-m}{NHC(Et)NHC₆H₃NO₂-m}] (8), respectively. Moreover, 8 both in the solid state and in solution undergoes the second step of the cyclometalation, generating [PtCl₂{NHC(Et)NHC₆H₃NO₂-m}₂] (9). In 4, the nitrile ligand is highly reactive toward nucleophilic addition and it undergoes facile hydration accompanied by the elimination of the nitrile, thus producing cis-[PtCl₄(NH₂C₆H₄NO₂-m){NHC(OH)Et}] (10), or methanol addition providing trans-[PtCl₄{NHC(Et)NHC₆H₄NO₂-m}{NHC(Et)OMe}] (11). All compounds, besides 9, were characterized by C, H, and N elemental analyses, high-resolution ESI-MS, IR, ¹H and ¹³C{¹H} NMR spectroscopic techniques. Complex 9, which was not isolated as a pure compound, was identified in the reaction mixture by ESI-MS and ¹H and ¹³C{¹H} NMR spectroscopies. Complexes trans-1, trans-2, 4, 5, 6, 8, 10, and 11 were additionally studied by X-ray diffraction.