Impact of the linker groups in bis(7-azaindol-1-yl) chelate ligands on structures and stability of Pt(N,N-L)R2 complexes

Abstract

New organoplatinum(II) complexes with the general formula of Pt(N,N-L)R₂, where L is a bis(7-azaindol-1-yl) chelate ligand, R is a methyl or a phenyl, have been synthesized and investigated with the aim to understand the impact of the linker group in the L ligand on the structure and the stability of the Pt(II) complexes. The L ligands used in our investigation belong to two classes: class I with an aliphatic linker between two 7-azaindolyl groups such as -CH₂- (BAM), -(CH₂)₃- (1,3-BAPr), and -(CH₂)₄- (1,4-BABu), class II with an aromatic linker such as 1,2-phenyl (1,2-BAB) 1,3-phenyl (1,3-BAB) and 1,4-dihydronaphthalene-1,4-epoxide (BAHE). The structures of these new mononuclear Pt(II) complexes have been determined by single-crystal X-ray diffraction analyses. For the 1,3-BAPr ligand, a dinuclear complex with the formula of [Pt(SMe₂)Ph₂]₂(1,3-BAPr) was also obtained and its structure was established by X-ray diffraction analysis. The linker group's impact on the N–Pt–N bite angle and the relative orientation of the two 7-azaindolyl rings was examined by using the crystal structural data. Intramolecular three-center four-electron Pt^II⋯H–C interactions have been established for all Pt(II) complexes with class I ligands by single-crystal X-ray diffraction and ¹H NMR spectroscopic analyses. Complexes Pt(1,3-BAPr)Me₂ and Pt(1,4-BABu)Me₂ have been found to have a poor stability, compared to the 1,2-BAB and BAM analogues. Two geometric isomers of the Pt(BAHE)Ph₂ complex have been identified by NMR spectra and the structure of one of the isomers has been determined by X-ray diffraction analysis, establishing that the BAHE ligand is most effective in blocking the 5^th coordination site of the Pt(II) center.