2-Acylpyrroles as Mono-anionic O, N-Chelating Ligands in Silicon Coordination Chemistry

Kryptopyrrole (2,4-dimethyl-3-ethylpyrrole) was acylated with, for example, benzoyl chloride to afford 2-benzoyl-3,5-dimethyl-4-ethylpyrrole ((LH)-H-1). With SiCl4 this ligand reacts under liberation of HCl and formation of the complex (L2SiCl2)-Si-1. In related reactions with HSiCl3 or H2SiCl2, the same chlorosilicon complex is formed under liberation of HCl and H-2 or liberation of H-2, respectively. The chlorine atoms of (L2SiCl2)-Si-1 can be replaced by fluoride and triflate using ZnF2 and Me3Si-OTf, respectively. The use of a supporting base (triethylamine) is required for the complexation of phenyltrichlorosilane and diphenyldichlorosilane. The complexes (L2SiCl2)-Si-1, (L2SiF2)-Si-1, (L2Si)-Si-1(OTf)(2), (L2SiPhCl)-Si-1, and (L2SiPh2)-Si-1 exhibit various configurations of the octahedral silicon coordination spheres (i. e. cis or trans configuration of the monodentate substituents, different orientations of the bidentate chelating ligands relative to each other). Furthermore, cationic silicon complexes (L3Si+)-Si-1 and (L2SiPh+)-Si-1 were synthesized by chloride abstraction with GaCl3. In contrast, reaction of (L2SiCl2)-Si-1 with a third equivalent of (LH)-H-1 in the presence of excess triethylamine produced a charge-neutral hexacoordinate Si complex with a new tetradentate chelating ligand which formed by Si-templated C-C coupling of two ligands L-1.