Group VIII Coordination Chemistry of a Pincer-Type Bis(8-quinolinyl)amido Ligand

Abstract

This paper provides an entry point to the coordination chemistry of the group VIII chemistry of the bis(8-quinolinyl)amine (BQA) ligand. In this context, mono- and disubstituted BQA complexes of iron, ruthenium, and osmium are described. For example, the low-spin bis-ligated Fe(III) complex [Fe(BQA)2][BPh4] has been prepared via amine addition to FeCl3 in the presence of a base and NaBPh4. Complexes featuring a single BQA ligand are more readily prepared for Ru and Os. Auxiliary ligands featuring a single BQA ligand, along with two other L-type donor ligands, allow for a variety of ligand types to occupy a sixth coordination site. Representative examples include the halide and pseudohalide complexes trans-(BQA)MX(PPh3)2 (M = Ru, Os; X = Cl, Br, N3, OTf), as well as the hydride and alkyl complexes trans-(BQA)RuH(PMe3)2 and trans-(BQA)RuMe(PMe3)2. Electrochemical studies are discussed that help to contextualize the BQA ligand with respect to its neutral counterpart 2,2′,2′′-terpyridine (terpy) in terms of electron-releasing character. Bidentate ligands have been explored in conjunction with the BQA ligand. Thus, the bidentate, monoanionic aryl(8-quinolinyl)amido ligand 3,5-(CF3)2-(C6H3)QA has been installed onto the (BQA)Ru platform to provide (BQA)Ru(3,5-(CF3)2-(C6H3)QA)(PPh3). A bis(phosphino)borate ligand stabilizes the five-coordinate complex [Ph2B(CH2PPh2)2]Ru(BQA). Finally, access to dinitrogen complexes of the types [(BQA)Ru(N2)(PPh3)2][PF6], [(BQA)Ru(N2)(PMe3)2][PF6], and [(BQA)Os(N2)(PPh3)2][PF6] is provided by exposure of the sixth coordination site under a N2 atmosphere.