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)][BPh(4)] has been prepared via amine addition to FeCl(3) in the presence of a base and NaBPh(4). 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(PPh(3))(2) (M = Ru, Os; X = Cl, Br, N(3), OTf), as well as the hydride and alkyl complexes trans-(BQA)RuH(PMe(3))(2) and trans-(BQA)RuMe(PMe(3))(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-(CF(3))(2)-(C(6)H(3))QA has been installed onto the (BQA)Ru platform to provide (BQA)Ru(3,5-(CF(3))(2)-(C(6)H(3))QA)(PPh(3)). A bis(phosphino)borate ligand stabilizes the five-coordinate complex [Ph(2)B(CH(2)PPh(2))(2)]Ru(BQA). Finally, access to dinitrogen complexes of the types [(BQA)Ru(N(2))(PPh(3))(2)][PF(6)], [(BQA)Ru(N(2))(PMe(3))(2)][PF(6)], and [(BQA)Os(N(2))(PPh(3))(2)][PF(6)] is provided by exposure of the sixth coordination site under a N(2) atmosphere.

New Chemistry with Anionic NNN Pincer Ligands

“…2) [39,46]. The BQA ligand is also known to bind to metal centers in a planar manner yielding complexes which are stable even in the presence of water or acid [47][48][49][50][51]. For example, (BQA)NiCl was found to adopt a square planar structure with the BQA ligand coordinating in a κ 3 -manner [27].…”

“…Complexes of the 4d and 5d metals are also known. For example, octahedral trans-(BQA)MX(PPh 3 ) 2 (M¼Ru, Os; X¼Cl, Br, N 3 , OTf), trans-(BQA)RuH (PMe 3 ) 2 , and trans-(BQA)RuMe(PMe 3 ) 2 as well as square planar (BQA)PtCl and (BQA)PdCl have been synthesized [27,51]. Square planar platinum(II) complexes such as (BPI)Pt(L) using BPI and additional strong field ligands have also been prepared [52].…”

SNS versus SNN Pincer Ligands: Electrochemical Studies and Their Palladium(II) Complexes as Electro‐Catalyst for Proton Reduction

“…Pincer complexes have been synthesized since the early 1970 s, and new designs (Scheme ) continue to emerge due to their rich chemistry . Complexes of pincer ligands have been employed as crystalline switches, as sensors and most commonly as precatalysts for numerous transformations .…”

“…Pincer complexes have been synthesized since the early 1970 s, [1] and new designs (Scheme 1) continue to emerge due to their rich chemistry. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Complexes of pincer ligands have been employed as crystalline switches, as sensors and most commonly as precatalysts for numerous transformations. [17] Pincer systems are ubiquitous due to their relative ease of synthesis, and most of the reported systems are planar, due to the aromatic backbone that is commonly used.…”

Cleavage of the βO4 linkage of lignin using group 8 pincer complexes: A DFT study

“…1) using group 8 (Fe, Ru and Os) pincer complexes. Group 8 metals have been widely utilized in pincer complexes [41], in which, with neutral ligands such as PNP and NNN, the metal center has an oxidation state of either (0) or (II), while with monoanionic ligands like PCP and NCN, the metal center will mostly have an oxidation state of (IIc) [41]. These monoanionic ligands contain an aryl anion, which is connected to the metal atom through a bond.…”