Synthesis and Characterization of a Redox-Active Bis(thiophenolato)amide Ligand, [SNS]^3–, and the Homoleptic Tungsten Complexes, W[SNS]₂and W[ONO]₂

Abstract

A new tridentate redox-active ligand platform, derived from bis(2-mercapto-p-tolyl)amine, [SNS(cat)]H(3), has been prepared in high yields by a four-step procedure starting from commericially available bis(p-tolyl)amine. The redox-active pincer-type ligand has been coordinated to tungsten to afford the six-coordinate, homoleptic complex W[SNS](2). To benchmark the redox behavior of the [SNS] ligand, the analogous tungsten complex of the well-known redox-active bis(3,5-di-tert-butylphenolato)amide ligand, W[ONO](2), also has been prepared. Both complexes show two reversible reductions and two partially reversible oxidations. Structural, spectroscopic, and electrochemical data all indicate that W[ONO](2) is best described as a tungsten(VI) metal center coordinated to two [ONO(cat)](3-) ligands. In contrast, experimental data suggests a higher degree of S→W π donation, giving the W[SNS](2) complex non-innocent electronic character that can be described as a tungsten(IV) metal center coordinated to two [SNS(sq)](2-) ligands.

Heterobimetallic and Heterotrimetallic Clusters Containing a Redox‐Active Metalloligand

“…The diamagnetic product was readily characterized by 1 H NMR spectroscopy and electrospray mass spectrometry. Single crystals of 1 were grown from diffusion of diethyl ether into a saturated solution of 1 in toluene and used to determine the solid‐state structure of the complex, which is isostructural to the previously‐reported tungsten derivative . The molybdenum derivative 1 has a six‐coordinate metal center that is intermediate between standard octahedral and trigonal prismatic geometries.…”

Octahedral to trigonal prismatic distortion driven by subjacent orbital π antibonding interactions and modulated by ligand redox noninnocence

“…This expectation is buttressed by its geometric structure, where its consecutive 5-membered chelate rings with all ligand atoms sp 2 -hybridized predispose it to adopt a mer geometry in an octahedron and appear ill-suited to the curvature that would be required for tridentate coordination in a trigonal prism. This expectation is confirmed experimentally, as all thirteen structurally characterized homoleptic bis-ONO complexes of transition metals (neutral species from Ti-Zn 8,9 plus Mo 9 and W, 10 and cationic Mn 11 and Co 12 ) are octahedral, with perpendicular ONO planes.…”

“…Second, distortions away from octahedral geometry in, e.g., the metal hexamethyls become less pronounced as one goes to the right in the periodic table, whereas W(ONO) 2 is clearly octahedral (in contrast to its thio analogue, where covalency is the likely structural driver). 10 Finally, DFT calculations, which reproduce the mild and serious distortions of Ru(ONO) 2 and Os(ONO) 2 , respectively, do not support this explanation. In particular, [Re(ONO) 2 ] + , where the metal-ligand bond polarity should be similar to Os(ONO) 2 , is calculated to be octahedral (D 2 -symmetric), like the isoelectronic W(ONO) 2 .…”

Synthesis, Characterization, and Reactivity of Iron(III) Complexes Supported by a Trianionic ONO3– Pincer Ligand

“…1−4 Trianionic pincer ligands originate as a subset of pincer ligands and are best suited to stabilize high-valent metal ions (M n+ , n ≥ 3) by providing three negatively charged donors to satisfy the electronic needs of electron-deficient metal centers. 5 In the past decade, trianionic pincer ligands featuring NCN, 6−9 OCO, 10−21 NNN, 22−26 CCC, 27 SNS, 28 and ONO 25,29−38 arrangements of donor atoms were synthesized, and a recently published review article summarizes the latest achievements in this field. 5 Trianionic pincer ligands provide a convenient framework for the development of new Fe(III) compounds.…”