Redox and Acid–Base Properties of Binuclear 4‐Terphenyldithiophenolate Complexes of Nickel

Abstract

This work reports on the redox and acid–base properties of binuclear complexes of nickel from 1,4‐terphenyldithiophenol ligands. The results provide insight into the cooperative electronic interaction between a dinickel core and its ligand. Donor/acceptor contributions flexibly adjust to stabilize different redox states at the metals, which is relevant for redox reactions like proton reduction. Proton transfer to the [S2Ni2] core and Ni−H bond formation are kinetically favored over the thermodynamically favored yet unproductive proton transfer to ligand.

Mechanistic Aspects of Redox‐Induced Assembly and Disassembly of S‐Bridged [2M‐2S] Structures

“…As a starting point, the series of isostructural bimetallic cations L ‐[2Ni‐2S] + shown in Figure , with L =PMe 3 ( 1 ), PPh 3 ( 2 ), and P(Cy) 3 ( 3 ; Cy=C 6 H 11 ) was selected. The mixed‐valent [2Ni‐2S] + cores in this series feature aryl thiolate‐bridged tetrahedral nickel sites that are antiferromagnetically coupled to adopt an electron localized S= 1/2 ground state structure . Cyclic voltammetry (CV) at a glassy carbon working electrode in 0.1 m n Bu 4 NPF 6 /1,2‐C 6 H 4 F 2 solution at 23 °C has shown that oxidation of L ‐[2Ni‐2S] + to putatively isostructural L ‐[2Ni‐2S] 2+ is electrochemically reversible at potential sweep rates ν ≤5000 mV s −1 , irrespective of the type of phosphine donor .…”

“…The mixed‐valent [2Ni‐2S] + cores in this series feature aryl thiolate‐bridged tetrahedral nickel sites that are antiferromagnetically coupled to adopt an electron localized S= 1/2 ground state structure . Cyclic voltammetry (CV) at a glassy carbon working electrode in 0.1 m n Bu 4 NPF 6 /1,2‐C 6 H 4 F 2 solution at 23 °C has shown that oxidation of L ‐[2Ni‐2S] + to putatively isostructural L ‐[2Ni‐2S] 2+ is electrochemically reversible at potential sweep rates ν ≤5000 mV s −1 , irrespective of the type of phosphine donor . Preparative scale oxidation of the three complexes L ‐[2Ni‐2S] + by using the 1,1′‐bisacetylferrocene cation in 1,2‐C 6 H 4 F 2 solution affords two structurally isomeric products, depending on the type of phosphine donor.…”

“…Additional evidence for the formation of metastable L ‐[2Ni‐2S] 2+ was obtained by monitoring the oxidation of 1 ‐[2Ni‐2S] + , as well as of an isostructural derivative in which t Bu groups substitute for mesityl, by variable temperature (VT) NMR spectroscopy. As shown in Scheme , facile oxidation occurs upon mixing CD 2 Cl 2 solutions of precursor and oxidant at T <−20 °C and yields 1 ‐[2Ni‐2S] 2+ quantitatively.…”

“…[b] E vs. Fc/[Fc] + . [c] E 0 ( L ‐[2Ni‐2S] +/0 ): 1 =−960, 2 =−757, 3 =−947 mV . [d] At 20≤ ν ≤1000 mV s −1 .…”

“…All manipulations of air‐ and moisture‐sensitive compounds were carried out under an atmosphere of dry argon by using standard Schlenk or glovebox techniques. Literature procedures were followed for the preparation of starting materials (Ph 3 P) 2 NiN(SiMe 3 ) 2 , 1,1′‐diacetylferrocenium bis(trifluoromethylsulfonyl)imide, [Fc′′]NTf 2 , 1 ‐[2Ni‐2S] 0/+ , 2 ‐[2Ni‐2S] 0/+ , 3 ‐[2Ni‐2S] 0/+ , and t Bu‐substituted 1 ‐[2Ni‐2S] + , with 1 =PMe 3 , 2 =PPh 3 , and 3 =PCy 3 . General information on the purification of other starting materials, solvents, and additional reagents is provided in the Supporting Information.…”