Binuclear complexes of Ni(i) from 4-terphenyldithiophenol

Abstract

Binuclear complexes of Ni(i) have been prepared from a 4-terphenyldithiophenol ligand. Steric effects were found to determine the formation of coordination isomeric structures that differ in the nature of metal-to-ligand bonding. Coordination of spatially demanding phosphine ligands PR3, R = C6H6, C6H11, at nickel sites results in a butterfly shaped thiolate-bridged Ni2(μ-S)2 motif. For smaller PMe3, the central π-system of the 4-terphenyl backbone adopts a bis-allyl like μ-syn-η(3):η(3)-C6H4 structure due to significant d-π* Ni(i)-to-ligand charge transfer. Delocalisation indices δ(Ni-Ni) derived from DFT calculations provide a metric to assess the strength of electronic coupling of the Ni sites based on solid state structural data, and indicated less strong electronic coupling for the bis-allyl like structure with δ(Ni-Ni) = 0.225 as compared to 0.548 for the Ni2(μ-S)2 structural motif. A qualitative reactivity study toward CNCH3 as an auxiliary ligand has provided the first insight into the chemical properties of the bimetallic complexes presented.

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

“…The structural parameters of the cyclohexadienide fragment are similar to those found in a mononuclear complex of Ni II reported by Agapie . The local structure at the Ni atoms is similar to that in [ 3 R ‐L] + , although shorter Ni–C distances of 2.045(3) and 2.052(3) Å are indicative of the higher oxidation state of +2 in [ 4 R ‐L] + . The diamagnetism of [ 4 R ‐L] + must result from antiferromagnetic coupling of the S =1 Ni II sites, and is probably mediated through (μ‐S) 2 ‐ and μ‐η 2 :η 2 ‐bonding to the ligand.…”

“…Each Ni atom adopts a tetrahedral coordination geometry with bond distances and angles to S‐, P‐, and C‐atoms that are equal within experimental accuracy (3 σ ≤0.02 Å). Ni‐S‐Ni angles of 63° and a Ni–Ni distance of 2.356 Å are slightly decreased as compared to the starting materials 2 Mes ‐L (65°, 2.383 Å). A comparison of the bond lengths and angles within the central π‐system to those of the flanking phenyl rings that enclose dihedral angles of ≈87° indicates μ‐η 2 :η 2 ‐bonding to the Ni atoms, in agreement with Ni–C distances of 2.139 and 2.150 Å.…”

“…We have reported on the properties of a 1,4‐terphenyldithiophenol as a multidentate ligand for mono‐ and binuclear complexes of Ni. κ‐S‐ and (μ‐S) 2 ‐coordination adjusts with σ‐donor/ π‐acceptor bonding of the central π‐system to stabilize Ni I and Ni II as shown in Scheme . Although the electronic ground state structures are different, the total number of electrons is the same.…”

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

“…In line with solid‐state structural data, strong antiferromagnetic coupling of two S= 1 Ni 2+ sites is proposed to result in a total S= 0 ground state, although the precise coordination geometry at nickel in dissolved samples is unknown. A coplanar arrangement of S= 0 Ni 2+ sites can be excluded since this would render vicinal 1 H nuclei at the central π‐system chemically and magnetically inequivalent and no N‐line pattern should be observed . Most notably, solutions of 3 ‐[2Ni‐2S] 2+ in, for example, 1,2‐C 6 H 4 F 2 display an intense absorption band at λ ( ϵ )=730 nm (6600 m −1 cm −1 ), which provides a diagnostic spectroscopic signature of [2Ni‐2S] 2+ cores as shown below.…”

“…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.…”