Nickel Hydrides Supported by a Non-Innocent Diphosphine Arene Pincer: Mechanistic Studies of Nickel−Arene H-Migration and Partial Arene Hydrogenation

Abstract

Nickel hydrides supported by a terphenyl diphosphine were synthesized and found to undergo nickel-to-arene H-transfers. Some of the resulting complexes also undergo the reverse (C-to-Ni) H-migration indicating the potential for storing H-equivalents in this type of pincer ligand. NMR spectroscopy, single crystal X-ray diffraction, and isotopic labeling studies investigating the mechanism of these processes are discussed.

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

“…The μ‐η 2 :η 2 ‐cyclohexadienide moiety features a tertiary sp 3 ‐C‐atom of distorted tetrahedral geometry and bond distances of ≥1.48 Å as compared to the other four C−C bonds (≤1.43 Å) that form a delocalized π‐system. 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 terphenyldiphosphine ligands introduced by Agapie combine this property with strongly σ‐donating phosphines. Notable examples include mono‐, di‐, and trinuclear complexes of Ni, dinuclear d 9 ‐Pd, M 2 ‐carbonyl cores of Fe, Co, and Ni, and complexes of Mo in which the ligand also functions as a two‐electron reservoir …”

“…[18] The terphenyldiphosphine ligandsi ntroduced by Agapie combine this property with strongly s-donating phosphines. Notable examples include mono-, [19] di-, [15c] andt rinuclear [20] complexes of Ni, dinuclear d 9 -Pd, [20b, 21] M 2 -carbonylc ores of Fe, Co, and Ni, [22] and complexes of Mo in which the liganda lso functions as at woelectron reservoir. [23] We have reported on the properties of a1 ,4-terphenyldithiophenol as am ultidentate ligand for mono-and binuclear complexeso fN i. k-S-and (m-S) 2 -coordination adjusts with s-donor/ p-acceptor bonding of the central p-system to stabilizeN i I and Ni II as shown in Scheme 2.…”

Exploring Mechanisms in Ni Terpyridine Catalyzed C–C Cross-Coupling Reactions—A Review

“…Non-innocent ligands [34][35][36][37][38][39] such as tpy contribute strongly to the electron inventory of such nickel complexes, and redox chemistry may often occur at the ligand in addition to the abovementioned oxidation states (0, +I, +II, +III, and +IV). For instance, since tpy is an excellent electron acceptor through its extended π system, a species resulting from the reduction of a nickel(II)-tpy complex can be described in two different resonance forms: as a divalent nickel bound to a radical anionic (tpy) The fundamental studies on the electronic structures of terpyridine nickel complexes have also prompted others to explore details of related pybox complexes (pybox = pyridine-2,6-bisoxazolidine).…”

Nickel-Mediated Hydrogenolysis of C–O Bonds of Aryl Ethers: What Is the Source of the Hydrogen?

“…23,24 The m -terphenyl diphosphine motif was also found to predispose the metal center toward interaction with the carbon at the 2′-position of the central ring. 25 Toward exploiting potential C-X activation chemistry, ligand variants with ether substitution at this position were prepared.…”