Tetraphenylborate as a Novel Bridging Ligand in a Zwitterionic Nickel(I) Dimer

Abstract

Heterolytic abstraction of anionic ligands such as halides or alkyl substituents can convert coordinatively saturated organometallic complexes into highly electrophilic, usually transient, cationic species that can serve as efficient initiators in various catalytic reactions. This strategy has been used in the development of many catalytic processes based on (quasi) square-planar d 8 metal precursors, including the recently reported systems for olefin polymerization reactions. [1] In this context, we have shown that abstraction of Cl À from the complexes [(R-ind)Ni(PPh 3 )Cl] (R-ind = indenyl and its substituted derivatives) [2] leads to the generation of a transient species (presumed to be [(R-ind)Ni(PPh 3 )] + ) that reacts with excess substrate to promote the oligomerization or polymerization of various olefins, [3] PhCCH, [4] and PhSiH 3 , [5] or catalyzes the hydrosilylation of olefins and ketones [6]

Trinuclear Nickel Complexes with Metal–Arene Interactions Supported by Tris- and Bis(phosphinoaryl)benzene Frameworks

“…Complexes with cofacial Ni I centers display the metals in close proximity (2.3-2.6 Å) consistent with a Ni I –Ni I bonding interaction. 1f,4a,5b,7 The metal-arene interactions in these complexes are typically supported by pendant donors, although a tetraphenylborate was reported to coordinate the Ni I 2 moiety without additional ligands. 7a A second type of Ni2–arene complex involves two Ni 0 centers ligated to opposite sides of the arene.…”

“…1f,4a,5b,7 The metal-arene interactions in these complexes are typically supported by pendant donors, although a tetraphenylborate was reported to coordinate the Ni I 2 moiety without additional ligands. 7a A second type of Ni2–arene complex involves two Ni 0 centers ligated to opposite sides of the arene. 5a,8 A third class includes dinickel complexes with metals coordinated on opposite faces of the arene, but in higher oxidation states.…”

“…5a,8 A third class includes dinickel complexes with metals coordinated on opposite faces of the arene, but in higher oxidation states. 4a,7b,9 A common metal-arene binding mode in these complexes is μ-η 3 :η 3 , with structural distortions of the ring away from planarity and elongation of the C–C bonds between the two η 3 metal coordination sites. 7b,9a This binding mode and the diamagnetism of these complexes has been interpreted as a formal reduction of the ring by Ni I to result in a diallyl moiety and two Ni II centers.…”

Reversible Halide‐Modulated Nickel–Nickel Bond Cleavage: Metal–Metal Bonds as Design Elements for Molecular Devices

“…An XRD study reveals that the two metal centers are on the same face of the central arene; both interact with the π system of the central ring and are bridged by the remaining μ 2 -chloride (Figure 2). The Ni-Ni distance (2.5248(3) Å) in 3 is longer than the distance observed for the Ni I -Ni I moiety supported by a p -terphenyl diphosphine system (2.3658(2) Å) [7] but comparable to distances observed for other dinckel(I) moieties supported by bridging arenes [10] or by only bridging halides. [11] Treatment of 3 with a chloride source leads to the clean regeneration of 2 ( 1 H NMR spectroscopy).…”

“…Corroborating this calculated interaction, the crystal structure of 2 shows the C7-C8 and C10-C11 distances to be shorter than the other C-C bonds of the central arene. Bifacial η 3 ,η 3 -bridging of an arene between two metal centers has been previously observed in dinuclear Ni, [10a, 18] Pt, [19] and Co complexes. [20] In contrast, in compound 2 , the arene bridges in η 3 ,η 1 –fashion, probably due to the steric constraints of the triphosphine.…”