Catalytic Transformation of Aldehydes with Nickel Complexes through η² Coordination and Oxidative Cyclization

Abstract

Chemists no longer doubt the importance of a methodology that could activate and utilize aldehydes in organic syntheses since many products prepared from them support our daily life. Tremendous effort has been devoted to the development of these methods using main-group elements and transition metals. Thus, many organic chemists have used an activator-(aldehyde oxygen) interaction, namely, η(1) coordination, whereby a Lewis or Brønsted acid activates an aldehyde. In the field of coordination chemistry, η(2) coordination of aldehydes to transition metals by coordination of a carbon-oxygen double bond has been well-studied; this activation mode, however, is rarely found in transition-metal catalysis. In view of the distinctive reactivity of an η(2)-aldehyde complex, unprecedented reactions via this intermediate are a distinct possibility. In this Account, we summarize our recent results dealing with nickel(0)-catalyzed transformations of aldehydes via η(2)-aldehyde nickel and oxanickelacycle intermediates. The combination of electron-rich nickel(0) and strong electron-donating N-heterocyclic carbene (NHC) ligands adequately form η(2)-aldehyde complexes in which the aldehyde is highly activated by back-bonding. With Ni(0)/NHC catalysts, processes involving intramolecular hydroacylation of alkenes and homo/cross-dimerization of aldehydes (the Tishchenko reaction) have been developed, and both proceed via the simultaneous η(2) coordination of aldehydes and other π components (alkenes or aldehydes). The results of the mechanistic studies are consistent with a reaction pathway that proceeds via an oxanickelacycle intermediate generated by the oxidative cyclization with a nickel(0) complex. In addition, we have used the η(2)-aldehyde nickel complex as an effective activator for an organosilane in order to generate a silicate reactant. These reactions show 100% atom efficiency, generate no wastes, and are conducted under mild conditions.

Aldehydes and ketones influence reactivity and selectivity in nickel-catalysed Suzuki–Miyaura reactions

“…Consistent with this, signals that are tentatively assigned to an h 2 (CO) complex are observed during the oxidative addition reactions of 3-Cl; various complexes of this type are known, [23][24][25][26][27][28][29][30] and have been implicated in nickel-mediated reactions. 31 The observed signals in the 31 P{ 1 H} NMR spectrum are consistent with a square planar complex (two doublets with 2 J PP of 31 Hz). This geometry is a result of electron donation from the bisphosphine ligand into the 3d(x 2 -y 2 ) orbital, which is also engaged in d to p* backbonding.…”

“…This work establishes how aldehydes and ketones can have positive or negative effects on nickel-catalysed reactions, depending on their location. The formation of h 2 -complexes has been implicated in some nickel-catalysed reactions 30,31,39,47,48 but this work shows that coordination effects can inuence even simple and ubiquitous Suzuki-Miyaura reactions.…”

The Importance of Ligand‐Induced Backdonation in the Stabilization of Square Planar d10 Nickel π‐Complexes

“…For example, we are exploring the organometallicc hemistry of nickel, [10][11][12][13][14] which has undergone ar enaissance in recent years. [15][16][17][18][19][20][21] Our focus has been the structure and reactivityo fn ickel p-complexes, which have been reported in aw ide range of catalytic processes, including the coupling of CO 2 and ethylene, [5,[22][23][24][25][26][27][28][29][30][31][32] intermolecular Tischenkoc oupling, [33][34][35] benzoxasilole synthesis, [36,37] the aldol reaction, [38] allylic alkylation, [39] allylic amination, [40] allylic amidation, [41] epoxide functionalization, [42] and Suzuki-Miyaura coupling. [43] Nickel p-complexes of heteroarenes have also been identified as key intermediates in nickel-catalysed catalystt ransfer polycondensation to form polythiophenes.…”

Nickel and Palladium Complexes with Reactive σ‐Metal‐Oxygen Covalent Bonds

“…[11] The number of applications of the special "organometallic-like" reactivity of transition metal compounds with MÀ N or MÀ O bonds has experienced a continuous growth. Some prominent examples of these are the Buchwald-Hartwig aryl amination [12] (now celebrating its 25th anniversary) and the analogous etherification reaction, [13] the Suzuki-Miyaura reaction, [14] reductive couplings of carbonyl and unsaturated compounds, [15] reduction of carbonyl compounds, [16] aerobic [17] or acceptorless [18] alcohol oxidation, hydrogen borrowing alkylation, [19] or various dehydrogenative coupling reactions, [20] just to cite a few of them (see Chart 1). In parallel, an intense effort has been deployed to understand the fundamental aspects of reactive metal-heteroatom bonds, either as catalytic intermediates or as stoichiometric reagents.…”