Bystanding F⁺ Oxidants Enable Selective Reductive Elimination from High‐Valent Metal Centers in Catalysis

Abstract

Reductive elimination from partially or completely oxidized metal centers is a vital step in a myriad of carbon–carbon and carbon–heteroatom bond–forming reactions. One strategy for promoting otherwise challenging reductive elimination reactions is to oxidize the metal center using a two-electron oxidant (i.e., from M(n) to M(n+2)). However, many of the commonly used oxidants for this type of transformation contain oxygen, nitrogen, or halogen moieties that are subsequently capable of participating in reductive elimination, leading to a mixture of products. This minireview examines an emerging solution to this widespread problem in organometallic chemistry, the use of bystanding F+ oxidants, and describes recent applications in Pd(II)/Pd(IV) and Au(I)/Au(III) catalysis. We then briefly discuss a rare example in which one-electron oxidants have been shown to promote selective reductive elimination in Pd(II)-catalyzed C–H functionalization, which we view as a promising future directing in the field.

Redox-Induced Aromatic C–H Bond Functionalization in Metal Complex Catalysis from the Electrochemical Point of View

“…The chemistry of palladium (Pd) compounds in higher oxidation states is extremely useful in oxidative functionalizations, in which a C-H bond can be catalytically converted into another functional group [1,[6][7][8][9][10][11][12]. One of the major problems in Pd(II)/Pd(III)/Pd(IV) chemistry, however, is that the co-oxidants used are either expensive to purchase (silver and other metal salts are often used), or to separate from the product mixture (particularly in the case of high molecular weight organic oxidants).…”

Unique distal size selectivity with a digold catalyst during alkyne homocoupling

“…Au(III) intermediates have been isolated and characterized [34][35][36] . Despite the great body of work reported in the literature for alkynes and gold, the reductive elimination of C sp bonds from Au(III) complexes has not been reported yet as far as we know 8 , and very few examples of stable Au(III)-diacetylide complexes appear in the literature 37,38 . This lack of precedents for Au(III)-diacetylides might indicate that the reactivity of the alkynes once s-bound to Au(III) is very high, including a potential reductive elimination.…”

“…Gold catalysis has been intensively studied during the last decade and, in particular, the use of the redox pair Au(I)/Au(III) has arisen much interest among chemists as a catalyst for new carbon-carbon and carbon-heteroatom bond-forming reactions [6][7][8][9][10] . Despite the increasing number of new transformations reported, particularly with alkynes 11,12 , fundamental studies covering the elemental steps of the goldcatalysed redox cycle remain scarce 13,14 .…”

Ruthenium(II)-catalyzed <I>Ortho</I> C-O Bond formation of Substituted Aromatics with Oxygen Nucleophiles through C-H Bond Activation

“…Several directing groups such as 2-pyridyl, carbonyl, ester, nitrile, carboxylic acid, N-acetyl and amide can be efficiently used for the reaction. With the assistance of these directing groups, acetoxylation (Henry, 1971;Yoneyama and Crabtree, 1996;Sanford et al, 2004;Yu et al, 2005;Yu et al, 2006;Corey et al, 2006;Wu et al, 2008;Chen et al, 2009;Cheng et al, 2010;Yu et al, 2010;Yu et al, 2011;Sanford et al, 2012;Kim et al, 2013), alkoxylation (Sanford et al, 2006;Wang and Yuan, 2010), hydroxylation (Yu et al, 2009;Dong et al, 2012) and benzoxylation (Sanford et al, 2005;Cheng et al, 2011) at the ortho C-H bond of directing group substituted aromatics with various oxygen nucleophiles have been studied. Palladium and copper complexes are efficient catalysts for this type of reaction.…”