C(sp³)–H cyanation by a formal copper(iii) cyanide complex

Abstract

A formal copper(iii) cyanide complex and its C–H cyanation reactivity are reported. The redox potentials of substrates, instead of C–H bond dissociation energies, were found to be the key determinant of the rates of PCET.

Copper–Carbon Homolysis Competes with Reductive Elimination in Well-Defined Copper(III) Complexes

“…Our groups have a long-term goal to understand the role of elusive metal intermediates, especially high-valent metal complexes, in catalytic reactions . In our previous studies, we have reported the synthesis of anionic [alkyl–Cu III –(CF 3 ) 3 ] − complexes, which could undergo predominantly C­(sp 3 )–CF 3 bond-forming reductive elimination reactions .…”

C–N Bond Formation at Discrete CuIII–Aryl Complexes

“…Notably, we refer to these copper complexes as “formal copper­(III)” for the purpose of bookkeeping purposes. Previous works on pyridinediamide copper complexes suggest that assigning the physical oxidation state for the copper center is difficult. ,− …”

“…An isopropyl-substituted pyridine diamide ( L H 2 ) ligand was selected for this study as it has been shown to stabilize high-valent Cu III centers. − First, the arylation of neutral L Cu II (MeCN) was attempted with pentafluorophenyl lithium (LiAr F5 ). However, treatment of a THF solution of L Cu II (MeCN) with LiAr F5 at −78 °C resulted in the formation of a black-brown precipitate of copper metal.…”

The role of basicity in selective C–H bond activation by transition metal-oxidos

“…However, a growing area of interest in inorganic chemistry are mechanisms of C-H bond activation that fall between these limits off the diagonal often referred to as "asynchronous", "nonsynchronous", or "imbalanced" PCET. [18][19][20][21][22][23][24][25][26][27][28][29][30] These types of reactions are still considered concerted, as compared to stepwise, because a thermodynamically stable intermediate is not formed during the transfer process but differ from balanced CPET as the degree of charge transfer or delocalization of either the proton or electron lags behind the other (Fig. 2).…”

“…We are not alone in finding discrepancies in rate data for C-H cleavage process by metal-oxido complexes. 18,20,24,28,30 For instance, Anderson has reported that the rates of reactivity of his Co III -oxido complex deviate from a BEP-type relationship in favor of a good correlation between log (k obs ) and the pK a (C-H) values from the C-H bonds of the substrates. 27 Like the Mn IIIoxido complexes, this Co III -oxido complex is strongly basic (pK a (Mn II OH) of ∼15 in DMSO), 27 leading in both cases to mechanistic suggestions that favor proton transfer (PT)-dominated imbalanced transition states (Fig.…”