Side-on cupric–superoxo triplet complexes as competent agents for H-abstraction relevant to the active site of PHM

Abstract

Copper complexes with N3S donors mimic the CuM site of copper monooxygenases and react with O2 affording side-on cupric-superoxo complexes capable of H-abstraction from dihydroanthracene and THF. Spectroscopic and DFT data of the Cu-superoxos support a spin triplet ground state for the side-on complexes, as well as a hemilabile thioether.

Copper–Oxygen Complexes Revisited: Structures, Spectroscopy, and Reactivity

“…159 The assignment was based on UV–vis spectroscopy, the observation of paramagnetically broadened resonances in NMR spectra, and DFT calculations. In the absence of more definitive structural data from additional experiments (i.e., resonance Raman, X-ray crystallography, and EXAFS), however, the formulation of this complex must be regarded as tentative.…”

On the Metal Cooperativity in a Dinuclear Copper–Guanidine Complex for Aliphatic C−H Bond Cleavage by Dioxygen

“…According to the literature, three main intermediates (Cu 1 S E , Cu 1 P H , Cu 1 O)a re considered for the hydroxylating activity of the enzyme PHM. [11,33,34] The formation of a Cu 1 P H complex (which could further react to afford a Cu 1 O species) by proton transfer from as olvent molecule to the O 2 unit of the Cu 1 S E complex, as assumed from DFT calculations in the literature, [33] could be excluded. The high pK a value of acetonitrile precludes this mechanism.I na ll three cases ([3]PF 6 ,[ 4]PF 6 ,a nd [5](PF 6 ) 3 ), intramolecular proton-coupled electron transfer (PCET, Scheme 6a)t ot he dioxygen unit attached to Cu B is assumed to be the first step of the reaction sequence, in analogy to the mechanism reported by Itoh et al [39] One may identify two possible reactions ites for hydrogen atom abstraction at the methylene bridge, denoted L and R in Scheme 6a.…”

“…The role of the Cu A atom is to provide electron density to the Cu B site for the subsequent hydroxylationp athway.S cheme 1b depicts one possible reaction pathway for the hydroxylation mechanism in PHM, as suggested by Amzel et al, [30] but other pathways have been proposed, involving, for example, the oxyl radical Cu 1 O formed from a Cu 1 S E species. [11,33,34] The mechanism of the electron-transfer pathway is not completely clear,s ince the synthesis of model Cu 1 S E complexes is generally hampered by their high reactivity.I ns ome cases,t he products of proton-coupled electron-transfer (PCET) reactions, for example, with TEMPOH (Scheme1a, b, TEMPO = 2,2,6,6-tetramethylpiperidinyloxyl), have been isolated. [35] Twotypes of hydroxylation are initiated by copper-dioxygen complexes:1 )aromatic hydroxylation [36] and aliphatic hydroxylation, [37] due to dinuclearo xo speciest hat are not relevant to the above-mentionede nzymes, and 2) aliphatic hydroxylation attributablet om ononuclear dioxygen complexes (Scheme 1a), as described in the following.…”

Structure and Reactivity of Copper Complexes Supported by a Bulky Tripodal N4 Ligand: Copper(I)/Dioxygen Reactivity and Formation of a Hydroperoxide Copper(II) Complex

“…To date, several end‐on superoxide copper(II) complexes (type A ) supported by N 4 , N 3 , and N 3 S ligands have been characterized, whereas only two examples are available regarding to the side‐on bound superoxide copper(II) complex (type B ) , . On the other hand, Tolman and co‐workers succeeded to isolate side‐on bound peroxide copper(III) complexes (type C ) by using monoanionic β‐diketiminate bidentate ligands and their analogues, which can stabilize the higher oxidation state of copper(III) with a square‐planar arrangement …”

“…To date, several end-on superoxide copper(II) complexes (type A) supported by N 4 , [4][5][6][7][8][9][10] N 3 , [11][12][13][14][15] and N 3 S [16] ligands have been characterized, whereas only two examples are available regarding to the side-on bound superoxide copper(II) complex (type B). [17,18] On the other hand, Tolman and co-workers succeeded to isolate side-on bound peroxide copper(III) complexes (type C) by using monoanionic β-diketiminate bidentate ligands and their analogues, which can stabilize the higher oxidation state of copper(III) with a square-planar arrangement. [19][20][21] Several hydroperoxide copper(II) complexes (type D) supported by N 3 [13] and N 4 [22][23][24][25][26][27][28] ligands have also been reported, most of which were synthesized by the reaction of corresponding copper(II) complexes and H 2 O 2 in the presence of base.…”