Ruthenium Porphyrins with Axial π‐Conjugated Arylamide and Arylimide Ligands

Abstract

A series of ruthenium porphyrins [Ru(IV)(por)(NHY)2] and [Ru(VI)(por)(NY)2] bearing axially coordinated π-conjugated arylamide and arylimide ligands, respectively, have been synthesized. The crystal structures of [Ru(IV)(tmp)(NHY)2] (tmp = 5,10,15,20-tetramesitylporphyrinato(2-)) with Y = 4'-methoxy-biphenyl-4-yl (Ar-Ar-p-OMe), 4'-chloro-biphenyl-4-yl (Ar-Ar-p-Cl), and 9,9-dibutyl-fluoren-2-yl (Ar^Ar) show axial Ru-N(arylamide) distances of 1.978(4), 1.971(6), and 1.985(13) Å, respectively. [Ru(IV)(tmp)(NH{Ar^Ar})2] is an example of metalloporphyrins that bind an arylamide ligand featuring a co-planar biphenyl unit. The [Ru(IV)(por)(NHY)2] complexes show a quasi-reversible reduction couple or irreversible reduction wave attributed to Ru(IV)→Ru(III) with Epc from -1.06 to -1.40 V versus Cp2Fe(+/0) and an irreversible oxidation wave with Epa from -0.04 to 0.19 V versus Cp2Fe(+/0). Reaction of the [Ru(IV)(por)(NHY)2] with bromine afforded [Ru(IV)(por)(NHY)Br]. PhI(OAc)2 oxidation of the [Ru(IV)(por)(NHY)2] gave [Ru(VI)(por)(NY)2]; the latter can be prepared from reaction of [Ru(II)(por)(CO)] with aryl azides N3Y. The crystal structure of [Ru(VI)(tmp)(N{Ar-Ar-p-OMe})2] features Ru-N(arylimide) distances of 1.824(5) and 1.829(5) Å. Alkene aziridination and C-H amination catalyzed by "[Ru(II)(tmp)(CO)]+π-conjugated aryl azides", or mediated by [Ru(VI)(por)(NY)2] with Y = biphenyl-4-yl (Ar-Ar) and Ar-Ar-p-Cl, gave aziridines and amines in moderate yields. The electronic structure of [Ru(VI)(por)(NY)2] was examined by DFT calculations.

Building from Ga‐Porphyrins: Synthesis of Ga‐Acetylide Complexes Using Acetylenes and Polyynes

“…Their use as light harvesting systems, for example, derives from an astonishing number of porphyrin units, arranged in a very defined organization . In synthetic systems, peripheral substituents in the meso ‐ and β‐positions, metallation of the free base macrocycle, and axial ligands can be used to modulate the properties of porphyrins . Differences in the effect of substitution are well‐founded in the orbitals they influence following the four‐orbital theory…”

Computational Studies on the Mechanism and Origin of the Different Regioselectivities of Manganese Porphyrin-Catalyzed C–H Bond Hydroxylation and Amidation of Equilenin Acetate

“…Inspired by numerous DFT studies of metalloporphyrin catalysis done by Shaik, 11 Nam, 12 Eisenstein, 13 and Groves, 14 we proposed a HAA/OR mechanism for both C(sp 2 )−H and C(sp 3 )−H bond hydroxylation (Scheme 2). For C(sp 2 )−H bond hydroxylation, an alternate oxygen-atom-transfer (OAT) mechanism 15,16 Based on previous mechanistic studies on cobalt porphyrin, 17 ruthenium porphyrin, 18 and iron porphyrin 19 catalyzed amination, we proposed a hydrogen-atom-abstraction/nitrogen-rebound (HAA/NR) mechanism for manganese porphyrin-catalyzed C(sp 2 )−H and C(sp 3 )−H bond amidation. In addition, the nitrogen-atom-transfer (NAT) mechanism 20 was also proposed for C(sp 2 )−H bond amidation.…”

“…Based on previous mechanistic studies on cobalt porphyrin, ruthenium porphyrin, and iron porphyrin catalyzed amination, we proposed a hydrogen-atom-abstraction/nitrogen-rebound (HAA/NR) mechanism for manganese porphyrin-catalyzed C­(sp 2 )–H and C­(sp 3 )–H bond amidation. In addition, the nitrogen-atom-transfer (NAT) mechanism was also proposed for C­(sp 2 )–H bond amidation.…”

RuV‐Acylimido Intermediate in [RuIV(Por)Cl2]‐Catalyzed C–N Bond Formation: Spectroscopic Characterization, Reactivity, and Catalytic Reactions

“…[16] To the best of our knowledge,n oe xample of M(NCOR) intermediates in catalytic reactions has been directly observed by spectroscopic analysis. [17] Herein we describe spectroscopic studies including ESI-MS and EPR, and also DFT calculations,o nR u(NCOR) species involved in CÀNb ond formation reactions catalyzed by ruthenium porphyrin (Ru(Por)) complexes;t hese Ru-(NCOR) species,g enerated in [Ru IV (Por)Cl 2 ]/N 3 COR(1) catalytic systems,c ould be formulated as Ru V -imido complexes,being different from the sulfonyl/arylnitrenoids [Ru VI -(Por)(NSO 2 Ar) 2 ] [18] and [Ru VI (Por)(NAr) 2 ] [19] involved in stoichiometric or [Ru II (Por)(CO)]-catalyzed reactions.T he [Ru IV (Por)Cl 2 ]/N 3 COR systems are applicable to catalytic CÀ Nbond formation reactions using substrates without DGs to transform i) alkenes 2 to aziridines 3 or oxazolines 4, ii)indoles 5 to C3-aminated derivatives 6,iii)silyl enol ethers 7 to a-amino ketones 8,i v) hydrocarbons 9 to C(sp 3 )-H amination products 10 (Figure 1b), together with functionalization of natural products and carbohydrate derivatives,with isolated product yields of up to 99 %(atotal of 75 examples). Notably,the Ru V (NCOR) species are unique examples of the nitrogen analogue of highly reactive Ru V (O) species [20,21] involved in, e.g.,[Ru IV (Por)Cl 2 ]-catalyzed oxygen atom transfer reactions (Figure 1aB).…”