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Controlled Interconversion of a Dinuclear Au Species Supported by a Redox-Active Bridging PNP Ligand Facilitates Ligand-to-Gold Electron Transfer.

ABSTRACT: Redox non-innocent ligands have recently emerged as interesting tools to obtain new reactivity with a wide variety of metals. However, gold has almost been neglected in this respect. Here, we report mechanistic investigations related to a rare example of ligand-based redox chemistry in the coordination sphere of gold. The dinuclear metal-centered mixed-valent Au^I -Au^III complex 1, supported by monoanionic diarylamido-diphosphine ligand PNP^Pr and with three chlorido ligands overall, undergoes a complex series of reactions upon halide abstraction by silver salt or Lewis acids such as gallium trichloride. Formation of the ultimate Au^I -Au^I complex 2 requires the intermediacy of Au^I -Au^I dimers 5 and 7 as well as the unique Au^III -Au^III complex 6, both of which are interconverted in a feedback loop. Finally, unprecedented ortho-selective C-H activation of the redox-active PNP ligand results in the carbazolyldiphosphine derivative PN*P^Pr via ligand-to-metal two-electron transfer. This work demonstrates that the redox-chemistry of gold may be significantly expanded and modified when using a reactive ligand scaffold.

SUBMITTER: Vreeken V

PROVIDER: S-EPMC5413818 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Controlled Interconversion of a Dinuclear Au Species Supported by a Redox-Active Bridging PNP Ligand Facilitates Ligand-to-Gold Electron Transfer.

Vreeken Vincent V Siegler Maxime A MA van der Vlugt Jarl Ivar JI

Chemistry (Weinheim an der Bergstrasse, Germany) 20170403 23

Redox non-innocent ligands have recently emerged as interesting tools to obtain new reactivity with a wide variety of metals. However, gold has almost been neglected in this respect. Here, we report mechanistic investigations related to a rare example of ligand-based redox chemistry in the coordination sphere of gold. The dinuclear metal-centered mixed-valent AuI -AuIII complex 1, supported by monoanionic diarylamido-diphosphine ligand PNPPr and with three chlori ...[more]

PMID: 28248000

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Project description:Meso tetraarylporphyrinato gold(iii) cations bearing different substituents at the aryl substituents (COOMe, COOH, NO2, NH2, NHAc, H, O n Bu, CF3) were prepared and characterised. Their reversible one-electron reductions were studied by (spectro)electrochemical means as well as by selective chemical one-electron reduction using cobaltocene. The preferred location of the spin density, namely gold centred or porphyrin centred, was probed by electron paramagnetic resonance spectroscopy (g values, 197Au hyperfine coupling) as well as by density functional theory calculations (spin densities). In all cases studied experimentally and theoretically, the gold(ii) valence isomer (5d9 electron configuration) is preferred over the porphyrin π radical anion. In the hexafluorophosphate salt of the nitro derivative a further nitro π radical anion valence isomeric species is significantly populated. In the presence of chloride ions this nitro π radical anion/AuII valence isomeric equilibrium evolves towards the porphyrin π radical anion. The electronic structures of the nitro π radical and the AuII σ radical valence isomers (5d x2-y2 orbital) could be calculated by DFT methods. The electron transfer pathway between the nitro π radical anion and the AuII valence isomer is well described by the location of the hexfluorophosphate counterion, the Au-N distances (corresponding to the totally symmetric stretching vibration), the symmetric stretching mode of the NO2 substituent and a meso-nitrophenyl rotation. The specific geometric and electronic properties of the favoured gold(ii) σ radical valence isomer, namely counterion dislocation and σ symmetry of the redox orbital, might stabilise charge-shifted states [(gold(ii) porphyrin)-donor˙+] by retarding the back electron transfer to give the ground state (gold(iii) porphyrin)-donor. This will guide the design of (photo-induced) electron transfer pathways with tetraarylporphyrinato gold(iii) complexes as electron acceptors.

Dataset Information

Controlled Interconversion of a Dinuclear Au Species Supported by a Redox-Active Bridging PNP Ligand Facilitates Ligand-to-Gold Electron Transfer.

Publications

Controlled Interconversion of a Dinuclear Au Species Supported by a Redox-Active Bridging PNP Ligand Facilitates Ligand-to-Gold Electron Transfer.

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