Varying chelation assisted as well as solvent dependent reactivity profiles of isostructural β-ketoiminate analogues explicate their non-spectator behaviour and fractional redox non-innocence.
Rigid, conjugated alkyne bridges serve as important components
in various transition-metal complexes used for energy conversion,
charge separation, sensing, and molecular electronics. Alkyne stretching
modes have potential for modulating charge separation in donor–bridge–acceptor
compounds. Understanding the rules of energy relaxation and energy
transfer across the metal center in such compounds can help optimize
their electron transfer switching properties. We used relaxation-assisted
two-dimensional infrared spectroscopy to track energy transfer across
metal centers in platinum complexes featuring a triazole-terminated
alkyne ligand of two or six carbons, a perfluorophenyl ligand, and
two tri(
p
-tolyl)phosphine ligands. Comprehensive
analyses of waiting-time dynamics for numerous cross and diagonal
peaks were performed, focusing on coherent oscillation, energy transfer,
and cooling parameters. These observables augmented with density functional
theory computations of vibrational frequencies and anharmonic force
constants enabled identification of different functional groups of
the compounds. Computations of vibrational relaxation pathways and
mode couplings were performed, and two regimes of intramolecular energy
redistribution are described. One involves energy transfer between
ligands via high-frequency modes; the transfer is efficient only if
the modes involved are delocalized over both ligands. The energy transport
pathways between the ligands are identified. Another regime involves
redistribution via low-frequency delocalized modes, which does not
lead to interligand energy transport.
This article deals with isomeric ruthenium complexes [RuIII(LR)2(acac)] (S=1/2) involving unsymmetric β‐ketoiminates (AcNac) (LR=R‐AcNac, R=H (1), Cl (2), OMe (3); acac=acetylacetonate) [R=para‐substituents (H, Cl, OMe) of N‐bearing aryl group]. The isomeric identities of the complexes, cct (cis‐cis‐trans, blue, a), ctc (cis‐trans‐cis, green, b) and ccc (cis‐cis‐cis, pink, c) with respect to oxygen (acac), oxygen (L) and nitrogen (L) donors, respectively, were authenticated by their single‐crystal X‐ray structures and spectroscopic/electrochemical features. One‐electron reversible oxidation and reduction processes of 1–3 led to the electronic formulations of [RuIII(L)(L⋅)(acac)]+ and [RuII(L)2(acac)]− for 1+‐3+ (S=1) and 1−–3− (S=0), respectively. The triplet state of 1+‐3+ was corroborated by its forbidden weak half‐field signal near g≈4.0 at 4 K, revealing the non‐innocent feature of L. Interestingly, among the three isomeric forms (a–c in 1–3), the ctc (b in 2 b or 3 b) isomer selectively underwent oxidative functionalization at the central β‐carbon (C−H→C=O) of one of the L ligands in air, leading to the formation of diamagnetic [RuII(L)(L′)(acac)] (L′=diketoimine) in 4/4′. Mechanistic aspects of the oxygenation process of AcNac in 2 b were also explored via kinetic and theoretical studies.
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