3 research outputs found
Synthesis, Structure, Photophysics, and a DFT Study of Phosphorescent C*N<sup>∧</sup>N- and C<sup>∧</sup>N<sup>∧</sup>N‑Coordinated Platinum Complexes
The reaction of <i>N</i>,<i>N</i>-diphenyl-2,2′-bipyridin-6-amine (<b>L1</b>) and <i>N</i>,<i>N</i>-diphenyl-6-(1<i>H</i>-pyrazol-1-yl)Âpyridin-2-amine (<b>L2</b>) with K<sub>2</sub>PtCl<sub>4</sub> produced C*N<sup>∧</sup>N-coordinated
cycloplatinated compounds with a five–six fused metallacycle <b>1a</b> and <b>2a</b>, respectively, which were then converted
into their phenylacetylide derivatives <b>1b</b> and <b>2b</b>, respectively. Similar reactions starting from 2-phenyl-6-(1<i>H</i>-pyrazol-1-yl)Âpyridine (<b>L3</b>) produced C<sup>∧</sup>N<sup>∧</sup>N-coordinated platinum complexes <b>3a</b> and <b>3b</b> with a five–five-fused metallacycle.
The structures of <b>1a</b>, <b>1b</b>, <b>2b</b>, <b>3a</b>, and <b>3b</b> were determined by X-ray crystallography.
The C*N<sup>∧</sup>N-coordinated platinum complexes are closer
to a square geometry, whereas the C<sup>∧</sup>N<sup>∧</sup>N-coordinated complexes display a nearly perfect planar geometry.
The π···π interactions were revealed in
the crystal packing for <b>1a</b>, <b>2b</b>, and <b>3a</b> with a π···π contact of 3.450,
3.422, and 3.414 Ã…, respectively. Two conformers were revealed
in the crystal structure of <b>2b</b>, one with the phenyl ring
of the phenylacetylide being approximately parallel with the coordination
plane and the other with the phenyl ring being approximately perpendicular
to the coordination plane. Both <b>1a</b> and <b>1b</b> are weakly emissive in the red region. Complexes <b>2a</b> and <b>3a</b> are also weakly emissive, but their acetylide
derivatives <b>2b</b> and <b>3b</b> emitted strongly green
light at room temperature with quantum yields of 43 and 62%, respectively.
DFT/TDDFT calculations were performed to elucidate the nature of their
electronic transitions. The calculations suggested that lowest singlet
and triplet excited states are characteristic of a mixed state involving
one or more charge-transfer transitions such as ILCT, MLCT, and LLCT
Synthesis, Structure, Photophysics, and a DFT Study of Phosphorescent C*N<sup>∧</sup>N- and C<sup>∧</sup>N<sup>∧</sup>N‑Coordinated Platinum Complexes
The reaction of <i>N</i>,<i>N</i>-diphenyl-2,2′-bipyridin-6-amine (<b>L1</b>) and <i>N</i>,<i>N</i>-diphenyl-6-(1<i>H</i>-pyrazol-1-yl)Âpyridin-2-amine (<b>L2</b>) with K<sub>2</sub>PtCl<sub>4</sub> produced C*N<sup>∧</sup>N-coordinated
cycloplatinated compounds with a five–six fused metallacycle <b>1a</b> and <b>2a</b>, respectively, which were then converted
into their phenylacetylide derivatives <b>1b</b> and <b>2b</b>, respectively. Similar reactions starting from 2-phenyl-6-(1<i>H</i>-pyrazol-1-yl)Âpyridine (<b>L3</b>) produced C<sup>∧</sup>N<sup>∧</sup>N-coordinated platinum complexes <b>3a</b> and <b>3b</b> with a five–five-fused metallacycle.
The structures of <b>1a</b>, <b>1b</b>, <b>2b</b>, <b>3a</b>, and <b>3b</b> were determined by X-ray crystallography.
The C*N<sup>∧</sup>N-coordinated platinum complexes are closer
to a square geometry, whereas the C<sup>∧</sup>N<sup>∧</sup>N-coordinated complexes display a nearly perfect planar geometry.
The π···π interactions were revealed in
the crystal packing for <b>1a</b>, <b>2b</b>, and <b>3a</b> with a π···π contact of 3.450,
3.422, and 3.414 Ã…, respectively. Two conformers were revealed
in the crystal structure of <b>2b</b>, one with the phenyl ring
of the phenylacetylide being approximately parallel with the coordination
plane and the other with the phenyl ring being approximately perpendicular
to the coordination plane. Both <b>1a</b> and <b>1b</b> are weakly emissive in the red region. Complexes <b>2a</b> and <b>3a</b> are also weakly emissive, but their acetylide
derivatives <b>2b</b> and <b>3b</b> emitted strongly green
light at room temperature with quantum yields of 43 and 62%, respectively.
DFT/TDDFT calculations were performed to elucidate the nature of their
electronic transitions. The calculations suggested that lowest singlet
and triplet excited states are characteristic of a mixed state involving
one or more charge-transfer transitions such as ILCT, MLCT, and LLCT
Redox-Active Bis(phenolate) N‑Heterocyclic Carbene [OCO] Pincer Ligands Support Cobalt Electron Transfer Series Spanning Four Oxidation States
A new
family of low-coordinate Co complexes supported by three redox-noninnocent
tridentate [OCO] pincer-type bisÂ(phenolate) N-heterocyclic carbene
(NHC) ligands are described. Combined experimental and computational
data suggest that the charge-neutral four-coordinate complexes are
best formulated as CoÂ(II) centers bound to closed-shell [OCO]<sup>2–</sup> dianions, of the general formula [(OCO)ÂCo<sup>II</sup>L] (where L is a solvent-derived MeCN or THF). Cyclic voltammograms
of the [(OCO)ÂCo<sup>II</sup>L] complexes reveal three oxidations accessible
at potentials below 1.2 V vs Fc<sup>+</sup>/Fc, corresponding to generation
of formally CoÂ(V) species, but the true physical/spectroscopic oxidation
states are much lower. Chemical oxidations afford the mono- and dications
of the imidazoline NHC-derived complex, which were examined by computational
and magnetic and spectroscopic methods, including single-crystal X-ray
diffraction. The metal and ligand oxidation states of the monocationic
complex are ambiguous; data are consistent with formulation as either
[(<sup>S</sup>OCO)ÂCo<sup>III</sup>(THF)<sub>2</sub>]<sup>+</sup> containing
a closed-shell [<sup>S</sup>OCO]<sup>2–</sup> diphenolate ligand
bound to a <i>S</i> = 1 CoÂ(III) center, or [(<sup>S</sup>OCO<sup>•</sup>)ÂCo<sup>II</sup>(THF)<sub>2</sub>]<sup>+</sup> with a low-spin CoÂ(II) ion ferromagnetically coupled to monoanionic
[<sup>S</sup>OCO<sup>•</sup>]<sup>−</sup> containing
a single unpaired electron distributed across the [OCO] framework.
The dication is best described as [(<sup>S</sup>OCO<sup>0</sup>)ÂCo<sup>II</sup>(THF)<sub>3</sub>]<sup>2+</sup>, with a single unpaired electron
localized on the d<sup>7</sup> CoÂ(II) center and a doubly oxidized,
charge-neutral, closed-shell <sup>S</sup>OCO<sup>0</sup> ligand.
The combined data provide for the first time unequivocal and structural
evidence for [OCO] ligand redox activity. Notably, varying the degree
of unsaturation in the NHC backbone shifts the ligand-based oxidation
potentials by up to 400 mV. The possible chemical origins of this
unexpected shift, along with the potential utility of the [OCO] pincer
ligands for base-metal-mediated organometallic coupling catalysis,
are discussed