Herein, we report on the synthesis and structural characterization of a series of trigonal and tetrahedral cationic copper(I) complexes, bearing phosphine or N-heterocyclic carbene ligands as donors, with benzthiazol-2-pyridine (pybt) and benzthiazol-2-quinoline (qybt) acting as π-chromophores. The compounds are highly colored due to their MLCT (MLCT = metal-to-ligand charge transfer) states absorbing between ca. λ = 400-500 nm, with ILCT (ILCT = intraligand charge transfer) states in the UV region. The relative shifts of the S→S absorption correlate with the computed highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, the qybt complexes generally being lower in energy than the pybt ones due to the larger conjugation of the quinoline-based ligand. The compounds exhibit, for Cu complexes, rare intense long-lived near-IR emission with λ ranging from 593 to 757 nm, quantum yields of up to Φ = 0.11, and lifetimes τ of several microseconds in the solid state as well as in poly(methyl methacrylate) films. Although a bathochromic shift of the emission is observed with λ ranging from 639 to 812 nm and the lifetimes are greatly increased at 77 K, no clear indication for thermally activated delayed fluorescence was found, leaving us to assign the emission to originate from a (Cu→pybt/qybt)MLCT state. The red to near-IR emission is a result of incorporation of the sulfur into the chromophore ligand, as related nitrogen analogues emit in the green to orange region of the electromagnetic spectrum. The photophysical results and conclusions have further been corroborated with density functional theory (DFT)/time-dependent DFT calculations, confirming the nature of the excited states and also the trends of the redox potentials.
We report that the anionic polymerization of P-mesityl and m-xylyl-substituted phosphaalkenes follows an unusual addition–isomerization mechanism. Specifically, the polymerization of ArPCPh2 [Ar = Mes (1a), m-Xyl (1b)] involves the hindered nucleophilic anion intermediate, Ⓟ–P(Ar)–CPh2 –, which undergoes a proton migration from the o-CH3 of the Mes/m-Xyl moiety to the −CPh2 moiety to afford a propagating benzylic anion. This mechanism is supported by the preparation of model compounds MeP(CHPh2)-4,6-Me2C6H2–2-CH2–CPh3 (2a) or MeP(CHPh2)-6-MeC6H3–2-CH2–CPh3 (2b), which were both crystallographically characterized. Polymerization of 1a or 1b in THF solution using n-BuLi (2 mol %) revealed 1H and 13C NMR signals assigned to −CH2– and −CHPh2 groups consistent with an addition–isomerization polymerization mechanism to afford poly(methylenephosphine) 3a or 3b. A large kinetic isotope effect (≤23) was determined for the n-BuLi-initiated polymerization of 1a-d 9 compared to 1a in THF at 50 °C, consistent with C–H (or C–D) activation as the rate-determining step. This C–H activation step was modeled using DFT computations which revealed that the intramolecular proton transfer from the o-CH3 of the Mes moiety to the −CPh2 moiety has an activation energy (E a = +18.5 kcal mol–1). For comparison, this computational value was quite close to the experimentally measured activation energy of propagation ArPCPh2 in THF [E a = 14.0 ± 0.9 kcal mol–1 (1a), 15.6 ± 2.8 kcal mol–1 (1b)].
An improved, one-pot synthesis of the linear sandwich compound [Sc(η -C H )(η -C H )] is presented. The synthetic procedure is amenable to boryl- and silyl-substituted cyclopentadienyl and cyclooctatetraenyl ligands, thereby yielding the first functionalized derivatives. We found that the synthesis of the silyl-substituted mixed sandwich complexes produces higher yields when the ligand exchange is carried out stepwise, by isolating the intermediate trimethylsilylated half-sandwich complex [Sc(η -C H SiMe )Cl(THF)] (THF=tetrahydrofuran). The molecular structures of the parent complex, as well as of its mono-boryl-substituted derivatives, have been determined by single-crystal X-ray diffraction. In addition, the optical and electrochemical properties of the mixed sandwich complexes are reported.
The regioselective borylation of pyridine precursors, followed by Suzuki coupling with dihalogenated linker molecules, provides access to tethered ligands. Complexation with MX2 salts results in the formation of dinuclear metal compounds. Syntheses and crystal structures are reported along with a discussion on the rigidity/flexibility of these new ligand systems.
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