Triplet Energy Transfer Insight in Coordination of Unsaturated Hydrocarbons by d⁰Bent Metallocenes (Zr, Hf)

Abstract

For a class of pi-complexes as energy donors, with the use of highly emissive d(0) metallocenes Cp(2)MCl(2) where M = Zr and Hf, it is shown that radiationless triplet energy transfer to unsaturated hydrocarbons in a rigid nonpolar methylcyclohexane (MCH) matrix (where molecular diffusion is absent) obeys the Perrin equation, occurs at radii R(0), being close to the diameter of interacting molecules, and is well described by an electron-exchange resonant (Dexter) mechanism of interaction. Principle correlation between values of the critical radius and a number of C atoms in a linear alpha-olefin is for the first time reported, viz. R(0) (Angstrom) = -2.47 + 1.35n (obtained for systems [Cp(2)HfCl(2) + CnH(2)n + MCH] at 77 K). Pronounced blue shifts (up to 1000 cm(-1)) of low-temperature emission spectra of Cp(2)ZrCl(2) in MCH in the presence of dienes, possessing nonconjugated C=C bonds, are observed, thus suggesting inner-sphere diene coordination. In view of the experimental data, inner- and outer-sphere coordinative interaction between the components of catalytic systems for polymerization (d(0) metallocene precatalysts and alkenes and dienes) is rationalized.

A Zirconium Photosensitizer with a Long-Lived Excited State: Mechanistic Insight into Photoinduced Single-Electron Transfer

“…The readily accessible d 0 electron configuration commonly found for early transition metals prevents detrimental ligand field deactivation pathways and allows for extended luminescence lifetimes. Prompted by the initial discovery of long-lived luminescent LMCT states in cyclopentadienyl Sc III complexes, , several examples of luminescent group III–V metal complexes with d 0 configuration have been reported. − However, most of these complexes do not exhibit reversible redox properties and often require excitation by UV light. In contrast, we recently reported the synthesis of the zirconium complex, Zr­( Me PDP) 2 (H 2 Me PDP = 2,6-bis­(5-methyl-3-phenyl-1 H -pyrrol-2-yl)-pyridine), that shows photoluminescence upon visible light excitation and can undergo reversible electron transfer in the ground state .…”

Photoluminescence of Seven‐Coordinate Zirconium and Hafnium Complexes with 2,2′‐Pyridylpyrrolide Ligands

“…[17] Much attention in this area has been devoted to 1str ow late transition metals [18][19][20][21][22][23][24][25][26][27] and low-valent groups 6a nd 7m etals [28][29][30][31][32][33] that retain the fundamental design principle of photoinduced charge separation via MLCT. [34] In pronouncedc ontrast, luminescent metalc omplexes relying on alternative mechanisms such as ligand-tometal charget ransfer (LMCT), [35][36][37][38][39][40][41][42][43] ligand-to-ligand charge transfer (LLCT), [44,45] or metal-centered excitations( i.e. d-d, f-f, or d-f) [46][47][48][49][50][51][52] are not as well-studied, but offer the potentialt o expand the palette of metals suitable for photosensitizer development.…”

Effect of the solvent on the radius of exchange interactions of d0-metal complexes with cyclopentadiene

“…12- 14 The sol vents were repeatedly purified from traces of impurities, oxygen, and moisture and degassed through several freeze pump thaw cycles in a high vacuum line by known procedures and stored in vacuo or under inert gas over a drying agent (Na-K alloy or molecular sieves) from which they were transferred in vacuo immediately prior to use. Cyclopentadiene was obtained from the corresponding dicyclopentadiene dimer (Acros Organics, 97%) immediately prior to use by distillation under Ar (the frac tion with b.p.…”