Bulking up Cp^BIG: A Penta-Terphenyl Cyclopentadienyl Ligand

Abstract

The modification of cyclopentadienyl ligands with carefully selected substituents is a widely used strategy for tuning their steric and electronic properties. We describe the synthesis of an extremely bulky penta-terphenyl cyclopentadienyl ligand (Cp T5 ) by arylation of cyclopentadiene. Deprotonation reactions with various group 1 metals and bases afforded a complete series of alkali metal salts MCp T5 (M = Li–Cs). The compounds were isolated as solvate-free salts, which were characterized by multinuclear nuclear magnetic resonance spectroscopy, ultraviolet–visible spectroscopy, and elemental analysis. Single-crystal X-ray diffraction studies of LiCp T5 , NaCp T5 (crystallized as a solvate with one tetrahydrofuran molecule per formula unit), and KCp T5 revealed the formation of metallocene-like sandwich structures in the solid state.

Molecular and Electronic Structure of Linear Uranium Metallocenes Stabilized by Pentabenzyl-Cyclopentadienyl Ligands

“…Cp ligands were among the first ligands coordinated to uranium and thorium ions, and Cp derivatives are still one of the most commonly utilized ligands for lanthanides, the early actinides uranium and thorium as well as some trans-uranics. More recently, so-called “super-bulky” Cp derivatives have attracted research efforts in organometallic s - and p -block metal chemistry. − In f -element chemistry, the widespread use and the manifold of available Cp R derivatives (e.g., Cp* = C 5 Me 5 , Cp′ = C 5 H 4 SiMe 3 , Cp′′ = 1,3-(Me 3 Si) 2 C 5 H 3 , Cp ‡ = 1,3-(Me 3 C) 2 C 5 H 3 ) led to novel accomplishments in U-based catalytic reactivity, the activation of small molecules, − and the first stabilization of uranium in the until-then unprecedented +II oxidation state . Cloke et al have shown impressively that even subtle variations of the Cp ligand’s steric profile result in significant changes in reactivity toward small molecules, such as CO and CO 2 . , Therefore, the synthesis of new precursors of the general form of [(Cp R ) 2 U III (FG)] or [(Cp R ) 2 U IV (FG) 2 ] (with Cp R = Cp derivative; FG = functional group = L or X or combinations of the two) continues to be a valuable tool to advance knowledge about fundamental aspects of organometallic uranium chemistry, and to discover new reactivity.…”

Coordination Polymers of Polyphenyl-Substituted Potassium Cyclopentadienides

“…Crystal structures of salts containing the anion [C 5 Ph 4 H] − and various σ-donating coordinated solvent ligands are represented by six sodium [13][14][15] and one potassium [16] derivatives that are either tight or solvent-separated ion pairs. The salts of the pentarylcyclopentadienes M + [C 5 Aryl 5 ] − are represented by sodium salt of [C 5 Ph 5 ] − [17]; lithium derivatives of [C 5 (3,5-Alkyl 2 C 6 H 3 ) 5 ] − [18]; lithium [19] sodium [19] and potassium [19] salts having anion [C 5 (3,5-Aryl 2 C 6 H 3 ) 5 ] − ; and lithium [20], potassium [20,21] or cesium [20] salts bearing anion [C 5 (4-AlkylC 6 H 4 ) 5 ] − . The structures of the last [C 5 Aryl 5 ] − series are solvent-separated ion pairs mainly of complex architecture or 1D coordination polymers.…”

IZCp and PZCp: Redox Non-innocent Cyclopentadienyl Ligands as Electron Reservoirs for Sandwich Complexes

“…A broad array of Cp derivatives have been developed to date by modifying the steric and electronic properties. In particular, designing Cp to be steric-congested and electron-deficient , is an effective strategy for changing the chemical properties, such as lowering the reactivity of anionic Cp (Figure a,b). In this regard, the report by the Kunz group that donor properties of Cp decrease with an increasing number of cationic imidazolium substituents could be a good example .…”