Substituent Effects and Supramolecular Interactions of Titanocene(III) Chloride: Implications for Catalysis in Single Electron Steps

Abstract

The electrochemical properties of titanocene(III) complexes and their stability in THF in the presence and absence of chloride additives were studied by cyclic voltammetry (CV) and computational methods. The anodic peak potentials of the titanocenes can be decreased by as much as 0.47 V through the addition of an electron-withdrawing substituent (CO2Me or CN) to the cyclopentadienyl ring when compared with Cp2TiCl. For the first time, it is demonstrated that under the conditions of catalytic applications low-valent titanocenes can decompose by loss of the substituted ligand. The recently discovered effect of stabilizing titanocene(III) catalysts by chloride additives was analyzed by CV, kinetic, and computational studies. An unprecedented supramolecular interaction between [(C5H4R)2TiCl2](-) and hydrochloride cations through reversible hydrogen bonding is proposed as a mechanism for the action of the additives. This study provides the critical information required for the rational design of titanocene-catalyzed reactions in single electron steps.

Substituent effects on the redox potentials of dihydroxybenzenes: theoretical and experimental study

“…Namazian 21 and Qhta 22 reported that there was a linear relationship between HOMO, LUMO, and the E values of the studied molecules. Herein we investigated the relationships between the orbital energies and E values of the mono-substituted and disubstituted derivatives of p-dihydroquinone and pyrocatechol, respectively.…”

Cp2TiX Complexes for Sustainable Catalysis in Single‐Electron Steps

“…We did not observe the formation of any dimers (Cp 2 TiX) 2 .D ue to the fact that the decomposition of Cp 2 TiCl has been suggestedt oo ccur via its dimer, [10d] our catalysts should be stable without additives. [a] Complex [12] [c] Recorded at as weep rate of 0.5 V·s À1 To understand this differenceq uantitatively, an analysiso ft he solvation of Cp 2 TiXa nd Cp 2 TiX + is necessary,w hich is beyond the scope of this study.F rom thesev alues, it is clear that just by varying the anionic ligand the values for E p,c , E p,a1 ,a nd E p,a2 (except for E p,a1 of 2 that pertains to Cp 2 Ti + )c hanges by at least 400 mV for electrochemically reduced Cp 2 TiX 2 .T hus, it can be expected that these complexes showd istinctly differing reactivity in oxi-Scheme3.E q C r scheme for the electrochemical reduction of Cp 2 TiX 2 .…”

“…[12] The drawback of this powerful approachi st hat particular ligands have to be preparedf or each complex and that the complexes requireh ydrochloride additives, such as Coll*HCl. First, the introduction of substituents to cyclopentadienyl ligandss ignificantly affects the redox potential of the titanocene complexes.…”

Titanocene‐Catalyzed Radical Opening of N‐Acylated Aziridines

“…[10] Instead, the stronger reductant [(C 5 Me 5 ) 2 TiCl] is required for efficient electron transfer to the carbonyl group (entries 2-4). [11] Catalyst loading can be reduced to 5mol %w ithout significant reduction in the yield of 2.Coll·HCl and Coll·HBr are both suitable acids for mediating catalytic turnover. [12] Scheme 1.…”

“…Thefunctional-group tolerance of the reaction is high (entries [11][12][13][14]. Thefunctional-group tolerance of the reaction is high (entries [11][12][13][14].…”