Attenuating Nucleophilicity of Titanocene Hydrides Beyond Steric Effects en Route to Fatty Alcohols.

Here, we introduce a new class of titanocene catalysts for epoxide hydrosilylation that frustrates their hydridicity and thereby emphasizes their electron transfer reactivity. This unique attenuation of hydridicity is accomplished by introducing Lewis acidic silicon centers to the cyclopentadienyl ligands for an intramolecular coordination of the titanium-bound hydride. The superiority of our rationally designed catalysts over classic titanocenes with alkyl-substituted cyclopentadienyl ligands is demonstrated in the dramatically improved regioselectivity of the hydrosilylation of monosubstituted epoxides to primary alcohols.

Titanocene(III)-Catalyzed Precision Deuteration of Epoxides.

We describe a titanocene(III)-catalyzed deuterosilylation of epoxides that provides β-deuterated anti-Markovnikov alcohols with excellent D-incorporation, in high yield, and often excellent diastereoselectivity after desilylation. The key to the success of the reaction is a novel activation method of Cp TiCl and (tBuC H ) TiCl with BnMgBr and PhSiD to provide [(RC H ) Ti(III)D] without isotope scrambling. It was developed after discovering an off-cycle scrambling with the previously described method.

Design Platform for Sustainable Catalysis with Radicals: Electrochemical Activation of Cp TiCl for Catalysis Unveiled.

The combination of synthesis, rotating ring-disk electrode (RRDE) and cyclic voltammetry (CV) measurements, and computational investigations with the aid of DFT methods shows how a thiourea, a squaramide, and a bissulfonamide as additives affect the E C equilibrium of Cp TiCl . We have, for the first time, provided quantitative data for the E C equilibrium and have determined the stoichiometry of adduct formation of [Cp Ti(III)Cl ] , [Cp Ti(III)Cl] and [Cp Ti(IV)Cl ] and the additives. By studying the structures of the complexes formed by DFT methods, we have established the Gibbs energies and enthalpies of complex formation as well as the adduct structures.

Condition Screening for Sustainable Catalysis in Single-Electron Steps by Cyclic Voltammetry: Additives and Solvents.

Cyclic voltammetry-based screening method for Cp TiX-catalyzed reactions is extended to the screening of solvents other than tetrahydrofuran for bulk electrolysis of the catalyst and radical arylation. It was found that CH CN can be used as a solvent for both processes without additives. Furthermore, in tetrahydrofuran, squaramide L2 is more efficient than the previously reported supramolecular halide binder, Schreiner's thiourea L1.

Demystifying CpTi(H)Cl and its Enigmatic Role in the Reactions of Epoxides with CpTiCl.

The role of CpTi(H)Cl in the reactions of CpTiCl with trisubstituted epoxides has been investigated in a combined experimental and computational study. Although CpTi(H)Cl has generally been regarded as a robust species, its decomposition to CpTiCl and molecular hydrogen was found to be exothermic (ΔG = -11 kcal/mol when the effects of THF solvation are considered). In laboratory studies, CpTi(H)Cl was generated using the reaction of 1,2-epoxy-1-methylcyclohexane with CpTiCl as a model.

Highly Active Titanocene Catalysts for Epoxide Hydrosilylation: Synthesis, Theory, Kinetics, EPR Spectroscopy.

A catalytic system for titanocene-catalyzed epoxide hydrosilylation is described. It features a straightforward preparation of titanocene hydrides that leads to a reaction with low catalyst loading, high yields, and high selectivity of radical reduction. The mechanism was studied by a suite of methods, including kinetic studies, EPR spectroscopy, and computational methods.

Amide-Substituted Titanocenes in Hydrogen-Atom Transfer Catalysis.

Two new catalytic systems for hydrogen-atom transfer (HAT) catalysis involving the N-H bonds of titanocene(III) complexes with pendant amide ligands are reported. In a monometallic system, a bifunctional catalyst for radical generation and reduction through HAT catalysis depending on the coordination of the amide ligand is employed. The pendant amide ligand is used to activate Crabtree's catalyst to yield an efficient bimetallic system for radical generation and HAT catalysis.