A Ruthenium Olefin Metathesis Catalyst with a Four-Membered N-Heterocyclic Carbene Ligand

The first ruthenium olefin metathesis catalyst bearing a four-membered N-heterocyclic carbene (5) was synthesized and characterized by NMR spectroscopy and X-ray crystallography. The synthesis of a (carbene)carbonylrhodium complex (6) was also reported, allowing the study of the electronic properties of this new carbene ligand. The complex 5 was screened toward different olefin metathesis reactions, and it showed a slow reactivity

A Stable Four-Membered N-Heterocyclic Carbene

The synthesis of the first four-membered N-heterocyclic carbene is described. Depending on the substituents on the nitrogen atoms, it is possible to characterize at room temperature the carbene dimer or the free carbene. Crystallographic analyses are provided for these carbene species

Reversible 1,2-Alkyl Migration to Carbene and Ammonia Activation in an N-Heterocyclic Carbene–Zirconium Complex

Addition of trimethylphosphine to a bis(phenolate)benzylimidazolylidene(dibenzyl)zirconium complex induces migration of a benzyl ligand from the metal center to the C_(carbine) atom. This process may be reversed, resulting in C_(sp)^3–C_(sp)^3 activation, by abstraction of the phosphine, an example of regulated, reversible alkyl migration. Addition of ammonia to the dibenzyl complex results in migration of one benzyl group and protonolysis of the other to generate a bis(NH_2)-bridged dimer via an NMR-observable intermediate NH_3 adduct

Mechanistic Insights on the Controlled Switch from Oligomerization to Polymerization of 1-Hexene Catalyzed by an NHC-Zirconium Complex

The benzimidazolylidene zirconium complex 1 switches from an oligomerization (without additive) to a polymerization catalyst by addition of an L-type ligand such as trimethylphosphine, while larger phosphines or amines completely inhibit catalysis. On the basis of the regioselectivity of the oligomers/polymers obtained, the time profiles of reactions as a function of added ligand, and the molecular structures of several cationic zirconium complexes, we propose a mechanistic framework for interpreting this complex catalytic behavior

Tuning the formal potential of ferrocyanide over a 2.1 V range

We report the synthesis and characterization of homoleptic borane adducts of hexacyanoferrate(II). Borane coordination blueshifts d–d transitions and CN IR and Raman frequencies. Control over redox properties is established with respect to borane Lewis acidity, reflected in peak anodic potential shifts per borane of +250 mV for BPh_3 and +350 mV for B(C_6F_5)_3. Electron transfer from [Fe(CN-B(C_6F_5)_3)_6]^(4−) to photogenerated [Ru(2,2′-bipyridine)_3]^(3+) is very rapid, consistent with voltammetry data. Coordination by Lewis acids provides an avenue for selective modification of the electronic structures and electrochemical properties of cyanometalates

Addition of a phosphine ligand switches an N-heterocyclic carbene-zirconium catalyst from oligomerization to polymerization of 1-hexene

A catalyst for the oligomerization of 1-hexene, generated by the activation of a benzimidazolylidene zirconium dibenzyl complex, switches to a polymerization catalyst on addition of a trialkylphosphine

Unexpected rearrangements in the synthesis of an unsymmetrical tridentate dianionic N-heterocyclic carbene

Starting from the same ethylenediamine species, three valuable carbene precursors were synthesized under differing conditions: a tridentate dianionic N-heterocyclic carbene bearing an aniline, a phenol and a central dihydroimidazolium salt, its benzimidazolium isomer by intramolecular rearrangement and a dicationic benzimidazolium-benzoxazolium salt by changing the Brønsted acid from HCl to HBF_4. A DFT study was performed to understand the rearrangement pathway. The structure of a bis[(NCO)carbene] zirconium complex was determined

Tuning the formal potential of ferrocyanide over a 2.1 V range

We report the synthesis and characterization of homoleptic borane adducts of hexacyanoferrate(II). Borane coordination blueshifts d–d transitions and CN IR and Raman frequencies. Control over redox properties is established with respect to borane Lewis acidity, reflected in peak anodic potential shifts per borane of +250 mV for BPh_3 and +350 mV for B(C_6F_5)_3. Electron transfer from [Fe(CN-B(C_6F_5)_3)_6]^(4−) to photogenerated [Ru(2,2′-bipyridine)_3]^(3+) is very rapid, consistent with voltammetry data. Coordination by Lewis acids provides an avenue for selective modification of the electronic structures and electrochemical properties of cyanometalates