Azoliniums, Adducts, NHCs and Azomethine Ylides: Divergence in Wanzlick Equilibrium and Olefin Metathesis Catalyst Formation.

The dimerization of a saturated N-heterocyclic carbene (NHC) to tricyclic piperazine in preference to the commonly observed Wanzlick dimerization is presented. Mechanistic investigations revealed that the N-fluorene substituent of the heterocycle is implicated in both ring opening of corresponding carbene dimer and tautomerization of NHC to an azomethine ylide. This has consequences for the fate of the NHC when generated from either an azolinium salt or a pentafluorophenyl adduct. The insights gained permitted the synthesis of a new indenylidene metathesis precatalyst, which exhibits exceptional selectivity and high TONS in self-metathesis of 1-octene.

Reactions of triflate esters and triflamides with an organic neutral super-electron-donor.

The bis-pyridinylidene 13 converts aliphatic and aryl triflate esters to the corresponding alcohols and phenols respectively, using DMF as solvent, generally in excellent yields. While the deprotection of aryl triflates has been seen with other reagents and by more than one mechanism, the deprotection of alkyl triflates is a new reaction. Studies with (18)O labelled DMF indicate that the C-O bond stays intact and hence it is the S-O bond that cleaves, underlining that the cleavage results from the extraordinary electron donor capability of 13. Trifluoromethanesulfonamides are converted to the parent amines in like manner, representing the first cleavage of such substrates by a ground-state organic reducing reagent.

Hybrid super electron donors - preparation and reactivity.

Neutral organic electron donors, featuring pyridinylidene-imidazolylidene, pyridinylidene-benzimidazolylidene and imidazolylidene-benzimidazolylidene linkages are reported. The pyridinylidene-benzimidazolylidene and imidazolylidene-benzimidazolylidene hybrid systems were designed to be the first super electron donors to convert iodoarenes to aryl radicals at room temperature, and indeed both show evidence for significant aryl radical formation at room temperature. The stronger pyridinylidene-imidazolylidene donor converts iodoarenes to aryl anions efficiently under appropriate conditions (3 equiv of donor). The presence of excess sodium hydride base has a very important and selective effect on some of these electron-transfer reactions, and a rationale for this is proposed.