Formation of a Delocalized Iridium Benzylidene with Azaquinone Methide Character via Alkoxycarbene Cleavage

Abstract

Lewis base directed α,α-dehydrogenation of 2-(methoxymethyl)­aniline gives a cationic iridium­(III) alkoxycarbene. This alkoxycarbene is found to be subject to pyridine-promoted C–O bond cleavage in the formation of a delocalized iridium benzylidene. X-ray diffraction and DFT calculations support a structural distortion away from a classic benzylidene structure stemming from azaquinone methide character. Treatment of the iridium azaquinone methide with ethylene results in formal ethylene insertion into the vinylic C–H bond, demonstrating an unusual mechanism for net C–C bond formation via benzylic C–O cleavage.

Group-Transfer Reactions of a Cationic Iridium Alkoxycarbene Generated by Ether Dehydrogenation

“…Numerous attempts at confirmation of this assignment through X-ray crystallography ultimately led to a structure solution for 3 from samples crystallizing as 3-component merohedral twins in the P2 1 space group (Figure ). The unambiguous characterization of 3 represents one of only a few cationic iridium alkoxycarbene complexes generated by ether dehydrogenation. − , …”

“…Prior to our studies, a single example of THF dehydrogenation to give a cationic iridium alkoxycarbene over a period of days had been reported by Schneider (Figure ). We have since demonstrated facile formation of cationic alkoxycarbene complexes via ether dehydrogenation in Lewis base-directed intra- and intermolecular examples, with evidence for reversible α-hydride insertion and C–O bond cleavage reactions in certain cases. , Despite the body of work on the generation of alkoxycarbene complexes via ether dehydrogenation, few stoichiometric transformations and only a single catalytic reaction have been reported. ,, We now report the synthesis of a cationic pincer-supported Ir­(I) alkoxycarbene complex generated by α,α-dehydrogenation of cyclopentyl methyl ether (CPME) and demonstrate its reactivity in atom- and group-transfer reactions with an alkyl azide, a ketene, and an alkyl nitrite. This complex serves as a catalyst in ether imination, showing that cationic iridium complexes are sufficiently competent at ether dehydrogenation to support catalytic transformations.…”

Reversible C(sp3)-Si Oxidative Addition of Unsupported Organosilanes: Effects of Silicon Substituents on Kinetics and Thermodynamics

“…14 Recently our group has been studying the conversion of ethers to alkoxycarbenes via the α,α-dehydrogenation at cationic iridium complexes. 15,16 We reported the synthesis of the cationic PNP pincer-supported Ir(I) alkoxycarbene complex 2 derived from cyclopentyl methyl ether (eq 1) and demonstrated its reactivity in atom-and group-transfer reactions. 17 During the course of our studies, we found that methoxytrimethylsilane does not undergo α,α-dehydrogenation to form a siloxymethylidene but, instead, reacts via Si-CH 3 oxidative addition to give the (methyl)Ir(III)silyl complex 4 (eq 2).…”

“…Recently our group has been studying the conversion of ethers to alkoxycarbenes via the α,α-dehydrogenation at cationic iridium complexes. , We reported the synthesis of the cationic PNP pincer-supported Ir­(I) alkoxycarbene complex 2 derived from cyclopentyl methyl ether (eq ) and demonstrated its reactivity in atom- and group-transfer reactions …”

Carbon–Carbon Bond Formation via Catalytically Generated Aminocarbene Complexes: Rhodium‐Catalyzed Hydroaminative Cyclization of Enynes with Secondary Amines

“…In 2005, Barluenga and coworkers reported cycloisomerization/cyclopropanation of alkynols via catalytically generated tungsten alkoxycarbene complexes to form tricyclic compounds (Figure 1 a). [2] To the best of our knowledge, this is the only example of a reaction considered to proceed through carbon-carbon bond formation on a catalytically constructed heteroatom-stabilized carbene ligand, and further developments are still desired for catalytic reactions involving in situ construction of this type of carbene complexes from stable organic substrates [3] and their use for subsequent bond formation.…”