Lithiation of Chromium and Tungsten Aminocarbene Complexes: An Easy Approach to Functionalized Aminocarbene Complexes

Abstract

Thiophene-and furan-derived aminocarbene complexes are regioselectively lithiated by BuLi at position 5, while lithiated aminocarbenes containing pyrrole or phenyl groups can be obtained by a bromine to lithium exchange reaction using BuLi. Such prepared lithiated aminocarbene complexes react with alkyl halides, aldehydes, ketones, acyl chlorides, and DMF, giving high yields of functionalized aminocarbene complexes hardly accessible by other ways.

Negishi Cross-Coupling Reaction as a Simple and Efficient Route to Functionalized Amino and Alkoxy Carbene Complexes of Chromium, Molybdenum, and Tungsten

“…Recently, we have observed that heterocyclic aminocarbene complexes 1a – d can be smoothly lithiated using BuLi at −78 °C. The formed lithiated carbenes 2a – d can be alkylated by primary alkyl halides and/or transformed to secondary and tertiary alcohols by the reaction with aldehydes or ketones, or acylated giving ketones . The feasibility of the lithiation of 1a – d led us to explore the potential of these lithiated carbene complexes in Negishi cross-coupling reactions (Scheme ).…”

Modular Synthesis of Fischer Biscarbene Complexes of Chromium

“…Due to the tendency of alkoxycarbene complexes to add organolithiums, only aminocarbene complexes can be successfully metalated . Thus, chromium aminocarbene complexes 1a – d were lithiated with BuLi and, after transmetalation with ZnBr 2 , subjected to Pd­(PPh 3 ) 4 -catalyzed coupling with a thiophene-derived bromoethoxycarbene complex of chromium 2a (Scheme ).…”

“…The solvents were dried and degassed by standard procedures; silica gel (Merck, Geduran Si 60, 63–200 μm) was used for column chromatography. Pentacarbonyl­[( N , N -dimethylamino)­(2-thienyl)­carbene]­chromium­(0) ( 1a ), pentacarbonyl­[( N , N -dimethylamino)­(2-furyl)­carbene]­chromium­(0) ( 1b ), pentacarbonyl­[( N , N -dimethylamino)­(5-bromo-1-methyl-2-pyrrolyl)­carbene]­chromium­(0) ( 1c ), pentacarbonyl­[( N , N -dimethylamino)­(4-bromophenyl)­carbene]­chromium­(0) ( 1d ), pentacarbonyl­[ethoxy­(5-bromo-2-thienyl)­methylene]­chromium(0) ( 2a ), and pentacarbonyl­[ethoxy­(5-bromo-2-thienyl)­methylene]­tungsten(0) ( 2b ) were prepared by the reported procedures; other compounds were purchased.…”

“…These complexes have been mostly prepared in the classical way, by the introduction of a carbene moiety to the preformed skeleton. , Recently we have shown that aminocarbene complexes containing aromatic or heteroaromatic groups can be lithiated. The subsequent reaction with electrophiles allows the preparation of functionalized carbene complexes and, after transmetalation to zinc, Negishi cross-coupling reactions . Herein we report that the cross-coupling methodology can be also used for the synthesis of different types of biscarbene complexes, including those containing both alkoxy- and aminocarbene moieties, in which two carbene groups are connected with a (hetero)­aromatic bridge.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…A c c e p t e d M a n u s c r i p t 83 Successful arylithium formation in the presence of aminocarbene complex functionality (e.g. formation of lithiothiophene 611 in Scheme 44) was achieved [938]. Heteroaryl substituted aminocarbene complexes (e.g.…”