Bismuth catalysis has traditionally relied on the Lewis acidic properties of the element in a fixed oxidation state. In this paper, we report a series of bismuth complexes that can undergo oxidative addition, reductive elimination, and transmetallation in a manner akin to transition metals. Rational ligand optimization featuring a sulfoximine moiety produced an active catalyst for the fluorination of aryl boronic esters through a bismuth (III)/bismuth (V) redox cycle. Crystallographic characterization of the different bismuth species involved, together with a mechanistic investigation of the carbon-fluorine bond-forming event, identified the crucial features that were combined to implement the full catalytic cycle.

A catalytic transfer-hydrogenation utilizing a well-defined Bi(I) complex as catalyst and ammonia-borane as transfer agent has been developed. This transformation represents a unique example of low-valent pnictogen catalysis cycling between oxidation states I and III, and proved useful for the hydrogenation of azoarenes and the partial reduction of nitroarenes. Interestingly, the bismuthinidene catalyst performs well in the presence of low-valent transition-metal sensitive functional groups and presents orthogonal reactivity compared to analogous phosphorus-based catalysis. Mechanistic investigations suggest the intermediacy of an elusive bismuthine species, which is proposed to be responsible for the hydrogenation and the formation of hydrogen.

A structural synthetic model of the iron(IV)-oxo-halide active species of non-heme iron dependent halogenases is reported. Compounds with general formula [Fe(IV)(O)(X)(Pytacn)](+) (1-X, X = Cl, Br) have been prepared and characterized spectroscopically and chemically with regard to their oxidizing ability. 1-X performs hydrogen-atom abstraction of C-H bonds at reaction rates 2-3 times faster than the corresponding solvato dicationic species, thus modelling the first step in C-H functionalization taking place in natural halogenation.

Herein we present a Bi-catalyzed cross-coupling of arylboronic acids with perfluoroalkyl sulfonate salts based on a Bi­(III)/Bi­(V) redox cycle. An electron-deficient sulfone ligand proved to be key for the successful implementation of this protocol, which allows the unusual construction of C­(sp2)–O bonds using commercially available NaOTf and KONf as coupling partners. Preliminary mechanistic studies as well as theoretical investigations reveal the intermediacy of a highly electrophilic Bi­(V) species, which rapidly eliminates phenyl triflate.

Thed evelopment of new C À Hf unctionalization protocols based on inexpensive cobalt catalysts is currently attracting significant interest. Functionalized 8-aminoquinoline compounds are high-potential building blocks in organic chemistry andpharmaceutical compoundsa nd new facile routes for their preparation would be highly valuable.R ecently, copper has been applied as catalyst for the functionalization of 8-aminoquinoline compoundsa nd found to operate through as ingle electron transfer (SET) mechanism, although requiring elevated reaction temperatures.H erein, we described the first example of ac obalt-catalyzed remote C À Hf unctionalization of 8-aminoquinoline compoundso perating through aS ET mechanism, exemplified using ap ractical and mild nitration protocol. Ther eactionu ses inexpensive cobaltn itrate hexahydrate [Co(NO 3 ) 2 ·6 H 2 O] as catalyst and tert-butyl nitrite (TBN) as nitro source. This methodology offers the basis for the facile preparationo fm any newf unctionalized 8-aminoquinoline derivatives. Scheme 4. Proposed mechanism for the nitration reaction at C-5. Scheme 5. (a) Competition reactions performed to investigate relative reactivity of substrates 17 and 19.Y ields calculated from 1 HNMR spectra of the crude reaction mixture using 1,3,5-trimethoxybenzene as internal standarda nd are based on conversion of corresponding substrate. Reaction conditions: substrate( 0.5 mmol;0 .25 mmol of each substrate), Co(NO 3 ) 2 ·6 H 2 O( 29.1 mg, 0.1 mmol, 20 mol%),T BN (267 mL, 90%, 4.0 equiv., 2.0 mmol), acetic acid (3.5 mL), room temperature, 18 h. (b) Summary of kinetic isotopeexperiment(KIE);for further details see the Supporting Information. 1686 asc.wiley-vch.de