New catalytic methods for the synthesis of selectively substituted aromatics through palladacycles

Abstract

Joint palladium and norbornene catalysis for selective aromatic functionalization via palladacycles is reported. Both alkylation and arylation of aromatics are considered after a brief outlook on the mechanism. These are multistep reactions that proceed in ordered sequences and are chemio-, regio-, and stereoselective. The study of the single steps with isolation of the organometallic species involved has allowed us to detect subtle steric and electronic effects which have been exploited to achieve catalytic reactions. Recent developments of aromatic alkylation and arylation are reported, in particular, condensed heterocyclic ring formation involving dialkylated arylpalladium complexes or both symmetrically and unsymmetrically substituted biphenylylpalladium complexes.

Sequential Unsymmetrical Aryl Coupling of o-Substituted Aryl Iodides with o-Bromophenols and Reaction with Olefins: Palladium-Catalyzed Synthesis of 6H-Dibenzopyran Derivatives

“…During the past decades, palladium catalyzed reactions have attracted the interest of several groups . We recently reported a new mode for the arylation of aryl iodides with different aryl bromides (Scheme ) . The criterion to achieve this reaction relies substantially on the presence of ortho electron-releasing substitutents in the aryl iodides and electron-withdrawing groups in the aryl bromides.…”

Access to Alkynylpalladium(IV) and -Platinum(IV) Species, Including Triorgano(diphosphine)metal(IV) Complexes and the Structural Study of an Alkynyl(pincer)platinum(IV) Complex, Pt(O2CArF)I(C⋮CSiMe3)(NCN) (ArF= 4-CF3C6H4, NCN = [2,6-(dimethylaminomethyl)phenyl-N,C,N]-)

“…Organopalladium(IV) species with a single phosphine donor have been reported, , and in a classic study Gillie and Stille obtained kinetic data suggesting the presence of an undetected cis -diphosphine intermediate “PdIMe 3 (PPh 2 Me) 2 ” in the reaction of cis -PdMe 2 (PPh 2 Me) 2 with iodomethane 27a. Complex 18 represents the first example of spectroscopic detection of the “PdC 3 P 2 X” donor set frequently proposed as possible intermediates in stoichiometric 27 and catalytic reactions, 2c,3d-g including for proposed alkynylpalladium(IV) intermediates,2d noting that the successful synthetic route to this donor set reported here is different from these proposals.…”

“…The possible intermediacy of (η 1 -alkynyl)palladium(IV) species has been discussed for several catalytic processes, , but there are no reports of the detection of any type of (η 1 -alkynyl)palladium(IV) species, and similarly, there are numerous proposals for the intermediacy of to date undetected “Pd IV R n P 2 ” ( n = 1,3a 2, 3b,c 3; 2c,3d-g P = phosphine donor) species. For the closely related congener platinum, (η 1 -alkynyl)platinum(IV) species have been proposed as intermediates in the high-temperature activation of Pt(C⋮CR) 2 (1,5-cyclooctadiene) precatalysts for hydrosilation reactions,4a and via oxidatively induced reductive elimination, for the synthesis of the macrocycle on addition of iodine to {CH 2 (CH 2 PPh 2 ) 2 - P,P ‘}Pt II (μ-C⋮C-X-C⋮C- C , C ) 2 Pt{CH 2 (CH 2 PPh 2 ) 2 - P,P ‘} (X = 3 , 3‘ ‘,4,4‘ ‘-tetrabutyl-2,2‘:5‘,2‘ ‘-terthiophene) 4b…”

Syntheses, Structures, and Reductive Elimination Studies of Six-Membered Diaryl Platinacycle Complexes

“…These studies are informative for simple diaryl complexes and the formation of biaryls. However, the formation of ring systems incorporating biaryls requires reductive elimination from metallacycle complexes. − Linking the aryl groups together in a metallacycle complex introduces additional factors in the reductive elimination process. Our group has shown that for Pt and Pd four- and five-membered metallacycles where the aryl groups have been linked into a polycyclic framework simple reductive elimination is shut down. , Instead, apparent bimolecular reductive elimination occurs catalytically on colloidal metal surfaces after transfer of the metallacycle ring from the complex to the metal colliod surface.…”