Deactivation of Cationic Cu^I and Au^I Catalysts for A³ Coupling by CH₂Cl₂: Mechanistic Implications of the Formation of Neutral Cu^I and Au^I Chlorides

Abstract

Care should be exercised when using CH2Cl2 as a solvent for reactions in which amines are a reagent, since undesirable deactivation of cationic copper(I) and gold(I) catalysts to form the corresponding inactive neutral chloride complexes [LMCl] (M=Cu or Au) can occur as a result of the generation of hydrogen chloride in the medium. CuI and AuI deactivation has been proved for the Mannich three‐component coupling reaction. A series of CuI and AuI complexes with potential mechanistic implications were isolated and characterized by X‐ray crystallography.

Cationic Copper(I) Complexes as Highly Efficient Catalysts for Single and Double A3‐Coupling Mannich Reactions of Terminal Alkynes: Mechanistic Insights and Comparative Studies with Analogous Gold(I) Complexes

“…Similar observations of CH 2 Cl 2 and benzyl and allyl chlorides decomposition by Cu I complexes have been reported in the literature 7b,c. In addition, deuterium‐labelling together with isolation and characterisation of Cu I and Au I intermediates provided insight into the reaction mechanism7a of propargylamine formation. To expand the scope of this reaction, herein, we describe a comparative study of the activity of cationic copper(I) and gold(I) complexes stabilised by bulky phosphine ligands8 (Buchwald phosphanes) in the A 3 coupling reaction, leading to mono‐ and bis‐propargylamines through activation of terminal aliphatic and aromatic dialkyne reagents.…”

“…The cationic copper(I) coordination complex [Cu(MeCN) 4 ][PF 6 ] ( 1 ),9 which is an air‐stable, crystalline solid, has been used as a precursor for the synthesis of cationic copper(I) dialkylbiarylphosphane complexes in non‐aqueous media. We reported previously that the reaction of 1 with the bulky 2‐di‐ tert ‐butylphosphinobiphenyl ligand ( 2 ) in CH 2 Cl 2 at 45 °C for 15 h led to the formation of cationic copper(I) complex 3 (Scheme , top) in good yield with respect to the initial copper(I) complex 1 7a. When complex 3 and aniline or pyrrolidine were reacted, cationic L–amine–Cu I or L–pyrrolidine–Cu I complexes 4 or 5 were formed, respectively, in good yields (Scheme 1, middle and bottom).…”

“…When complex 3 and aniline or pyrrolidine were reacted, cationic L–amine–Cu I or L–pyrrolidine–Cu I complexes 4 or 5 were formed, respectively, in good yields (Scheme 1, middle and bottom). Complexes 3 , 4 and 5 were fully characterised by analytical data, NMR spectroscopy, ESI‐MS, combustion elemental analysis, and single‐crystal X‐ray crystallography 7a…”

“…However, until now, most reported A 3 coupling reactions are conducted by using expensive metals as catalysts,5 involve high reaction temperatures5c, e, 6 or consume large amounts of bases 2a. 5e In a recent contribution in this area, we showed that Au I and Cu I catalysts reacted with CH 2 Cl 2 , which was used as a reaction solvent, to give less active chloride forms of the catalysts 7a. Similar observations of CH 2 Cl 2 and benzyl and allyl chlorides decomposition by Cu I complexes have been reported in the literature 7b,c.…”

Selective Gold Recovery and Catalysis in a Highly Flexible Methionine-Decorated Metal–Organic Framework

“…The average Au-S bond distances of 2.75(7) (Au Au Au Au I are somewhat longer than those reported so far for Au III whereas the Au-Cl ones of 2.50(7) (Au Au Au Au I , fall in the typical range of related gold(I) and gold(III) compounds found in the literature [27][28][29]. Aurophilic interactions 30 are present in Au the shortest Au···Au separations being 3.04(2) Å (Figures S4-S5).…”