Catalytic Use of Low‐Valent Cationic Gallium(I) Complexes as π‐Acids

Abstract

Transformations of alkene and alkyne substrates relevant to p-Lewis acid catalysis have been performed using low-valent Ga(I) species for the first time. [Ga(I)(PhF) 2 ] + [Al(OR F ) 4 ] À and gallium dichloride (i. e. [Ga(I)] + [GaCl 4 ] À ) proved to be efficient catalysts for cycloisomerizations, Friedel-Crafts reactions, transfer hydrogenations, and reductive hydroarylations. Their activity is compared to more common Ga(III) complexes. This study shows that even the readily available and yet overlooked gallium dichloride salt can be a more active p-Lewis acid catalyst than gallium trichloride or other Ga(III) species.

Exploring the Versatility of 7‐Alkynylcycloheptatriene Scaffolds Under π‐Acid Catalysis

“…As mentioned in the introduction, the cycloheptatrienyl test allowed us to identify new π‐acid catalysts, such as the low‐valent cationic indium(I) complex [In(PhF) 2 ][Al(pftb) 4 ] {pftb = OC(CF 3 ) 3 } . The reactions were less selective with the Ga(I) analog [Ga(PhF) 2 ][Al(pftb) 4 ],, but we found a case where this rare type of low‐valent gallium complex promotes a singular skeletal reorganization. We used this catalyst to study the rearrangement of 7‐alkynylcycloheptatriene 1e , exhibiting a 2,2‐dimethyl‐1,3‐dioxane tether, and faced a very unusual transformation which was dependent on the nature and loading of the catalyst (Table ).…”

Recent Developments on the Use of Group 13 Metal Complexes in Catalysis

“…The indium analogue of 3 shows a similar activity . More recently, the readily accessible gallium(I) complex [Ga(PhF) 2 ][Al{OC(CF 3 ) 3 } 4 ] ( 4 , Scheme ) was also shown to catalyze transfer hydrogenation even with methoxy‐ and nitro‐containing substrates …”

“…Both Ga species 3 and 4 also catalyze the intramolecular hydroarylation of alkynes, and the resulting styrene derivative can either undergo a second hydroarylation step or be reduced via transfer hydrogenation as discussed above (Scheme ). The two catalysts are tolerant of ether, ester and nitro functional groups, and the use of Ga I catalyst 4 decreases unwanted polymerization side reactions …”

“…[34] More recently,t he readilya ccessible gallium(I) complex [Ga(PhF) 2 ][Al{OC(CF 3 ) 3 } 4 ]( 4,S cheme 3) was also shown to catalyzet ransfer hydrogenation even with methoxy-and nitrocontaining substrates. [35] Both Ga species 3 and 4 also catalyze the intramolecular hydroarylation of alkynes, [28,35] and the resulting styrene derivative can either undergo as econd hydroarylation step or be reduced via transfer hydrogenation as discussed above (Scheme 4). The two catalysts are tolerant of ether,e ster and nitro functional groups,a nd the use of Ga I catalyst 4 decreases unwanted polymerization side reactions.…”

“…The two catalysts are tolerant of ether,e ster and nitro functional groups,a nd the use of Ga I catalyst 4 decreases unwanted polymerization side reactions. [35] Scheme3.Transfer hydrogenation of alkenes catalyzed by species 3 and 4.…”