Ethyl‐Zinc(II)‐Cation Equivalents: Synthesis and Hydroamination Catalysis

Abstract

Ion-like ethylzinc(II) compounds with weakly coordinating aluminates [Al(OR(F))4](-) and [(R(F)O)3Al-F-Al(OR(F))3](-) (R(F)=C(CF3)3) were synthesized in a one-pot reaction and fully characterized by single-crystal X-ray diffraction, NMR and vibrational spectroscopy, and by quantum chemical calculations. The catalytic activity of ion-like Et-Zn[Al(OR(F))4] in intermolecular hydroamination and in the unusual double hydroamination of anilines and alkynes was investigated. Favorable performance was also found in comparison to the Et2Zn/[PhNMe2H](+)[B(C6F5)4](-) system generated in situ at lower catalyst loadings of 2.5 mol %.

Facile and systematic access to the least-coordinating WCA [(RFO)3Al–F–Al(ORF)3]− and its more Lewis-basic brother [F–Al(ORF)3]− (RF = C(CF3)3)

“…However, the [ZnEt] + cation is small enough to co-ordinate to these alkoxy groups. 2 Here, both Zn–O distances are nearly equal (209.8 pm on average), while in [ZnEt][Al(OR F ) 4 ] they differ by ∼5 pm (211.2 and 205.8 pm on average). The non-existing difference between the Zn–O distances in [ZnEt][al–f–al] not only is evidence for the weaker coordination of [al–f–al] – compared to [Al(OR F ) 4 ] – , but also for the inferior accessibility of the oxygen atoms.…”

Ethylzinc‐ and Zinc–bis–fluoroalkoxides

“…Interestingly, the zinc atoms of all EtZn moieties in structures 1–3 are trigonal planarly coordinated. Their bonding situation is reminiscent (Table ) to EtZn(μ‐OR ar ) 2 ZnEt ( d Zn‐C =1.946 Å) and EtZn(Al(OR F ) 4 ) ( d Zn‐C =1.943 Å) . While the Zn−C distances are very similar, the zinc oxygen distances in 1–3 (1.993 to 2.057 Å) are shorter compared to EtZn(Al(OR F ) 4 ) (2.085 Å).…”

From Ion‐Like Ethylzinc Aluminates to [EtZn(arene)2]+[Al(ORF)4]− Salts

“…Based on our published reaction [Eq. (1)], we set out to prepare the compound MeZn(Al(OR F ) 4 ) by replacing diethylzinc with dimethylzinc.…”

“…The [Al(OR F ) 4 ] − WCA also stabilizes highly reactive cations such as [CX 3 ] + , [P 9 ] + , or binary E−X cations (E=P, As; X=halogen) . Furthermore, we have recently published the facile one‐pot synthesis of ion‐like EtZn(Al(OR F ) 4 ), which constitutes an ideal starting material for such an approach. Moreover, EtZn(Al(OR F ) 4 ) is a very potent pre‐catalyst for single‐ and double‐hydroamination of alkynes .…”

“…Furthermore, we have recently published the facile one‐pot synthesis of ion‐like EtZn(Al(OR F ) 4 ), which constitutes an ideal starting material for such an approach. Moreover, EtZn(Al(OR F ) 4 ) is a very potent pre‐catalyst for single‐ and double‐hydroamination of alkynes . Such catalysis is considered to involve direct interaction of the π‐donating alkyne with [EtZn] + giving the related [EtZn(alkyne) x ] + cation.…”