Organozinc Fluoride and Trifluoromethyl Compounds Supported by the Bis(2-pyridylthio)methyl Ligand

Abstract

The bis(2-pyridylthio)methyl ligand, [Bptm], has been employed in the synthesis of {[Bptm]Zn(μ-F)} 2 , a rare example of an organozinc fluoride compound. The dimeric nature of {[Bptm]Zn(μ-F)} 2 , which possesses an uncommon [Zn(μ-F)] 2 motif, contrasts with the monomeric structures reported for the other halide derivatives, [Bptm]ZnX (X = Cl, Br, I); this difference is supported by density functional theory calculations which indicate that the fluoride derivative favors a dimeric form with bridging fluoride ligands, whereas the other derivatives favor monomeric structures with terminal halide ligands. {[Bptm]Zn(μ-F)} 2 reacts with Me 3 SiCF 3 to afford the organozinc trifluoromethyl complex, namely [Bptm]ZnCF 3 . The Zn−CF 3 bond in this complex is longer than the Zn−CH 3 bond of the previously reported methyl derivative [Bptm]ZnMe, an observation that is precedented in related zinc compounds but counter to other metal complexes. The infrared frequency corresponding to the asymmetric C−F stretch of [Bptm]ZnCF 3 is unusually low for a metal trifluoromethyl species but is comparable to those for other zinc and cadmium complexes.

Synthesis and Application of Well‐Defined Fluoroalkyl Zinc Complexes

“…In addition, when the reaction of I−(CF 2 ) n −I (n=3, 4, 6) 8 with ZnEt 2 was carried out in hexanes, the reaction system gave dizinc reagents 2 a – c in 82–86 % yields [24] . Shlian and Parkin showed that trifluoromethylation of [Zn(bptm)(μ‐F)] 2 9 with Me 3 SiCF 3 in C 6 D 6 at 90 °C for 24 h afforded [Zn(CF 3 )(bptm)] 3 , whose Zn−CF 3 bond length was 2.016(3) Å, shorter to those in [Zn(CF 3 ) 2 (py) 2 ] [2.056(3) Å and 2.069(4) Å] and longer than the corresponding Zn−CH 3 bond length (1.984(3) Å) in [Zn(CH 3 )(bptm)], respectively [25] . Moreover, the reaction of ZnEt 2 10 , fluoroalkyl iodides (R F I) 11 as well as 1,3‐dimethyl‐3,4,5,6‐tetrahydro‐2(1 H )‐pyrimidinone (DMPU) in hexane at −20~0 °C or −15~23 °C provided the white powders [Zn(R F ) 2 (DMPU) 2 ] 4 a – f in 67–95 % yields ( 4 a : 90 %, 4 b : 86 %, 4 c : 95 %, 4 d : 88 %, 4e: 67 %, 4 f : 87 %) [26,27] .…”

“…From 2014 to 2022, an efficient protocol for the preparation of perfluoroalkyl zinc complexes 1-6 was reported by the groups of Vicic, Parkin, Monfette, Mikami and Li (Scheme 2). [24][25][26][27][28] Vicic and co-workers reported that the reaction between Br(CF 2 ) 4 Br 7 and metallic zinc in diglyme at 80 °C for 20 min delivered 76 % yield of [Zn 2 (CF 2 ) 4 (digylme) 2 (Br) 2 ] 1, which had excellent thermal stability in acetonitrile. [24] It is interesting that complex 1 precipitates from a solution of diglyme and can be obtained by simple filtration without further purification.…”

“…[24] Shlian and Parkin showed that trifluoromethylation of [Zn(bptm)(μ-F)] 2 9 with Me 3 SiCF 3 in C 6 D 6 at 90 °C for 24 h afforded [Zn(CF 3 )(bptm)] 3, whose ZnÀ CF 3 bond length was 2.016(3) Å, shorter to those in [Zn(CF 3 ) 2 (py) 2 ] [2.056(3) Å and 2.069(4) Å] and longer than the corresponding ZnÀ CH 3 bond length (1.984(3) Å) in [Zn(CH 3 )(bptm)], respectively. [25] Moreover, the reaction of ZnEt 2 10, fluoroalkyl iodides (R F I) 11 as well as 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) in hexane at À 20~0 °C or À 15~23 °C provided the white powders [Zn(R F ) 2 (DMPU) 2 ] 4 a-f in 67-95 % yields (4 a: 90 %, 4 b: 86 %, 4 c: 95 %, 4 d: 88 %, 4e: 67 %, 4 f: 87 %). [26,27] As one of the products, [Zn(CF 3 ) 2 (DMPU) 2 ] 4 a, was reacted with TMEDA (tetramethylethylenediamine) in DMF at room temperature for 10 min to generate quantitative 19 F NMR yield of [Zn(CF 3 ) 2 (TMEDA)] 5, [26] whose TMEDA ligand was exchanged with 2,2'-bipyridine (bpy) in CH 2 Cl 2 to give 95 % yield of [Zn(CF 3 ) 2 (bpy)] 6 with melting point 69~72 °C.…”