BF₄⁻ as source for the preparation of BF₂ bridged copper(II) dimethylglyoxime complexes

Abstract

The reaction of copper(II) tetrafluoroborate with dimethylglyoxime (H2dmg) leads to the formation of the dinuclear complexes [Cu2(dmg)(Hdmg)(EtOH)(H2dmg)]BF4 (1) and [Cu2(dmg ⋅ BF2)(Hdmg)(H2dmg)]BF4 (2). In 2, BF2 deriving from BF4− has been inserted into the oxime groups to form an O,O‐bidentate difluoroboron complex. Co‐crystallization of 1 and 2 impeded a thorough characterization of 2. In further attempts to prepare pure 2, the difluoroboron complexes [Cu(dmg ⋅ BF2)2(MeCN)] (3) and [Cu(dmg ⋅ BF2)(Hdmg)] (4) have been obtained. Attempts to isolate the BF2‐bridged ligand failed. Even though BF4− readily is decomposed to formally form BF2+ that is inserted into the resulting complexes and F−, the nascent F− ions are not a suitable F− source for organic fluorination reactions. Nevertheless, the described, facile route to prepare O,O‐bidentate difluoroboron complexes without the usage of the highly toxic BF3 ⋅ OEt2 but BF4− instead is of interest for synthetically working chemists.

Solvatomorphism with polar protic/aprotic and non-polar solvents in a series of complexes derived from the 5-phenylimidazole/tetrafluoroborate/copper(ii) reaction system

“…(c) It is well known in organic chemistry that the nitro group can play diverse roles that make several transformations; 64 and (d) Reactions in which fluoride species attack to glassware to form silicon–fluoride compounds have been described in the literature. 48…”

“…47 During the last 40 years or so, there have been reports showing that the BF 4 − ion is not always stable, and that reaction with the ligand or the metal ion in coordination complexes may occur, often resulting in F − -containing compounds. 48,49 Another interesting aspect of the chemistry of BF 4 − is that sometimes it can coordinate to metal ions in a terminal (monodentate) or bridging manner, but seldom coordination is strong. 50–52 We have, therefore, chosen as a source of copper( ii ) the Cu(BF 4 ) 2 ·6H 2 O salt in order to study the tetrafluoroborate coordination ability and provide the copper( ii ) ion with the conditions to realize the optimal coordination geometry from the 5-phenylimidazole/tetrafluoroborate ligand system available.…”