New examples of –C–F–Ae (Ae = alkaline earth) and –C–F–K bonding

Abstract

From redox transmetallation/protolysis reactions of alkaline earth metals, Mg, Ca, and Sr with bispentafluorophenylmercury and N,N′-bis(2-trifluoromethylphenyl)formamidine (CF₃FormH) in tetrahydrofuran (thf), the complexes [Ae(CF₃Form)₂(thf)₂] (Ae = Mg 1, Ca 2) and [Sr(CF₃Form)₂] 3 have been isolated. Reaction of 3 with 18-crown-6 yielded the charge separated [Sr(CF₃Form)(18-crown-6)(thf)][Sr(CF₃Form)₃] 3a, and from heating 3 in C₆D₆, crystals of [Sr₄(CF₃Form)₄L₄] (L = oxidomethyl(2-trifluoromethyl)phenylamide) 3b were obtained. The crude product 4 from a synthesis with Ba similar to those of 1–3 yielded the large cage [Ba₁₉(CF₃Form)₆L₆F₂₆(diglyme)₆] 4a. Complexes 1 and 2 are monomeric with chelating CF₃Form ligands, six coordination of the Ae metal, and cis and trans thf ligands respectively. In 3, trans chelating CF₃Form ligands are supported by –CF₃–Sr coordination. Charge-separated 3a, has a nine-coordinate cation, whilst the unique nine-coordinate tris(formamidinato)strontiate(II) anion has three –CF₃–Sr interactions. In the cage 3b, each Sr atom is nine coordinate with chelating CF₃Form and 2-CF₃C₆H₄NCHO⁻ ligands, two bridging oxygens from the latter ligands, and three –CF₃–Sr interactions. The Ba₁₉ cage 4a has a central BaF₈ unit, which is linked by bridging fluorides to three different Ba atoms, which also have CF₃–Ba bonds. The complexes [K₂(CF₃Form)₂(dme)]_∞ 5 and [K₃(CF₃Form)₃]_∞ 6a were obtained by deprotonation of CF₃FormH with K(N(SiMe₃)₂) and KH respectively, and a similar treatment of N-(2,6-difluorophenyl)acetamide with the silylamide gave potassium N-acetyl-N-(2,6-difluorophenyl)amide 7. Complexes 5 and 6a are 1-D polymers with two and three differently coordinating CF₃Form ligands respectively. The structures are based on chelating bridging CF₃Form ligands supported by –CF₃–A bonding including rare chelating CF₃ groups. 7 forms a 2-D polymer sheet, based on tridentate FNO ligands.