Highly tunable fluorinated trispyrazolylborates [HB(3-CF₃-5-{4-RPh}pz)₃]⁻ (R = NO₂, CF₃, Cl, F, H, OMe and NMe₂) and their copper(<scp>i</scp>) complexes

Abstract

The ethene and carbon monoxide adducts of copper(I) with seven trispyrazolylborate ligands ([HB(3-CF3-5-{4-RPh}pz)3](-); R = NO2 (4a), CF3 (4b), Cl (4c), F (4d), H (4e), OMe (4f) and NMe2 (4g)) were synthesized and characterized. The ligands were synthesized from their corresponding pyrazoles and sodium tetrahydridoborate and were obtained as solvent adducts of their sodium salts after workup. When the pyrazole with the most electron-withdrawing substituent (R = NO2) is used the asymmetric ligand [HB(3-CF3-5-{4-NO2Ph}pz)2(3-{4-NO2Ph}-5-CF3pz)](-) (4a') is formed as the major product. Copper(I) complexes with ethene or CO as a co-ligand were prepared in good yields and were structurally characterized using (1)H NMR, (13)C NMR and infrared spectroscopy. Single crystal X-ray crystallography analyses revealed the structures of Na4a', Na4b, four copper ethene complexes and four copper carbonyl complexes. The structures of the copper(I) complexes show Cu(I) ions in pseudo-tetrahedral coordination environments consisting of three nitrogen atoms of the trispyrazolylborate ligand and the carbonyl or η(2)-coordinated ethene ligands, with nearly identical coordination environments around the Cu(I) ion. The compound [Na(4a')(H2O)]n crystallizes as one-dimensional chains with intermolecular NaO2N interactions. The sodium ions were found in severely distorted octahedral geometries with three nitrogen atoms from the trispyrazolylborate ligand, one aqua ligand and two oxygen atoms from the nitro group of an adjacent molecule. The compound [Na2(4b)2(μ-H2O)2] crystallizes as a centrosymmetric water-bridged dimer: two five-coordinate square-pyramidal sodium ions each are coordinated facially by three nitrogen atoms from a trispyrazolylborate ligand and two bridging water ligands. Below the base of the pyramidal structure one intermolecular and two intramolecular NaF short contacts are present. The (1)H and (13)C NMR spectra of the copper-ethene complexes show signals for the ethene ligands in the range of 4.84-4.96 ppm and 84.9-86.8 ppm respectively. The infrared spectra of the carbonyl complexes show CO stretching frequencies in the range of 2096-2120 cm(-1). Both the NMR signals for the ethene ligands and infrared signals for the carbonyl ligands were found to show good correlations with the Hammett σp parameters of the substituents on the phenyl rings of the ligands.