Isomer distribution and structure of (2,2′-biphenyldiolato)bis(β-diketonato)titanium(IV) complexes: A single crystal X-ray, solution NMR and computational study

Synthesis, Characterization, and Electrochemistry of Diferrocenyl β-Diketones, -Diketonates, and Pyrazoles

The synthesis of FcC(O)CH(R)C(O)Fc (Fc = Fe(η⁵-C₅H₄)(η⁵-C₅H₅); R = H, 5; ⁿBu, 7; CH₂CH₂(OCH₂CH₂)₂OMe, 9), [M(κ²O,O′-FcC(O)CHC(O)Fc)_n] (M = Ti, n = 3, 10; M = Fe, n = 3, 11; M = BF₂, n = 1, 12), and 1-R′-3,5-Fc₂-^cC₃HN₂ (R′ = H, 13; Me, 14; Ph, 15) is discussed. The solid-state structures of 5, 7, 9, 12, 13, 15, and 16 ([TiCl₂(κ²O,O′-PhC(O)CHC(O)Ph)₂]) show that 7 and 9 exist in their β-diketo form. Compound 13 crystallizes as a tetramer based on a hydrogen bond pattern, including one central water molecule. The electrochemical behavior of 5–7 and 9–16 was studied by cyclic and square-wave voltammetry, showing that the ferrocenyls can separately be oxidized reversibly between −50 and 750 mV (5–7, 9, 12–15: two Fc-related events; 10, 11: six events, being partially superimposed). For complex 10, Ti-centered reversible redox processes appear at −985 (Ti^II/Ti^III) and −520 mV (Ti^III/Ti^IV). Spectro-electrochemical UV-Vis/NIR measurements were carried out on 5, 6, and 12, whereby only 12 showed an IVCT (intervalence charge-transfer) band of considerable strength (ν_max = 6250 cm⁻¹, Δν_½ = 4725 cm⁻¹, ε_max = 240 L·mol⁻¹·cm⁻¹), due to the rigid C₃O₂B cycle, enlarging the coupling strength between the Fc groups.

Observed hydrolysis of fluorine substituted bis(β-diketonato)-dichlorotitanium(IV) complexes

Novel fluorine substituted mononuclear Ti(β-diketonato)2Cl2 complexes have been synthesised and shown to be involved in a partial hydrolysis reaction in solution, in which the hydrolyzed dinuclear {Ti(β-diketonato)2Cl}2(μ-O) is in equilibrium with the monomer. This is in contrast to the solution behaviour of the non CF3-containing Ti(CH3COCHCOCH3)2Cl2, Ti(PhCOCHCOCH3)2Cl2 and Ti(PhCOCHCOPh)2Cl2 complexes, under the same conditions. Variable temperature ((1)H and (19)F) NMR spectra and X-ray structure analyses reveal that the partially hydrolyzed dinuclear complex exists both in solution and in solid state, bridging through a single μ-oxo bridge and having one labile chloro-ligand per titanium center. Inclusion of electron-withdrawing CF3 groups into the already electron-deficient Ti complexes, led to the formation of {Ti(CF3COCHCOCF3)2Cl}2(μ-O) (dinuclear) and [Ti(CF3COCHCOCF3)2(μ-O)]4 (tetranuclear) complexes in CDCl3 containing trace amounts of water. DFT calculated free energies of hydrolysis support the existence of Ti(CH3COCHCOCH3)2Cl2 as a monomer and Ti(CF3COCHCOCF3)2Cl2 as a equilibrium mixture of the monomer and partially hydrolyzed dinuclear {Ti(β-diketonato)2Cl}2(μ-O) in CDCl3 solution.