Synthesis, Structure, Magnetism, and Spectroscopic Properties of Some Mono- and Dinuclear Nickel Complexes Containing Noninnocent Pentane-2,4-dione Bis(S-alkylisothiosemicarbazonate)-Derived Ligands

Abstract

Deprotonation of [Ni II (H 2 L 1 )]I‚0.5CH 3 OH (1), where (H 2 L 1 ) -represents the ligand pentane-2,4-dione bis(Smethylisothiosemicarbazonate(-), in an ethanol solution of aqueous ammonia under argon affords air-sensitive red-brown [Ni II (HL 1 )]‚C 2 H 5 OH (2). Air oxidation of 2 in ethanol/NH 3 yields the paramagnetic green-black dinuclear species [Ni(L 1 -L 1 )Ni] (3) where the ligand (L 1 -L 1 ) 6is formed by oxidative C-C coupling at the methine carbon atoms of (L 1 ) 3-. In this formulation the nickel ions are trivalent. Reaction of 3 in ethanol with concentrated HCl affords red diamagnetic [Ni II (H 2 L 1 -L 1 H 2 )Ni1I I ]Cl 2 ‚0.5C 2 H 5 OH (4). This reaction is a 2 electron reduction of 3 with concomittant protonation at the ligand. Deprotonation of 4 in C 2 H 5 OH/ammonia under argon gives red-brown [Ni II (HL 1 -L 1 H)Ni II ]‚C 2 H 5 OH (5). Replacement of the S-methyl groups in (H 2 L 1 ) -by two dodecyl groups, (CH 2 ) 11 CH 3 , gives the ligand (H 2 L 2 ) -; the complexes [Ni II (H 2 L 2 )I (6) and their dinuclear, oxidized forms [Ni(L 2 -L 2 )Ni] (7) have been prepared analogously. The molecular structure of 3 (C 18 H 28 N 12 Ni 2 S 4 ) has been determined by X-ray crystallography. Crystal data for 3: space group P1 h with a ) 11.475(2) Å, b ) 13.615(1) Å, c ) 18.207(6) Å, R ) 83.87(1)°, β ) 88.36(1)°, γ ) 72.58(1)°, V ) 2698.7(10) Å 3 , and Z ) 2. The structure refinement converged to R ) 0.066 for 8865 unique reflections. Electronic and NMR spectra, the magnetism, and electrochemistry of new compounds are reported. It is shown that 3,4-diacetyl-2,5-hexanedione-tetrakis(Salkylisothiosemicarbazonates) are noninnocent ligands in 3 and 7.

Nickel‐Assisted Oxidative C–C Coupling and Subsequent Cleavage to C=O of Active Methylene Group in a Tetradentate Ligand System: Di‐ and Mononuclear Complexes with Transformed Ligands

“…The asymmetric unit of the previously reported analogous dinuclear complex [Ni(L 2 -L 2 )Ni] (Scheme 1) contains two molecules. [8] It may be noted that one of them also forms discrete dimers as observed for 5, and the other one forms infinite chains due to the uneven stacking of the two halves of each dinuclear molecule with the two halves of the two adjacent dinuclear molecules. [8] Here the intermolecular Ni···Ni distances are shorter than that in 5.…”

“…[8] It may be noted that one of them also forms discrete dimers as observed for 5, and the other one forms infinite chains due to the uneven stacking of the two halves of each dinuclear molecule with the two halves of the two adjacent dinuclear molecules. [8] Here the intermolecular Ni···Ni distances are shorter than that in 5. The Ni···Ni distances are 3.202 and 3.617 Å in the infinite chain, while the corresponding value is 3.402 Å in the dimer.…”

“…[6] Reactions of metal acetates with the pyrazoline derived from acetylacetone and thiosemicarbazide 6-by oxidative C-C coupling. [8] There is no further report on the reactivity or formation of any other product from [Ni(L 2 -L 2 )Ni]. In our previous work, [5] we could not prepare [Ni(HL)], but we found that the reaction of bzpyzn with nickel acetate in the presence of air provides a green paramagnetic species.…”

“…[4c, 5,8,11] In all four structures, there is no displacement of the metal center from the N 2 O 2 square plane around it. The mean deviations from the plane constituted by the nickel, two imine N, and two amide O atoms are within 0.002-0.019 Å.…”

(E)-2,4-Dibromo-6-(hydrazinylidenemethyl)phenol

“…Hydrazine-based Schiff bases are of great interest due to their ability to behave as noninnocent ligands (Arion et al, 1997;Knof et al, 1993;Mukhopadhyay & Pal, 2009). These compounds also play an important role in the development of photomolecular devices, as probes for biological macromolecules and in organic synthesis (Boyer et al, 2010;Samojlowicz et al, 2009;Nagaraju et al, 2012).…”