Preparation, Structure, and Redox Activity of Nickel(II), Palladium(II), and Copper(II) Cofacial Binuclear Bis(β-keto Enamine) Complexes
The synthesis of the new bis(0-keto enamine) ligand BBIH2, or 5-tert-butyl-m-xylylenebis(acetylacetone imine) (3,3'-[5-(l,l-dimethylethyl)-l,3-phenylenebis(methylene)]bis(4-amino-3-penten-2-one)), and the properties of three of its cofacial binuclear metal complexes are described. Ni2(BBI)2-2DMF (Ni2 C50 H74 N6 O6; DMF = (CH3)2 NCHO): monoclinic, space group P21/c (No. 14); a = 13.091 (2), b = 11.206 (2), c = 18.015 (4) A; β = 95.92 (1)°; Z = 2; R = 0.049 (Rw= 0.062) for 3583 reflections and 289 parameters. Pd2(BBI)2.2DMF (Pd2 C50 H74 N6 O6): monoclinic, space group P21/c (No. 14); a = 13.251 (3), b = 11.196 (2), c = 17.962 (5) A; β = 96.42 (2)°; Z = 2; R = 0.032 (Rw= 0.051) for 3850 reflections and 289 parameters. Cu2(BBI)2-0.5C-H2 C12-H2 O (cu2 C44-5 H63 C1N4 O5): monoclinic, space group C2/m (No. 12); a = 26.802 (5), b = 9.887 (2), c = 9.021 (2) A; β = 90.48 (1)°; Z = 2; R = 0.053 (Rw= 0.084) for 1634 reflections and 142 parameters. Ni2(BBI)2.2DMF (Ni---Ni = 4.4305 (7) A) and Pd2(BBI)2.2DMF (Pd---Pd = 4.3471 (4) A) are isostructural, with the cis-anti-M2(BBI)2 geometric isomer stabilized by weak hydrogen bonding to the DMF oxygen atoms. The high crystallographic symmetry of the metal complex in Cu2(BBI)2(Cu- - -Cu = 4.321 (1) A) has prevented identification of the specific M2(BBI)2 isomer present. Ni2(BBI)2 and Cu2(BBI)2 exhibit quasireversible two-electron-oxidation waves in cyclic voltammetry (CH2 C12 solution), whereas the analogous mononuclear complexes M(acim)2(acimH = 2-amino-2-penten-4-one) show only irreversible one-electron oxidation. Initial electrochemical oxidation of Pd2(BBI)2, while involving only one electron, is ca. 0.4 V easier than that of Pd(acim)2. Thus, the binuclear species exhibit new types of redox processes, and their relatively rigid structure appears to lead to unusual kinetic stability. © 1989, American Chemical Society. All rights reserved.
Publication Source (Journal or Book title)
Bradbury, J., Hampton, J., Martone, D., & Maverick, A. (1989). Preparation, Structure, and Redox Activity of Nickel(II), Palladium(II), and Copper(II) Cofacial Binuclear Bis(β-keto Enamine) Complexes. Inorganic Chemistry, 28 (12), 2392-2399. https://doi.org/10.1021/ic00311a028