Browsing by Author "Kagwanja, Stanley M."

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Formation of trimetallic complexes containing redox-active nitrosyl molybdenum tris(3,5-dimethylpyrazolyl)-borato groups. Schiff base compounds containing two Mo and one Cu centre
(Elsevier, 1994) Kagwanja, Stanley M.; Jones, Christopher J.; Maher, John P.; McCleverty, Jon A.
The reaction of [Mo(NO)Tp*Cl2] [Tp* = tris(3,5-dimethylpyrazolyl)borate] with copper(II) Schiff base complexes derived by condensation of two mole equivalents of 2,5-dihydroxybenzaldehyde with α,ω-diamines [1,2-C6H4(NH2)2, NH2(CH2)nNH2, n = 2–5] affords trimetallic species containing three potential redox centres. The IR, UV-vis and EPR spectroscopic properties of these compounds are described and it is shown that, with increasing chain length in the diimino bridges of the Schiff base complexes, there are small distortions from planarity, probably towards tetrahedral structures. From cyclic and differential pulse voltammetry it is shown that the trimetallic species primarily undergo two accessible sequential one-electron reductions associated with the {Mo(NO)Tp*Cl} centres, and by determination of conproportionation constants for the mono-reduced species, it is established that there is weak interaction between these two centres. Attempts to obtain reduced trimetallic species are described.
Reaction of molybdenum mononitrosyl halides with Schiff bases: Hydrolysis of azomethine links,formation of monometallic tris
(Elsevier, 1996-06) Kagwanja, Stanley M.; Jeffery, John C.; Johns, Christopher J.; McCleverty, John A.
The reaction of 2 mol equiv. of [Mo(NO){HB(dmpz)3}X2] ((HBdmpz)3 = tris(3,5-dimethylpyrazolyl)borate; X = Cl or I) with Schiff base ligands derived by condensation of 2 mol equiv. of para- and meta-hydroxybenzaldehyde with 1,4-C6H4(NH2)2 and 1,6-NH2(CH2)6NH2 afforded monometallic complexes [Mo(NO) {H(dmpz3)} X(OC6H4 CHO)]. Sodium borohydride reduction of the Schiff bases obtained from the hydroxybenzaldehydes and 1,4-C6H4(NH2)2 followed by reaction with [Mo(NO){HB(dmpz)3 Cl2}] afforded the bimetallic species [{Mo(NO)HB(dmpz)3}Cl{(OC6H4CH2NH)2C6H4}]. These compounds were characterized spectroscopically and the structure of a closely related compound, [Mo(NO){HB(dmpz)3}Cl{OC6H3(3-CHO)(4-OH)}], has been determined crystallographically.
Synthesis and electrochemical studies of heterobinuclear complexes containing copper and molybdenum nitrosyl groups linked by Schiff base ligands
(Springer, 2000-08) Lutta, Samwel T.; Kagwanja, Stanley M.
Abstract The reaction of [MoCl(NO)Tp * = tris(3,5-dimethylpyrazolylborate] with copper Schiff base complexes derived by condensation of one mole each of 2,5-dihydroxybenzaldehyde and salicylaldehyde with α,ω diamines [NH2(CH2) n NH2, n = 2–4] yields heterobinuclear complexes with two potential redox centres. I.r., electronic and e.s.r. spectroscopic properties of these complexes are described. Cyclic voltammetric data of the base complexes in DMSO reveal that the copper redox centres undergo irreversible one electron reduction at potentials which vary slightly with the polymethylene carbon chain backbone of the Schiff base ligands. Incorporation of [MoCl(NO)Tp *]+ groups in the copper Schiff base complexes, results to a slight anodic shift (100 mV) in the reduction potential of the copper centre which remains invariant as the polymethylene carbon chain lengthens. Electrochemical data of the heterobinuclear complexes using CH2Cl2 and DMSO as solvents indicate the solvent dependence of the reduction potentials of these complexes. In CH2Cl2, the reduction potential of the copper centre shifts cathodically by 100 mV, while that of the molybdenum centre shifts anodically by 200 mV. However, accumulated electrochemical data of the heterobinuclear complexes indicate minimal electronic interactions between the copper and molybdenum redox centres.
Trimetallic complexes containing Nickel or Palladium and two Molybdenum nitrosyl groups
(1997) Kagwanja, Stanley M.; Johns, Christopher J.; McCleverty, Jon A.
The reaction of [Mo(NO){HB(dmpz)3}Cl2] [HB(dmpz)3 = tris(3,5-dimethylpyrazolyborate] with nickel(II) and palladium(II) Schiff-base complexes derived by condensation of two mole equivalents of 2,5-dihydroxybenzaldehyde with α,ω-diamines [1,2-C6H4(NH)2),(CH2)nNH2, n = 2–4 for Ni, n = 2 for Pd) affords trimetallic species. From cyclic, square wave and differential pulse voltammetric data it is shown that the species may be reduced to a dianion and that the sites of reduction are probably the two molybdenum nitrosyl fragments. From the electrochemical and limited EPR spectral data obtained from reduced species, it is clear that there is very weak electronic and minimal magnetic interaction between the redox centres.