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Donor Ligand, Basal Ligand and Solvent Effects on the Equilibrium Constants of Triphenylphosphinecobalt(III) Schiff Base Complexes with Phosphite Ligands

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The equilibrium constants and the thermodynamic parameters were spectrophotometrically measured for the 1:1 adduct formation of [Co(Salen)(PPh3)]ClO4.H2O, and [Co(7,7’-Me2Salen)(PPh3)]ClO4.H2O as acceptors, with P(OR)3 (R = methyl, ethyl , and i-propyl) as donors, in acetonitrile (CH3CN) and dimethylformamide (DMF) as solvents at constant ionic strength (I = 0.1 M NaClO4), and various temperatures (t = 10-50 °C). Our results revealed the following trends: stability of the cobalt(III) Schiff base complexes toward a given phosphite donor, [Co(7,7י-Me2Salen)(PPh3)]+ < [Co(Salen)(PPh3)]+; binding of the donors (phosphites) toward a given cobalt(ةةة) Schiff base complex, P(OEt)3 > P(OMe)3 > P(O-iPr)3; influence of solvent on the stability of a given cobalt(III) Schiff base complex toward a given phosphite donor, CH3CN < DMF.

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