DINUCLEAR COBALT(II) COMPLEXES OF PYRAZOLE LIGANDS WITH CHELATING SIDE ARMS

A series of pyrazole-based potential ligands bearing polydentate amine substituents in the 3- and 5-positions of the heterocycle has been sy nthesized [3,5-bis(R2NCH2)-pyzH; R2N = Me2N(CH2)(3)NMe (2aH), {Me2N(CH 2)(3)}(2)N (2bH), (Et2NCH2CH2)(2)N (2cH)]. Upon reaction with two equi valents of CoCl2 they form complexes LCo2Cl3 (3a-c; L = 2a-c, respecti vely) which are shown crystallographically to contain a dinuclear meta l core bridged by both the pyrazolate unit and a chlorine atom, with e ach cobalt center carrying a further terminal chlorine atom. Two of th e Ligand side arms in 3b, c are dangling, thus leading to five-coordin ation of the cobalt(II) centers in all cases. Addition of two equivale nts of NaBPh4, to solutions of 3b, c induced coordination of the forme rly dangling side arms to the metal centers by substitution of the ter minal chlorine atoms. The resulting compounds [LCo2Cl](BPh4), (4b, c, respectively) were characterized by X-ray structure analyses. They can be viewed as dinuclear linked versions of tran-type complexes [(tran = tris (aminoalkyl)amine] with distorted trigonal-bipyramidal coordina tion spheres around cobalt(II). Conformational analyses employing forc e-field calculations were carried out for 4b, c in order to rationaliz e the conformations observed in the solid state with regard to the acc essible conformational space.