Dinuclear Cobalt(II) Complexes of Pyrazole Ligands with Chelating Side Arms

Abstract

Abstract A series of pyrazole‐based potential ligands bearing polydentate amine substituents in the 3‐ and 5‐positions of the heterocycle has been synthesized [3,5‐bis(R 2 NCH 2 )‐pyzH R 2 N = Me 2 N(CH 2 ) 3 NMe ( 2aH ), [Me 2 N(CH 2 ) 3 ] 2 N ( 2bH ), (Et 2 NCH 2 CH 2 ) 2 N ( 2cH )]. Upon reaction with two equivalents of CoCl 2 they form complexes LCo 2 Cl 3 ( 3a – c ; L = 2a – c , respectively) which are shown crystallographically to contain a dinuclear metal core bridged by both the pyrazolate unit and a chlorine atom, with each cobalt center carrying a further terminal chlorine atom. Two of the ligand side arms in 3b , c are dangling, thus leading to five‐coordination of the cobalt(II) centers in all cases. Addition of two equivalents of NaBPh 4 to solutions of 3b , c induced coordination of the formerly dangling side arms to the metal centers by substitution of the terminal chlorine atoms. The resulting compounds [LCo 2 Cl](BPh 4 ) 2 ( 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 coordination spheres around cobalt(II). Conformational analyses employing force‐field calculations were carried out for 4b , c in order to rationalize the conformations observed in the solid state with regard to the accessible conformational space.