3d Metal Complexes Supported by a Bis(imidazolin‐2‐imino)pyridine Pincer Ligand – Synthesis, Structural Characterisation, and Magnetic Properties

The coordination chemistry of the tridentate pincer ligand TL t Bu , which contains two electron‐rich imidazolin‐2‐imine moieties, has been explored. The reaction of TL t Bu with metal dihalides gave complexes of the general formula [(TL t Bu )MX 2 ] (M = Mn, Fe, Co, Ni; X = Cl, Br). These complexes were characterized by X‐ray diffraction analysis, which showed them to have different geometries in the solid state. Although [(TL t Bu )MnCl 2 ] ( 1 ) is best described as distorted square‐pyramidal, the complexes [(TL t Bu )FeCl 2 ] ( 2 ) and [(TL t Bu )CoCl 2 ] ( 3 ) show distorted tetrahedral geometries with the TL t Bu ligand bound in a κ 2 fashion and one of its imidazolin‐2‐imine fragments not coordinated to the metal atom. [(TL t Bu )NiBr]Br ( 4 ) crystallizes with a slightly distorted square‐planar cation. The reaction of the triflate (OTf) salts [M(OTf) 2 · n MeCN] (M = Mn, n = 1; M = Fe, Co, n = 2; OTf = CF 3 SO 3 ) with TL t Bu resulted in [(TL t Bu )M(OTf)][OTf] (M = Mn, 5 ; M = Fe, 6 ) and [(TL t Bu )Co(NCMe)][OTf] 2 ( 7 ). Complexes 6 and 7 were characterized by X‐ray diffraction analysis, and both showed distorted square‐planar geometries. Magnetic measurements of 5 , 6 and 7 showed them to possess a S = 5/2, 2 and 1/2 ground states, respectively. The bromide ions in complex 4 were exchanged by reaction with AgBF 4 to afford [(TL t Bu )Ni(NCMe)][BF 4 ] 2 ( 8 ), which showed a distorted square‐planar geometry in the solid state. The reactions of 1 and 6 with AgOTf resulted in the oxidation of the complexes and the formation of [(TL t Bu )MnCl(OTf)][OTf] ( 9 ) and [(TL t Bu )Fe(OTf) 2 ][OTf] ( 10 ), respectively. Complexes 9 and 10 both display distorted square‐pyramidal geometries in the solid state. The ground state of 10 was found to be S = 5/2 by superconducting quantum interference device (SQUID) magnetometry measurements. The oxidation of 5 , 6 and 7 with the iodosobenzene derivative ( t BuSO 2 )C 6 H 4 IO was investigated. Although the reactions of 6 and 7 gave no evidence for the formation of transient oxo species, crystals were obtained from the reaction of 5 . These crystals showed the formation of [TL t Bu *Mn(OH)](OTf) 2 ( 11 ), in which one of the t Bu groups of the TL t Bu ligand has undergone a C–H activation by a putative Mn IV =O bond. The complex shows a distorted square‐pyramidal geometry in the solid state, and the carbon atom of the CH‐activated t Bu group occupies the apical position.