Ligand-controlled nuclearity in nickel bis(benzimidazolyl) complexes

Abstract

A series of nickel complexes supported with a tripodal ligand bis(1-methylbenzimidazolyl-2-methyl)amine (L) or bis(1-methylbenzimidazolyl-2-methyl)-10-camphorsulfonamide (L') on a Ni(II) ion were synthesized and fully characterized. The complexes, [LNiCl(micro-Cl)]2.4CH(3)OH (1), [LNi(CH(3)CN)3](ClO4)2.2CH(3)CN (3), and [L2(2)Ni(2)(micro-OAc)3]X (X = Cl- (5) or ClO4- (7)), coordinated with the tridentate L ligand, all possess an octahedral structure at the nickel center; in contrast, the geometry of the complexes, L'NiCl2 (2), [L'Ni(CH(3)CN)3](ClO4)2.2CH(3)CN (4), and L'Ni(OAc)2.0.5Et(2)O (6), employing the L' ligand are either tetrahedral or octahedral. Due to the weak coordinating ability of the sulfonamide group and the steric hindrance of the camphorsulfonyl group of L', the tripodal L' becomes a bidentate ligand in the presence of chloride or acetate groups, which have a stronger electron donating ability than acetonitrile, bound to the nickel center. It is noteworthy that the nuclearity of the nickel complexes can be controlled by the coordination ability of the central nitrogen of the supporting bis-methylbenzimidazolyl ligand.

Formation of a Metal-to-Nitrogen Bond of Normal Length by a Neutral Sufonamide Group within a Tridentate Ligand. A New Approach to Radiopharmaceutical Bioconjugation

“…The evidence for angles close to 109.5° (Table 2) clearly indicates that binding to Re I results in sp 2 -to-sp 3 re-hybridization of the tertiary sulfonamide nitrogen. This finding that all angles are close to the tetrahedral value is a common feature in the complexes of many metals in various oxidation states (Ni II , Co II , Mn II , Cu II , La III ) 26,27,32,33 with a bound sulfonamide. One useful approach to appreciating the sp 3 nature of the sulfonamide nitrogen is to determine the distance by which the N lies out of the plane defined by the S atom and the two C atoms attached to N. For complexes 1 , 2 , 4 , and 5 , this out-of-the-plane distance ranges from 0.486–0.515 Å.…”

“…Likewise, for complexes with other metals and differing widely in the ligands and geometries, values of 0.38–0.51 Å are typically found. 26,27,32,33 In contrast, for complexes in which the sulfonamide nitrogen is not bound, the out-of-the-plane distances in reported structures typically range from 0.06–0.125 Å. 26,27 …”

“…In almost all cases, the metal-bound tertiary sulfonamide nitrogen and the donors of the adjacent chelate rings occupy the face of an octahedron 26,28,33 or have a similar arrangement in complexes with other geometries. 29,30 In other words, these three N-donor atoms and the metal atom typically do not define a common plane.…”

“…In most cases reported in the literature, the M–N bond is long, and the N– S bond is relatively short. 26,27,32 …”

“…Indeed, these are among the very few crystallographically characterized complexes containing tertiary sulfonamide N donors with any metal. 26-33 In previously reported sulfonamide complexes, the bound sulfonamide is either constrained within a ring system or has elongated bonds. 26-33 …”