Substituted N-picolylethylenediamines of the type (ArNHCH2CH2){(2-C5H4N)CH2}NR [R = Me, 4-CH2CH(C6H4)CH2, (2-C5H4N)CH2] and their transition metal(ii) halide complexes

Abstract

Alkylation of (ArNHCH₂CH₂){(2-C₅H₄N)CH₂}NH with RX [RX = MeI, 4-CH₂CH(C₆H₄)CH₂Cl) and (2-C₅H₅N)CH₂Cl] in the presence of base has allowed access to the sterically demanding multidentate nitrogen donor ligands, {(2,4,6-Me₃C₆H₂)NHCH₂CH₂}{(2-C₅H₄N)CH₂}NMe (L1), {(2,6-Me₃C₆H₃)NHCH₂CH₂}{(2-C₅H₄N)CH₂}NCH₂(C₆H₄)-4-CHCH₂ (L2) and (ArNHCH₂CH₂){(2-C₅H₄N)CH₂}₂N (Ar = 2,4-Me₂C₆H₃L3a, 2,6-Me₂C₆H₃L3b) in moderate yield. L3 can also be prepared in higher yield by the reaction of (NH₂CH₂CH₂){(2-C₅H₄N)CH₂}₂N with the corresponding aryl bromide in the presence of base and a palladium(0) catalyst. Treatment of L1 or L2 with MCl₂ [MCl₂ = CoCl₂·6H₂O or FeCl₂(THF)_1.5] in THF affords the high spin complexes [(L1)MCl₂] (M = Co 1a, Fe 1b) and [(L2)MCl₂] (M = Co 2a, Fe 2b) in good yield, respectively; the molecular structure of 1a reveals a five-coordinate metal centre with L1 bound in a facial fashion. The six-coordinate complexes, [(L3a)MCl₂] (M = Co 3a, Fe 3b, Mn 3c) are accessible on treatment of tripodal L3a with MCl₂. In contrast, the reaction with the more sterically encumbered L3b leads to the pseudo-five-coordinate species [(L3b)MCl₂] (M = Co 4a, Fe 4b) and, in the case of manganese, dimeric [(L3b)MnCl(µ-Cl)]₂ (4c); in 4a and 4b the aryl-substituted amine arm forms a partial interaction with the metal centre while in 4c the arm is pendant. The single crystal X-ray structures of 1a, 3b·MeCN, 3c·MeCN, 4b·MeCN and 4c are described as are the solution state properties of 3b and 4b.