2-(4′,4′-Dimethyl-3′,4′-dihydrooxazol-2′-yl)phenol: Some First-Row Transition Metal Complexes of This Naturally Occurring Binding Group

Abstract

The synthesis and characterization of monomeric MnIII, CoII, NiII, CuII, and ZnII phenolates derived from a biologically relevant ligand, 2‐(4′,4′‐dimethyl‐3′,4′‐dihydrooxazol‐2′‐yl)phenol (1), are described. The addition of Mn(OAc)2 · 4 H2O to an ethanolic solution of 1 affords an unexpected 1:3 complex [Mn(OR){O(Ox)}2] (2) [R = C6H4CONHC(Me2)CH2OH, Ox = 2‐(4,4‐dimethyl‐2‐oxazolinyl)phenyl] in which one of the five‐membered oxazoline rings is partially hydrolyzed. The complexes [M{O(Ox)}2] [M = Co (3), Ni (4), Cu (6), or Zn (7)] were prepared in good yield by the reactions of 1 with the corresponding metal acetates. Novel formation of the six‐coordinate NiII complex 5 with neutral acetic acid was observed during the crystallization process. The complexes were characterized by elemental analysis, magnetic susceptibility, as well as EPR, 1H NMR, electronic, and mass spectral techniques. Complexes 2, 3, 5, 6, and 7 were characterized by single crystal X‐ray diffraction studies. Complex 2 is six‐coordinate whereas complexes 3, 6, and 7 are four‐coordinate with two oxazoline bidentate ligands. The geometry around the metal center is found to be distorted tetrahedral for all of the four‐coordinate complexes. Complex 5 is octahedral with four coordination sites occupied by the two bidentate oxazoline ligands and the other two are occupied by two neutral acetic acid molecules. The hydroxy groups of the coordinated acetic acid are hydrogen‐bonded to the phenolate oxygen atoms of the oxazoline ligands. The variable‐temperature 1H NMR spectroscopic studies of complex 7 indicate that the interconversion between the (M) and (P) helix is slow at low temperatures.

Divalent Cobalt and Copper Coordination Complexes of κ2-N, O-Derivatives of (Z)-1-R-2-(2’-oxazolin-2’-yl)-eth-1-en-1-ates: Structure and Reactivity Patterns

“…This material features very similar bonding parameters (τ4 =0.829; Co−Nav = 1.961 Å; Co−Oav = 1.936 Å). [77] <Insert Scheme 3> As noted above, solutions (e.g., CH2Cl2) of 2a-c are unstable over several days at ambient temperatures in open air. The mixtures of both complexes 2a and 2b noticeably darkened in colour and began to precipitate black-green coloured materials.…”

Synthesis and Structural Elucidation of Ni(II), Cu(II), Zn(II) and Cd(II) Metal Complexes of Oxazoline Based Ligands

“…The shifting of ν (C-O) band confirms deprotonation of phenolic proton and subsequent coordination to metal ion. The IR spectra of all the 2-phox complexes show two absorption bands in 530-585 cm −1 and 430-471 cm −1 region, which are assignable to (M-O) and (M-N) vibrations, respectively [20].…”

“…The phenolic-OH frequency appears at 3340 cm -1 which remains unchanged even after complexation suggesting the non involvement of the group in coordination [22]. Furthermore, new bands at 475 cm -1 and 504 cm -1 for Zn(II) and Cd(II) complexes, respectively, may be assigned to M-N stretching [20]. New absorption bands at 569 cm -1 and 572 cm -1 have been assigned to (M-O) vibrations of Zn(II) and Cd(II) complexes, respectively.…”

Divalent cobalt and copper coordination complexes of κ2-N, O-derivatives of (Z)-1-R-2-(2′-oxazolin-2′-yl)-eth-1-en-1-ates: Structure and reactivity patterns

“…[44] Bond lengths and angles of the ligand framework are typical [43,45] and the Co−O and Co−N interactions are also of normal length for enolates and oxazolines bound to formally Co 2+ , respectively. [26,41,[63][64][65][66][67][68][69][70][71][72][73][74][75][76][77] A useful structural comparison can be made to the species bis-(2-[2'-oxazolin-2'yl]phenolato)cobalt(II). This material features very similar bonding parameters (τ4 =0.829; Co−Nav = 1.961 Å; Co−Oav = 1.936 Å).…”