A New Class of Biomimetically Relevant “Scorpionate” Ligands. 1. The (2-Hydroxyphenyl)bis(pyrazolyl)methanes:  Synthesis and Structural Characterization of Some Cobalt(II) Complexes

Abstract

The syntheses of a new class of potentially biomimetic, tripodal, mixed functionality ligands, (2-hydroxyphenyl)bis(pyrazolyl)methane (L1), (2-hydroxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L2), and (2-hydroxyphenyl)bis(3-isopropylpyrazolyl)methane (L3), are described. These ligands have been used to prepare the cobalt(II)4. X-ray structural analysis of 1-4 gave the following structural parameters: 1, C 30 H 34 N 8 CoO 6 , triclinic, a ) 8.286(2) Å, b ) 10.053(3) Å, c ) 10.562(2) Å, R ) 109.66(2)°, β ) 96.57(1)°, γ ) 91.11(3)°, space group P1 h, Z ) 1; 2, C 38 H 38 N 8 CoO 6 , triclinic, a ) 8.746(5) Å, b ) 10.900(5) Å, c ) 11.399(8) Å, R ) 70.82(4)°, β ) 75.13(5)°, γ ) 81.46(4)°, space group P1 h, Z ) 1; 3, C 20 H 26 N 4 Cl 4 CoO, monoclinic, a ) 10.934(2) Å, b ) 12.404(2) Å, c ) 19.267(3) Å, β ) 98.33(1)°, space group P2 1 /n, Z ) 4; 4, C 58 H 70 N 12 BCo 3 F 4 O 9 , monoclinic, a ) 14.798(5) Å, b ) 23.657(8) Å, c ) 20.614(7) Å, β ) 97.75(2)°, space group P2 1 /n, Z ) 4.

Redox‐Active p‐Quinone‐Based Bis(pyrazol‐1‐yl)methane Ligands: Synthesis and Coordination Behaviour

“…In contrast, the iPr 3 SiOÀC ipso bond lengths in 2 c (1.372(1) ) and 5 (1.385(2) ) are roughly the same. Differences similar to those noted for 2 c and 5 have also been observed between the free ligand (2-hydroxyphenyl)-bis(pyrazol-1-yl)methane (LH: HO À C ipso 1.372(7) [28] ) and its corresponding complex [NiL 2 ] (NiO À C ipso 1.309(13) [46] ). We attribute the shorter NiO À C ipso bonds in 5 and [NiL 2 ] to www.chemeurj.org a larger degree of O!Aryl p bonding, which leads to more O À C double bond character compared with the protonated free ligands.…”

“…In 1997, Higgs and Carrano established (2-hydroxyphenyl)bis(pyrazol-1-yl)methanes as a new class of biomimetically relevant scorpionate ligands. [28] Because p-quinones have not only been recognised as ubiquitous electrontransfer agents in biology, but also as important redox cofactors ("quinoenzymes"), [29] replacement of the 2-hydroxyphenyl substituent in (2-hydroxyphenyl)bis(pyrazol-1-yl)methanes by a p-hydroquinone moiety as in C could provide interesting perspectives for modelling the active sites of phydroquinone-containing metalloenzymes, such as copperdependent amine oxidases (cofactor: topaquinone = 2,4,5-trihydroxyphenylalaninequinone). [30][31][32] Further evidence for the potential of C-type ligands in homogeneous catalysis stems from Bäckvall et al who employed p-hydroquinone as a co-catalyst in Pd II -catalysed aerobic oxidations of monoolefins and conjugated dienes.…”

Recent Advances in the Design and Coordination Chemistry of Heteroscorpionate Ligands Bearing Stereogenic Centres

“…This conformation is similar to that found in the (2-hydroxyphenyl)bis(pyrazolyl)methane derivative. [18] The cyclopentadiene and phenyl rings are probably in this quasiantiparallel disposition to minimize steric interactions between the two rings. In addition, the structures of the lithium compounds were established on the basis of full-geometry optimizations at a DFT level and it was found that they agree very well with those determined by X-ray crystal structure studies.…”

Synthesis, structure and biological activity of diorganotin derivatives with pyridyl functionalized bis(pyrazol‐1‐yl)methanes

“…Melting points were measured with an X-4 digital micro melting-point apparatus and are uncorrected. (2-Hydroxyphenyl)bis(pyrazol-1-yl)methane and (2-hydroxyphenyl)bis(3,5-dimethylpyrazol-1-yl)methane [21] were prepared by the published methods.…”