Trispyrazolylborate ligands reactions

OAT reactions interconvert dioxo-Mo(VI) and oxo-Mo(IV) complexes of tridentate trispyrazolylborate ligands such as L-Ng. Depending upon the co-ligands and reaction conditions, particularly solvent, a number of events follow OAT from (L-N3)Mo02X (X = Cl, Br, NCS, OPh, SPh) to PPhg (Scheme 4) these events dictate the final product of the reaction (127,128). In dry noncoordinating solvents such as toluene, the initially... 

Studies of the electron transfer reactions of oxomolybdenum complexes of trispyrazolylborate ligands with Fe(III) porphyrins show that the reduction of (TPP)Fe Cl by (L-NglMo OCUdmf) (Eq. (26)) proceeds cleanly and quantitatively in dmf and is first order in Mo and zero order in Fe (261). 

Many model studies have focused on methaemerythrin, i.e. the oxidized Fe(III)-Fe(III) form of haemerythrin which contains an 0x0 (rather than hydroxy) bridge. Methaemerythrin does not bind O2, but does interact with ligands such as [N3] and [SCN]. Reaction 28.8 makes use of the trispyrazolylborate ligand, [HBpz3] , to model three His residues the product (28.14) contains antiferro-magnetically coupled Fe(III) centres. 

The coordination of tris(pyrazolyl)amine and bis(pyrazolyl)amine ligands toward [Rh(/r-Cl)(cod)]2 was studied and the crystal structure of the trimetallic compound Rh3Cl3(cod)3(tdma) was reported. Trispyrazolylborate ligands also provided a series of complexes of the type TpRh(LL) (LL = nbd or cod), whose NMR spectroscopic properties and structural features were studied. The fluxional behavior of complexes of formula Tp Rh(LL) (LL = nbd, 2CO, cod R = H, Me, Ph, Br) was studied by means of NMR spectroscopy. Two K -square-planar isomers and one re -pentacoordinated complex were observed. The structure of the complex K -Tp Rh(nbd) was confirmed by X-ray diffraction. The hapticity of the Tp ligand was also studied on the basis of the i B-H) obtained by IR spectroscopy. Reactions of [Rh(/r-Cl)(nbd)]2 with a series of bis- and tris(azolyl) methanes 388, 389, 390, 391, and 392 were also reported. ... 

The preparation and characterization of several octahedral Ru(II) complexes containing s-trans coordinated dienes have been reported. The Zn mediated reduction of Ru(acac)3 in the presence of a 1,3-diene affords (diene)Ru(acac)2 complexes as a mixture of diastereo-mers (eg. 129)13a b. Reaction of [(trispyrazolylborate)RuCl]jt or [(NH3)4Ru(acetone)2]2+ [CIO4 ]2 with acyclic dienes yields complex 130 or cation 131 respectively130,14. Coordination of the ligand as an s-trans diene was indicated either by crystal structure or by determining C2v symmetry on the basis of NMR spectroscopy. 

Trispyrazolylborates are models for tris-histidine active sites in zinc enzymes, e.g., the matrix metalloproteinases involved in breakdown of extracellular matrices. Inhibition of these metalloproteinases may prove valuable in the treatment of, inter alios, cancer and arthritis, so efforts are being made to find appropriate ligands to block the zinc active site. The search has recently moved on from hydroxamates to hydroxypyridinones - l-hydroxy-2-pyridinone is a cyclic analogue of hydroxamic acid. As reported in Section II.B.2 earlier, hydroxypyridinones form stable five-coordinate complexes on reaction with hydrotris(3,5-phenylmethylpyrazolyl)borate zinc hydroxide. Modeling studies suggest that hydroxypyridinonate ligands should be able to access the active site in the enzyme with ease (110). 

Only a handful of pseudotetrahedral or octahedral oxosulfido-Mo(VI) and -Mo(V) complexes are known, and their chemistry is described in Section 11. Mononuclear sulfido-Mo(V) complexes are unstable due to their susceptibility to redox, polynucleation, and hydrolysis reactions. Trispyrazolylborate derivatives such as sfructuraUy characterized Tp Mo SX2 (X = Cl, OPh derivative X2 = bdt, catecholate) are most commonly encountered. The Tp complexes exhibit short Mo=S bonds (ca. 2.13 A), intense S(ls)- - n (Mo=S) XAS transitions characteristic of terminal thio ligands, and EPR iso see g-Factor) values substantially lower than their 0x0 analogues. ... 

The substitution of the trans halide ligand and two equatorial ligands by tris-chelate ligands is a commonly employed synthetic reaction. Cyclopen-tadienyl derivatives were made according to Eq. (S3) (35,II 1,120.121) and Eq. (84) (69,88). Quite a variety of trispyrazolylborate derivatives were... 

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