3,5-Dimethylpyrazole, transition metal

Tautomeric rearrangements of transition-metal complexes with azole ligands are relatively scarce. The fluxional behavior of the rhodium complex 43 with a neutral 3,5-dimethylpyrazole was explained as the result of rapid processes of metallotropy and prototropy occurring simultaneously (Scheme 24) [74JOM(C)51],... 

The present paper describes the synthesis of N-(2-hydroxyethyl)-3,5-dimethylpyrazole and the synthesis of the tosylated compound N-(2-p-tol-uenesulfonylethyl)-3,5-dimethylpyrazole which can be used for the synthesis of larger chelating ligands. The tosylation is carried out in a water/acetone mixture, unlike most classical tosylations, which are performed in pyridine.7 A high yield of pure tosylated product is obtained from this reaction. A water/acetone mixture as the solvent for the synthesis of other tosylates may very well be also successful. Since the compound N-(2-hydroxyethyl)-3,5-dimethylpyrazole may itself act as a didentate N,0 ligand in coordination compounds with transition metal ions,9 an example using Cu(II) is provided below. 

It is possible to use ancillary ligands in addition to phosphonic acids in building up nanosized cluster compounds of late transition metal ions. Thus, the reaction of CuCl2 with tert-butylphosphonic acid in the presence of 3,5-dimethylpyrazole affords a dodecanuclear copper phosphonate with an interesting cage structure,3 Similarly, large vanadium phosphonate clusters with up to 18 vanadium atoms have been assembled from phosphonic acids.35... 

Dimethylbis(pyrazol-1 -yl)- and bis(3,5-dimethylpyrazol-l-yl)-dimethylgallate ions act as bidentate chelating agents towards transition-metal ions." The [Me2B(pz)2] ion acts similarly, but the A1 and In analogues do not appear to form transition metal complexes. The crystal structure of (78), has been determined. The space group is Pljc. The whole molecule is in a pseudo-chair conformation, with two six-membered Ga—(N— N)2— Ni rings in boat conformations. The co-ordination at the Ni atom is planar." ... 

Carbon-carbon double bonds, besides being susceptible to addition of oxygen or cleavage, can also react at allylic positions. Synthetic utility requires that there be good regioselectivity. Among the transition-metal oxidants, the CrOs-pyridine reagent in methylene chloride and a related complex in which 3,5-dimethylpyrazole is used in, place of pyridine are the most satisfactory for allylic oxidation. 

Tiirkoglu G, Heinemann FW, Burzlaff N. Transition metal complexes bearing a 2,2-bis(3,5-dimethylpyrazol-l-yl)propionate Hgand one methyl more matters. Dalton Trans. 2011 40 4678 886. 

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