Synthesis and reactivity of 3,5-dimethyl-4-aminomethylpyrazole ligands. An entry to new water-soluble pyrazolate rhodium(I) complexes

Abstract

The new pyrazoles 3,5-dimethyl-4-(ethylamino)methylpyrazole (HL 1) and 3,5-dimethyl-4-(isopropylamino)methylpyrazole (HL 2), both containing aminoalkyl groups at position 4 have been prepared by aminoalkylation of 3,5-dimethylpyrazole and by the reaction between 1-chloromethyl-3,5-dimethylpyrazolium chloride and NH 2R amines. The reaction between HL 1, HL 2 and [RhCl(COD)] 2 resulted in complexes of formula [Rh 2(HL 1) 2(COD) 2]Cl 2 ( 1) and [Rh 2(HL 2) 2(COD) 2]Cl 2 ( 2), which contained the pyrazole ligands in the ‘zwitterionic’ pyrazolate-ammonium forms. The X-ray structure analysis of 2 confirmed the neutral nature of bridging-pyrazolate ligands and revealed that 1 and 2 belonged to the [Rh 2(Pz) 2L 2] family of compounds. The same reaction with two equivalents of NaOMe resulted in neutral pyrazolate complexes [Rh 2(L 1) 2(COD) 2] ( 5) and [Rh 2(L 2) 2(COD) 2] ( 6). The reaction between both cationic and neutral pyrazolate complexes and a 1:1 CO–H 2 mixture (20 atm) led to the dinuclear pyrazolate-bridged tetracarbonyl compounds 3, 4, 7 and 8 in good yields. Tetracarbonyl complexes 3 and 4 were not isolated in pure state. All the complexes synthesized are soluble in polar solvents such as water.