New Copper Complexes with N,O-Donor Ligands Based on Pyrazole Moieties Supported by 3-Substituted Acetylacetone Scaffolds.

The new 3-monosubstituted acetylacetone ligands, 3-(phenyl(1 H -pyrazol-1-yl)methyl)pentane-2,4-dione (HL acPz ) and 3-((3,5-dimethyl-1 H -pyrazol-1-yl)(phenyl)methyl)pentane-2,4-dione (HL acPzMe ), were synthesized and used as supporting ligands for new copper(II) and copper(I) phosphane complexes of the general formulae [Cu(HL acX ) 2 (L acX ) 2 ] and [Cu(PPh 3 ) 2 (HL acX )]PF 6 (X = Pz (pyrazole) or PzMe (3,5-dimethylpyrazole)), respectively. In the syntheses of the Cu(I) complexes, the triphenylphosphine coligand (PPh 3 ) was used to stabilize copper in the +1 oxidation state, avoiding oxidation to Cu(II). All compounds were characterized by CHN analysis, 1 H-NMR, 13 C-NMR, FT-IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The ligands HL acPz ( 1 ) and HL acPzMe ( 2 ) and the copper complex [Cu(PPh 3 ) 2 (HL acPz )]PF 6 ( 3 ) were also characterized by X-ray crystallography. The reactivity of these new compounds was investigated and the new compounds 4-phenyl-4-(1 H -pyrazol-1-yl)butan-2-one ( 7 ) and 4-(3,5-dimethyl-1 H -pyrazol-1-yl)-4-phenylbutan-2-one ( 8 ) were obtained in basic conditions via the retro-Claisen reaction of related 3-monosubstituted acetylacetone, providing efficient access to synthetically useful ketone compounds. Compound 8 was also characterized by X-ray crystallography.