Mono-β-diketonate Metal Complexes of the First Transition Series.

Mono-β-diketonate compounds have been fleetingly observed in base metal catalyzed reactions, which are of current interest as alternatives to precious metal catalyzed reactions. Their isolation has been challenging due to synthetic and structural limitations of acac-type ligands, leading to the development of a related NacNac ligand platform. Herein we report the synthesis of a β-diketone capable of kinetically stabilizing relevant catalytic intermediates.

Copper(II) as a Platform for Probing the Steric Demand of Bulky β-Diketonates.

The synthesis and characterization of a series of copper bis(β-diketonate) complexes, functionalized with sterically hindered -biphenyl and -terphenyl functional groups, are reported. X-ray structural analysis reveals that the ligands exhibit several modes of flexibility in order to accommodate the steric demand. Increased steric bulk of the ligands influences the Cu electrochemical reduction, which is likely due to inhibited ligand rotation.

Sterically encumbered β-diketonates and base metal catalysis.

Metal coordination complexes of the sterically hindered β-diketonate, 2,6-dimesitylbenzoyl pinacolone (esac), are reported for Co, Ni, Cu, and Zn. All four form ML2-type complexes with typical coordination behavior for late-metal β-diketonates, however the effects on established electrochemistry and reactivity vary somewhat per metal. For example, the striking chemical and electrochemical inertness of CoII(esac)2 to oxidation and disproportionation is atypical.

Synthesis of Sterically Hindered β-Diketones via Condensation of Acid Chlorides with Enolates.

Bulky β-diketones have rarely exceeded dipivaloylmethane (DPM) in steric demand, largely due to synthetic limitations of the Claisen condensation. This work demonstrates hindered acid chlorides to be selective electrophiles in noncoordinating solvents for condensations with enolates. An improved synthesis of DPM is described (90% yield), and crowded β-diketones featuring bulky o-biphenyl or m-terphenyl fragments were prepared in good to excellent yields.