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

Abstract

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. Their efficient synthesis requires isolable acyl triflate and lithium enolate reactants. Further, the syntheses of several transmetalation salts are reported and used in transmetalation reactions with a series of late, first-row transition metal compounds (FeII, CoII, NiII, CuI, CuII) of interest in base metal catalysis. In all, a dozen single-crystal XRD structures are reported, among other methods of characterization (i.e., IR, UV-vis, NMR, HRMS). The majority of the compounds present as mono-β-diketonate small-molecule bridged dimers. They serve as effective precatalysts and are accurately modeled by DFT calculations, validating the use of computational methods for determining structures and mechanisms. Their reactivity with various small molecules and solvents is also described. The utility of bis(2,6-dimesitylbenzoyl)methane (L) as a supporting ancillary ligand and a tool for further rational development of this class of ligands is discussed.