NacNac

NacNac is a class of anionic bidentate ligands. 1,3-Diketimines are often referred to as "HNacNac", a modification of the abbreviation Hacac used for 1,3-diketones. These species can exist as a mixture of tautomers.^[1]

Tautomers of a substituted HNacNac ligand precursor and an idealized complex (right) of the conjugate base (M = metal, L = other ligand)

Preparation of ligands and complexes

Acetylacetone and related 1,3-diketones condense with primary alkyl- or arylamines resulting in replacement of the carbonyl oxygen atoms with NR groups, where R = aryl, alkyl. To prepare 1,3-diketimines from bulky amines, e.g. 2,4,6-trimethylanilines, prolonged reaction times are required. 2,6-Diisopropylaniline is a common bulky building block.

Deprotonation of HNacNac compounds affords anionic bidentate ligands that form a variety of coordination complexes.^[2] Some derivatives with large R groups can be used to stabilize low valent main group and transition metal complexes.^[3] Unlike the situation for the acetylacetonates, the steric properties of the coordinating atoms in NacNac⁻ ligands is adjustable by changes in the R substituent. Attachment to a metal center is usually carried out by initial deprotonation of HNacNac with n-butyllithium; the lithium derivative is then treated with a metal chloride to eliminate lithium chloride. In some cases, HNacNacs also serve as charge-neutral 1,3-diimine ligands.

Structure of [(C₆H₃-2,6-(i-Pr)₂)₂NacNac]NiSCPh₃ viewed down the C₂ axis, illustrating the steric bulk of this NacNac ligand (CPh₃ removed for clarity). Color code=gray = C, white = H, blue=N, yellow=S, green=Ni).^[4]

Related NacNac ligands

Synthesis of Jäger's N₂O₂ ligand.^[5]

NacNac ligands are diimine analogues of acetylacetonate ligands. An intermediate class of ligands are derived from monoimino-ketones.^[5][6] The first Dipp-NacNac ligand was synthesized by Dr. Francis S. Mair in 1998.^[7]

See also

• Diimine