Tuning steric and electronic effects in transition-metal β-diketiminate complexes

Abstract

β-Diketiminates are widely used supporting ligands for building a range of metal complexes with different oxidation states, structures, and reactivities. This Perspective summarizes the steric and electronic influences of ligand substituents on these complexes, with an eye toward informing the design of new complexes with optimized properties. The backbone and N-aryl substituents can give significant steric effects on structure, reactivity and selectivity of reactions. The electron density on the metal can be tuned by installation of electron withdrawing or donating groups on the β-diketiminate ligand as well. Examples are shown from throughout the transition metal series to demonstrate different types of effects attributable to systematic variation of β-diketiminate ligands.

Effects of Ligand Halogenation on the Electron Localization, Geometry and Spin State of Low‐Coordinate (β‐Diketiminato)iron Complexes

“…This is consistent with more general observations on β-diketiminate complexes, where steric effects are greater than electronic effects. [3] Therefore, substitution of halogens for the purposes of ligand protection is likely to be a useful strategy that will not cause major electronic changes at the metal, but it will be important to make the supporting ligand isosteric for closer concurrence between the spin state, structure, and nuclearity of analogous complexes.…”

“…[2] However, halogenation can influence the β-diketiminate complexes, affecting the electron density on the metal and its reactivity. [3] Thus it is important to evaluate the influence of ligand halogenation on the properties of β-diketiminate metal complexes. [4] …”

Rapid, Regioconvergent, Solvent-Free Alkene Hydrosilylation with a Cobalt Catalyst

“…Higher reactivity was observed under the same conditions with less bulky supporting ligands. 24 Catalyst 2e, with the least bulky supporting ligand, was active at low loading (0.05 mol %) at room temperature without any solvent: after 1 h, a 97% yield of hexylsilane was formed with >98% linear selectivity. 1% of Markovnikov product and <1% disubstituted silane were detected by GC-MS, and no dehydrogenated hydrosilylation products were observed.…”

Iron‐Catalyzed Hydroboration: Unlocking Reactivity through Ligand Modulation

“…[4] In the recent literature reports, elegant examples have been presented using iron pre-catalysts. b-Diketiminate ligands have shown exceptional reactivity when used in conjunction with ah ost of main-group elements and transition metals, [8] but the powero ft his ligand in iron catalysis is vastly underexplored. [6] Previously,w eh ave exploited iron pre-catalystst hat are capableo fu ndergoing redox neutral, s-bond-metathesis-type reactivity, [7] avoiding the need for activationb yaGrignard or otherr educing agent, and we were intrigued by their potentialt oundergo catalytic HB.…”