Zinc-Mediated Transmetalation as a Route to Anionic N-Heterocyclic Olefin Complexes in the p-Block

Abstract

Anionic N-heterocyclic olefins (aNHOs) are suited well for the stabilization of low-coordinate inorganic complexes, due to their steric tunability and strong σand π-electron donating abilities. In this study, the new two-coordinate zinc complex ( Me IPrCH) 2 Zn ( Me IPrCH = [(MeCNDipp) 2 CCH] − , Dipp = 2,6diisopropylphenyl) is shown to participate in a broad range of metathesis reactions with main group element-based halides and hydrides. In the case of the group 14 halides, Cl 2 E•dioxane (E = Ge and Sn), transmetalation occurs to form dinuclear propellane-shaped cations, [( Me IPrCHE) 2 (μ-Cl)] + , while the aNHO-capped phosphine ligand Me IPrCH-PPh 2 is obtained when ( Me IPrCH) 2 Zn is combined with ClPPh 2 . Lastly, ZnH 2 elimination drives transmetalation between ( Me IPrCH) 2 Zn and hydroboranes and hydroalumanes, leading to Lewis acidic aNHO-supported -boryl and -alane products.

Tridentate NacNac Stabilized Tin and Nickel Complexes: Access to a Monomeric Nickel Hydride and Its Catalytic Application

“…Given the synthetic potential of a transmetalation reaction, we decided to carefully study this synthetic route, evaluate its scope for another ligand system, and further explore the transmetalation chemistry between two main-group elements or a main-group element and a transition metal. A further impetus comes from recent transmetalation chemistry by the groups of Jones, Zeckert, Beckmann, Roesky, and others. − Herein, we describe the synthesis and characterization of a tin­(II) compound ( 2 ) based on a nacnac framework with a picolyl side arm. Subsequently, we have shown 2 undergoes smooth transmetalation with Ni to generate analogous Ni complex ( 4 ).…”

Reaction of a bis(pentafulvene)titanium complex with an N-heterocyclic olefin: C–H-activation leads to resonance between a titanium vinyl and titanium alkylidene complex

“…a second equivalent of the NHO used), proceed via direct halosilane elimination of a preformed silylated NHO or via salt metathesis whereas in the herein reported example no byproducts are formed. 20,21 Here we demonstrate the direct formation of this ligand class in the coordination sphere of titanium by formal intramolecular proton transfer to one pentafulvene ligand. Although in principal there is a second pentafulvene ligand to potentially react with, no second C–H activation occurs regardless of the stoichiometry used for this reaction.…”

“…This has been exploited first by Rivard and coworkers, and later by Ghadwal et al , and more recently again the Rivard group reported stable and base-free divinylgermanes, divinylgermylenes, and expanded this protocol to a series of homoleptic tetrylenes and a zinc complex. 20 To date, all reported examples of compounds bearing the anionic N-heterocyclic vinyl ligand require either stoichiometric amounts of an external base ( e.g. a second equivalent of the NHO used), proceed via direct halosilane elimination of a preformed silylated NHO or via salt metathesis whereas in the herein reported example no byproducts are formed.…”

Group 4 Transition Metal Complexes with Anionic N‐Heterocyclic Olefin Ligands

“…To our knowledge, there are only two examples of aNHO‐transition metal complexes. One example was reported by our group, wherein two aNHO ligands are bound to a Zn(II) center yielding a linear two‐coordinate species ( E , Chart 1) [8a] . The second very recent example by Beckhaus is the aNHO complex F , obtained from the reaction of an NHO with a bis(π‐η 5 :σ‐η 1 ‐pentafulvene)titanium precursor (Chart 1) [8b]…”

“…Given our recent report of the lithiated aNHO ( Me IPrCH)Li ( Me IPrCH=[(MeCNDipp) 2 C=CH] − ; Dipp=2,6‐ i Pr 2 C 6 H 3 ), and its ability to form main group element complexes by salt metathesis [8a,17] low‐coordinate Group 4 metal complexes supported by anionic N ‐heterocyclic olefins were selected as synthetic targets in this study.…”