F-Block N-Heterocyclic Carbene Complexes

Abstract

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Reactivity and Properties of Metal Complexes Enabled by Flexible and Redox-Active Ligands with a Ferrocene Backbone

“…When a strong Lewis donor such as THF is coordinated to scandium, the Fe-Sc distance is long indicating a minimal interaction; when no such donors are present, like in the case of [(NN TBS )Sc(-Cl)] 2 , a rather short Fe-Sc distance was observed suggesting the presence of a significant donor-acceptor type interaction. 81 2 and the long distance close to that of (NN TBS )ScMe(THF) 2 . 44 Despite the fact that the Fe-Sc bond energy is estimated to be less than 10 kcal/mol and is much weaker than a typical chemical bond, the relatively large change in the Fe-Sc distance has a huge impact on the geometry of metal complexes, especially on the shielding effect of the ferrocene backbone.…”

“…H 2 (phosfen) could be readily synthesized from fc(N 3 ) and a substituted phosphine. The cyclic voltammetry of H 2 (phosfen) and the corresponding Y(III) and Ce(IV) complexes (phosfen)Y(OtBu) and (phosfen)Ce(OtBu) 2 showed a reversible redox event at a more negative potential compared to the corresponding salfen analogues. 59 Therefore, we achieved control of lactide polymerization by chemically oxidizing or reducing the catalyst at a remote site of catalysis, the ferrocene backbone of the phosfen ligand (Figure 2).…”

“…43,59,78 (NN fc ): Initially, we sought out to employ salt metathesis between K 2 (NN fc ) and MX 3 (THF) y (M = rare-earth metal, X = Cl or Br, y = 3-4) and found that the reaction was poorly reproducible and usually accompanied by a side product, the bis-ligand-adduct K[(NN fc ) 2 M], which was difficult to remove. 81 At the same time, we and other groups independently published protocols to prepare key metal benzyl synthetic intermediates, M(CH 2 Ar) 3 (M = Sc, Y, La, and Lu, Ar = Ph, 3,5-C 6 H 3 Me 2 ), from MX 3 (X = Cl, Br), [95][96][97][98] which, in turn were obtained directly from metal oxides.…”

“…44 Reacting (NN TBS )ScI(THF) 2 and KC 8 in benzene resulted in the equimolar formation of a scandium hydride [(NN TBS )Sc(-H)] 2 and a scandium phenyl (NN TBS )ScPh(THF) product. A mechanistic study was consistent with a proposed benzene dianionic intermediate (Figure 1).…”

“…Noticeable examples include N-heterocyclic carbenes with a tethered anionic anchor (Chart 1a) 1,2 and XP 3 type (X = B or N) triphosphine ligands with an additional donor X in the backbone (Chart 1b). 3,4 When the former coordinate to electropositive metals, the N-heterocyclic carbene acts as a labile donor that can readily dissociate.…”