The Scope of Ambiphilic Acetate‐Assisted Cyclometallation with Half‐Sandwich Complexes of Iridium, Rhodium and Ruthenium

Abstract

C−−H activation by acetate-assisted cyclometallation of a phenyl group with half-sandwich complexes [{MCl(2)Cp*}(2)] (M=Ir, Rh) and [{RuCl(2)-(p-cymene)}(2)] can be directed by a wide range of nitrogen donor ligands including pyrazole, oxazoline, oxime, imidazole and triazole, and X-ray structures of a number of complexes are reported. All the ligands tested cyclometallated at iridium, however ruthenium and rhodium fail to cause cyclometallation in some cases. As a result, the nitrogen donors have been categorised based on their reactivity with the three metals used. The relevance of these cyclometallation reactions to catalytic synthesis of carbocycles and heterocycles is discussed.

Enantiopure Ferrocene‐Based Planar‐Chiral Iridacycles: Stereospecific Control of Iridium‐Centred Chirality

“…Two methods are generally employed for the synthesis of half‐sandwich iridacycles from [IrCp*Cl 2 ] 2 by C−H activation. Neutral chloride‐coordinated complexes 1 a are obtained with NaOAc, with ligand exchange generating an iridium‐coordinated acetate which participates in a concerted metallation‐deprotonation (CMD) pathway (method 1) . Alternatively, addition of NaOH and KPF 6 in MeCN results in the formation of cationic complexes 1 b , with evidence from related reactions pointing again to a CMD pathway via an iridium‐coordinated hydroxide intermediate (method 2)…”

“…The formation solely of ( R p *, S Ir *)‐ 8 a and ( S p , R Ir )‐ 10 (and by extension ( R p , S Ir )‐ 14 a / b ) on cycloiridation may also be explained, in part, by the intermediacy of a cationic coordinatively unsaturated complex of general structure 19 . The proposal that acetate‐promoted cycloiridation (method 1) proceeds through the initial formation of an iridium‐coordinated acetic acid complex, followed by ligand exchange, requires the intermediacy of cation 19 for the complexes synthesised in this work (Scheme ). A similar water or t BuOH‐coordinated intermediate likely results from the use as base of hydroxide or tert ‐butoxide, respectively.…”

Autocatalytic Intermolecular versus Intramolecular Deprotonation in CH Bond Activation of Functionalized Arenes by Ruthenium(II) or Palladium(II) Complexes

“…They were identified in the 1 H NMR spectra performed with time by comparison with authentic samples; non‐reported complexes that have been independently synthesized and fully characterized (the Supporting Information, Figures S1–S6). Complex A 2 was synthesized by treating the related reported complex containing a RuCl bond ( D 2 )5l by AgOAc in CH 2 Cl 2 (see the Supporting Information). Complexes B 2 + and C 2 + were synthesized with PF 6 − as the counteranion, by using the same procedure as for the 2‐phenylpyridine derivatives8 B 1 + and C 1 + (see the Supporting Information).…”

Variable coordination of amine functionalised N-heterocyclic carbene ligands to Ru, Rh and Ir: C–H and N–H activation and catalytic transfer hydrogenation

“…As has been observed in other studies, it was clear that the cyclometallation reaction proceeded much faster and more efficiently for Ir than Rh. 35,36 Using NaO t Bu as the base in place of NaOAc gave an intractable mixture of products, with no evidence for the formation of 4. However, unlike with Rh the reaction did proceed with Ag 2 O as the base, but the reaction was much slower.…”