Synthesis of and Structural Insights into Contact Ion Pair and Solvent-Separated Ion Pair Diphenyliridate Complexes

Abstract

Lithium diphenyliridate complexes bearing cycloocta-1,5-diene (COD) as a ligand were synthesized by treating [IrCl(cod)] 2 with phenyllithium and subsequent recrystallization. Xray crystallographic analysis of the complexes showed both contact ion pair and solvent-separated ion pair structures depending on the coordination environment around the Li cation. Natural bond orbital analysis revealed that the anionic charge formally described on Ir efficiently delocalizes to not only the phenyl moieties but also the COD ligand. This result contrasts to the rhodium-analogues, where the anionic charge is more localized at the metal center, suggesting stronger π-back-donation from Ir to ligands than that of Rh.

Mechanistic Insight into Rh-Catalyzed C(sp2)–O Bond Cleavage Applied to Cross-Coupling Reaction of Benzofurans with Aryl Grignard Reagents

“…From [RhCl­(cod)] 2 , the anionic rhodate complex A , [MgBr­(thf) n ]­[RhAr 2 (cod)], is initially formed by the reaction of two molecules of ArMgBr 11 with the Rh precatalyst. Although rhodate A was identified by spectroscopic analyses in our previous report, , it is not the actual catalytically active species. Equilibrium between the COD-ligated rhodate A and rhodates possessing two monodentate olefin ligands (substrate 10 or product 12 ) exists, and the latter, trans -geometry B , is the actual intermediate, in which the Mg cation of rhodate B coordinates to the ethereal oxygen in the coordinating substrate 10 .…”

“…Preliminary mechanistic studies suggested that these reactions were promoted by an anionic diarylrhodium “rhodate” complex but not by neutral arylrhodium intermediates (ArRh) . Stoichiometric and catalytic reactions using isolated diarylrhodate 4 afforded the coupling product, suggesting the intermediacy of diarylrhodate as the catalytically active species. ,, These so-called “ate” complexes are known to exhibit characteristic reactivities and have been proposed as active species in the cleavage of unreactive chemical bonds, including C–O bonds. ,,,,,, Since mechanistic studies of ate-complex-catalyzed C–O bond cleavage reactions are exceedingly rare, mechanistic insights into this reaction can provide useful information for the development of new synthetic methods.…”

Lithium Hexaphenylrhodate(III) and -Iridate(III): Structure in the Solid State and in Solution

“…The difficulty in producing hexaaryl d 6 metal complexes is partly due to the shorter covalent radii of d 6 late transition metals compared with those of d 0 and d 3 metals ( vide infra ) . The key to the successful synthesis of the novel hexaaryl d 6 metal complexes is stabilization of the Rh 3– and Ir 3– centers by the interaction of the Ir–C σ-bond and the π-bonding electrons of the phenyl moieties , with Li cations. This interaction delocalizes the negative formal charge on the anionic Rh and Ir centers to the two Li cations to stabilize the higher anionic state.…”

Nature of the Short Rh–Li Contact between Lithium and the Rhodium ω-Alkenyl Complex [Rh(CH2CMe2CH2CH═CH2)2]−

“…12,44 Despite this variety in the description of the M−M interaction, modern computational studies generally suggest that the interactions between Li or Mg and late transition metals are predominantly ionic and that covalent (dative) interactions play a minor role at best. 37,43,52,53,58 Rhodium forms a variety of heterobimetallic complexes with main-group metals, 59−61 transition metals, 62 and f-block elements. 63 Of these, one complex is known, [Li(TMEDA)]-[(COD)Rh(CH 2 SiMe 3 ) 2 ], 31 in which the Li−Rh distance is shorter than the 2.70 Å sum of the covalent radii of lithium (1.28 Å) and rhodium (1.42 Å).…”

“…Several dozen compounds are known that exhibit relatively short M–M distances between a group 8 transition metal and a Li − ,− or a Mg − center. In some of these compounds, the two metal centers are best described as noninteracting and are held in close proximity by electron-rich anionic ligands. ,, In other compounds, the M–M interaction has been described in a variety of ways: ion pairing, ,, dative bonding (coordinate bonding), p–d π bonding, and three-center bonding mediated by an anionic ligand. ,, In a few cases, covalent interactions have been suggested. , Despite this variety in the description of the M–M interaction, modern computational studies generally suggest that the interactions between Li or Mg and late transition metals are predominantly ionic and that covalent (dative) interactions play a minor role at best. ,,,, …”