12097-36-8

Upstream product

• 73456-63-0 [(CH₂CHCHCH₂)2RhO]2 
• 127-08-2 potassium acetate 
• 12092-47-6 di-μ-chloro-bis(1,5-cyclooctadiene)dirhodium 
• 115338-66-4 rhodium{C₆H₃(CH₂NMe₂)2-o,o'}(1,5-cyclooctadiene) 

Relevant academic research and scientific papers

Rh(I)-bisphosphine-catalyzed asymmetric, intermolecular hydroheteroarylation of α-substituted acrylate derivatives

Asymmetric hydroheteroarylation of alkenes represents a convenient entry to elaborated heterocyclic motifs. While chiral acids are known to mediate asymmetric addition of electron-rich heteroarenes to Michael acceptors, very few methods exploit transition metals to catalyze alkylation of heterocycles with olefins via a C-H activation, migratory insertion sequence. Herein, we describe the development of an asymmetric, intermolecular hydroheteroarylation reaction of α-substituted acrylates with benzoxazoles. The reaction provides 2-substitued benzoxazoles in moderate to excellent yields and good to excellent enantioselectivities. Notably, a series of mechanistic studies appears to contradict a pathway involving enantioselective protonation of a Rh(I)-enolate, despite the fact that such a mechanism is invoked almost unanimously in the related addition of aryl boronic acids to methacrylate derivatives. Evidence suggests instead that migratory insertion or beta-hydride elimination is enantiodetermining and that isomerization of a Rh(I)-enolate to a Rh(I)-heterobenzyl species insulates the resultant α-stereocenter from epimerization. A bulky ligand, CTH-(R)-Xylyl-P-Phos, is crucial for reactivity and enantioselectivity, as it likely discourages undesired ligation of benzoxazole substrates or intermediates to on- or off-cycle rhodium complexes and attenuates coordination-promoted product epimerization.

Direct in situ synthesis of cationic N-heterocyclic carbene iridium and rhodium complexes from neat ionic liquid: Application in catalytic dehydrogenation of cyclooctadiene

A direct synthetic route to cationic N-heterocyclic carbene (NHC) complexes of rhodium and iridium from neat dialkyl-imidazolium ionic liquids (ILs) has been found. The method uses complexes bearing basic anionic ligands, [M(COD)(PPh3)X], X = OEt, MeCO2, which react with the inactivated imidazolium cation in the absence of external bases yielding one M-NHC moiety and the free protonated base. This new one-pot synthesis leaving pure, catalytically active IL solutions is faster, cleaner and more efficient than traditional syntheses of such NHC complexes. The observed reactivity also gives insight into NHC incorporation of rhodium and iridium catalyzed reactions performed in common dialkyl-imidazolium ILs. The complexes synthesised in this manner are compared with their bis-phosphine analogues in terms of activity for catalytic dehydrogenation of 1,5-cyclooctadiene and 1,3-cyclooctadiene in neat [BMIM][NTf2] as solvent. Even at high temperature, no ligand exchange reaction is observed with [(COD)M(PPh3)2] [NTf2] catalysts. As expected, the yields of all the reactions were low, iridium was much more active in C-H activation than rhodium and the NHC ligands were more stable than triphenylphosphine. For all catalysts, the isomerisation of 1,5-cyclooctadiene is the major reaction. However, the phosphine-NHC complex of iridium seems to be more selective for dehydrogenation than its bis-phosphine counterpart, which is more active in transfer-hydrogenation and less stable under the applied conditions. Different reaction conditions were tried in order to optimise selectivity for dehydrogenation over isomerisation and transfer-hydrogenation. Surprisingly, with 1,3-cyclooctadiene as substrate selectivity for dehydrogenation is much higher than with 1,5-cyclooctadiene for all catalysts.

Ortho-chelated arylrhodium(I) complexes. X-ray structure of RhI[C6H3(CH2NMe2) 2-o,o′-C,N ](COD)

The reaction of Lin[C6H3(CH2NMe 2)-o-R-o′]n with [RhCl(diene)]2 yields the ortho-chelated arylrhodium(I) complexes Rh[C6H3(CH2NMe 2)-o-R-o′](diene) (R = CH2NMe2, diene = COD (1a) or NBD (1b); diene = COD, R = Me (2) or H (3)). The solid-state structure of 1a was determined by a single-crystal X-ray diffraction study. C20H31N2Rh: triclinic, space group P1, with lattice parameters a = 10.169 (1) ?, b = 13.036 (1) ?, c = 14.688 (2) ?, α = 79.54 (1)°, β = 77.04 (1)°, γ = 79.53°; V = 1845.6 (4) ?3, Z = 4; D(calcd) = 1.448 g cm-3. Refinement with 4696 observed reflections converged at R = 0.0395. The structure of 1a consists of a rhodium(I) center that has a square-planar coordination comprising the two double bonds of COD and a C atom and one of the N atoms of the monoanionic aryl ligand. In solution compounds 1 and 2 exhibit dynamic behavior which involves a reversible dissociation of the Rh-N bond and rotation of the aryl moiety around Rh-C. This process, which generates a highly unsaturated T-shaped 14 electron species, is accompanied by the relief of steric repulsions within the complex. Complex 1 reacts with a range of electrophilic reagents leading to Rh-C bond breakage (HX, X = acac, Cl, Br, OAc, OH, OMe, L-alanyl; MXnLm, SnMe2Br2, NiBr2(PBu3)2, ZrCl4, PdCl2(NCPh)2, HgCl2, PtBr2(COD), and [IrCl(COD)]2). A redox reaction of 1 with AgX (X = OAc, NO3) leads to the formation of RhIIIX2[C6H3(CH2NMe 2)2-o,o′](H2O).