Rhodium(I)‐NHC Complexes Bearing Bidentate Bis‐Heteroatomic Acidato Ligands as gem‐Selective Catalysts for Alkyne Dimerization

Abstract

A series of Rh(κ 2 -BHetA)(η 2 -coe)(IPr) complexes bearing 1,3-bis-hetereoatomic acidato ligands (BHetA) including carboxylato (O,O), thioacetato (O,S), amidato (O,N), thioamidato (N,S), and amidinato (N,N), have been prepared by reaction of the dinuclear precursor [Rh(µ-Cl)(IPr)(η 2 -coe)]2 with the corresponding anionic BHetA species. The Rh I -NHC-BHetA compounds catalyze the dimerization of aryl alkynes, showing excellent selectivity for the head-to-tail enynes. Among them, the acetanilidato-based catalyst has shown an outstanding catalytic performance reaching unprecedented TOF levels of 2500 h -1 with complete selectivity for the gem isomer. Investigation of the reaction mechanism supports a non-oxidative pathway in which the BHetA ligand behaves as proton shuttle through intermediate κ 1 -HBHetA species. However, in the presence of pyridine as additive, the identification of the common Rh III H(C≡CPh)2(IPr)(py)2 intermediate gives support for an alternative oxidative route.

Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity

“…In CD [10][11][12]. These data are fully consistentw ith the structuralf ormulations, in agreement with those previously reported for E-4-Me, [20] and supported by elucidation in the solid state by single crystal Xray diffraction (Figures 1a nd 3).…”

“…[5,6] Application of these ligands in transition metal promoted terminal alkyne coupling reactions is of contemporary interest, with examples A-C showcasing the capacity of this ligand class to enforceh igh product selectivity. [7,8,9] Along with advances made employing other ancillary ligands, [10,11] an umber of rhodium pincers have emerged as state of the art catalysts. Mesoionic carbene-based Rh(CNC) complex A,f or instance, is noteworthy for the efficient gem-selective homocoupling of terminal alkynes (1 mol %, 80 8C).…”

“…Reactions of 1-n with HCCAr'. Solid-state structures of gem-3-16, E-5-16 and gem-5-16:thermal ellipsoids drawn at 30 %, 50 %and 50 %p robability,r espectively;anions, solvent molecules, minor disordered components (2 tBu and methylene chain, E-5-16;1 tBu, gem-[5][6][7][8][9][10][11][12][13][14][15][16], and most hydrogen atoms omittedf or clarity.S elected bond lengths ()a nd angles (deg): gem-3-16:Rh1-C2,1 .920(5);C2-C3, 1.212…”

Variation on the π‐Acceptor Ligand within a RhI−N‐Heterocyclic Carbene Framework: Divergent Catalytic Outcomes for Phenylacetylene‐Methanol Transformations

“…The phosphite complex 10 is the most efficient among the catalysts presented in this study. Almost full conversion of phenylacetylene was attained with 98 % selectivity to the gem ‐enyne 15 a (entry 10), although it is not competitive with other Rh−NHC alkyne dimerization catalysts [11h,12c] . Finally, the cyanido trimer 12 also promotes alkyne dimerization but less selectively (entry 12).…”

Preparation of Butadienylpyridines by Iridium‐NHC‐Catalyzed Alkyne Hydroalkenylation and Quinolizine Rearrangement

“…On this background we now report on the synthesis of an Ir‐NHC‐BHetA (BHetA=bis‐heteroatomic acidato) [26] catalysts for the hydroalkenylation of terminal alkynes with 2‐vinylpyridine yielding 2‐(4 R ‐butadienyl)pyridines with exclusive Z , E configuration along with the unprecedented 2‐butadienyl‐5 R ‐pyridines.…”