Selecting Double Bond Positions with a Single Cation- Responsive Iridium Olefin Isomerization Catalyst

Abstract

<div><div><div><p>The catalytic transposition of double bonds holds promise as an ideal route to alkenes with value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst is developed for the selective production of either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on non-covalent modifications.</p></div></div></div>

Reactivity of Iridium Complexes of a Triphosphorus-Pincer Ligand Based on a Secondary Phosphine. Catalytic Alkane Dehydrogenation and the Origin of Extremely High Activity

“…Crystals were obtained through slow evaporation of benzene, and the molecular structure was determined by single-crystal XRD (Figure 2). (14); C1-P1-Ir1, 107.66 (10); C7-P1-Ir1, 109.62 (10) Stoichiometric Reactions of ( tBu P H PP)Ir and ( tBu PPP)Ir Complexes: Experimental Studies. A toluene-d8 solution of ( tBu P H PP)IrH3 was heated at 80 °C under 1 atm ethylene for 15 min, leading the straw-yellow solution to turn dark green.…”

“…Numerous examples of pincer ligands engaging in novel catalytic and stoichiometric MLC-related reactions have been and continue to be reported. [1][2][3][4][5][6][7][8][9][10][11][12] Yet despite the large number of pincer ligands for which MLC is based on a coordinating N atom, [13][14][15][16][17][18][19] there are very few examples involving the next congener, phosphorus. In particular, in spite of the great value that has been proven for addition of H2 across M-N bonds, there are relatively few examples of H2 addition across a phosphorus metal bond, [20][21][22][23][24][25] and even fewer examples of the reverse, elimination of H2.…”

“…Thermal ellipsoids are shown at 50% probability. Selected distances (Å) and angles (°): P1-Ir1, 2.2311(8); P2-Ir1, 2.2786(9); P3-Ir1, 2.2880(9); P1-Ir1-P3, 84.78(3); P1-Ir1-P2, 85.28(3); P2-Ir1-P3, 167.79(3); C1-P1-C7, 113.39(14); C1-P1-Ir1, 107.66(10); C7-P1-Ir1, 109.62(10)…”

Controlled selectivity through reversible inhibition of the catalyst: Stereodivergent semihydrogenation of alkynes

“…2), 3-2t was obtained selectively after 48 h, following C=C bond shift to the 3-position (92% yield, > 20:1 of 3-2t/2-2t). 71 Interestingly, NACET was found to be too poisonous to allow for efficient isomerization in this case, but the addition of a catalytic amount of HexNH2 to Ru-1 enabled it to selectively catalyze the isomerization of the C=C bond to the 2-position, affording product 2-2t in 89% yield (> 20:1 of 2-2t/3-2t).…”

Secondary Phosphine Oxide-Activated Nickel Catalysts for Site-Selective Alkene Isomerization and Remote Hydrophosphination

“…regioisomeric alkene mixtures) 1,5-8 to be employed, and unlock new reactivity modes through formal (sp 3 )CH functionalization at typically less-activated sites 9 . Methodologies using catalyst systems derived from noble metals (e.g., Pd, Ir) [10][11][12][13][14][15][16] and base metals (e.g., Ni, Fe) [17][18][19][20][21][22][23][24] have been conceived for alkene isomerization over the years. Nonprecious nickel catalysis represents an attractive platform for reaction development.…”