Ligand-Controlled Regiodivergent Hydrosilylation of Conjugated Dienes Catalyzed by Mono(phosphine)palladium(0) Complexes

Abstract

Mono­(phosphine)­palladium­(0) complexes, [Pd­(η2:η2-C6H10O)­(PR3)] (1), catalyze hydrosilylation of electron-deficient conjugated dienes with HSiPh3. Hydrosilylation of methyl penta-2,4-dienoate with HSiPh3 catalyzed by [Pd­(η2:η2-C6H10O)­(PR3)] (R = Me (1a), Et (1b), OEt (1d), O i Pr (1e)) proceeds to give the 1,2-E product in quantitative yield with exclusive Markovnikov selectivity. In contrast, their triphenylphosphine and -phosphite analogues, [Pd­(η2:η2-C6H10O)­(PR3)] (R = Ph (1f), OPh (1g)), mainly produce the 1,4-Z product (1,2-E/1,4-Z = 3/7). The regioselectivity in the hydrosilylation of methyl 2,4-pentadienoate is also controlled by organosilanes. Mechanistic studies suggest that the reaction using a compact and basic mono-phosphorus complex proceeds by the Chalk–Harrod mechanism involving the reductive elimination from an (η3-allyl)­(silyl)­palladium­(II). A poor electron-donating mono-phosphorus ligand such as P­(OPh)3 destabilizes a Pd­(II) species and promotes direct reductive elimination to give the 1,4-Z product. On the other hand, a compact and electron-donating phosphorus ligand, such as PMe3, PEt3, and P­(OMe)3, favors to give the more stable (η3-allyl)­(silyl)­palladium­(II) intermediate by the allyl rotation, followed by reductive elimination to give the 1,2-E product.

Recent Advances in Ligand-Controlled Regio- or Stereodivergent Transition-Metal-Catalyzed Hydroelementation (H[E]) (E = H, B, Si, Ge) of C–C Unsaturated Systems

“…In terms of reducing agent, hydrosilanes 70 as one of the cheapest and tunable hydride reagents are effective for the regiodivergent hydrosilylation reactions of (conjugated) alkenes and (conjugated) alkynes, 33,37,42,54,59 while HBpin as an alternative to hydrosilanes is viable for the regiodivergent hydroboration reactions of (conjugated) alkenes, (conjugated) alkynes, and allenes and for the stereodivergent allene hydroboration. 30,53,61,[65][66] It is interesting that formic acid is shown to work as a surrogate of H2 for regiodivergent semi-hydrogenation of allenamides.…”

Palladium‐Catalyzed Hydrosilylation of Unactivated Alkenes and Conjugated Dienes with Tertiary Silanes Controlled by Hemilabile Hybrid P,O Ligand

“…Fe, Co, Cu, and NaHBEt 3 catalysts tend to result in 1,2‐hydrosilylation, [7] while Pt, Fe, and Co catalysts lead to 2,1‐hydrosilylation [8] . While diene hydrosilylation has traditionally been restricted to primary and secondary silanes, the Komine group has demonstrated a Pd‐catalyzed reaction for the 1,4‐hydrosilylation of conjugated diene with tertiary silanes [9] . Despite this advancement, the use of commercially relevant tertiary silanes in 1,2‐hydrosilylation of conjugated diene remains quite limited [10] .…”

“…[8] While diene hydrosilylation has traditionally been restricted to primary and secondary silanes, the Komine group has demonstrated a Pd-catalyzed reaction for the 1,4-hydrosilylation of conjugated diene with tertiary silanes. [9] Despite this advancement, the use of commercially relevant tertiary silanes in 1,2-hydrosilylation of conjugated diene remains quite limited. [10] Herein, a novel hemilabile P,O ligand was employed in conjunction with Pd catalysts, resulting in enhanced reactivity in the hydrosilylation of alkenes with tertiary silanes and unprecedented selectivity in the Pd-catalyzed hydrosilylation of dienes.…”

Hydrosilylation of Carbonyl Compounds Catalyzed by Iridium(I) Complexes with (−)‐Menthol‐Based Phosphorus(III) Ligands

“…Complexes bearing phosphorus(III) ligands have played a crucial role in various reactions as catalytic systems, with emphasis on the reduction of carbonyl compounds. [29][30][31][32][33][34][35][36][37] This includes phosphine -PH x R 3-x , [28][29][30][31][32][33][34][35][36][37][38][39][40] phosphite -P(OR) 3 , [41][42][43] phosphonite -P(OR) 2 R', [44][45][46] and phosphinite -P(OR)R' 2 [42,[47][48][49] ligands. Among numerous examples of phosphorous-based ligands, especially attractive are ligands with naturally occurring moieties due to their abundance in biomass, providing lower synthesis costs, high activity, and a wide range of chiral substances of natural origin, such as menthol.…”