Rhodium-catalysed direct hydroarylation of alkenes and alkynes with phosphines through phosphorous-assisted C-H activation

Abstract

Biarylphosphines have been widely applied as ligands in various synthetic methods, especially in transition-metal-catalysed carbon-carbon and carbon-heteroatom bond cross-coupling reactions. Based on the outstanding properties of the parent scaffolds, a general method for in situ modification of the commercial tertiary phosphine ligands to access a series of ligands is in high demand. Here we show that a rhodium-catalysed system is introduced for the hydroarylation of alkenes and alkynes with tertiary phosphines through P(III)-chelation assisted C-H activation. A series of ligand libraries containing alkyl and alkenyl substituted groups with different steric and electronic properties are obtained in high yields. Furthermore, several experimental studies are performed to uncover the key mechanistic features of the linear-selective hydroarylation of alkenes and branch-selective hydroarylation of alkynes.

Fig. 1

Towards a catalytic process for hydroarylation of alkenes and alkynes with diarylphosphines through P(III)-chelation-assisted C−H activation. a O-Chelation-assisted hydroarylation. b N-Chelation-assisted hydroarylation. c Precedent studies on P-chelated transition metal-olefin complexes. d Transition-metal-catalysed C–H borylation and arylation of diarylphosphines. e Rh-catalysed P(III)-chelation-assisted hydroarylation of alkenes and alkynes with diarylphosphines

Fig. 2

Rhodium-catalysed direct hydroarylation of alkenes with phosphines. Reaction conditions: 2.5 mol% [Rh(cod)Cl]₂, 1 (0.20 mmol), 2 (0.20 mmol), NaHCO₃ (0.60 mmol) in 1 mL toluene, at 140 °C, 3–4 h, under argon. All reported yields are isolated yields. ^aUsing 2 (0.60 mmol) at 150 °C for 24 h. ^b5 mol% [Rh(coe)₂Cl]₂, 1 (0.20 mmol), 2 (0.60 mmol), K₂CO₃ (0.60 mmol) in 1 mL toluene, at 150 °C, 24 h, under argon. ^cUsing 5 mol% [Rh(cod)Cl]₂, 2 (0.60 mmol) at 150 °C for 24 h

Fig. 3

Rhodium-catalysed direct hydroarylation of alkynes with phosphines. Reaction conditions: 2.5 mol% [Rh(cod)Cl]₂, 1 (0.20 mmol), 4 (0.40 mmol) in 0.5 mL toluene, at 120 °C, 12 h, under argon. All reported yields are isolated yields. ^aUsing 1 (0.20 mmol), 4 (0.60 mmol)

Fig. 4

Further investigations. a Rh-catalysed di-selective hydroarylation of alkenes with phosphines. b Rh-catalysed anti-Markovnikov hydroxylation of alkyne 6 with phosphine 1a

Fig. 5

Testing the developed binaphthyl-based chiral phosphine ligands. a Rh-catalysed C–H alkylation of with (R)-H-MOP (8). b Rh-catalysed asymmetric addition of arylboronic acids to isatins

Fig. 6

Mechanistic studies experiments. Investigation of the reaction intermediates by X-ray analysis, ³¹P NMR spectroscopy and HRMS

Fig. 7

Deuterium labelling experiments. a Deuteration experiments of D-1a with alkene 2a and alkyne 4a. b The kinetic isotope effects of C–H alkylation and alkenylation

Fig. 8

Proposed mechanism. A tentative reaction mechanism involves coordination of Rh species with P atom, C–H activation, insertion of alkenes and alkynes to form the desired products