Efficient and stable tripodal Phosphine-Controlled Pd-Catalyst for anti-Markovnikov hydroaminocarbonylation of alkenes with aromatic amines

Abstract

The tripodal phosphine [L1, 1,1,1-tris(diphenylphosphino-methyl)ethane] was applied to control the activity, regioselectivity, and stability of the involved Pd-catalyst in anti-Markovnikov hydroaminocarbonylation of alkenes with aromatic amines for the synthesis of linear-amides. Due to the unique characters of L1 in terms of the steric bulkiness, the switching-coordination mode from tripodal phosphine to bidental one, and the robustness against moisture and oxygen, L1 conferred to Pd-catalyst with the high activity, good regioselectivity, and excellent stability for this carbonylation, leading to 44 ∼ 87 % yields of the target amides with L/B of greater than 80/20. The in situ high-pressure FT-IR analysis and the DFT calculations verified that L1 not only promoted the formation and stability of PdII-H active species (ν ca. 1932 cm−1) but also facilitated the anti-Markovnikov’s addition of alkenes with PdII-H bond due to the favorable energy level of linear intermediate (B-1). In addition, since L1 can coordinate to Pd(II)-center as a bidental chelator as fulfill catalysis and then coordinate to Pd(0)-center as an tripodal pincer, Pd-catalyst was protected timely by L1 against metal-deposition (Pd0-black precipitation) to guarantee its stability for recycling uses for 5 runs without activity loss.