Homodinuclear Rare-Earth Metal Complexes as Efficient Precatalysts for the Stereoselective Hydrosilylation of Inactivated Internal Diaryl Alkynes with (Aryl)(vinyl)silanes or Diphenylsilane

Abstract

The hydrosilylation of internal alkynes is an important protocol for the synthesis of trisubstitued alkenyl silanes, which are very useful building blocks in synthetic chemistry and materials science. However, the hydrosilylation of inactivated internal diaryl alkynes with (aryl)(vinyl)silanes or diphenylsilane faces challenges of the lack of active catalyst and difficulty in controlling stereoselectivity. Herein, the bridged pincer homodinuclear rare-earth metal complexes [μ-η²-{κ³_OCO-1-(2-C₄H₇OCH₂)-3-(Ph₂P(O)CH)C₈H₄N}RE(CH₂SiMe₃)]₂ (RE = Lu(1a), Yb(1b), Er(1c), Y(1d), Dy(1e), Gd(1f)), [μ-η²-{κ³_OCO-1-MeOCH₂CH₂-3-(Ph₂P(O)CH)C₈H₄N}RE(CH₂SiMe₃)]₂ (RE = Lu(2a), Y(2b)) and [μ-η²-{κ³_OCN-1-(2-C₅H₄N)-3-(Ph₂P(O)CH)C₈H₄N}RE(CH₂SiMe₃)]₂ (RE = Lu(3a), Yb(3b), Er(3c)) were synthesized. Meanwhile, the pincer mononuclear complexes κ³_OCO-[1-(2-C₄H₇OCH₂)-3-(Ph₂P(O)CH₂)C₈H₄N]Lu(CH₂SiMe₃)₂ (1a'), and κ³_OCO-[1-MeOCH₂CH₂-3- (Ph₂P(O)CH₂)C₈H₄N]Lu(CH₂SiMe₃)₂ (2a') were prepared for comparison of their catalytic activities with the homodinuclear complexes. These homodinuclear complexes displayed high catalytic activity in the hydrosilylation of inactivated internal diaryl alkynes with RSiH₃ (R = C₆H₅-, 4-CH₃C₆H₄-, C₈H₁₇-, C₆H₁₃-), (aryl)(vinyl)silanes and diphenylsilane, affording the vinylsilane products in moderate to high yields with excellent stereoselectivity. Among the complexes surveyed, the homodinuclear complex 1d exhibited the highest activity. Moreover, the bis-hydrosilylation of two different internal alkynes with RSiH₃ was also developed. Control experiments evidence supports that the synergistic interaction between the bimetallic centers in these complexes played a crucial role in their high efficiency demonstrated in the reaction.

Keywords

Indolyl-based pincer ligand / Rare-earth metal / Hydrosilylation / Internal alkynes / Catalysis / (Aryl)(vinyl)silanes / Stereoselectivity / Hydride

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