Reaction of an N/Al FLP-based aluminum hydride toward alkynes: deprotonated alumination versus hydroalumination with regioselective cis-addition character

Abstract

Reactions of an N/Al FLP-based aluminum dihydride (o-TMP-C₆H₄)AlH₂ (1, TMP = N(CMe₂CH₂)₂CH₂) with several terminal and internal alkynes were studied. 1 reacted with HCCR by deprotonated alumination to yield (o-TMP-C₆H₄)Al(CCR)₂ (R = Ph (2), 1-C₄H₃S (3)) and with HCCPPh₂ by deprotonated alumination followed by HCCPPh₂ C(sp)–H-activation addition to yield [o-(TMP)H-C₆H₄]Al(CCPPh₂)₃ (4). Furthermore, 1 reacted with R¹CCR² to produce mono-hydroalumination compounds (o-TMP-C₆H₄)AlH(CR¹CHR²) (R¹,R² = Ph,Ph (5), Ph,Et (6) and SiHMeR′,Ph (7, R′ = N(SiMe₂Ph)-2,6-iPr₂C₆H₃), all as monomers, as well as {(o-TMP-C₆H₄)AlH[C(PPh₂)CHPh]}₂ (8), a dimer formed due to the intermolecular P/Al donor–acceptor interaction. Moreover, bis-hydroalumination compounds (o-TMP-C₆H₄)Al(CR¹CHR²)₂ (R¹,R² = SiHMe₂,PPh₂ (9) and SiHPh₂,PPh₂ (10)) were produced. Natural Bond Orbital (NBO) analysis was performed, which revealed the inequivalent charge distribution on the CC carbon atoms of the alkynes that have two different substituents. The electronic matching interaction between the Al–H and CC bonds is discussed. The hydroalumination reaction exhibits the regioselective cis-addition character.