Ligand coordination modulates reductive elimination from aluminium(iii)

Abstract

Oxidative addition of inert bonds at low-valent main-group centres is becoming a major class of reactivity for these species. The reverse reaction, reductive elimination, is possible in some cases but far rarer. Here, we present a mechanistic study of reductive elimination from Al(iii) centres and unravel ligand effects in this process. Experimentally determined activation and thermodynamic parameters for the reductive elimination of Cp*H from Cp*2AlH are reported, and this reaction is found to be inhibited by the addition of Lewis bases. We find that C-H oxidative addition at Al(i) centres proceeds by initial protonation at the low-valent centre.

Calcium‐Catalyzed Arene C−H Bond Activation by Low‐Valent AlI

“…[14] Similar,S chnçck-elsC p*Al [15] has been shown to undergo reversible OA/RE with the activated diene C À Hb ond in Cp*H giving Cp* 2 AlH. [16] Similar to this reactivity,C rimmin described cleavage of the activated allylic CÀHb ond in propene by ( DIPP BDI)Al in benzene (80 8 8C, 14 h). [17] Reaction of ad ialumene with PhCCH also resulted in CÀHa ctivation (Sche-me 2c), apart from [2+ +2]-cycloaddition.…”

Calcium‐Catalyzed Arene C−H Bond Activation by Low‐Valent AlI

“…[14] Similar,S chnçk-kelsCp*Al [15] has been shown to undergo reversible OA/RE with the activated diene C À Hb ond in Cp*H giving Cp* 2 AlH. [16] Similar to this reactivity,C rimmin described cleavage of the activated allylic C À Hb ond in propene by ( DIPP BDI)Al in benzene (80 8 8C, 14 h). [17] Reaction of ad ialumene with PhCCH also resulted in CÀHa ctivation (Scheme 2c), apart from [2+ +2]-cycloaddition.…”

The Road Travelled: After Main‐Group Elements as Transition Metals

“…Fischer and co‐workers reported the reductive elimination of Cp*H from Cp*AlH 2 to yield the reactive [Cp*Al] 4 species . Further study by Cowley and co‐workers reported the effect of coordinated ligands on the promotion of this reductive elimination step and found that increasing coordination number and electron density at the Al(III) centre inhibits reductive elimination . In related work, by Braunschweig and co‐workers showed that Lewis bases were capable of mediating the Al(II) to Al(I)/Al(III) disproportionation .…”