Reaction Progress Kinetics Analysis of 1,3-Disiloxanediols as Hydrogen-Bonding Catalysts

1,3-Disiloxanediols
are effective hydrogen-bonding catalysts that
exhibit enhanced activity relative to silanediols and triarylsilanols.
The catalytic activity for a series of 1,3-disiloxanediols, including
naphthyl-substituted and unsymmetrical siloxanes, has been quantified
and compared relative to other silanol and thiourea catalysts using
the Friedel Crafts addition of indole to trans-β-nitrostyrene.
An in-depth kinetic study using reaction progress kinetic analysis
(RPKA) has been performed to probe the catalyst behavior of 1,3-disiloxanediols.
The data confirm that the disiloxanediol-catalyzed addition reaction
is first order in catalyst over all concentrations studied with no
evidence of catalyst self-association. 1,3-Disiloxanediols proved
to be robust and recoverable catalysts with no deactivation under
reaction conditions. No product inhibition is observed, and competitive
binding studies with nitro-containing additives suggest that 1,3-disiloxanediols
bind weakly to nitro groups but are strongly activating for catalysis.