Solid–State Molecular Organometallic Catalysis in Gas/Solid Flow (Flow-SMOM) as Demonstrated by Efficient Room Temperature and Pressure 1‑Butene Isomerization

The
use of solid–state molecular organometallic chemistry
(SMOM–chem) to promote the efficient double bond isomerization
of 1-butene to 2-butenes under flow–reactor conditions is reported.
Single crystalline catalysts based upon the σ-alkane complexes
[Rh­(R2PCH2CH2PR2)­(η2η2-NBA)]­[BArF4] (R
= Cy, tBu; NBA = norbornane; ArF = 3,5-(CF3)2C6H3) are prepared by hydrogenation
of a norbornadiene precursor. For the tBu-substituted system
this results in the loss of long-range order, which can be re-established
by addition of 1-butene to the material to form a mixture of [Rh­(tBu2PCH2CH2PtBu2)­(cis-2-butene)]­[BArF4] and [Rh­(tBu2PCH2CH2PtBu2)­(1-butene)]­[BArF4], in an order/disorder/order phase change. Deployment under flow-reactor
conditions results in very different on-stream stabilities. With R
= Cy rapid deactivation (3 h) to the butadiene complex occurs, [Rh­(Cy2PCH2CH2PCy2)­(butadiene)]­[BArF4], which can be reactivated by simple addition
of H2. While the equivalent butadiene complex does not
form with R = tBu at 298 K and on-stream conversion
is retained up to 90 h, deactivation is suggested to occur via loss
of crystallinity of the SMOM catalyst. Both systems operate under
the industrially relevant conditions of an isobutene co-feed. cis:trans
selectivites for 2-butene are biased in favor of cis for the tBu system and are more leveled for Cy.