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(R 2 PCH 2 CH 2 PR 2 )(η 2 η 2 -NBA)][BAr F 4 ] (R = Cy, t Bu; NBA = norbornane; Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ) are prepared by hydrogenation of a norbornadiene precursor. For the t Busubstituted 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, 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(Cy 2 PCH 2 CH 2 PCy 2 )(butadiene)][BAr F 4 ], which can be reactivated by simple addition of H 2 . While the equivalent butadiene complex does not form with R = t Bu 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 t Bu system and are more leveled for Cy.

Rhodium-alkene complexes of the pincer ligand κ 3 -C 5 H 3 N-2,6-(OP i Pr 2 ) 2 (PONOP- i Pr) have been prepared and structurally characterized: [Rh(PONOP- i Pr)(η 2 -alkene)][BAr F 4 ] [alkene = cyclooctadiene (COD), norbornadiene (NBD), ethene; Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ]. Only one of these, alkene = COD, undergoes a reaction with H 2 (1 bar), to form [Rh(PONOP- i Pr)(η 2 -COE)][BAr F 4 ] (COE = cyclooctene), while the others show no significant reactivity. This COE complex does not undergo further hydrogenation. This difference in reactivity between COD and the other alkenes is proposed to be due to intramolecular alkene-assisted reductive elimination in the COD complex, in which the η 2 -bound diene can engage in bonding with its additional alkene unit. H/D exchange experiments on the ethene complex show that reductive elimination from a reversibly formed alkyl hydride intermediate is likely rate-limiting and with a high barrier. The proposed final product of alkene hydrogenation would be the dihydrogen complex [Rh(PONOP- i Pr)(η 2 -H 2 )][BAr F 4 ], which has been independently synthesized and undergoes exchange with free H 2 on the NMR time scale, as well as with D 2 to form free HD. When the H 2 addition to [Rh(PONOP- i Pr)(η 2 -ethene)][BAr F 4 ] is interrogated using p H 2 at higher pressure (3 bar), this produces the dihydrogen complex as a transient product, for which enhancements in the 1 H NMR signal for the bound H 2 ligand, as well as that for free H 2 , are observed. This is a unique example of the partially negative line-shape effect, with the enhanced signals that are observed for the dihydrogen complex being explained by the exchange processes already noted.