Controlling Structure and Reactivity in Cationic Solid-State Molecular Organometallic Systems Using Anion Templating

The role that the supporting anion has on the stability, structure, and catalytic performance, in solid-state molecular organometallic systems (SMOM) based upon [Rh-(Cy2PCH2CH2PCy2)(eta(2)eta(2)-NBD)][BAr4X], [1-NBD] [BAr4X], is reported (X = Cl, F, H; NBD = norbornadiene). The tetra-aryl borate anion is systematically varied at the 3,5-position, Ar-X = 3,5-X2C6H3, and the stability and structure in the solid-state compared with the previously reported [1-NBD][BAr4CF3] complex. Single-crystal X-ray crystallography shows that the three complexes have different packing motifs, in which the cation sits on the shared face of two parallelepipeds for [1-NBD] [BAr4Cl], is surrounded by eight anions in a gyrobifastigium arrangement for [1-NBD][BAr4F], or the six anions show an octahedral cage arrangement in [1-NBD][BAr4H], similar to that of [1-NBD][BAr4CF3]. C-X center dot center dot center dot X-C contacts, commonly encountered in crystal-engineering, are suggested to be important in determining structure. Addition of H 2 in a solid/gas reaction affords the resulting 6-alkane complexes, [Rh- (Cy2PCH2CH2PCy2)(eta(2)eta(2)-NBD)][BAr4X], [1-NBD] [BAr4X] (NBA = norbornane), which can then proceed to lose the alkane and form the zwitterionic, anion-coordinated, complexes. The relative rates at which hydrogenation and then decomposition of sigma-alkane complexes proceed are shown to be anion dependent. [BAr4CF3](-) promotes fast hydrogenation and an indefinitely stable sigma-alkane complex. With [BAr4H](-) hydrogenation is slow and the sigma-alkane complex so unstable it is not observed. [BAr4Cl](-) and [BAr4F](-) promote intermediate reactivity profiles, and for [BAr4Cl] , a single-crystal to single-crystal hydrogenation results in [1-NBA] [BAr4Cl]. The molecular structure derived from X-ray diffraction reveals a sigma- alkane complex in which the NBA fragment is bound through two exo interactions-different from the endo selective binding observed with [1-NBA][BAr4CF3]. Periodic DFT calculations demonstrate that this selectivity is driven by the microenvironment dictated by the surrounding anions. [1-NBA] [BAr4X] are catalysts for gas/solid 1-butene isomerization (298 K, 1 atm), and their activity can be directly correlated to the stability of the sigma-alkane complex compared to the anion-coordinated decomposition products.