Stoichiometric and Catalytic Solid–Gas Reactivity of Rhodium Bis-phosphine Complexes

Abstract

The complexes [Rh( i Bu 2 PCH 2 CH 2 P i Bu 2 )L 2 ][BAr F 4 ] [L 2 = C 4 H 6 , (C 2 H 4 ) 2 , (CO) 2 , (NH 3 ) 2 ; Ar F = 3,5-C 6 H 3 (CF 3 ) 2 ] have been synthesized by solid−gas reactivity via ligand exchange reactions with, in some cases, crystallinity retained through single-crystal to single-crystal transformations. The solid-state structures of these complexes have been determined, but in only one case (L 2 = (NH 3 ) 2 ) is the cation ordered sufficiently to enable its structural metrics to be determined by single crystal X-ray diffraction. The onward solid-state reactivity of some of these complexes has been probed. The bisammonia complex [Rh( i Bu 2 PCH 2 CH 2 P i Bu 2 )(NH 3 ) 2 ][BAr F 4 ] undergoes H/D exchange at bound NH 3 when exposed to D 2 . The bis-ethene complex [Rh( i Bu 2 PCH 2 CH 2 P i Bu 2 )(C 2 H 4 ) 2 ][BAr F 4 ] undergoes a slow dehydrogenative coupling reaction to produce a material containing a 1:1 mixture of the butadiene complex and a postulated mono-ethene complex. The mechanisms of these processes have been probed by DFT calculations on the isolated Rh cations. All the solid materials were tested as heterogeneous catalysts for the hydrogenation of ethene. Complexes with weakly bound ligands (e.g., L 2 = (C 2 H 4 ) 2 ) are more active catalysts than those with stronger bound ligands (e.g., L = (CO) 2 ). Surface-passivated crystals, formed through partial reaction with CO, allow for active sites to be probed, either on the surface or the interior of the single crystal.

Reversible Encapsulation of Xenon and CH2Cl2 in a Solid‐State Molecular Organometallic Framework (Guest@SMOM)

“…While these systems also promote catalysis (e.g. 1‐butene isomerization) this may occur at, or close to, the crystal surface . A key question, then, is how substrate/product molecules move in and out of the crystalline lattice on the timescale of synthesis (minutes to hours).…”

“…This provides a clue as to how gases (e.g. H 2 /D 2 , hydrocarbons, CO) are primed for reaction at the metal center in solid/gas SC–SC SMOM reactions. Moreover, inspection of the extended packing diagram of [2‐NBD][(Xe) 0.5 ⊂ BAr F 4 ] (Figure C) reveals that the Xe atoms sit in hydrophobic channels formed by the CF 3 ‐groups of the [BAr F 4 ] − anions.…”

Reversible Encapsulation of Xenon and CH2Cl2 in a Solid‐State Molecular Organometallic Framework (Guest@SMOM)

“…[1] That s-alkane complexes are unstable and transient in solution, even at low temperature, [11] demonstrates the stabilizing effect of the noncovalent anion microenvironment. [1,12] Ak ey question, then, is how substrate/product molecules move in and out of the crystalline lattice on the timescale of synthesis (minutes to hours). 1-butene isomerization) this may occur at, or close to,t he crystal surface.…”

“…However,a fter one week an ew, Xe@SMOM, product is formed, [Rh(Cy 2 PCH 2 PCy 2 )(NBD)]-[(Xe) 0.5 &BAr (3) ]. This provides aclue as to how gases (e.g.H 2 /D 2 , [8] hydrocarbons, [1] CO [12] )are primed for reaction at the metal center in solid/gas SC-SC SMOM reactions.M oreover,i nspection of the extended packing diagram of .W hen coupled with the encapsulated microenvironment in which the Rh-center sits,t here is aremarkable similarity between these guest@SMOM systems the hydrophobic channels that direct substrates and products towards,a nd away from, the active sites in metalloenzymes such as soluble methane monooxygenase hydroxylase or hydrogenases [21a-c] Thee ncapsulation of Xenon can also be followed by 31 P{ 1 H} and 129 Xe SSNMR spectroscopy at 298 K. Af reshly prepared sample of [2-NBD][(Xe) 0.5 &BAr F 4 ] was packed under an atmosphere of Xe (atmospheric pressure). Welldefined Xe···F intermolecular contacts are rare.E xamples include:[ C 6 F 5 Xe][B(CF 3 ) 4 ] À [Xe···F = 2.913(4) ], [29] Xe-(C 6 F 5 ) 2 [Xe···F 3.30(1)-3.536(9) ].…”

Fluoroarene Complexes with Small Bite Angle Bisphosphines: Routes to Amine–Borane and Aminoborylene Complexes

“…Empirically the P–Rh–P bite angle has an inverse effect on arene binding in [Rh(bisphosphine)(arene)] + cations, with η 6 ‐arene binding more favourable for smaller bite angle ligands,, , for which we also suggest amine–borane σ‐complexation is weaker. One way to mitigate these competing effects is to use more weakly binding arene ligands.…”