Inverse Isotope Effects in Single-Crystal to Single-Crystal Reactivity and the Isolation of a Rhodium Cyclooctane σ-Alkane Complex

Abstract

The sequential solid/gas single-crystal to single-crystal reaction of [Rh(Cy 2 P(CH 2 ) 3 PCy 2 )(COD)][BAr F 4 ] (COD = cyclooctadiene) with H 2 or D 2 was followed in situ by solid-state 31 P{ 1 H} NMR spectroscopy (SSNMR) and ex situ by solution quenching and GC-MS. This was quantified using a two-step Johnson–Mehl–Avrami–Kologoromov (JMAK) model that revealed an inverse isotope effect for the second addition of H 2 , that forms a σ-alkane complex [Rh(Cy 2 P(CH 2 ) 3 PCy 2 )(COA)][BAr F 4 ]. Using D 2 , a temporal window is determined in which a structural solution for this σ-alkane complex is possible, which reveals an η 2 ,η 2 -binding mode to the Rh(I) center, as supported by periodic density functional theory (DFT) calculations. Extensive H/D exchange occurs during the addition of D 2 , as promoted by the solid-state microenvironment.

The borderless world of chemical bonding across the van der Waals crust and the valence region

“…In summary, a representation of the M⋯H and M⋯C penetration indices as a function of the incidence angle of the C–H bond, even if showing a poor correlation, allows us to draw several conclusions: (i) the M⋯H penetration increases as the incidence angle tends to 180°, while the M⋯C penetration varies very little with that angle; (ii) so far, the highest M⋯H penetrations are close to 100%, and correspond to the cyclooctane, 134 norbornane 135 and cyclooctane 134 Rh complexes and an Os complex 136 with two phenylic C–H groups occupying two sites of the coordination octahedron, all with coordination mode 4; (iii) those high M⋯H penetrations appear at Rh–H–C angles larger than 110° and predominate over the M⋯C penetrations that are below the 75% mark; (iv) for incidence angles below 100° the M⋯H and M⋯C penetrations are similar, as is the case of the n -hexane 132 and n -pentane 123 rhodium complexes. The structures shown in Fig.…”

On the σ-complex character of bis(gallyl)/digallane transition metal species

“…5, Scheme 2 ). To our surprise, these reactions led to the formation of the isolable GaIII compound PhiPDippGaMe2, 6 presumably through a disproportionation process, which would simultaneously form a GaI species. 31,32 No stable GaI species was observed in the disproportionation reaction of the free digallane, with only the protonated ligand observed in the 31 P{ 1 H} NMR spectra of crude reaction mixtures, in addition to 6 ( δ = −17.4 ppm), and an elemental gallium mirror observed within the reaction vessel.…”

“… 4 Since that time, countless examples of related H 2 complexes have been reported, and their electronic nature has been thoroughly investigated particularly in relation to the continuum of oxidation addition. 5 Further examples of σ-complexes involving heteroatomic E–H bonds have also been discovered (E = C, 6 Si, 7 B, 8 Al 9 ), aligning with the importance of such E–H fragments in catalytic transformations. Accessing stable σ-complexes of homoatomic E–E bonds, beyond the H–H bond, poses a considerably greater challenge due to the lack of bond polarisation.…”

Effects of surface acidity on the structure of organometallics supported on oxide surfaces

“…Indeed, solvation of organometallic cations by polar halogenated solvents usually prevents formation of s-CH alkane intermediates in solution, [155][156][157][158][159] and only recently have these types of compounds become widely available in using in-crystallo 160 organometallic chemistry of cationic Rh(I) olefin complexes with H 2 in porous single crystals in the absence of solvent. [161][162][163][164][165][166] This concept extends beyond generation of M-H + sites on weakly coordinating supports. [Cp*IrMe(PMe 3 )][SZO] in Fig.…”