Selective C–H Activation at a Molecular Rhodium Sigma-Alkane Complex by Solid/Gas Single-Crystal to Single-Crystal H/D Exchange

The controlled catalytic
functionalization of alkanes via the activation
of C–H bonds is a significant challenge. Although C–H
activation by transition metal catalysts is often suggested to operate
via intermediate σ-alkane complexes, such transient species
are difficult to observe due to their instability in solution. This
instability may be controlled by use of solid/gas synthetic techniques
that enable the isolation of single-crystals of well-defined σ-alkane
complexes. Here we show that, using this unique platform, selective
alkane C–H activation occurs, as probed by H/D exchange using
D2, and that five different isotopomers/isotopologues of
the σ-alkane complex result, as characterized by single-crystal
neutron diffraction studies for three examples. Low-energy fluxional
processes associated with the σ-alkane ligand are identified
using variable-temperature X-ray diffraction, solid-state NMR spectroscopy,
and periodic DFT calculations. These observations connect σ-alkane
complexes with their C–H activated products, and demonstrate
that alkane-ligand mobility, and selective C–H activation,
are possible when these processes occur in the constrained environment
of the solid-state.