Selectivity of Rh⋅⋅⋅H−C Binding in a σ-Alkane Complex Controlled by the Secondary Microenvironment in the Solid State

By using single-crystal to single-crystal solid-state molecular organometallic (SMOM) techniques, the σ -alkane complex [Rh( t Bu 2 PCH 2 CH 2 CH 2 P t Bu 2 )( η 2 , η 2 -C 7 H 12 )][BAr F 4 ] (Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ) is synthesized and structurally characterized, in which the alkane (norbornane) binds through two exo -C-H···Rh interactions. In contrast, the bis-cyclohexyl phosphine analogue shows endo -alkane binding. Comparison of the two systems, supported by periodic DFT calculations, NCI plots and Hirshfeld surface analyses, trace this different regioselectivity to subtle changes in the local microenvironment surrounding the alkane ligand. A tertiary periodic structure supporting a secondary microenvironment that controls binding at the metal site has parallels with enzymes. The new σ -alkane complex is also a catalyst for solid/gas 1-butene isomerization, and catalyst resting states are identified for this.