A Series of Crystallographically Characterized Linear and Branched σ-Alkane Complexes of Rhodium: From Propane to 3-Methylpentane

Using solid-state molecular organometallic (SMOM) techniques, in particular solid/gas single-crystal to reactivity, a series of σ-alkane complexes the general formula [Rh(Cy2PCH2CH2PCy2)(ηn:ηm-alkane)][BArF4] have been prepared (alkane = propane, 2-methylbutane, hexane, 3-methylpentane; ArF 3,5-(CF3)2C6H3). These new characterized using single crystal X-ray diffraction, NMR spectroscopy and DFT computational techniques present variety Rh(I)···H–C binding motifs at metal coordination site: 1,2-η2:η2 (2-methylbutane), 1,3-η2:η2 (propane), 2,4-η2:η2 (hexane), 1,4-η1:η2 (3-methylpentane). For linear alkanes propane some additional interactions with geminal C–H bonds are also evident. The stability these respect alkane loss solid state varies identity alkane: from that decomposes rapidly 295 K 2-methylbutane is stable instead undergoes an acceptorless dehydrogenation form bound alkene complex. In each case sits pocket defined by {Rh(Cy2PCH2CH2PCy2)}+ fragment surrounding array [BArF4]− anions. complex, small energy, driven part lack stabilizing short contacts anions, correlates fleeting this species. 2-Methylbutane forms more within pocket, as result complex considerably stable. However, larger 3-methylpentane ligand shows lower stability. Empirically, there therefore appears be optimal fit between size shape overall Such observations related guest/host solution supramolecular chemistry holistic role 1°, 2°, 3° environments metalloenzymes.