title: Solid-state synthesis and characterization of σ-alkane complexes, [Rh(L2)(η(2),η(2)-C7H12)][BAr(F)4] (L2 = bidentate chelating phosphine).
abstract: The use of solid/gas and single-crystal to single-crystal synthetic routes is reported for the synthesis and characterization of a number of σ-alkane complexes: [Rh(R2P(CH2)nPR2)(η(2),η(2)-C7H12)][BAr(F)4]; R = Cy, n = 2; R = (i)Pr, n = 2,3; Ar = 3,5-C6H3(CF3)2. These norbornane adducts are formed by simple hydrogenation of the corresponding norbornadiene precursor in the solid state. For R = Cy (n = 2), the resulting complex is remarkably stable (months at 298 K), allowing for full characterization using single-crystal X-ray diffraction. The solid-state structure shows no disorder, and the structural metrics can be accurately determined, while the (1)H chemical shifts of the Rh···H-C motif can be determined using solid-state NMR spectroscopy. DFT calculations show that the bonding between the metal fragment and the alkane can be best characterized as a three-center, two-electron interaction, of which σCH → Rh donation is the major component. The other alkane complexes exhibit solid-state (31)P NMR data consistent with their formation, but they are now much less persistent at 298 K and ultimately give the corresponding zwitterions in which [BAr(F)4](-) coordinates and NBA is lost. The solid-state structures, as determined by X-ray crystallography, for all these [BAr(F)4](-) adducts are reported. DFT calculations suggest that the molecular zwitterions within these structures are all significantly more stable than their corresponding σ-alkane cations, suggesting that the solid-state motif has a strong influence on their observed relative stabilities.
authors.affiliation: Department of Chemistry, Chemistry Research Laboratories, University of Oxford , Mansfield Road, Oxford OX1 3TA, U.K.
authors.forename: Sebastian D
authors.initials: SD
authors.lastname: Pike
authors.forename: F Mark
authors.initials: FM
authors.lastname: Chadwick
authors.forename: Nicholas H
authors.initials: NH
authors.lastname: Rees
authors.forename: Mark P
authors.initials: MP
authors.lastname: Scott
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Weller
authors.forename: Tobias
authors.initials: T
authors.lastname: Krämer
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Macgregor