A Rhodium–Pentane Sigma‐Alkane Complex: Characterization in the Solid State by Experimental and Computational Techniques

Abstract

The pentane σ‐complex [Rh{Cy2P(CH2CH2)PCy2}(η2:η2‐C5H12)][BArF 4] is synthesized by a solid/gas single‐crystal to single‐crystal transformation by addition of H2 to a precursor 1,3‐pentadiene complex. Characterization by low temperature single‐crystal X‐ray diffraction (150 K) and SSNMR spectroscopy (158 K) reveals coordination through two Rh⋅⋅⋅H−C interactions in the 2,4‐positions of the linear alkane. Periodic DFT calculations and molecular dynamics on the structure in the solid state provide insight into the experimentally observed Rh⋅⋅⋅H−C interaction, the extended environment in the crystal lattice and a temperature‐dependent pentane rearrangement implicated by the SSNMR data.

Coordinating Ability of Anions, Solvents, Amino Acids, and Gases towards Alkaline and Alkaline‐Earth Elements, Transition Metals, and Lanthanides

“…Not unexpectedly,t he alkanes appear as the less coordinating family of solvents andg ases.N otwithstanding,o ne example of a s-bonded n-pentane complex hasb een structurally characterized, in whicht he alkane is coordinatedt oaRh atom through the hydrogens of the 2,4-positions. [152] Moreover, all analysed alkanes except n-octane show in our semi-coordinated searches at least one example of incipientc oordination, mostly to coordinatively unsaturated metal atoms.Asa nexample, Figure 11 shows am olecule of hexane that presentsa short contactt oaNi atom enclosed by ap orphyrinato ligand. [151] Neither n-propane nor ethane appear in Table 5, because of the smalln umber of crystal structures in which they co-crystallise with at ransition metal.H owever,i nn one of the known structures (11f or propane and 3f or ethane) is the alkane coordinated or semi-coordinated.…”

Structural characterization of framework–gas interactions in the metal–organic framework Co2(dobdc) by in situ single-crystal X-ray diffraction

“…These distances contrast with the relatively short M···C distances (around 2.4–2.5 Å) in alkane σ-complexes, which involve donation from the alkane C–H σ bond to the metal center. 16 – 18 Although the Co II –CH 4 interaction in Co 2 (dobdc) and analogous noncovalent M–CH 4 interactions should clearly be distinguished from the bonds formed in true metal–alkane σ-complexes, characterization of such weak M–CH 4 interactions has become increasingly important in the evaluation of materials for natural gas storage. 22 …”

“…As particularly striking examples, this solid–gas reactivity has been leveraged to follow the exchange of small molecules (N 2 , CO, NH 3 , C 2 H 4 , H 2 , and O 2 ) on an iridium pincer complex 12 and to isolate rhodium-alkane σ-complexes through the hydrogenation of their corresponding alkene complexes. 16 – 18 Although these reports reinforce the growing utility of molecular single-crystal matrices, their general applicability remains limited by the scarcity of structures that retain crystallinity upon binding and reaction of the molecular guests. 2 In addition, the tendency of molecules to pack closely in the crystalline state engenders only small or transient apertures in the crystal.…”

London dispersion effects in the coordination and activation of alkanes in σ-complexes: a local energy decomposition study

“…All these complexes were fully characterized by X-ray crystallography and solid state NMR. 49,[64][65][66] Their structures are shown in Scheme 2c.…”