Detection of σ-alkane complexes of manganese by NMR and IR spectroscopy in solution: (η⁵-C₅H₅)Mn(CO)₂(ethane) and (η⁵-C₅H₅)Mn(CO)₂(isopentane)

Abstract

Irradiation (355 nm) of CpMn(CO)3 in liquid ethane at 133 K yields CpMn(CO)2(η2-C–H-ethane) characterised by IR and 1H NMR spectroscopy with a lifetime of ca. 360 s; the corresponding isopentane complex is formed in propane/isopentane mixtures and exists in three isomeric forms.

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

“…When this influence of the secondary coordination environment is removed, the relative stabilities of related σ-complexes become leveled. For example Mn(η 5 -C 5 H 5 )(CO) 2 (butane) 16 and Mn(η 5 -C 5 H 5 )(CO) 2 (isobutane) 19 have very similar lifetimes of ∼5–6 min at ∼135 K in liquid alkane solvent.…”

“…Using these methodologies, σ-alkane complexes from methane to dodecane have been generated. 13 , 14 Chart 1 shows examples characterized using NMR spectroscopy where methane, 15 propane, 16 cyclopentane, 17 pentane, 18 2-methylbutane, 19 and 2,2-dimethylbutane 20 act as ligands.…”

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

“…Their structure is shown in Scheme 2a. The series includes neutral complexes differing for the size of the alkane such as [CpMn(CO) 2 (alkane)] (alkane = C 2 H 6 , n-C 7 H 16 ) [56][57][58][59] and [CpRe(CO) 2 (alkane)] (alkane = CH 4 , n-C 5 H 12 , n-C 7 H 16 ) 56,57,60 as well as the positively charged [(HEB)Re(CO) 2 (n-C 5 H 12 )] + (HEB = hexaethylbenzene). 61 Note that for the longer alkanes many conformers are possible, depending on their relative orientation with the TM.…”

Contrasting electronic requirements for CH binding and CH activation in d6 half‐sandwich complexes of rhenium and tungsten

“…The first area concerns characterization and stabilization of metal‐alkane complexes generated in situ . In most cases, studies have been carried out in low temperature matrices or solutions using half‐sandwich complexes or complexes with multidentate ligands such as Tp (tris‐pyrazolylborate) . Ball and Geftakis characterized the cyclopentane complex CpRe(CO) 2 (C 5 H 10 )] (Cp = η 5 ‐C 5 H 5 ) using 1 H NMR spectroscopy, at ∼180 K. This is the most stable σ‐alkane complex characterized in solution with a lifetime of ∼1 h. A η 2 ‐(CH) σ‐coordination to the metal center has been proposed based on the decrease in the CH coupling constant .…”

“…Not many of the alkane complexes are stable at room temperature, but George and coworkers demonstrated that a d 6 complex [CpRe(CO) 2 (n‐C 7 H 16 )] for example, can have a lifetime of as much as ∼30 ms at room temperature . More recently, they have even isolated a metal‐ethane and a metal‐isopentane complex . But stabilization of these complexes in the solid state is not readily achieved.…”