[Fp(CH₄)]⁺, [η⁵-CpRu(CO)₂(CH₄)]⁺, and [η⁵-CpOs(CO)₂(CH₄)]⁺: A Complete Set of Group 8 Metal–Methane Complexes

Abstract

Here, we report the NMR spectroscopic analysis of the group 8 transition metal methane σ-complexes [η5-CpM­(CO)2(CH4)]­[Al­(OC­(CF3)3)4] (M = Fe, Ru) at −90 °C in the weakly coordinating solvent 1,1,1,3,3,3-hexafluoropropane. The iron­(II)–methane complex has a 1H resonance at δ −4.27, a 13C resonance at δ −53.0, and 1 J C–H = 126 Hz for the bound methane fragment. The ruthenium­(II)–methane complex has a 1H resonance at δ −2.10, a 13C resonance at δ −48.8, and a 1 J C–H = 126 Hz for the bound methane fragment. DFT and ab initio calculations support these experimental observations and provide further detail on the structures of the [η5-CpM­(CO)2(CH4)]+ (M = Fe, Ru) complexes of the Group 8 metals. Both the iron centered methane complex, [η5-CpFe­(CO)2(CH4)]­[Al­(OC­(CF3)3)4], and the ruthenium centered methane complex, [η5-CpRu­(CO)2(CH4)]­[Al­(OC­(CF3)3)4], are significantly less stable than the previously reported osmium–methane complex [η5-CpOs­(CO)2(CH4)]­[Al­(OC­(CF3)3)4].

Effects of surface acidity on the structure of organometallics supported on oxide surfaces

“…Similar strategies using cationic transition metal complexes in solution to mediate these reactions are unlikely for a simple reason, alkanes are rarely compatible solvents with cations. Indeed, solvation of organometallic cations by polar halogenated solvents usually prevents formation of σ-CH alkane intermediates in solution, 155–159 and only recently have these types of compounds become widely available in using in-crystallo 160 organometallic chemistry of cationic Rh( i ) olefin complexes with H 2 in porous single crystals in the absence of solvent. 161–166…”

Enhancement of Knölker Iron Catalysts for Imine Hydrogenation by Predictive Catalysis: From Calculations to Selective Experiments

“…In addition, the proton transfer to the keto group of the cyclopentadienone ligand was found to be obligatorily assisted by an ethanol molecule, which induced the competition with the decarbonylation step to define the rate-determining step (rds) . The cyclopentadienone was not a spectator, but the range between nonplanarity and planarity of its five-membered ring (5-MR) was significant throughout the reaction pathway . More importantly, electronically, the introduction of electron-withdrawing groups (EWGs) on the cyclopentadienone favors the resonance structure with 6π electrons in the 5-MR increasing the aromaticity and the π density of this ring and decreasing the net population on the metal.…”

Solid‐State Confinement Effects in Selective exo‐H/D Exchange in the Rhodium σ‐Norbornane Complex [(Cy2PCH2CH2PCy2)Rh(η2:η2‐C7H12)][BArF4]

“…In solution, the low polarizability and sterically hindered nature of aliphatic C−H bonds means that alkanes are poor ligands at transition metal centres, and are readily displaced by solvent, counterions or entropically favoured agostic interactions. Thus, although σ‐alkane complexes have been observed directly in solution, produced through photolysis of metal‐carbonyl precursors, or protonation of metal‐alkyls, they are generally of limited stability, with short half‐lives even at the very low temperatures used for their spectroscopic characterisation (see Scheme 1 ,A ) [4–8] . These factors have frustrated attempts to isolate σ‐alkane complexes in the solid state and their definitive [9] crystallographic characterisation through recrystallization from solution has so far proved elusive.…”

“… A) Recent examples of direct observation of σ‐alkane complexes in solution formed through (i) photolysis and (ii) alkyl protonation (anions omitted) [4–7] . B) Indirect evidence for σ‐alkane complexes: (iii) selective α‐H/D via σ‐alkane complex intermediates and (iv) inverse k H / k D isotope effects on alkane reductive elimination [10] …”

“…Thus, although σalkane complexes have been observed directly in solution, produced through photolysis of metalcarbonyl precursors, or protonation of metal-alkyls, they are generally of limited stability, with short halflives even at the very low temperatures used for their spectroscopic characterisation (see Scheme 1,A). [4][5][6][7][8] These factors have frustrated attempts to isolate σalkane complexes in the solid state and their definitive [9] crystallographic characterisation through recrystallization from solution has so far proved elusive. Indirect evidence for the existence of σ-alkane complexes is also seen in the observation of H/D exchange processes at the metal-bound carbon in alkyl deuterides, L n M(CH 2 R)(D).…”