Exploring Rhenium Arene Piano-Stool Chemistry with [Re(η-CH)(NCCH)]: A Powerful Semi-Solvated Precursor.

Thermal treatment of the Re hydride complex [ReH(η-CH)(η-CH)] in CHCN results in the formation of [Re(η-CH)(NCCH)]. This semi-solvated complex is remarkably stable under an ambient atmosphere and exhibits a fast CHCN self-exchange, which facilitates substitution reactions. The CHCN ligands are replaced by σ-donating phosphines such as trimethyl phosphine (PMe), triphenyl phosphine (PPh), or the bidentate 1,2-bis(diphenylphosphino)ethane (dppe) to afford [Re(η-CH)(NCCH)(PR)] (if R = Me, then = 2; if R = Ph, then = 1 or 2) or [Re(η-CH)(dppe)(NCCH)], respectively. [Re(η-CH)(NCCH)] also reacts with π-acceptors such as 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), or CO (1 atm) to give [Re(η-CH)(L)(NCCH)] (L = bipy or phen) and [Re(η-CH)(CO)(NCCH)], respectively. The latter does not show any signs of decomposition after being exposed to an ambient atmosphere for multiple days. Additionally, [Re(η-CH)(NCCH)] reacts with π-donors such as the dienes 2,3-dimethyl-1,3-butadiene (DMBD), norbornadiene (NBD), or 1,5-cyclooctadiene (COD) to give [Re(η-CH)(η-diene)(NCCH)] (diene = DMBD, NBD, and COD). All three complexes are extremely stable and do not decompose during purification by preparative high-performance liquid chromatography (aqueous acidic gradient). In the presence of 18-crown-6, [Re(η-CH)(NCCH)] reacts with lithium cyclopentadienyl to give the sandwich complex [Re(η-CH)(η-CH)]. Loss of the coordinated benzene was observed when treating [Re(η-CH)(NCCH)] with diphenylacetylene (PhC≡CPh), yielding the tetra-coordinated [Re(NCCH)(η-PhC≡CPh)].