Exploring Rhenium Arene Piano-Stool Chemistry with [Re(η(6)-C(6)H(6))(NCCH(3))(3)](+): A Powerful Semi-Solvated Precursor

[Image: see text] Thermal treatment of the Re(III) hydride complex [ReH(η(5)-C(6)H(7))(η(6)-C(6)H(6))](+) in CH(3)CN results in the formation of [Re(η(6)-C(6)H(6))(NCCH(3))(3)](+). This semi-solvated complex is remarkably stable under an ambient atmosphere and exhibits a fast CH(3)CN self-exchange, which facilitates substitution reactions. The CH(3)CN ligands are replaced by σ-donating phosphines such as trimethyl phosphine (PMe(3)), triphenyl phosphine (PPh(3)), or the bidentate 1,2-bis(diphenylphosphino)ethane (dppe) to afford [Re(η(6)-C(6)H(6))(NCCH(3))(3–x)(PR(3))(x)](+) (if R = Me, then x = 2; if R = Ph, then x = 1 or 2) or [Re(η(6)-C(6)H(6))(dppe)(NCCH(3))](+), respectively. [Re(η(6)-C(6)H(6))(NCCH(3))(3)](+) also reacts with π-acceptors such as 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), or CO (1 atm) to give [Re(η(6)-C(6)H(6))(L)(NCCH(3))](+) (L = bipy or phen) and [Re(η(6)-C(6)H(6))(CO)(NCCH(3))(2)](+), respectively. The latter does not show any signs of decomposition after being exposed to an ambient atmosphere for multiple days. Additionally, [Re(η(6)-C(6)H(6))(NCCH(3))(3)](+) 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(6)-C(6)H(6))(η(4)-diene)(NCCH(3))](+) (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(6)-C(6)H(6))(NCCH(3))(3)](+) reacts with lithium cyclopentadienyl to give the sandwich complex [Re(η(5)-C(5)H(5))(η(6)-C(6)H(6))]. Loss of the coordinated benzene was observed when treating [Re(η(6)-C(6)H(6))(NCCH(3))(3)](+) with diphenylacetylene (PhC≡CPh), yielding the tetra-coordinated [Re(NCCH(3))(η(2)-PhC≡CPh)(3)](+).