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

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 ] + .