Facile C H aryl and O H bonds activation at dirhenium site of [Re2(CO)8(THF)2] complex

• [Re 2 (CO) 8 (THF) 2 ] promotes facile oxidative addition of toluene and benzene. • Multinuclear NMR spectroscopy is used to study the oxidative addition and reductive elimination at dirhenium metal sites. • Heterolytic activation of water on dinuclear metal fragment is evidenced by isotopic NMR experiments. • A polymorphic crystal form of [Re 2 (µ-H)(µ-OH)(CO) 8 ] is elucidated by single crystal X-ray diffraction. The activation of small molecules is a topic of great interest and previously we reported on the easy activation of different types of E H bonds at the dinuclear complex [Re 2 (CO) 8 (THF) 2 ] ( 1 ) where labile THF molecules coordinate to adjacent rhenium(0) atoms. Here we extend the reactivity of 1 reporting on the oxidative addition of benzene and toluene at room temperature to give [Re 2 (μ-H)(μ-κ C -Ar)(CO) 8 ], Ar = −C 6 H 5 ( 2 ) and −C 6 H 4 Me ( 3 ). Compound 3 is a new example of μ-κ C -Ar dinuclear rhenium complex and has been obtained as para and meta isomers ( 3a , b ). It is known from the literature that 2 can activate arenes and heteroarenes via reductive elimination of benzene and oxidative addition of C H bonds to the dinuclear fragment. Here we have studied the reaction of 2 with C 6 D 6 and H 2 C C(H)Ph and determined the kinetic constants by 1 H NMR (1.4 × 10 −5 s −1 at 308 K and 1.1 × 10 −5 s −1 at 298 K, respectively). The results indicate that the rate-determining step of the reaction is the reductive elimination of benzene, while the oxidative addition is fast. Water and methanol react with 1 in toluene at room temperature to give the hydroxo and methoxo hydrido complexes [Re 2 (μ-H)(μ-OR)(CO) 8 ], R H ( 5 ) and CH 3 ( 6 ). On reacting 1 with water in deuterated toluene, and monitoring by 1 H/ 2 H NMR, a preferential deuteration of the hydride site to give [Re 2 (μ-D)(μ-OH)(CO) 8 ] is evidenced. This finding excludes the oxidative addition of water on the dinuclear “Re 2 (CO) 8 ” fragment while supporting a heterolytic addition of water via protonation at the µ-κ C -tolyl group, elimination of toluene and addition of OH − . Single crystal X-ray diffraction analyses have been performed for complexes 3a , 5 and 6 and their solid state structures have been determined. In particular, the crystal structure of 5 results in a new polymorphic form ( 5b ) and it is discussed in comparison with the already known one ( 5a ).