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

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 - 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(mu-H)(mu-xC-Ar)(CO)(8)], Ar =- C6H5 (2) and -C6H4Me (3). Compound 3 is a new example of mu-xC-Ar x 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 - H bonds to the dinuclear fragment. Here we have studied the reaction of 2 with C6D6 and H2C--C(H)Ph and determined the kinetic constants by H-1 NMR (1.4 x 10(-5) s(- 1) at 308 K and 1.1 x 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(mu-H)(mu-OR) (CO)(8)], R=H (5) and CH3 (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(mu-D)(mu-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 mu -x 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).