摘要:
The square-planar monohydride complex RhH-{xant((PPr2)-Pr-i)(2)} (1; xant((PPr2)-Pr-i)(2) = 9,9-dimethy1-4,5-bis-(diisopropylphosphino)xanthene) activates C-H bonds of arenes. Heating of benzene solutions of 1 at 80 degrees C affords RhPh{xant((PPr2)-Pr-i)(2)} (2). Under the same conditions, toluene gives Rh(m-tolyl){xant((PPr2)-Pr-i)(2)} (3a) and Rh(p-tolyl){xant((PPr2)-Pr-i)(2)} (3b) in a 78:22 molar ratio, whereas m-xylene leads to Rh(C6H3-3,5-Me-2){xant((PPr2)-Pr-i)(2)} (4). At room temperature, fluorobenzene and 1,3-difluorobenzene generate Rh(C6H4-2-F){xant((PPr2)-Pr-i)(2)} (5) and Rh(C6H3-2,6-F-2){xant((PPr2)-Pr-i)(2)} (6), respectively. Complex 1 also promotes the B-H bond activation of pinacolborane (HBpin) and catecholborane (HBcat). The reactions initially give the trans-dihydride derivatives RhH2(BR2){xant((PPr2)-Pr-i)(2)} (BR2 = Bpin (7), Bcat (8)), which lose H-2 to afford the square-planar Rh(BR2){xant((PPr2)-Pr-i)(2)} (BR2 = Bpin (9), Bcat (10)). Complex 2 reacts with HBpin to regenerate 1 and to give Ph-Bpin. Similarly, complex 9 regenerates 1 and gives Ph-Bpin by reaction with benzene. In agreement with these transformations, complex 1 catalyzes the direct C-H borylation of arenes. The selectivity of the process appears to be governed by the kinetic of the C-H bond activations of the arenes. Benzylic borylation is not observed for methylbenzenes. The first X-ray structure of a square-planar rhodium boryl complex is also reported.