Photolysis of arene chromium tricarbonyl complexes in presence of amine-boranes: Observation of σ-borane complexes in solution

Activation of the B-H sigma-bond of amine-boranes on the chromium(0) center of arene chromium tricarbonyl complexes (eta(6)-arene) Cr(CO)(3) (arene = fluorobenzene, 1a; benzene, 1b and mesitylene, 1c) has been studied. Photolysis of 1b in presence of ammonia-borane (H(3)N center dot BH(3), AB) and tert-butylamine-borane ((t)BuH(2)N center dot BH(3), TBAB) resulted in H(2) evolution and precipitation of a BNH(x) polymer. On the other hand, photolysis in the presence of trimethylamine-borane (Me(3)N center dot BH(3), TMAB) resulted in the formation of a sigma-borane complex (2) along with Cr(CO)(5)(eta(1)-HBH(2)center dot NMe(3)) (3). The sigma-borane complexes (eta(6)-arene) Cr-( CO)(2)(eta(1)-HBH(2)center dot NMe(3)) (arene = fluorobenzene, 2a; benzene, 2b and mesitylene, 2c) were characterized in solution by (1)H, (11)B, and (13)C NMR spectroscopy. Electron withdrawing substituents on the arene ring provide the more stable sigma-borane moiety in this series of complexes. (C) 2011 Elsevier B.V. All rights reserved.