The Synthesis, Characterization and Dehydrogenation of Sigma‐Complexes of BN‐Cyclohexanes

The coordination chemistry of the 1,2‐BN‐cyclohexanes 2,2‐R(2)‐1,2‐B,N‐C(4)H(10) (R(2)=HH, MeH, Me(2)) with Ir and Rh metal fragments has been studied. This led to the solution (NMR spectroscopy) and solid‐state (X‐ray diffraction) characterization of [Ir(PCy(3))(2)(H)(2)(η(2)η(2)‐H(2)BNR(2)C(4)H(8))][BAr(F) (4)] (NR(2)=NH(2), NMeH) and [Rh(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))(η(2)η(2)‐H(2)BNR(2)C(4)H(8))][BAr(F) (4)] (NR(2)=NH(2), NMeH, NMe(2)). For NR(2)=NH(2) subsequent metal‐promoted, dehydrocoupling shows the eventual formation of the cyclic tricyclic borazine [BNC(4)H(8)](3), via amino‐borane and, tentatively characterized using DFT/GIAO chemical shift calculations, cycloborazane intermediates. For NR(2)=NMeH the final product is the cyclic amino‐borane HBNMeC(4)H(8). The mechanism of dehydrogenation of 2,2‐H,Me‐1,2‐B,N‐C(4)H(10) using the {Rh(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))}(+) catalyst has been probed. Catalytic experiments indicate the rapid formation of a dimeric species, [Rh(2)(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))(2)H(5)][BAr(F) (4)]. Using the initial rate method starting from this dimer, a first‐order relationship to [amine‐borane], but half‐order to [Rh] is established, which is suggested to be due to a rapid dimer–monomer equilibrium operating.