| Sumario: | The C, N, N''-donor aryl-diimineborate pincer ligand of the complexes OsH2{¿3-C, N, N-[C6H3RCH = NB(cat)N = CHC6H4R]}(PiPr3)2 (R = H, Me) has been generated in a one-pot procedure, by the reaction of the hexahydride OsH6(PiPr3)2 with catecholborane (catBH) and two molecules of the corresponding aryl nitrile. The osmium-pincer bonding situation has been analyzed by means of atoms in molecules (AIM), natural bond orbital (NBO), and energy decomposition analysis coupled with the natural orbitals for chemical valence (EDA-NOCV) methods. According to the results, the complexes exhibit a rather strong electron-sharing Os-C bond, two weaker donor-acceptor N-Os bonds, and two ?-back-donations from the transition metal to vacant p* orbitals of the formed metallacycles. In addition, spectroscopic findings and DFT calculations reveal that the donor units of the pincer are incorporated in a sequential manner. First, the central Os-N bond is formed, by the reaction of the dihydrideborate ligand of the intermediate OsH3{¿2-H, H-(H2Bcat)}(PiPr3)2 with one of the aryl nitriles. The subsequent oxidative addition of the o-C-H bond of the aryl substituent of the resulting ¿1-N-(N-boryl-arylaldimine) affords the Os-C bond. Finally, the second Os-N bond is generated from a hydride, an ortho-metalated N-boryl-arylaldimine, and the second aryl nitrile.
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