Assembly of a Dihydrideborate and Two Aryl Nitriles to Form a C,N,N′-Pincer Ligand Coordinated to Osmium

The C,N,N'-donor aryl-diimineborate pincer ligand of the complexes OsH2{kappa(3)-C,N,N-[C6H3RCH=NB(cat)N=CHC6H4R]}-((PPr3)-Pr-i)(2) (R = H, Me) has been generated in a one-pot procedure, by the reaction of the hexahydride OsH6((PPr3)-Pr-i)(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 pi-back-donations from the transition metal to vacant pi* 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{kappa(2)-H,H-(H(2)Bcat)}((PPr3)-Pr-i)(2) with one of the aryl nitriles. The subsequent oxidative addition of the o-C-H bond of the aryl substituent of the resulting kappa(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.

Automated summary

The C,N,N'-donor aryl-diimineborate pincer ligand of the complexes OsH2{kappa(3)-C,N,N-[C6H3RCH=NB(cat)N=CHC6H4R]}-((PPr3)-Pr-i)(2) has been generated in a one-pot procedure, showing a strong electron-sharing Os-C bond, two weaker donor-acceptor N-Os bonds, and pi-back-donations from the transition metal to vacant pi* orbitals of the formed metallacycles. Spectroscopic findings and DFT calculations reveal a sequential incorporation of donor units in the pincer, forming central Os-N bond first, followed by the Os-C bond and the second Os-N bond.