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

Abstract

The C,N,N'-donor aryl-diimineborate pincer ligand of complexes OsH2{κ 3 -C,N,N-[C6H3RCH=NB(cat)N=CHC6H4R]}(P i Pr3)2 (R = H, Me) has been generated in a one-pot procedure, by the reaction of the hexahydride OsH6(P i Pr3)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, it exhibits a rather strong electron-sharing Os-C bond, two weaker donor-acceptor N-to-Os bonds, and two π-backdonations from the transition metal to vacant π* 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. Firstly, the central Os-N bond is formed, by the reaction of the dihydrideborate ligand of intermediate OsH3{κ 2 -H,H-(H2Bcat)}(P i Pr3)2 with one of the aryl nitriles. The subsequent oxidative addition of the ortho-C-H bond of the aryl substituent of the resulting κ 1 -N-(N-boryl-arylaldimine) affords the Os-C bond. Lastly, the second Os-N bond is generated from a hydride, an orthometalated Nboryl-arylaldimine and the second aryl nitrile.

Homogeneous catalysis with polyhydride complexes

“…118 In the case of catBH, the ortho metalated borylaldimine adds a second nitrile molecule to form the pincer derivatives OsH 2 {κ 3 - C , N , N -[C 6 H 3 RCHNB(cat)NCHC 6 H 4 R]}(P i Pr 3 ) 2 (R = H ( 101 ), Me ( 102 )), which are even more stable. 185…”