PNS-Type Ruthenium Pincer Complexes

The PNS pincer-type ligand 1 and the novel
Ru­(PNS)
complexes 2–8 were synthesized and
characterized. The (PNS)­RuH­(Cl)­CO complex 2 was prepared
by reaction of ligand 1 with RuH­(Cl)­CO­(PPh3)3. 2 reacted with KHMDS (potassium bis­(trimethylsilyl)­amide)
to form the symmetrical dimeric complex 4 via the intermediacy
of the dearomatized complex (PNS*)­Ru­(H)­CO 3, in which
deprotonation of the benzylic-S “arm” took place. Reaction
of 2 with excess NaH gave the dimeric 4,
by a formal intermolecular attack of the benzylic “arm”
on a second ruthenium center. Complex 4 underwent spontaneous
transformation in solution to the dinuclear complex 5 via C–S bond cleavage, resulting in the loss of a S-bound tBu group. Treatment of 2 with KHMDS in the presence
of PEt3 resulted in the trapping of intermediate 3 in the form of the dearomatized complex 8.
Reaction of 2 with LiHBEt3 gave the trans-dihydride complex 6, which reacted with
CO2 to give the formato complex 7, in which
the formato ligand is located trans to the hydride.
Complexes 2, 4, and 5 were
also investigated as catalysts for the dehydrogenative coupling of
alcohols with amines.