Three
unsymmetrical NNN ligands with a 2-hydroxypyridyl fragment
were used to react with RuHCl(PPh3)3(CO), affording
the three bidentate ruthenium hydride complexes [(R1-C5H3N-CH2-C5H3N-C5H3N-R2)RuH(PPh3)2(CO)][Cl] (R1 = R2 = OH, 2a; R1 = OH, R2 = H, 2b; R1 =
H, R2 = OH, 2c), respectively. When 2a,b were treated with t-BuOK,
the two tridentate products [(O-C5H3N-CH2-C5H3N-C5H3N-R2)RuH(PPh3)(CO)] (R2 = OH, 3a; R2 = H, 3b) were obtained, via selective
deprotonation of the −OH group of PyCH2PyOH moiety,
indicating that this −OH group is more acidic than that of
the PyPyOH moiety. The reaction of 2c with t-BuOK generated the bidentate product [(C5H4N-CH2-C5H3N-C5H3N-O)RuH(PPh3)2(CO)] (3c) and the
tridentate product [(C5H4N-CH2-C5H3N-C5H3N-O)RuH(PPh3)(CO)] (3d). 3d could be further transformed
to the diruthenium complex [(C5H4N-CH-C5H3N-C5H3N-O)Ru(PPh3)(CO)]2 (3e) via C–H activation of
the −CH2– group in boiling toluene. The catalytic
activity for β-alkylation of secondary alcohols with primary
alcohols of these eight ruthenium complexes was tested, and the bidentate
complexes 2c and 3c exhibit the highest
activity. Complex 3c can be regarded as the intermediate
of 2c. These results are important for developing more
efficient bifunctional catalysts for such reactions.