Transfer Hydrogenation (pH Independent) of Ketones
and Aldehydes in Water with Glycerol: Ru, Rh, and Ir Catalysts with
a COOH Group near the Metal on a (Phenylthio)methyl-2-pyridine Scaffold
posted on 2014-07-28, 00:00authored byOm Prakash, Hemant Joshi, Kamal Nayan Sharma, Pancham Lal Gupta, Ajai K. Singh
The
reactions of 2-(pyridine-2-ylmethylsulfanyl)benzoic acid (L) with [(η5-Cp*/η6-benzene)MCl(μ-Cl)]2, (benzene, M = Ru; Cp*, M = Rh, Ir) at room temperature followed
by treatment with NH4PF6 result in a new class
of water-soluble half-sandwich complexes [(η5Cp*/η6-benzene)M(L)Cl][PF6] (1–3, respectively, for M = Ru, Rh, Ir). Their
characteristic HR-MS and 1H and 13C{1H} NMR spectra have been found. The single-crystal structures of 1–3 have been established with X-ray crystallography.
The Ru–S, Rh–S, and Ir–S bond lengths are 2.4079(6),
2.3989(10), and 2.3637(14) Å, respectively. Complexes 1–3 have been found to be efficient for catalytic
transfer hydrogenation (TH) of carbonyl compounds in water with glycerol
as a hydrogen donor. Glycerol has been explored for TH in water for
the first time. The efficiency in water of other hydrogen sources,
viz. HCOOH, citric acid, ascorbic acid, and 2-propanol, is less and/or
is pH dependent. Catalysis with glycerol as a hydrogen source is pH
independent and appears to be homogeneous. Higher reactivity for the
Rh complex in comparison to the Ru and Ir species has been observed.
DFT calculations are generally consistent with the experimental values
of bond lengths and angles and catalytic reactivity order.