pH-selective hydrogenation of water-soluble carbonyl compounds and alkeneswith [Cp*Ir-III(H2O)(3)](2+) (CP* = eta(5)-C5Me5) as a catalyst precursor in very acidic media

Citation
N. Makihara et al., pH-selective hydrogenation of water-soluble carbonyl compounds and alkeneswith [Cp*Ir-III(H2O)(3)](2+) (CP* = eta(5)-C5Me5) as a catalyst precursor in very acidic media, ORGANOMETAL, 20(3), 2001, pp. 497-500
Citations number
34
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
ORGANOMETALLICS
ISSN journal
0276-7333 → ACNP
Volume
20
Issue
3
Year of publication
2001
Pages
497 - 500
Database
ISI
SICI code
0276-7333(20010205)20:3<497:PHOWCC>2.0.ZU;2-E
Abstract
The organometallic aqua complex [Cp*Ir-III(H2O)(3)](2+) (1) acts as a catal yst precursor for hydrogenation of water-soluble carbonyl compounds and alk enes in water (5-20 mM of 1, 100 mM of the substrates) in a pH range of abo ut -1 to 4 under H-2 at a pressure of 0.1-0.7 MPa at 25 degreesC. The solut ion pH was adjusted by using 0.1-10 M HClO4/H2O and 0.1 M NaOH/H2O. The aqu eous hydrogenation shows unique pH-selectivity to be governed by the follow ing three factors: (i) pH-dependent structural change of the catalyst precu rsor 1, which is deprotonated to form a catalytically inactive dinuclear co mplex, [(Cp*Ir-III)(2)(mu -OH)(3)](+) (2), above pH 4, (ii) stability of a putative iridium hydride active catalyst depending upon pH, and (iii) diffe rence in the proton affinity of the substrates, i.e., Lewis basicity of the carbonyl oxygen atoms of the carbonyl compounds and the C=C moieties of th e alkenes. Turnover frequencies of the hydrogenations are also discussed on the basis of Lewis acidity of the carbocations that accept a hydride ion f rom the active catalyst.