The rate‐determining step in the hydrogenation of aldehydes or ketones by hydrido complexes and acids appears to be the hydride transfer from the complex to the protonated carbonyl compound. The resulting alcohol is initially bound as ligand, as confirmed by an X‐ray crystal structure analysis of the alcohol complex 1.
Ionic hydrogenation of acetone by Cp(CO) 3 WH and HOTf (OTf ) OSO 2 CF 3 ) gives the 2-propanol complex [Cp(CO) 3 W(HO i Pr)] + OTf -. 1 H NMR data suggest O-H‚‚‚O hydrogen bonding between the alcohol OH and an oxygen of the triflate anion in solution, and a crystal structure of this complex shows that hydrogen bonding also exists in the solid state. The short O‚‚‚O distance of 2.63(1) Å indicates a strong hydrogen bond. Hydrogenation of other ketones and aldehydes gives related [Cp(CO) 3 W(alcohol)] + OTfcomplexes. Aldehydes are selectively hydrogenated over ketones, and alkyl ketones are selectively hydrogenated over aromatic ketones. Hydrogenation of acetophenone gives ethylbenzene, with no intermediate tungsten complexes being observed. Reaction of 1-phenyl-1,3-butanedione with Cp(CO) 3 WH and HOTf gave {Cp(CO) 3 W[CH 3 CH(OH)CH 2 C(dO)Ph]} + OTf -, the structure of which was determined by X-ray diffraction. The alcohol complexes [Cp(CO) 3 W(alcohol)] + OTfdecompose in solution to give free alcohols and Cp(CO) 3 WOTf. The cationic dihydride [Cp(CO) 2 (PMe 3 )-W(H) 2 ] + OTfhydrogenates aldehydes and ketones; in these reactions a metal hydride serves as both the proton and hydride donor.
The reaction of
PhCH(OCH3)2 with
Cp(CO)3WH and HOTf gives
[Cp(CO)3W(PhCH2OCH3)]+OTf-.
The
structure of this benzyl methyl ether complex was determined by single
crystal X-ray diffraction and was shown to
have the ether bonded to tungsten through the oxygen. This
compound was isolated as a kinetic product of the
reaction; it decomposes in solution by releasing free
PhCH2OCH3 and forming
Cp(CO)3WOTf. An analog with the
BAr‘4
- counterion [Ar‘ =
3,5-bis(trifluoromethyl)phenyl] is more stable. The
reaction of the vinyl acetal
CH2CHCH(OEt)2 with
Cp(CO)3WH and HOTf produces
[Cp(CO)3W(η2-EtOCHCHCH3)]+OTf-,
in which the
ether is bonded to tungsten through the CC bond of the vinyl ether.
The crystal structure of this compound shows
that the WC(OEt) distance (2.69(3) Å) is significantly
longer than the WC(CH3) distance (2.37(3) Å).
There are
weak CH···O hydrogen bonds between both vinyl CH's and
oxygens of triflate counterions. Evidence is
presented
that some of these weak hydrogen bonds are maintained in
CD2Cl2 solution but not in
CD3CN.
terschied zur planaren Konformation (7.4 kcalmol-') und die mit IGLOL' berechnete chemische Verschiebung fur C2 (169)[12] stimmen gut mit den fur 3a experimentell ermittelten Daten uberein. Abb. I . Schakalzeichnung der Molekulstruktur des Anions in 3a im Kristall. Wichtige Abstinde [pm] und Winkel ["I:
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.