Ketone CO Research Articles

Comparative photochemistry of some tricarbonyl(η4-polyene)iron complexes in frozen gas matrices at ca. 12 K

Ultraviolet irradiation of [Fe(η4-polyene)(CO)3] complexes [polyene = 1,3-butadiene (C4H6), cyclobutadiene (C4H4), 2,4-cyclopentadien-1-one (C4H4CO), cyclopentadiene (C5H6), 1,3-cyclohexadiene (C6H8), 1,3-cycloheptadiene (C7H10), 1,3-cyclo-octadiene (C8H12), or 1,3,5,7-cyclo-octatetraene (C8H8)] in frozen gas matrices at ca. 12 K results in two competing processes. One is partial dechelation of the polyene ligand to form [Fe(η2-polyene)(CO)3] species and the other is dissociation of a CO ligand to produce co-ordinatively unsaturated [Fe(η4-polyene)(CO)2] species. The photogenerated species were characterised by i.r. spectroscopy. Evidence is presented which indicates that [Fe(η2-polyene)(CO)3] species are responsible for s-cis⇄s-trans, ‘tub’⇄‘chair’, and π⇄σ rearrangements in [Fe(η4-C4H6)(CO)3], [Fe(η4-C8H8)(CO)3], and [Fe(η4-C4H4)(CO)3] respectively. The possibility of ring opening to form a metallocyclic intermediate is discussed in relation to the photoconversion of [Fe(η4-C4H4)(CO)3] into [Fe(η4-C4H4CO)(CO)3] in a carbon monoxide matrix. In a 13CO-doped methane matrix, facile 13CO/12CO exchange occurred for the Fe(CO)3 fragment of [Fe(η4-C4H4CO)(CO)3] but no exchange was found for the ketonic CO group. Ring-to-metal hydrogen migration forming [Fe(η5-C5H5)(CO)2H] and [Fe(η5-C7H9)(CO)2H] has been found to occur for [Fe(η4-C5H6)(CO)3] and [Fe(η4-C7H10)(CO)3] complexes via the co-ordinatively unsaturated fragments [Fe(η4-C5H6)(CO)2] and [Fe(η4-C7H10)(CO)2]. The intermediacy of η2-bound polyene species of the type [Fe(η2-polyene)(CO)4] has been established in the photodissociation of polyene ligands and the formation of [Fe(CO)5] in carbon monoxide matrices.

Photochemistry of pentacarbonylmethylmanganese and acetylpenta-carbonylmanganese in frozen gas matrices at 12 K. Infrared spectroscopic evidence for the formation of methyl- and acetyl-tetracarbonyl-manganese species

Infrared spectroscopic evidence is presented to show that on photolysis of [Mn(CO)5R](RCH3 or CH3CO) complexes at high dilutions in Ar, CH4, and CO matrices at 12 K new species [Mn(CO)4R] are produced. Carbon- 13 labelling of CO and energy-factored force-field fitting was carried out for [Mn(CO)5(CH3)] and [Mn(CO)4(CH3)]. For [Mn(CO)4(CH3)] the CH3 ligand was shown to occupy an equatorial position in a trigonal-bipyramidal structure with C2v symmetry. The observations of CO ejection, a new ketonic CO stretching band, and the formation of a species with a common [Mn(CO)4] fragment from both [Mn(CO)5(CH3CO)] and [Mn(CO)5(CH313CO)], were interpreted as confirming the existence of the co-ordinatively unsaturated species [Mn(CO)4(CH3CO)] as the intermediate in the decarbonylation reaction. Formation of trans-[Mn(12CO)4(13CO)(CH3)] on reverse photolysis in experiments starting with cis-[Mn(12CO)4(13CO)(CH3)] was interpreted as demonstrating that the [Mn(CO)4(CH3)] species is fluxional. The implications of fluxionality for the mechanism of the carbonylation reaction are discussed.

ChemInform Abstract: NEW METHOD FOR REDUCTION OF KETONES AND PRIMARY ALCOHOLS TO HYDROCARBONS‐ REACTION OF THE DERIVED SELENIDES WITH TIN HYDRIDES

AbstractDurch Reaktion der Selenide (I), (III) und (V) mit Triphenylstannan in siedendem Toluol erhält man die Reduktionsprodukte (II), (IV) bzw. (VI).

New method for reduction of ketones and primary alcohols to hydrocarbons: reaction of the derived selenides with tin hydrides

Phenyl selenides and selenoacetals are reduced by triphenyltin hydride in a process that constitutes an efficient method for hydrogenolysis of ketone CO and primary alcohol C–OH bonds.

NMR—the chemical shift—IV The anisotropies of the carbonyl group

The calculation of chemical shift values by the method used in Part I has been extended to a derivation of the shielding effect of the ketonic CO group. The calculations include consideration of both the magnetic anisotropy screening and the electric field screening effect in this substituent. Using the complete series of monoketoandrostanes, the values of the anisotropies of the CO double bond and of K, a parameter descriptive of the electric screening effect, have been derived for various, coincidental locations of the magnetic and electric dipoles along the As with the CC double bond, our results necessitate a substantial modification of the conventional picture of the shielding ‘cone’ around the CO group. The general validity of these concepts has been illustrated by their application to a variety of substances, including a selection of diterpenes and their ketonic derivatives.

NMR—the chemical shift—IV: The anisotropies of the carbonyl group

The calculation of chemical shift values by the method used in Part I has been extended to a derivation of the shielding effect of the ketonic CO group. The calculations include consideration of both the magnetic anisotropy screening and the electric field screening effect in this substituent. Using the complete series of monoketoandrostanes, the values of the anisotropies of the CO double bond and of K, a parameter descriptive of the electric screening effect, have been derived for various, coincidental locations of the magnetic and electric dipoles along the ▪ As with the CC double bond, our results necessitate a substantial modification of the conventional picture of the shielding ‘cone’ around the CO group. The general validity of these concepts has been illustrated by their application to a variety of substances, including a selection of diterpenes and their ketonic derivatives.

The coumarin tavicone from the roots ofFerula karatavica

By the chromatographic separa t ion of the neut ra l fraction of the r e s i n of the roots of Fe ru la kara tav ica Rgl. et Schmalh. on AI~O~ we have isolated a coumar in with the composit ion C23Hz604 (M + 366), mp 141-142 ° C (ethanol), [ol]~ -77 ° (benzene), which we have called tavieone. Yield 1%. IR spec t rum in paraffin oil, cml : 1730 (ketonic CO group in a f ive -membered ring), 1705 (CO of a lactone), 830 (double bond). On acid hydrolys is , tavieone formed umbel l i ferone.