Dorothy H. Gibson

Carbon dioxide coordination chemistry: metal complexes and surface-bound species. What relationships?

Syntheses, studies of bonding and structures of carbon dioxide complexes have been well- developed in recent years as has the synthesis and characterization of metal formate complexes because of their perceived relationships to intermediates in the catalytic activation of carbon dioxide. Vibrational spectroscopy, usually infrared spectroscopy, has played a key role in the development of this chemistry. Surface scientists studying the reactions of CO2 and its reduction by hydrogen are now able to use powerful techniques for acquiring vibrational data in the infrared region which help to identify surface-bound species. As more results emerge from these groups, it is apparent that there are many similarities in the spectral properties and reactions of the coordination compounds of CO2 and their surface-bound analogs.

Conformational isomerism in η5-cyclopentadienyl-η3-allylruthenium carbonyl complexes

Abstract Phase transfer catalysis provides a high yield synthetic route to endo - and exo -η 5 -cyclopentadienyl-η 3 -allylruthenium carbonyl and the corresponding η 3 -2-methallyl derivatives. In both cases, the endo isomer thermally isomerizes to the more stable exo isomer. Activation parameters for the isomerizations are substantially greater than those for the corresponding iron compounds. but a similar mechanism involving η 3 →η 1 →η 3 transformations is implied. Prolonged photolysis of the η 3 -allyl or 2-methallyl complexes leads to photostationary states in which the exo isomer is predominant.

Synthesis and characterization of ruthenium, rhenium and titanium formate, acetate and trifluoroacetate complexes. Correlation of IR spectral properties and bonding types

Abstract New formate ( 1 – 3 ; 4b , 6 and 7 ), acetate ( 8 , 9) and trifluoroacetate ( 12 , 13 and 15 ) complexes have been synthesized and characterized by elemental analysis and by IR and 1 H and 13 C NMR spectroscopies. New data or new synthetic procedures are provided for several known complexes ( 4a , 5 , 19 , 11 and 14 ). X-ray structural data for cis -Ru(bpy) 2 (CO)(OCHO)(PO 2 F 2 ) ( 4b ) clearly identify the η 1 -bound formate ligand bound to an octahedral ruthenium center and the data for fac -Re(CO) 3 (PPh 3 (OCOMe) ( 9 ) show an η 2 -bound acetate ligand bound to an octahedral rhenium center. Infrared spectral data for four types of formate complexes, three bonding types of acetates and the two known types of trifluoroacetate ligands are discussed. Comparisons of the v OCO bands for the carboxylate ligands in all of the complexes show that these bands are useful in identifying the bonding type of each carboxylate ligand.

Reductions of metal carbonyls by quaternary ammonium borohydrides

Abstract Quaternary ammonium borohydrides, used directly or generated in phase transfer reactions, are highly effective reagents for preparing metal carbonyl anions from metal carbonyls [Mo(CO) 6 , Mn 2 (CO) 10 , Re 2 (CO) 10 , CO 2 (CO) 8 , Fe 3 (CO) 12 , Ru 3 (CO) 12 and (η 5 -C 5 H 5 ) 2 Mo 2 (CO) 6 ] and from some metal carbonyl halides [BrMn(CO) 5 and η 5 -C 5 H 5 Mo(CO) 3 Cl]. Where strongly basic anions would be formed from a halide [BrMn(CO) 4 PPh 3 and η 5 -C 5 H 5 Ru(CO) 2 Br], the reactions provide efficient syntheses of the corresponding hydrides instead. The anion η 5 -C 5 H 5 Fe(CO) 2 − is not accessible by these techniques; reaction of η 5 -C 5 H 5 Fe(CO) 2 Br yields the iron dimer (via the highly nucleophilic anion) and the dimer is unreactive toward Q + BH 4 − . Reductions of Re 2 (CO) 10 conducted in CH 2 Cl 2 provide Re 2 (CO) 9 Cl − in high yield.

Synthesis of allyl-transition metal complexes by phase transfer catalyzed reactions of metal carbonyl halides: III. Considerations of the mechanisms☆

Abstract Mechanisms are proposed for the hydroxide ion-initiated reactions of metal carbonyl halides which lead to allyl-transition metal complexes under phase transfer conditions. Evidence is presented for intermediate anionic metallocarboxylic acids in reactions leading to η 3 -allyl products of molybdenum, iron, ruthenium and manganese, whereas η 1 complexes are shown to result from halide displacement reactions in which simple metal carbonyl anions are generated. In some cases phosphorus-containing ligands inhibit the hydroxide-promoted reactions of metal carbonyl halides with allyl bromide; a rationale involving decreased acidity of the carbonyl ligands is presented. Syntheses of η 3 -C 3 H 5 Mn(CO) 3 P(OCH 3 ) 3 and η 3 -C 3 H 5 Mn(CO) 2 [P(OCH 3 ) 3 ] 2 by phase transfer catalysis are also described.

Substituent effects in the 13C NMR spectra of iron carbonyl complexes with organic π-donors

Abstract The carbon spectra of nine tetracarbonylallyliron cations and seven acyclic dieneiron tricarbonyl complexes have been obtained. The effects of alkyl substituents (particularly methyl groups) on the chemical shift positions of ligand carbon atoms are described. The CO resonance signals for the cations are not averaged at ambient temperature thus indicating a high barrier to site exchange of these groups.

Synthesis of allyl complexes of iron, manganese and molybdenum by phase transfer catalysis

Abstract Synthetic methods are described for the convenient and efficient preparation of σ- and π-allyl complexes of iron, manganese and molybdenum from metal carbonyl halides and allyl halides in phase transfer catalyzed reactions.

Prototropic rearrangements of unsaturated hydrocarbons promoted by iron carbonyls

Abstract Results from the thermal and photochemical reactions of cis -1,3-pentadiene and 4-methyl-1,3-pentadiene with iron pentacarbonyl are described together with those obtained from the thermolysis and photolysis of their η2-iron tetracarbonyl and η4-iron tricarbonyl complexes. Consideration of these results, and some recent related work of others, allows a new reaction path to be formulated for alkene and diene isomerizations promoted by iron carbonyls.

The photoelectron spectra of some iron tricarbonyl complexes of 4π-electron donor ligands

Abstract The photoelectron spectra of eighteen compounds which are dienes or diene—iron tricarbonyl complexes have been investigated. A comparison of the photoelectron spectra of the dienes and corresponding iron carbonyl complexes has yielded the values of the perturbation energies for the two π orbitals of the diene moiety caused by interaction with Fe(CO) 3 . These perturbation energies are relatively constant (Δπ 1 = 0.89 ± 0.07 eV, Δπ 2 = 0.22 ± 0.06 eV) throughout the series. They have been employed to estimate the π ionization energies of the organic transient species cyclobutadiene (8.29 and 11.95 eV) and trimethylenemethane (8.36 and 11.79 eV), two novel molecules which have not been studied successfully by photoelectron spectroscopy to date.

Anti to syn isomerization in π-allyliron carbonyl complexes

Abstract Tetracarbonylallyliron cations having anti -1 substituents are isomerized to the corresponding syn isomers upon heating; these results have led us to reinterpret some other isomerizations involving π-allyl ligands of iron in terms of anti to syn rearrangements.