Niall J. Gogan

Pyrrole chemistry XXV: A simplified synthesis of some 3-substituted pyrroles

Abstract A new synthesis is reported which allows the rapid preparation in good yield of 3-aroyl-, 3-acetyl- and 3-nitro- pyrroles from pyrrole utilizing the 1-benzenesulfonyl group as a blocking group.

Complexes of ligands containing phenyl and cyclopentadienyl rings. Synthesis, characterization and spectroscopic studies on tricarbonylmanganese derivatives

Abstract A series of (benzoylcyclopentadienyl)manganese tricarbonyl derivatives have been prepared and characterized. In addition several other Mn(CO) 3 complexes containing both a phenyl and a cyclopentadienyl ring have been prepared and characterized including the benzylcyclopentadienyl, phenylcyclopentadienyl and styrylcyclopentadienyl complexes. They have been studied by UV, IR and proton NMR. The ketonic v (CO) is significantly affected by o - or α-substitution. Shifts in τ values in the proton NMR spectra on substitution are interpreted in terms of both electronic and steric effects.

ESR of organometallics : I. The anion of (benzoylcyclopentadienyl)manganese tricarbonyl and some methyl substituted derivatives

Abstract The radical anions of (benzoylcyclopentadienyl)manganese tricarbonyl, (1-benzoyl-2-methylcyclopentadienyl)manganese tricarbonyl and (1-benzoyl-3-methylcyclopentadienyl)manganese tricarbonyl have been prepared by alkali metal and electrolytic reduction in 1,2-dimethoxyethane (DME) or tetrahydrofuran (THF). The best ESR spectra are obtained by potassium reduction in DME. Each anion shows a major splitting from the 55Mn nucleus and smaller splittings from the p- and o-protons of the phenyl ring.

ESR of organometallics : II. spectral studies and extended huckel calculations on substituted benzoylcyclopentadienylmanganese tricarbonyl anions

Abstract ESR studies and extended Huckel molecular orbital calculations have been carried out on the radical anion of benzoylcyclopentadienylmanganese tricarbonyl and on the mono- and di-methyl substituted derivatives. A good agreement between the calculated and observed hyperfine constants is observed. The results support the view that there is extensive electron delocalization over the molecule with most of the spin density on the manganese atom the ketonic group and the phenyl ring. The change in spin density distribution on varying the substituent position shows that the major effect is electronic in nature.

Complexes of ligands containing phenyl and cyclopentadienyl rings. Synthesis, characterization and spectroscopic studies on tricarbonylmanganese tricarbonylchromium derivatives☆

Abstract A series of tricarbonylchromium (benzoylcyclopentadienyl)-manganese tricarbonyl derivatives have been prepared and characterized. In addition, several other Cr(CO)3Mn(CO)3 complexes containing both a phenyl and a cyclopentadienyl ring have been prepared and characterized including the phenylcyclopentadienyl, benzylcyclopentadienyl and styrylcyclopentadienyl complexes. All the complexes have been studied by UV, IR and proton NMR spectroscopy. The proton NMR spectrum shows that the electron-withdrawing effect of the Cr(CO)3 group is transmitted to the cyclopentadienyl ring in the benzoylcyclopentadienyl series but not in the benzyl case. The v(CO)s of the Mn(CO)3 group are only slightly affected by complexing of the Cr(CO)3 group on the arene ring. In general substituent effects follow the expected trends.

ESR of organometallics III Electronic effects in the tricarbonylchromium (benzoylcyclopentadienyl) manganese tricarbonyl anion and some substituted derivatives

Abstract The ESR spectra of the tricarbonylchromium (benzoylcyclopentadienyl) manganese tricarbonyl anion and some substituted derivatives have been determined. The results show that the Cr(CO) 3 group withdraws spin density from both the phenyl protons and the manganese atom to the extent where A(H) is reduced by about one half and A(Mn) by about one third. Comparison of the experimental results with extended Huckel calculations shows that there is extensive delocalization of spin density throughout the organic system and that there is considerable π-overlap between the Cr atom and the phenyl ring. The conclusions are in general agreement with those resulting from IR and 1 H-NMR measurements. The ESR results for the -Cl and -OCH 3 derivatives without a Cr(CO) 3 group are also reported.

Esr of organometallics : IV. Anions of monosubstituted benzophenonechromium tricarbonyl complexes

Abstract The radical anions RC 6 H 4 COC 6 H 4 R 1 Cr(CO) 3 − (R = H, o -CH 3 , p -CH 3 , p -OCH 3 , p -Cl, p -F and R 1 = H; R = H, R 1 = o -CH 3 , p -CH 3 ) were prepared by potassium reduction in 1,2-dimethoxyethane and their ESR spectra measured. Each has a spectrum width of about half that of the corresponding ligand. Both coordination isomers of the o -CH 3 complexes and the ligand have spectra consisting of four lines assigned to splittings from the para - and ortho -protons of the unsubstituted ring with A p = A o . The p -CH 3 complexes both have 7-line spectra assigned to splittings from the two sets of o -protons one set having half the hyperfine splitting of the other. The reduction in hyperfine splitting of the uncomplexed as well as the complexed ring protons is an indication that the unpaired electron density is delocalized throughout the ligand system.

Chromium and manganese carbonyl π-complexes of 2-benzylpyrrole and 2-phenylpyrrole. Spectra and electronic effects☆

Abstract Cr(CO) 3 and Mn(CO) 3 complexes of 2-benzylpyrrole and 2-phenylpyrrole and the complexes in which both a Cr(CO) 3 and an Mn(CO) 3 group are attached to complex of 2-phenylpyrrole, have been isolated. In each case the Cr(CO) 3 group is π-bonded to the phenyl ring and the Mn(CO) 3 group to the pyrrolyl ring. The NMR spectra can be interpreted in terms of electronic effects transmitted through the σ-electron system and in ring current effects. The IR carbonyl stretching frequencies show little effect of one M(CO) 3 group on the other.

13C NMR and SCCCMO studies on substituted benzophenonetricarbonylchromium complexes

Abstract 13C NMR studies on benzophenonetricarbonylchromium and its p-F, p-Cl and p-OCH3 derivatives, with the substitutents on the uncomplexed rings, show a small substituent effect on the complexed ring and on the carbons of the Cr(CO)3 group. The SCCCMO calculations show π-electron donation from the ring to the metal but greater σ-electron back-donation which leaves the ring more negatively charged than before complexation. The chromium atom is more positively charged than it is in benzenetricarbonylchromium. The trends is calculated CO bond orders are in agreement with the trends in CO infrared stretching frequencies.

Chromium(III) chelates of some 2-acylpyrroles☆

Abstract Hexacarbonylchromium(O) reacts with 2-acylpyrroles (RCOC 4 H 3 NH, R = H, CH 3 or C 6 H 5 ) in refluxing n -octane to form the tris(2-acylpyrrolato) chromium(III) complexes, Cr(RCOC 4 -H 3 N) 3 . The complexes are stable dark yellow or red crystalline solids with magnetic moments in the usual range for chromium(III) octahedral complexes. Their u.v., i.r. and mass spectra can be interpreted in terms of a chelate structure in which both the pyrrolato nitrogen and the oxygen of the carbonyl group are complexed to the metal to form a five-membered chelate ring.