Edo Janssen

27Al-NMR-Spektroskopie zur Charakterisierung von Organoaluminium-Verbindungen

Abstract 27Al NMR parameters of organoaluminium compounds of the type (RnAlX3-n)m (n = 0, 1, 2, 3; m = 1, 2, 3) and (R2 AlO(CH 2 ) 2 Y )2 (Y = OR′, NR′2) were determined. In related organoaluminium compounds the chemical shift δ(27Al) is an indicator for the coordination number of aluminium atoms: In the investigated monomeric compounds R3Al, with three-coordinated aluminium δ(27Al) lies between 280 and 210 ppm, whereas for four-coordinated aluminium in (RnAlX3-n)m complexes (n = 1, 2, 3; m = 2,3) δ(27Al) is between 180 and 125 ppm. In organoaluminium compounds with five-coordinated aluminium atoms δ(27Al) was found between 125 and 100 ppm. Inorganic complexes of the type XAl(OAlX2)2-(OBR)4 have distinct 27Al shift ranges for their four- (δ ∼ 90) and five- (δ ∼ 45) coordinated aluminium atoms. Owing to the relationship between δ(27Al) and the coordination number, organoaluminium compounds of unknown structure and the adducts of RnAlX3-n units with donors can be easily characterised by 27Al NMR spectroscopy.

Drei- oder Vierfach-Koordination des Aluminiums in Alkylaluminiumphenoxiden und deren Unterscheidung durch 27Al-NMR-Spektroskopie

The 27Al NMR spectra for a series of aryloxyaluminium compounds [RnAl(OAr)3−n]m (R  methyl, isobutyl; n  0–2; m  1, 2, 3) with various alkyl substituents in the 2 and 6 positions of the phenoxy rings have been measured. The δ(27Al) resonances give an indication of the number of aryloxy ligands and the coordination number of each Al atom. Monomeric R2AlOAr compounds have δ(27Al) resonances around 190 ppm whereas dimeric analogues give signals at 167 ppm. The 27Al NMR resonances for monomeric RAl(OAr)2 are found at ca. 100 ppm while those for [Al(OAr)3]2, where the aluminium atoms are solely bonded to aryloxy groups, lie at ca. 50 ppm. Characteristic shifts of the resonances were also observed for complexes of these compounds with THF, whereby it was found that the resulting change Δδ(27Al) decreases with increasing number of aryloxy ligands. The crystal structures of three selected compounds, 3, 8 and 11, were determined by X-ray crystallography.

Elektrochemische synthesen metallorganischer verbindungen III. Darstellung und umwandlung von π-cyclooctenyl-1,5-cyclooctadiencobalt

Abstract By electrolysis of cobalt(II)-acetylacetonate in the presence of 1,5-cyclooctadiene there is obtained π-cyclooctenyl-1,5-cyclooctadienecobalt (I). By heating of I to 60° in 1,5-cyclooctadiene, π-bicyclo[3.3.0]octadienyl-(1,5-cyclooctadiene)cobalt (II) and cyclooctene are formed.

Elektrochemische synthese metallorganischer verbindungen : V. Das verhalten von cyclooctatetraen bei der elektrochemischen reduktion in tetrahydrofuran

Abstract The ion pairs [R4El]+[COT]− and [R4El]+2[COT]2− (El = N, P) are observed as intermediates in the electrochemical reduction of cyclooctatetraene in the presence of tetraorganoonium cations. The preparation of these ion pairs has been examined, and their reactions in THF have been followed by polarography and cyclic voltammetry and the reaction products isolated and identified. Two polarographic waves are observed for COT, independent of the alkyl group (R = butyl, ethyl or methyl) in the tetraalkylammonium cation. In contrast to the interpretation of COT reduction in acetonitrile these two waves are assigned to reduction to the radical ion and the dianion. The reactions of the ion pairs [R4N]+2[COT]2− (R = butyl, ethyl) lead (by Hofmann elimination) to cyclooctatrienes and their alkyl derivatives, causing a third polarographic wave. The behavior of ion pairs of ammonium cations with the anthracene dianion is similar; [P(C4H9)4]+2[COT]2− forms butylidenephosphorane R3PCHC3H7 and cyclooctatriene. The standard potentials of alkali and alkali earth metal ions, which were determined in THF, are used in the discussion of the electrochemical formation of the COT dianion.

Radiation chemistry of ethers. Part VI. Photolysis at 254 nm of the diethyl ether–oxygen charge transfer complex

Oxygen-saturated diethyl ether exhibits a charge transfer absorption band (λmax. 215 nm) with considerable absorption at 254 nm. Photolysis was carried out with a low pressure mercury arc. Photolysis of products was avoided by keeping conversion low, and chain reactions were minimized by working at –30°. The major products(quantum yields) were: H2O2(0·24), 1-ethoxyethyl hydroperoxide (0·04), ethyl acetate (0·26), acetaldehyde (0·18), ethanol (0·18), ethyl formate (0·04), methanol (0·035), formaldehyde (0·005), and ethyl vinyl ether (0·013). A satisfactory material balance was obtained. The products formed are consistent with a primary photoprocess involving transfer of an electron to the O2 to give O2–. Further, deprotonation of the ether radical cation in the presence of O2 leads to the 1-ethoxyethylperoxyl radical. With the exception of 1-ethoxyethyl hydroperoxide all major products are believed to arise from disproportionation reactions of these two radicals.

Additionen von vinyl- und allyl-titan-bindungen an ethylen

Abstract Reaction of Cp 2 TiCl ( 1 ) with the alkylmagnesium halides 2a – 2d , 2g (alkyl = Me, Et, Pr, iso-Pr, hexyl) and ethylene give bis(η 5 -cyclopentadienyl)(η 3 -1-methylallyl)titanium ( 3 ). Mechanistic investigations indicate that hydrogen transfer from ethylene either to the initially formed Cp 2 alkyltitanium or to Cp 2 ethyltitanium, formed by βH-elimination to Cp 2 -titaniumhydride and addition to ethylene, leads to liberation of alkane or alkene and ethane and formation of Cp 2 vinyltitanium F as an intermediate. Insertion of ethylene (even below 0°C) into the vinyltitanium bond of F leads to Cp 2 3-butenyltitanium, which isomerizes to 3 . Reaction of 3 at ca. 80°C with ethylene in toluene occurs in part with hydrogen transfer to give the butene isomers 4 , 5 and F and in part with addition of the allyltitanium bond to ethylene to give the 2,4-hexadiene isomers 6a – 6c by βH-elimination. The compounds 6a – 6c are also formed in the catalytic codimerization of butadiene with ethylene in the presence of 3 . This reaction has a regioselectivity of > 99%.

Koordinations-Komplexe Lewis-basischer Dialkylaluminiumalkoxide mit Trialkylaluminium

Abstract The organoaluminium complexes [R2AlO(CH2)3Y]2 and [R2 AlO(CH 2 ) 2 Y ]2 (Y = OR′, NR2′) react with [R3Al]2 to yield the new compounds R2 Al ← Y(CH 2 ) m O AlR3 (m = 2,3). The α-oxygen atom, which serves as bridge in the dimers, functions as n-donor in the 1:1 adducts with trialkylaluminium. The solution structure and the fluxional behaviour of these new complexes was elucidated by 1H, 13C, and 27Al NMR spectroscopy.

“Ethylaluminiumdiethoxid” - Ein Gemisch einer Vielzahl von Verbindungen

Abstract Using a combination of 27 Al NMR and mass spectroscopy the “ethyl-aluminiumdiethoxide” has been identified as a mixture of six tetramers [Et n Al 4 (OEt) 12- n ] ( B ) ( n = 1–6) and several trimeric associates [Et n Al 3 (OEt) 9- n ] ( A ) ( n = 1–5). From 27 Al NMR data it was concluded that the tetramers consist of one central octahedral aluminium atom which is coordinated to six OEt groups and of three four-coordinated aluminium atoms in the outer sphere each of which is associated to the centre via two of these OEt bridges (structure B ). The trimers possess a central five-coordinated aluminium atom attached to five OEt groups, four of which also function as bridging ligands to the two four-coordinated aluminium atoms in the outer sphere (structure A ).