Cornelius G. Kreiter

Übergangsmetall-carben-komplexe XXVII. Ringsubstituierte (Methoxyphenylcarben)-pentacarbonylchrom(o)-komplexe

Abstract The preparation of a series of ring-substituted (methoxyphenylcarbene)-pentacarbonylchromium(O) complexes (CO) 5 CrC(OCH 3 )R (R= p -(CH 3 ) 2 NC 6 H 4 , p -CH 3 OC 6 H 4 , p -CH 3 C 6 H 4 , p -FC 6 H 4 , p -ClC 6 H 4 , p -BrC 6 H 4 , p -CF 3 C 6 H 4 , m -(CH 3 ) 2 NC 6 H 4 , m -CH 3 OC 6 H 4 , m -CIC 6 H 4 , m -CF 3 C 6 H 4 , o -CH 3 OC 6 H 4 , o -CF 3 C 6 H 4 , 2,4,6-(CH 3 ) 3 C 6 H 2 ,2,6-(CH 3 O) 2 C 6 H 3 ) and also (methoxyphenylcarbene)-, (methoxy-1-naphthylcarbene)-, and (methoxybenzylcarbene)pentacarbonylchromium(0) is described. The IR, 1 H NMR, and electronic spectra of these new compounds are discussed. The ionization potentials of several compounds are given. The σ-donor/π-acceptor behavioral of the different carbene ligands C(OCH 3 )R is investigated by means of the ν(Cue5f8O) absorptions, the CO force constants and the ionization potentials of the compounds. The rotational energy of activation about the C carbene ue5f8OCH 3 bond in the complexes is determined by temperature dependent 1 H NMR spectra. The variations in the bonding, which is caused by a single substituent in different positions on the phenyl ring, are discussed and compared with the values of their Jaffe σ-constants.

Spektroskopische untersuchungen an organometallischen verbindungen : XXXIII. 1H-NMR-spektren von σ-cyclopentadienylen von metallen der IV. Gruppe☆☆☆

Zusammenfassung Es werden die Protonenresonanzspektren von Metall-σ-Cyclopentadienylen der IV. Gruppe bei verschiedenen Temperaturen angegeben und auf der Grundlage einer Valenztautomerie diskutiert.

Kinetik und Mechanismus der Aminolyse von (Methoxyphenylcarben)pentacarbonylchrom(0) - Eine reaktion 4. Ordnung mit negativer Arrhenius-Aktivierungsenergie☆

Abstract The kinetics of the reaction of (methoxyphenylcarbene)pentacarbonylchromium(0), Cr(CO)5C(OCH3)C6H5 (I), with primary amines RNH2 (R = n-C4C9, C6H11, CH2C6H5) have been studied in n-decane, dioxane, methanol and dioxane/methanol ( 1 1 ) as solvents. The formation of the aminophenylcarbene complexes Cr(CO)5C(NHR)C6H5 (II) follows the fourth-order rate law d[(II)]/dt = KA·[(I)]·[RNH2]·[HX]·[Y] where HX represents a proton donating and Y a proton accepting agent. The results of the kinetic studies are conistent with a consecutive step mechanism which starts with the formation of a 1 1 -adduct of the carbene complex (I) and the proton donor HX and includes the activation of the attacking amine by the proton acceptor Y. The existence of hydrogen bonds between (I) and HX, and between RNH2 and Y is shown by NMR measurements. The mechanism explains the unexpected result that the rate of formation of (II) decreases with increasing temperature, i.e. a negative Arrhenius activation energy is observed. The mechanismsof the aminolysis of carboxylic esters and of the carbene complex (I) (which may formally be considered as a very reactive analog of an ester) are compared. Mechanistic similarities and differences will be discussed.

Spektroskopische untersuchungen an metallorganischen verbindungen XLV. 1H-NMR-spektren von naphthalin-chrom(0)-tricarbonyl und seinen derivaten2

Abstract Anhand der 1H-NMR-Spektren einer Reihe von substituierten Naphthalinmetall-tricarbonylen gelingt die Strukturermittlung der verschiedenen Isomeran. Ferner Jassen sich Regeln zur Vorbersage der Komplexbildung angeben. Die Darstellungen der Substanzen werden beschrieben.

Einschiebung von inaminen in metall—carbenkohlenstoff-bindungen

Pentacarbonyl[methoxy(methyl)carbene]chromium(0) and pentacarbonyl[methoxy(phenyl)carbene]chromium(0) react in hexane at room temperature with diethylaminoethyne and l-diethylamino-1-propyne to give 11 compounds. These are identified as insertion products of the alkyne entity into the metal—carbene bond by spectroscopic methods.

Photochemische addition konjugierter diene an tricarbonyl-η-1,3,5-cycloheptatrien-chrom(0) ☆

Abstract Conjugated dienes, e.g. 1,3-butadiene or trans , trans -2,4-hexadiene, undergo [4 s + 6 s ] cycloaddition with tricarbonyl-η-1,3,5-cycloheptatrienechromium(0) (I) on irradiation with UV light in n-pentane at 263 K, and the bright red tricarbonyl-η-bicyclo[4.4.1]undeca-1,3,7-trienechromium(O) complexes Cr(CO) 3 C 11 H 14 (II) and Cr(CO) 3 C 13 H 18 (III) are formed in high yields. The structures of II and III were determined by IR, NMR and mass spectra and confirmed by an X-ray structure analysis for III.

Gehinderte ligandenbewegungen in übergangsmetall komplexen : III. Olefinrotation in cclopentadienyl-mangan-dicarbonyl- äthylen und cyclopentadienyl-chrom-carbonyl- nitrosyl-äthylen☆

Abstract The temperature dependence of the 1 H NMR spectra indicates that the ethylene ligand in the isoelectronic complexes, cyclopentadienylmanganese dicarbonyl ethylene, C 5 H 5 Mn(CO) 2 (CH 2 =CH 2 ) (I), and cyclopentadienylchromium carbonyl nitrosyl ethylene, C 5 H 5 Cr(CO)(NO)(CH 2 =CH 2 ) (II), undergoes a hindered rotation around the metalue5f8olefin bond axis. In addition to the ethylene complexes I and II, the corresponding complexes containing trans -D 2 - ethylene, C 5 H 5 Mn(CO) 2 ( trans -CHD=CHD)(ID) and C 5 H 5 Cr(CO)(NO)- ( trans -CHD=CHD) (IID), have been prepared and studied in order to support the analysis of the 1 H NMR spectra of I and II. The activation barriers for the ligand motion were fond to be Δ G ‡ 1 68 = 8.4 ± 0.2 kcal/mole in the case of I and ID, and Δ G ‡ 2 38 = 11.4 ± 0.2 kcal/mole in the case of II and IID.

Spektroskopische Untersuchungen an organometallischen Verbindungen XXVI. 1H-NMR-Spektren von Cyclopentadienyl-verbindungen des vierbindigen Zinns

The 1H-NMR spectra of stannanes of the type (C5H5)4-nSnRn, with Rue5fbCH3, C2H5, n-C4H9, and C6H5 and n=0, 1, 2, and 3, are reported and discussed. The five cyclopentadienyl protons show only one sharp signal at approx. τ=4, which has satellites at both sides originating from Hue5f8117Sn- and Hue5f8119Sn-coupling. These coupling constants 117SnC5H5 and 119SnC5H5 show a dependence on the type and number of additional substituents of the stannanes.

Übergangsmetall—carbin-komplexe

Abstract cis -Tetracarbonyltrimethylphosphinemethylmethoxycarbenechromium(0) reacts with BF 3 with splitting off of the methoxy group and substitution of a CO ligand. The product formed was identified as mer -(BF 4 )Cr(CO) 3 [P(CH 3 ) 3 ](CCH 3 ). This new complex, which contains a BF 4 -group coordinated to the Cr-atom, is most sensitive to moisture. With water it reacts to give { mer -H 2 OCr(CO) 3 [P(CH 3 ) 3 ](CCH 3 )} + [BF 4 ] − . IR, 1 H NMR, 13 C NMR and 31 P NMR spectra of the new compounds are discussed.

Gehinderte Ligandenbewegungen in Übergangsmetallkomplexen : VII. Rotation der olefinliganden L = malein- und furmarsäuredimethylester in komplexen des typs C5H5Mn(CO)2L und C5H5Cr(CO)(NO)L

Abstract The restricted rotation of the olefin ligands L = dimethyl maleate and dimethyl fumarate in complexes of the type C 5 H 5 Mn(CO) 2 L and C 5 H 5 Cr(CO)-(NO)L, respectively, has been investigated on the basis of their temperature-dependent 1 H NMR spectra. The olefinic ligand is arranged preferably in a position where the Cue5fbC double bond is parallel to the plane of the cyclopentadienyl ring. The possible stereoisomers are discussed using this model. The 1 H NMR spectra of C 5 H 5 Cr(CO)(NO)( trans -CH 3 OOCue5f8CHue5fbCHue5f8COOCH 3 ) provide direct evidence that the configuration (R or S) at the metal is stable up to 120°C, and that the restricted motion of the olefin is exclusively rotation around the metal—olefin bond. The activation barriers of the olefin rotation are found to be appreciably lower in the C 5 H 5 Mn(CO) 2 L complexes (Δ G ≠ ( T C ) 11–12 kcal mol −1 ) than in the isoelectric C 5 H 5 Cr(CO)(NO)L compounds (Δ G ≠ ( T C ) 15–20 kcal mol −1 ).