Jürgen Kaub

Photochemische reaktionen von übergansmetall-olefinkomplexen: III. [4 + 6]-cycloaddition konjugierter diene an hexacarbonyl-μ-η6:6(-1,1′-bi(2,4,6-cycloheptatrien-1-yl)dichrom(O)☆

Abstract UV irradiation of hexacarbonyl-μ-η6:6-1,1′-bi(2,4,6-cycloheptatrien-1-yl)dichromium(O) (I) in THF in the presence of 1,3-butadiene (A), E-1,3-pentadiene (B) and EE-2,4-hexadiene (C) causes preferentially a twofold [4 + 6]-cycloaddition and formation of the hexacarbonyl-μ-2–5 : 8.9-η-2′–5′ : 8′,9′-η-11,11′-bi(bicyclo-[4.4.1]undeca-2,4,8-trien-11-yl)dichromium(O) complexes (IVA–IVC). Partial decomplexation after the first [4 + 6]-cycloaddition yields isomeric tricarbonyl-2–5:8,9-η- (IIA–IIC) and tricarbonyl-2′–7′-η-{11-(2′,4′,6′-cycloheptatrien-1′-yl)bicyclo[4.4.1]undeca-2,4,8-triene}chromium(O) complexes (IIIA–IIIC). With 2,3-dimethyl-1,3-butadiene (D) mainly dicarbonyl-2–6 : 2′–4′-η-{1-(2′,3′-dimethyl-3′-buten-1′,2′-diyl)-7-(8″,9″-dimethylbicyclo[4.4.1]undeca-2″, 4″,8″-trien-11″-yl)cyclohepta-3,5-dien-2-yl}chromium(O) (VD) besides small amounts of pentacarbonyl-μ-2–6 : 2′–4′-η-2″–7″-η-{1-(2′,3′-dimethyl-3′-buten-1′,2′-diyl)-7-(2″, 4″,6″-cycloheptatrien-1″-yl)cyclohepta-3,5-dien-2-yl}dichromium(O) (VID) and tricarbonyl-2′-7′-η-{11-(2′,4′,6′-cycloheptatrien-1′-yl)-8,9-dimethyl-bicyclo[4.4.1]undeca-2,4,8-triene}-chromium(O) (IIID) is obtained. VD adds readily CO to yield tricarbonyl-2–5 : 8,9-η-11,11′-bi(8,9-dimethyl-bicyclo[4.4.1]undeca-2,4,8-trien-11-yl)chromium(O) (VIID). Finally D adds to VID under formation of pentacarbonyl-μ-2–6 : 2′–4′-η-2″–5″ : 8″,9″-η-{1-(2′,3′-dimethyl-3′-buten-1′,2′-diyl)-7-(8″,9″-dimethyl-bicyclo[4.4.1]- undeca-2″,4″,8″-trien-11″-yl)cyclohepta-3,5-dien-2-yl}dichromium(O) (VIIID). From IVA–IVC the hydrocarbon ligands (IXA–IXC) can be liberated by P(OCH3)3 in good yields. The structures of the compounds IIA–IXC were determined by IR

Photoreaktion von hexacarbonyl-di(μ5-methylcyclopentadienyl) dimolybdän mit konjugierten dienen

Abstract UV-irradiation of hexacarbonylbis(μ5-methylcyclopentadienyl)dimolybdenum (I) at 253 K in presence of 1,3-butadiene (IIIa) yields in a first step tetracarbonylbis(μ5-methylcyclopentadienyl)dimolybdenum (II). In successive photochemical reactions II interacts with IIIa to result in a mixture of four complexes which was resolved by column chromatography at low temperature. μ4-1,3-Butadiene-di-carbonyl-μ-η1:2-carbonylbis(η5-methylcyclopentadienyl) dimolybdenum (Va), a derivative of the unstable pentacrbonylbis(η5-methylcyclopentadienyl)dimolybdenum with a 4-electron bridging carbonyl ligand is obtained as the main product, in moderate yield. The E and Z isomers of η3-(2-buten-1-yl)-dicarbonyl-η5-methylcyclopentadienylmolybdenum (E-IVa, Z-IVa), and μ-η2:2-1,3-butadiene-dicarbonylbis(η5-methylcyclopentadienyl)dimolybdenum (VIIa) were obtained as by products. Similarly the acyclic conjugated dienes, 2-methyl-1,3-butadiene (IIIb), E-1,3-pentadiene (IIIc) and 2,3-dimethyl-1,3-butadiene (IIId), react with II to give dicarbonyl-η3-enyl-η5-methylcyclopentadienylmolybdenum (IVb–IVd), dicarbonyl-μ-η1:2-carbonyl-η4-diene-bis (η5-methylcyclopentadienyl)dimolybdenum (Vb–Vd) and dicarbonyl-μ-η2:2-1,3-dienebis(η5-methylcyclopentadienyl)dimolybdenum (VIIb–VIId). Dicarbonyl-μ-η1:2-carbonyl-η4-E-1,3-pentadienebis(η5-methylcyclopentadienyl)dimo-lybdenum (Vc) is in thermal equilibrium with tricarbonyl-η2-E-1,3-pentadienebis(η5-methylcyclopentadienyl)dimolybdenum (VIc). In contrasts, reaction of I with 1,3,5-hexatriene (IIIe) yields only tetracarbonyl-μ-(η3:3-E, E-2,5-hexadien-1,4-diyl)bis(η5-methylcyclopentadienyl) dimolybdenum (IVe) in small amounts. The dicarbonyl-μ-η1:2-carbonyl-η4-dienebis(η5-methylcyclopentadienyl)dimolybdenum complexes (Va–Vd) show hindered intramolecular exchange of the η1:2-bridging carbonyl with the other two carbonyl ligands, with barries of activation of 53 kJ/mol (Va) and 56 kJ/mol (Vd). The complexes IVa–VIId were identified from their IR spectra in the CO region and from their 1H and 13C NMR spectra. The crystal and molecular structure of Vd was determined b X-ray crystallography.

Photoreaktion von Hexacarbonyl-bis(η5-methylcyclopentadienyl)dimolybdän mit cyclischen konjugierten Dienen

Abstract UV-irradiation of hexacarbonyl-bis(η 5 -methylcyclopentadienyl)dimolybdenum (I) in presence of 1,3-cyclopentadiene (IIIA), 1,3-cyclohexadiene (IIIB), and 1,3-cyclooctadiene (IIID) at 253 K in n-pentane yields the dicarbonyl-η 3 -cycloenyl-η 5 -methylcyclopentadienylmolybdenum complexes (IVA, IVB, IVD) in moderate yields. With 1,3,5-cycloheptatriene (IIIE) the corresponding dicarbonyl-η 3 -cycloheptadienyl-η 5 -methylcyclopentadienylmolybdenum (IVE) is isolated. IIIB, because of its diene component, there is IR spectroscopic evidence for the formation of dicarbonyl-μ-η 1:2 -carbonyl-η 4 -1,3-cyclohexadiene-bis(η 5 -methylcyclopentadienyl)dimolybdenum (V). In contrast, 1,3-cycloheptadiene (IIIC) reacts with I to give the dinuclear tricarbonyl-μ-η 1:4 -1,3-cycloheptadien-1-yl-hydrido-bis(η 5 -methylcyclopentadienyl)dimolybdenum (VI). The complexes IVA–VI were identified from the v (CO) region in their IR spectra and from their 1 H NMR spectra. The crystal and molecular structure of VI was determined by an X-ray diffraction study.

Darstellung und Struktur der zweikernigen tert-Butyliminovanadium(IV)-Komplexe: [(tC4H9N)2V2Cp2X2] (X = OtC4H9, Cl)

Abstract [(μ-NtC4H9)2V2Cp2(OtC4H9)2] (2) and [(μ-Cl)2V2Cp2(NtC4H9)2] (6) have been prepared by reaction of LitC4H9 with tC4H9N=VCp(OtC4H9)Cl and tC4H9N=VCpCl2, respectively. The molecular structure has been investigated by X-ray diffraction analysis. NMR and ESR Spectra indicate two types of tert-butyliminovanadium(IV) complexes: 2 (diamagnetic) and 6 (paramagnetic).

Gehinderte Ligandbewegungen in Übergangsmetallkomplexen: XXXIV. η4:(2)-5-H-Benzocyclohepten-dicarbonyltrimethylphosphit-chrom(0), ein ungewöhnlicher Elektronenmangel-Komplex☆☆☆

Abstract Pentacarbonyltrimethylphosphitechromium(0) (I) reacts with 5 H -benzocycloheptene (II), in n-pentane, upon irradiation with UV light, at 200 K, to give in moderate yield the grass-green η 4:(2) -5 H -benzocycloheptenedicarbonyltrimethylphosphitechromium(0) (III) (superscript two in parentheses indicates a weaker bond). The crystal and molecular structure of III has been determined by X-ray diffraction studies. The chromium atom is coordinated to the seven-membered ring. The CrC bond distances indicate that there is a distinctly weaker interaction between the metal and the two carbons atoms, which are common to both condense rings. At 160 K the 1 H NMR spectrum of III corresponds to the molecular structure in the solid state. The temperature dependence of the NMR signals between 160 and 240 K indicates a reversible interchange of III with isomeric η 4:CH -5 H -benzocycloheptenedicarbonyltrimethylphosphitechromium(0) (IV), which is only present in small quantities. At higher temperatures hindered rotation of the [Cr(CO) 2 &[;P(OCH 3 ) 3 &];] fragment, and finally a 1,5-H shift of H(5- endo within the 5H-benzocycloheptene ligand are observed. The barriers of activation for the three independent processes were found to be Δ G ‡ 220 = 37.6, Δ G ‡ 280 = 57.8 and Δ G ‡ 320 = 61.1 kJ mol −1 .

Chrom(0)-und Molybdän(0)-Komplexe von 11-Isopropyliden-bicyclo[4.4.1]undeca-2,4,8-trienen / Chromium(0) and Molybdenum(0) Complexes of 11-Isopropylidene-bicyclo[4.4. 1]undeca-2,4,8-trienes

11-Isopropylidene-bicyclo[4.4.1]undeca-2,4,8-triene (IBU, 1A) and five alkyl substituted derivatives (1B-1F) contain a conjugated diene unit and two isolated CC-double bonds, one exocyclic and one incorporated into the bicvclus, each suited for complexation to transition metals. With [Cr(CO)3(CH3CN)3] (2) 1A-1F form [Cr(CO)3(η6-IBU)] complexes (3A−3F). in which the IBU ligands are coordinated to the chromium via the diene unit and the exocyclic CC-double bond. The corresponding [Mo(CO)3(η6-IBU)] complexes (5A−5F) are obtained from the reactions of [Mo(CO)3(diglyme)] (4) with 1A−1F. In addition, the isomeric [Mo(CO)3(η6-IBU)] complexes (6A−6D) are formed, in which the IBU ligands are bound to molybdenum via the three cyclic CC-double bonds. The complexes 3A−3F, 5A−5F and 6A−6D were studied by IR and NMR spectroscopy (1H. 13C) and characterized by C, H elemental analyses. The crystal and molecular structure of 1A was determined by X-ray structure analysis.