Cyclopentadiene Complexes Research Articles

Organic Syntheses via Transition Metal Complexes. 86. Regioselective [C3 + C2] Cyclopentadiene Annulation to Enamines with Alkynylcarbene Complexes of Chromium and Tungsten as Novel C3 Building Blocks

Alkynylcarbene complexes (CO)5MC(OEt)C⋮CPh (10) (M = Cr, W) react with tertiary 1-aminocycloalkenes CHC(NR2)CH2 17−23 (cyclopentenes, -hexenes, and -heptenes, dihydronaphthalenes and -phenanthrenes; NR2 = NMe2, pyrrolidino, and morpholino) to afford cyclopentadiene annulation products 24−30 in an overall [3 + 2] cycloaddition process. The reaction is highly regioselective and proceeds under very mild conditions in 60−99% yields. 1-Metalla-1,3,6-heptatrienes (CO)5MC(OEt)CHC(Ph)−CHC(NR2)CH (G) and 1-metalla-1,3,5-hexatrienes (CO)5MC(OEt)CHC(Ph)−CC(NR2)CH2 (H) are formed as key intermediates. Compounds H cyclize to give cyclopentadiene complexes as precursors to the cyclopentadienes 24−30. Hydrolysis of 1-metalla-1,3,6-heptatrienes G leads to the production of pyran-2-ylidene complexes, e.g., 32a,b.

Organische Synthesen mit Übergangsmetall‐Komplexen, 54 Cyclopentadiene aus 1‐Metalla‐1,3‐dienen und Alkinen durch Cyclisierung intermediärer 1‐Metalla‐1,3,5‐triene (Metall = Wolfram)

Organic Syntheses via Transition Metal Complexes, 54. — Cyclopentadienes from 1‐Metalla‐1,3‐dienes and Alkynes by Cyclization of Intermediate 1‐Metalla‐1,3,5‐trienes (Metal = Tungsten)We report on first examples of the formation of cyclopentadienes from a 1‐metalla‐1,3‐diene LnM=C‐C=C [LnM = W(CO)5] and an alkyne in [3 + 2] cycloaddition multistep reactions. In a first step the alkyne Et2N‐C=C‐Me (2) adds to the 1‐metalla‐1,3‐diene (CO)5W = C(OEt)‐CH=CHPh (1b) to give 1‐metalla‐1,3,5‐trienes (CO)5W=C(NEt2)‐CMe=C(OEt)‐CH=CHPh (3b) and (CO)5W=C(OEt)‐CH=C(NEt2)‐CMe=CHPh (4b). In a second step 3b cyclizes to thecyclopentadiene complex 5, which has an η1 ylide‐type structure as established by an X‐ray analysis. Hydrolysis of 5 leads to the formation of a 3‐aminocyclopentenone 7. The 1‐metalla‐1,3,5‐triene 4b yields a cyclopentadiene complex 8. In contrast to 5 the carbon skeleton of 8 has a connectivity different from that of the C3 unit of the 1‐metalla‐1,3‐diene 1.

PMR spectra of substituted cyclopentadiene complexes of cobalt

1. The PMR spectra of a series of cobalt cyclopentadiene complexes were studied. It was shown that the values of the spin-spin interaction constants of the Hexo and Hendo protons with H1,4 protons of the diene ring are not a function of the nature of the substituent and its position in the complex and can be used for the identification of exo-/endo-isomers. 2. The heterocyclic effect of the alkyl substituents was studied as a function of their nature and position in the complex.

Mass spectrometry of transition metal ?-complexes. Communication 35. Cyclopentadienyl (?4-cyclopentadiene) cobalt

1. A study of the fragmentation of 5-exo-substituted cyclopentadiene complexes of cobalt by the action of electron impact has shown the ease of the elimination of radicals from the gem position of the cyclopentadiene ligand with the formation of the corresponding cobalticinium cations. 2. The decomposition of the molecular ions of cobalt diene complexes with cleavage of the metal-ligand bonds proceeds with predominant elimination of the diene ligand. The migration of the endo-hydrogen atom to the cobalt atom is likely a characteristic feature of the fragmentation. 3. The direction of the fragmentation of the alkylcobalticinium cations formed upon the decomposition of the molecular ions of 5-exo-substituted cobalt diene complexes and directly upon the ionization of alkylcobaltocenes coincide, on the whole.

Homogeneous reduction of carbon monoxide

Hydride additions to eighteen electron iron cations containing both cyclopentadienyl and carbonyl Ligands occur regioselectively onto coordinated carbon monoxide to generate formyls which undergo further reduction or disproportionate to iron methyls. Alternatively Ligand loss converts the iron formyls to carbonyl hydrides. The carbonyl hydride [(η 5-C 5H 5)Fe(Ph 2PCH 2CH 2PPh 2)(CO)H] exists in equilibrium with the corresponding formyl complex which in polar solvents disproportionates to the methyl complex [(η 5-C 5H 5)Fe(Ph 2PCH 2CH 2PPh 2)CH 3] but in non polar solvents rearranges to the cyclopentadiene complex [(η 4-C 5H 6)Fe(Ph 2PCH 2CH 2PPh 2)CO]. Deuterium labelling studies have shown this latter migration to be an intramolecular transfer of hydride from the iron to the endo-position of the cyclopentadiene. Hydride reduction of the cation [(η 5-C 5H 5)Fe(PMe 3)(CO) 2] +PF 6 − generates via the formyl [(η 5-C 5H 5)Fe(PMe 3)(CO)CHO] the methyl complex [(η 5-C 5H 5)Fe(PMe 3)(CO)CH 3]. Carbon monoxide insertion into this iron methyl generates the corresponding acetyl complex [(η 5-C 5H 5)Fe(PMe 3)(CO)COCH 3] which is reduced by BH 3.THF to the ethyl complex [(η 5-C 5H 5)Fe(PMe 3)(CO)CH 2CH 3]. Successive clean homologations by treatment with CO and BH 3.THF gives after four carbonylations [(η 5-C 5H 5)Fe(PMe 3)(CO)COCH 2CH 2CH 2CH 3] which on oxidation yields entirely CO-derived pentanoic acid. The carbonyl hydride [(η 5-C 5H 5)Fe(PMe 3)(CO)H] in the presence of carbon monoxide produces the cyclopentadiene complex [(η 4-C 5H 6)Fe(PMe 3)(CO) 2] via an intermolecular hydride transfer from an intermediate formyl which is catalysed by [(η 5-C 5H 5)Fe(PMe 3)(CO) 2] +PF 6 −.

Sulfuric acid as a hydride ion acceptor in cobalt(I) cyclopentadiene complexes

Sulfuric acid as a hydride ion acceptor in cobalt(I) cyclopentadiene complexes

Hydride reduction of the cations {(η5-C5H5)Fe[(Ph2PCH2)3CMe]}PF6, {(η5-C5H5)-Ru[(Ph2PCH2CH2)2PPh]} PF6, and {(η5-C5H5)Ru[(Ph2PCH2)3CMe]} PF6: regioselectivity and mechanism

Reduction of the cation [η5-C5H5) Fe(tripod)] PF6 with lithium aluminium hydride gives (η5-C5H5)FeH-(tripod)via an SN1 mechanism, involving prior dissociation of a phosphine ligand leading to direct attack of hydride on the metal, in contrast with the related ruthenium cations [(η5-C5H5)RuL3]PF6(L3= triphos or tripod) which give the cyclopentadiene complexes (η4-C5H6RuL3via exo-hydride attack on the cyclopentadienyl ligand [tripod =(Ph2PCH2)3CMe; triphos =(Ph2-PCH2CH2)2PPh].

Optisch aktive übergangsmetall-komplexe : XXIX. Substituenteneinfluss auf die geschwindigkeit der racemisierung von (+) 579-C 5H 5Mn(NO)[P(C 6H 5) 3]COR

In the reaction of (+) 579-{C 5H 5Mn(NO)[P(C 6H 5) 3]CO}PF 6 with LiCH 3, LiC 6H 5, and Li- p-C 6H 4-X, respectively, the cyclopentadiene complexes (+) 579-(5- exo-R)C 5H 5Mn(NO)[P(C 6H 5) 3]CO and the acyl complexes (+) 579-C 5H 5Mn(NO)[P(C 6H 5) 3]COR are formed. Contrary to the configurationally stable cyclopentadiene complexes the acyl complexes racemise in solution according to a 1st order reaction. The racemisation was studied polarimetrically in the temperature range 0-40°C. It turned out, that electron releasing substituents X in the CO- p-C 6H 4X ligand strongly decrease the half lives, whereas electron attracting substituents increase the half lives considerably. There is a linear relationship between the σ-constants of the substituents and the rates of racemisation. The racemisation of the benzoyl complex (+) 579-C 5H 5Mn(NO)[P(C 6H 5) 3]COC 6H 5 is concentration dependent and is retarded by added P(C 6H 5) 3. This is explained by the formation of chiral intermediates in the triphenylphosphine dissociation reaction.

Über nitrosyl-metall-komplexe : XIII. Ring-addition und carbonyl-addition bei der umsetzung von[C 5H 5Mn(CO)(NO)P(C 6H 5) 3]PF 6 mit nukleophilen

[C 5H 5Mn(CO)(NO)P(C 6(C 6H 5) 3]PF 6 reacts with either LiCH 3 or LiC 6H 5 with formation of the ring addition products 5- exo-RC 5H 5Mn(CO)(NO)P(C 6H 5) 3 ad well as carbonyl addition products C 5H 5Mn(COR)(NO)P(C 6H 5) 3. [C 5H 5Mn(CO)(NO)P(C 6H 5) 3]PF 6 produces with NaBH 4 the cyclopentadiene complex C 5H 6Mn(CO)(NO)P(C 6H 5) 3 and the acetyl derivative C 5H 5Mn(COCH 3)(NO)P(C 6H 5) 3. Also the preparation of the ring addition products 5- exo-RC 5H 5Mn(CO) 2NO from LiCH 3 and LiC 6H 5, respectively, in very low yields, is described. All compounds were characterised by IR, 1H NMR and mass spectra. If the LiC 6H 5 used is prepared from bromobenzene, the new nitrosyl complex Mn(NO) 2[P(C 6H 5) 3] 2Br is formed as a by-product of the reaction of [C 5H 5Mn(CO)(NO)P(C 6H 5) 3]PF 6 with LiC 6H 5.

Reactions of organolithium and grignard reagents with the cyclopentadienyliron tricarbonyl cation and its derivatives

Reactions of CH 3Li, C 6H 5Li, and C 6H 5CH 2MgCl with [(C 5H 5)Fe(CO) 2Y] +-[B(C 6H 5) 4] − [Y  Co, P(C 6H 5) 3, and CS] have been investigated. The organolithium reagents used act either as reducing agents or as nucleophilic reagents towards the cyclopentadienyliron tricarbonyl cation and its thiocarbonyl analogue. Benzyl-magnesium chloride reacts with the cyclopentadienyl ring of [(C 5H 5)Fe(CO) 3] + and [(C 5H 5)Fe(CO) 2P(C 6H 5) 3] + producing neutral cyclopentadiene complexes.