Ibrahim Jibril

Stereoselective additions to carboxylic acid dianions and β-lactone substituted ester enolates

New stereoselective syntheses are reported for racemic 4-epi-blastmycinone (6) and δ-multistriatine (13) utilizing the anti-configurated γ, β-unsaturated β-hydroxy-carboxylic acids 2a/b. A diastereo- and enantioselective aldoltype addition of phenylacetic acid dianion to benzaldehyde has been achieved by employing optically active alkoxide amide bases. Finally, highly stereocontrolled additions to the novel β-lactone substituted ester enolates 22 are described.

μ3-P- und μ3-As-verbrückte cluster als liganden

Abstract The trihalophosphane complexes LnMPHal3 (LnM = Cp(CO)2Mn, (CO)5Cr, (CO)5W; Hal = Cl, Br), upon treatment with Co2(CO)8, mainly yield clusters of the type Co3(CO)9(μ4-P)MLn with the (μ3-P)Co3(CO)9) unit acting as ligand. The analogous arsenic compound Co3(CO)9(μ4-As)Cr(CO)5 is obtained from the arsinidine complex [(CO)5Cr]2AsCl with NaCo(CO)4. In addition to the syntheses and reactios of these clusters several reactions leading to clusters with μ4-P-, μ4-As-, μ4-PR- and μ2-PR2 groups by reductive dehalogenation of coordinated halophosphanes are reported. The different types of compounds are documented by six X-ray-structure analyses.

Diphosphor, phosphor-, arsen- und antimonatome als clusterbaugruppen

Abstract Reactions of Fe2(CO)9 with LnMPHal3 (LnM = 16-electron fragment: Cp(CO)2Mn, (CO)5Cr, (CO)5Mo, (CO)5W) yield clusters of the type F3(CO)9(μ4-P)2(MLn)2 (II). Compounds II contain the trigonal bipyramidal cluster framework Fe3(CO)9(μ3-P)2, the basis of which is a closed triangle formed by three Fe(CO)3 units; the apical positions of the trigonal bipyramid are occupied by phosphorus atoms. Each of the capping phosphorus atoms binds an additional MLn fragment. Compounds of type II are also obtained from Fe2(CO)6(μ3-P)2(MLn)2 (I) by formal addition of an Fe(CO)3 group. A further general synthetic approach to clusters Fe3(CO)9(μ4-X)2 (MLn)2 (X = P, As, Sb) is the reaction of halo-phosphinidene, arsinidene or stibinidene complexes, (LnM)2XHal (X = P, As, Sb) with Na2Fe(CO)4. Similar procedures are used for the construction of compounds III and IV. Complexes III contain phosphorus as a μ4-spiro centre; compounds IV contain metallacyclic phosphanes (CO)4 FeP(R)Fe (CO)4 as ligands. From (CO)5CrPBr3 and Fe2(CO)9 the cluster Fe2(CO)7(PP)[Cr(CO)5]2 (V) is obtained in which a diphosphorus unit is side-on and end-on coordinated as an eight-electron ligand. The identity of the new compounds is documented by analytic and spectroscopic data as well as by X-ray-structure analyses of seven compounds.

“Atmende” cluster: Addition und eliminierung als elementarschritte der ligandensubstitution an (μ3-RP)Fe3(CO)10

Abstract The closed tetrahedral clusters RPFe 3 (CO)( 10- n )L n ( 1 ) (R = alkyl, aryl; L = phosphite, isonitrile; n = 0, 1, 2) add ligands L by opening of metal—metal bonds in a stepwise manner to give RPFe 3 (CO)( 10- n )L( n +1 ), ( 2 ) and RPFe 3 (CO)( 10- n )L( n +2 ) ( 3 ) respectively. By stepwise elimination of L the closed tetrahedral clusters 1 are obtained from the MM bond-opened species 3 and 2 , respectively. Elimination of CO from 3 or 2 yields substituted clusters of type 2 or 1 , respectively, again in a stepwise manner. This reaction sequence, documented by several examples, demonstrates that clusters behave like “breathing objects” which reversibly add substrates to their inner surface and “expire” them under reformation of metal—metal bonds. Hence, ligand substitution does not occur as a dissociatively initiated process on the outer surface of a cluster but involves addition-elimination sequences on the inner surface of the polyhedron.

Uncatalyzed asymmetric Diels-Alder addition of cyclopentadiene to (E)- and (Z)-(R)-4,5-di-O-isopropylidene-pent-2-enonates

The uncatalyzed Diels-Alder addition of cyclopentadiene to the acrylic ester derivatives {=1} proceeds with high diastereo- and enantioface selectitivity.

Radikalkomplexe vom typ Cp(CO)2MnXR. (X = S, Se)

Abstract CpMn(CO) 2 ER (E = S, Se) compounds [1] belong to the rare radical derivatives of the CpMn(CO) 2 fragment. We describe herein the syntheses, electrochemistry, and organometallic reactions of Cp ★ Mn(CO) 2 SR 1 ( 1a : R = t-C 4 H 9 , 1b : R = 2-adamantyl) and CpM(CO) 2 SePh ( 2 ).

Controlled synthesis of (1,3-tBu2-C5H3)2TiCl2 and (1,3-tBu2-C5H 3)TiCl3. Crystal structure and reactions of (1,3-tBu2-C5H3)TiCl3

The compounds (1,3-tBu2C5H3)2TiCl2 (I) and (1,3-tBu2C5H3)TiCl3 (II) were prepared in good yields from TiCl4 and (1,3-tBu2-C5H3)Li. Reactions of II with methanol, ethane-1,2-diol, sodium oxalate, and 2-pyrazine carboxylic acid afforded various organotitanium complexes. The crystal structure of II was determined.

Organometallic Sulfur Complexes. IVa. Synthesis and Characterization of [Fe(ButC5H4)(CO)2]2 and [Fe(1, 3-di-ButC5H3)(CO)2]2 and the S-Bonded Thiocarboxylate Derivatives, Fe(ButC5H4)(CO)2Scor and Fe(1, 3-di-ButC5H3)(CO)2Scor

Abstract The new substituted cyclopentadienyl organoiron dimers [Fe- (ButC5H4)(CO)2]2, I and [Fe(1,3-di-ButC5H3)(CO)2]2, II, were prepared from the reaction of Fe2(CO)9 with t-butylcyclopentadiene, or 1,3-di-t-butylcyclopentadiene. The equilibrium concentration of the trans-geometrical isomer decreases in the order II>I> [FeCp(CO)2]2 as a result of increasing bulkiness of Cp-substituents and increasing the steric repulsion in the cis-configurations. The 1H NMR spectra of I and II showed an anisotropic shielding effect of the bridging metal-carbonyl on the cyclopentadienyl protons.

The chemistry of dinitrogen residues. Part 2. Organohydrazido(1–)-derivatives of titanium(IV). X-Ray crystal structures of [Ti(C5H5)Cl2(NPhNH2)] and [Ti(C5H5)Cl2(NHNMe2)]

The structures of [Ti(C5H5)Cl2(NPhNH2)] and [Ti(C5H5)Cl2(NHNMe2)] are described. Both contain side-on hydrazide(1–) fragments with N–N single bonds but an asymmetric TiNN unit. These compounds, and several other homologues, react with protic acids to generate the hydrazine.

Organoiron Selenium Complexes. Synthesis and Characterization of tert-Butyl Substituted Cyclopentadienyldicarbonylselenocarboxylate Iron Complexes, Cp′Fe(CO)2SeCOR (Cp′ = C5H5, t-BuC5H4, 1,3-t-Bu2C5H3)

Abstract The organoiron selenides [(C5H5)Fe(CO)2]2(μ-Se) (I), [(t-BuC5H4)Fe(CO)2]2(μ-Se2) (II), and [(1,3-t-Bu2C5H3)Fe(CO)2]2(μ-Se2) (III) were prepared from the reaction of the organoiron dimers [(C5H5)Fe(CO)2]2, [(t-BuC5H4)Fe(CO)2]2 and [(1,3-t-Bu2C5H3)Fe(CO)2]2 with elemental selenium. The above selenides (I), (II) and (III) react with acid chlorides, RCOCl to give the Se-bonded monoselenocarboxylate derivatives [Cp′Fe(CO)2SeCOR] (Cp′ = C5H5, t-BuC5H4, 1,3-t-Bu2C5H3; R = 4-;O2NC6H4, 3,5-(O2N)2C6H3). The presence of tert-butyl substituents on the cyclopentadienyl ring introduces significant changes in the properties of these systems relative to the unsubstituted cyclopentadienyl analogues.