Birgit C. Wassermann

Palladium-catalyzed cross-methylation of aryl triflates by intramolecularly stabilized dialkyl-aluminum, -gallium and -indium reagents

Abstract Several phenyl and naphthyl triflates undergo catalytic cross-methylation with the monomeric and dimeric dimethyl-aluminum, -gallium and -indium complexes 1a , 1b , 1c , 3a , 3b and 3c in the presence of either PdCl 2 (PPh 3 ) 2 , Pd(PPh 3 ) 4 or Pd(binap)(OAc) 2 . 4-Bromophenyl triflate reacts selectively via the triflate function. Structural features of the substrate and the methylating agent, as well as the nature and quality of the palladium catalyst have a considerable influence on the cross-coupling process.

Si(CH2CH2SnH3)4 — a unique organotin hydride featuring 12 SnH units in a dendritic molecule. Single-crystal X-ray structures of tetrakis(2-stannylethylene)silane and tetrakis[2-(triphenylstannyl)ethylene]silane

Abstract Fourfold hydrostannation of tetravinylsilane affords the first generation metallodendrimer Si(CH2CH2SnPh3)4 (1). Selective bromination yields Si(CH2CH2SnBr3)4 (2), which can be reduced by LiAlH4 to give Si(CH2CH2SnH3)4 (3), containing 12 reactive SnH bonds. These novel dendritic organotin compounds were characterized by elemental analysis, spectroscopic studies (1H-, 13C-, 119Sn-NMR; IR) and by single-crystal X-ray structure determination. The molecular structures of 1 and 3 reveal increased conformational constraint in 1; the average SnH bond length in 3 is 1.60(7) A.

Synthesis and Characterization of Intramolecularly Stabilized Chiral Dimethylindium Alkoxides and their Use as Cross Coupling Reagents

The enantiomerically pure dimeric N, O-5-chelates [Me2In(μ-OCH2CH(R)NMe2)]2 {R = Me (S) (2); R = iPr (S) (3); R = iBu (S) (4); R = Bz (S) (5)}, and [Me2In-{μ-(1R, 2S)-OCH(Ph)CH(Me)NMe2}]2 (6), as well as the achiral dimeric N, O-6-chelate [Me2In(μ-O(CH2)3NMe2)]2 (7) have been synthesized from trimethylindium and equimolar amounts of the corresponding enantiomerically pure dimethylamino alcohols or of the achiral dimethylaminopropanol by elimination of methane. Their 1H NMR, 13C NMR, and mass spectra as well as the X-ray single crystal structure analyses of [Me2In{μ-O(CH2)2NMe2}]2 (1), 3, 5, 6 and 7 are described and discussed. The coordinative NIn bonds of the five-coordinate indium complexes show dynamic dissociation/association processes. 1—6 were found to be useful reagents for the partial kinetic resolution of 2-carbomethoxy-1, 1′-binaphthyl triflate. Synthese und Charakterisierung intramolekular stabilisierter chiraler Dimethylindiumalkoxide und deren Verwendung als Kreuz-Kupplungs-Reagentien Die enantiomerenreinen dimeren N, O-5-Chelate [Me2In(μ-OCH2CH(R)NMe2)]2 {R = Me (S) (2); R = iPr (S) (3); R = iBu (S) (4); R = Bz (S) (5)}, und [Me2In-{μ-(1R, 2S)-OCH(Ph)CH(Me)NMe2}]2 (6), sowie das achirale dimere N, O-6-Chelat [Me2In(μ-O(CH2)3NMe2)]2 (7) werden aus Trimethylindium und equimolaren Mengen der enstsprechenden enantiomerenreinen Dimethylaminoalkohole bzw. von achiralem Dimethylaminopropanol unter Methan-Abspaltung erhalten. Die 1H-NMR, 13C-NMR und Massenspektren sowie die Rontgenstrukturanalysen von [Me2In{μ-O(CH2)2NMe2}]2 (1), 3, 5, 6 und 7 werden diskutiert. Die koordinativen NIn-Bindungen der funffach koordinierten Indium Komplexe zeigen in Losung ein dynamisches Dissoziation/Assoziations Verhalten. 1—6 eignen sich als Reagentien fur die kinetische Enantiomerentrennung von 2-Carbomethoxy-1, 1′-binaphthyltriflat.

Synthese und Charakterisierung chiraler Organogallium- und -aluminiumalkoholate mit intramolekularer Stickstoffstabilisierung. Röntgenstrukturanalyse von Dimethylgallium-(S)-2-dimethylamino-3-methyl-1-butanolat, Dimethylgallium-(S)-2-dimethylamino-3-phenyl-1-propanolat und Dimethylgallium-(R)-2-dimethylamino-1-butanolat

Abstract The reactions of trimethylgallium and trimethylaluminium with optically active alcohols yield [Me 2 GaOCH 2 CHRNMe 2 ] 2 [R=Me ( S ) 6 , i Pr ( S ) 7 , i Bu ( S ) 8 , Bz ( S ) 9 , Et ( R : S >90:10) 10 ] and [Me 2 AlOCH 2 CHRNMe 2 ] 2 [R= i Bu ( S ) 11 , Et ( R : S >90:10) 12 ], respectively. The compounds have been characterized by 1 H-, 13 C-NMR and mass spectroscopy. They undergo a dynamic process with respect to the dissociation and association of the GaN or AlN dative bond resulting in equilibria between four- and five-coordinate metal atoms. The structures of 7 , 9 and 10 were determined by single crystal X-ray diffraction. The molecules exist as dimers containing a M 2 O 2 four-membered ring. 6 – 11 exclusively consist of dimers with enantiomerically equal ligands; 12 , on the contrary contains diastereomeric dimers featuring different NMR spectra.

Intramolekular schwefelstabilisierte Aluminium- und Galliumalkyle

Die intramolekular schwefelstabilisierten Organoaluminium- und Organogalliumverbindungen Me2Al(CH2)3SEt (1), Me2Ga(CH2)3SEt (2), MeClAl(CH2)3SEt (3), MeClGa(CH2)3SEt (4), Cl2Al(CH2)3SEt (5) und Cl2Ga(CH2)3SEt (6) werden aus Me2MCl, MeMCl2 bzw. MCl3 (M = Al, Ga) und ClMg(CH2)3SEt erhalten. Bei der Umsetzung von 5 bzw. 6 mit BrMg(CH2)5MgBr entstehen (CH2)5Al(CH2)3SEt (7) und (CH2)5Ga(CH2)3SEt (8). AlCl3 bzw. GaCl3 reagieren mit zwei bzw. drei Aquivalenten ClMg(CH2)3SEt unter Bildung von ClAl[(CH2)3SEt]2 (9) und ClGa[(CH2)3SEt]2 (10) bzw. Al[(CH2)3SEt]3 (11) und Ga[(CH2)3SEt]3 (12). Diese Verbindungen wurden durch Elementaranalysen, Massenspektren, 1H-, 13C- und 27Al-NMR-Untersuchungen sowie 6 durch Einkristall-Rontgenstrukturanalyse charakterisiert. Intramolecularly Sulfur stabilized Aluminum and Gallium Alkyl Derivatives The intramolecularly sulfur stabilized organoaluminum and organogallium compounds Me2Al(CH2)3SEt (1), Me2Ga(CH2)3SEt (2), MeClAl(CH2)3SEt (3), MeClGa(CH2)3SEt (4), Cl2Al(CH2)3SEt (5), and Cl2Ga(CH2)3SEt (6) are synthesized from Me2MCl, MeMCl2, and MCl3 (M = Al, Ga), respectively, and ClMg(CH2)3SEt. The reaction of 5 and of 6 with BrMg(CH2)5MgBr yields (CH2)5Al(CH2)3SEt (7) and (CH2)5Ga(CH2)3SEt (8), respectively. AlCl3 and GaCl3 react with two as well as three equivalents of ClMg(CH2)3SEt forming ClAl[(CH2)3SEt]2 (9) and ClGa[(CH2)3SEt]2 (10) as well as Al[(CH2)3SEt]3 (11) and Ga[(CH2)3SEt]3 (12), respectively. The compounds were characterized by elemental analyses, mass spectroscopy, 1H, 13C, and 27Al NMR investigations as well as 6 by single crystal X-ray structure analysis.

Novel asymmetric triorganotin hydrides containing the (−)-menthyl ligand

Abstract Synthesis and characterization of (−)-menthylmethyl-t-butyltin hydride and (−)-menthylmethylisopropyltin hydride, asymmetric triorganotin hydrides with the chiral tin center linked to a chiral carbon of an optically active substituent, and of (−)-menthyldimethyltin hydride are reported.

Fragmentable Heterogeneous Cocatalysts for the Metallocene-Catalyzed Polymerization of Olefins, II (1). Preparation, Characterization and Testing of the Cocatalysts and Microscopic Evaluation of the Polyethylene

Surface modified silica were reacted with different aluminiumalkyls AlR2R’ (R = Me, Et, i-Bu, R’ = H, Me, Et, i-Bu), oligomeric methylaluminoxane (MAO) and combinations of both, to yield heterogeneous cocatalysts. These cocatalyts were employed to polymerize ethylene using zirconocene dichloride as the catalyst. The polymerization activity profiles have been recorded and compared with the information gained from the scanning electron microscopy (SEM) images of the polymers. The fragmentation of the heterogeneous cocatalyts upon polymerization has been demonstrated. The degree of fragmentation and the polymerization activity depend on the preparation of the silica supports and on the preparation of the heterogeneous cocatalysts using these supports. The most reactive, fragmentable heterogeneous cocatalysts show polymerization activities slightly higher than MAO in homogeneous solution and almost 1.5 times higher than commercially available MAO on silica (=MAO on Sylopol).

Fragmentable Heterogeneous Cocatalysts for the Metallocene-Catalyzed Polymerization of Olefins, I. Surface Modification of Silica and Characterization of the Resulting Carriers

Surface modification of pre-dried spherical silica nano-particles with diameters of 235 nm and 10 to 20 nm and of commercially available non-spherical silica materials using various aminoalkyltrialkoxysilanes and α-ω-bis(alkoxysilyl)organyls (organyl = alkanediyl, aminoalkanediyl, polyether, polysiloxane) has been performed in suspension in solvents with water. The quantity of water has a dominating influence, as compared to the amounts and the ratios of silanes employed, on the surface morphology of the modified silicas. The morphologies observed range from weakly linked aggregates of spherical particles to large agglomerates covered by thick irregular layers of organopolysiloxane, as demonstrated by scanning electron microscopy. These carriers can be modified further with organoaluminium compounds to yield heterogeneous cocatalysts for the polymerization of ethylene.