Kaspar Evertz

ansa-Metallocene derivatives: XVII. Racemic and meso diastereomers of group IV metallocene derivatives with symmetrically substituted, dimethylsilanediyl-bridged ligand frameworks. Crystal structure of R,S-Me2Si(3-t-Bu-5-MeC5H2)2ZrCl2☆

Abstract The formation of racemic and meso diastereomers of the disubstituted ansa-zirconocenes (CH3)2Si(1-C5H3-3-R)2ZrCl2 (R  t-butyl, trimethylsilyl, α,α-dimethylbenzyl and 1-phenylcyclohexyl) from dimethylsilanediyl-bridged, symmetrically substituted bis-cyclopentadienyl dianion derivatives and ZrCl4·2THF has been studied under a variety of conditions. Rac/meso ratios close to 1 were obtained in all cases. Similar product ratios were observed for analogous titanium and hafnium complexes with R  trimethylsilyl. A significant increase in the rac/meso product ratio was observed when an additional substituent was present next to the dimethylsilyl bridge as in (CH3)2Si(1-C5H2-3-R-5-CH3)2ZrCl2 (R  CH(CH3)2, C(CH3)3). It is suggested that intermediates with one η1-bound ring ligand control the stereochemical course of the ansa-metallocene formation. The crystal structure of R,S-(CH3)2Si(1-C5H2-3-C(CH3)3-5-CH3)2ZrCl2 is reported.

ansa-Metallocene derivatives XVIII. Chiral titanocene derivatives accessible from substituted dihydropentalene and azulene precursors☆

The product of an Mg/CCl4-induced reductive coupling of guaiazulene reacts with TiCl3·3THF to yield, after oxidation with HCl/O2, R,S-8,8′-biguaiazulenide titanium dichloride, which contains a CC bond between its two guaiazulenide ligand moieties. A similar reaction sequence starting from 3-phenyl-1,2-dihydropentalene gives unbridged R,S-bis(4-exo-phenyl-4H-5,6-dihydropentalenide)titanium dichloride.

Oxidative Addition von Thiolen an Stibinidenkomplexe

Abstract The stibinidene complex [Cp′(CO) 2 Mn] 2 SbSPh ( 1 (Cp′ = η 5 CH 3 C 5 H 4 ) could not be obtained from the reaction of the iodostibinidene complex [Cp′(CO) 2 Mn] 2 SbI ( 2 ) with thiophenol. Instead, 2 reacts with thiophenol to give the product of an oxidative addition process, Cp′(CO) 2 MnSb(SPh) 3 ( 3 ) and the radical complex, Cp′(CO) 2 MnSPh ( 4 ). The compounds 3 and 4 could also be obtained from the reaction of Cp′(CO) 2 MnTHF with Sb(SPh) 3 . The structure of 3 has been determined by X-ray crystallography.

Verbindungen mit Zwei -SMn(CO)2Cp-Zentren: Getrennte Radikale oder S-S-Bindugen?

Abstract The complexes [L(CO)2MnSR] (L=Cp, Cp′, Cp) are without exception stable as mononuclear radical complexes. The compounds L(CO)2MnS(X)SMn(CO)2L (X = (CH2)21, (CH)2)32, (CH2)43, 1,3-C6H44) were examined in order to find out whether a dimerization of the radicals [L(CO)2MnSR] might be induced by intramolecular forces: 1 and 4 are diradicals while 2 and 3 are diamagnetic molecules containing SS-bonds in relatively unstrained five and six membered cycles. NMR- and EPR-spektra show the partial rupture of these bonds. Scyclic voltammetry reveals two reversible oxidation peaks for all the compounds 1-4. Reversible reduction signals, however, are only observed for the complexes 1 and 4 which have no SS-bond; the reduction of the compounds 2 and 3 is irreversible because it induces scission of the SS-bond. The preparative oxidation of 4a (L = Cp′) using AgPF6 leads to the tetranuclear dication [Cp′(CO)2Mn]2SC6H4S[Mn(CO)2CP′] (5), the spectra of which document a trigonal planar coordination of both sulfur centers. The results are furteher substantiated by X-ray analyses of 2, 3 and 4.

Synthese und Reaktionen Et2NP-verbrückter Carbonyleisencluster

Abstract Et2NPCl2 reacts with Fe2(CO)9 to give compound (CO)4Fe(PCl2NEt2) (1), which with additional Fe2(CO)9 gives the compounds (μ2-Et2NPCl)(μ2-Cl)Fe2(CO)6 (2); (μ3-Et2NP)Fe3(CO)10 (3) and (μ3-Et2NP)2Fe3(CO)9 (4). Photochemical reaction of 3 with diphenylacetylene yields the cluster 5 in which the C2 entity of the alkene is added to a PFe edge of the decarbonylated educt 3. The (μ3-Et2NP) bridged cluster 4, upon photochemical activation, adds diphenylacetylene, without decarbonylation, across the phosphorus centers to give 6. Excess diphenylacetylene leads to a substitution derivative of 6 (7) in which two carbonyl groups in 6 are substituted by μ2-η2-bonded diphenylacetylene. The structure of 7 has been confirmed by an X-ray diffraction analysis.

Dehydrierung von phenylarsan und seinen pentacarbonylchrom-derivativen: Abfangreaktionen für diphenyldiarsen, PHAsAsPh

Abstract The compound (Cr(CO)5As(C6H5)H)2, 1, reacts under thermal Pt-catalysis with dienes in Diels—Alder type reactions to give the cycloadducts 2. Whereas the formation of the acrolein adduct 3 suggests a stepwise reaction, the isolation of diarsene-complexes 4 in the system Pd/C / L (L = donor ligand) suggests a synchronous mechanism. As side products in these reactions, oligocyloarsane-complexes RnAsn(Cr(CO)5)m (n = 4, 5; m = 1, 2), 5, are formed.

Reaktionen von Phosphanen und Arsanen mit Diselenkomplexen

Abstract The compound [Cp′Mn(CO) 2 ]Se 2 ( 1 ) reacts with primary arsanes and phosphanes, and migration of the carbonylmetal fragment Cp′Mn(CO) 2 (Cp′ = CH 3 C 5 H 4 ) from the selenium to the arsenic or phosphorus center occurs. Products of these reactions are diselena-diarsetanes ( 4 ) or diselena-diphosphetanes ( 5 ). During the reaction of arsanes with 1 , arsinidene complexes ( 2 ) are obtained in very good yields. Compounds with a PSeP unit ( 6 ) can be isolated as by-products of the reaction of phosphanes with 1 .

Diaminodiphosphen- und aminophosphiniden-komplexe

Abstract 2,2′,6,6′-Tetramethylpiperidylphosphorousdichloride, (pip)PCl 2 , reacts with Na 2 -M 2 (CO) 10 (M = Cr, Mo, W) to give phosphinidene and diphosphene complexes. The diphosphene compounds [(pip)P=P(pip)]M(CO) 5 (Ia to Ic) are obtained as stable products for all three metals. The phosphinidene compounds (pip)[M(CO) 5 ] 2 are only obtained for M = Cr(IIa) and M = W (IIb). X-ray analyses reveal that the NR 2 substituents in I as well as in II are oriented in such a way relative to the phosphorus centered π-systems that they cannot participate in π-conjugation. This bonding situation is analyzed by EHT methods.

Cyclisation of arylnitrenium ions to the aporphine ring system: remarkable formation of a sixteen-membered ring by an intramolecular electrophilic aromatic substitution

The delocalised π-cations from 1-(m-nitreniobenzyl)-1,2,3,4-tetrahydroisoquinolines cyclise to 9-and 11-aminoaporphines, but the p-nitrenium isomers do not form a 5-membered ring unless the ring undergoing attack is strongly activated; on the other hand, 1-(p-nitreniobenzyl)-7-benzyloxy-6-methoxy-2-methyl- 1,2,3,4-tetrahydroisoquinoline undergoes a remarkable intramolecular electrophilic substitution to give (8)(confirmed by an X-ray study) containing a 16-membered ring.

Thermolysis of 1-(N-acetyl-N-aryl)amino-2,4,6-triphenylpyridinium tetrafluoroborates: a new source of arylnitrenium ions

Thermolysis of 1-(N-acetyl-N-aryl)amino-2,4,6-triphenylpyridinium tetrafluoroborates provides a new and synthetically useful source of arylnitrenium ions under non-acidic conditions; a p-semidine-type byproduct is obtained from the phenylamino compound.