摘要:

AbstractIn contrast to their all‐carbon analogues, phosphaalkyne cyclooligomers only became accessible a few years ago. A milestone in the chemistry of cyclotetramers was the synthesis and structural characterization of the tetraphosphacubane5, obtained as a thermolysis product of tert‐butylphosphaacetylene (1). Since then, the construction of eleven cyclotetramers has been achieved, covering seven different frameworks (A‐G). As a consequence of the use of kinetically stabilized phosphaalkynes as starting materials, all known cyclotetramers bear sterically demanding substituents (tert‐butyl, tert‐pentyl, 1‐adamantyl). Cyclotetramerizations are not only achieved by thermolysis of1, but also by alternative and selective routes such as transition‐metal‐mediated, Lewis acid‐ and base‐induced processes, as well as by cycloadditions to phosphaalkyne cyclotrimers. Interestingly, these tetramers can be interconverted by various valence isomerizations. The results of thermal and photochemically‐induced rearrangements are in good agreement with MO calculations carried out for the parent compounds. Phosphaalkyne cyclotetramers exhibit a highly interesting reactivity and other peculiar features. One outstanding example is the tetraphosphacubane5, which shows unusual structural and spectroscopic properties as a result of its uniqu

ISSN:0009-2940    

DOI:10.1002/cber.19971300703

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe syntheses of 1,3‐di‐tert‐butyl‐2,2,4,4‐tetrachlorocyclodisilazane (3) and of di‐tert‐butyl‐2,2,4,4‐tetrafluorocyclodisilazane (4) are reported. The X‐ray crystal structure of3and the electron‐diffraction gas‐phase structure of4have been determined. Both cyclodisilazanes possess planar four‐membered rings and nearly planar configurations at the nitrogen atoms. The Si‐N bond lengths are 171.1(1) pm and 170.6(3) pm and the Si ⃛Si transannular distances 245.0(1) and 241.3

ISSN:0009-2940    

DOI:10.1002/cber.19971300704

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractCurrent research in radiopharmaceutical chemistry is aimed at the design of technetium‐based receptor‐binding radiotracers because of the excellent nuclide properties of the isotope99mTc. Tc tracers and the corresponding complexes of rhenium, as the inactive surrogate of Tc, are required to imitate organic agonists or antagonists of the receptor. We have started studies with ergolines, which are known to be dopamine substitutes. The present report deals with the functionalization of 8α‐amino‐6‐methyl‐ergoline (2) with a 2‐mercaptoacetyl group, and the subsequent synthesis of the first rhenium complex containing a pendent ergoline moiety [Re‐ O(SSS)(RS)] (HSSSH = HS‐CH2CH2‐S‐CH2CH2‐SH and RSH = 8a‐amino‐N‐(2‐mercaptoacetyl)‐6‐methyl‐ergoline) (4). The molecular structure of the rhenium complex was determin

ISSN:0009-2940    

DOI:10.1002/cber.19971300705

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe 2‐phosphanyl‐4,5‐dimethylphosphinines1‐5are powerful bridging ligands able to stabilize metal‐metal single and triple bonds between low‐valent transition metal centres. Their reaction with Mn2(CO)10in refluxing xylene yields the corresponding Mn2(CO)8complexes6and7. Reaction with [Fe2Cp2(CO)4] under UV irradiation similarly yields the Fe‐Fe‐bridged Fe2Cp2(CO)2complexes8and9. An additional observation is that the 2‐phosphininyl‐3,4‐dimethylphosphaferrocene10is formed upon reaction of the 2‐phospholylphosphinine5with [Fe2Cp2(CO)4] at high temperature under CO pressure. A clean addition occurs at the Mo≡Mo triple bond of [Mo2Cp2(CO)4] to give the Mo‐Mo single‐bonded complexes11‐15. The thermolysis of these complexes succeeds when the phosphanyl group is a phosphonite P(OEt)2(13) or P(OAr)2(14), affording cleanly the Mo2Cp2(CO)4triple‐bonded complexes16and17, respectively. The metal‐metal triple bonds of these complexes readily add two molecules of CO to reform13and14, or one molecule oftBu‐N≡C to give18and19. The X‐ray crystal structure analysis of the MO2C2(CO)4complex13a, with the 2‐P(OEt)2‐ phosphinine, shows agaucheorientation of the two Cp rings and very short P‐Mo bonds of 2.3565(4) and 2.406(2) Å to

ISSN:0009-2940    

DOI:10.1002/cber.19971300706

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractReduction of [Yb(Odpp)3(THF)2(HOdpp = 2,6‐diphenylphenol; THF = tetrahydrofuran) with ytterbium powder and mercury metal yields [Yb(Odpp)2(THF)3] (1) which on crystallization from DME gives [Yb(Odpp)2(DME)2] (2) (DME = 1,2‐dimethoxyethane). Crystallization of the reactant [Yb(Odpp)3(THF)2] from DME yields [Yb(Odpp)3(DME)]. (DME)0,5(3) and of [Nd(Odpp)3(THF)2] from DME/THF the analogous [Nd(Odpp)3(DME)].(THF) (4). The X‐ray crystal structure of1reveals distorted trigonal bipyramidal five‐coordinate ytterbium with axial Odpp ligands [O‐Yb‐O 164.6(3)˚], and unsymmetrically distributed equatorial THF ligands [O‐Yb‐O 137.5(3), 138.8(3), 83.7(4)°]owing to two close H(Ph)...Yb approaches (3.1‐3.2 Å). In 2, there is trigonal prismatic six‐coordination with an Odpp ligand on each triangular face and DME ligands bridging the triangular faces. Both 3 and 4 have distorted square planar five‐coordination for the lanthanoid metals with an apical Odpp ligand andcisoidOdpp ligands and a chelating

ISSN:0009-2940    

DOI:10.1002/cber.19971300707

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe reaction of N‐isopropyl‐2‐(isopropylamino)troponimine, [(i‐Pr)2ATI]H, with KH in THF affords [(i‐Pr)2ATI]K. This is a useful starting material for the preparation of the mono‐, bis‐ and tris‐substituted compounds [[i‐Pr)2ATI]YCl2‐(THF)2}2, [(i‐Pr)2ATI2Y[O(2,6,t‐Bu2C6H3)] and [(i‐Pr)2‐ATI]3Ln (Ln = Y, La, Sm), which can be obtained from ([i‐Pr)2ATI]K and LnX3and LnX3(X = Cl, I), or Y[O(2,6‐t‐BuC6H3)]3. All compounds have been characterized by spectroscopic methods. The monosubstituted yttrium complex {[(i‐Pr)2ATI]YCl2(THF)2}2has also been investigated

ISSN:0009-2940    

DOI:10.1002/cber.19971300708

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe title complexes8and9are easily prepared in two or three steps from iron carbonyls and isobutene diol5by Meerwein alkylation of the intermediate acyl complexes6and7. With carbon and heteroatom nucleophiles like enolates and triphenylphosphane they form either stable4‐substituted alkene‐carbene complexes10and11, or substituted trimethylenemethane tricarbonyliron complexes like12. Oxidation with H2O2/NaOH both of the alkene‐carbene complexes11and of the less stable β‐oxo‐substituted trimethylene‐methane complexes13, as obtained from reaction of8with lithium enolates, yields the corresponding substituted allyl carbamates15or the allyl alcohols14, which are formally bis‐ and monosubstituted derivatives, respectively, of the starting

ISSN:0009-2940    

DOI:10.1002/cber.19971300709

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe cobaltaheterocycles [C5H5Co{κ2(C,S)‐C(=CH2)‐N(R)C(=S)S](PMe2Ph)] (5‐7), which contain both an exocyclic CC and CS bond, were prepared from the iminoacylcobalt compounds [C5H5Co(C(CH3)=NCH} (PMe2Ph)]I (2‐4) on treatment with either CS2/NaOCH3or K[S2CNMe2], respectively. While protonation of5(R = CH3) and7(R = CH2Ph) with HBF4occurs at the exocyclic CCH2bond to give cations containing a CoC(CH3)N(R)C(=S)S ring, the methylation of5and7with [OMe3]BF4takes place at the exocyclic CS bond and generates five‐membered heterocycles heterocycles with an SCH4substituent. The reaction of5‐7with S8leads to the elimination of the phosphane ligand and affords the bicyclic dithiolenecobalt complexes14‐16in moderate to good yields. On treatment of5‐7with C2(CO2R′)2 (R′ = Me,Et), an insertion of the alkyne into the CCH2bond occurs and five‐membered ring systems19‐22with an unsaturated exocyclic =C(CO2R′)‐C(CO2R′)=CH2group are formed. As in the case of5and7, protonation and methylation reactions of19also take place at different sites leading to cations wi

ISSN:0009-2940    

DOI:10.1002/cber.19971300710

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA dimethylpolysiloxane chain is covalently bound to the monomeric Lewis acid catalyst (1R)‐(+)‐oxovanadium(1V) bis[3‐ heptafluorobutanoylcamphorate] [(+)‐5a] at the C‐10 position of the camphor moiety yielding the novel chiral polymeric (1S)‐( +)‐oxovanadium(1V) bis[3‐heptafluorobutanoylcamphorate]‐dimethylpolysiloxane [( +)‐6a][1]. The Lewis acid promoted hetero Diels‐Alder reaction of trans‐l‐methoxy‐3‐(trimethylsilyloxy)‐ 1,3‐butadiene (1) and benzaldehyde (2) is studied in the presence of the enantiomerically pure monomeric (5a,5b) and polymeric (6a, 6b) catalysts. The monomeric and polymeric catalysts of identical chirality[1]invoke opposite enantioselectivities toward the formation of 2‐phenyl‐ 2,3‐dihydro‐4H‐pyrone (4). This remarkable result is corroborated by numerous control experiments. Thus, it is demonstrated that the environment of the active site of the catalyst is changed when the complex is fixed to a polymeric chain. In contrast to5and6, the monomeric12and polymeric13europium(III) tris[3‐heptafluorobutanoylcamphorates] of identical chirality invoke the same enantioselectivity toward the formation of4. The concept of polymer attachment is utilized to recover the catalyst from the reaction mixture by precipitation an

ISSN:0009-2940    

DOI:10.1002/cber.19971300711

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe syntheses and X‐ray crystal structures of two chiral bis[2‐(oxazolinyl)phenolato]‐oxovanadium(IV) complexes are reported. Their catalytic activity in oxidative transformations and C‐C bond‐forming reactions has been inv

ISSN:0009-2940    

DOI:10.1002/cber.19971300712

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY