摘要:

AbstractThe main reaction pathways which lead to the breaking of C–F bonds in perfluoroalkanes and ‐arenes are discussed. Emphasis is placed on recent developments and on the mechanistic patterns that eme

ISSN:0009-2940    

DOI:10.1002/cber.19971300203

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractCyclopentadienyl ring metathesis occurs between [Ca(C5Me5)2] and [Ln(C5H5)3] complexes in toluene to generate the mixed ring compounds [Ln(C5Me5)2(C2H5)] (Ln1‐La,1‐Nd).1‐Nd has been characterized with X‐ray diffraction as a sterically crowded monomer. Only one ring is exchanged between [Ca(C5Me5)2(thf)x] and [La(C5H5)3(thf)x] in toluene to yield [La(C5Me5)C5H5)2(thf)] (2). In reaction with [M(C5H5)2] (MSn, Pb, Mn), [Ca(C5M5)2(thf)x] yields the corresponding [M(C5Me5)2] complexes. K[C5Me5] reacts with [La(C5H5)3(thf)], [Sn(C5H5)2] and [Pb[C5H5)2] in toluene to yield the ring‐exchanged products2, [Sn(C5Me5)2], and [Pb(C5Me5)2],

ISSN:0009-2940    

DOI:10.1002/cber.19971300204

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe metal‐vapor reactions of Co atoms with 1,3‐tBu2CpH(1a), 1,3‐tBu2CpH(1a), 1,2,4‐tBu3CpH(1b)and EtMe4CpH(1c)are described. With1athe two mononuclear complexes [(η5‐tBu2Cp) (η4‐tBu2‐1,3‐cyclopentadiene)Co](2a)and [(η5‐tBu2Cp)2Co](3a)were isolated, together with the dinuclear cobalt cluster [{(η5‐tBu2Cp)Co}2H3](4a)and trace amounts of the tetranuclear cluster [{(η5‐tBu2Cp)CoH}4](5a). The molecular structures of3aand4awere determined by X‐ray diffraction. Reaction of1bwith Co atoms afforded a single product, the dinuclear cluster [{(η5‐tBu3Cp)Co}2H3](4b), whose molecular structure was determined by single‐crystal X‐ray diffraction. Both,4aand4bexhibit extremely short Co‐Co distances [2.244(1)(4a)and 2.242(1) Å(4b)], as found for the Me5Cp analog [{(η5‐Me5Cp)Co}2H3](4c). Reaction of an isomeric mixture of Me4EtCpH(1c)with Co atoms furnished the mononuclear sandwich [ (η5‐Me4EtCp)(η4‐Me4Et‐1,3‐ cyclopentadiene)Co](2b), the trinuclear hydridocobalt cluster [{(η5‐Me4EtCp)Co}3H4](6a)and the tetranuclear hydridocobalt cluster [{(η5‐Me4EtCp)Co}4H4](5c). The molecular structure of5cwas determined by X‐ray crystallography and revealed a tetrahedral arrangement of the cobalt atoms. The electrochemical behavior of the dinuclear complexes4a‐4cwas studied by cyclic voltammetry. Reversible redox couples were found for all three compounds, with a correlation between the degree of alkyl substitution and their respective cathodic shifts. Compounds4aand4breact with CO to yield the mononuclear and dinuclear complexes [ (η5‐ CpR)Co(CO)2] (R1,3‐tBu2, 1,2,4‐tBu3) (7aand7b) as well as [{(η5‐CpR)CO}2(CO)2] (8aand8b). Reaction of the trinuclear hydridocobalt cluster6aand its Me5Cp analog6bwith AgBF4in the presence of PEt3yielded the heteronuclear clusters [{η5‐Me4CPR)Co}3AgP(Et)3H4]+[BF4]−

ISSN:0009-2940    

DOI:10.1002/cber.19971300205

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe reactions of protected α‐bromoglycine esters R1(O)CNHCH(Br)CO2R2(R1Ph, OCMe3; R2Me,tBu) with organometallic anions of acetylferrocene, CpFe(CO)(PPh3)‐C(O)CH3, (OC)5MC(OMe)CH3(MCr, W), (OC)3Cr(η6‐diphenylmethane), (OC)3Cr[η6‐fluorene), (OC)3Cr(η6‐dihydroanthracene) and of (OC)3Cr(‐η6aniline) and (OC)3Cr(η6‐o‐toluidine) provide a method for the introduction of organometallic fragments into the side chains of α‐amino acids.The complexes may be useful as markers for α‐amino acids in peptides.The compound (OC))3Cr(η‐o‐C6H4(CH3)NHC‐(H)(CO2Me)NHC(O

ISSN:0009-2940    

DOI:10.1002/cber.19971300206

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractFlash pyrolysis of a gas mixture containing iodine, oxygen and argon yields the hitherto unknown iodine superoxide, which can be identified by its UV absorption (λmax= 254 nm) after trapping the pyrolysate at 12 K. Irradiation converts iodine superoxide into iodine dioxide, identified by its IR and UV spectra

ISSN:0009-2940    

DOI:10.1002/cber.19971300207

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe reaction of a mixture of Fe(CO)2(PEt3)2N2(1a) and [Fe‐(CO)2(PEt3)2]2N2(1b) with acetylene leads to three complexes: Fe(CO)2(PEt3)2(π‐HC≡CH) (2a), Fe(CO)2(PEt3)2(H)(C≡CH) (2b), and Fe(CO)2(PEt3)2CCH2(2c). Upon chromatography on silylated silica gel the mixture of2a‐cis completely transformed into2c. The analogous reaction of1a, bor of Fe(CO)2[P(OiPr)3]2N2(1d) with HC≡CSiMe3affords the primary oxidative addition products Fe(CO)2L2(H)(C≡CSiMe3) [L  PEt3,3a; L  P(OiPr)3,3c]. The presence of a small amount of Al2O3in hexane irreversibly converts3aand3cinto the vinylidene compounds Fe(CO)2L2CC(H)SiMe3[L  PEt3,4a; L  P(OiPr)3,4c]. The chromatographic work‐up of4cadditionally leads to the hydrolysis product Fe(CO)2[P(OiPr3)2]2CCH2(2d). The reaction of the phosphite‐substituted derivative Fe(CO)2[P(OMe)3]2I‐(1c) with silylacetylene allows detection of the acetylene species Fe(CO)2[ P(OMe)3]2(HC ≡CSiMe3) (3b), as well as the acetylido hydrido derivative Fe(CO)2[P(OMe)3]2(H)(CCSiMe3) (4b). In a slow subsequent process, or with promotion by Al2O3in hexane, the vinylidene compound Fe(CO)2[P(OMe)3]2CC(H)SiMe3is formed.3bor4bare hydrolyzed to Fe(CO)2[P(OMe)3]2CCH2(5c) in the presence of SiO2. The reaction of disilylacetylene with1a‐dresults in the formation of disilylvinylidene complexes Fe(CO)2L2CC(SiMe3)2(L  PMe3,7a; LPEt3,7b; L  PiPr3,7c). An intermediate acetylene derivative could be isolated for L  PEt3(6a) and spectroscopically detected for L  P(OMe)3(6b), but could not be traced for L  P(OiPr)3. Further studies were devoted to the reactions of silyl diynes (Me3SiC≡CR, R  C≡CSiMe3,p‐C6H4‐C‐CSiMe3) with1a‐c. In all cases the acetylene compounds Fe(CO)2L2(Me3−SiC≡CR) [L  PEt3, R  C≡CSiMe3,8a; R p‐C6H4‐C≡CSiMe3,9a; L  P(OMe)3R  CSiMe3,8b; R p‐C6H4‐C≡CSiMe3,9b] were isolated, but only for8bwas an equilibrium process observed to form the corresponding vinylidene derivative Fe(CO)2[P(OMe)3]2CC(SiMe3)C‐C‐SiMe3(10b).10bhydrolyzes upon chromatography on silica gel to give Fe(CO)2[P(OMe)3]2CCH‐C≡CSiMe3(11b): Finally, the reaction ofp‐diethynylbenzene with1a‐cwas explored. The acetylido hydrido species Fe(CO)2L2(H)C≡C‐p‐C6H4‐C≡CH was isolated in the case of L  PEt3(12a) and spectroscopically detected for L  P(OMe)3(12b).12band12atransform spontaneously and in the presence of Al2O3in hexane, respectively, to the vinylidene comple

ISSN:0009-2940    

DOI:10.1002/cber.19971300208

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe reaction of various sterically congested sodium enolates, generated by quantitative deprotonation of stable enols (of diphenylacetaldehyde in the case of5), with dichlorotitanocene afforded a series of novel titanium enolates1‐5. The crystal structure of1could be determined. Due to the considerable steric shielding of the β,β‐diaryl moiety, all the titanium enolates exhibit an oustanding stability towards hydrolysis, which increases with the higher steric demand of the substitutents at the C‐C double bond. The kinetics of the hydrolysis, which is pseudo‐first‐order in THF/water (1 : 1) and acetonitrile/water (1 : 1), was investigated by UV spectroscopy. The pseudo‐first‐order rate constants measured in these solvent mixtures are in the range 6.4 · 10−4s−1

ISSN:0009-2940    

DOI:10.1002/cber.19971300209

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA variety of bent metallocene dichloride/methylalumoxane catalysts, derived from the zirconocene complexes10,12‐18, have been employed in intramolecular olefin‐coupling reactions yielding monomeric or dimeric products. This was achieved by using optimized reaction conditions employing low substrate concentrations (1.0‐1.8 M) and rather long reaction times. Under these particular conditions, 1,5‐hexadiene was cyclodimerized to give 1‐methylene‐3‐(cyclopentylmethyl)cyclopentane (11). 1,6‐Heptadiene was cleanly converted to methylenecyclohexane, andcis‐1,2‐divinylcyclopentane (19) andcis‐1,2‐divinylcylohenxane (22) were cyclized to yield 2‐methylenebicyclo[3.3.0]octane (20) and 7‐methylenebicyclo[4.3.0]nonane (23), respectively. In many cases, the cyclization products were accompanied by isomers originating from double‐bond shift reactions that often occur rapidly at these catalyst systems under the specific reaction conditions chosen to keep the pro

ISSN:0009-2940    

DOI:10.1002/cber.19971300210

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractTitanium complexes of the general type Ti(η5:η1‐C5H4Si‐Me2NCH2C6H3X2‐2,5)Cl2(XH, F), containing a linked benzylamido‐cyclopentadienyl ligand, were prepared by reaction of Ti(η5‐C5H4SiMe2Cl)Cl3with lithium amide Li(NHCH2C6H3X2‐2,5). A single‐crystal X‐ray structural analysis of Ti(η5: η1‐C5H4SiME2NCH2C6H3F2‐2,5)Cl2revealed a conformation in the solid state in which the aryl ring is turned away from the metal center. Ti(η5:η1‐C5H4SiMe2NCH2C6H5)Cl2can be alkylated with a variety of reagents to form extremely sensitive complexes of the type Ti(η5‐C5H4SiMe,2NCH2C6H5)R2(RMe, CH2C6H5, CH2SiME3, CH2CMe2C6H5). Reaction of Li2[C5Me4SiMe2NCH2C6H5] with TiCl3(THF)3gave Ti(η5: η1‐C5Me4SiMe2NCH2C6H5)Cl2, which can also be alkylated to form dialkyl complexes of the type Ti(η5:η1‐C5Me4SiMe2NCH2C6H5)R2(RMe, CH2C6H5, CH2SiMe3, C6H5).A single‐crystal X‐ray structural analysis of Ti(η5:η1‐C5Me4SiMe2NCH2C6H5)(CH2C6H5)2suggests the presence of α‐agostic bonding of one of

ISSN:0009-2940    

DOI:10.1002/cber.19971300211

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractPhenylene‐1,2‐bis(phosphane) reacts with two mole‐equivalents of tris[(triphenylphosphane)gold(I)]oxonium tetrafluoroborate in dichloromethane at −78°C to give high yields of a hexanuclear complex {C6H4]P(AuPPh3)3]2}2+· 2 BF‐4(1). The variable‐temperature31P{1H}‐NMR spectra of the product in CD2Cl2at ‐ 80°C are compatible with a static structure featuring three Ph3PAu units associated with each of the two C6H4P2phosphide functions, as derived from a clear doublet/quartet pattern. At 50°C in CDCl3, however, there is rapid intramolecular scrambling of these Ph3PAu units, which gives rise to a triplet/septet pattern with theJ(P,P) value reduced to exactly one half of the value at the lo

ISSN:0009-2940    

DOI:10.1002/cber.19971300212

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY