摘要:

AbstractP(III) double bond systems possess two closely spaced frontier orbitals, a π‐orbital and a σ‐orbital. In the parent iminophosphane the orbital sequence is σ (HOMO) and π* (LUMO). Thus, it is isolabal to a singlet carbene and undergoes self‐dimerization via a [2 + 1] cycloaddition. The resulting three membered ring system can be considered as a complex of two iminophosphanes. Contrary to the classical cyclopropanation reaction, in the pseudo‐carbene iminophosphane the corresponding [2 + 1]reaction is only slightly exothermic, as established by ab initio calculations at the SCF/CEPA‐1 and the MCS

ISSN:1042-7163    

DOI:10.1002/hc.520020203

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe symmetrical and unsymmetrical 1,3‐diphospha‐propenes3and4were obtained from the corresponding diposphiranes1and2. The chemical behavior of these compounds has been studied. Phosphonium‐phosphaalkenes7aand10ahave been obtained in the reactions with aluminium trichloride. Whereas the symmetrical diphosphaallene13can be obtained by reaction of1or3with lithio compounds, the unsymmetrical diphosphaalene14cannot be prepared by a similar route. Reduction of3aand4a(obtained with a different conformation) by lithium aluminum hydride afforded phosphino‐phosphaalkenes17aand18a(with a similar conformation); further dehydrochlorination with amines led to the symmetrical and unsymmetrical diphosphaalenes13and14, respectively. The formation of allenes strongly depends on the conformation of the starting diphosphap

ISSN:1042-7163    

DOI:10.1002/hc.520020204

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractEffets ofpπpπconjugation in phosphaalkenes have been considered by taking into account the results of X‐ray structural studies and ab initio quantum‐chemical calculations. The structural consequences of the conjugation depend to a certain extent on the character of the substituent and the place of its attachment to the double PC bond. Depending on the location of the substituent, bond polarization may strengthen or weaken (compensate for) the conjugation effects. A high contribution of the s‐character of the lone electron pair of the P atom is an essential feature of the electron structure of a ph

ISSN:1042-7163    

DOI:10.1002/hc.520020205

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractPhosphaalkynes, RCP (R = But, Adamantyl), add across the RhRh double bond of [Rh2Cp 2*(CO)2] to give either [Rh2Cp 2*(μ‐CO)(COPCR)] or [Rh2Cp 2*(CO){PCRC(O)CRP}] depending on the stoichiometry of the reaction (Cp* = η5‐C5Me5). The structures of these complexes have been elucidated by NMR spectroscopy and by a single crystal X‐ray study on [Rh2Cp 2*(CO){PCAdC(O)CPAd}]. Small amounts of the 1,3‐diphosphacyclobutadiene complexes [RhCp*(P2C2R2)] and the trinuclear compound [Rh3Cp 3*(CO)2] are also formed in these reactions. The reactions of RCP with [CoRhCp2*(CO)2] are also described.A preliminary account of part of this work has appeared inJ. Chem. Soc.,

ISSN:1042-7163    

DOI:10.1002/hc.520020206

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe η4‐diphosphacyclobutadiene complexes [M(η5‐C5R5)(η4‐P2C2Bu 2t)] (M  Co, Rh; R  H, Me), react with Rh(I), Pt(O), and Pt(II) centers via the phosphorus lone paris of the rings of afford mixed metal complexes. The crystal and molecular structure of the novel hexarhodium complex [Rh2Cl2{Rh(P2C2Bu 2t)}]4(Cp  N5‐C5H5) is pre

ISSN:1042-7163    

DOI:10.1002/hc.520020207

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have shown that the MNDO‐PM3 semiempirical molecular orbital method is capable of yielding calculated structures of oxaphosphetanes and ylides that are comparable with the experimentally known structures.The MNDO‐PM3 method also reproduces the geometric and thermodynamic parameters of the “mythyical Witting half‐reaction”, previously calculated using a more elaborate and costly ab initio molecular orbital approach. In addition, using the SADDLE routine, we were able to find a transition state for this half‐reaction. This transition state resembles geometrically the transition state found using the ab initio approach (4‐31G* level). The energy of activation was calculated to be 9.2 kcal/mole, which is fairly comparable with the ab initio reslt of 5.2 kcal/mole.According to our calculations, and in general agreement with findings of Volatron and Eisenstein [11], the mythical Witting reaction reaction would be expected to proceed through a planar transition state for the cycloaddition of the ylide and the aldehyde in a process that superficially seems to be a synchronous one. However, an analysis of the evolution of the bond orders and the localized molecular orbitals throughout the reaction indicates that the PO bond has not been formed in the transition state, whereas the CC bond is about 40% formed. Therefore, the mythical Wittig half‐reaction is best described as a very asynchronous cycloaddition (a bordeline two step mechanism) with a planar geometry in the transition state, composed of a multi‐centered mPCCO bond orbital and with the phosphorus and the oxygen atoms sharing a strong attractive charge interaction. A similar description results from computations of the Wittig reactions of H3CHCH3and (C6H5)3PCHCH3with H3CCHO, which is incons

ISSN:1042-7163    

DOI:10.1002/hc.520020208

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe secondary phosphorylphosphane complexes used in the synthesis of phosphaalkene complexes from carbonyl compounds by the so‐called „phospha‐Wittig”︁ reaction can be obtained by two routes. In the first one, a primary lithiophosphine complex is condensed with a chlorophosphite. The resulting PP compound is oxidized at the free phosphorus by 3‐chloroperbenzoic acid. In the second one, bis(phosphoryl)phosphane complexes are allowed to react with sodium methylate in methanol or with water. One of the two PP bonds of the starting produt is thus cleaved to give the „phospha‐Wittig”︁ reagent. Both routes give better yields and are less sensitive to steric hindrance than the prev

ISSN:1042-7163    

DOI:10.1002/hc.520020209

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe 4‐chloro‐1,6‐dihydrophosphinine derivatives, prepared as a mixture of 3‐ and 5‐methyl isomers from the thermolysis of dichlorocarbene adducts with 1‐R‐3‐methylphospholene oxide (R  Me, MeO, EtO, n‐PrO, i‐PrO), participate in Diels‐Alder reactions with dimethyl acetylenedicarboxylate and N‐phenylmaleimide. The former reactant is of special value since the 2‐phosphabicyclo[2.2.2]octa‐5,7‐diene framework is thermally labile and undergoes retrocycloaddition by a different path, eliminating the CP bridging unit as a low‐coordinate species. Thus, in the case of R  Me, the initial phosphine oxides (a mixture of isomers) have been reduced to the phosphines and these undergo straightforward fragmentations on heating at 50°C to produce 2‐phosphapropene. The reactions of this transient species with water and alcohols have been investigated. Unlike the case of stabilized phosphaalkenes, hydration occurs smoothly without catalysis to produce Me2P(O)H; addition of alcohols gives phosphinites, Me2POR. The structure of the Diels‐Alder adducts was confirmed by31P,1H, and13C NMR spectroscopy. Each of the isomeric 1,6‐dihydrophosphinine oxides gives two diastereomeric adducts; partial separation of some of the resulting four‐component mixtur

ISSN:1042-7163    

DOI:10.1002/hc.520020210

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIn the presence of tributylbismuthine, allyl bromide was found to react with either aldehydes or ketones to give the corresponding homoallylic alcohols and their allylic ethers in good total yields.

ISSN:1042-7163    

DOI:10.1002/hc.520020211

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe31P NMR spectra of complexes of the type Pt(SeSN2)(PR3)2and Pt(Se2N2(PR3)2) display trans2J{77Se31P} couplings of ca. 30–80 Hz, with no corresponding cis coupling; in contrast Pt(TeSN2)(PMe2Ph2has both trans and cisJ{125Te31} coupling of 146 Hz and 103 Hz respectively. The31spectra of the complexes Pt(S215N2)(PMe2)P2nd [Pt(S215N2)Cl(PMe2)Ph)]−show both2J‐ and4J{15N31P} couplings, which alter substantially upon protonation of the S2N22−ligand. The15N NMR spectra of Pt(S215N2H)Cl(PMe2Ph) and Pt(S315N)Cl(PMe2Ph) show the presence of both31P15N and195Pt15N couplings but no significant15N

ISSN:1042-7163    

DOI:10.1002/hc.520020212

出版商:VCH Publishers, Inc.    

年代:1991

数据来源: WILEY