bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reaktivität von Cyclopentenyl‐Anion‐analogen Heterocyclen: Homophosphole — Synthese, 1,5‐Elektrocyclisierung, Inversion am Phosphor‐Atom
Authors: Klärner Frank‐Gerrit , Oebels Dirk , Sheldrick William S. 
Published: July 2007

Reactivity of Cyclopentenyl‐Anion‐Analogous Heterocycles: Homophospholes — Synthesis, 1,5‐Electrocyclization, and Inversion at the Phosphorus Atom*[1]The key step of a novel homophosphole synthesis is the reaction of phospholes 3a‐d with diazomethane in the presence of water leading to the oxidized 1,3‐dipolar cycloadducts anti‐7a‐d. The 1,5‐electrocyclization of homophosphole was observed by the temperature‐dependent rate of racemization of optically active anti‐8b (ΔH≠(31.24±0.59) kcal/mol; ΔS≠–(2.32±1.47) cal/mol K). In order to determine the activation parameters for the inversion at the phosphorus atom a (60:40) mixture of syn‐ and anti1‐homophosphole syn‐ and anti‐8b was prepared by H2O2 oxidation of anti‐8b complexed by CuCl and subsequent reduction with Cl3SiH. The enantiomerization [(+)‐anti‐8b → (–)‐anti‐8b] proceeds at 169.5°C 22 times faster than the inversion at the phosphorus atom (anti‐8b→syn‐8b). This shows unambiguously that the electrocyclic ring opening does not require a planar configuration at the phosphorus atom and can start from the nonplanar anti configuration due to a dihedral angle of ca. 0° between the orbital of the lone pair at the phosphorus atom and the cyclopropane Walsh orbitals favourable for a strong electronic interaction in this configuration. From the comparison of the activation parameters for the inversion at the phosphorus atom in the homophosphole (syn‐8b ⇆ anti‐8b) and the dihydrophosphole [(–)‐23 ⇆ (+)‐23] one can extrapolate, that the homoaromatic resonance stabilization in the planar homophosphole is small (ca. —2 kcal/mol) contrary to the surprisingly large aromatic stabilization in the planar phosphole (ca. —20 kcal/mol).
Reaktivität s̀1‐bishomoaromatischer Heterocyclen: Elektrocyclische Reaktionen und Cycloadditionen von syn‐ und anti1‐Bishomofuran und ‐Bishomothiophen
Authors: Golz Thomas , Hammes Susann , Klärner Frank‐Gerrit 
Published: July 2007

Reactivity of s̀1‐Bishomoaromatic Heterocyles: Electrocyclic Reactions and Cycloadditions of syn‐ and anti1‐Bishomofuran and ‐BishomothiopheneProfessor William von E. Doering zum 75. Geburtstag gewidmet.
The title compounds syn‐4a, b and anti‐4a, b, synthesized by the CuCl‐catalyzed reaction of homofuran 1a or homothiophene 1b with diazomethane, are very different in their thermal stability. syn‐4a isomerizes to 2,3‐dihydrooxepine (7a) readily at 130°C whereas the rearrangement anti‐4a → 7a requires a temperature of about 370°C. A similar difference in thermal reactivity is observed between syn‐4b and anti‐4b. But syn‐4b undergoes in addition to the rearrangement to 2,3‐dihydrothiepine (7b) a dimerization (to 12?) on thermolysis in [D6]benzene solution at 140°C, whereas mainly isomerization to 9b, cis‐10b, and 11 (product of the elimination of sulfur from cis‐10b) occurs on thermolysis in the gas phase. The formation of 7a and 7b, respectively, is explained by the electrocyclic ring opening of syn‐4a or syn‐4b leading to the carbonyl ylide 5a or the thiocarbonyl ylide 5b followed by a sigmatropic 1,4 hydrogen shift. To rationalize the additional products in the thermolysis of syn‐4b an electrocyclic conrotatory ring closure in 5b leading to the highly strained episulfide trans‐10b is assumed to complete with the hydrogen shift. Under the reaction conditions trans‐10b is unstable and either dimerizes in solution or isomerizes in the gas phase. The formation of 9b in the thermolysis of syn‐4b indicates that a two‐step pathway may compete with the concerted process. syn‐4a, b react with various π acceptor‐substituted olefins to form cycloadducts of the general type 6a, b. The cycloaddition occurs stereospecifically cis with respect to the configuration of the starting olefin and non‐stereoselectively with respect to the endo/exo ratio. The kinetic analysis of the reaction of syn‐4a with fumaronitrile (FN), N1‐phenylmaleinimide (NPMI) or dimethyl dicyanofumarate (DCFM) shows unambiguously, that the adducts are formed by a 1,3‐dipolar cycloaddition of the intermediate carbonyl ylide 5a rather than a homo‐Diels‐Alder reaction of syn‐4a (in contrast to the cycloaddition of homofuran 1a). A comparison between the enthalpies of reactions syn‐4a → 5a (ΔHR ≤ 22.4 kcal/mol) and syn‐4d → 5d (ΔHR ≥ 47.5 kcal/mol) shows the carbonyl ylide to be a 1,3‐diradical, highly resonance‐stabilized by the heteroatom (resonance energy R.E. ≈︁ –25 kcal/mol).
Neue Beobachtungen zur Stereoselektivität von Monoiodcarben‐Additionen
Authors: Dehmlow Eckehard V. , Soufi Johanna , Stammler Hans‐Georg , Neumann Beate 
Published: July 2007

New Observations Concerning the Stereoselectivity of Monoiodocarbene AdditionsContrary to our earlier claim, CHI gives endo/exo isomer mixtures with cyclooctene. However, only endo1‐iodo compounds 7, 8, 10–12 are obtained from COD and COT. Tricyclic compound 7 rearranges partially to bicyclic 9, X‐ray structure determinations of 7 and 9 were performed.
Synthese, NMR‐Spektren und Photoelektronen‐Spektren von cyclischen Keten‐N,X1‐acetalen (2‐Alkyliden‐N‐heterocyclen)
Authors: Quast Helmut , Ach Manfred , Kindermann Markus K. , Rademacher Paul , Schindler Michael 
Published: July 2007

Synthesis, NMR Spectra, and Photoelectron Spectra of Cyclic Ketene N, X1‐Acetals (2‐Alkylidene‐N‐heterocycles)Deprotonation by sodium hydride of the N1‐methyl‐2‐alkyl‐azolium salts 10c, 14–16 and 18 and of the perimidinium salt 20 as well affords the corresponding ketene N,X1‐acetals 1c, 3–5, 7, and 8 as air‐sensitive distillable oils or low‐melting crystals. The α1‐carbon atoms of cyclic ketene N,X1‐acetals resonate at very high field with the smallest chemical shift of no more than δ39 for the 5‐methylenedihydrotetrazol 2a. Geometries of 1a, b, 2a, and b were optimized on the Hartree‐Fock level with polarized double‐ζ basis sets, followed by IGLO calculations of the NMR chemical shifts. These are in excellent agreement with the unusual carbon‐13 shifts observed. The electronic structures of 1a, b, 2a, b, 3a, b, 4b, 5b, 6a, and b are investigated by photoelectron spectroscopy and semi‐empirical quantum chemical calculations. The observed ionization potentials are assigned to molecular orbitals on the basis of Koopmans' theorem. The order of reactivity in 1,3‐dipolar cycloaddition reactions of cyclic ketene N,X1‐acetals resembles that of the chemical shifts of their α1‐carbon atoms.
Induktiver Effekt, negative Hyperkonjugation und Gegenion sind nicht die Ursache der besonderen Eigenschaften des Bicyclo[3.2.1]octa‐3,6‐dien‐2‐yl‐Anions. — Eine NMR‐Studie mit phenylsubstituierten Modellen
Authors: Christl Manfred , Müller Heinrich 
Published: July 2007

Inductive Effect, Negative Hyperconjugation, and Gegenion do not Cause the Unusual Properties of the Bicyclo[3.2.1]octa‐3,6‐dien‐2‐yl Anion. An NMR Study with Phenyl‐Substituted ModelsThe 13C‐NMR spectra of the phenyl‐substituted bicyclo[3.2.1]oct‐3‐en‐2‐yl anions of 41‐K and 61‐Li show that in the corresponding dienyl anions of 31‐K and 51‐Li not only C‐6,7 have unusual chemical shifts but also C‐2,3,4. The values of the phenyl groups prove the larger negative charge in the allyl system of 41‐K and 61‐Li as compared to that of 31‐K and 51‐Li, respectively. Thus, the C6–C7 π bond in 31‐K and 51‐Li causes the reduction of the negative charge in the allyl subunit. Different from the effect of the C6–C7 π bond in 31‐K, the anellated three‐membered ring in the tricyclo[3.3.1.02,4]1‐nonenyl anion of 71‐K has no influence on the chemical shifts of the phenyl‐substituted allyl anion moiety. Experiments aimed at the exchange of the metal cations of 31‐K, 51‐Li, and 61‐Li for a tetramethylammonium ion were successful only with 51‐Li. The NMR data of 51‐Li and 51‐NMe4 are virtually identical. In the case of 31‐Li and 61‐Li, the treatment with tetramethyl‐ammonium chloride caused an SN2 process with formation of the methylbicyclooctadienes 8a and 10, respectively. Also, 51‐Li underwent this reaction, however so slow that significant concentrations of 51‐NMe4 could be observed in solution. 7Li‐NMR spectra were taken from 51‐Li, 61‐Li, and the solution containing 51‐NMe4.
Über Substitutionsreaktionen an 1,3‐Dithietan‐1,1,3,3‐tetraoxid (Disulfen)
Authors: Frasch Markus , Sundermeyer Wolfgang 
Published: July 2007

Substitution Reactions of 1,3‐Dithietane 1,1,3,3‐Tetraoxide (Disulfene)Alkylation of 1,3‐dithietane 1,1,3,3‐tetraoxide (disulfene, 5) with alkyl iodides in the presence of NaH provides a mixture of cis/trans1‐isomers 4a‐c (Me, Et, iPr), which are further alkylated to 7a, b or brominated to 1a, b. Only by using the respective nonafluorobutanesulfonic acid esters (nonaflates, C4F9SO2OR) silylations, germylation, or stannylation of 5 is achieved with formation of the 2,4‐disilyl (6a, b, d, e), ‐digermyl (3f), and ‐distannyl (3g) compounds as well as the mixed alkyl/silyl species 2a, b. Attempts to synthesize compounds with a 2,4‐bridged structure by treatment of 5 with I–(CH2)3–I/NaH were unsuccessful, but yielded the unusual dispiro disulfene 8, whereas the dicyclic 2,4‐bridged compound 9 has been obtained from 5 and the respective 1,2‐disilyl ester of ethane. The first example of a 1λ6,3λ6‐1,3‐dithiete 10 is obtained by tetrasilylation of 5 accompanied by a rearrangement of two of the bulky Et3Si groups to the sulfone groups.
Silaheterocyclen, XXIII. Synthese und Thermolyseverhalten von Si‐funktionellen 2‐Silaazetidinen
Authors: Auner Norbert , Weingartner Armin W. , Bertrand Guy 
Published: July 2007

Silaheterocycles, XXIII[1]. – Synthesis and Thermolysis Reactions of Si‐Functionalized 2‐SilaazetidinesDichloroneopentylsilene (1) is formed in situ by the reaction of trichlorovinylsilane with LitBu. The [2 + 2] cycloaddition to imines yields Si, Si1‐dichloro‐functionalized 2‐silaazetidines in a preparative scale. With aldimines as trapping agents for 1, the resulting SiN four‐membered ring compounds are isolated as syn/anti1‐isomers (e.g. syn/anti‐15 and ‐16; syn/anti ≈︁ 2:1). Silene 1 is not liberated from the silaazetidines on heating, but the Si, Si1‐dichloro‐substituted silanimine Cl2SiNtBu (24) is formed. This can be trapped by Me3SiOMe or Ph2CNtBu to give the addition products 25 and 26, respectively. The pathways are discussed which lead to stereoisomeric SiN ring compounds by a multiple‐step mechanism including zwitterionic intermediates (1,4‐dipoles). In addition there is strong evidence for the formation of 1, depending on the trapping reagent used. This fact may be explained by donor→silene interactions. The thermolysis products of silaazetidines support the formulation of a stepwise decomposition to an alkene and Cl2SiNR derivatives.
Tetraaza‐λ31‐diphospha‐stanna‐bicyclo[3.1.1]heptane: reaktive Vorstufen neuer Heterobicyclen
Authors: Linti Gerald , Nöth Heinrich , Schneider Ellen , Storch Wolfgang 
Published: July 2007

Tetraaza‐λ31‐diphospha‐stanna‐bicyclo[3.1.1]heptanes: Reactive Precursors of New Heterobicycles2,4,6,7‐Tetraaza‐1λ3,5λ31‐diphospha‐3‐stannabicyclo[3.1.1]heptane (4) is obtained by stannazane cleavage of the diazadistannetidine (Me2SnNtBu)2 (2) with the diazadiphosphetidine (CIPNtBu)2 (1). A chloro derivative of 4, compound 8, is formed by substitution of one methyl group attached to the tin atom in 4 against chlorine in a 1:1 reaction with PhBCl2, while additional PhBCl2 leads to an exchange of the MeClSn against the PhB group to give 9. Oxidation of both phosphorus atoms of compound 4 with sulfur leads to 7. An unexpected introduction of a diphenyldiphosphane unit with formation of 11 proceeds by stannazane cleavage of 4 with PhPCl2. The structures of the bicyclic products 4, 7, 8, and 11 are ascertained by detailed NMR studies, particularly by means of 15N‐NMR spectra, and by X‐ray structure determinations. All heterobicycles contain a planar diazadiphosphetidine unit. The ring system 8 features an additional Sn – N bond due to transannular interaction of the tin atom with one of the nitrogen atoms of the four‐membered P2N2 ring fragment. The PP bond distance in 11 with 2.175 Å is one of the shortest found in heterocycles containing P2 units.
Metal‐Metal Bonding in Paramagnetic Chromium(III) Complexes – An MO‐Theoretical Case Study
Authors: Janiak Christoph , Silvestre Jérǒme , Theopold Klaus H. 
Published: July 2007

AbstractThe electronic structures of the edge‐sharing bioctahedral chromium(III) dimers {C5H5Cr(CH3)(μ1‐Cl)}2 (2) and {Me5C5Cr(CH3)(μ1‐CH3)}2 (4* (Cp* derivative), 4 (Cp derivative)), the trinuclear complex {C5H5Cr(μ1‐Cl)}3(μ1‐CH) (3), and the face‐sharing bioctahedral chromium(III) compounds {Me5C5Cr}2(μ1‐CH2) (6*, 6) [{Me5C5Cr}2(μ1‐CH3)3]+ (7*, 7) have been studied MO‐theoretically by the extended Hückel method. Proceeding from 2 over 3 to 4*, or from 6* to 7* a 3‐center/4‐electron chloride or methylene bridge is replaced by a 3‐center/2‐electron methyl group (a methylidyne cap in the trimer). The 3c/2e bridges give rise to an increased metal – metal overlap population due to Cr – Cr bonding within the core levels. In the series of 2 – 3 – 4* this is accompanied by a decrease in the Cr – Cr distance (329 – 284 – 260 pm) and effective magnetic moment, μeff (2.53 – 2.05 – 1.53 μB per Cr at room temp.). The latter can be ascribed to an increased splitting within the chromium d‐block because of the shorter metal‐metal separation. The bioctahedra 6* and 7* feature even shorter Cr – Cr contacts than 4* (239 and 242 pm), primarily because of their face‐sharing geometry. However, their effective magnetic moments (per Cr) are 2.33 and 1.32 μB at room temp. The high magnetic moment for 6* can be understood from the orbital interactions in the frontier orbital metal d block: A face‐sharing bioctahedron shows one σ, two δ, and no π type overlap, while an edge‐sharing bioctahedron (4) has σ, π, and δ interaction between the metals. In the former this destabilizes only σ* sufficiently to prevent occupation by electrons (leaving five orbitals for six electrons, possible spin multiplicities S0, 1, 2) while for the latter both σ* and π* are destabilized beyond electron occupation (leaving four MOs for six electrons, possible spin multiplicities S0, 1). 4*, 6* and 7* are unusual examples of metal – metal bonded complexes containing octahedral CrIII ions.
Synthese und Struktur von Phosphiren‐Iminen und Iminophosphaspiro[2.2]pentanen
Authors: Barion Detlef , David Gabriele , Link Manfred , Nieger Martin , Niecke Edgar 
Published: July 2007

Synthesis and Structure of Phosphirene Imines and Iminophosphaspiro[2.2]pentanesThe reaction of the iminophosphanes R1PNR2[1, R22,4,6‐tBu3C6H2;R1Me (a) Et (b), PhCHCH (c), Cl (d); R2tBu, R1Et3C (e)] with the alkynes R3C  CR4 [2, R3R4Ph (a), CO2Me (b)] affords the corresponding phosphirene imines 3a – g. A [2 + 1] cycloadduct 3h is also formed in the reaction of the alkyne 2c (R3H, R4Ph) with 1d, while in the case of 1b the 1,2‐addition product 4 is obtained. As demonstrated by the [2 + 1] cycloaddition reaction of the P1‐alkylated iminophosphanes 1a, b with methylene‐cyclopropanes 5a, b, the formation of the iminophosphaspiro[2.2]pentanes 6a, b is observed. The structures of the P/C heterocycles 3a, b and 6b have been determined by NMR spectroscopy and X‐ray analysis.
Schwefel(IV)1‐Verbindungen als Liganden, 19. Kationische Ruthenium‐Sulfen‐Komplexe: Synthese und Reaktionen. Kristallstrukturanalyse von [Cp*(Me3P)2Ru(CH2SO2)]PF6
Authors: Schenk Wolfdieter A. , Urban Peter , Dombrowski Eberhard 
Published: July 2007

Sulfur(IV) Compounds as Ligands, 19[1]. – Cationic Ruthenium‐Sulfene Complexes: Synthesis and Reactions. Crystal Structure Analysis of [Cp*(Me3P)2Ru(CH2SO2)]PF6Methylene addition to coordinated sulfur dioxide yields the novel η2(C, S) sulfene complexes [Cp(dppm)Ru(CHRSO2)]PF6 (RH:3, Me: 4) and [Cp*(Me3P)2Ru(CH2SO2)]PF6 (5). An X‐ray structure determination of 5 reveals a relatively short C – S bond (167.5 pm). The sulfene complexes are powerful carbon electrophiles as shown by the rapid addition of halides, pseudohalides, amines, including „nonnucleophiles”︁ such as ethyldiisopropylamine and DBU, and phosphanes to 3. The regioselectivity of the reaction of 3 with enamines is opposite to that of free sulfene, i.e. coordination of the sulfene to ruthenium effects umpolung.
Ein L3ZnOH‐Komplex als funktionelles Modell des Enzyms Carboanhydrase
Authors: Alsfasser Ralf , Ruf Michael , Vahrenkamp Heinrich 
Published: July 2007

An L3ZnOH Complex as a Functional Model of the Enzyme Carbonic AnhydraseThe tridentate ligand hydrotris(3‐tert1‐butyl‐5‐methylpyrazolyl)borate (L3) reacts with zinc perchlorate hexahydrate to form L3ZnOH (1) which is the first mononuclear neutral zinc hydroxide complex. 1 is a structural model of the enzyme carbonic anhydrase due to its tetrahedral coordination with three N‐heterocycles and one OH ion as ligands. Its functional analogy to the enzyme involves (a) reversible uptake of CO2 forming the unstable bicarbonate complex L3ZnOCOOH (4) in solution from which the dinuclear carbonate complex L3ZnOC(O)OZnL3 (3) crystallizes, (b) reaction with dialkyl pyrocarbonates forming the complexes L3ZnOC(O)OR (5) which are stable esters of the bicarbonate complex and which are easily hydrolyzed to ROH, CO2, and L3ZnOH, (c) thermal decarboxylation of the ethyl carbonate complex 5b resulting in the ethanolate complex L3ZnOEt (6) which is extremely sensitive to hydrolysis, (d) “inhibition” by small anions due to conversion of 1 into the complexes L3ZnX (7; XCl, CN, N3, OAc). The identity of the various L3Zn derivatives is established by NMR methods and structure determinations.
(E, Z)1‐Equilibria, 17 Demonstration of the Nitrogen Inversion Mechanism of Imines in a Schiff Base Model
Authors: Knorr Rudolf , Ruhdorfer Jakob , Mehlstäubl Johann , Böhrer Petra , Stephenson David S. 
Published: July 2007

AbstractExperimental differentiation between pure CN double bond rotation and nitrogen inversion in N1‐arylimines is possible with a single compound (13b) under the proviso of slow rotation about the N–aryl single bond. Labelling by 1H and 13C nuclei at the diastereotopic faces of the CN moiety as well as of the N–aryl group is the clue to a successful stereodynamic analysis, as performed by variable‐temperature NMR spectroscopy of 13b, a sterically congested and chiral model compound. Interpretation of similar measurements on a second model (13d) is less straightforward. The experimental observation of time‐averaged Cs symmetry by NMR coalescences is only compatible with a mechanism of (E/Z) stereomutation either by pure inversion at sp2 nitrogen or by a contribution from CN rotation together with a synchronized (geared) controtation about the N–aryl single bond. However, the latter combination is concluded to be predominantly inversion‐like by comparisons with related imines.
A Cholestenyl‐Substituted Bis(indenyl)zirconocene‐Derived Homogeneous Ziegler Catalyst for Stereoselective Propene Polymerization
Authors: Erker Gerhard , Aulbach Michael , Wingbermühle Doris , Krüger Carl , Werner Stefan 
Published: July 2007

Abstract(–)1‐5‐Cholesten‐3β1‐yl tosylate (6) undergoes SN2 substitution with indenyllithium to give (–)1‐3‐(5‐cholesten‐3α1‐yl)indene (7), which is subsequently deprotonated by methyllithium to give the cholestenyl‐substituted indenyllithium reagent 8. Its reaction with 0.5 molar equivalents of ZrCl4(THF)2 furnished the three bis[3‐(5‐cholesten‐3α1‐yl)indenyl]ZrCl2 diastereoisomers in a ratio of 9a: 9b: 9c60 : 16 : 24. The major organometallic reaction product 9a was recovered isomerically pure and used for the generation of an active homogeneous metallocene/alumoxane Ziegler‐type catalyst for stereoselective propene polymerization. The catalyst derived from the non‐bridged chirally substituted bis(indenyl)zirconocene complex 9a produces partially isotactic polypropylene almost completely by enantiomorphic site control in the temperature range from – 50 to + 15°C.
Michael‐Type Reactions between Electron‐Deficient 1,3‐Dienes and Dimethylgermylene/Water
Authors: Wienken Stefan , Neumann Wilhelm P. 
Published: July 2007

AbstractA new type of reaction between dimethylgermylene (Me2Ge) (1), generated in situ from a 7‐germanobornadiene, and electron‐deficient 1,3‐dienes RR′CCH – CHCH – Z [ZC(O)Me, CO2R″ 2a – f] or cyclic dienones 8, 9 in the presence of water is described. The Michael‐type behaviour of the system Me2Ge/H2O is clearly shown by the nucleophilic addition to the unsaturated systems resulting in the formation of β1‐ and δ1‐adducts, the new allylgermanes 3a – g, 4a –c, 10a, b, 11. The cis configuration of the resulting double bond of the δ adducts 4a–c is remarkable. With open‐chain dienes cycloaddition of 1 without participation of water, yielding germacyclopentenes 5a, b or germacyclopentanes 7a, b, competes with the Michael‐type reaction. A slight variation of the substitution pattern of the dienes has a strong influence on the reaction course.
Synthese homochiraler 3‐Oxa‐2,7‐diazabicyclo[3.3.0]octane aus Aminosäuren durch intramolekulare 1,3‐dipolare Cycloaddition von Nitronen
Authors: Aurich Hans Günter , Frenzen Gerlinde , Gentes Christian 
Published: July 2007

Synthesis of Homochiral 3‐Oxa‐2,7‐diazabicyclo[3.3.0]octanes from Amino Acids by Intramolecular 1,3‐Dipolar Cycloaddition of NitronesN1‐Allylamino alcohols 9 were prepared from amino acids by various methods. Swern oxidation of 9 afforded aldehydes 11. By reaction of 11 with N1‐alkylhydroxylamines nitrone intermediates 4 were formed which spontaneously underwent an intramolecular 1,3‐dipolar cycloaddition to yield the bicyclic compounds 6. The cycloaddition proceeds diastereoselectively furnishing homochiral compounds 6 from homochiral starting materials. The structure of 6aA was confirmed by X‐ray structural analysis.
Synthesis and Crystal Structure of the First “1,2‐Diphospha[4]radialene”
Authors: Brieden Walter , Kellersohn Thomas 
Published: July 2007

Abstract1,2‐Diphosphetane 4, the first “1,2‐diphospha[4]radialene”, has been prepared in 83% yield by the reductive coupling reaction of 2,3‐bis(chloroisopropylphosphanyl)butadiene 3a with lithium in THF. The X‐ray crystal structure of 4 was determined, and it shows that 4 is a highly strained 1,2‐diphosphetane.
Beiträge zur Chemie des Bors, 216. Über die Komplexbildung von 1,3,2,4‐Diphosphadiboretanen mit Pentacarbonylchrom sowie über die Darstellung und Reaktivität von Borylidenphosphan‐Komplexen
Authors: Linti Gerald , Nöth Heinrich , Paine Robert T. 
Published: July 2007

Contributions to the Chemistry of Boron, 216[1]. – On the Complex Formation of 1,3,2,4‐Diphosphadiboretanes with Pentacarbonylchromium and the Preparation and Reactivity of Borylidenephosphane Complexes2,4‐Bis(dialkylamino)1‐1,3,2,4‐diphosphadiboretanes (R2NBP‐CMe3)2with sterically undemanding amino substituents are prepared together with the corresponding bis(phosphanyl)1‐boranes R2NB(PHCMe3)2by the reaction of R2NBCl2with Li‐P(H)CMe3. Complexes of 1,3,2,4‐diphosphadiboretanes with one or two pentacarbonylchromium fragments were obtained by the reaction of the ligands with Cr(CO)5·THF or Cr(CO)5·NMe3. If substituents are sterically demanding, cycloreversion is observed with formation of [(aminoborylidene)1‐phosphanyl‐P]pentacarbonylchromium compounds tmpBPR[Cr(CO)5] (10, 29) with an allene‐like structure. Complex29may also be prepared by HCl elimination from tmp‐B(Cl)–P(H)CMe3[Cr(CO)5] (34) with lithium diisopropylamide. This reaction can by reversed be the addition of HCl. The diphosphadiboretane11reacts with HCl, ethanol, and secondary amines with cleavage of all BP bonds. The X‐ray structures of complexes (Et2NB – PCMe3)2[Cr(CO)5]2(23) and (iPr2NB – PCEt3)2[Cr(CO)5] (25) as well as of the diphosphadi‐boretanes (Me2NB – PCMe3)2(11) and (iPr2NB – PCEt3)2(24) are presented. The intra ring angles of23remain almost unchanged upon complexation. In contrast, the B2P2ring of25is slightly folded and its noncoordinated P atom approaches a planar environment.