bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Novel Approach to Ferrocenes with Planar Chirality
Authors: Ganter Christian , Wagner Trixie 
Published: July 2007

AbstractThe 2‐metalation of enantiomerically pure (S)‐(2‐methoxy‐methylpyrrolidin‐1‐yl)ferrocene FcSMP (1) with BuLi proceeds with high diastereoselectivity (up to 98% de) to yield the Ph2P‐substituted ferrocene (S,Sp)‐2a after quenching with Ph2PCl. The SMP moiety was removed by heating of 2a at reflux in acetic anhydride to give planar chiral (Sp)‐2‐diphenylphosphanylferrocenylmethyl acetate (5). The diastereoisomer (S,Rp)‐2b was synthesized from 1 by intermediately blocking the primary metalation site with a Me3Si group which can be removed afterwards by treatment with KOtBu in DMSO. Compound 2a was treated with [(C3H5)PdCl]2 to give the complex [(C3H5)Pd·2a]PF6 (7·PF6). The structure of 7·PF6 was determined by a single‐crystal X‐ray diffraction study and showed 2a to act as a bidentate P,N‐chelate ligand.
Oligonuclear Organometallic Complexes with Boron‐Nitrogen Bridges
Authors: Jäkle Frieder , Priermeier Thomas , Wagner Matthias 
Published: July 2007

AbstractThe facile formation of boron‐nitrogen bridges allows the one‐step assembly of oligonuclear organometallic complexes. By the reaction of 1‐(dibromoboryl)ferrocene (1a) and 1,1′‐bis(dibromoboryl)ferrocene (1b) with 1‐[(dimethylamino)methyl]ferrocene (2) and (η6‐aniline)tricarbonylchromium derivatives (3, 4) dinuclear to pentanuclear units (5–10) were obtained. The homodimetallic compound FcBBr2‐NMe2CH2Fc (5, Fc: ferrocene) closely resembles a propylene‐bridged complex. Its dative B‐N link is stable at temperatures as high as 100°C. Each of the heterooligonuclear aggregates 7–10 is tied together by covalent B‐N bonds, which are isoelectronic with ethylene bridges. In FcB(Br)‐N(Me)Bct [7, Bct: (η6‐C6H5)Cr(CO3)] and 1,1′‐Fc[B(Br)‐N(Me)Bct]2 (9) B‐N π bonding dominates over the N‐Bct π interaction as indicated by spectroscopical data and an X‐ray analysis of 9. The N‐lithiated compounds BctNRLi (4a, b; R = H, Me) possess a remarkably increased N‐Bct π donation compared to the protonated parent compounds, which results in a further perturbation of the local C3v symmetry of the (C6H5)Cr(CO3) framework.
Halfsandwich‐Type Osmium Complexes Containing Phosphanylmethanide and Phosphanyl Alcoholate Anions as Bidentate Ligands
Authors: Werner Helmut , Henig Gerhard , Wecker Ulrich , Mahr Norbert , Peters Karl , Schnering Hans Georg Von 
Published: July 2007

AbstractThe mononuclear dichloroosmium(II) complexes [(mes)‐Os(L)Cl2] (2‐5) with the phosphanyl ether L = iPr2PCH2‐CH2OMe and phosphanyl esters L = IPr2P(CH2)nCO2R as ligands are obtained from [(mes)OsCl2]n and L in almost quantitative yield. While compound 3 (L = iPr2PCH2CH2CO2Me) reacts with Mg/Hg in THF in the presence of ethanol to give the monohydrido derivative 6, treatment of 4 (L = iPr2PCH2‐CO2Me) or 5 (L = iPr2PCH2CO2Et) with Al2O3/NaH in THF yields the phosphanylmethanide complexes [(mes)‐Os{k2(P,C)‐iPr2PCHCO2R}Cl] (7, 8). In contrast to the reaction of 4 with Mg/Hg in THF/EtOH which yields the dihydrido compound [(mes)OsH2{k(P)‐iPr2PCH2CO2Me}] (10), the corresponding reaction of 4 with excess PhMgBr does not lead to an OsPh2 species but instead gives the new chelate complex [(mes)OsPh{k2(P,O)‐iPr2PCH2CPh2O}] (11). The crystal and molecular structures of 7 and 11 were determined.
The 13C Chemical Shift of the ipso Carbon Atom in Phenyllithium
Authors: Berger Stefan , Fleischer Ulrich , Geletneky Christian , Lohrenz John C. W. 
Published: July 2007

AbstractPhenyllithium was labeled with 6Li and 13C at the ipso carbon atom, and the tetramer was measured by solid‐state NMR. The chemical shift tensor data were obtained by a moment analysis of the spinning side bands and were compared with the results obtained by calculations with the IGLO method. Although no splitting by dipolar spin coupling to 6Li was found the very good agreement between IGLO predictions and experimental results allowed alignment of the tensor axis to the molecular frame and interpretation of the data. The large deshielding of the isotropic chemical shift is mainly due to a decrease of the ΔE term in s̀.
Contributions to the Chemistry of Boron, 231. Synthesis and Structures of Borylated Hydrazines
Authors: Hommer Herbert , Nöth Heinrich , Sachdev Hermann , Schmidt Martin , Schwenk Holger 
Published: July 2007

AbstractThe diboration of the diazene PhN = NSiMe3 (15) by diborane(4) derivatives provides a new synthetic route to N,N'‐diborylated hydrazines. The product formed depends on the type of the diborane(4) compound. Thus, addition of dimesityldiboron dichloride to 15 in a 1:1 ratio afforded (mesCIB)PhN‐N(SiMe3)(BClmes) (16) while bis(dimethyl‐amino)diboron dichloride was found to react in a 1:2 ratio to give a triazadiborolidine derivative 17. In addition, it was demonstrated that in the solid state Me2N–N(BPh2)2 (8) is a derivative of a three‐membered dihydroazadiboriridine C while its isomer, (Ph2B)MeN–NMe(BPh2) (7), forms no BN coordinative bond. The new 3,6‐difluoro‐1,2,4,5‐tetraza‐3,6‐diborine 13 shows a twist conformation. The molecular structures of all these compounds were determined by X‐ray crystal structure analysis, and the influence of the B substituent on the conformation is discussed.
Auf‐ und Abbau von Azadecaboranen; Aza‐nido‐nonaborat
Authors: Roth Martin , Paetzold Peter 
Published: July 2007

Synthesis and Degradation of Azadecaboranes; Aza‐nido‐nonaborateThe boranes arachno‐B9H13(NRH2 (1a‐c: R = p‐ClC6H4, p‐MeC6H4, PhCH2) are dehydrogenated at 140°C to give nido‐RNB9H11 (2a‐c), from which the azaboranes closo‐RNB9H9 (3a‐c) are formed on further dehydrogenation at 460°C. These azaboranes are deboronated either by the attack of the amine iPrNH2 or by one of the fluorides [NBu4]F or [S(NMe2)3][Me3SiF2] in THF. One of the four boron atoms adjacent to nitrogen in the closo species is removed and then detected in the borazine (HNBiPr)3 or the borate BF4, respectively, whereas the novel anions nido‐RNB8H9 (4a‐c) remain. The structure of 4a‐c corresponds to that of nido‐SB8‐H9‐, according to NMR spectra. Primary amines R'NH2 deboronate the closo‐boranes 3a, b in a solvent less polar than THF to give the amine – azanonaboranes arachno‐RNB8H10‐(NR'H2) (5a‐c: R' = iPr, Pr, Bu). The nido product [iPrNH3][(p‐ClC6H4)NB8H9 is converted into a mixture of the arachno products 5a and (p‐ClC6H4)NB8H10(NPrH2) (5d) by the action of PrNH2, making plausible that anions of type 4 are intermediates during the transformation of 3 into 5.
Synthese und Reaktivität von Silicium‐Übergangsmetall‐Komplexen, 35. Metallo‐silanole und Metallo‐siloxane, 9. Synthese des diastereomerenreinen Ferrio‐silanols (RS,SR)‐Cp(OC)(Ph3P)Fe‐Si(Me)(Ph)(OH) und Struktur von (RR,SS)‐Cp(OC)(Ph3P)Fe‐Si(Me)(Ph)Cl
Authors: Malisch Wolfgang , Neumayer Michael , Fey Oliver , Adam Waldemar , Schuhmann Rosemarie 
Published: July 2007

Synthesis and Reactivity of Silicon Transition Metal Complexes, 3534. Mitteilung: W. Malisch, R. Lankat, W. Seelbach, J. Reising, M. Noltemeyer, R. Pikl, U. Posset, W. Kiefer, Chem. Ber., 1995, 128, 1109.

.
— Metallo Silanols and Metallo Siloxanes, 9

8. Mitteilung: W. Malisch, S. Schmitzer, R. Lankat, M. Neumayer, F. Prechtl, W. Adam, Chem. Ber., 1995, 128, 1251, voranstehend.

.
— Synthesis of the Diastereomerically Pure Ferrio Silanol (RS,SR)‐Cp(OC)(Ph3P)Fe‐Si(Me)(Ph)(OH) and Structure of (RR,SS)‐Cp(OC)(Ph3P)Fe‐Si(Me)(Ph)Cl

Herrn Professor Max Schmidt zum 70. Geburtstag gewidmet.
Irradiation of the ferrio chlorosilane Cp(OC)2Fe‐Si(Me)‐(Ph)Cl (1) in the presence of Ph3P leads to Cp(OC)(Ph3P)‐Fe‐Si(Me)(Ph)Cl (2) which is formed as a mixture of diastereomers separated by crystallization. Pure (RR,SS)‐2 is converted highly stereoselectively into (RR,SS)‐Cp(OC)(Ph3P)‐Fe‐Si(Me)(Ph)H (3) with LiAlH4, and further with dimethyldioxirane into (RS,SR)‐Cp(OC)(Ph3P)Fe‐Si(Me)(Ph)(OH) (4). This ferrio silanol diasteromer is alternatively obtained by Cl/OH exchange with KOH from 2. Diastereomerically pure (RR,SS)‐2 is characterized by a single‐crystal structure analysis.
An Efficient Catalyst for the Conversion of Hydrosilanes to Alkoxysilanes
Authors: Lorenz Catrin , Schubert Ulrich 
Published: July 2007

AbstractThe copper(I) hydride [Ph3PCuH]6 is an efficient catalyst for the alcoholysis of primary and secondary silanes. The reactions proceed at room temperature within a few hours and give the alkoxysilanes in high yields. Only with bulky alcohols or silanes are longer reaction times and/or increased temperatures required. The presence of air accelerates the reactions and gives rise to higher yields of alkoxysilanes, particularly with bulky alcohols. Diols react with PhRSiH2 (R = Me, Ph) to afford 1,3‐dioxo‐2‐silacycloalkanes and with tertiary silanes to furnish the bissilylated diols. When unsaturated alcohols (2‐propen‐1‐ol or 2‐propyn‐1‐ol) are employed, the double or triple bond is retained.
Reaction of Alkylzirconocene Cation Complexes with (R–CC–)2SiR2 Reagents: Preparation of Heterodimetallic Compounds Containing a μ‐Alkynyl Ligand Bridge Between Zirconium and Silicon
Authors: Röttger Dirk , Erker Gerhard , Fröhlich Roland , Kotila Sirpa 
Published: July 2007

AbstractThe methylzirconocene cation, employed as the [Cp2ZrCH3(THF)]+BPh4− reagent 1a reacts with (R′CC)2SiR2 substrates (6a–d) by means of carbometallation of an alkynyl group to yield the mixed metal ring systems 8a–d, containing both a 1,1‐disubstituted μ‐alkenyl and an alkynyl bridge between zirconium and silicon (e.g. shown by X‐ray crystal structure analyses of complexes 8a and 8c). A similar addition reaction takes place upon treatment of the (butadiene)zirconocene/tris(pentafluorophenyl)‐borane 1:1 addition product 9 with (CH3–CC)2Si(CH3)2 (6c) to give 10. Here the incipient alkyl zirconocene cation character of the metallocene/borate betaine complex 9 shows up in the alkynyl silane carbometallation reaction.
The Reduction of Oxalic Amidines with Metallic Lithium: Preparation of Lithiated Bisamides [R″N(RR′N)C=C(NRR′)NR″]Li2 and Their Use as Intermediates in a Novel Synthesis of Tetraaminoethenes
Authors: Wenzel Matthias , Lindauer Dirk , Beckert Rainer , Boese Roland , Anders Ernst 
Published: July 2007

AbstractReduction of the 1,4‐diaza‐1,3‐butadiene substructure of hexasubstituted oxalic amidines with lithium metal yields the new lithium diamides 3. Subsequent reaction of 3 with various electrophiles gives the title substances 4, 5, and the acylated derivative 6, respectively. The first SET step in this reaction is the formation of monolithium radical anions 2, which were detected by EPR spectroscopy. The second electron transfer leads to the deeply colored dianions 3. – In the case of compound 3a [cis‐3a · 3 Et2O], the X‐ray crystal structure reveals the cisoid arrangement of the bidental ligand and three molecules of diethyl ether which are located in a 2:1 fashion in the first coordination sphere of the lithium cations. The NMR 2D‐1H,6Li‐HOESY investigations of 3a in [D10]diethyl ether/diethyl ether (8:1) show Li+ contacts to the hydrogen atoms of the ether molecules and to the ortho‐hydrogen atoms of the aryl moieties. Results of semiempirical calculations (PM3) are throughout in acceptable agreement with the experimental data and explain the unusual coordination pattern of the lithium cations of compounds 3.
Synthesis of Novel Tridentate N,O,S and N,N,O Ligands of the Tripod Type in Racemic and Enantiomerically Pure Form
Authors: Berkessel Albrecht , Frauenkron Matthias , Nowak Thorsten , Schwenkreis Thomas , Seidel Lutz , Steinmetz Adrian , Bolte Michael 
Published: July 2007

AbstractA series of seven chiral, tripodal N,O,S and N,N,O ligands were prepared in which N stands for a secondary amine or imidazole donor, O for a phenol, and S for a thioether or thiol metal‐binding group. Key steps are (1) the construction of ortho‐hydroxyacetophenones bearing the phenolic binding group and either a thioether, a protected thiol or an imidazole substituent in the α‐position, and (2) subsequent reductive amination with a primary amine. The modular synthesis allows a rapid construction of a variety of structurally related ligands. In three cases, the enantiomers of the racemic products could be separated after condensation with (R)‐glyceraldehyde acetonide as chiral auxiliary. The relative configurations of the cyclic N,O‐ and N,N‐acetals thus obtained were established by NOE spectroscopy. X‐ray structural analysis of two crystalline N,O‐ and N,N‐acetals allowed the assignment of absolute configurations. Hydrolysis of the dia‐stereomerically pure acetals afforded the enantiomerically pure ligands in high yield. By comparison of their CD spectra, absolute configuration could also be assigned to the third pair of enantiomerically pure ligands.
Synthesis and Structure of Bis(2,4‐di‐tert‐butyl‐1,3‐cyclopentadien‐1‐yl)‐disulfane, S2(tBu2C5H3)2, and Bis[2,4‐di‐tert‐butyl‐5‐(trimethylsilyl)‐1,3‐cyclopentadien‐1‐yl]disulfane, S2 [tBu2(Me3Si)C5H2]2
Authors: Thaler Georg , Wurst Klaus , Sladky Fritz 
Published: July 2007

AbstractReaction of 1,3‐di‐tert‐butylcyclopentadienyllithium and 1,3‐di‐tert‐butyl‐4‐(trimethylsilyl)cyclopentadienyllithium with S2Cl2 gives bis(2,4‐di‐tert‐butyl‐1,3‐cyclopentadien‐1‐yl)di‐sulfane (1) and bis[2,4‐di‐tert‐butyl‐5‐(trimethylsilyl)‐1,3‐cyclopentadien‐1‐yl) disulfane (2), respectively. The structure of 2 was determined by single‐crystal X‐ray diffraction. Compounds 1 and 2 are the first biscyclopentadienylchalcogens with the chalcogen in vinylic position.
Activation of Carbon Dioxide, VI. Ligand Effects in the Catalytic Hydrogenation of Carbon Dioxide to Formic Acid Using in situ Catalysts Formed from [{(cod)Rh(μ‐Cl)}2] and Monodentate and Bidentate Phosphorus Ligands
Authors: Graf Elisabeth , Leitner Walter 
Published: July 2007

AbstractHighly active catalysts for the hydrogenation of CO2 to formic acid in DMSO/NEt3 are formed in situ from [{(cod)Rh(μ‐Cl)}2] and various monodentate or bidentate ligands with phosphorus as the donor atom. Formic acid concentrations up to 2.3 · 0.2 mol l–1 can be obtained in less than 6 hours at ambient temperature under a total initial pressure of 40 atm by using rhodium concentrations of 5 · 10–3 mol l–1. The changes in catalytic activities observed upon structural changes of monodentate ligands are discussed in terms of classical ligand parameters like basicity and steric demand of the PR3 group, while with bidentate ligands R2P(CH2)nPR2 the chain length n plays a dominant role for the activity of the catalyst. The effects cannot be explained by a direct impact of the ligand on catalytically active intermediates only, but influences on the formation of these species must also be taken into account.
Chirale Tripodliganden mit Phosphor‐ und Schwefeldonoren. Synthese und Komplexchemie
Authors: Reinhard Gunther , Soltek Rainer , Huttner Gottfried , Barth Annette , Walter Olaf , Zsolnai Laszlo 
Published: July 2007

Chiral Tripod Ligands with Phosphorus and Sulfur Donors. Synthesis and Complex ChemistryNeopentane based tripod ligands CH3C(CH2X)(CH2Y)‐(CH2Z) with mixed donor groups X,Y,Z (PR2, SR, SH) are accessible via two different strategies. The functionalized thietane CH3(CH2X)ČH2SCH2 allows stepwise introduction of P or S donors by substitution of the mesylate function and subsequent nucleophilic cleavage of the thietane ring. Tripod ligands 5 [CH3C(CH2X)(CH2Y)(CH2Z)] with up to three different donor groups (X = SH; Y = PPh2; Z = P(4‐Tol)2, SCH2Ph, PPh2) are thus available. As an alternative the neopentane derivatives 8 [CH3C(CH2X)(CH2Y)(CH2Cl)] which are easily assessible from CH3C(CH2OSO2Me)(CH2Br)‐(CH2Cl) (7) by stepwise substitution with phosphides LiPAr2 (Ar = aryl) may be transformed to 9 [CH3C(CH2X)(CH2Y)(CH2SBzl)]. Under controlled conditions the S—benzyl bond of 9 is cleaved reductively without concomitant cleavage of P—Ar bonds. Ligand 5a [CH3C(CH2PPh2)2(CH2SH)] reacts with Ni(BF4)2 · 6 H2O to yield the dinuclear species [(CH3C(CH2PPh2)2‐(CH2S)Ni)2]2+ (10). The two ligands are bonded in an equivalent way with each of the two nickel centers interacting with one of the two phosphane functions of the ligand; the thiolate functions form μ2‐SR bridges between the two nickel atoms. The SCH2 group at the four‐membered S2Ni2 ring are in mutual cis position with the four‐membered ring bent along the sulfur–sulfur axis by 70°. The internal strain in 10 is analyzed by comparing its structure with the ones of [(CH3C(CH2‐PPh2)3NiSPh)2]2+ (11) and [(CH3C(CH2OH)(CH2PPh2)2‐NiOH)2]2+ (12).
Chalcogen Transfer to Bis[2‐(dimethylaminomethyl)phenyl]silanediyl by Isocyanates and Isothiocyanates
Authors: Belzner Johannes , Ihmels Heiko , Kneisel Boris O. , Herbst‐Irmer Regine 
Published: July 2007

AbstractReaction of hexakis[2‐(dimethylaminomethyl)phenyl]cyclo‐trisilane (1) with isocyanates results in the clean formation of cyclic di‐ or trisiloxanes 3 and 4a and the corresponding isonitrile. Single‐crystal X‐ray analysis of tetrakis[2‐(dimethylaminomethyl)phenyl]cyclodisiloxane (4a) reveals each silicon center to interact with two amino groups forming Si ⃛N distances, which differ significantly in length. Phenyl isothio‐cyanate reacts with 1 with transfer of sulfur to yield penta‐coordinated bis[2‐(dimethylaminomethyl)phenyl]silanethione (11).
Metal‐Assisted Assembly of Chain and Macrocyclic As–S Ligands from Ethylcycloarsathiane (C2H5AsS)n
Authors: Häusler Thomas , Sheldrick William S. 
Published: July 2007

AbstractTreatment of cyclo‐(EtAsS)n with [RuCl2(Ph3P)3] and [Re‐Br(CO)5] affords the respective complexes [RuCl2{cyclo‐(EtAsS)4}(Ph3P)] (1) and [{Re(CO)3}2{μ‐(Et4As4S5)}] (2). Whereas 1 contains a η3 As coordinated intact cyclotetramer (EtAsS)4, ring cleavage leads to the chain anion Et4As4S52−, stabilised as a bridging hexadentate ligand in 2. Reaction of MCl3 with cyclo‐(EtAsS)n in toluene in a Carius tube enables the metal‐mediated temperature controlled assembly of the novel 16‐ and 14‐membered macrocyclic hexadentate As–S ligands in (M{cyclo‐(Et6As8S10)}] (3: M = Os; 4: M = Ru) and [Ru{cyclo‐(Et4As6S10)}] (5). The structures of the products were established by X‐ray crystallography.
Synthesis and Structure of Tris(trialkylstannyl)‐ and Tris(dialkylhalostannyl)amines; Stabilization of the Sn3N Skeleton by Intramolecular Sn–X–Sn Bridges
Authors: Appel Andrea , Kober Christian , Neumann Christine , Nöth Heinrich , Schmidt Martin , Storch Wolfgang 
Published: July 2007

AbstractTris(triorganylstannyl)amines (R2R'Sn)3N (1, 2) with substituents R = R' = Me, Bu or R = Me and R' =iPr,tBu are obtained by metathesis from R2R'SnX and NaNH2in liquid ammonia or by transamination of R3SnNMe2with NH3. Tris(diorga‐nylhalostannyl)amines (R2XSn)3N (3) are synthesized by stannazane cleavage of (Me3Sn)3N (1) with R2SnX2. Information from multinuclear magnetic resonance spectra ascertain the planarity of the Sn3N skeleton of type2and3, as well as the relationship between the coupling constants1J(119Sn15N) and2J(119Sn117Sn) and the Sn–N bond length as determined by the X‐ray structure analysis of1, 3band3r. Compound3bshows an almost undistorted D3hsymmetry with a planar Br3Sn3N skeleton and SnN bond lengths of 1.99 Å, which beside those of3aare the shortest found so far. According to MNDO approximate andab initiocalculations π interactions between the lone electron pair at the N atom and empty orbitals at the Sn atoms can be excluded. Therefore, the tristan‐nylamines discussed here have a trigonal planar nitrogen center with its lone electron pair in ap‐type orbital. Further characteristic features of the molecular structures of typ3compounds are the intramolecular Sn–X–Sn bridges (X = Cl, Br, I) found in the solid state as well as in solution. The molecular geometries of the tristannylamines are supported by MS fragmentation patterns as well as by infrared and Raman spectra.
Ring‐Enlargement and Ring‐Opening Reactions of Benzoxazole, Thiazoles, and Benzisoxazole by Zirconocene‐Alkyne Complexes
Authors: Arndt Perdita , Lefeber Claudia , Kempe Rhett , Rosenthal Uwe 
Published: July 2007

AbstractZirconocene alkyne complexes Cp2Zr(L)(Me3SiC2R) (L = Py, THF; R = SiMe3 tBu) react with heterocyclic compounds like benzoxazole and related thiazoles to yield ring‐expanded adducts (1–3) and (4, 5) by formal C‐X (X = O, S) bond cleavage and coupling with the coordinated alkyne. In the case of benziso‐xazole, the alkyne is not coupled but eliminated, and with ring‐enlargement of the benzisoxazole a N‐bridged dimer (6) is formed. The obtained complexes 1, 3, and 6 were characterized by NMR spectra and crystal structure analysis.
Synthesen und Strukturen von neuen 1,3,5‐Triphospha‐2,4,6‐trisilacyclohexanen und Untersuchung ihrer Ligandeneigenschaften gegenüber [M(CO)3]‐Komplexfragmenten (M = Cr, Mo)
Authors: Drieß Matthias , Pritzkow Hans , Reisgys Michael 
Published: July 2007

Syntheses and Structures of New 1,3,5‐Triphospha‐2,4,6‐trisilacyclohexanes and Investigation of Their Ligand Properties Toward [M(CO)3] Complex Fragments (M = Cr, Mo)*The synthesis of the new P3Si3‐heterocyclohexanes 1b‐1e are reported. They are easily accessible by salt elimination reaction of the corresponding dichloro organosilanes with lithium cyclohexylphosphanide. Their NMR‐spectroscopic properties, structural features and reactivity toward [M(CO)3(NCMe)3] are compared to those of the previous described derivative 1a. The structure of 1b has been established by X‐ray crystallography, showing that the Si3P3six‐membered ring has a slightly distorted chair‐like conformation and the organo substituents at silicon and phosphorus are located in the equatorial positions. The phosphorus atoms are pyramidal surrounded [sum of bond angles 302.1 (P1), 304.8 (P2) and 303.1° (P3)] and the Si‐P distances are identical with those in 1a and in other silacyclophosphanes. The complexation of the triphosphane‐coronands 1b‐e with [M(CO)3(NCMe)3] (M = Cr, Mo) gives the desired triphos‐phane crown‐like complexes 2b‐e and 3e in 38–53% yield. The X‐ray crystal structures of the Cr complexes 2b and 2e exhibit that the organo groups at silicon, surprisingly, being axial oriented and the cyclohexyl groups being in equatorial positions, whereas in case of the Mo analogue of 2e, that is 3e, all organo substituents prefer equatorial sites. The different configuration of the free ligand 1b compared with that in the complex 2b and the different configuration of the ligand 1e in the complexes 2e and 3e is due to the steric congestion (bulky aryl and [M(CO)3] groups) in these molecules. The change of configurations can be achieved by phosphorus inversion during the complexation process; the ease of inversion is rationalized by a intrinsic low inversion barriere at phosphorus (10–20 kcal mol−1) in silacyclophosphanes. Another complex type has been observed for the previous reported unusual Cr complex 2a, in which one Si‐H bond ousts a phosphorus atom in the coordination to the Cr center. The different structures of the Cr complexes 2b‐d compared to the structure of 2a clearly proves that the formation of a Si, H, Cr three‐center two‐electron bond in 2a is determined by the second ortho‐methyl group at the aryl substituent (mesityl) and the tiny metal center (Cr).
Synthesis and Characterization of a Novel Cyclobutadiene‐octatetrayne Polymer
Authors: Altmann Markus , Enkelmann Volker , Bunz Uwe H. F. 
Published: July 2007

AbstractThe synthesis of 3a starting from compound 1 is described. Copper‐catalyzed oxidative coupling of 3b under Hay conditions gives the novel polymer 9 with octatetrayne‐cyclobutadiene units.