Zwitterionic Products Research Articles

Olefin–Borane “van der Waals Complexes”: Intermediates in Frustrated Lewis Pair Addition Reactions

The nature of the borane-olefin interactions that take place prior to frustrated Lewis pair addition reactions has been probed employing a Lewis acidic borane tethered to a vinyl group through an alkyl chain. (1)H{(19)F} HOESY spectral data obtained at -50 °C demonstrated the spatial proximity of the boryl and vinyl groups and computational data support the initial formation of a van der Waals borane-olefin complex. Such species serve as intermediates undergoing facile addition reactions with phosphine bases to afford cyclic zwitterionic products.

Synthesis and Reactivity of Alkynyl‐Linked Phosphonium Borates

The phosphine tBu(2 PC[triple bond]CH (1) was reacted with B(C(6)F(5)) to give the zwitterionic species tBu(2)P(H)C[triple bond]CB(C(6)F(5))(3) (2). The analogous species tBu(2)P(Me)C[triple bond]CB(C(6)F(5))(3) (3), tBu(2)P(H)C[triple bond]CB(Cl)(C(6)F(5))(2) (4), tBu(2)P(H)C[triple bond]CB(H)(C(6)F(5))(2) (5), and tBu(2)P(Me)C[triple bond]CB(H)(C(6)F(5))(2) (6) were also prepared. The salt [tBu(2)P(H)C[triple bond]CB(C(6)F(5))(2)(THF)][B(C(6)F(5))(4)] (7) was prepared through abstraction of hydride by [Ph(3)C][B(C(6)F(5))(4)]. Species 5 reacted with the imine tBuN=CHPh to give the borane-amine adduct tBu(2)PC[triple bond]CB[tBuN(H)CH(2)Ph](C(6)F(5))(2) (8). The related phosphine Mes(2)PC[triple bond]CH (9; Mes=C(6)H(2)Me(3)) was used to prepare [tBu(3)PH][Mes(2)PC[triple bond]CB(C(6)F(5))(3)] (10) and generate Mes(2)PC[triple bond]CB(C(6)F(5))(2). The adduct Mes(2)PC[triple bond]CB(NCMe)(C(6)F(5))(2) (11) was isolated. Reaction of Mes(2)PC[triple bond]CB(C(6)F(5))(2) with H(2) gave the zwitterionic product (C(6)F(5))(2)(H)BC(H)=C[P(H)Mes(2)][(C(6)F(5))(2)BC[triple bond]CP(H)Mes(2)] (12). Reaction of tBu(2)PC[triple bond]CB(C(6)F(5))(2), a phosphine-borane generated in situ from 5, with 1-hexene gave the species [tBu(2)PC[triple bond]CB(C(6)F(5))(2)](CH(2)CHnBu)[tBu(2)PC[triple bond]CB(C(6)F(5))(2)] (13) and subsequent reaction with methanol or hexene resulted in the formation of [tBu(2)P(H)C[triple bond]CB(C(6)F(5))(2)](CH(2)CHnBu)[tBu(2)PC[triple bond]CB(C(6)F(5))(2)](OMe) (14) or the macrocycle {[tBu(2)PC[triple bond]CB(C(6)F(5))(2)](CH(2)CH(2)nBu)}(2) (15), respectively. In a related fashion, the reaction of 13 with THF afforded the macrocycle [tBu(2)PC[triple bond]CB(C(6)F(5))(2)](CH(2)CHnBu)[tBu(2)PC[triple bond]CB(C(6)F(5))(2)][O(CH(2))(4)] (16), although treatment of tBu(2)PC[triple bond]CB(C(6)F(5))(2) with THF lead to the formation of {[tBu(2)[triple bond]CB(C(6)F(5))(2)][O(CH(2))(4)]}(2) (17). In a related example, the reaction of Mes(2)PC[triple bond]CB(C(6)F(5))(2) with PhC[triple bond]CH gave {[Mes(2)PC[triple bond]CB(C(6)F(5))(2)](CH[triple bond]CPh)}(2) (18). Compound 5 reacted with AlX(3) (X=Cl, Br) to give addition to the alkynyl unit, affording (C(6)F(5))(2)BC(H)=C[P(H)tBu(2)](AlX(3)) (X=Cl 19, Br 20). In a similar fashion, 5 reacted with [Zn(C(6)F(5))(2)]⋅C(7)H(8), [Al(C(6)F(5))(3)]⋅C(7)H(8), or HB(C(6)F(5))(2) to give (C(6)F(5))(3)BC(H)=C[P(H)tBu(2)][Zn(C(6)F(5))] (21), (C(6)F(5))(3)BC(H)=C[P(H)tBu(2)][Al(C(6)F(5))(2)] (22), or [(C(6)F(5))(2)B](2)HC=CH[P(H)tBu(2)] (23), respectively. The implications of this reactivity are discussed.

Compounds Featuring the Structural Fragment P-C-P

This article summarizes some of our investigations of compounds featuring the structural fragment P‒C‒P. Phosphorus atoms in different oxidation states and coordination numbers display different chemical behaviors. This may lead to unique chemical properties when they are bridged by a methylene group in a P‒CH2‒P system. For example, the PIII‒CH2‒PVunit is able to add different unsaturated compounds to give zwitterionic products with oppositely charged phosphorus atoms. In addition, the two hydrogen atoms in P‒CH2‒P may also take part in different transformations, resulting in the formation of carbodiphosphoranes or in the formation of a direct P-P bond to give three-membered ring diphosphiranes.

Alkene Addition of Frustrated P/B and N/B Lewis Pairs at the [3]Ferrocenophane Framework

o-Vinyl/α-NRR′-substituted [3]ferrocenophane derivatives (R = R′ = Me (8), R = H, R′ = tBu (11), R = R′ = H (13)) were prepared via a Wittig olefination route starting from the corresponding aldehyde. The NMe2 group was further exchanged for Pmes2 (9). The bulky α-substituents NHtBu and Pmes2 form frustrated Lewis pairs with B(C6F5)3 that undergo cooperative intramolecular addition reactions to the adjacent alkene. In the case of 13 stable Lewis pair adduct (14) formation is observed instead. The corresponding α-dimesitylphosphino[3]ferrocenophanyl-substituted butadiene (16) and acrolein (23) derivatives were synthesized via multistep synthetic pathways. Upon treatment with B(C6F5)3, intramolecular 1,4-addition of the frustrated Lewis pairs to the adjacent doubly unsaturated moieties takes place to yield the zwitterionic products 17 and 24, respectively. The complexes 9, 10, 12, 16, 17, 20, 22, and 23 were characterized by X-ray diffraction.

Phosphirenium-borate zwitterion: formation in the 1,1-carboboration reaction of phosphinylalkynes

Reaction of the acetylene Mes(2)P-C≡C-Ar with B(C(6)F(5))(3) at rt gives a zwitterionic phosphirenium product, which reacts further at >100 °C to complete the 1,1-carboboration reaction.

Ring-Opening Polymerization of rac-Lactide by Bis(phenolate)amine-Supported Samarium Borohydride Complexes: An Experimental and DFT Study

The synthesis and ring-opening polymerization (ROP) capability of bis(phenolate)amine-supported samarium borohydride and amide complexes are reported, together with a DFT study. Reaction of Na2O2NL (L = OMe, NMe2, py, or Pr) with Sm(BH4)3(THF)3 gave the borohydride complexes Sm(O2NL)(BH4)(THF) (L = OMe (2), NMe2 (3), or py (4)) or Sm(O2NPr)(BH4)(THF)2 (5). Compounds 4 and 5 lost THF in vacuo, forming phenolate O-bridged dimers 1 and 6, respectively. Reaction of H2O2NL with Sm{N(SiHMe2)2}3(THF)2 formed monomeric Sm(O2NL){N(SiHMe2)2}(THF) (L = OMe (7), NMe2 (8), or py (9)) with tetradentate O2NL ligands, but dimeric Sm2(μ-O2NPr)2(O2NPr)(THF) (10) with tridentate O2NPr. Reaction of Sm{N(SiMe3)2}3 with H2O2NL (L = OMe or NMe2) led to zwitterionic products Sm(O2NL)(HO2NL). The bulkier amide compounds Sm(O2NL){N(SiMe3)2}(OEt2)n (n = 1, L = OMe (12) or py (13); n = 0, L = NMe2 (14)) were prepared by reaction of Sm(O2NL)(BH4)(THF) with KN(SiMe3)2. The X-ray structures of 2, 5, 6, 7, 10, 13, and 14 were determined...

Remarkably variable reaction modes of frustrated Lewis pairs with non-conjugated terminal diacetylenes

The frustrated Lewis pair P(o-tolyl)(3)/B(C(6)F(5))(3) reacts with 1,7-octadiyne by acetylene C-C coupling to yield the zwitterionic product 2a. In contrast, the P(o-tolyl)(3)/B(C(6)F(5))(3) Lewis pair reacts with 1,6-heptadiyne by a sequence involving 1,1-carboboration of a terminal acetylene to eventually yield the heterocyclic product 4.

Facile Cyclometalation Reactions of Cp–Zirconium Complexes with Weakly Lewis Acidic Pendent Boron Functionalities

Methyl anion abstraction from group 4 metallocene dimethyl complexes by B ACHTUNGTRENNUNG(C6F5)3 or functionally related maingroup element Lewis acids (e.g. MAO) represents the most important activation pathway in homogeneous metallocene Ziegler–Natta olefin polymerization catalysis. It seemed tempting to search for intramolecular versions of this reaction. The simplest approach would be to attach a suitable Lewis acid functionality to the cyclopentadienyl (Cp) ring of a metallocene or related group 4 metal complex system by means of a saturated hydrocarbon tether. We and others have previously shown that such bifunctional systems are readily obtained by hydroboration of alkenyl-functionalized zirconocene dichlorides. The chemistry of related complexes with active s-hydrocarbyl ligands at the group 4 metal center proved to be more challenging. Typical previously reported examples include complexes 1 and 3 (see Scheme 1). The former turned out to be unstable with regard to “self attack” of the strongly electrophilic borane on the adjacent Cp ring. This electrophilic aromatic substitution sequence resulted in the clean formation of the stable zwitterionic product 2 with liberation of benzene. The bifunctional complex 3 was reported to react by a sequence of alkyl abstraction reactions to eventually form 4. These examples all contained the strongly electrophilic B ACHTUNGTRENNUNG(C6F5)2 group. We have now found that even systems featuring the much weaker 9-borabicycloACHTUNGTRENNUNG[3.3.1]nonane (9BBN) electrophile tethered to a Cp ring system show related reactivities. Herein we wish to describe some selected representative examples, mostly from the ZrCp3 series, that show how general such consecutive reactions take place at bifunctional alkyl group 4 metal complexes, even when a weakly Lewis acidic borane functionality is attached to a Cp ring by an oligomethylene tether. [Zr ACHTUNGTRENNUNG(allyl-Cp)ACHTUNGTRENNUNG(CH3)ACHTUNGTRENNUNG(Cp2)] (7) was synthesized along the pathway that we previously developed for the preparation of the parent [Zr ACHTUNGTRENNUNG(CH3)ACHTUNGTRENNUNG(Cp3)] complex. We have shown that it is advantageous to introduce the [Zr]-CH3 functionality at an early stage in the synthesis. Consequently, we treated the starting material [Zr ACHTUNGTRENNUNG(CH3)(Cl) ACHTUNGTRENNUNG(Cp2)] (5) with the K ACHTUNGTRENNUNG(allyl-Cp) reagent 6 (see Scheme 2). Workup of the reaction mixture from toluene eventually gave the functionalized tris(cyclopentadienyl)Zr product 7 in 55% yield. Complex 7 was characterized spectroscopically (H NMR in CD2Cl2: d=0.28/16.3 ( H/C; [Zr]-CH3), 5.64 (s, 10H; Cp), 5.25/5.66 (AA’BB’, 2H each; C5H4), 3.19 (CH2), 5.02/ 5.07 ppm (=CH2) and by X-ray crystal structure analysis (single crystals were obtained from a toluene/heptane mix[a] Dipl.-Chem. M. Emmert, Dr. G. Kehr, Dr. R. Frchlich, Prof. Dr. G. Erker Organisch-Chemisches Institut der Universit t M nster Corrensstr. 40, 48149 M nster (Germany) Fax: (+49)251-83-36503 E-mail : erker@uni-muenster.de [] This author was responsible for X-ray crystal structure analyses. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200900981, and contains experimental details and characterization of the compounds 7–18. CCDC721637 (10), -721638 (7), and -721639 (12) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Scheme 1.

Synthesis, spectra and crystal structures of zwitterionic mercury(II) complexes formed by the ligand, [Ph 2PCH 2PPh 2CH 2C(O)Ph] +

The reactions of phosphonium salt, [PPh 2CH 2PPh 2CH 2C(O)Ph]Br with Hg(II) halides in methanol formed the zwitterionic products with the composition [HgCl 2(Br)( PPh 2CH 2PPh 2CH 2C(O)Ph)] ( 2), [HgBr 3( PPh 2CH 2PPh 2CH 2C(O)Ph)] ( 3), [HgBr 2(I)( PPh 2CH 2PPh 2CH 2C(O)Ph)] ( 4). A product of composition, [HgCl 3( PPh 2CH 2PPh 2CH 2C(O)Ph)] ( 5) was obtained when the ylide, Ph 2PCH 2PPh 2 CHC(O)Ph was treated with HgCl 2 in CH 2Cl 2 and crystallized under aerobic conditions. The complexes were characterized by elemental analysis, IR, 1H, 31P NMR spectra and also by X-ray crystallography. The absence of significant coordination chemical shifts in the 31P NMR spectra indicates the presence of formal negative charge on mercury. The single crystal X-ray structures confirm the presence of Hg–P bond and also reveal a distorted tetrahedral geometry around the mercury atom in all the structures.

Reactions of phosphines with electron deficient boranes

A series of classical B(C(6)F(5))(3)-phosphine adducts are shown to be reactive molecules. Reaction of (THF)B(C(6)F(5))(3) with phosphines are shown to effect ring-opening of THF affording the zwitterionic phosphonium-borate species of the form R(2)PH(C(4)H(8)O)B(C(6)F(5))(3) and R(3)P(C(4)H(8)O)B(C(6)F(5))(3). Alternatively, treatment of (THF)B(C(6)F(5))(3) with a lithium phosphide (R(2)PLi, R = tBu, Ph Mes) affords species of the form [Li(THF)(x)][R(2)P(C(4)H(8)O)B(C(6)F(5))(3)]. Additionally, double THF ring-opening is also demonstrated to give species of the form [Li(THF)(x)][R(2)P(C(4)H(8)OB(C(6)F(5))(3))(2)]. In addition a series of classical borane-phosphine adducts are also shown to undergo thermal rearrangement reactions to give the zwitterionic products of aromatic substitution R(2)PH(C(6)F(4))BF(C(6)F(5))(2) and R(3)P(C(6)F(4))BF(C(6)F(5))(2). The mechanism of these substitutions is considered. A series of crystallographic studies of phosphine-borane adducts, THF ring-opened zwitterions and para-attack zwitterionic phosphonium borates are reported and discussed.

Synthesis of a new tricylic ring system: [1,2,3]triazolo[1,5-b]cinnolinium salt

Synthesis of the first representative of the linearly fused [1,2,3]triazolo[1,5-b]cinnolinium heteroaromatic cation as a quaternary salt is reported. Improved reaction conditions for preparation of some precursors have been elaborated. Reaction of the new heteroaromatic salt with nucleophiles resulted in regioselective formation of zwitterionic products.

Synthesis of Novel Biomimetic Zwitterionic Phosphorylcholine‐Bound Chitosan Derivative

AbstractSummary: Water‐soluble biomimetic chitosan derivative conjugating zwitterionic phosphorylcholine was efficiently prepared through Atherton‐Todd reaction under the mild conditions, and the possible formation mechanism of zwitterionic product was related to the nucleophilic attack of adjacent 3‐hydroxyl on the D‐glucosamine residue to phosphorus with the help of base. UV absorption and melting behaviors of DNA/phosphorylcholine‐bound chitosan derivative showed that the phosphorylcholine‐bound chitosan derivative could be a new carrier for long‐circulating macromolecular drug delivery.Structure of zwitterionic PC‐chitosan.magnified imageStructure of zwitterionic PC‐chitosan.

Synthesis of New Stable Crystalline Zwitterionic Products from the Reactions of 1‐Methylimidazole, Acetylenic Esters and Strong Cyclic CH‐Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

On the Reaction of Ph2PNHPPh2 with RNCS (R=Et, Ph, p‐NO2C6H4): Preparation of the Zwitterionic Ligand EtNHC(S)Ph2PNPPh2C(S)NEt (HSNS) and the Zwitterionic Metalate [(SNS)Rh(CO)

The reaction of Ph(2)PNHPPh(2) (PNP) with RNCS (Et, Ph, p-NO(2)(C(6)H(4))) gives addition products resulting from the attack of the P atoms of PNP on the electrophilic carbon atom of the isothiocyanate. When PNP is reacted with EtNCS in a 1:2 molar ratio, the zwitterionic molecule EtNHC(S)PPh(2)==NP(+)Ph(2)C(S)N(-)Et (HSNS) is obtained in high yield. HSNS can be protonated (H(2)SNS(+)) or deprotonated (SNS(-)), behaving in the latter form as an S,N,S-donor pincer ligand. The reaction of HSNS with [(acac)Rh(CO)(2)] (acac=acetylacetonate) affords the zwitterionic metalate [(SNS)Rh(CO)]. Other products can be obtained depending on the R group, the PNP/RNCS ratio (1:1 or 1:2), and the reaction temperature. The proposed product of the primary attack of PNP on RNCS, Ph(2)PN==PPh(2)C(S)NHR (A), cannot be isolated. Reaction of A with another RNCS molecule leads to 1:2 addition compounds of the general formula RNHC(S)PPh(2)==NP(+)Ph(2)C(S)N(-)R (1), which can rearrange into the non-zwitterionic product RNHC(S)PPh(2)==NP(S)Ph(2) (2) by eliminating a molecule of RNC. Two molecules of A can react together, yielding 1:1 PNP/RNCS zwitterionic products of the formula RNHCH[PPh(2)==NP(S)Ph(2)]PPh(2)==NP(+)Ph(2)C(S)N(-)R (3). Compound 3 can then rearrange into RNHCH[PPh(2)==NP(S)Ph(2)](2) (4) by losing a RNC molecule. When R=Et (a), compounds 1 a, 2 a (HSNS), and 4 a have been isolated and characterized. When R=Ph (b), compounds 2 b and 4 b can be prepared in high yield. When R=p-NO(2)C(6)H(4) (c), only compound 3 c is observed and isolated in high yield. The crystal structures of HSNS, [(SNS)Rh(CO)], and of the most representative products have been determined by X-ray diffraction methods.

Synthesis of new stable crystalline zwitterionic products from the reactions of 1-methylimidazole, acetylenic esters and strong cyclic CH-acids

The reactive 1:1 intermediate produced in the reaction between 1-methyl imidazole and dialkyl acetylenedicarboxylates was trapped by strong cyclic CH-acids such as N,N′-dimethylbarbituric acid, Meldrum's acid, cyclohexan-1, 3-dione, indan-1,3-dione, cyclopentan-1,3-dione and tetronic acid to yield stable 1,4-diionic imidazolium betaines in excellent yields.

Some Unusual Reactions in Organophosphorus Chemistry

AbstractFor Abstract see ChemInform Abstract in Full Text.

A New Crystalline Zwitterionic Product from the Reaction of Bu3P and DMAD

AbstractTributylphosphane reacts with DMAD to give the crystalline adduct 2 which is stabilised by extensive delocalisation and whose formation involves an unusual rearrangement. The isomeric structure 7 for the previously reported adduct with triphenylphosphane is supported by 13C NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

A Novel Concept for Combinatorial Chemistry in Solution: Synthesis of Highly Substituted Pyrrolidines by Multicomponent Domino Reactions

AbstractThe multicomponent domino Knoevenagel hetero‐DielsAlder hydrogenation process of N‐[(benzyloxy)carbonyl(Cbz)‐protected amino aldehydes with N,N‐dimethylbarbituric acid and the trimethylsilyl enol ethers 1–3 leads to the formation of the substituted pyrrolidines 12–15. Under the same conditions, reaction of the trimethylsilyl enol ether 4, obtained from acetophenone, gave the primary amines 18a,b probably due to a hydrogenolytic cleavage of the intermediately formed pyrrolidines. The zwitterionic products were obtained in high purity simply by precipitation with Et2O.

Alkylderivatives of Stanna- closo-dodecaborate

The reactions of [SnB 11H 11] 2− with organic halides like 1-chloro-3-iodopropane, allylbromide, propargylbromide and 2,6-bis-(bromomethyl)pyridine lead in a nucleophilic substitution at room temperature to the products [Bu 3MeN][Cl(CH 2) 3SnB 11H 11] ( 4), [Bu 3MeN][H 2CCHCH 2SnB 11H 11] ( 6), [Bu 4N][HCCCH 2SnB 11H 11] ( 7), and [Bu 4N] 2[2,6-(H 11B 11SnCH 2) 2(C 5H 3N)] ( 8). In water Na 2[SnB 11H 11] reacts with 2-bromoethylamine hydrobromide at 50 °C and 3-bromopropylamine hydrobromide at 70 °C to the zwitterionic products [H 11B 11Sn(CH 2) n NH 3] ( n=2, 3), which were characterized by X-ray crystal structure analysis. [H 11B 11Sn(CH 2) 2NH 3] crystallizes with one equivalent of water under the formation of NHO hydrogen bonding. In the case of chloroiodomethane and diiodomethane the substitution reaction proceeds differently and the monosubstituted components were not detected. The disubstituted compound [Bu 3MeN] 2[H 2C(SnB 11H 11) 2] ( 5), whose structure could be confirmed by X-ray crystal structure analysis, is the only observed reaction product.

Some Unusual Reactions in Organophosphorus Chemistry

Methylenephosphinophosphorane 1 reacts with azides without evolution of nitrogen to give zwitterionic phosphorazide 3 and iminophosphorazide 4 , which are in equilibrium to each other; 1 reacts with hexafluoroacetone (HFA) in a different way to give zwitterionic product 5 , which may have the ylidic structure 5' . HFA and thio-HFA react analogously with methylenediphosphines 6 to give corbodiphosphoranes 7 . Reaction of 6 with activated alkenes 9 gives monoylide 10 , which is a useful synthone for the synthesis of fluorosubstituted conjugated triene 12 and diylides 13 and 14 . Reaction of 10 with TOB gives unusually stable betaine 15 . Reaction of the other activated alkene 16 with 6 unexpectedly gave the unusual zwitterionic compound 17 .