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Antoine Baceiredo

Publications and source records attributed to Antoine Baceiredo.

18 recordsLinked to original sources
PubMed2007

Theoretical study on the mechanism of the [2+1] thermal cycloaddition between alkenes and stable singlet (phosphino)(silyl)carbenes.

The mechanism and the origins of the stereocontrol observed in the reaction between differently substituted alkenes and stable (phosphino)(silyl)carbenes giving cyclopropanes have been studied computationally. These cyclopropanation reactions proceed via asynchronous concerted mechanisms involving early transition structures with a significant charge transfer from the carbene to the alkene moiety. The geometric features of these transition structures preclude a significant overlap between the orbitals required for secondary orbital interactions between the reactants. The stereoselectivity observed experimentally stems from favorable electrostatic and steric interactions between the reactants leading to the stereoisomers in which the phosphanyl and carbonyl or aryl groups are cis to each other.

Alkenes↗
PubMed2006

Synthesis of extended polyphosphacumulenes.

Addition of two equivalents of (Me(3)Si)(2)CLiCl to the C-[(diphenyl) (diisopropylamino)phosphonio]-P-(diisopropylamino)phosphaalkene 2 affords the 1sigma(4),3sigma(3)-diphosphabuta-1,2,3-triene E1 in 55 % yield. Derivative E1 was fully characterized, including a single-crystal X-ray diffraction study. Alkylation of E1 with methyl trifluoromethanesulfonate gives rise to the first C-phosphonio-bis(methylene)phosphorane 5, which was isolated in 84 % yield. Because the second carbon center is also nucleophilic, cumulene E1 reacts as a "pincer" with BF(3)OEt(2), leading to the formation of a novel four-membered PCBC heterocycle 6 with a betaine-like structure. Addition of three equivalents of P-[diphenyl(diisopropylamino)]methylene phosphorane to (diisopropylamino)dichlorophosphane, followed by addition of one equivalent of CCl(4), and subsequent deprotonation with lithium hexamethyldisilazide gave rise to 1sigma(4),3sigma(3),5sigma(4)-triphosphapenta-1,2,3,4-tetraene F1, which was isolated in 62 % yield.

Journal Article↗
PubMed2006

Reaction of C-silylated alpha-diazophosphines as nucleophiles toward carbonyl compounds: a mechanistic study and application to the synthesis of alkynes and alpha-hydroxyphosphonamides.

Diversely substituted alpha-hydroxyphosphonamides and alkynes have been efficiently synthesized through the reaction of C-silylated alpha-diazophosphines with different types of aldehydes (2 equiv) in a neutral medium under very mild conditions. The reaction with some chiral aldehydes is highly diastereoselective leading to phosphonamides as single diastereomers. The novel reaction is influenced by electronic and steric effects being precluded for aromatic aldehydes containing electron-releasing substituents on the phenyl ring and for bulky aliphatic aldehydes. The mechanistic studies of these processes, which are highly exothermic, provide evidence for a nucleophilic attack of the diazophosphine to the aldehyde leading to a betaine that rapidly rearranges to a diazomethylenephosphorane, which has been detected or captured in some instances. The diazomethylenephosphorane reacts with a second molecule of aldehyde according to a Wittig-type condensation, and the rate-determining step of the whole process is believed to be the decomposition of the resultant oxaphosphetane to afford the hydroxyphosphonamide and a diazocumulene. Finally, this intermediate loses molecular nitrogen giving a transient carbene that rapidly evolves toward the alkyne.

Journal Article↗
PubMed2005

Theoretical and experimental investigation of the basicity of phosphino(silyl)carbenes.

[reaction: see text] The reactivity of phosphino(trimethylsilyl)carbenes 1 with several organic acids has been examined in order to evaluate the pKa values of the conjugate acids. Carbenes 1 react efficiently with C-organic acids such as 1,3-dimesitylimidazolium chloride, phenylacetylene, acetonitrile, and acetyltrimethylsilane, which have pKa's in DMSO in the range 18-31. However, the reaction of the conjugate acids 1H+ with the anion perturbs the determination of the genuine basicity of 1. Theoretical calculations have been performed in order to quantify the basicity of phosphino(trimethylsilyl)carbenes 1 and to compare them with that of N-heterocyclic carbenes 2. The pKa of 1H+ in DMSO has been computed to be in the 23.0-23.4 range, so that 1 is not strong enough as a base to spontaneously deprotonate organic acids such as phenylacetylene, acetonitrile, or acetyltrimethylsilane. However, its conjugate acid 1H+ is a strong electrophile and easily reacts with the nucleophilic conjugate bases of these acids leading to the formation of the corresponding phosphorus ylides.

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PubMed2004

Stable optically pure phosphino(silyl)carbenes: reagents for highly enantioselective cyclopropanation reactions.

The stability of phosphino(trimethylsilyl)carbenes bearing cyclic diamino substituents on phosphorus is strongly dependent on the steric hindrance of the nitrogen substituents. Phosphinocarbenes 3 and 7, derived from the trans-N,N'-diisopropylcyclohexane-1,2-diamine and N,N'-diisopropyl-1,2-ethanediamine, are not observed; instead the 1,3-diphosphete 4 and a novel six-membered heterocycle 8, which results from the dimerization of 3 and the reaction of 7 with its diazo precursor 6, respectively, have been isolated. In contrast, the phosphino(silyl)carbene 14 derived from N,N'-di-tert-butyl-1,2-ethanediamine has been isolated in high yield. By using the enantiomerically pure (S,S)-, and (R,R)-N,N'-di-tert-butyl-1,2-diphenyl-1,2-ethanediamines, the first optically pure phosphino(sily)carbenes (S,S)-17 and (R,R)-17 have been prepared. They react with methyl acrylate to give the corresponding cyclopropanes (S,S,R,R)-19 and (R,R,S,S)-19 with a total syn diastereoselectivity and an excellent enantioselectivity (de>98 %).

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PubMed2003

Stereoselective synthesis of phosphoranyl aryloxiranes through the addition of a nucleophilic stable carbene to aromatic aldehydes.

The [2+1] addition of the stable (phosphanyl)(silyl)carbene 1 to aromatic aldehydes affords phosphoranyl aryloxiranes, a new class of polyfunctional epoxides, in high yields and excellent diastereoselectivity. No reaction is observed for aldehydes bearing strongly electron-donating groups. Theoretical calculations show a good correlation between Gibbs activation energy and the electronic nature of the substituent on the phenyl ring.

Journal Article↗
PubMed2003

Synthesis of carbenes through substitution reactions at a carbene center.

An (amino)(phosphino) carbene can be transformed into (amino)(phosphonio) carbenes, which undergo nucleophilic intermolecular as well as intramolecular substitution reactions at the carbene center. A variety of carbenes can be synthesized starting from a single carbene precursor. The resulting gamut of electronic and steric effects possible should open the way not only to a detailed study of the mechanism, but also to the subsequent improvement of catalytic reactions that involve carbene-transition metal complexes.

Journal Article↗
PubMed2002

A rare example of a rearrangement involving four structural isomers: alpha-phosphinonitrile/C-phosphinoketenimine/1-aza-4- phosphabutadiene/1,2-dihydro-1,2-azaphosphete.

The stable compound [bis(dicyclohexylamino)phosphino](trimethylsilyl)-carbene (1) reacts with dimethyl cyanamide to afford the original 1,2-dihydro-1,2-azaphosphete 4a (51% yield). The surprising formation of this heterocycle involves the transient formation of a nitrile, a keteneimine, and a 1-aza-4 lambda 3-phosphabutadiene derivative. By using substituent effects and different synthetic routes, all of these structural isomers have been isolated.

Journal Article↗
PubMed2002

Stable (amino)(phosphino)carbenes: difunctional molecules.

(Amino)(phosphino)carbenes are stable due to the donation of the nitrogen lone pair, the phosphino group remains strongly pyramidalized. Reactions can be performed selectively at the carbene center, but also at the phosphorus center leading to new stable carbenes. These difunctional molecules can be considered as hybrid ligands.

Journal Article↗
PubMed2002

Synthesis and rearrangement of diphosphorus analogues of amidinium salts.

Transient diphosphinocarbocations IIP are generated either by addition of phosphenium salts to the stable [bis(diisopropylamino)phosphino](silyl)carbene or by chloride abstraction from C-phosphino-P-chloro phosphorus ylides. In contrast to their nitrogen anlogues (amidinium salts) IIN, which feature a planar 3-center-4p-electron system, calculations show that IIP should exist as IIPb, in which one phosphorus is planar, while the other remains pyramidal. With small substituents at phosphorus, derivatives of type IIP rearrange by a 1,3-shift of a phosphorus substituent to the other phosphorus center to give C-phosphoniophosphaalkenes. When bulky substituents are present at phosphorus, derivatives IIP undergo ring closure, giving rise to the corresponding cyclic valence isomers IIIP, in which the carbon atom bears a negative charge. Diphosphinocarbocations IIP can be trapped by acetonitrile giving regioselectively the corresponding [2+3] cycloadduct.

Journal Article↗
PubMed1997

N-Phosphino- and N-Phosphonionitrilimines: From Nucleophilic to Electrophilic 1,3-Dipoles.

N-[Bis(diisopropylamino)phosphino]-C-[bis(diisopropylamino)thioxophosphoranyl]nitrilimine (1) reacts with electron-poor dipolarophiles such as maleimide, methyl vinyl ketone, and 1,4-naphthoquinone via HOMO(dipole)-controlled [2+3] cycloadditions, while N-[bis(diisopropylamino)(methyl)phosphonio]-C-[bis(diisopropylamino)thioxophosphoranyl]nitrilimine (2a) reacts with electron-rich dipolarophiles such as norbornadiene and ethyl trans-pyrrolineacrylate via LUMO(dipole)-controlled [2+3] cycloadditions. Carbon disulfide reacts with 1 via a formal [4+2] cycloaddition leading to phosphazene containing heterocycle 11 in 75% yield. Dipole 1 is cleaved by HCl, giving the corresponding (thioxophosphoranyl)diazomethane 15, while addition of HCl to 2a leads to hydrazonoyl chloride 16, in 70% isolated yield. Hydrazone 17' (95%) and phosphazine 18(80%) are obtained by a 1,3-addition of BuLi to 1 and PhOLi to 2a, respectively. Trimethylphosphine reacts with 2a by a phosphine-carbene coupling reaction, giving the ylide 20 which is isolated in 75% yield.

Journal Article↗
PubMed1996

X-ray Crystal Structure, ab Initio Calculations, and Reactivity of 1,3,2lambda(5)-Diazaphosphetes: A New Type of 4-pi-Electron 4-Membered Heterocycle.

The structure of P,P-bis(diisopropylamino)-4-phenyl-1,3,2lambda(5)-diazaphosphete, 1a, has been determined by a single-crystal X-ray diffraction study (C(19)H(33)N(4)P, monoclinic system, space group P2(1), a = 9.482(1) Å, b = 11.374(3) Å, c = 9.668(2) Å, beta = 97.16(1) degrees, Z = 2). According to quantum chemical calculations at an RHF level of optimization utilizing the 6-31g(d,p) basis set, 1a has a zwitterionic structure with the negative charge delocalized on the NCN allylic fragment and the positive charge localized at the phosphorus. Heterocycle 1a reacts with water and benzaldehyde affording N-phosphoranylbenzamidine 3 (95% yield) and the expected aza-Wittig adduct 4 (85% yield), respectively. Addition of 1 equiv of methyl trifluoromethanesulfonate and of 2 equiv of BH(3).THF to 1a affords cyclic phosphonium salt 5 (94% yield) and the bis(borane) adduct 6a (90% yield), respectively. Dimethyl acetylenedicarboxylate slowly reacts with 1a giving rise to 1,3,4lambda(5)-diazaphosphinine, 9, in 70% yield. The X-ray crystal structures of products 2,3, and 6a are reported (2: C(26)H(38)N(5)P, monoclinic system, space group C2/c, a = 16.337(8) Å, b = 19.810(2) Å, c = 8.800(2) Å, beta = 117.68(2) degrees, Z = 4. 3: C(19)H(35)N(4)OP, orthorhombic system, space group P2(1)2(1)2(1), a = 9.090(1) Å, b = 12.955(2) Å, c = 17.860(3) Å, Z = 4. 6a: C(19)H(39)B(2)N(4)P, orthorhombic system, space group P2(1)2(1)2(1), a = 10.340(1) Å, b = 13.247(1) Å, c = 16.996(1) Å, Z = 4).

Journal Article↗
PubMed1996

Synthesis of Stable Multifunctional C-Phosphonio Phosphorus Vinyl Ylides.

Trifluoromethanesulfonic acid reacts at 240 K with bis[bis(diisopropylamino)phosphino]diazomethane, 1, affording the corresponding cationic (phosphino)(P-hydrogenophosphonio)diazomethane derivative 2, which eliminates dinitrogen above 250 K, leading to (phosphino)(phosphonio)carbene 3 isolated in 76% yield (mp 88 degrees C). Bis(diisopropylamino)phosphenium salt 5a adds at 240 K to P-chlorodiazomethylenephosphorane 4 giving (phosphino)(P-chlorophosphonio)diazo derivative 6a, which leads, after N(2) elimination, to the corresponding carbene 7a. Addition of potassium tert-butoxide to 3 gives rise to the transient diphosphinocarbene 8, which rearranges into phosphaalkene 9. Sodium tetrafluoroborate, tert-butyllithium, and tributyltin hydride react with 3 to afford P-fluoro-P'-hydrogenocarbodiphosphorane 10, P,P'-dihydrogenocarbodiphosphorane 12, and stannyl-substituted methylene salt 15, respectively. tert-Butyl isocyanide reacts with phosphoniocarbene 3 giving heterocycle 19, whereas with carbene 7 phosphonioketeneimine 18 and bis(diisopropylamino)phosphinonitrile are obtained.

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