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Guy Bertrand

Publications and source records attributed to Guy Bertrand.

47 records · Page 3Linked to original sources
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.

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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.

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PubMed2002

Singlet diradicals: from transition states to crystalline compounds.

Singlet diradicals are usually not energy minima. As observed by femtosecond spectroscopy, they readily couple to form final sigma bonds. Substituent effects allow lifetimes to increase into the microsecond range. Taking advantage of the properties of hetero-elements, a diradical has been prepared that is indefinitely stable at room temperature. The availability of diradicals that can be handled under standard laboratory conditions will lead to further insight into their chemical and physical properties, raising the likelihood of practical applications, especially in the field of molecular materials such as electrical conductors and ferromagnets.

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PubMed2000

Stable Carbenes.

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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.

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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).

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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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