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Pierre Braunstein

Publications and source records attributed to Pierre Braunstein.

At least 37 records · Page 2Linked to original sources
PubMed2004

Stepwise synthesis, structures, and reactivity of mono-, di-, and trimetallic metal complexes with a 6pi + 6pi quinonoid zwitterion.

The benzoquinonemonoimine N,N'-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C(6)H(2)(NHCH(2)t-Bu)(2)(O)(2)] 6, which is a rare example of an organic zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6pi electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the pi-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N-H function, and the isolated sodium salt 9, which is stable under N(2), reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh(3))] or trans-[NiCl(Ph)(PPh(3))(2)], to afford the monometallic complexes 10-15 in which the pi-system is localized. A second in situ deprotonation of the remaining N-H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(mu-Cl)](2) (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in which the pi-system of the quinonoid ligand is delocalized between the two metal centers. Deprotonation of both N-H amino functions of the square-planar complex trans-[Ni(N,O)(2)] 15 with NaH and reaction with [Pd(8-mq)(mu-Cl)](2) affords the heterotrimetallic (Pd, Ni, Pd) complex 18 in which the pi-system of the two quinonoid ligands is delocalized between the three metal centers. The crystal structures of the monometallic complexes 10 and 13 and of the dipalladium complex 17 are reported and consequences of metal coordination discussed. Complex 15 was tested in catalytic ethylene oligomerization with AlEtCl(2) as cocatalyst.

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PubMed2004

Toward a 6pi+6pi zwitterion or a bioinhibitors-related OH-substituted aminoquinone: identification of a key intermediate in their pH controlled synthesis.

Their pH-controlled reactivity places the N,N'-dialkyl-2-amino-5-lithium alcoholate-1,4-benzoquinonemonoimines [C(6)H(2)(NHCH(2)R') (=NCH(2)R')(=O)(OLi)] 7 (R'=tBu) and 8 (R'=p-C(6)H(4)-tBu) at the crossroads of a new versatile strategy for the preparation of two very different classes of substituted quinones. We describe new 2-(N-alkyl)amino-5-hydroxy-1,4-benzoquinones, which are parent molecules to biologically active substituted aminobenzoquinones, for which changes of the N-substituent will become readily possible. The results of the first X-ray structural determination of such compounds ([C(6)H(2)(NHCH(2)tBu)(OH)(=O)(2)] 13) are also reported and we compare the influence of the number of N-substituents of the C(6) ring on the supramolecular networks resulting from self-assembling of 13, zwitterionic N,N'-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C(6)H(2)(=NHCH(2)tBu)(2)(=O)(2)] 9 and N,N',N",N"'-tetraneopentyl-2,5-diamino-1,4-benzoquinone diimine [C(6)H(2)(NHCH(2)tBu)(2)(=NCH(2)tBu)(2)] 15.

Benzoquinones↗
PubMed2004

Stable, chloride-induced monohapto-bonding mode for an allyl ligand in a Pd(II) complex bearing a new bidentate phosphonite-oxazoline ligand.

Bidentate ligands can lead to stable eta(1)-allyl complexes of Pd(II). A novel chelating phosphonite-oxazoline P,N ligand, abbreviated NOPO(Me2), has been prepared by reaction of 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin with the lithium alcoholate derived from 4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydrooxazole. Its reaction with [Pd(eta(3)-C(3)H(5))(micro-Cl)](2) afforded the new eta(1)-allyl Pd complex [PdCl(eta(1)-C(3)H(5))(NOPO(Me2))] 2 in 91% yield. This constitutes a still rare example of structurally characterized eta(1)-allyl Pd(II) complex. Chloride abstraction led to the corresponding cationic eta(3)-allyl complex [Pd(eta(3)-C(3)H(5))(NOPO(Me2))]PF(6) 3, which has also been characterized by X-ray diffraction. CO insertion into the Pd-C sigma-bond of the eta(1)-allyl ligand of 2 afforded the corresponding 3-butenoyl palladium complex [PdCl[C(O)C(3)H(5)](NOPO(Me2))] 4 under mild conditions, which supports the view that CO insertion into eta(3)-allyl palladium cationic complexes occurs via first coordination of the counterion to form a more reactive eta(1)-allyl intermediate.

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PubMed2004

Dinuclear nickel complexes with bidentate N,O ligands: synthesis, structure, and catalytic oligomerization of ethylene.

The new dicationic dinuclear complexes [Ni(micro-Cl)(2)(N,OH)(2)]Cl(2) (11, N,OH = 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-propan-2-ol; 12, N,OH = 2-pyridin-2-yl-propan-2-ol) were prepared in good yields and evaluated as precatalyts in the oligomerization of ethylene, using MAO or AlEtCl(2) as cocatalyst. These paramagnetic complexes were characterized by single-crystal X-ray diffraction in the solid state and in solution with the help of the Evans method, which revealed agreement between the octahedral coordination spheres found in solution and in the solid state. The N donor atoms of each chelating ligand are in mutual cis position, and the OH donors are mutually trans situated. Selectivities for 1-butene within the C(4) fraction of 61% (11) and 58% (12) were observed in the presence of 200 equiv of MAO, but better turnover frequencies (28 300 (11) and 20 400 (12) mol of C(2)H(4)/(mol of Ni.h)) were obtained when 800 equiv of MAO was used. In the presence of 6 equiv of AlEtCl(2), the activities were considerably increased, up to 174 300 (11) and 97 100 (12) mol of C(2)H(4)/(mol of Ni.h), and the selectivity for C(4) olefins was 70% and 64%, respectively.

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PubMed2004

Nickel and iron complexes with oxazoline- or pyridine-phosphonite ligands; synthesis, structure and application for the catalytic oligomerisation of ethylene.

The bis(oxazolinyl)phenylphosphonite ligand (bis(4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydrooxazole)phenylphosphonite, NOPONMe2)) and the new pyridine-phosphonite ligand (2-ethyl(1'-methyl-1-hydroxy)pyridine-6H-dibenz[c,e][1,2]oxaphosphorin) have been used for the preparation of the mononuclear complexes [NiCl2(NOPONMe2)] 18 and [NiCl2(6)2] 19, respectively, which catalyze the oligomerisation of ethylene with activities up to 57300 mol C2H4 mol Ni(-1) h(-1) (19 in the presence of only 6 equivalents of AlEtCl2). The selectivities for C4 dimers were as high as 90% (18 in the presence of only 2 equivalents of AlEtCl2) with selectivities for 1-butene of 21-22% of the C4 fraction. In the presence of 400 or 800 equivalents of MAO as cocatalyst, complex 19 yielded turnover frequencies of 7400 mol C2H4 mol Ni(-1) h(-1) and 13200 mol C2H4 mol Ni(-1) h(-1), respectively. The selectivities for 1-butene and ethylene dimers were similar to those obtained with AlEtCl2. The fact that 19 with a cyclic phosphonite moiety leads to higher activities and selectivities than 18 which contains an acyclic phosphonite group underlines the importance of the ligand on the catalytic properties of its metal complex. An unprecedented dinuclear iron complex [FeCl2(4,4-dimethyl-2-[(1-hydroxy-1-methyl)ethyl]-4,5-dihydrooxazolate)]2 20 was also obtained which contains two pentacoordinated metal centers coordinated by a bridging-chelating oxazoline-alcoholate. Complexes 18-20 are paramagnetic in solution, as determined by the Evans method.

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PubMed2004

Nickel complexes with new bidentate P,N phosphinitooxazoline and -pyridine ligands: application for the catalytic oligomerization of ethylene.

The phosphinitooxazoline 4,4-dimethyl-2-[1-oxy(diphenylphosphine)-1-methylethyl]-4,5-dihydrooxazole (9), the corresponding phosphinitopyridine ligands 2-ethyl-[1'-methyl-1'-oxy(diphenylphosphino)]pyridine (11) and 2-ethyl-6-methyl-[1'-methyl-1'-oxy(diphenylphosphino)]pyridine (12), which have a one-carbon spacer between the phosphinite oxygen and the heterocycle, and the homologous ligand 2-propyl-[2'-methyl-2'-oxy(diphenylphosphino)]pyridine (13), with a two-carbon spacer, were prepared in good yields. The corresponding mononuclear [NiCl(2)(P,N)] complexes 14 (P,N = 9), 15 (P,N = 11), and 16 (P,N = 12) and the dinuclear [NiCl(micro-Cl)(P,N)](2) 17 (P,N = 13) Ni(II) complex were evaluated in the catalytic oligomerization of ethylene. These four complexes were characterized by single-crystal X-ray diffraction in the solid state and in solution with the help of the Evans method, which indicated differences between the coordination spheres in the solution and the solid state. In the presence of methylalumoxane (MAO) or AlEt(3), only the decomposition of the Ni complexes was observed. However, complexes 14-17 provided activities up to 50000 mol C(2)H(4)/(mol Ni).h (16 and 17) in the presence of only 6 equiv of AlEtCl(2). The observed selectivities for ethylene dimers were higher than 91% (for 14 or 15 in the presence of only 1.3 equiv of AlEtCl(2)). The activities for 14-17 were superior to that of [NiCl(2)(PCy(3))(2)], a typical dimerization catalyst taken as a reference. The selectivities of the complexes 14-17 for ethylene dimers and alpha-olefins were the same order of magnitude. From the study of the phosphinite 9/AlEtCl(2) system, we concluded that in our case ligand transfer from the nickel atom to the aluminum cocatalyst is unlikely to represent an activation mechanism.

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PubMed2004

Reactions of the tetrahedral clusters [MCo(3)(CO)(12)](-) (M = Ru, Fe) with functional mono- and diynes.

The tetrahedral cluster [RuCo(3)(CO)(12)](-) reacts with various alkynes, including the new PhCtbd1;CC(O)NHCH(2)Ctbd1;CH (L(1)()), to afford the butterfly clusters [RuCo(3)(CO)(10)(micro(4)-eta(2)-RC(2)R')](-) (1, R = R' = C(O)OMe; 2, R = H, R' = Ph; 3, R = H, R' = MeC=CH(2); 4, R = H, R' = CH(2)OCH(2)Ctbd1;CH; 5, R = H, R' = CH(2)NHC(O)Ctbd1;CPh), in which the ruthenium atom occupies a hinge position and the alkyne is coordinated in a micro(4)-eta(2) fashion. Reaction of the anions 1-3 with [Cu(NCMe)(4)]BF(4) led to selective loss of the 12e fragment Co(CO)(-) to form [RuCo(2)(CO)(9)(micro(3)-eta(2)-RC(2)R')] (6, R = R' = C(O)OMe; 7, R = H, R' = Ph; 8, R = H, R' = MeC=CH(2)). To prepare functionalized RuCo(3) or FeCo(3) clusters that could be subsequently condensed with a silica matrix via the sol-gel method, we reacted [MCo(3)(CO)(12)](-) (M = Ru, Fe) with the alkyne PhCtbd1;CC(O)NH(CH(2))(3)Si(OMe)(3)(L(2)()) and obtained the butterfly clusters [MCo(3)(CO)(10)(micro(4)-eta(2)-PhC(2)C(O)NH(CH(2))(3)Si(OMe)(3))](-) 9 and 10, respectively. Air-stable [RuCo(3)(CO)(10)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))](-) (11) was obtained from 1,4-bis(trimethylsilyl)butadiyne and reacted with [Cu(NCMe)(4)]BF(4) to give [RuCo(2)(CO)(9)(micro(3)-eta(2)-HC(2)Ctbd1;CSiMe(3))] (12), owing to partial ligand proto-desilylation, and not the expected [RuCo(2)(CO)(9)(micro(3)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))]. Reaction of 11 with [NO]BF(4) afforded, in addition to 12, [RuCo(3)(CO)(9)(NO)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))] (13) owing to selective CO substitution on a wing-tip cobalt atom with NO. The thermal reaction of 11 with [AuCl(PPh(3))] led to replacement of a CO on Ru by the PPh(3) originating from [AuCl(PPh(3))] and afforded [RuCo(3)(CO)(9)(PPh(3))(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))](-) (14), also obtained directly by reaction of 11 with one equivalent of PPh(3). Proto-desilylation of 11 using TBAF/THF-H(2)O afforded [RuCo(3)(CO)(10)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CH)](-) (15) which, by Sonogashira coupling with 1,4-diiodobenzene, yielded the dicluster complex [[RuCo(3)(CO)(10)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;C)]](2)C(6)H(4)](2)(-) (16). The crystal structures of NEt(4).3a, NEt(4).4a, 6, NEt(4).11b, NEt(4).14, and [N(n-Bu)(4)].15a have been determined by X-ray diffraction. Preliminary results indicate the potential of silica-tethered alkyne mixed-metal clusters, obtained by the sol-gel method, as precursors to bimetallic particles.

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PubMed2004

Acid-base sensors based on novel quinone-type dyes.

We present a detailed study on the acid-base behaviour of a family of "potentially antiaromatic" p-benzoquinonediimine ligands. These 12pi electron molecules can be considered as constituted of two chemically connected but electronically not conjugated 6pi-electron subunits. Upon successive protonation, "mono" and "double" cyanine-type chromophores are generated in solution and allow a precise and sensitive spectrophotometric detection. These molecules represent a new class of tunable quinones whose electronic and structural properties can be triggered by proton input, as established by a complete physico-chemical study involving a combination of potentiometric and spectrophotometric methods (absorption and emission).

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PubMed2003

Enolphosphato-phosphines: a new class of P,O ligands.

The new bifunctional ligands Ph(2)PCH[double bond]CPh[OP(O)(OR)(2)] (1) (1a, R = Et; 1b, R = Ph) represent the first examples of P,O derivatives resulting from the association of a phosphine moiety and an enolphosphate group. The Z stereochemistry about the double bond provides a favorable situation for these ligands to act as P,O-chelates. Neutral and cationic Pd(II) complexes have been synthesized and characterized, in which 1a or 1b acts either as a P-monodentate ligand or a P,O-chelate, via coordination of the oxygen atom of the P[double bond]O group. In the latter case, it has been observed that phosphines 1a and 1b can display a hemilabile behavior, owing to successive dissociation and recoordination of the O atom. Competition experiments revealed that phosphine 1a presents a higher chelating ability than 1b, a feature ascribed to the more electrodonating properties of the ethoxy groups in 1a compared to the phenoxy groups in 1b. P,O-Chelation affords seven-membered metallocycles, which is unusual for P,O-chelates. Complexes trans-[PdCl(2)[Ph(2)PCH[double bond]C(Ph)OP(O)(OPh)(2)](2)] (2b), [PdCl[Ph(2)PCHdouble bond]C(Ph)OP(O)(OEt)(2)](mu-Cl)](2) (3a), [complex--see text] (8a'), and [complex--see text] (10a) have been structurally characterized. Interestingly, the seven-membered rings in 8a' and 10a adopt a sofa conformation with the double bond lying almost perpendicular to the plane containing the Pd, the two P, and the two O atoms.

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PubMed2003

Novel "Potentially antiaromatic", acidichromic quinonediimines with tunable delocalization of their 6 pi-electron subunits.

We present a novel family of "potentially antiaromatic" alkyl-substituted p-benzoquinonediimine pH-dependent chromophores. It appears from the structural data that these overall 12 pi-electron molecules should be better considered as constituted by two chemically connected but electronically not conjugated 6 pi-electron subunits. Molecule 5 appears to be the first example of two separated, conjugated, and localized 6 pi-electron systems that can be tuned by reversible protonation to become delocalized. The mono- and diprotonated derivatives have been characterized by spectroscopic methods and X-ray diffraction. These systems develop supramolecular interactions in the solid state that clearly reflect the degree of protonation and depend on the nature of the counterion. These compounds constitute new chromophores for which the color can be tuned depending on the degree of protonation, going in solution from yellow for 5 to red for 5.HCl and blue for 5.2HCl. Theoretical calculations have provided a deeper insight into the electronic structure of these molecules and allowed an assignment of the experimental UV-vis spectra. The visible and near-UV spectrum of the neutral and protonated benzoquinonediimines can be classically assigned from the coupling of two 6 pi-electron polymethine units. TD-DFT calculations confirm the observed red shift of the two lowest pi --> pi* transitions of the benzoquinonediimines upon protonation and relate it to the moderate energy lowering of the HOMO --> LUMO transition induced by the delocalization of the polymethine pi system.

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PubMed2003

A 6 pi + 6 pi potentially antiaromatic zwitterion preferred to a quinoidal structure: its reactivity toward organic and inorganic reagents.

A straightforward synthesis of the zwitterionic benzoquinonemonoimine 8 is reported. This molecule is a rare example of a zwitterion being more stable than its canonical forms. It is shown that 8 is best described as constituted of two chemically connected but electronically not conjugated 6 pi electron subunits. Its reactivity with electrophiles such as H(+), CH(3)(+), and metal salts leads to the synthesis of new 12 pi electron molecules 12 (H(+)), 14 (CH(3)(+)), and 20 (Pd(2+)), respectively, in which one or both 6 pi electron subsystems localize into an alternation of single and double bonds, as established by X-ray diffraction. The acidity of the N[bond]H protons of 8 can be modulated by an external reagent. Dependent on the electrophile used, the control of the pi system delocalization becomes possible. When the electrophile simply adds to the zwitterion as in 12, 14, or 15, there is no more negative charge to be delocalized and only the positive charge remains delocalized between the nitrogen atoms. Furthermore, when a reaction with the electrophilic reagent results in deprotonation, as in 17-21, there remains no charge in the system to be delocalized. DFT calculations were performed on models of 8, 12, 14, 20, and on other related zwitterions 9 and 10 in order to examine the influence of the fused cycles on the charge separation and on the singlet-triplet energy gap. An effect of the nitrogen substituents in 8 is to significantly stabilize the singlet state. The dipole moment of 8 was measured to be 9.7 D in dichloromethane, in agreement with calculated values. The new ligands and complexes described in this article constitute new classes of compounds relevant to many areas of chemistry.

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PubMed2002

Bonding behavior of Co(CO)(3)L (L = CO, PPh(3)) building blocks in platinum-cobalt carbonyl clusters.

The reaction of [Co(CO)(4)](-) with [Pt(2)Cl(mu-PPh(2))(PPh(3))(3)] (1:1 ratio), which was prepared in situ by reaction of aqueous HCl with the orthometalated complex [Pt(2)(mu-PPh(2))(mu-o-C(6)H(4)PPh(2))(PPh(3))(2)], afforded the deep green triangular cluster [Pt(2)Co(mu-PPh(2))(CO)(4)(PPh(3))(2)], 7. X-ray crystallographic analysis reveals that this new cluster contains two formally monoanionic fragments, PPh(2-) and Co(CO)(4-), that bridge a d(9)-d(9) Pt(I)-Pt(I) metal-metal bond. Whereas tetracarbonylcobaltate is generally bonded to only one metal center as a 2e donor ligand, it is best viewed here as a formally 4e donor anionic metalloligand. This model leads then to the usual 16e count for each Pt center and relates this metalloligand to other anionic bridging ligands, such as PPh(2-). A comparative EHMO bonding analysis of [Co(CO)(3)L](-) (L = CO, PR(3)) fragments is presented which takes into account the possible coordination geometries about cobalt, trigonal bipyramidal (with C(3v) local symmetry) or edge-capped tetrahedral when referring to the ligand polyhedron (with C(2v) or C(s) symmetry). The results support the description of this unusual bridging bonding mode.

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PubMed2002

Reactivity of the heterometallic clusters [HMCo3(CO)12] and [Et4N][MCo3(CO)12] (M = Fe, Ru) toward phosphine selenides, including selenium transfer. Crystal structures of [HRuCo3(CO)7(mu-CO)3(mu-dppy)], [MCo2(mu3-Se)(CO)7(mu-dppy)], and [RuCo2(mu3-Se)(CO)7(mu-dppm)] [dppy = Ph2(2-C5H4N)P, dppm = Ph2PCH2PPh2].

The reactivity of [HMCo3(CO)12] and [Et4N][MCo3(CO)12] (M = Fe, Ru) toward phosphine selenides such as Ph3PSe, Ph2P(Se)CH2PPh2, Ph2(2-C5H4N)PSe, Ph2(2-C4H3S)PSe, and Ph2[(2-C5H4N)(2-C4H2S)]PSe has been studied with the aim to obtain new selenido-carbonyl bimetallic clusters. The reactions of the hydrido clusters give two main classes of products: (i) triangular clusters with a mu3-Se capping ligand of the type [MCo2(mu3-Se)(CO)(9-x)L(y)] resulting from the selenium transfer (x = y = 1, 2, with L = monodentate ligand; x = 2, 4, and y = 1, 2, with L = bidentate ligand) (M = Fe, Ru) and (ii) tetranuclear clusters of the type [HMCo3(CO)12xL(y)] obtained by simple substitution of axial, Co-bound carbonyl groups by the deselenized phosphine ligand. The crystal structures of [HRuCo3(CO)7(mu-CO)3(mu-dppy)] (1), [MCo2(mu3-Se)(CO)7(mu-dppy)] (M = Fe (16) or Ru (2)), and [RuCo2(mu3-Se)(CO)7(mu-dppm)] (12) are reported [dppy = Ph2(2-C5H4N)P, dppm = Ph2PCH2PPh2]. Clusters 2, 12, and 16 are the first examples of trinuclear bimetallic selenido clusters substituted by phosphines. Their core consists of metal triangles capped by a mu3-selenium atom with the bidentate ligand bridging two metals in equatorial positions. The core of cluster 1 consists of a RuCo3 tetrahedron, each Co-Co bond being bridged by a carbonyl group and one further bridged by a dppy ligand. The coordination of dppy in a pseudoaxial position causes the migration of the hydride ligand to the Ru(mu-H)Co edge. In contrast to the reactions of the hydrido clusters, those with the anionic clusters [MCo3(CO)12]- do not lead to Se transfer from phosphorus to the cluster but only to CO substitution by the deselenized phosphine.

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PubMed2002

Unprecedented zwitterion in quinonoid chemistry.

The first 12 pi-electron zwitterionic structure in quinonoid chemistry is described with the N,N,O,O-molecule 6 in which the positive charge is pi-delocalized between the nitrogen atoms and the negative charge between the oxygen atoms; depending on the crystallization solvent, a 1D-tape-like H-bonded network can be generated in the solid-state.

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