Bandeau LBPB

Ambiphilic derivatives: Unusual coordination modes and Catalytic applications

  • B-​Centered Reactivity of Persistent P-​Stabilized Boryl Radicals
    A. J. Rosenthal, S. Mallet-Ladeira, G. Bouhadir,* E.-D. Sosa-Carrizo, K. Miqueu,* D. Bourissou*
    Organometallics, 2017, Article ASAP

    OM 2017

    A new P-stabilized boryl radical [iPr2P(naph)BMes] 2a was obtained by reduction of the corresponding phosphino-bromoborane 1a with Na(Hg). The persistent radical 2a has been characterized by EPR, and its structure has been thoroughly studied by DFT. The corresponding Gomberg-type dimer has been analyzed by NMR and XRD, and the Gibbs free energy associated with the dimerization process has been evaluated by VT EPR. The replacement of the Ph substituents at phosphorus for iPr groups has a slight but noticeable impact: it increases the spin density at boron and favors the radical over its Gomberg-type dimer. An original cross-coupling product between 2a and the trityl radical Ph3C has also been authenticated crystallographically. The P-stabilized boryl radicals 2a,b are readily trapped by TEMPO to give the corresponding B–O adducts 3a,b (naphthyl-bridged phosphine-boranes without P → B interaction). The reaction of 2a,b with Ph3CCl substantiates their ability to participate in halogen transfer reactions.

  • Amino and Alkyl B-​Substituted P-​Stabilized Borenium Salts
    M. Devillard, G. Bouhadir, S. Mallet-Ladeira, K. Miqueu, D. Bourissou*
    Organometallics, 2016, 35, 3788-379
    OM 2016

    The ability of the phosphino-naphthyl moiety to stabilize amino- and alkylborenium cations has been studied. Surprisingly, the phosphine–aminochloroborane precursor 2 was found to exist in neutral open form (without P→B interaction) in benzene solution and in the solid state but to ionize spontaneously in chloroform to generate the P-stabilized borenium salt 3. Addition of gallium trichloride shifts the process forward and affords the corresponding tetrachlorogallate borenium salt 3′. The phosphine group of 2 remains available for external reactivity, as shown by the ready formation of the corresponding phosphine gold(I) chloride complex 4. The P-stabilized cyclohexylborenium cation 6 has also been prepared by reacting the corresponding bromoborane 5 with gallium tribromide. Compound 6 is a very rare example of an alkyl-substituted borenium salt. The structures of 2, 3′, and 4–6 have been unambiguously ascertained by multinuclear NMR spectroscopy and X-ray crystallography.

  • Diverse reactivity of borenium cations with >N–H compounds
    Devillard, S. Mallet-Ladeira, G. Bouhadir*, D. Bourissou*
    Chem. Commun., 2016 , 52, 8877-8880.

    TOC CC 2016 8877

    The Ph2P-stabilized borenium 1 reacts cleanly with PhNH2, NH3 and HNTf2 to give a variety of boron compounds, namely the amino-substituted borenium 2 (substitution reaction at B), the neutral phosphine–borane 3, the mixed P/N-stabilized boronium 4 and the dicationic boron species 6. Remote modulation of the Lewis acidity at boron has been studied by preparing the related iPr2P-stabilized borenium 7 and reacting it with dihydrogen.

  • A Significant but Constrained Geometry Pt→Al Interaction: Fixation of CO2 and CS2, Activation of H2 and PhCONH2
    Devillard, R. Declercq, E. Nicolas, A. W. Ehlers, J. Backs, N. Saffon-Merceron, G. Bouhadir*, J. C. Slootweg*, W. Uhl*, D. Bourissou*
    J. Am. Chem. Soc., 2016, 138, 4917–4926.

    TOC JACS 2016 4917

    Reaction of the geminal PAl ligand [Mes2PC(═CHPh)AltBu2] (1) with [Pt(PPh3)2(ethylene)] affords the T-shape Pt complex [(1)Pt(PPh3)] (2). X-ray diffraction analysis and DFT calculations reveal the presence of a significant Pt→Al interaction in 2, despite the strain associated with the four-membered cyclic structure. The Pt···Al distance is short [2.561(1) Å], the Al center is in a pyramidal environment [Σ(C–Al–C) = 346.6°], and the PCAl framework is strongly bent (98.3°). Release of the ring strain and formation of X→Al interactions (X = O, S, H) impart rich reactivity. Complex 2 reacts with CO2 to give the T-shape adduct 3 stabilized by an O→Al interaction, which is a rare example of a CO2 adduct of a group 10 metal and actually the first with η1-CO2 coordination. Reaction of 2 with CS2 affords the crystalline complex 4, in which the PPtP framework is bent, the CS2 molecule is η2-coordinated to Pt, and one S atom interacts with Al. The Pt complex 2 also smoothly reacts with H2 and benzamide PhCONH2 via oxidative addition of H–H and H–N bonds, respectively. The ensuing complexes 5 and 7 are stabilized by Pt–H→Al and Pt–NH–C(Ph) = O→Al bridging interactions, resulting in 5- and 7-membered metallacycles, respectively. DFT calculations have been performed in parallel with the experimental work. In particular, the mechanism of reaction of 2 with H2 has been thoroughly analyzed, and the role of the Lewis acid moiety has been delineated. These results generalize the concept of constrained geometry TM→LA interactions and demonstrate the ability of Al-based ambiphilic ligands to participate in TM/LA cooperative reactivity. They extend the scope of small molecule substrates prone to such cooperative activation and contribute to improve our knowledge of the underlying factors.

  • Complexes of ambiphilic ligands: reactivity and catalytic applications
    Bouhadir, D. Bourissou*
    Chem. Soc. Rev., 2016, 45, 1065-1079.

    Rinoi Chem Soc Rev 2016

    Since the mid 2000's, the incorporation of Lewis acid moieties in ligands for transition metals has been studied extensively. So-called ambiphilic ligands were shown to possess rich and unusual coordination properties and special focus was given to the coordination of Lewis acids as σ-acceptor ligands (concept of Z-type ligands). Recent studies have demonstrated that the presence of Lewis acids at or nearby transition metals can also strongly impact their reactivity. These results are surveyed in this review. The stoichiometric transformations and catalytic applications of complexes deriving from ambiphilic ligands are presented. The different roles the Lewis acid can play are discussed.

  • A Phosphine-Coordinated Boron-Centered Gomberg-Type Radical
    A. J. Rosenthal, M. Devillard, K. Miqueu,* G. Bouhadir,* D. Bourissou*
    Angew. Chem., Int. Ed. 2015, 54(32), 9198-9202.

  ACIE 2015 Boron radical

The P-coordinated boryl radical [Ph2P(naphthyl)BMes]. (Mes = mesityl) was prepared by (electro)chemical reduction of the corresponding borenium salt or bromoborane. Electron paramagnetic resonance (EPR) analysis in solution and DFT calculations indicate large spin density on boron (60–70 %) and strong P–B interactions (P→B σ donation and B→P negative hyperconjugation). The radical is persistent in solution and participates in a Gomberg-type dimerization process. The associated quinoid-type dimer has been characterized by single-crystal X-ray diffraction.

  • A Stable but Highly Reactive Phosphine-Coordinated Borenium: Metal-free Dihydrogen Activation and Alkyne 1,2-Carboboration
    M. Devillard, R. Brousses, K. Miqueu,* G. Bouhadir,* D. Bourissou, D.*
    Angew. Chem. Int. Ed. 2015, 54(19), 5722-5726.

 ACIE 2015 Borenium

Borenium cations have been found to be valuable analogues of boranes as a result of their cationic character which imparts high electrophilicity. Herein, we report the synthesis, characterization, and reactivity of a new type of borenium cation employing a naphthyl bridge and a strong intramolecular P®B interaction. The cation reacts with H2 in the presence of PtBu3 (frustrated Lewis pair (FLP) approach) but also on its own. The mechanism of the reaction between the borenium cation and H2 in the absence of PtBu3 has been investigated using deuterium-labeling experiments and DFT calculations. Both experiments and calculations imply the side-on coordination of H2 to the B center, followed by heterolytic splitting and B-C bond cleavage. An uncommon syn 1,2-carboboration has also been observed upon reaction of the borenium ion with 3-hexyne.

  • Hydroboration of Carbon Dioxide Using Ambiphilic Phosphine-Borane Catalysts: On the Role of the Formaldehyde Adduct
    R. Declercq, G. Bouhadir,* D. Bourissou,* M.-A. Legare, M.-A. Courtemanche, K. S. Nahi, N. Bouchard, F.-G. Fontaine,* L. Maron
    ACS Catalysis 2015, 5(4), 2513-2520.

 

ACS Cat 2015 CO2

 Ambiphilic phosphine–borane derivatives 1-B(OR)2-2-PR′2–C6H4 (R′ = Ph (1), iPr (2); (OR)2 = (OMe)2 (1a, 2a); catechol (1b, 2b) pinacol (1c, 2c), −OCH2C(CH3)2CH2O– (1d)) were tested as catalysts for the hydroboration of CO2 using HBcat or BH3·SMe2 to generate methoxyboranes. It was shown that the most active species were the catechol derivatives 1b and 2b. In the presence of HBcat, without CO2, ambiphilic species 1a, 1c, and 1d were shown to transform to 1b, whereas 2a and 2c were shown to transform to 2b. The formaldehyde adducts 1b·CH2O and 2b·CH2O are postulated to be the active catalysts in the reduction of CO2 rather than being simple resting states. Isotope labeling experiments and density functional theory (DFT) studies show that once the formaldehyde adduct is generated, the CH2O moiety remains on the ambiphilic system through catalysis. Species 2b·CH2O was shown to exhibit turnover frequencies for the CO2 reduction using BH3·SMe2 up to 228 h–1 at ambient temperature and up to 873 h–1 at 70 °C, mirroring the catalytic activity of 1b.

  • Cooperation between Transition Metals and Lewis Acids: A Way to Activate H2 and H-E bonds
    M. Devillard, G. Bouhadir,* D. Bourissou*
    Angew. Chem. Int. Ed. 2015, 54(3), 730-732.

 

ACIE 2015 highlight

 The presence of a Lewis acid, typically a borane, in the coordination sphere of transition metals (Ni, Fe, Pt) offers a new way to activate H2 and strong H-E (E=Si, C) bonds.

 

Selected publications :

Phosphino-Boryl-Naphthalenes: Geometrically Enforced, Yet Lewis Acid Responsive P → B Interactions
S. Bontemps, M. Devillard, S. Mallet-Ladeira, G. Bouhadir, K. Miqueu, D. Bourissou*
Inorg. Chem. 2013, 52, 4714-4720.

Phosphine-Boronates: Efficient Bifunctional Organocatalysts for Michael Addition
O. Baslé, S. Porcel, S. Ladeira, G. Bouhadir,* D. Bourissou*
Chem. Commun. 2012, 48, 4495-4497.

Reaction of Singlet Dioxygen with Phosphine–Borane Derivatives: From Transient Phosphine Peroxides to Crystalline Peroxoboronates
S. Porcel, G. Bouhadir, N. Saffon, L. Maron, D. Bourissou
Angew. Chem. Int. Ed. 2010, 49, 6186-6189.

1,1-ferrocenyl phosphine-borane: synthesis, structure and evaluation in Rh-catalyzed hydroformylation
M. W. P. Bebbington, S. Bontemps, G. Bouhadir, M. J. Hanton, R. P. Tooze, H. van Rensburg, D. Bourissou
New J. Chem. 2010, 34, 1556-1559.

Hydrogen fluoride adduct of an ambiphilic phosphine–borane: NMR characterization and theoretical analysis of the bonding situation
S. Moebs-Sanchez, N. Saffon, G. Bouhadir, L. Maron, D. Bourissou
Dalton Trans. 2010, 39, 4417-4420.

Copper(I) Complexes derived from Mono- and Di-Phosphino-Boranes: Cu→B Interactions Supported by Arene Coordinations
M. Sircoglou, S. Bontemps, M. Mercy, K. Miqueu, S. Ladeira, N. Saffon, L. Maron, G. Bouhadir, D. Bourissou
Inorg. Chem. 2010, 49, 3983-3990.

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