Ligands ambiphiles phosphine-borane (synthèse et coordination)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Lewis Pairing and Frustration of Group 13/15 Elements Geometrically Enforced by (Ace)Naphthalene, Biphenylene and (Thio)Xanthene Backbones

International audienceThe synthesis, structure, and reactivity of mixed group 13/group 15 compounds (E 13 = B, Al, Ga, In; E 15 = N, P, Sb, Bi) featuring a rigid (ace)naphthalene or (thio)xanthene backbone are discussed in this review. The backbone may either enforce or prevent E 15 →E 13 interactions, resulting in Lewis pairing or frustration. The formation of strong E 15 →E 13 interactions is possible upon peri-substitution of (ace)naphthalenes. This gives the opportunity to access and study highly reactive species, as exemplified by P-stabilised borenium salts and boryl radicals. In turn, rigid expanded spacers such as biphenylenes, (thio)xanthenes and dibenzofurans impose long distances and geometrically prevent E 15 →E 13 interactions. Such P-B derivatives display ambiphilic coordination properties and frustrated Lewis pair behaviour towards small molecules, their preorganised structure favouring reversible interaction/activation. Throughout the review, the importance of the scaffold in enforcing or preventing E 15 →E 13 interactions is highlighted and discussed based on experimental data and theoretical calculations

Ambiphilic Compounds: Synthesis and Structure of a Phosphane-Borane with a Flexible Diphenyl Ether Tether

The preparation of desired phosphane-borane 1 involves selective lithiation trapping of 2-bromo-2′-iododiphenyl ether 3 to give bromophosphane 4 followed by a second lithiation/electrophilic trapping to install the boron fragment. The structure of the new phosphane-borane was verified by single-crystal X-ray diffraction studies. A problematic intramolecular cyclization of lithiated intermediate 7 in THF was prevented by the use of toluene as the solvent. This result will also be of interest to chemists seeking to prepare related unsymmetrical diphosphanes

Etude des modes de coordination des ligands ambiphiles PE (E=B,AI,Ga)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Strong metal-borane interactions in low-valent cyclopentadienyl Rhodium complexes

International audienceThe first examples of half-sandwich Rh(I) complexes stabilized by borane coordination have been prepared and structurally characterized. As substantiated by NMR spectroscopy and single-crystal x-ray diffraction, the phosphine-borane ligand iPr2P-(o-C6H4)-BFxyl2 1 [Fxyl = 3,5-(F3C)2C6H3] engages in tight eta 3-BCC or eta 1-B coordination, depending on the metal environment

Photoisomerizable Heterodienes Derived from a Phosphine Borane

(Chemical Equation Presented) Stable relations: Reaction of phenylazide with a phosphine borane derivative gives rise to an intramolecularly stabilized phosphazide 1 (R = iPr, R′ = mesityl) that undergoes an unprecedented photoisomerization process associated with a change from an N α→B to an Nβ→B interaction (see scheme). The generality and possible reversibility of such phenomena are demonstrated with the related phosphazine adduct 2

Synthesis of a C(sp 2 )‐bridged Phosphine‐Borane by Ionic Coupling

International audienceThe vinyl carbenoid H2C=CBr(Li) has been used as key precursor to prepare a geminal C(sp 2)-bridged phosphine-borane. Starting from bromoethene, two sequences of lithiation/electrophilic trapping, with ClPiPr2 and FBMes2 respectively, affords iPr2P-C(=CH2)-BMes2 3 [Mes = 2,4,6-(H3C)3C6H2]. This new phosphine-borane 3 was characterized by multi-nuclear NMR and mass spectroscopy. It adopts a monomeric open structure without P→B interaction. A few crystals of a secondary product 4 have been analysed by X-ray diffraction, revealing an unusual dimeric structure

Lewis Acid-Assisted C(sp 3 )–C(sp 3 ) Reductive Elimination at Gold

International audienceThe phosphine-borane iPr2P(o-C6H4)BFxyl2 (Fxyl = 3,5-(F3C)2C6H3) 1-Fxyl was found to promote the reductive elimination of ethane from [AuMe2(μ-Cl)]2. Nuclear magnetic resonance monitoring revealed the intermediate formation of the (1-Fxyl)AuMe2Cl complex. Density functional theory calculations identified a zwitterionic path as the lowest energy profile, with an overall activation barrier more than 10 kcal/mol lower than without borane assistance. The Lewis acid moiety first abstracts the chloride to generate a zwitterionic Au(III) complex, which then readily undergoes C(sp3)–C(sp3) coupling. The chloride is finally transferred back from boron to gold. The electronic features of this Lewis-assisted reductive elimination at gold have been deciphered by intrinsic bond orbital analyses. Sufficient Lewis acidity of boron is required for the ambiphilic ligand to trigger the C(sp3)–C(sp3) coupling, as shown by complementary studies with two other phosphine-boranes, and the addition of chlorides slows down the reductive elimination of ethane