Stannylenes and Germylenes Stabilized by Tetradentate Bis(amidine) Ligands with a Rigid Naphthalene Backbone.

An unusual series of germylenes and stannylenes stabilized by new tetradentate bis(amidine) ligands RNC(R')N-linker-NC(R')NR with a rigid naphthalene backbone has been prepared by protonolysis reaction of Lappert's metallylenes [M(HMDS)2] (M = Ge or Sn). Germylenes and stannylenes were fully characterized by NMR spectroscopy and X-ray diffraction analysis. DFT calculations have been performed to clarify the structural and electronic properties associated with tetradentate bis(amidine) ligands. Stannylene L1Sn shows reactivity through oxidation, oxidative addition, and transmetalation reactions, affording the corresponding gallium and aluminum derivatives.

Synthesis and structures of homoleptic germylenes and stannylenes with sulfonimidamide ligands.

An unusual series of germylenes and stannylenes with homoleptic symmetric and unsymmetric N-substituted sulfonimidamide ligands PhSO(NiPr)(NHiPr) 1 and PhSO(NMes)(NHiPr) 2 have been prepared by protonolysis reaction of Lappert's metallylenes [M(HMDS)2] (M = Ge or Sn) with two equivalents of the appropriate sulfonimidamide. The homoleptic germylenes [PhSO(NiPr)2]2Ge 3 and [PhSO(NMes)(NiPr)]2Ge 4, and stannylenes [PhSO(NiPr)2]2Sn 5 and [PhSO(NMes)(NiPr)]2Sn 6 were fully characterized by NMR spectroscopy and by X-ray diffraction analysis. DFT calculations have been performed to understand the electronic properties brought by the sulfonimidamide ligand.

Synthesis, Characterization and Reactivity of a σ-Donating Ni0 -Stabilized Silyliumylidene Ion.

The synthesis of a silyliumylidene cation complex 2 stabilized by a Ni0 -based donating ligand is reported. Experimental and theoretical studies demonstrate that the highly electrophilic SiII center is stabilized by a dative Ni→Si σ-interaction and π-donations from the amino- and Ni-moieties. Due to the energetically close frontier orbitals localized on the Si and Ni atoms, complex 2 presents a competitive reactivity at Si and Ni sites.

A Silylene Stabilized by a σ-Donating Nickel(0) Fragment.

A donor-stabilized silylene 4 featuring a Ni0 -based donating ligand was synthesized. Complex 4 exhibits a pyramidalized and nucleophilic SiII center and shows a peculiar behavior due to the cooperative reactivity of Si and Ni centers. Calculations indicate that the orientation of Ni-ligands with respect to the silylene moiety is crucial in determining the role of the Ni-fragment (Lewis acid or Lewis base) towards silylene. Indeed, a simple 90° rotation of the Si-Ni bond, reverses the role of Ni, and transforms a classical silylene→Ni0 complex into an unprecedented Ni0 →silylene complex.

Complexes of Dichlorogermylene with Phosphine/Sulfoxide-Supported Carbone as Ligand.

Due to their remarkable electronic features, recent years have witnessed the emergence of carbones L2C, which consist in two donating L ligands coordinating a central carbon atom bearing two lone pairs. In this context, the phosphine/sulfoxide-supported carbone 4 exhibits a strong nucleophilic character, and here, we describe its ability to coordinate dichlorogermylene. Two original stable coordination complexes were obtained and fully characterized in solution and in the solid state by NMR spectroscopy and X-ray diffraction analysis, respectively. At 60 °C, in the presence of 4, the Ge(II)-complex 5 undergoes a slow isomerization that transforms the bis-ylide ligand into an yldiide.

Germylene-ß-sulfoxide Hemilabile Ligand in Coordination Chemistry.

We describe herein the synthesis of a germylene-ß-sulfoxide ligand, 1, and its abilities in coordination chemistry. Treatment of 1 with metal complexes [W(cod)(CO)4], [Mo(nbd)(CO)4] and [Ni(cod)2] afforded the corresponding (1)-chelated metal complexes (1)-W(CO)4 (2a), (1)-Mo(CO)4 (2b), and (1)-Ni(cod) (4a), clearly showing a bidentate ligation of the metal by the germanium(II) and sulfur centers. Coordination with [Ru(PPh3)3Cl2] afforded an unprecedented bridged bis(ruthenium) complex 3b. In the case of 4a, the hemilability of the bidentate ligand 1 was demonstrated by sulfoxide substitution by a CO ligand.

Symmetric and non-symmetric bis-metallylene iron complexes, precursors of iron germanide nanoparticles.

We report herein the synthesis of symmetric and non-symmetric bis-amidinato-germylene Fe(CO)3 complexes, as well as the preparation of the corresponding disymmetric germylene-stannylene and germylene-silylene complexes by selective displacement of a carbonyl ligand under UV-a light irradiation. The symmetric bis-germylene Fe(CO)3 complex has been applied in the synthesis of iron germanide nanocrystals.

A non-symmetric sulfur-based O,C,O-chelating pincer ligand leading to chiral germylene and stannylene.

New chiral heteroleptic germanium(ii) and tin(ii) metallylenes were obtained using 1-(para-tolylsulfinyl)-3-tosyl-5-tert-butyl-benzene as a non-symmetric O,C,O-chelating pincer ligand. Crystallographic analysis and DFT calculations indicate that the non-symmetric sulfinyl-sulfonyl pincer ligand acts as an O,C,O-coordinating pincer-type-ligand with predominant sulfinyl intramolecular S[double bond, length as m-dash]O coordination to germanium(ii) and tin(ii) centers.

Designed single-source precursors for iron germanide nanoparticles: colloidal synthesis and magnetic properties.

The synthesis of iron germanide nanoparticles at the nanoscale is a challenging task. Here, we describe the preparation of nanocrystals of the hexagonal Fe1.67Ge phase via the thermolysis of single source precursors [{iPrNC(tBu)NiPr}RGe]Fe(CO)4 (where R = Cl, N(SiMe3)2) under mild conditions (200 °C). These bimetallic precursors and the corresponding germylenes [{iPrNC(tBu)NiPr}RGe] were fully characterized by spectroscopic techniques as well as single crystal X-ray diffraction. While the structural features of the molecular species were shown to be almost identical, the results of the thermolysis were highly dependent on the nature of R. When R = Cl, multimodal size distributions and non-controlled phases were obtained. In contrast, the thermolysis of [{iPrNC(tBu)NiPr}{N(SiMe3)2}Ge]Fe(CO)4 yielded pure ferromagnetic Fe1.67Ge nanoparticles with a mean diameter close to 6 nm and a narrow size distribution (<12%). These results were rationalized in terms of Ge-substituent bond energy thanks to a computational study.

Germylene-sulfoxide as a potential hemilabile ligand: application in coordination chemistry.

We describe here the synthesis of heteroleptic organogermylenes containing a sulfoxide donor function for their application in coordination chemistry. While complexation reaction with [W(cod)(CO)4] and [Mo(nbd)(CO)4] afforded bis(germanium)(ii) transition-metal complexes, a bidentate complex coordinated by germanium(ii) and the oxygen atom of the sulfinyl group was obtained from [Ru(PPh3)3Cl2].

Bis-Sulfonyl O,C,O-Chelated Metallylenes (Ge, Sn) as Adjustable Ligands for Iron and Tungsten Complexes.

The synthesis and characterization of an E2 CE2 bis-sulfonyl aryl pincer ligand and its efficiency for the stabilization of compounds containing low-valent Group 14 elements (Ge and Sn) are reported. Complexation reaction of these metallylenes with iron or tungsten complexes resulted in the modulation of the oxygen atoms of the sulfonyl groups implicated in the stabilization of the Group 14 elements, demonstrating the original adjustable character of the bis-sulfonyl O2 S-C-SO2 aryl pincer.

A bis-sulfonyl O,C,O aryl pincer ligand and its tin(II) complex: synthesis, structural studies, and DFT calculations.

The efficiency of the deprotonated aryl bis-sulfone [2,6-{(p-tolyl)SO2}2C6H3](-) as an O,C,O-coordinating pincer-type ligand was described. The bis-sulfone precursor was synthesized using a straightforward palladium-catalyzed cross-coupling reaction. As a result of directed ortho metalation (DoM) through sulfonyl groups, a selective lithiation of the aryl group was achieved and the corresponding carbanion was isolated and its structure determined by single-crystal X-ray diffraction analysis. A heteroleptic tin(II) complex has been prepared by a nucleophilic substitution reaction. Crystallographic analysis and DFT calculations indicate that the bis-sulfonyl moiety acts as a new O,C,O-coordinating pincer-type ligand with intramolecular S=O coordination to a tin(II) center. The cis form with the two nonbonded oxygen atoms of the sulfonyl groups on the same side is preferentially obtained.

Synthesis of γ-lactams and γ-lactones via intramolecular Pd-catalyzed allylic alkylations.

CONSPECTUS: Lactones and lactams are a well-known class of natural products and can be used as building blocks in organic synthesis. In addition, they can be found in many natural sources and synthetic drugs and have a broad range of biological or odorant properties. Chemists can create these useful compounds through palladium catalysis, which is a highly efficient tool for organic synthesis and is conveniently functional group tolerant. In this Account, we describe our work over the past 15 years in intramolecular Pd-catalyzed allylations where we have tethered the nucleophile and the electrophile by either an amide or an ester moiety, to produce γ-lactams and γ-lactones. We discuss in detail how the nature of the heteroatom tether influences the regioselectivity of the reaction. For example, a ketone [-C(O)CH2-] tether leads to mixtures of 5-exo and 7-endo cyclization products, while ester or amide [-C(O)X-] tethers afford sole 5-exo products. However, in the case of X = O, we were required to overcome two issues in the synthesis of γ-lactones. First of all, the tethering ester function can compete with the allylic leaving group in the oxidative addition to the Pd(0) center. Second, in this case, the proportion of the conformers that have a suitable geometry for cyclization is very low. When we insert a juxtaposed silyl group on the allyl fragment, the molecule can undergo oxidative addition and functionalization of the lactone via Hiyama cross-coupling. We also performed DFT calculations on these systems, which allowed us to better understand the behavior of [-C(O)X-] and [-C(O)CH2-] tethers. Computations also let us rationalize the different reactivities that we observed as a function of the geometry (Z or E) of the starting substrates. In addition, we were able to synthesize natural products or analogs (α-kainic acid, isoretronecanol, and picropodophyllin). We could turn these allylation reactions into asymmetric transformations and incorporate them into domino sequences. Thus, an allylation/Mizoroki-Heck sequence allowed us to straightforwardly access an aza-analog of picropodophyllin, as well as reach the lysergic acid backbone. Finally, we found that through carbopalladation of allenes, we could efficiently synthesize the key η(3)-allylpalladium intermediates that were then ready for allylation reactions.

2,2,7,7,12,12,17,17-Octa-methyl-21,22,23,24-tetra-thia-2,7,12,17-tetra-germapenta-cyclo-[16.2.1.1(3,6).1(8,11).1(13,16)]tetra-cosa-3,5,8,10,13,15,18,20-octa-ene.

The title compound, [Ge4(CH3)8(C4H2S)4], crystallizes with one-half mol-ecule in the asymmetric unit, the whole mol-ecule being generated by inversion symmetry. The dihedral angle between adjacent thio-phene rings is 72.84 (14)°. In the crystal, mol-ecules are linked by C-H⋯π inter-actions, leading to the formation of chains along [100].

Functionalized 2,3-dihydrofurans via palladium-catalyzed oxyarylation of α-allyl-ß-ketoesters.

The palladium-catalyzed reaction of (hetero)aryl bromides, chlorides, and nonaflates with α-allyl-ß-ketoesters provides ready efficient access to functionalized 2,3-dihydrofurans. The reaction tolerates several useful substituents including chloro, fluoro, ether, ketone, ester, cyano, and nitro groups.

A smart palladium catalyst in ionic liquid for tandem processes.

New catalytic systems based on in situ and preformed palladium nanoparticles in ionic liquids (characterised by TEM) starting from palladium acetate or dipalladiumtris(dibenzylideneacetone) have been applied in the synthesis of 4-phenylbutan-2-one (II), a model compound for the preparation of fragrances. Imidazolium-based ionic liquid containing a methyl hydrogenophosphonate anion leads to an efficient Pd-catalyzed tandem coupling/reduction process, taking advantage of the multi-role of this solvent (nanoparticles stabiliser, base, hydrogen transfer agent). The influence of the mono-phosphine ligands (1-3) on the catalyst has been evaluated, showing that the ligand-free palladium system turns into the most appropriate for the formation of II using Pd(OAc)(2) as precursor. Fine-tuning conditions involved in this multi-parameter process have led us to propose a plausible mechanism based on the hydrogen transfer coming from the methyl hydrogenophosphonate anion.

Cavitand supported tetraphosphine: cyclodextrin offers a useful platform for Suzuki-Miyaura cross-coupling.

The cyclodextrin-tetraphosphine hybrid coined α-Cytep allows turnover numbers up to 340,000,000,000 and turnover frequencies up to 1,000,000,000 h(-1) to be reached in Suzuki-Miyaura reactions. These exceptional figures are clearly linked to the outstanding longevity of the reactive species induced by the ligand α-Cytep and illustrates the rising potential of cyclodextrins in catalytic applications.

γ- and δ-lactams through palladium-catalyzed intramolecular allylic alkylation: enantioselective synthesis, NMR Investigation, and DFT rationalization.

The Pd-catalyzed intramolecular allylic alkylation of unsaturated amides to give γ- and δ-lactams has been studied in the presence of chiral ligands. Ligand (R)-3,5-tBu-MeOBIPHEP (MeOBIPHEP = 6,6'-dimethoxybiphenyl-2,2-diyl)bis(diphenylphosphine)) afforded the best results and allowed the cyclization reactions to take place in up to 94:6 enantiomeric ratio. A model Pd-allyl complex has been prepared and studied through NMR spectroscopic analysis, which provided insight into the processes responsible for the observed enantiomeric ratios. DFT studies were used to characterize the diastereomeric reaction pathways. The calculated energy differences were in good agreement with the experimentally observed enantiomeric ratios.

Aryl sulfoxides from allyl sulfoxides via [2,3]-sigmatropic rearrangement and domino Pd-catalyzed generation/arylation of sulfenate anions.

Allylic sulfoxides, via [2,3]-sigmatropic rearrangement and oxidative addition of the resulting allylic sulfenate esters to Pd(0), are found to be excellent precursors of sulfenate anions. This hitherto unknown reactivity is applied in a new Pd(0)-catalyzed domino sequence involving sulfenate anion generation followed by arylation to afford aryl sulfoxides.