Using the phospha-Michael reaction for making phosphonium phenolate zwitterions.

The reactions of 2,4-di--butyl-6-(diphenylphosphino)phenol and various Michael acceptors (acrylonitrile, acrylamide, methyl vinyl ketone, several acrylates, methyl vinyl sulfone) yield the respective phosphonium phenolate zwitterions at room temperature. Nine different zwitterions were synthesized and fully characterized. Zwitterions with the poor Michael acceptors methyl methacrylate and methyl crotonate formed, but could not be isolated in pure form.

To Bond or Not to Bond: Metal-Metal Interaction in Heterobimetallic Rare-Earth Metal-Silver Complexes.

The reaction of 2,4-Bu-6-(PPh)PhOH (HOAr) with silver(I) triflate in a 3:1 molar ratio gave the mononuclear coinage metal complex (HOAr-κ)AgOTf (). Treatment of HOAr with Ln[N(SiMe)] (Ln = La, Sm, Y, Yb) in a 3:1 molar ratio yielded the mononuclear rare-earth metal complexes Ln(OAr-κ,) (). The heterobimetallic rare-earth metal-silver complexes Ln(OTf)(μ-OAr-1κ,2κ)Ag () were prepared from monometallic precursors by reactions of equimolar amounts of with Ln[N(SiMe)] or with silver(I) triflate, respectively.

Mono- and Disamarium Azacryptand Complexes: A Platform for Cooperative Rare-Earth Metal Chemistry.

Mono- (HLSm) and disamarium complexes (LSm) were prepared by reaction of the azacryptand N[(CH)NHCH--CHCHNH(CH)]N (HL) with 1 or 2 equiv of Sm[N(SiMe)], respectively. The disamarium complex features free coordination sites on both metal centers available for bridging ligands shielded by phenylenes from tetrahydrofuran (THF) coordination. The reaction of LSm with KCN and 18-crown-6 yielded the adduct [LSm-μ-η:η-CN][K(18-crown-6)(THF)] featuring a bridging cyanide.

Phosphinoindenyl and phosphazidoindenyl complexes of lanthanum and samarium: synthesis, characterisation, and hydroamination catalysis.

The phosphinoindenyl rare-earth metal complexes [1-(PhP)-η-CH]LnN(SiMe), Ln = La (1-La), Sm (1-Sm), were prepared by heating two equivalents of 1-(PhP)CH with Ln[N(SiMe)] in toluene at 100 °C. The treatment of 1-La with one equivalent of benzonitrile gave (PhCN)[1-(PhP)-η-CH]LaN(SiMe), 2, while no adduct was formed in case of the samarium derivative 1-Sm. The reaction of 1-La and 1-Sm with two equivalents of benzyl azide yielded the (phosphazido)indenyl complexes {1-[BnN-κ(Ph)P]-η-CH}{1-[BnN-κ,'(Ph)P]CH}LnN(SiMe), Ln = La (3-La), Sm (3-Sm), respectively.

Differential uranyl(v) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study.

The uranyl(vi) 'Pacman' complex [(UO)(py)(HL)] (L = polypyrrolic Schiff-base macrocycle) is reduced by CpTi(η-MeSiC[triple bond, length as m-dash]CSiMe) and [CpTiCl] to oxo-titanated uranyl(v) complexes [(py)(CpTiOUO)(py)(HL)] and [(ClCpTiOUO)(py)(HL)] . Combination of Zr and Zr synthons with yields the first Zr-uranyl(v) complex, [(ClCpZrOUO)(py)(HL)] . Similarly, combinations of Ae and Ae synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(v) complexes [(py)(ClMgOUO)(py)(HL)] , [(py)(thf)(ICaOUO)(py) (HL)] ; the zinc complexes [(py)(XZnOUO)(py)(HL)] (X = Cl , I ) are formed in a similar manner.

β-Amino- and Alkoxy-Substituted Disilanides.

Our recent study on formal halide adducts of disilenes led to the investigation of the synthesis and properties of β-fluoro- and chlorodisilanides. The reaction of the functionalized neopentasilanes (MeSi)SiSiPhNEt and (MeSi)SiSiMeOMe with KOBu in the presence of 18-crown-6 provided access to structurally related β-alkoxy- and amino-substituted disilanides. The obtained EtNPhSi(MeSi)SiK·18-crown-6 was converted to a magnesium silanide and further on to EtNPhSi(MeSi)Si-substituted ziroconocene and hafnocene chlorides.

Disilene Fluoride Adducts versus β-Halooligosilanides.

Extending the chemistry of disilene fluoride adducts studied earlier by us, we investigated the formation of 1,1-bis(trimethylsilyl)fluorodiphenylsilylsilanide, which was prepared by reaction of (MeSi)SiSiPhF with KOBu. The formed FPhSiSi(MeSi)K displays distinctively different structural and spectroscopic features compared to the earlier reported F(MeSi)SiSi(SiMe)K. While the latter eliminates metal fluoride upon reaction with MgBr, the respective magnesium silanide is formed from FPhSiSi(MeSi)K.

Group 4 Metal and Lanthanide Complexes in the Oxidation State +3 with Tris(trimethylsilyl)silyl Ligands.

A number of paramagnetic silylated d group 4 metallates were prepared by reaction of potassium tris(trimethylsilyl)silanide with group 4 metallates of the type K[CpMCl] (M = Ti, Zr, Hf). The outcomes of the reactions differ for all three metals. While for the hafnium case the expected complex [CpHf{Si(SiMe)}] was obtained, the analogous titanium reaction led to a product with two Si(H)(SiMe) ligands.

Ring opening polymerisation of lactide with uranium(iv) and cerium(iv) phosphinoaryloxide complexes.

The C-symmetric uranium(iv) and cerium(iv) complexes MeSiOM(OAr), M = U (1), Ce (2), OAr = OCH-6-Bu-4-Me-2-PPh, have been prepared and the difference between these 4f and 5f congeners as initiators for the ring opening polymerisation (ROP) of l-lactide is compared. The poorly controlled reactivity of the homoleptic analogue U(OAr) (3) demonstrates the importance of the M-OSiMe initiating group. The incorporation of a nickel atom in 1 to form the U-Ni heterobimetallic complex MeSiOU(OAr)Ni (4) may be the first example of the use of the inverse trans influence to switch the reactivity of a complex.

Using Functionalized Silyl Ligands To Suppress Solvent Coordination to Silyl Lanthanide(II) Complexes.

The reaction of the potassium 1,3-trisilanediide MeSi[Si(MeSi)K] with SmI and YbI was found to give the respective disilylated complexes MeSi[Si(MeSi)]Sm·2THF and MeSi[Si(MeSi)]Yb·2THF. Desolvation of coordinated solvent molecules in these complexes made their handling difficult. However, using a number of functionalized silanide ligands, complexes with a diminished number or even no coordinated solvent molecules were obtained ((RSi)Ln(THF) (x = 0-3)).

Basic Reactivity Pattern of a Cyclic Disilylated Germylene.

In order to estimate the reactivity of disilylated germylene phosphine adducts, a cyclic version of this compound class was reacted with a number of different reagents. Reactions with the chalcogens sulfur, selenium, and tellurium led to dimers of the heavy ketone analogues. Reactions with water and ethyl bromide proceeded to give the respective oxidized germanol and germyl bromide.

σ-Bond Electron Delocalization in Oligosilanes as Function of Substitution Pattern, Chain Length, and Spatial Orientation.

Polysilanes are known to exhibit the interesting property of σ-bond electron delocalization. By employing optical spectroscopy (UV-vis), it is possible to judge the degree of delocalization and also differentiate parts of the molecules which are conjugated or not. The current study compares oligosilanes of similar chain length but different substitution pattern.

Metal-Metal Bonding in Uranium-Group 10 Complexes.

Heterobimetallic complexes containing short uranium-group 10 metal bonds have been prepared from monometallic IU(IV)(OAr(P)-κ(2)O,P)3 (2) {[Ar(P)O](-) = 2-tert-butyl-4-methyl-6-(diphenylphosphino)phenolate}. The U-M bond in IU(IV)(μ-OAr(P)-1κ(1)O,2κ(1)P)3M(0), M = Ni (3-Ni), Pd (3-Pd), and Pt (3-Pt), has been investigated by experimental and DFT computational methods. Comparisons of 3-Ni with two further U-Ni complexes XU(IV)(μ-OAr(P)-1κ(1)O,2κ(1)P)3Ni(0), X = Me3SiO (4) and F (5), was also possible via iodide substitution.

Neutral "Cp-Free" Silyl-Lanthanide(II) Complexes: Synthesis, Structure, and Bonding Analysis.

Complexes featuring lanthanide silicon bonds represent a research area still in its infancy. Herein, we report a series of Cp-free lanthanide (+II) complexes bearing σ-bonded silyl ligands. By reactions of LnI2 (Ln = Yb, Eu, Sm) either with a 1,4-oligosilanyl dianion [K-Si(SiMe3)2SiMe2SiMe2Si(SiMe3)2-K)] (1) or with 2 (Me3Si)3SiK (3) the corresponding neutral metallacyclopentasilanes ({Me2Si(Me3Si)2Si}2)Ln·(THF)4 (Ln = Yb (2a), Eu (2b), Sm (2c)), or the disilylated complexes ({Me3Si}3Si)2Ln·(THF)3 (Ln = Yb (4a), Eu (4b), Sm (4c)), were selectively obtained.

Open-shell lanthanide(II+) or -(III+) complexes bearing σ-silyl and silylene ligands: synthesis, structure, and bonding analysis.

Complexes featuring lanthanide (Ln)-Si bonds represent a highly neglected research area. Herein, we report a series of open-shell Ln(II+) and Ln(III+) complexes bearing σ-bonded silyl and base-stabilized N-heterocyclic silylene (NHSi) ligands. The reactions of the Ln(III+) complexes Cp3Ln (Ln = Tm, Ho, Tb, Gd; Cp = cyclopentadienide) with the 18-crown-6 (18-cr-6)-stabilized 1,4-oligosilanyl dianion [(18-cr-6)KSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2K(18-cr-6)] (1) selectively afford the corresponding metallacyclopentasilane salts [Cp2Ln({Si(SiMe3)2SiMe2}2)](-)[K2(18-cr-6)2Cp](+) [Ln = Tm (2a), Ho (2b), Tb (2c), Gd (2d)].

Coordination Chemistry of Cyclic Disilylated Germylenes and Stannylenes with Group 11 Metals.

Reactions of EtP adducts of bissilylated germylenes and stannylenes with gold, silver, and copper cyanides led to cyanogermyl or -stannyl complexes of the respective metals. In the course of the reaction the phosphine moved to the metal, while the cyanide migrated to the low-coordinate group 14 element. The respective gold complexes were found to be monomeric, whereas the silver and copper complexes exhibited a tendency to dimerize in the solid state.

σ-Bond electron delocalization of branched oligogermanes and germanium containing oligosilanes.

In order to evaluate the influence of germanium atoms in oligo- and polysilanes, a number of oligosilane compounds were prepared where two or more silicon atoms were replaced by germanium. While it can be expected that the structural features of thus altered molecules do not change much, the more interesting question is, whether this modification would have a profound influence on the electronic structure, in particular on the property of σ-bond electron delocalization. The UV-spectroscopic comparison of the oligosilanes with germanium enriched oligosilanes and also with oligogermanes showed a remarkable uniform picture.

Formation and properties of a bicyclic silylated digermene.

In the presence of PMe3 or N-heterocyclic carbenes, the reaction of oligosilanylene dianions with GeCl2⋅dioxane gives germylene-base adducts. After base abstraction, the free germylenes can dimerize by formation of a digermene. An electrochemical and theoretical study of a bicyclic tetrasilylated digermene revealed formation of a comparably stable radical anion and a more reactive radical cation, which were characterized further by UV/Vis and ESR spectroscopy.

Cyclic Disilylated and Digermylated Germylenes.

The preparation of triethylphosphine adducts of cyclic disilylated or digermylated germylenes was achieved by reaction of 1,4-dipotassio-1,1,4,4-tetrakis(trimethylsilyl)tetramethyltetrasilane with GeBr·(dioxane) and PEt. Phosphine abstraction with B(CF) allowed formation of the base-free germylenes, which undergo 1,2-trimethylsilyl shifts to the germylene atom to form the respective silagermene or digermene, which further dimerize in [2 + 2] cycloadditions to tricyclic compounds. The reasons responsible for the germylenes' completely different reactivities in comparison to the previously studied analogous stannylenes and plumbylenes were elucidated in a theoretical study.

Coordination Chemistry of Disilylated Germylenes with Group 4 Metallocenes.

Reaction of the PEt adduct of a disilylated five-membered cyclic germylene with group 4 metallocene dichlorides in the presence of magnesium led to the formation of the respective germylene metallocene phosphine complexes of titanium, zirconium, and hafnium. Attempts to react the related NHC adduct of a disilylated four-membered cyclic germylene under the same conditions with CpTiCl did not give the expected germylene NHC titanocene complex. This complex was, however, obtained in the reaction of CpTi(btmsa) with the NHC germylene adduct.

Conformational Control of Polysilanes: Use of CH(2) Spacers in the Silicon Backbone.

By the reaction of a number of oligosilyl potassium compounds with (trimethylsilyl)chloromethane, derivatives containing the (trimethylsilyl)methyl substituent were prepared. Using X-ray single-crystal structure analysis and UV spectroscopy the conformational properties of some of the compounds were studied. It was found that the (trimethylsilyl)methylated examples exhibit UV absorption properties which correspond to lower energy transitions in comparison to those of analogous trimethylsilylated molecules.