Homoleptic tetrakis(silyl) complexes of Pd(0) and Pt(0) featuring metal-centred heterocubane structures: evidence for the existence of the corresponding mononuclear Pd(I) and Pt(I) complexes.

We report on the first homoleptic tetrakis(silyl) complexes of zerovalent Group 10 metals. The compounds [MLi4{Si(3,5-Me2pz)3}4] (M=Pd and Pt; 3,5-Me2 pz=3,5-dimethylpyrazolyl) exhibit very appealing metal-centred heterocubane structures with the central d(10) metal atoms surrounded by four silicon and four lithium atoms. Both compounds were characterised in detail, including X-ray crystal-structure analysis and 2D NMR spectroscopic methods such as (7)Li,(29 Si and (7)Li,(195)Pt HMQC. Cyclic voltammetry studies, in combination with density functional theory (DFT) calculations, revealed that the corresponding mononuclear cationic d(9)-M(I) and dicationic d(8)-M(II) complexes are accessible by stepwise one-electron oxidation of the title compounds. Electron paramagnetic resonance (EPR) investigations provided evidence for the existence of the corresponding paramagnetic palladium(I) and platinum(I) complexes.

Heterobimetallic cuprates consisting of a redox-switchable, silicon-based metalloligand: synthesis, structures, and electronic properties.

A series of bimetallic silyl halido cuprates consisting of the new tripodal silicon-based metalloligand [κ(3)N-Si(3,5-Me2pz)3Mo(CO)3](-) is presented (pz = pyrazolyl). This metalloligand is straightforwardly accessible by reacting the ambidentate ligand tris(3,5-dimethylpyrazolyl)silanide ({Si(3,5-Me2pz)3}(-)) with [Mo(CO)3(η(6)-toluene)]. The compound features a fac-coordinated tripodal chelating ligand and an outward pointing, "free" pyramidal silyl donor, which is easily accessible for a secondary coordination to other metal centers. Several bimetallic silyl halido cuprates of the general formula [CuX{µ-κ(1)Si:κ(3)N-Si(3,5-Me2pz)3Mo(CO)3}](-) (X = Cl, Br, I) have been synthesized. The electronic and structural properties of these complexes were probed in detail by X-ray diffraction analysis, electrospray mass spectrometry, infrared-induced multiphoton dissociation studies, cyclic voltammetry, spectroelectrochemistry, gas-phase photoelectron spectroscopy, as well as UV/Vis and fluorescence spectroscopy. The heterobimetallic complexes contain linear two-coordinate copper(I) entities with the shortest silicon-copper distances reported so far. Oxidation of the anionic complexes in methylene chloride and acetonitrile solutions at E(1/2)(0( = -0.60 and -0.44 V (vs. ferrocene/ferrocenium (Fc/Fc(+))), respectively, shows substantial reversibility. Based on various results obtained from different characterization methods, as well as density functional theory calculations, these oxidation events were attributed to the Mo(0)/Mo(I) redox couple.

A triangulo palladium cluster consisting of µ3-capping silyl ligands.

We report on the utility of multifunctional, κ(1)Si:κ(3)S-coordinated tris(methimazolyl)silanide ligands [Si(mt(Me))(3)](-) for the stabilisation of a triangulo palladium cluster [Pd(3){Si(mt(Me))(3)}(2)] (3) consisting of very unusual µ(3)-capping SiR(3) donors. Differences to the corresponding platinum chemistry were supported by NMR spectroscopy and DFT calculations.

7Li,15N heteronuclear multiple quantum shift correlation-a fast and reliable 2D NMR method on natural abundant nuclei.

A straightforward natural abundance 2D HMQC NMR experiment between lithium-7 and nitrogen-15 is reported; this fast, reliable and routinely implementable method represents a powerful spectroscopic tool to study complex structures or intermediate species in solution, in particular those containing nitrogen-lithium bonds.

Syntheses, structures, and reactivity of poly(pyrazolyl)silanes, -disilanes, and the ambidentate kappa(1)Si/kappa(3)N-coordinating tris(3,5-dimethylpyrazolyl)silanide ligand [Si(3,5-Me2pz)3]- ((Me)Tpsd).

The reaction conditions for the synthesis [Si(2)((Me)pz)(6)] (1) and [Si((Me)pz)(4)] (4) have been investigated in detail in order to obtain suitable precursor compounds for the synthesis of the hitherto unknown Janus-head ligand tris(3,5-dimethylpyrazolyl)silanide ([Si((Me)pz)(3)](-), (Me)Tpsd). Within the monomeric lithium salt [Li(thf)((Me)Tpsd)] (5), the ambidentate silanide ligand is bound in a kappa(3)N-fashion to the Li cation, featuring an uncoordinated, anionic silicon bridgehead. Treatment of the silanide with various electrophiles such as Me(3)SiCl, Me(3)SnCl and Ph(3)SnCl gave in each case the expected salt metathesis reaction with the formation of Si-Si and Si-Sn bonds, respectively. The products [Me(3)Si-Si((Me)pz)(3)] (6) and [Me(3)Sn-Si((Me)pz)(3)] (7) and [Ph(3)Sn-Si((Me)pz)(3)] (8) are the first backbone-functionalized derivatives originating from the tris(pyrazolyl)silanide. Overall, it could be concluded that the anionic ligand backbone of (Me)Tpsd is much more accessible for electrophiles compared to the carbon analogue ([C((Me)pz)(3)](-), (Me)Tpmd).

Multidentate ligand systems featuring dual functionality.

Multifunctional ligands with podand topology provide intrinsically well-defined coordination geometries. Several subgroups of multidentate ligand systems comprising dual functionality have been developed so far. Recent advances made in this research area reflect its topicality. Work on metal complexes of ambiphilic ligands consisting of Lewis-acidic Group 13 element bridgehead atoms and additional donor functionalities is in the current focus of interest. The intrinsic topology of tetradentate ligands may introduce a fascinating reactivity and interesting electronic properties to the metal complexes. Janus-head type ligands are very promising candidates for the preparation of multimetallic complexes.