Multidentate silyl ligands in transition metal chemistry.

Silyl ligands are of great interest in transition metal coordination chemistry since they exhibit a strong trans-influence and create electron rich metals centres, which are in turn eligible to activate reagents. This review presents and discusses the use of multidentate Si-based ligand systems in transition metal coordination chemistry. These include tri- and tetradentate pincer and scorpionate-type ligands, which have been developed in recent years in order to tailor both steric and electronic properties for achieving a defined control over the reactivity of a transition metal complex. A discussion of synthetic and structural aspects of several subgroups of ligand architectures is presented. Some compounds allow for a detailed insight into the activation process of silanes or are capable of activating small molecules.

K⊂{[FeII(Tp)(CN)3]4[CoIII(pzTp)]3[CoII(pzTp)]}: a neutral soluble model complex of photomagnetic Prussian blue analogues.

Straightforward access to a new cyanide-bridged {Fe4Co4} "molecular box" containing a potassium ion, namely K⊂{[FeII(Tp)(CN)3]4[CoIII(pzTp)]3[CoII(pzTp)]} (1) (with Tp and pzTp = tris- and tetrakis(pyrazolyl)borate, respectively), is provided, alongside its full characterisation. A detailed analysis of the molecular structure (X-ray diffraction, mass spectrometry, NMR spectroscopy) and electronic properties (EPR spectroscopy, SQUID magnetometry, UV/Vis spectroscopy, cyclic voltammetry) reveals that 1 shows slow magnetic relaxation and a remarkable photomagnetic effect at low temperature which is reminiscent of some FeCo Prussian Blue Analogues (PBAs), and is ascribed to a photo-induced electron transfer. However, in contrast with these inorganic polymers, the overall neutral compound 1 is soluble and remarkably stable in organic solvents such as CH2Cl2. Moreover, 1 shows interesting redox versatility, with electrochemical experiments revealing the possible access to six stable redox states.

Time-resolved IR spectroscopy of a trinuclear palladium complex in solution.

This paper presents a combined spectroscopic and theoretical analysis of a trinuclear [Pd3{Si(mt(Me))3}2] complex (mt(Me) = methimazole) which has been demonstrated to be a potential catalyst for coupling reactions. It is a highly symmetric model system (D3 in the electronic ground state) for the investigation of electronic states and the structure of polynuclear transition metal complexes. Different time-resolved IR spectroscopic methods covering the femtosecond up to the microsecond range as well as density functional computations are performed to unravel the structure and character of this complex in the electronically excited state. These are the first time-resolved IR studies on a trinuclear Pd complex. Based on the interplay between the computational results and those from the IR studies a (3)A state is identified as the lowest lying triplet state which has C2 symmetry.

From MgBr via single-electron transfer (SET) to a paramagnetic Mg(II) compound and back to Mg(I): [MgBr(L(1))˙]2 and [K(thf)3]2[Mg2(L(1))2], L(1) = RN=C(Me)C(Me)=NR, R = 2,6-diisopropylphenyl.

Since Mg(+) ions are isoelectronic to Na atoms, an easy single electron transfer (SET) can be expected for MgBr. Even at 190 K, the radical MgBr (obtained via its sophisticated condensation) in a metastable solution transfers its electron to a diazadiene entity. A paramagnetic Mg(II) compound [MgBr(L(1))˙]2 (4; L(1) = DippN=C(Me)C(Me)=NDipp) is formed consisting of a singly reduced ligand. As shown by EPR investigations, dimeric 4 dissociates in ethereal solvents to two monomeric subunits. In addition, 4 can subsequently be reduced with potassium to furnish again a Mg(I) compound, namely [K(thf)3]2[Mg2(L(1))2] (3).

In-depth exploration of the photophysics of a trinuclear palladium complex.

A detailed theoretical and spectroscopic study on the electronically excited states of a trinuclear palladium complex is presented both in the gas phase and solution. The application of DFT and TDDFT methods as well as a variety of spectroscopic methods to the chosen complex [Pd3{Si(mt(Me))3}2] (1, mt(Me) = methimazole) leads to the first detailed analysis of the photophysics of a symmetric trinuclear complex. In combination with the calculations, energies, structures and lifetimes of the excited electronic states (with an (3)A1 state as the lowest one) are characterized by applying the resonant-2-photon-ionization method in a molecular beam experiment as well as luminescence, time-correlated single photon counting and excited state femtosecond absorption spectroscopy in solution. These investigations are of fundamental interest to analyze photophysical properties of metal containing complexes on a molecular level.

Two New Carbaalanes: Compounds with an Al(7)C(5) and a

The hydroalumination of aluminum ethynides leads to the formation of carbaalanes as a new class of compounds, which have clusters exclusively formed by carbon and aluminum atoms. Two novel carbaalanes with Al(7)C(5) and Al(7)C(4) clusters are described-the latter is a remarkable analogue of closo-[B(11)H(11)](2-) with respect to its structure and the number of cluster electrons.