Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis.

The application of bimolecular reductive elimination to the activation of iron catalysts for alkene-diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, (PDI)FeCH and (PDI)FeCH (PDI = 2,6-(2,6-R-CHN═CMe)CHN), and the alkyl-substituted examples, (APDI)FeCH (APDI = 2,6-(CHN═CMe)CHN), have molecular structures significantly distorted from planarity and = 3/2 ground states.

Zwitterionic and anionic multinuclear pentacoordinate silicon(IV) complexes with bridging (R,R)-tartrato(4-) ligands and SiO5 skeletons: synthesis and reactivity in aqueous solution.

Two nutrients in one molecule: A zwitterionic λ(5)Si,λ(5)Si'-disilicate (1) was synthesized and characterized. It contains ligands that exclusively derive from natural products ((R,R)-tartaric acid, choline). Hydrolysis of 1 yields 2, which shows a remarkable kinetic stability in water.

Neutral pentacoordinate halogeno- and pseudohalogenosilicon(IV) complexes with an SiSONCX skeleton (X=F, Cl, Br, I, N, C): synthesis and structural characterization in the solid state and in solution.

A series of neutral pentacoordinate silicon(IV) complexes with an SiSONCX skeleton (X=F, Cl, Br, I, N, or C) was synthesized and structurally characterized by multinuclear solution-state and solid-state NMR spectroscopy and single-crystal X-ray diffraction. These compounds contain an identical tridentate dianionic S,N,O ligand, a monodentate (pseudo)halogeno ligand (F, Cl, Br, I, NCS, N(3), or CN), and a monodentate organyl ligand (methyl, phenyl, 4-(trifluoromethyl)phenyl, or pentafluorophenyl). For most of these compounds, a dynamic equilibrium between the pentacoordinate silicon(IV) complex and two isomeric tetracoordinate silicon species in solution was observed.

Neutral pentacoordinate silicon(IV) complexes with silicon-chalcogen (S, Se, Te) bonds.

The neutral pentacoordinate silicon(IV) complexes 1 (SiS2ONC skeleton), 2 (SiSeSONC), 3 (SiTeSONC), 6/9 (SiSe2O2C), 7 (SiSe2S2C), and 8/10 (SiSe4C) were synthesized and structurally characterized by using single-crystal X-ray diffraction and multinuclear solid-state and solution-state (except for 6-9) NMR spectroscopy. With the synthesis of compounds 1-3 and 6-10, it has been demonstrated that pentacoordinate silicon compounds with soft chalcogen ligand atoms (S, Se, Te) can be stable in the solid state and in solution.

Optically active zwitterionic lambda(5)Si,lambda(5)Si'-disilicates: syntheses, crystal structures, and behavior in aqueous solution.

The zwitterionic lambda(5)Si,lambda(5)Si'-disilicates 1-8 were synthesized and characterized by solid-state and solution NMR spectroscopy. In addition, compounds 26 H(2)O, 32 CH(3)CN, 45/2 CH(3)CN, 6CH(3)OH, 7, and 8CH(3)OHCH(3)CN were studied by single-crystal X-ray diffraction. The optically active (Delta,Delta,R,R,R,R)-configured compounds 1-8 contain two pentacoordinate (formally negatively charged) silicon atoms and two tetracoordinate (formally positively charged) nitrogen atoms.

Sila-haloperidol, a silicon analogue of the dopamine (D2) receptor antagonist haloperidol: synthesis, pharmacological properties, and metabolic fate.

Haloperidol (1 a), a dopamine (D(2)) receptor antagonist, is in clinical use as an antipsychotic agent. Carbon/silicon exchange (sila-substitution) at the 4-position of the piperidine ring of 1 a (R(3)COH --> R(3)SiOH) leads to sila-haloperidol (1 b). Sila-haloperidol was synthesized in a new multistep synthesis, starting from tetramethoxysilane and taking advantage of the properties of the 2,4,6-trimethoxyphenyl unit as a unique protecting group for silicon.