Heteroaromaticity approached by charge density investigations and electronic structure calculations.

In this paper we present the results of a high-resolution single crystal X-ray diffraction experiment at 15 K on a benzothiazol-substituted phosphane and a subsequent charge density study based on multipole refinement and a topological analysis according to Bader's quantum theory of atoms in molecules. Although two valence shell charge concentrations (VSCCs) in the non-bonding region of each phosphorus and sulfur atom were found, the integration of both heteroatomic basins emphasizes charge depletion. Nevertheless they are attractive for C-H···P and C-H···S hydrogen bonding in the solid state. The nature of the P-C bonds and the question of aromaticity in the heterocycles were subject to our investigations. The ellipticities along the bonds were analysed to approach delocalization. The source function is employed to visualise atomic contributions to aromaticity. Theoretical calculations have been carried out to compute nuclear chemical shifts, induced ring currents and a variety of delocalization indices. All applied measures for delocalization point in the same direction: while heteroaromaticity is present in the benzothiazolyl substituents, the bridging P-C bonds are only involved marginally, almost preventing total conjugation of the phosphane. The charge density distributions around the phosphorus and the sulfur atoms have very similar features but turn out to be chemically very different from each other. Commonly used simplifying concepts have difficulties in providing a comprehensive view on the electronic situation in the molecule. Our results raise doubts on the validity of the common interpretation of VSCCs as one-to-one representations of Lewis lone pairs.

Assembly and stepwise oxidation of interpenetrated coordination cages based on phenothiazine.

A breath of fresh air is sufficient for the eightfold S-monooxygenation of an interpenetrated double cage based on eight phenothiazine ligands and four square-planar-coordinated Pd(II) cations. Besides these two cages, which were both characterized by X-ray crystallography, an eightfold S-dioxygenated double-cage was obtained under harsher oxidation conditions.

Mixed valence η6-arene cobalt(I) and cobalt(II) compound.

The first carbonyl free mixed valence cobalt(I)/cobalt(II) compound [2{L2Co(I)(η(6)-C7H8)}](2+) [Co(II)2Cl6](2-) (1) [L = PhC(N(t)Bu)2SiCl] was obtained by the reaction of four equivalents of anhydrous CoCl2 with five equivalents of N-heterocyclic chlorosilylene L. In contrast, the reaction of L with CoBr2 yielded [L2CoBr2] (2). Compound 1 was formed by the cleavage of Co-Cl bonds, the reduction of Co(II) to Co(I) and by the coordination of a toluene molecule. The chlorosilylene (L) functions as a reducing agent as well as a neutral σ-donor ligand. The toluene molecule coordinates to the Co(I) atom in an η(6)-fashion.

An inclusion complex of hexamolybdate inside a supramolecular cage and its structural conversion.

A self-assembled cage compound consisting of four concave ligands and two square-planar-coordinated Pd(II) ions was found to quantitatively encapsulate a hexamolybdate dianion [Mo(6)O(19)](2-) in solution. The addition of 1 equiv more of [Mo(6)O(19)](2-) to the inclusion complex resulted in the formation of a precipitate from which single crystals were grown. X-ray analysis showed that a structural conversion had taken place upon crystallization: one hexamolybdate anion was found to be wrapped in a chiral, cyclic arrangement of three ligands in the absence of any Pd(II) ions to give a compound of the formula {[Mo(6)O(19)](2-)@(ligand)(3)+2H(+)}. We postulate the stabilization of this arrangement by attractive C-H···O and CF(3)-pyridine interactions.

Facile access to transition-metal-carbonyl complexes with an amidinate-stabilized chlorosilylene ligand.

Three transition-metal-carbonyl complexes [V(L)(CO)(3)(Cp)] (1), [Co(L)(CO)(Cp)] (2), and [Co(L(2))(CO)(3)](+)[CoCO)(4)](-) (3), each containing stable N-heterocyclic-chlorosilylene ligands (L; L=PhC(NtBu)(2)SiCl) were synthesized from [V(CO)(4)(Cp)], [Co(CO)(2)(Cp)], and Co(2)(CO)(8), respectively. Complexes 1-3 were characterized by NMR and IR spectroscopy, EI-MS spectrometry, and elemental analysis. The molecular structures of compounds 1-3 were determined by single-crystal X-ray diffraction.

Double N-H bond activation of N,N'-bis-substituted hydrazines with stable N-heterocyclic silylene.

The reaction of N-heterocyclic silylene (NHSi) L [L = CH{(C[double bond, length as m-dash]CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}Si] with benzoylhydrazine, 1,2-dicarbethoxyhydrazine, 1,2-diacetylhydrazine and 1,2-bis(tert-butoxycarbonyl)hydrazine in 1 : 1 molar ratio resulted in compounds 1-4 with an almost quantitative yield and five coordinate silicon atoms. Compounds 1-4 were formed by double N-H bond activation by deliberate selection of N,N'-bis-substituted hydrazine compounds bearing the -C(O)NHNH- unit. Compounds 1-4 were characterized by NMR spectroscopy, EI-MS and elemental analysis. The molecular structures of compounds 1-3 were unambiguously established by single crystal X-ray structural analysis.

A stable cation of a CSi3P five-membered ring with a weakly coordinating chloride anion.

Don't count on counterions: The cyclic five-membered CSi(3)P cation 1 is synthesized in the reaction of benzamidinato-stabilized chlorosilylene and methyl phosphaalkyne. The presence of four π electrons in 1 means it can be considered as a formal, heavier analogue of the cyclopentadienyl cation. Surprisingly the small counteranion (Cl(-)) does not contribute to the ring stability.

Striking stability of a substituted silicon(II) bis(trimethylsilyl)amide and the facile Si-Me bond cleavage without a transition metal catalyst.

Silicon(II) bis(trimethylsilyl)amide (LSiN(SiMe(3))(2), L= PhC(NtBu)(2)) (2) has been synthesized by the reaction of LSiHCl(2) with KN(SiMe(3))(2) in 1:2 molar ratio in high yield where 1 equiv of the latter functions as a dehydrochlorinating agent. 2 exhibits a high stability up to 154 °C and can be handled in open air for a short period of time without any appreciable decomposition. An amazing five-membered cyclic silene (3) results from the cleavage of one Si-Me bond of 2 with an adamantyl phosphaalkyne. 3 is the first example of a heavy cyclopentene derivative which consists of four different elements, C, N, Si, and P. Both compounds are characterized by multinuclear NMR spectroscopy, EI-mass spectrometry, and single crystal X-ray diffraction studies.

Syntheses of group 7 metal carbonyl complexes with a stable N-heterocyclic chlorosilylene.

Two structurally characterized manganese [L(2)Mn(CO)(4)](+)[Mn(CO)(5)](-) (1) and rhenium [L(3)Re(CO)(3)](+)[ReCO)(5)](-) (2) silylene complexes were prepared in one pot syntheses by reacting 1 equivalent of Mn(2)(CO)(10) with 2 equivalents of stable N-heterocyclic chlorosilylene L {L = PhC(NtBu)(2)SiCl} and 1 equivalent of Re(2)(CO)(10) with 3 equivalents of L in toluene at room temperature. Both complexes 1 and 2 were characterized by single-crystal X-ray structural analysis, NMR and IR spectroscopy, EI-MS spectrometry, and elemental analysis.

Formation of silicon centered spirocyclic compounds: reaction of N-heterocyclic stable silylene with benzoylpyridine, diisopropyl azodicarboxylate, and 1,2-diphenylhydrazine.

Three silicon centered spirocyclic compounds 1-3, possessing silicon fused six- and five-membered rings have been prepared by the reaction of NHSi (L) [L = CH{(C=CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}Si] with benzoylpyridine, diisopropyl azodicarboxylate, and 1,2-diphenylhydrazine, respectively, in a 1:1 ratio. The three spirocyclic compounds (1- 3) were obtained by three different pathways. The reaction of L with benzoylpyridine leads to the activation of the pyridine ring, and dearomatization occurred. Treatment of diisopropyl azodicarboxylate with L favors a [1 + 4]- rather than a [1 + 2]-cycloaddition product, and the azo compound was converted to hydrazone derivative. Finally the reaction of 1,2-diphenylhydrazine and L results in the elimination of hydrogen by activating one of the C-H bonds present in the phenyl ring. All three complexes 1- 3 were characterized by single crystal X-ray structural analysis, NMR spectroscopy, EI-MS spectrometry, and elemental analysis. In addition the optimized structures of probable products and possible intermediates were investigated using density functional theory (DFT) calculations.