Showing papers in "Reviews in Inorganic Chemistry in 2011"

(Guanidine)copper complexes: structural variety and application in bioinorganic chemistry and catalysis

Abstract: Abstract In this paper, guanidine copper compounds are reviewed with an emphasis on structural characteristics and their application in bioinorganic chemistry and catalysis. The literature survey includes the copper coordination chemistry of biological guanidine derivatives, peralkylated guanidines including bicyclic ones and of further nitrogen-rich guanidine-type systems such as azoimidazoles, triazolopyrimidines and triaminoguanidines. From a sporadic interest dating back to the 1960s, research on this ligand class and its use in copper coordination chemistry has gained new impetus since 2000. With the synthesis of examples with sophisticated substitution at the characteristic CN3 framework, complex problems can be addressed in several fields of chemistry. This paper analyses the different types of guanidines for their special donor properties and highlights the specific advantages of guanidines as neutral donor ligands in copper coordination chemistry where a great variety of coordination modes was found. These compounds offer the ability to distribute the formal positive charge of the metal throughout the guanidine unit and represent more than simple σ-donating ligands.

5-Membered heterocycles with directly-bonded sandwich and half-sandwich termini as multi-redox systems: synthesis, reactivity, electrochemistry, structure and bonding

Abstract: Abstract The synthesis, structure, bonding motif, reaction behavior, electrochemistry, spectro-electrochemistry and some potential applications of multi-sandwich and/or half-sandwich substituted 5-membered heterocycles including group 3–6 main group elements and/or d-block transition metals, as well as current trends in this field of chemistry, are reported.

Rare earth-transition metal-cadmium intermetallics – crystal chemistry and physical properties

Abstract: Abstract Recent results on the crystal chemistry and physical properties of intermetallic rare earth-transition metal-cadmium compounds are reviewed. The structural chemistry is compared to related magnesium and zinc compounds.

Calcium-based organometallics and superbases – alkyl-, aryl-, and amidocalcium compounds

Abstract: Abstract Calcium-based organometallics gained tremendous interest for several reasons, such as extraordinary reactivity, unexpected structures due to d-orbital participation in many bonding situations, preparative access with high yields, and far-reaching applications in catalysis and stoichiometric reactions. Arylcalcium compounds are prepared by the direct synthesis of activated calcium metal and iodoarenes. Whereas in meta- and para-positions many other substituents are tolerated, a para-phenyl group destabilizes this compound; thus 2,4,6-triphenylphenylcalcium iodide immediately degrades tetrahydrofuran and finally yields an inverse sandwich of the type [(thf)3Ca(μ-C6H3-1,3,5-Ph3)Ca(thf)3] with calcium(I) atoms. Stable alkylcalcium derivatives have to be shielded by either substituted silyl groups or aryl substituents in order to kinetically protect the reactive Ca-C bonds and to delocalize the negative charge for reduction of the nucleophilicity. Calcium bis(phosphorano)methanediides contain doubly deprotonated central methylene groups which can bind to one or in a bridging mode to two calcium ions. Calcium dialkylamides form another family of extremely reactive calcium complexes which tend to cleave ethers. Handling and manipulating of phenyl-substituted amides of calcium are less challenging. Ether degradations of tetrahydrofuran yields ethylene and vinylate; however, the vinylate is not stable under these reaction conditions. Hydrogenation, hydroamination, and hydrophosphanylation of unsaturated compounds are discussed as representative examples for calcium-based catalytic applications.

Isomers in the chemistry of iron carbonyls

Abstract: Abstract The chemistry of iron carbonyls covers wide fields, as shown by a survey covering the crystallographic and structural data of over 560 examples; approximately 10.5% of those examples exist as isomers and are summarized in this paper. Included are distortion (96.7%) and cis-trans (3.3%) isomerism. These are discussed in terms of coordination about iron atom, bond length and interbond angles. Distortion isomers differ only by degree of distortion in Fe-L bond distances and L-Fe-L bond angles, which are the most common. There are iron atoms in the oxidation states, zero, +2 and +3 and cis-trans isomerism (zero only). The iron atoms are two (bent), four (mostly tetrahedral), five (mostly trigonal-bipyramid) and a pseudo-octahedral coordinated with different degree of distortion.

Crystallographic and structural analysis of iron heterometallic hexa- and heptanuclear complexes

Abstract: Abstract This review covers over 100 heterohexa- and almost 60 heteroheptameric iron clusters. There are six categories of the heterohexameric complexes: Fe5M, Fe4M2, Fe3M3, Fe2M4, FeM5 and Fe4MM′, and eight categories of the heteroheptameric complexes: Fe6M, Fe5M2, Fe4M3, Fe3M4, Fe2M5, FeM6, FexMyM′z and FeRu4CuAu. The heterometals include the non-transition and transition metals. The shortest Fe-M (non-transition) and Fe-M (transition) in the heterohexa- series are 2.444(3) Å for Fe-Ge and 2.404(20) Å for Fe-Cu, and in the heterohepta- series are 2.316(2) Å for Fe-Ge and 2.438(3) Å for Fe-Au. Correlations between structural parameters, heterometals and ligand donor atoms are developed and an overall summary of the metal-metal distances is given.

Isomers in the chemistry of manganese coordination compounds

Abstract: Abstract The coordination chemistry of manganese covers wide fields, as shown by a survey covering the crystallographic and structural parameters of over 700 examples. About 10% of those complexes exist as distortion isomers and are summarized. These are discussed in terms of the coordination about the Mn(I) to Mn(IV) mixed valence Mn(II)/Mn(III); Mn(III)/Mn(IV) and correlations are drawn between donor atoms, bond length and interbond angles. Distortion isomers differ only by degree of distortion in Mn–L bond distances and L–Mn–L bond angles. Interestingly, in the chemistry of manganese coordination complexes, only distortion isomers are present. The isomers crystallized in the following systems: monoclinic (×40)>triclinic (×22)>orthorhombic (×8)>tetragonal (×4), trigonal and cubic each (×1). The nuclearity ranges from monomeric to polymeric, and a wide range of ligand systems are found, with O and N donor atoms by far prevailing. The manganese are three-, four-, five-, six- and seven-coordinated, from which six-coordinated by far prevails.