Showing papers in "Advances in Inorganic Chemistry in 1986"

The Coordination Chemistry of 2,2′:6′,2″-Terpyridine and Higher Oligopyridines

Abstract: Publisher Summary This chapter presents a discussion on the coordination chemistry of 2,2’: 6’, 2”-terpyridine and higher oligopyridines. The potentially terdentate ligand 2,2’: 6’, 2”-terpyridine presented, was first isolated by Morgan and Burstall as one of the numerous products from the reaction of pyridine with iron (III) chloride. There has been a considerable increase in the use of these ligands in recent years, prompted in part by the attractive photochemical and photophysical properties exhibited by complexes of the related ligands 2,2’-bipyridine and 1,10-phenanthroline. The chapter discusses stabilization of unusual complexes and states that low oxidation states are characterized by an excess of electron density at the metal atom; stabilization may be achieved by the use of ligands capable of reducing that electron density. One of the simplest ways to reduce the electron density is to design ligands with low-lying vacant orbitals of suitable symmetry for overlap with filled metal orbitals. This results in the transfer of electron density from the metal to the ligand (back-donation). In general, ligand nonbonding or π antibonding orbitals are of the correct symmetry for such overlap. The oligopyridines are ideally suited to such roles; they possess a filled highest occupied molecular orbital (HOMO) and a vacant lowest unoccupied molecular orbital (LUMO) of suitable energies for interaction with metal d orbitals. The chapter also discusses monodentate, bidentate, and bridging; terdentate and higher polydentate; cyclometallated, and others.

Catenated Nitrogen Ligands Part I. Transition Metal Derivatives of Triazenes, Tetrazenes, Tetrazadienes, and Pentazadienes

Abstract: Publisher Summary The observation that, with a few notable exceptions, coordination to transition metals imparts stability to catenated nitrogen systems promises exciting developments in the future. Although organic molecules containing up to 10-linked nitrogen atoms have been synthesized, metal complexes are known to date only for systems containing 2-, 3-, 4- , or 5-nitrogen chains. The chemistry of two-nitrogen ligands-notably hydrazines, diazenes, and, of course, dinitrogen itself- has received an enormous boost in recent years from the work on nitrogen fixation. The three-nitrogen systems include, in addition to the azide anion, triazenes, and their N-oxides. Complexes containing ArN=N–N(Ar)C(O) or “phosphazide” (ArN=N–N=PR 3 ) ligands are presented. The chemistry of four-nitrogen ligands is dominated by complexes of tetrazadienes, RN=N–N=NR, which are discussed together with the few isolated examples of tetrazene derivatives. The latter include a binuclear tungsten derivative of the hypothetical iso-tetrazene molecule (H 2 N) 2 N=N. The chapter discusses the first transition metal derivatives of pentazadienes RN=N–N(H)–N=NR. Cyclic catenated nitrogen ligands are also discussed. Diaryl-, alkylaryl-, and, to a lesser degree, dialkyltriazenes are readily available. Consequently most triazenide complexes are synthesized from the free triazene or one of its salts. The chapter presents examples of the applications of spectroscopic techniques to the study of tetrazadiene complexes.

High-Nuclearity Carbonyl Clusters: Their Synthesis and Reactivity

Abstract: Publisher Summary This chapter discusses the synthesis and reactivity of high-nuclearity carbonyl clusters (HNCC). The chapter defines HNCC as homo- or heteronuclear carbonyl clusters of transition and main group metals containing five or more metal atoms, each of which is linked to the metal core by at least one M—M bond. The chapter discusses the chemistry of the HNCC in terms of reaction type rather than metal by metal. All the HNCC that have been characterized to date by X-ray crystallographybare listed in a table together with the methods used for their synthesis and references to their spectroscopic data. Synthetic methods used for the preparation of HNCC may be classified in to two broad categories, depending on whether or not they involve the use of redox conditions; they are—syntheses not involving redox conditions and syntheses requiring reducing or oxidizing conditions. The synthesis of HNCC by redox condensation involves the reaction of an anionic mononuclear or polynuclear carbonyl species with a neutral, cationic, or even anionic fragment. A relatively small number of HNCC have been synthesized by oxidation of other carbonyl clusters. The oxidation reactions of a number of large carbide clusters have been found to provide relatively selective synthetic routes to clusters of reduced nuclearity. Oxidation of HNCC often results in cluster fragmentation or, as a consequence of redox condensation. X-Ray diffraction has often been successful in the determination of hydrogen atom position in HNCC hydrides.

Inorganic Chemistry of Hexafluoroacetone

Abstract: Publisher Summary This chapter presents a study on the inorganic chemistry of hexafluoroacetone (HFA). The difference in reactivity compared to organic ketones is caused by the strong electron-withdrawing effect of the fluorine atoms in HFA that leads to an electron-deficient carbonyl group. This is manifested in the inability to protonate the oxygen atom in super acidic media. Depending on the nature of the reaction partners, there are various pathways leading to different products. The chapter focuses on synthetic “inorganic” aspects of HFA chemistry, with attention to literature coverage since 1966. Reaction conditions and spectroscopic data are mentioned if necessary for structural and mechanistic considerations. Hydroxy- and alkoxysilanes are attacked by HFA to form hemiketals and ketals. The reaction of HFA with substituted vinyltrimethylsilyl ethers in the presence of Lewis acids with subsequent hydrolysis provides a good route to alcohols containing the hexafluoroisopropyl group. The reactions of germanium and tin compounds with HFA are very similar to those of silicon compounds. But because of differences in polarity and bond strengths some reactions yield products different from those of their silicon analogues. Reactions of open-chain and cyclic germoxanes and cyclic germadioxanes with HFA, and others have been investigated.