Alexander P. Sadimenko

COMMON AND LESS-COMMON COORDINATION MODES OF THE TYPICAL CHELATING AND HETEROAROMATIC LIGANDS

Abstract Data on the different modes of bonding the metals to the most widely spread chelating [β-diketones, o -oxyazomethines, o -oxy(mercapto) derivatives of azoles and azines] and heteroaromatic ligands are generalized and systematized. It is shown that, besides the common β-diketonates, aldiminates, phenolates and mercaptophenolates structures, these complex compounds exhibit less-common modes of coordination. Five- and six-membered heterocycles form σ- as well as π-complexes.

Five-and Six-Membered Heteroaromatic Compounds as σ and π Ligands

Publisher Summary This chapter discusses the role of five- and six-membered heteroaromatic compounds as σ and π ligands. It also provides an overview of the multitude of structural types that can arise when heterocycles are used as ligands in organometallic derivatives. They are flexible models for the problem of competitive coordination of the hard and soft acids with the nonconjugated donor sites. They have great industrial importance in catalytic and other processes. In the chapter, the interaction of metals with the donor sites of the heteroaromatic ligands, including heteroatoms and the π-system of the heteroring is focused. They are classified as ambidentate σ and π - donor ligands and may form two types of complex compounds: the common σ and the less common π complexes. Synthetic methods for the preparation of coordination compounds of heterocycles are (1) the direct interaction of components, (2) ligand exchange, (3) the synthesis of hetarene complexes from the zero-valent metals, and (4) the synthesis of hetarene metal chelates. The basic method of synthesis is the direct interaction of ligands and metal species. Electrosynthesis is widely applied for the preparation of hetarene chelates. Donor atoms (E) and aromatic rings form the basis for the ability of heteroaromatic ligands to form complex compounds with the localization of the coordination bond.

Chapter 5 Hetarylazomethine Metal Complexes

Publisher Summary This chapter discusses hetarylazomethine metal complexe. This reactivity pattern is illustrated by the interaction of the aforementioned metal sources with cyclic and acyclic azomethines. Complexes of acyclic azomethines involve chelates of Schiff bases, b-aminovinylketones, and b-aminovinylimines containing heterocyclic moieties. In the multinuclear coordination compounds under this chapter, the heterocyclic frameworks play the role of the aldehyde, amine, and/or adduct-forming constituents. In the oligonuclear structures, heterocycles may also play the role of the intermetal bridges. The data collected in this chapter are generalized and systematized with emphasis on the specified functions in the structure of azomethine ligands and heterocyclic frameworks.

Organometallic compounds of furan, thiophene, and their benzannulated derivatives

Publisher Summary This chapter reviews that Furan is typically ŋ 1 (C) coordinated in a series of organometallic compounds. However, it is its ŋ 2 (C=C) coordination that opened a perspective toward a broad series of derivatized furans. It can be a bridging ligand forming ŋ 1 (C): ŋ 2 (C=C) bridges. It enters into ring opening reactions. However, the intrinsic ŋ5-donor function of π-excessive heterocycles is suppressed and the data on its existence are still controversial. It discusses that benzannulated furans are coordinated, preferentially at the aromatic ring (ŋ 6 -mode). It also reviews that a wide range of coordination modes attests to the versatility of thiophene ligands. There are ŋ 5 -complexes and some of them can be reduced to the ŋ 4 -species. In the latter, the nucleophilicity of the sulfur atom is greatly enhanced, thereby making this group of organometallic compounds a source of the various bridging coordination modes or remarkable ring opening reactions. The ŋ 2 -coordinated thiophenes also contain a highly activated heterocycle that can be derivatized or ring-opened. The ŋ 1 (C) pattern is widespread, but ŋ 1 (S) species are scarce if not included in the composition of a bridge. There are several pathways for direct ring opening. In addition, the μ-ŋ 2 , ŋ 1 and m-ŋ 2 , ŋ 2 modes of binding organometallic frameworks were observed.

Organometallic Complexes of Phosphinopyridines and Related Ligands

Publisher Summary This chapter focuses on organometallic complexes of phosphinopyridines and its related ligands. An important and broad class of chelating ligands, it comprises of phosphinopyridines and related compounds, including bis (phosphino)pyridines, bis- and tris-pyridyl phosphines, pyridyl phosphinooxides (selenides), pyridylphosphinoalkanes, P,N- and P,O- (P,S- and P,Se-) forms of various nature. The chapter discusses all these types of complexes. 2,6-Bis(diphenylphosphino)pyridine is the basis of the organometallic ligand prepared from the pyridine derivative and [Fe(CO) 5 ] with sodium hydroxide in n-butanol. Bis(2-pyridyl)phosphine with trimethyl aluminum gives [Me 3 Al (m-C 5 H 4 N)(PC 5 H 4 N) 2 ] and on deprotonation, phosphide [Me 3 Al (m-C 5 H 4 N)P]. 2,6-Lutidine-functionalized bis(phosphoranimine) with [Pb(N (SiMe 3 ) 2 ) 2 Et 2 O] affords 1,3-diplumbacyclobutane. Bis(phosphino)pyridines are typically P,P-coordinated initially. However, subsequently, they form various bridges in which pyridine heteroatoms may be fully involved, partially involved, or not involved, as polynuclear complexes. Also Bis- and tris-pyridyl phosphines often initiate P-coordination.

Chapter 3 Organometallic Complexes of Polypyridine Ligands V: Their Analogues, and N,O(S)-Chelating Pyridines

Publisher Summary This chapter focuses on the organometallic chemistry of Polypyridine ligands and covers some illustrations mainly on organocopper and organogold compounds, complexes of the rare earth elements, and organometallic chemistry of pyridylphosphinines and biphosphinines. This chapter also deals with the organometallic derivatives of the N,O(S)-chelating pyridines. The chapter provides an overview of coordination situations and shows that the materials can be grouped by metals, starting from Nontransition metal derivatives, and then sequentially across the groups of transition metals. The chapter concludes that late transition metal complexes of polypyridines are rare. Rare earth metals tend to transform polypyridines into radical-anion or dianion forms, or even structurally modify them by activation.

Organometallic Complexes of Pyridyl Schiff Bases

Abstract Organometallic complexes of pyridyl Schiff bases including pyridylimines, 2,6-diiminopyridines, pyridyl oximes, hydrazines, hydrazones, thiosemicarbazones, dithiocarbazates and related ligands are reviewed. Material on their synthesis and coordination modes is placed in a sequence from nontransition to late transition metals and lanthanides. The role of the discussed compounds in catalysis, materials chemistry, and microbiology is highlighted.

GC–MS evaluation of Cymbopogon citratus (DC) Stapf oil obtained using modified hydrodistillation and microwave extraction methods

Bioactive compounds of Cymbopogon citratus essential oil, using different media have been tentatively identified with the aid of gas chromatography-mass spectrometry (GC-MS). Hydrodistillation was complemented using weakly acidic and alkaline media for the oil extraction. Solvent-free microwave extraction (SFME) was also used. Analyses of the oils revealed the presence of 7, 16, 22, and 15 compounds in the water-distilled (WD), microwave-distilled (MD), acid-distilled (AD), and base-distilled (BD), essential oils, respectively. Total yield of the volatile fractions was 0.73%, 0.64%, 0.70%, and 0.45%, respectively. Citral was found to be the major component, the base extraction having the highest content. This was followed by 2-isopropenyl-5-methylhex-4-enal, p-cymene, and 2-thujene. The antimicrobial, antibacterial, and antioxidant activities and assessment of medicinal/nutritional uses of the essential oils are subjects of future studies.

Organometallic Chemistry of Polypyridine Ligands I

Publisher Summary The chapter describes the organometallic chemistry of polypyridine ligands with non-transition and early transition metals, and manganese group metals. Organometallic compounds of polypyridine ligands with iron group metals attracted attention due to their unique photochemical and electrochemical properties, ability to form molecular assemblies and nanocrystallites, and to catalyze photochemical and electrochemical reduction of carbon dioxide. The chapter discusses the organoiron, organoruthenium, and organoosmium complexes of polypyridine ligands. Emphasis is on the synthetic and coordination aspects, as well as reactivity. The organoiron, organoruthenium, and organoosmium complexes includes mono-polypyridine complexes; bis-polypyridine complexes; cyclometalation; dinuclear complexes; polynuclear complexes and clusters; 4,4’-bipyridine complexes; polypyridylphosphines; and catalytic aspects. Polypyridine complexes of the iron group typically contain chelated ligands that occur in different variations in the mononuclear complexes with one or two such ligands. The organoruthenium and organoosmium compounds of polypyridine ligands offer alternative coordination modes of these ligands.

Organometallic Complexes of Pyridines and Benzannulated Pyridines

Publisher Summary This chapter discusses the organometallic complexes of pyridines and benzannulated pyridines.The general trends in the coordination modes of the five-membered heterocycles are analyzed in the chapter. Trends in the coordination chemistry of variously substituted pyridines follow from the analysis of the modes of their protonation and molecular complex formation; the nature of pyridyl and quinolyl molecules, ions, and radicals; and those for acridine. The complexes of pyridines with non-transition and early transition elements are discussed in the chapter. Complexes of pyridines with chromium group derivatives involves common coordination modes and η 6 -(π)-coordination mode. The optimal way for their synthesis is to start with the pyridine ligands containing bulky alkyl or silyl substituents in the ortho positions of the heteroring. The chapter also discusses the complexes of pyridines with manganese, iron, cobalt, and nickel group derivatives. The chemical and photochemical properties of the η 1 (N)-coordinated and variously substituted Group VI and VII carbonyl derivatives as well as their analogues are also reviewed in the chapter. Organometallic chemistry in the cobalt group is entirely a list of various η 1 (N) coordinated species.