Recent Synthetic, Structural

It is apparent from the above discussions that recent synthetic, structural, bonding, and reactivity studies have established transition metal containing metallacarborane complexes as an important area of study in organometallic chemistry. 

RECENT SYNTHETIC, STRUCTURAL, SPECTROSCOPIC, AND THEORETICAL STUDIES ON MOLECULAR PHOSPHORUS OXIDES AND OXIDE SULFIDES... 

To rapidly construct complex structures, a recent synthetic strategy uses the Diels-Alder cycloaddition in sequence with another Diels-Alder reaction or with other reactions without isolating the intermediates (domino, tandem, cascade, consecutive, etc., reactions) [4-6]. Scheme 1.2 illustrates some examples. 

The syntheses and spectroscopic and electrochemical characterization of the rhodium and iridium porphyrin complexes (Por)IVI(R) and (Por)M(R)(L) have been summarized in three review articles.The classical syntheses involve Rh(Por)X with RLi or RMgBr, and [Rh(Por) with RX. In addition, reactions of the rhodium and iridium dimers have led to a wide variety of rhodium a-bonded complexes. For example, Rh(OEP)]2 reacts with benzyl bromide to give benzyl rhodium complexes, and with monosubstituted alkenes and alkynes to give a-alkyl and fT-vinyl products, respectively. More recent synthetic methods are summarized below. Although the development of iridium porphyrin chemistry has lagged behind that of rhodium, there have been few surprises and reactions of [IrfPorih and lr(Por)H parallel those of the rhodium congeners quite closely.Selected structural data for rr-bonded rhodium and iridium porphyrin complexes are collected in Table VI, and several examples are shown in Fig. 7. ... 

Production of all naturally occurring polymers in vivo is catalyzed by enzymes. Polymerizations catalyzed by an enzyme ( enzymatic polymerizations ) have received much attention as new methodology [6-11], since in recent years structural variation of synthetic targets on polymers has begun to develop highly selective polymerizations for the increasing demands in the production of various functional polymers in material science. So far, in vitro syntheses of not only biopolymers but also non-natural synthetic polymers through enzymatic catalysis have been achieved [6-11]. 

Finally, with regard to synthetic structurally unrelated PAF antagonists, it has been recently reported that a series of 5-aryl-2,3-dihydroimidazo[2,l-r/]iso-quinolines, as represented by (24), display PAF antagonistic properties [175]. However, the effectiveness of these compounds in inhibiting the binding of [3H]PAF to its various receptors remains to be reported. 

In this section, the literature about Diels-Alder reactions will be presented in a conceptual and illustrative way. After a profound introduction dealing with the development of mechanistic understanding of the Diels-Alder reaction, some interesting recent synthetic developments and applications will be presented. The reaction types and fields of interest are structured in such a way that they can be easily linked to ongoing research from the past ten years. Special attention will be paid to the application of chiral auxiliaries and chiral Lewis acids in asymmetric Diels-Alder reactions. 

Another example of cation control over borate structure is found in the recently elucidated structure of the industrially important synthetic zinc borate Zn[B304(0H)3] [2 ZnO 3 B3O3 3 H2O], shown in Fig. 12 [45]. This compound has a polytriborate structure reminiscent of that found in colemanite (Fig. 7a) [29]. Yet, due to the different coordination requirements of the Ca and Zn cations, the anionic polyborate chains in these two compounds have different spatial arrangements. In the case of colemanite, parallel triborate chains are linked together into extended sheets by coordination with interstitial (and H2O). These sheets are bound... 

As mentioned in the introduction, recent synthetic developments now allow access to the 1,2-thiazine structure via disconnection type C (Figure 23). This process can be accomplished by a Friedel-Crafts-type cyclization of sulfamoyl chlorides. The initial report of this reaction utilized a stoichometric amount of aluminium chloride promoter <19920PP463>. Recently, however, A -ethyl phenethylsulfamoyl chloride 214 was shown to undergo Friedel-Crafts cyclization to form sultam 215 with just a catalytic amount of In(OTf)3 (Equation 33) <2002SL1928>. 

A recent review on abiological iron-sulfur clusters should be the primary entry reference to anyone wishing to gain information on this wide field [2]. Indeed, Ogino et al. provide a comprehensive source of data, of synthetic, structural, spectroscopic, and electrochemical nature, on many synthetic iron-sulfur clusters. The electrochemical properties of Roussin s black anion [3] have been investigated... 

A more recent synthetic concept is based on the reaction of diethylamino-sub-stituted silyl-lithium compounds with triflate derivatives of silanes or oligosi-lanes. It leads to stepwise lengthening of Si-Si chains which can be used to assemble polymeric structures [74]. 

Recent reviews (1997MI1,1997CR2267, 03ACI5134, 02PISC311) report on the chemistry and applications of expanded porphyrins. We highlight the most recent synthetic routes and chemical characteristics of only pyr-rolic systems, presented in the order of increasing structural complexity. Expanded systems having heterocyclic species other than pyrrole have been avoided. 

Recent synthetic and spectroscopic work has concentrated on the study of structurally related linear-chain palladium complexes (7, 8), on the possibility of synthesising related nickel complexes, and on the study of mixed-metal mixed-valence complexes of the sort... 

In heteroporphyrins, at least one of the pyrrolic nitrogens is replaced with a different atom, usually a chalcogen. Examples of pertinent structures are given in Fig. 26. The chemistry of heteroporphyrins was reviewed in detail in [6, 201, 202], Here we will highlight the most characteristic features of aromaticity and tautomerism in heteroporphyrins, with an emphasis on the more recent synthetic advances in the field. 

A review of the recent synthetic progress on ozonides at the Karlsruhe University has appeared <1997MI145>. Two older reviews on the structure of the reactive intermediates 1-3 involved in these reactions deserve to be mentioned Carbonyl oxides zwitterions or diradicals <1990AGE344> and Preparation, properties, and reactions of carbonyl oxides < 1991CRV335>. Reviews on cyclic peroxides < 1995COS225> and dioxiranes < 1989CRV1187> are also relevant. 

The depth profiles of the two isoprenoid thiophenes (Figure 16a-b) are similar. Both profiles show maxima (at 56m and 83m) in Facies A. Recently, the structures of both C26 isoprenoid thiophenes have been unambiguously elucidated by coinjection experiments and comparison of mass spectral data with synthetic standards (45). The first and second eluting isomers (XVIII and XIX respectively, Figure 15) possess a regular (2,6,10,14,18-pentamethylheneicosane) and an irregular (2,6,10,14,19-... 

The use of surfactants in the food industry has been known for centuries. Naturally occurring surfactants such as lecithin from egg yolk or soybean and various proteins from milk are used for the preparation of many food products, such as mayonnaise, salad creams, dressing, and desserts. Polar lipids such as monoglycerides have been introduced as emulsifiers for food products. More recently, synthetic surfactants such as sorbitan esters (Spans) and their ethoxylates (Tweens), sucrose esters, have been used in food emulsions. It should be mentioned that the structures of many food emulsions is complex, and in... 

Recent synthetic studies have shown that carborane skeletons larger than the icosahedron can be constructed by the insertion of additional BH units. The reaction scheme and structure motifs of these carborane species are shown in Fig. 13.4.15. Treatment of 1,2-(CH2)3-1,2-C2BioHio (1) with excess lithium metal in THF at room temperature gave [(CH2)3-l,2-C2BioHio][Li4(THF)s] 2 (2) in 85% yield. X-ray analysis showed that, in the crystalline state, both the hexagonal and pentagonal faces of the carbon-atoms-adjacent arachno-carborane tetra-anion in 2 are capped by lithium ions, which may in principle be substituted by BH groups. 

Elvirol (51), a metabolite of Elvira biflora, represents a structural type which could be derived in nature by ring cleavage of sesquicarane precursor [c/. (50)]. Recent synthetic routes25,26 to this sesquiterpenoid are oulined in Schemes 9 and 10. 

Recent synthetic studies (Scheme 34) have shown that the seco-amorphane structure (332) previously assigned to humbertiol is incorrect.139... 

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