Borane , compounds with derivatives

Although the allylation reaction is formally analogous to the addition of allylic boranes to carbonyl derivatives, it does not normally occur through a cyclic TS. This is because, in contrast to the boranes, the silicon in allylic silanes has little Lewis acid character and does not coordinate at the carbonyl oxygen. The stereochemistry of addition of allylic silanes to carbonyl compounds is consistent with an acyclic TS. The -stereoisomer of 2-butenyl(trimethyl)silane gives nearly exclusively the product in... 

The material reviewed in this Chapter hitherto has focused on metallacarboranes in which the metal atom is a vertex in an icosahedral cage framework. Until recently, monocarbollide metal compounds with core structures other than 12 vertexes were very rare since suitable carborane precursors were not readily available." However, Brellochs recent development of the reaction of decaborane with aldehydes to give 10-vertex monocarboranes permits a considerable expansion in this area of boron cluster chemistry. As a consequence, several intermediate-sized monocarboranes are now easily accessible and we have recently begun to exploit the opportunities that these present. In particular, we have focused thus far on complexes derived from the C-phenyl-substituted species [6-Ph- zJo-6-CBgHii] It is clear from these initial studies that a wealth of new chemistry remains to be discovered in this area, not only from among the metal derivatives of PhCBg car-boranes such as those discussed in this section, but also in the metal complexes of other newly available carboranes. 

Gmelin Handbook Volumes on Boron and its Compounds (a) Main Volume (1926) (b) Supplement vol. 1 (1954) (c) Compounds 8 (NSSV 33), The tetrahydroborate ion and its derivatives (1976) (d) Compounds 9 (NSSV 34), Boron-halogen compounds , Part 1 (1976) (e) Compounds 10 (NSSV 37), Boron compounds with coordination number 4 (1976) (f) Compounds 15 (NSSV 46), Amine-boranes (1977) (g) Compounds 19 (NSSV 53), Boron-halogen compounds , Part 2 (1978) (h) Supplement Volumes (1980-82), Springer-Verlag, Berlin. 

Because they serve as versatile starting materials for a variety of other boranes, the dihalo boranes, particularly the fluoro and chloro derivatives, are the most important members of this class of compounds. Their chemistry, along with other pentafluor-ophenyl boron halides, has been reviewed recently from a personal perspective by Chi vers,15 whose PhD thesis described early explorations into the chemistry of these compounds. Most of the known literature on these compounds deals with pentafluor-ophenyl compounds, but the chemistry is likely extendable to other compounds with different AiF groups. 

Thus ailylboration of carbonyl compounds with B-allylic derivatives of 9-BBN, followed by transesterification with ethanolamine, provides a simple, convenient method for the synthesis of homoallylic alcohols It has been reported that enantiomerically enriched allylic boranes provide homoallylic alcohols with high degree of enantio- and diastereoselectivity. The scheme is illustrated in Eqs. 48 and 49... 

The state of the art of reductions with metal hydrides a decade ago was the subject of comprehensive reviews. A detailed survey of reductions of carbonyl compounds with alkali and alkaline earth metal hydrides, borane and derivatives, alane and derivatives, metal borohydrides, metal aluminohydrides, silanes, stannanes and transition metal hydrides was compiled. The properties, preparation and applications of each reagent were discussed together with methods for their determination, handling techniques... 

The generalization of the residual dipolar couplings for arbitrary quadrupolar/Zeeman ratios has been presented.The predictions of the essentially numerical treatment compare well with previously derived high-field analytical models, as well as with experimental solid state NMR spectra observed in a borane compound possessing a spin pair. An alter-... 

Analogs of monoisopinocampheylborane have been prepared in the search for monoalkylbo-l anes with a higher steric requirement than the parent compound. These boranes, which are derived from a-pinene, contain 2-ethyl-, 2-phenyl- or 2-(l,3-dithianylmethyl)apopinene as the alkyl unit86 88. 

The adherence to close-packed structural arrangements lends support to the idea that these compounds can be used as models for metal surface chemistry—with respect to chemisorbed species and their mobility and reactions of substrates on these surfaces. It also indicates a marked deviation from the behavior of boranes and their derivatives. Structures based upon some polyhedra favored by boron, such as the pentagonal bipyramid, triangulated dodecahedron, and especially the icosahedron, are absent so far in metal-carbonyl cluster chemistry. In this connection, it has been mentioned that [M(CO)3],g compounds should be the closest analogs to On skeletal electron counting... 

Another route to metalloborane derivatives with metal-boron single bonds is the reaction of certain cationic transition metal compounds with borane anions (20). Addition of solid [(C5H5)Fe(CO)2(cyclohexene)]-PFe to an ether solution of NaBioHia at room temperature formed yellow 6-[(C5Hr>)Fe(CO)2]BioHi3 in 50% yield. The pattern of the B NMR spectrum of this derivative was very similar to other 6-substituted deca-borane derivatives, and on this basis it was proposed that an iron-boron single bond had been formed at B(6) of the decaborane cage as illus-... 

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

Arylboronic and arylborinic acids have been produced from the hydrolysis of intermediates in the reactions of aryl-tin and aryl-lead compounds with diborane. The preparation of di[bis(trimethylsilyl)methyl]chloroborane from the reaction of bis(trimethylsilyl)methyl-lithium and boron trichloride has been published. A new reagent for O-ethylboranediylation, ethylbis-(2-isopropyl-6-methyl-4-pyrimidinyloxy)borane (3) has been synthesized and used to prepare O-ethyl-boranediyl derivatives of alcohols, phenols, alkanediols, D-mannitol, and l-arabinose. Borane-methyl sulphide reportedly reacts smoothly with primary, secondary, and tertiary alcohols and phenols to provide a general and convenient synthesis of borate esters. ... 

Liquid crystals are also an important class of compounds they have become an inseparable part of our day-to-day lives through their presence in almost all display devices. They are mainly composed of an anisotropic rigid core and a terminal alkyl substituent. Several derivatives of closo-boranes, along with a metallacarbollide, form liquid crystals, and many more clusters are under investigation. Ongoing research in this field should provide us with a better understanding of the structure-property relationships of similar type of materials. 

The development 0/ the chemistry of boranes continues with outstanding results It has produced a convenient route to the less stable, terminally unsaturated compounds from the more stable, highly substituted ethylene derivatives , a facile procedure for the asymmetric synthesis of alcohols of high optical purity , and a... 

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