Borane Lewis base adduct

H-D Exchange Reaction of Borane-Lewis Base Adducts by Rhenium Polyhydride Complexes... 

Thus we examined the reactions of borane-Lewis base adducts with rhenium polyhydride complexes to synthesize highly fluxional polyhydride(borane) complexes. However, treatment of several boranes with the rhenium complexes in deuterated solvents resulted in an unexpected reaction H-D exchange between the boranes and solvents. This is the first example of H-D exchange between sp carbon and sp boron, and closely associated with metal-catalyzed deuteration of alkanes. ... 

Studies on the rate of hydroboration of 1-octene by several borane-Lewis base adducts indicate that the mechanism proceeds via prior dissociation of the adduct which is contrary to the direct attack mechanism proposed on the basis of ab initio calculations. Hydroboration of representative alkenes by borinane dimer in n-heptane proceeds through dissociation of the dimer followed by reaction of the monomer and alkene. Borinane shows similar behaviour to 9-BBN, both molecules differing markedly from other common monofunctional reagents. The factors that affect the stereoselectivities achieved by various hydroborating reagents have been investigated theoretically and the analysis developed into a predictive tool. The reduction of ketones and hydroboration of alkenes by catecholborane is catalysed by lithium bromide. 

Tetracoordinate Boron in Pyridine/Borane Lewis Base Adducts... 

In addition to tricoordinate boron which acts as a strong electron acceptor because of its vacant p-orbital, negatively charged electron-donating tetracoordinate boron in two variations, zwitterionic molecules and as pyridine/borane Lewis base adducts, shows interesting nonlinear optical properties. 

Kakizawa T, Kawano Y, Shimoi M. Syntheses and structures of manganese complexes of borane—Lewis base adducts, [CpMn(CO)2(ll -BH3-L)] (L = NMe3, PMes). Organometallics. 2001 20 3211—3213. 

The structures, relative stabilities, and relative Lowry-Bronsted acidities of carboranes and boranes as well as related anions, Lewis base adducts, and heteroelement analogs are rationalized primarily on the basis of rudimentary coordination numbers. The principal factors, in decreasing order of importance, are (a) the various deltahedra and deltahedral fragments, (b) the placement of bridge and endohydrogens, (c) the placement of carbon and other heteroelements, and d) the resulting coordination number of boron. 

In 1971, a note 164) was published favoring the hypothesis that the carboranes, boranes, their isoelectronic anions, Lewis base adducts, and heteroatom-substituted analogs should be viewed as constructed about the vertices of either the most spherical series of triangular-faceted polyhedra (deltahedra) found to be characteristic of the dicarba-cZoao-carboranes (Fig. 1) or, with one lone exception, fragments of the series of deltahedra produced by the successive removal of the highest coordinated vertices that sequentially define the nido and arachno classes. This position was in conflict with the then prevalent shibboleth that all nido and arachno compounds [except B5H9 (I-N5)] had or would prove to have icosahedral fragment structures. 

In the boron compounds so far discussed, electron-deficiency is relieved where possible by the formation of multicentred bonds. In boron-nitrogen compounds, however, boron atoms often share nitrogen lone pairs, as is illustrated by the existence of the well-known Lewis-add-Lewis-base adducts this effect is also demonstrated by the frequent planarity of the QNB skeleton in dimethylaminoborane derivatives. In dimethylaminodichloro-borane, (CH8)2NBCl2, all the heavy atoms are copolanar, and a short B-N bond, 1.379 0.006 A, is observed. The authors suggest that this... 

Theoretical and experimental investigations of Lewis base adducts of boranes with pyridine derivatives with an overall neutral net charge show that they possess large hyperpolarizability values. 

Recently, Manners and co-workers have found another type of reaction, the inorganic process corresponding to Rh-catalysed dehydrocoupling of borane adducts, which is homogeneous or heterogeneous catalysed depending on the substrate, in particular the nature of the Lewis base, phosphine or amine respectively [15]. 

In aprotic solvents that can act as electron pair donors such as ethers, tertiary amines, and sulfides, borane forms Lewis acid-base adducts. 

Group 13/15 compounds have a long-standing history in inorganic chemistry and have been known for almost two centuries. First reports on such compounds go back to 1809, when Gay Lussac synthesized F3B4—NH3,1 the historical prototype of a Lewis acid-base adduct, by reaction of BF3 and NH3. Since this initial study, numerous Lewis acid-base adducts of boranes, alanes, gallanes and indanes MX3, MF13 and MR3 (M = B, Al, Ga, In X = F, Cl, Br, I R = alkyl, aryl) of the type R3M <- ER 3 (E = N, P, As) (Type A) have been synthesized and... 

The reaction between a Lewis acid R3M and a Lewis base ER3 is of fundamental interest in main group chemistry. Synthetic and computational chemists have investigated the influence of both the Lewis acid and the base on the solid state structure and the thermodynamic stability of the corresponding adduct, that is usually expressed in terms of the dissociation enthalpy De. This led to a sophisticated understanding of the nature of dative bonding interactions. In particular, reactions of boranes, alanes and gallanes MR3 with amines and phosphines ER3, typically leading to adducts of the type R3M <— ER3, have been studied.10... 

Steric interactions between bulky substituents such as t-Bu, leading to larger C-E-C bond angles, obviously affect the Lewis basicity caused by the increased -character of the electron lone pair. However, the strength of the Lewis acid-base interaction within an adduct as expressed by its dissociation enthalpy does not necessarily reflect the Lewis acidity and basicity of the pure fragments, because steric (repulsive) interactions between the substituents bound to both central elements may play a contradictory role. In particular, adducts containing small group 13/15 elements are very sensitive to such interactions as was shown for amine-borane and -alane adducts... 

Lithium Salts Based on Heterocyclic Anions. Lithium salts based on organic anions where the formal charge is delocalized throughout substituted heterocyclic moieties were also reported sporadically, which included, for example, lithium 4,5-dicyano-l,2,3-triazolate ° and lithium bis(trifluoro-borane)imidazolide (Lild). ° The former was developed as a salt to be used for polymer electrolytes such as PEO, and no detailed data with respect to electrochemistry were provided, while the latter, which could be viewed as a Lewis acid—base adduct between LiBp4 and a weak organic base, was intended for lithium ion applications (Table 13). 

Borane, BH3, is an avid electron-pair acceptor, having only six valence electrons on boron. Pure borane exists as a dimer in which two hydrogens bridge the borons. In aprotic solvents that can act as electron donors such as ethers, tertiary amines, and sulfides, borane forms Lewis acid-base adducts. 

An interesting recent illustration of the Lewis base behaviour of these cyclic ligands is the formation of a bis-adduct of the pentamer cyclo-(PPh)5 with borane monomer [eqn (11.11)]. ... 

In reactions between Lewis acids and bases such as amines and boranes or boron halides, bulky substituents on one or both species can affect the stability of the acid-base adduct. Perhaps the most straightforward type of effect is simple steric hindrance between substituents on the nitrogen atom and similar large substituents on the boron atom. Figure 9.3 is a diagrammatic sketch of the adduct between molecules of tripropylamine and triethylborane. This phenomenon is known as front or F-... 

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