Borane shape

Using the dodecahydropentaboratefl -) ion in reaction with (Ph jPljCuCl results in a change in the borane shape, leading to a tetraborane derivative ... 

In this case the covalency of boron is brought up to four because the donor molecule supplies the necessary electrons. The adduct formed, trimethylamine-borane, is a stable white solid. Other compounds of a similar kind are known, all derived from the simple structure H3N -> BH3. This compound is isoelectronic with ethane, i.e. it contains the same number of electrons and has the same shape. 

For the amino-borane dehydrocoupling using [Rh(l,5-cod)(p-Cl)]2 as starting catalyst, an induction period and a sigmoid-shaped kinetic curve (plot of substrate conversion versus time) were also observed, consistent with metal-particle formation. But, for Ph2PH BH3... 

The shapes of the deltahedra in the apparently hypoelectronic clusters of the heavier group 13 metals bear an interesting relationship to their electron counts. All such hypoelectronic deltahedra can be derived formally from the standard closo-borane structures (Figure 1-2) by flattening one or more vertices towards... 

Wade electron counting rules borane-like cluster nomenclature. On initially studying compounds such as boranes (boron hydrides) and carboranes (or carbaboranes boron—carbon hydrides), Wade (1976) proposed a number of rules which have then been extended to several compounds and which relate the number of skeletal electrons with the structure of deltahedral clusters. A polyhedron which has only A-shaped, that is triangular, faces is also called a deltahedron. 

In the hands of Lipscomb and others 76,143, 145a, 153,189, 190), such localized bond schemes, particularly when obtained via self-consistent field (SCF) molecular orbital (MO) treatments, have proved particularly valuable for rationalizing the shapes and interatomic distances and estimating the charge distribution in many higher boranes. 

So far, in this survey, attention has been focused on the shapes and sizes of cluster species, their preparation and reactions having been mentioned only in passing. However, the close link between the shapes of borane-type clusters and the numbers of bonding electrons they contain makes it possible to predict the likely outcome of reactions that may change these numbers. 

The borane technique, described earlier for In203 preparation, was also used to deposit ZnO on Sn/Pd-activated glass using a solution of Zn(N03)2 and dimethylamine borane at 50°C [59], The films were randomly oriented polycrys-talhne ZnO, and the crystals were hexagonal shaped, with a typical size of 0.2 jim, at moderately high dimethylamine borane concentrations at low concentrations, the grains were smaller and more irregular. 

Bochmann has also produced a novel class of large dianionic borates XV based on the non-labile fefra-cyano Ni and Pd(II) metallates [K12 M(CN) i 2. 215a The metals in these WCAs are strictly square planar and as such the anion assumes a flat rather than spherical shape, with a torus of fluorination on the periphery of the plane. The bis-trityl salts of these dianions afford catalysts that are not as productive as those formed from the XIV class (X = CN), although they are still much more active than borane activated catalysts. The lower activity was attributed to the inherently greater cation/anion attraction in a monocation/dianion pair. 

Many of these polyhedral shapes will be important when nomenclating boranes. (See Chapter 5). 

Plastic crystals are almost crystalline solids, except that the molecular constituents in the primitive unit cell rotate freely in place this confers to them a certain degree of plasticity. Examples are certain cage-shaped boranes (e.g., B10H14), carboranes (e.g., Bi0C2Hi2), and buckminsterfullerene (Ceo) at room temperature. These plastic crystals usually order into normal crystalline solids at low temperatures. 

Diborane (B2H6) is a dimer composed of two molecules of borane (BH3). The bonding in diborane is unconventional, using three-centered (banana-shaped) bonds with protons in the middle of them. Diborane is in equilibrium with a small amount of borane (BH3), a strong Lewis acid with only six valence electrons. 

In the First Edition of Regular Polytopes, Coxeter stated, ... the chief reason for studying regular polyhedra is still the same as in the times of the Pythagoreans, namely, that their symmetrical shapes appeal to one s artistic sense [23], The success of modem molecular chemistry does not diminish the validity of this statement. On the contrary. There is no doubt that aesthetic appeal has much contributed to the rapid development of what could be termed polyhedral chemistry. One of the pioneers in the area of polyhedral borane chemistry, Earl Muetterties, movingly described his attraction to the chemistry of boron hydrides, comparing it to M. C. Escher s devotion to periodic drawings [24], Muetterties words are quoted here [25] ... 

The diagonal lines connecting clusters of equal nuclearity reveal another important relationship - as the number of cluster electron pairs increases in a step-wise fashion the cluster opens up into a net and then a web. As was pointed out in Chapter 1, this is a recurring motif - the more electron rich, the more open the structure. One can continue. Addition of three pairs of electrons to a c/oso-borane generates an even more open shape albeit a less well-accepted nomenclature. The... 

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