Boron Compounds containing Metals

Boron Compounds containing Metals.—K number of complexes of di- and 

Open-chain vinylboranes can also act as ligands in the formation of metal complexes. An example is the preparation of compound (36) by the photochemical reaction of iron pentacarbonyl with chlorodivinylborane. Various B-N compounds can be compared to alkenes in their abilities to complex to transition metals. Several new complexes with cyclic diborylethene ligands have been prepared, for example tetradecker sandwich complexes of Co and Fe from (37), a tricarbonylcobalt complex from (38), and a cyclopenta-dienylcobalt complex from (39).  

Pentaphenylborole, a formally anti-aromatic compound that can be prepared by reaction of 1,1-dibutyl-2,3,4,5-tetraphenylstannole with dichloro(phenyl)-borane, is reduced by potassium to the formally aromatic dianion, and acts as a four-electron ligand in forming transition-metal complexes.  

---

Elemental boron is a refractory material that is usually isolated either as a shiny black crystalline solid or a softer, browner, more impure amorphous solid. Reduction of readily available boron compounds containing boron oxygen bonds to elemental boron is energy intensive and costly. This has limited the extent of conunercial use of this material. Many related refractory boron compounds have been prepared and characterized including metal borides, boron carbides, boron nitrides, and various boron metal alloys. These refractory materials and elemental boron are also discussed in some detail in the article Borides Solid-state Chemistry. Other general references are available on elemental boron and other refractory boron compounds. " ... 

Noth and co-workershave considered the B shifts of several metal derivatives of bis(dimethlamino)boranes these shifts are, for convenience of comparison, shown in Table XIV. Noth and Schmid have discussed co-ordination compounds containing metal-boron bonds and the B shifts are also reproduced in Table XIV. 

Organosilylboron compounds are prepared by the reaction of haloorganosilanes with either boron compounds containing halogen and the Na/K alloy, or an alkali metal boride (Scheme 3.28) ... 

Compounds containing fluorine and chlorine are also donors to BF3. Aqueous fluoroboric acid and the tetrafluoroborates of metals, nonmetals, and organic radicals represent a large class of compounds in which the fluoride ion is coordinating with trifluoroborane. Representative examples of these compounds are given in Table 5. Coordination compounds of boron trifluoride with the chlorides of sodium, aluminum, iron, copper, 2inc, tin, and lead have been indicated (53) they are probably chlorotrifluoroborates. 

Next to Cr C2, TiC is the principal component for heat and oxidation-resistant cemented carbides. TiC-based boats, containing aluminum nitride, AIN, boron nitride, BN, and titanium boride, TiB2, have been found satisfactory for the evaporation of metals (see Boron compounds, refractory boron compounds Nitrides). 

Typically, Be-containing alloys and intermetallic phases have been prepared in beryllia or alumina crucibles Mg-containing products have been synthesized in graphite, magnesia or alumina crucibles. Alloys and compounds containing Ca, Sr and Ba have been synthesized in alumina , boron nitride, zircon, molybdenum, iron , or steel crucibles. Both zircon and molybdenum are satisfactory only for alloys with low group-IIA metal content and are replaced by boron nitride and iron, respectively, for group-IIA metal-rich systems . Crucibles are sealed in silica, quartz, iron or steel vessels, usually under either vacuum or purified inert cover gas in a few cases, the samples were melted under a halide flux . 

The boron-capped transition metals macrobicyclic clathrochelates also belong to the family of compounds containing a ring-junction boron atom. Their main types 177a-d are shown in Figure 18 and the corresponding references are presented in Table 12. 

Cyclic compounds containing a heavier group 14 element, chalcogens, and a boron are prepared by the reaction of boron dichalcogenolates bearing a bulky substituent with group 14 metal dichlorides (Scheme 2).25... 

Tricoordinated boron compounds (boranes) are coordinatively unsaturated and their chemistry is dominated by reactions in which complexes are formed. These complexes are either neutral molecules (borane complexes), anions (borates) or boron cations. Space limitations mean that little or no attention will be paid to complexes containing several boron atoms and to species of the type L-BH3, [BH,]- and [L2BH2]+ (L = neutral ligand), discussed in detail in several books and reviews. Similarly, little attention will be paid to the plethora of metal borates and the cyclic and polymeric amino- and phosphino-boranes. 

Various neutral and, especially, anionic boron species are well known as ligands in transition metal complexes. In the majority of cases, however, one or more H, N or other basic atom of the boron compounds is coordinated to the transition metal (e.g. Chapters 13.8, 13.6 and 19). In the last 20 years, however, several complexes containing boron-transition metal bonds have been prepared with ligands such as sBX, -BX2 or BX3 (Table 14). 

---