Group 13 elements boron

The most important results of the complexes (CO)4Fe-ECp can be summarized as follows. The Fe-B bond between iron and the lightest group-13 element boron has a significantly higher electrostatic (61.6%) than covalent character (38.4%). The covalent contributions to the Fe-E bonds increase for the heavier group-13 elements E where it becomes as large as the electrostatic contribution. The covalent bonding comes mainly from the Fe <— ECp a-donation. The contribution of the Fe ECp Tr-backdonation is much smaller, i.e. < 20% of the total term. 

In the previous chapter we described the special chemistry of sulfur, and you have previously met that of phosphorus. These two elements may be thought of as analogues of oxygen and nitrogen but many reactions are possible with S and P that are quite impossible with O and N. This chapter will concentrate on the organic chemistry of three other main group elements boron, which is unusual in this context because it is a first row element, and silicon and tin, which are in the same group as... 

Fig. 8.3 Warren R. Roper (born in 1938) studied chemistry at the University of Canterbury in Christchurch, New Zealand, and completed his Ph.D. in 1963 under the supervision of Cuthbert J. Wilkins. He then undertook postdoctoral research with James P. Collman at the University of North Carolina at Chapel Hill in the US, and returned to New Zealand as Lecturer in Chemistry at the University of Auckland in 1966. In 1984, he was appointed Professor of Chemistry at the University of Auckland and became Research Professor of Chemistry at the same institution in 1999. His research interests are widespread with the emphasis on synthetic and structural inorganic and organometallic chemistry. Special topics have been low oxidation state platinum group metal complexes, oxidative addition reactions, migratory insertion reactions, metal-carbon multiple bonds, metallabenzenoids and more recently compounds with bonds between platinum group metals and the main group elements boron, silicon, and tin. His achievements were recognized by the Royal Society of Chemistry through the Organometallic Chemistry Award and the Centenary Lectureship. He was elected a Fellow of the Royal Society of New Zealand and of the Royal Society London, and was awarded the degree Doctor of Science (honoris causa) by the University of Canterbury in 1999 (photo by courtesy from W. R. R.)...

Third Group. Elemental boron is present in polymeric form in the solid state. With the boranes (borohydrides), main-chain bonds are only partly B—B they are also partly B—H—B in character. 

In Group III, boron, having no available d orbitals, is unable to fill its outer quantum level above eight and hence has a maximum covalency of 4. Other Group 111 elements, however, are able to form more than four covalent bonds, the number depending partly on the nature of the attached atoms or groups. 

Instead of depending on the thermally generated carriers just described (intrinsic conduction), it is also possible to deUberately incorporate various impurity atoms into the sihcon lattice that ionize at relatively low temperatures and provide either free holes or electrons. In particular. Group 13 (IIIA) elements n-type dopants) supply electrons and Group 15 (VA) elements (p-type dopants) supply holes. Over the normal doping range, one impurity atom supphes one hole or one electron. Of these elements, boron (p-type), and phosphoms, arsenic, and antimony (n-type) are most commonly used. When... 

Boranes also form derivatives ia which main group elements occupy a bridging position between two boron atoms, rather than a polyhedral vertex. An extensively studied system is -R MB Hg, where R = H, CH, C2H3, halogen, and M = Si, Ge, Sn, Pb (185). The stmcture of l-Br- J.-[(CH3)3Si]-B3H2... 

Heteroboranes, compounds where one or more of the cage borons are replaced by a main group element (33), are not themselves commercially available. However, carborane sdoxanes containing > -carborane [16986-21 -6], C2H22B2Q, are available under the trade name of Dexsd for the stationary phase in gas—Hquid chromotography (qv) (34). The carborane, l,7-dicarba-c/(9j (9-dodecaborane(10) (35), contributes enhanced chemical and thermal stabiHty to the sdoxane polymer. 

Covalent fluondes of group 3 and group 5 elements (boron, tin, phosphorus, antimony, etc ) are widely used m organic synthesis as strong Lewis acids Boron trifluoride etherate is one of the most common reagents used to catalyze many organic reactions. A representative example is its recent application as a catalyst in the cycloadditions of 2-aza-l,3-dienes with different dienophiles [14] Boron trifluoride etherate and other fluonnated Lewis acids are effective activators of the... 

The hydrides of the later main-group elements present few problems of classification and are best discussed during the detailed treatment of the individual elements. Many of these hydrides are covalent, molecular species, though association via H bonding sometimes occurs, as already noted (p. 53). Catenation flourishes in Group 14 and the complexities of the boron hydrides merit special attention (p. 151). The hydrides of aluminium, gallium, zinc (and beryllium) tend to be more extensively associated via M-H-M bonds, but their characterization and detailed structural elucidation has proved extremely difficult. 

The Group 13 metals differ sharply from the non-metallic element boron both in their greater chemical reactivity at moderate temperatures and in their well-defined cationic chemistry for aqueous solutions. The absence of a range of... 

Cluster and cage structures are widespread in the chemistry of main group elements, being particularly extensive in the case of boron (Chap. 6). For transition elements the principal... 

As is typical of second-row elements, boron has properties that distinguish it from the other elements in Group 13 as well as from the rest of the metalloids. The unique features of boron chemistry can be attributed to... 

Two approaches have been used in the synthesis of these types of compounds. Small boron-phosphorus ring compounds can serve as building blocks, and addition and elimination reactions with other main group elements can then extend the cage structure (see Schemes 23 and 24, Section 12.12.6.4.5). Alternatively, an unsaturated carbenoid fragment can be added to the bicyclic fragment as illustrated in Scheme 31 <1998IC490>. 

All the elements discussed so far, except hydrogen, have been metals. Group III contains one element, boron, that is not a metal. The elements of Group III are ... 

Boron clusters are the best understood clusters of the main group elements [7,8]. Today we are capable of explaining and predicting their geometric structures and... 

Gabel, D. Endo, Y. Boron Clusters in Medicinal Applications. In Molecular Clusters of the Main Group Elements-, Driess, M., Noth, H., Eds. Wiley-VCH Weinheim, 2004 pp 95-125. 

The main group duster chemistry discussed in this book can be considered to originate from two important, but apparently unrelated developments in inorganic chemistry in the 1930s. The first was the identification of the neutral boron hydrides by Stock [1]. The second was the observation by Zintl and co-workers [2-5] of anionic clusters formed from potentiometric titrations of post-transition metals (i.e., heavy main group elements) with sodium in liquid ammonia. 

The polyhedral boranes and carboranes discussed above may be regarded as boron clusters in which the single external orbital of each vertex atom helps to bind an external hydrogen or other monovalent atom or group. Post-transition main group elements are known to form clusters without external ligands bound to the vertex atoms. Such species are called bare metal clusters for convenience. Anionic bare metal clusters were first observed by Zintl and co-workers in the 1930s [2-5], The first evidence for anionic clusters of post-transition metals such as tin, lead, antimony, and bismuth was obtained by potentiometric titrations with alkali metals in liquid ammonia. Consequently, such anionic post-transition metal clusters are often called Zintl phases. 

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