Boron coordination chemistry

As a result of the systematic application of coordination-chemistry principles, dozens of previously unsuspected stnicture types have been synthesized in which polyhedral boranes or their anions can be considered to act as ligands which donate electron density to metal centres, thereby forming novel metallaboranc elusters, ". Some 40 metals have been found to act as acceptors in this way (see also p. 178). The ideas have been particularly helpful m emphasizing the close interconnection between several previously separated branches of chemistry, notably boron hydride clu.ster chemistry, metallaboranc and metallacarbaborane chemistry (pp. 189-95). organometallic chemistry and metal-metal cluster chemistry. All are now seen to be parts of a coherent whole. 

Iminoboranes, R-N=B-R, are isoelectronic with alkynes and contain 2-coordinate boron their chemistry has recently been review-... 

Nickel atoms in BajNi B form distorted, puckered 3.6.3.6-kagome nets stacked in six layers perpendicular to the c axis. The densely packed framework of trigonal-Ni prisms again result in boron-pair formation, although Ba atoms are too large to be sandwiched between two Ni layers, and only four Ba can be accommodated within six Ni layers. Superconductivity is found for ( a, Sr, Ba)2pt9Bg borides with a structure related to Ba2Ni9Bfi and e o,B2 however, with respect to crystal chemistry and boron coordination, only the subcell is derived so far. 

Analogues of imidazolylidene bearing two adjacent boron atoms in the heterocycle (3) have been synthesized and their coordination chemistry has been studied.16 They were shown to be better er-donors than their classical counterparts. The imidazo[l,5-ajpyridine has been shown to be a modular base for new stable NHCs (4).17 The same platform also allowed the isolation of abnormal NHCs (5) with a mesoionic structure and a strong a-donor character. 

The chemistry of the boron trihalides has been extensively studied. These compounds are strong Lewis acids and form a wide range of simple 1 1 adducts that have served as model compounds for the study of Lewis acid-base interactions. Many reviews of their coordination chemistry have appeared (41, 60, 66,120, 174, 178) and these are summarized in the more recent reviews appearing in the mid-1960s (41,120). 

Boron-Nitrogen Compounds Rhenium Organometallic Chemistry Technetium Rhenium Inorganic Coordination Chemistry. 

Lothar Weber was born in 1944 in Langenols in Schlesien. He studied at the Universitat Marburg and received his doctorate there under the direction of Professor Gunter Schmid in 1973. Thereafter he carried out postdoctoral studies with Professor Barry M. Trost at the University of Wisconsin in Madison, USA. On his return to Marburg, he began the experimental work leading to his habilitation, which was completed in 1982 at the Universitat Essen. His work focused on the coordination chemistry of sulfur ylides. In 1985, he became a C2 Professor and then joined the Fakultat fiir Chemie der Universitat Bielefeld. His research interests include the chemistry of compounds with low-coordinate elements of the fifth main group, the synthesis of homo- and heterocycles with heavy elements, as well as new aspects in boron chemistry. 

The coordination chemistry of boron was reviewed some time ago and the structure and properties of compounds of the general formula BX3 L, where X and L can be one of a wide variety of substituents and electron pair donors, respectively (15). Indeed, the reactions of tricoordinate boron compounds in general are thought to proceed via addition of the reaction partner in a Lewis acid-base reaction to yield a tetracoord-inate intermediate that then undergoes further reaction. Stable tetra-coordinate boron compounds are subject to ligand displacement reactions for which a variety of mechanisms obtain (16). The coordination chemistry of transition metals is vast and includes not only structimal facts (17) but considerable information on the mechanistic behavior of these species as well (18). In our brief comparison we will restrict ourselves to low oxidation state chemistry and group 16 metals (19). 

Diborane-ammonia Systems. Consider the formal analogy between the chloroammines of platinum and the ammonia adducts of diborane. It is useful to consider the hydrogen atoms attached to boron in the ammonia addition compounds of diborane as negative hydridic ligands, comparable to the chloride ions found in coordination chemistry. Although this concept may have been considered heresy some years ago, it was made easier to accept when Chatt (2) and his colleagues demonstrated the reaction ... 

A review of the chemistry of Group III complexes shows that many of the concepts of Werner s coordination chemistry may be applied to these elements. Furthermore, the differences observed in the complexing behavior between ammonia and trimethylamine refiect fundamental differences in the amines. Ammonia tends to give ionic compounds, whereas trimethylamine tends to give non-ionic products. Trends observed with the metal halides can be extrapolated into hydrides of boron, aluminum, and gallium. An extension of Werner s concepts provides a significant... 

After the early reviews in 19712 and 19723 on poly(pyrazolyl)borate chemistry and pyrazole-derived ligands, and the boron pyrazole compounds chemistry described in 1986,4 Trofimenko reported in 1986s and in 19936 a summary on the coordination chemistry of poly(pyrazolyl)-borates. In 1999 Trofimenko described the coordination chemistry of scorpionate ligands in a book.7... 

---