Including their Metal Complexes

This chapter covers the 1993 literature of carbaborane and metallacarbaborane chemistry. Its format is similar to that of last yearl with sections arranged according to carbaborane composition, CxBy and CxByMz the metal complexes are included in the corresponding CxBy-section. Theoretical results have been collected together in section 2. Woik directed specifically at BNCT is decribed in section 16. The literature has been surveyed by use of Current Contents. The crystal structure figures (4), (8), (9), (14), (15), (18) and (23) have been redrawn using atomic coordinates. 

A useful review covering aspects of conqilexes formed betwen caibabwane clusters and d-and/-block metals has appeared. This is particularly timely with regard to the /-block metals, an area that has begun to emerge relatively recently. 

Over the past few years, these annual rqxHts have seen the development of the use of the NMR/IGLO/ob initio method. This has now been applied to a study of three isomers of 

Holbrey et al. have developed a molecular mechanics model for l,2-C2BioHi2 and derivative cages distances are constrained in the model. The study has been extended to include macrocyclic thioether systems in which the C-substituents in l,2-C2R2BioHio are linked into a (typically thio) macrocycle (see also section 14). 

The isolobal principle is a useful concept for cluster chemists generally. A recent paper has explored the isolobal relationship between BH and Ru(CO)3 units using as the model compounds, (BH)3(CH)2 ii.e. US-C BsHs) and Ru(CO)3) 3(01)2- 2 

In volume 29 of Inorganic Synthesis edited by Grimes, a chsqrter has been devoted to compounds of boron. Included here are pr arative routes to c/oso-l,5-Et2-l,5-C2B3Et3,ll nido-2,6,8,10-Et4-2,6,8,10-C4BgEte, l trimethylsilyl-substituted derivatives of 2,3-dicarba-mdo-hexaborane(8), lithium, sodium, and dilithium salts of 2,3-bis(trimethylsilyl)-2,3-dicarba-md - 

The experimental observation of the rearrangement of 2-ethyl-o-carboranylcarbene to 1-vinyl-o-carborane by Jones et tU. in 1982 and suggestions about the mechanism d rearran ment have prompted related the( etical investigations using GAUSSIAN 88/90 programs at the MP2/6-31G //3-21G+ZPC level. These probe the possibility of 13-vertex intermediates. Thetuetical 

ASIS effects have been correlated with calculated charge densities for closo-C2BsH7 and chloro-derivatives.26 

A paper of general interest is a review which concerns the chemistry of boron analogues of biomolecules (345 references). Also of general appeal are the first examples of the use of two-dimensional B- correlation NMR spectroscopy.  

Lipscomb and Massa have extended a method of cage construction (using the Descartes-Euler relationship) to consider multicage structures. For example, B22 ( 5a). B30 Dsh), 635 (7 ) polycarbon cages and B20H16 have been examined, and the method should be relevant to carbaborane structures, 

Carbaborane rearrangements are regularly a topic of debate amongst theorists. Recent studies by Johnson and cowoilcer concentrate on the advantages and limitations of several mechanisms of rearrangement for C2B10H12. A conclusion is that a six-fold DSD mechanism based on an anticubeoctahedral structure is a prefmed route.  

Composition C4B, C4B2) C3B2 and C2B3 (including ring stacking) 

Pentamethylcyclopentadienyl iron(II) complexes involving T 5-2,3,5-tricarbahexaboranyl and n5-2,3-dihydro-l,3-diborolyl ligands have been synthesised and spectroscopically characterised. A crystal structure analysis of the 16 v.e. sandwich complex (7) illustrates that there is extreme folding of the C3B2-ring and thus stacking cannot occur below this ring.  

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A number of X-ray diffraction studies were performed in order to determine the heterocyclic ring structures including their metal complexes and to determine the intermolecular interactions. 

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