Conjuncto boranes

Balakrishnarajan and Jemmis [32, 33] have very recently extended the Wade-Mingos rules from isolated borane deltahedra to fused borane ("conjuncto ) delta -hedra. They arrive at the requirement of n I m skeletal electron pairs corresponding to 2n + 2m skeletal electrons for such fused deltahedra having n total vertices and m individual deltahedra. Note that for a single deltahedron (i.e., m = 1) the Jemmis 2n + 2m rule reduces to the Wade-Mingos 2n I 2 rule. 

Boranes are usually named by indicating the number of B atoms with a latin prefix and the number of H atoms by an arabic number in parentheses, e.g. B5H9, pentaborane(9) B5H11, pentaboranefl 1). Names for anions end in ate rather than ane and specify both the number of H and B atoms and the charge, e.g. BsHs" octahydropentaboratefl—). Further information can be provided by the optional inclusion of the italicized descriptors closo-, nido-, arachno-, hypho- and conjuncto-, e.g. ... 

Conjugation reactions, 14 139-140 noncovalent methods for, 14 140 Conjuncto-boranes, 4 172 Connectivity, in multiphasic solids, 11 100-101... 

In the following section, we give a survey of the known types of heteroboranes in question and discuss the structures in terms of the Wade-Williams rules. Readers, who are interested in the synthesis of heteroatom clusters, in their skeletal transformations, or in reactions at the ligand sphere, are referred to the cited literature. conjuncto- Boranes with heteroatoms in the skeleton are not considered in this brief discussion. 

Of the characterized higher boranes larger than B10Hu, all except BnH15 are of the conjuncto class, consisting of two or more cluster units joined in some manner (for two examples see Fig. 5-3). A variety of synthetic approaches has been employed to prepare these hydrides, in most cases generating products serendipitously with no real control over the product compositions or structures. Typical examples are as follows ... 

Special prefixes closo-, nido- arachno-, catena-, hypho-, dado-, isodoso-, isonido-, isoarachno-, canasto-, anello-, predoso-, hyperdoso-, pileo-, and conjuncto- are found in the literature to describe borane structures. 

Figure 2 The conjuncto borane BiJho 3 and the adduct BaHnNCCHs 4 whose spectra were either unassigned or incorrectly assigned in earlier work.

Figure 3 Computed (vertical axis) versus experimental11B chemical shifts in ppm for the conjuncto borane BiJrha-...

The hypho (Gr., net ) series of boranes, with electronic formula 2n 8, has been suggested to augment the closo, nido, and arachno series. Although no neutral boranes fit this scheme, some borane derivatives do. It is also possible to construct units consisting of more than one of the above types. These are called conjuncto (Latin, joined subunits ) structures. 

A useful route to B-B bonded conjuncto-boranes involves the photolysis of parent nido-boranes. Thus, ultraviolet irradiation of B5H9 (9) yields the three isomers of conjuncto-Q o f,... 

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