Carboranes connecting units

A series of alkyl-substituted macrocycles featuring mercury atoms connected by c/-carborane units has been recently synthesized. Examples of such macrocycles include the hexamethyl derivative 58 and the hexadecamethyl derivative 59 whose alkyl-substituted carborane backbones impart improved solubility in hydrocarbon solvents.7 While 58 was synthesized from doso-9, 12-Mc -1 T-I.i -110I R and Hg(OAc)2, compound 59 was obtained as a... 

As an alternative to the reductive generation of a nido borane or carborane cluster from a closo parent, one can regard a nido species as the product of decapitation or deboronation of a closo parent. Formal removal of a B kf unit, normally from a high connectivity site in a closo borane or carborane, followed by protonation of the anionic residue around the open face generated, leaves a neutral nido residue. 

The relationship of nido and arachno boranes and carboranes to notional parent closo boranes and carboranes, by removal of BH units from selected sites, usually of high connectivity, can be illustrated simply by exploring how the MOs of a closo system B,I I, (or isoelectronic neutral carborane C2B, H ) will be affected by the theoretical experiment of removing one or two... 

Structures of Boranes and Carboranes. As mentioned above, elementary boron occurs in its most stable modification as B12 icosahedric units connected to each other by six boron-boron two-center bonds. Boron-boron distances within the icosahedron range from 1.73 to 1.79 A. From a structural point of view, boranes can be systematized by considering them as derivatives of the elementary icosahedron, but built by B-H units. Some examples of geometrical forms that can be derived from icosahedron were shown in Fig. 2.27. 

The dimensions of the rhomboid macrocycle 42, which consists of two Pt(PEt3)2 units connected by two meta-carborane dicarboxylate dianions, were found to be 9.19 and 7.01 A, respectively (Das et al., 2005). 

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