Carboranes CH

The proton NMR spectra of the diamagnetic complexes have been useful in confirming parts of the structure of these compounds. The carborane CH resonance appears as a broad singlet in most proton spectra. The 11B NMR spectra of the diamagnetic complexes have to date been useless for structural purposes because of the complex overlap of the various doublets. 

A third isomeric species (II) has been isolated when B7C2H,, 2 is reacted with cobalt(ll) chloride at 70° C. This compound has only one carborane (CH) resonance in the proton NMR, suggesting that the two carbon atoms occupy equivalent positions in the cage. The favored structure of the three possible choices is illustrated in Fig. 10 (II). This choice is based on the... 

The structure of the bimetallic 10-vertex cluster was shown by X-ray diffraction to be (84). When the icosahedral carborane l,2-C2BioHi2 was used, the reaction led to the first supraicosahedral metallocarboranes with 13- and 14-vertex polyhedral structures (85)-(89). Facile isomerism of the 13-vertex monometallodicarbaboranes was observed as indicated in the scheme above (in which = CH and O = BH). 

In another paper Zakhardin s group investigated the reaction of arenediazonium salts with carboranes in which one of the CH protons was replaced by copper(i). The... 

Carborane, Bk>C2Hi2, is quite soluble in aromatic solvents and is sparingly soluble in aliphatic solvents. The infrared spectrum has been previously reported.25 The proton nuclear magnetic resonance spectrum of a chloroform-d3 solution of carborane contains a broad CH resonance at 6.46 t. 

As discussed in the introduction (Section 3.2.1), derivatives of the diboracyclo-propane 1C are non-classical organoboranes having 8 SE, and according to the 2n+2 SE rule may be classified as the simplest doso-carboranes of the series CH(BH) H ( = 2). Compounds IB and 1C have been computed [5] to be 17.5 and 47.6 kcal mol-1 lower in energy, respectively, than the classical diboracyclopropane 1A. They are 2e aromatics and possess planar-tetracoordinate centers in IB this unusual geometry is found at the carbon and one boron atom, in 1C at both boron atoms (Scheme 3.2-2). 

Reaction of 13a with elemental Li in Et20 yields 15a, the first derivative of the simplest polyhedral closo-carborane of the anionic series [CH(BH) ] (n = 4) (Scheme 3.2-9). Polyhedral members with n = 3 are transition states of type 5 as shown in Section 3.2.2.1. 

The carborane 64c was characterized by a consistent set of NMR data, ab initio MO calculations, and by X-ray structure analysis [88]. The synthetic potential of 64c is indicated by its reaction with Fe(CO)3 fragments to give 69 [87]. The di-ferracarborane 69 is isostructural with nido-decaborane(14), because two BH and four BH(H) fragments were replaced by two isolobal Fe(CO)3 and four CH fragments, respectively. 

In order to recognize the patterns that pervade carborane chemistry, it is instructive to conduct a molecular census, to ascertain where and in what coordination-number environments the various groups, e.g., BH, BHj, CH, CHg, CHj, and Lewis base equivalents (B LB, BH LB, and BH2 LB, where LB = Lewis base) are most frequently found. Table II itemizes the various groups obvious trends may be observed and examples of the extreme cases are given. 

There are a number of heteroatoms that can substitute for either boron or carbon in the carboranes. The groups that are as electron-deficient as BH groups are listed vertically to the left of the center line in Table V, whereas those that are as capable as carbon in donating electrons are listed to the right of the center line. The transition elements for the most part electronically substitute for boron and occupy high-coordination sites, but upon electron demand the transition element may also substitute for carbon and concomitantly occupy low-coordination sites. Several transition element moieties, by contrast, are one more electron deficient than boron and occupy, as would be anticipated, high-coordination positions and require additional electron donors (CH groups) to counter the electronic deficit (XIII-24). 

In abridged form, we shall discuss in order (o) BH-substituted heteroatom carborane analogs (Fig. 22), (6) CH-substituted heteroatoin carborane analogs (Fig. 23), (c) transition element group (TEG)-substi-... 

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