Nido Carboranes anionic

The original synthesis of metallacarborancs is effected by deprotonation of nido-carborane anions in a manner like that employed to prepare ferrocene, e.g. ... 

The nido-carborane anion, 7,8-C2B9H12, and derivatives are generally formed by deboronating ort o-carboranes with suitable bases (COMC (1982) 5.4.2.6.6) but a direct route to two derivatives of the anion has been developed in good yields from decaborane and polarized alkynes.78... 

The structures of the products" (Fig. 3.20) show that the iron atom effectively plugs the gap created by removal of a BI cationic unit from the closo carborane. As this BH unit was one of the two that were adjacent to the two carbon atoms, the nido carborane anion [C2B9Hii]2 coordinates to the metal... 

There are now at least a dozen synthetic routes to metallocarboranes including (i) coordination using nido-carborane anions as ligands, (ii) polyhedral expansion reactions, (iii) polyhedral contraction reactions, (iv) polyhedral subrogation and (v) thermal metal transfer reactions. These first five routes were all devised by... 

Figure 11.7 displays the structures of two other metallacarboranes, one containing the Re(CO)3 fragment (CSCREC) and one with TaCb (VUPBAJ). Metallacarboranes in which either one or two metal ions are sandwiched between a pair of nido-carborane anions have also been synthesized. The structures of three such complexes are shown in Figure 11.8. The first structure (NIDBOR) contains a Ni(IV) ion sandwiched between two nido-1, - 2 9 11 (or 7,8-dicarbollide)...

The discovery (116) of the base-promoted degradation of the isomeric closo-Q,. . cages provided one of the most important carborane anion systems, the isomeric nido-Q,. ][ , anions,... 

Figure 68 The neutral ortho- or anionic nido-carborane attached pyrrole molecule (111, 112,113, and 114) used in the synthesis of conducting organic polymers 115, 116, etc. (Adapted from refs. 141 and 142.)...

Ab initio computations have so far proved to be reliable structural tools for neutral carboranes and their anions. They have been used to predict the carborane geometries for six-vertex, eight-vertex, and 11-vertex nido-carboranes,67-69 and for 5-12 vertex r/aro-carboranes.70,71 However, carborane anions in the presence of a group I metal cation may form ion-pair anions with one cation tightly bound to the carborane anion (see Chapter 3.03).72,73 Even computations on a salt with a carborane anion in a non-coordinating solvent would need to include the cation for computed shifts that tally with observed NMR data.74... 

CBgHi4, previously made from ortfo-carborane in three steps with an overall yield of 45%,89 can now be made in a one-pot procedure from B10Hi4 with 48% yield.90 The well-known nido-1 anion can be formed from... 

LnCl3, only the full-sandwich complexes were formed.204 The reactions of the larger, nido-C2B9-carborane, anion... 

The controlled synthesis of carbons adjacent nido- and arachno-carborane anions can be achieved by the reduction of C (cage)-C (cage)-linked o-carboranes with group 1 metals.234-237 Typical examples are illustrated in Scheme 22. These have been found to undergo metallation reactions similar to their carbons apart analogs, forming full- and half-sandwich complexes of lanthanide metals.238... 

In the early 1960s it was recognized (6,187) that there were bonding similarities between the pentagonal face of the isomeric [nirio-(y HjJ2- ions and the well-known cyclopentadienide ion (Cp ) [CydJ- (Fig. 16). The isomeric nido-C2B9H1 J2- ions, which are commonly known as dicarbollide ions, and many other carborane anions, form stable complexes with most of the metallic elements. Indeed nearly all metals can be combined with polyborane hydride clusters to produce an apparently limitless variety of cluster compounds. 

In addition to that said above, complexes with closopolyhedral hydroborate metal-containing fragments are known, for example 564, obtained through the interaction of tetramethylammonium salt of nido-B9H12 anion and nickelocene [957], An up-to-date covering of carborane and metallacarborane structures and properties is given in Ref. 184f. 

Three-dimensional aromaticity has been demonstrated, for instance in the case of Cram s cyclophane in 1951 [46, 47] and, more recently, for von Rague Schleyer s adamantane dication [48], half-sandwich carbocations, and nido-carboranes. Ferrocene and various other or-ganometallic compounds also are three-dimensional aromatics. Spherical aromaticity is exhibited by closo-carboranes, borane anions, and, to a lesser extent, C60, although these compounds are isotropic. 

Metallacarboranes have both metal and carbon atoms in the cage skeleton. In contrast to the metallaboranes, syntheses of metallacarboranes via low- or room-temperature metal insertion into carborane anions in solution are more controllable, usually occurring at a well-defined QB, open face and forming a single isomer. Other preparative routes, such as metal insertion into neutral carboranes at high temperature, involve more complex processes and tend to give less clean-cut results, and such approaches are rarely employed today. Typical syntheses that are based on readily available 11-vertex and 7-vertex nido-carborane ligands are as shown ... 

Closo cages have a p.e.c. of 4n + 2 electrons, whereas nido-carboranes require 4n + 4 electrons. The larger doso-carboranes can be reduced by alkali metals to nido anions. The latter can then often be converted into doso-metallocarboranes on treatment with a metal halide ... 

FIGURE 7.3 Structures of ammo polyhedron (a) boron anion, (b) carboranyl anion, (c) dual-chain nido-carborane, and (d) sugar-derived carborane for liposome encapsulation. 

Removal of one of the boron atoms adjacent to both the carbon atoms of ortho-catborme by action of base results in the formation of anionic 7,8-dicarba-ntVft)-undecaborate (ntdo-carborane) [7,8-C2B9Hi2] . This approach is often used to increase the water solubility of carborane-containing biomolecules [10]. Recently, an efficient method of direct functionalization of the parent nido-carborane has been described [11]. 

FIGURE 15.15 DFT analysis of the model complex 18g. (Reprinted with permission from Crespo, O. et al., Luminescent nido-carborane-diphosphine anions [(PR2>2C2B9H,o]-(R = Ph, iPr). Modification of their luminescence properties upon formation of three-coordinate gold(l) complexes. Inorg. Ghent, 42, 2061-2068. Copyright 2003 American Chemical Society.)... 

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