Hydrogen bonding carborane

The structure of the disilanol l,7-bis[hydroxy(dimethyl)silylmethyl]-m-carborane has a hydrogen-bonded network reminiscent of the sil-oxanediol type shown in Fig. 10c, in which pairs of molecules are hydrogen-bonded together and then these pairs are further linked to give a double chain (290). 

The solid-state structure of ort o-carborane was determined for the first time in 1996 featuring HMPA as a weak hydrogen bond adduct in the solid state.569 The geometry of ort o-carborane, I T BjoH, is a distorted icosahedron with a bond of 1.62 A between the cage carbons (C1-C2). This bond is remarkably elastic being elongated up to 1.85 A... 

Two early examples of CTV being incorporated into network structures involves CTV acting as a hydrogen bond acceptor when the hydrogen bond donor is the acidic C-H groups of o-carborane [79]. Carboranes form C-H hydrogen bonds of this type in a number of other instances [80], and may also act as spherical guest molecules for CTV [77]. 

Fig. 16 Puckered hexagonal 2D hydrogen bonded network of (o-carborane)2(CTV) 33 where the carborane molecule is disordered with three icosohedral vertices having mixed C and B character. The other type of carborane (not shown) is an intracavity guest for the CTV [79]... 

Fig. 18 2D hydrogen bonded network structure of [(DMF)(CTV)]2(H20)4(o-carborane)] 35 with water tetramers hydrogen bonding to CTV molecules [82]... 

Arene ruthenium and osmium complexes play an increasingly important role in organometallic chemistry. They appear to be good starting materials for access to reactive arene metal hydrides or 16-electron metal(O) intermediates that have been used recently for carbon-hydrogen bond activation. Various methods of access to cyclopentadienyl, borane, and carborane arene ruthenium and osmium complexes have been reported. 

HMPA (hexamethylphosphoramide) OP(NMe2)3 4 does not deboronate the C2B10H12 isomers at room temperature but acts as an hydrogen bond acceptor for the acidic hydrogens at the carbon atoms of these clusters to yield 1 1 carboranerHMPA adducts on crystallization.6 These C-H--0 hydrogen bonded supramolecular structures provide the first definitive X-ray structures of the unsubstituted carboranes. 

This paper discusses reactions between the commercially available base imino-tris(dimethylamino)phosphorane HNP(NMe2)3 5 and the icosahedral carboranes 1-3 where base 5 is found to be either an effective dcboronating agent, a good hydrogen bond acceptor or both. 

Under nitrogen, a 1 1 ratio mixture of carborane 2 and base 5 in toluene at -20°C gave crystals identified as a 1 1 polymeric adduct 11.12 The crystal structure of 11 revealed the presence of two C-H—N hydrogen bonds per molecule. A 2 1 crystalline adduct 12, where one C-H—N hydrogen bond per base molecule would be expected, could not be obtained. 

Figure 3.13. Carboranyl C-H—O hydrogen bonding links in 1 1 adducts of (Me2N)3PO with carboranes, [(Me2N)3PO H2C2BioHio].

Under N2, a 1 1 ratio mixture of para carborane 3 and base 5 in toluene at -20°C gave crystals identified by multinuclear NMR spectroscopy as a 1 1 adduct 15. Likewise, a 1 2 ratio mixture of 3 and 5 gave a 1 2 adduct 16. An X-ray structural determination of the latter adduct showed two base molecules to be linked solely to one carborane molecule via C-H" N hydrogen bonds. 

Figure 2 X-Ray structures of inclusion motifs in crystalline CTVs. (a) A misaligned stack of a-phase CTV (b) intracavity complexation of 1,1,1-trichloroethane (c) baU-and-socket structure from the complex (o-carborane)(CTV)2 hydrogen bonds between the acidic carborane C-H and CTV are indicated as dashed lines (d) hand-shake motif in 6. (e) Solvent-filled channel in clathrate complex of 7, where self-inclusion and tt-tt stacking interactions result in an open structure.

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