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Review: development of hybrid organic-inorganic π conjugated, silane, siloxane and coordination polymers containing boron clusters, which have received considerable academic and technological interest due to the combination of the electronic, optical and thermal properties of traditional inorganic materials with desirable properties of organic plastics, including mechanical flexibility and low production costs; 55 refs.

The accurate selection of a ligand for a metal-catalyzed homogeneous reaction can be as decisive as the selection of the metal. Incorporating a carborane cage as a backbone to produce new phosphines often leads to remarkable properties, which are not accessible employing conventional organic entities. The synergy effects between the o-carborane cluster and the P atom in these closo- and nido-carboranylphosphines is observed from two points of view: the cluster and the P atom. The P atoms in the closo-carboranylmonophosphines grant to the cluster a unique plasticity on the Ccluster Ccluster distance. The cooperation between the carboranyl moiety and the P atom may result in mono-, di- and tridendicity according to the necessities of the metal, not an ever-available property for organic phosphines.

Boranes, heteroboranes and metallacarboranes, all named as boron clusters, offer an alternative to typical organic molecules or organic molecular materials. Carbon and boron share the important property of self-catenation thus these elements can produce individually large and sophisticated molecules. Boron clusters and organic molecules display electronic, physical, chemical and geometrical characteristics manifestly different. These differences highlight the complementarity of organic molecules and boron clusters, and therefore the feasibility or necessity to produce hybrid molecules incorporating both types of fragments. To join these two types of fragments, or alternatively these two types of molecular compounds, tools are needed. In this review the current methods of producing boron clusters with carbon, B–C, nitrogen, B–N, phosphorus, B–P and sulphur bonds, B–S, are indicated. As there are many existing borane clusters of different sizes, heteroboranes and metallacarboranes, the revision of methods to generate the B–C, B–P, B–S, and B–N bonds has been restricted to the most widely used boron clusters; [B12H12]2−, dianionic and an example of a borane, 1,2-C2B10H12, neutral and an example of a heteroborane, and [Co(C2B9H11)2]−, monoanionic and an example of a metallacarborane.

Electrospray ionization-ion-trap mass spectrometry shows that B2I122- converts to an intact B12 cluster by successive stripping of single iodine radicals or ions.

A molecular mechanics model for o-carborane cages has been developed, using distance restraints to hold the polyhedron in position. The combination of o-carborane cage interatomic distance restraints (a modified central force field) and CHARMm parameters gives a good representation of the carborane cage geometry. Molecular dynamic simulations of macrocyclic thioethers ligated to the carbons of the carborane have been carried out. The rigid cage section seems to provide an accessible interconversion route between conformers of the macrocycle, effectively an entatic state. The new carborane 1,2-(6′-oxa-3′,9′-dithiaundecane-1′,11′-diyl)-1,2-dicarba-closo-dodecborane, the four-step synthesis and crystal structure of which are presented, provided a contrasting macrocyclic appendage with thioethers indirectly linked to the o-carborane cage through ethane bridges. Molecular dynamics simulation of this molecule was also carried out.

Reaction of [RuH(AcO)(PPh 3 ) 3 ] and [NMe 4 ][7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 ] in methanol yields [RuH(7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 )(PPh 3 ) 2 ] (1). The reaction of [RuCl 2 (PPh 3 ) 3 ] and [NMe 4 ][7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 ] in a 1:1 or 1:2 ratio in methanol yields [RuX(7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 )(PPh 3 ) 2 ] (X = Cl, H) (2). NMR spectroscopic analyses of 1 and 2 indicate that the centers have an octahedral geometry and the carborane acts as a tricoordinating ligand to ruthenium(II) by means of P-Ru, B(11)-H→Ru and B(2)-H→Ru agostic bonds. A chloride or hydride and two PPh 3 ligands complete the coordination sphere of the metal. The formation of two B-H→Ru agostic bonds rather than a second P-Ru bond appears to be due to steric factors. Reaction of [NMe 4 ][7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 ] with [RuCl 2 (PMePh 2 ) 4 ] in ratios of 1:1 and 2:1 in methanol yields complexes [Ru(7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 11 ) 2 ] (3) and [RuH(7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 11 ) 2 ] (4) respectively, which incorporate two nido-carboranylphosphine ligands.

Reaction of 1,2-dimercapto-1,2-dicarba-closo-dodecaborane under basic conditions with appropriate dihalogenated organic compounds results in the formation of macrocycles incorporating 7,8-dicarbaundecaborate or 1,2-dicarba-closo-dodecaborane units. Polymers are obviated by using high dilution. The crystal structure of 1,2-(3′-oxapentane-1′,5′-dithiolato-SS′)-1′,2′-dicarba-closo-dodecaborane has been determined. It crystallizes in space group P21/a with four formula units in a cell of dimensions a= 11.708(2), b= 10.209(3), c= 12.613(3)A, and β= 109.04(2)°.