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Treatment of an anhydrous CoCl 2 with the [Na][C 2 B 8 H 11 ] ( 1 ) generated in situ from the neutral ten-vertex dicarbon carborane [5,6- nido -C 2 B 8 H 12 ] ( 2 ) with NaH in THF at ambient temperature affords the new cobaltacarborane commo cluster closo,nido -[CoH(2,4-C 2 B 8 H 10 )(7,8-C 2 B 8 H 11 )] 1− isolated as its air-stable [Ph 4 P] + ( 3 ) and [Ph 3 PMe] + ( 4 ) salts. As was found from the crystallographically determined structure of 4 and based on the 1 H NMR spectroscopic data for both 3 and 4 , these anionic salts are composed of the Co–H unit that is sandwiched between two {C 2 B 8 } cages; one of these cages, the formally doubly charged [C 2 B 8 H 10 ] 2− ligand, is involved in the η 6 -coordination to the metal center, but another singly charged [7,8-C 2 B 8 H 11 ] 1− ligand, which retains one bridged B–H–B hydrogen atom, is involved through its CB 3 -open face in the η 4 -coordination to the cobalt atom. At room temperature, complexes 3 and 4 exhibited fluxional behavior in solution where the exchange between terminal Co–H and bridging B–H–B hydrogen atoms occurs. This is discussed in detail based on the comparable room- and low-temperature 1 H NMR spectra of 3 .

The heating of the isomeric [1-(η6-1,4-Me2C6H4)-3-Cl-isonido-1,2,4-RuC2B8H9] (1) or [1-(η6-1,4-Me2C6H4)-6-Cl-isonido-1,2,4-RuC2B8H9] (2) complexes (i) in a 1,4-Me2C6H4 solution at 85 °C as well as (ii) in a melt at 165 °C afforded mixtures of isomeric isonido- and closo-ruthenacarboranes, which differ in the positions of the chlorine substituent and the carbon atoms in the cage ligand. Structures of all new isomeric complexes have been established on the basis of analytical and multinuclear NMR data and were characterized by single-crystal X-ray diffraction studies. Also presented are the results of the quantum chemical calculations for the ground and the transition states of the reaction (i), which proved to be basis for the suggestion of interconversion scheme for these isomers.

A novel 12-vertex monocarbon hydridorhodacarborane closo -2,2-(Ph 3 P) 2 -2- H -1-(Me 3 N)-2,1-RhCB 10 H 10 1 has been synthesized by the reaction of Rh(PPh 3 ) 3 Cl ( 2 ) with nido -B 10 H 12 CNMe 3 ( 3 ) under alkaline conditions. At low temperature 1 exists as a mixture of two preferred conformers in solution, both having C S symmetry, in accord with the hindered rotation of the (Ph 3 P) 2 RhH vertex with respect to the CB 4 face of the monocarbon carborane cage. Complex 1 readily reacts with chlorine-containing reagents to form mononuclear 16-electron closo -2-(Ph 3 P)-2-Cl-1-(Me 3 N)-2,1-RhCB 10 H 10 ( 5 ), whose structure was unambiguously confirmed by an X-ray diffraction study. The results of an X-ray diffraction study of the closely related dicarbon carborane derivative closo -3,3-(Ph 3 P) 2 -3-Cl-3,1,2-RhC 2 B 9 H 11 ( 10 ), prepared from closo -3,3-(Ph 3 P) 2 -3- H -3,1,2-RhC 2 B 9 H 11 by analogy with 5 , are also reported.

The stable carbenium cations in the zwitterionic complexes closo-3,3,3-(CO)3- 3,1,2-ReC2B9 H 10-1- C +RR′ (R = R′ = H; R = H, R′ = Me; R = R′ = Me) have been prepared by protonation of closo-3,3,3-(CO)3-3,1,2-ReC2B9H10-1-CH2OR (R = H, Me) and closo-3,3,3-(CO)3-3,l,2-ReC2B9H10-1-CRCH2 (R=H, Me). Some of the reactions of the zwitterions with neutral and charged nucleophilic reagents have been studied. The crystal and molecular structure of closo-3,3,3-(CO)3-3,1,2-ReC2B9 H 10- 1- C + Me2 has been established. It is shown that the carbocationic centre in these zwitterions is stabilized by direct ReC interaction.