Kenneth P. Callahan

Ten Years of Metallocarboranes

Publisher Summary Metallocarboranes are only been known for ten years, and research into their synthesis and characterization has involved a small number of workers. Practical applications of these unique compounds are not been rapidly forthcoming. Recent work has shown catalytic activity in certain of these compounds and may signify future commercial value and industrial importance of metallocarboranes. The preparative methods of metallocarboranes are discussed in this chapter, for the synthesis of all the known metallocarboranes has been accomplished by one or more of these routes. This chapter focuses on the synthesis, structures, properties, and reactions of η-bonded metallocarboranes. Complexes of 2-carbon carboranes and species that have between nine and fourteen total polyhedral vertices are described in the chapter. The approach to the subject has been to divide the metallocarboranes according to the size of the polyhedron–starting with twelve-vertex compounds, which constitute the majority of the effort, to the larger polyhedral, so far unknown in the B n H n 2 - and C 2 B n-2 H, series, and then to the lower polyhedral. Further subdivisions within each polyhedral size include synthesis, structures, and properties of monometallic complexes, reactions of monometallic, bimetallic preparations and reactions, and, in two instances, trimetallic compounds. This catalyst systemis extremely stable and may be recovered quantitatively from alkene isomerizations and hydrogenation reactions.

Polyhedral Rearrangements Involving Five- and Six-Coordinate Carbon.

Abstract Polyhedral carboranes and metallocarboranes characteristically contain C atoms having coordination numbers of 5 and 6 within the polyhedral surface. Thermal carbon and metal atom migration reactions are observed in these species and we here report results obtained with polyhedra containing 10, 11, 12 and 13 vertices. Thermodynamic activation parameters have been measured for several representative rearrangement reactions and their mechanistic significance is discussed. General rules which appear to govern carbon and metal atom migration reactions are advanced.

Electrochemical reduction of trimetallic [M(M′S4)2]2– ions (M = NiII, PdII, or PtII; M′= Mo or W)

Trimetallic [M(M′S4)2]2– ions (M = NiII, PdII, or PtII; M′= Mo or W) exhibit reversible electrochemical reduction in nonaqueous solvents; the existence of formal monovalent (M = Ni or Pd) and zerovalent (M = Ni, Pd, or Pt) complexes is indicated.

CARBORANES AND METALLOCARBORANES

Abstract : One of the most significant developments in modern boron chemistry was the discovery of the carboranes. The substitution of CH(3+) vertices for BH(2+) units in boron hydride polyhedra opened up an entire new field of chemical endeavor. Chemical investigations of the carboranes uncovered yet another area of boron chemistry, that of metallocarboranes. The chemistry of these species, which contain transitional metal vertices incorporated into the polyhedral framework, is just beginning to be elucidated. Several reactions common in carborane chemistry have recently been found to be generally applicable to metallocarboranes. These reactions (including rearrangement, contraction (elimination), and expansion) and the significance of the chemical similarity of these two types of heteroboranes are discussed. (Modified author abstract)

Metallocarboranes: Past, Present, and Future

The first metallocarborane complex, [3,3’-FeII(l,2-C2B9H11)2]2−1 the carborane analog of ferrocene, was first synthesized ten years ago. This compound bridged boron hydride and carborane chemistry with that of the transition metals, and heralded the explosive proliferation of metallocarborane chemistry.

Preparation and crystallographic characterization of a 2:1 adduct of ethynyldicarbadodecaborane(12) and trans-IrCl(CO)(PPh3)2

Ethynyldicarbadodecaborane(12) reacted with trans-IrCl(CO)(PPh3)2 to afford the 2:1 adduct IrCl(CO)(PPh3)2(B10C4H11)(B10C4H13); X-ray crystallographic study showed the presence of σ-2-carboranylacetylide and σ-trans-2-carboranylvinyl substitutents.

Synthesis and characterization of thiovanadyl (VS2+) complexes

The existence of the thiovanadyl ion, VS2+, has been established by reaction of VO(salen) and VO(acen)[H2salen =NN′-ethylenebis(salicylideneamine); H2acen =NN′-ethylenebis(acetylacetonylideneamine)] with B2S3 to form the thiovanadyl compounds; infrared and e.s.r. spectroscopy indicate that the VS bond has greater covalency but is weaker than its vanadyl analogues.