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Boron-containing compounds are essential micronutrients for animals and plants despite their low-level natural occurrence. They can strengthen the cell walls of the plants and they play important role in supporting bone health. However, surprisingly, boron-containing compounds are seldom found in pharmaceutical drugs. In fact, there are no inherent disadvantages reported so far in terms of the incorporation of boron into medicines. Indeed, drugs based on boron-containing compounds, such as tavaborole (marked name Kerydin) and bortezomib (trade name Velcade) have been investigated and they are used in clinical treatment. In addition, following the advanced development of boron neutron capture therapy and a new emerging proton boron fusion therapy, more boron-containing medicinals are to be expected. This review discusses the current status and perspectives of delivery strategy for boron-containing drugs.

Polyhedral carborane clusters have been widely used as suitable ligands to coordinate with transition metals to construct various metal complexes. Most of the studies are on either dicarbollide anion ([7-R1-8-R2-7,8-nido-C2B9]2−; R1,R2 = H, alkyl, aryl, etc.) or functionalized closo-carborane (1-R3-2-R4-1,2-closo-C2B10H10; R1,R2 = H or functional groups). Carborane-based ligands demonstrate varying coordinating models to form structurally unique metal complexes with interesting reactivity. This mini-review describes the syntheses and catalytic applications of the type complexes, specifically emphasizing their catalytic activity for olefin polymerization. Future perspectives in this area of research will also be discussed in this mini-review.

Palladium (0) nanoparticles with small size and narrow size distribution were synthesized conveniently and supported on CNTs. The supported nano-Pd 0 was found to be a highly efficient and recyclable catalyst for the aminocarboranylation reaction of aryl halide. Thus, a series of carboranyl amides, 1-R-2-[CH 2 NHC(=O)Ar]-1,2-C 2 B 10 H 10 (R = H, Me; Ar = C 6 H 5 , 4-Me-C 6 H 5 , 4-MeO-C 6 H 5 and 2-C 5 NH 4 ), were synthesized and fully characterized. The catalyst was recyclable at least three times with sustained activity.

Recently, boron compounds have attracted increasing attention both in academic laboratories and in the pharmaceutical industry. Boron, in particular the 10B isotope, has the unique capability of absorbing a slow neutron to initiate a nuclear reaction with release of energetic particles such as α- and Li-particles, which is not observed in its carbon analogues. The nuclear capture reaction concept has been adopted in radiation therapy and used in boron neutron capture therapy (BNCT). BNCT is a potentially promising treatment for malignant brain tumors as well as other cancers, despite the limitation of a scarcity of neutron sources. There is the need in advanced research centers to construct high boron-containing composites as BNCT agents and develop more efficient drug carriers. This review discusses recent works on the development of boron-based therapeutic nanomaterials as BNCT agents.

The condensation reaction of carboranylmethyl ammonium chloride, 1-(CH2NH3Cl)-1,2-C2B10H11 (1) with phenyl aldehydes produced phenyl(carboranylmethyl)imine ligands, 1-(CH2N = CC6H4R-2)-1,2-C2B10H11 (2 R = H; 3 R = OH). Deprotonation of 2 and 3 with n-BuLi followed by metalation with TiCl4 led to the formation of phenyl(carboranylmethyl)imidotitanium (IV) chlorides, [1-(CH2N = CC6H4R-2)-1,2-C2B10H10]TiCl3 (4 R = H; 5 R = O). Compounds 4 and 5 were found to catalyze the polymerization of ethylene in the presence of co-catalyst MAO to produce high molecular weight polyethylene. In addition, compounds 4 and 5 were also active for copolymerization of ethylene and methyl-10-undecannoate to generate corresponding copolymers.

Tailor made N-heterocyclic carbene (NHC) catalyst precursors namely (+) and (−) 1-methyl-3-menthoxymethyl imidazolium chloride have been synthesized in high yield with a literature modified procedure. A reaction of catalyst precursor with potassium tert butoxide in situ generates the NHC catalyst. The zwitterionic ring opening polymerization of lactide (LA) mediated by a catalytic system composed of NHC catalyst at 25°C under argon atmosphere led to a cyclic poly(lactide) of a high molecular weight with a narrow molecular weight distribution. The cyclic poly(lactide) was characterized by NMR spectroscopy, Gel Permeation Chromatography (GPC) and Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The NHC catalysts are active for lactide polymerization in the presence of air and elevated temperatures at 55°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

An account of recent research on the syntheses, structures, properties, and catalytic applications of the nanoparti- cles/compositesformedbetweennanostructuredandsupportedpolyhedralcarboranecagesandmetalsisgiven. Thedevelopment of other nanomaterials, such as dendrimers is also briefly discussed.

The Hoveyda-Grubbs catalyst has been successfully immobilized on surface-modified magnetic nanoparticles with a loading amount of 0.28 mmol ruthenium/g (magnetic support). The supported catalysts were active for the self-metathesis of methyl oleate and macro-monomer in a quantitative conversion, respectively. In addition, the catalyst can be easily separated by using a magnet and reused several times with sustained activity.

An account of the current research carried out in our laboratories is presented. Included is the incorporation of several group 14 elements into charge-compensated carboranes. These species present a bonding pattern not found in other main group carboranes. In addition to our continuing studies of the syntheses and structures of organometallic compounds, the use of these compounds as catalysts and catalyst precursors has been investigated. The isotopic exchange reactions between 10B enriched boron hydrides with naturally abundant boranes catalyzed by Ru(0) nanoparticles has been studied. The Ru(0) nanoparticles were obtained by the reduction of [CpRuCp∗RuCp∗]PF6 (Cp∗ = C5Me5) with hydrogen and stabilized by the ionic liquid trihexyltetradecylphosphonium dodecylbenzenesulfonate [THTdP][DBS]. This was found to be an excellent, long lived catalyst for the exchange reaction of B-10 enriched diborane and naturally abundant decaborane(14). Other approaches to the production and use of nano-metal catalysts have also been explored. The reduction of the iridium carborane, (PPh3)2IrH(7,8-C2B9H11) with hydrogen in the presence of trihexyltetradecylphosphonium methylsulfonate, [THTdP][MS], produced an Ir(0) nanoparticles that catalyzed the phenylborolation as did our Ir(sal = N-R = salicylaldiminato; COD = cyclooctadiene complex. Progress in the use of single wall carbon nanotubes (SWCNT) as boron delivery agents was also discussed.