Alexander M. Kalsin

Electrostatic self-assembly of binary nanoparticle crystals with a diamond-like lattice

Self-assembly of charged, equally sized metal nanoparticles of two types (gold and silver) leads to the formation of large, sphalerite (diamond-like) crystals, in which each nanoparticle has four oppositely charged neighbors. Formation of these non–close-packed structures is a consequence of electrostatic effects specific to the nanoscale, where the thickness of the screening layer is commensurate with the dimensions of the assembling objects. Because of electrostatic stabilization of larger crystallizing particles by smaller ones, better-quality crystals can be obtained from more polydisperse nanoparticle solutions.

Size Selection During Crystallization of Oppositely Charged Nanoparticles

Opposites attract (selectively): Oppositely charged nanoparticles characterized by different size distributions form 3D supracrystals (see figure) only if the distributions overlap. Crystal quality decreases rapidly with decreasing degree of overlap, and, irrespective of the ratio of particle diameters/charges, no crystals are observed for non-overlapping distributions.

Transfer Hydrogenation of Ketones Catalyzed by Surface-Active Ruthenium and Rhodium Complexes in Water

An improved, high-yield, one-pot synthetic procedure for water-soluble ligands functionalized with trialkyl ammonium side groups H2 N(CH2 )2 NHSO2 -p-C6 H4 CH2 [NMe2 (Cn H2n+1 )](+) ([HL(n) ](+) ; n=8, 16) was developed. The corresponding new surface-active complexes [(p-cymene)RuCl(L(n) )] and [Cp*RhCl(L(n) )] (Cp*=η(5) -C5 Me5 ) were prepared and characterized. For n=16 micelles are formed in water at concentrations as low as 0.6 mM, as demonstrated by surface-tension measurements. The complexes were used for catalytic transfer hydrogenation of ketones with formate in water. Highly active catalyst systems were obtained in the case of complexes bearing C16 tails due to their ability to be adsorbed at the water/substrate interface. The scope of these catalyst systems in aqueous solutions was extended from partially water soluble aryl alkyl ketones (acetophenone, butyrophenone) to hydrophobic dialkyl ketones (2-dodecanone).

Reduction of iridocenium salts [Ir(η5-C5Me5)(η5-L)]+ (L = C5H5, C5Me5, C9H7); ligand-to-ligand dimerisation induced by electron transfer

Redox properties of iridium complexes [Ir(η5-C5Me5)(η5-L)]+ (1+, L = C5H5; 2+, L = C5Me5; 3+, L = C9H7) were studied by cyclic voltammetry (CV). All three complexes can be reduced to 19-electron radicals 1–3. The stability and reactivity of these radicals depend on the electronic and steric properties of the ligands. The mixture of dimers [(η5-C5Me5)Ir(μ-η4:η4-C5H5C5Me5)Ir(η5-C5H5)] (4a) and [(η5-C5H5)Ir(μ-η4:η4-C5Me5C5Me5)Ir(η5-C5H5)] (4b) was formed as a result of reduction of 1+ with NaHg in THF. Both chemical and electrochemical reduction of 2+ gave the dimer [(η5-C5Me5)Ir(μ-η4:η4-C5Me5C5Me5)Ir(η5-C5Me5)] (5) in low yield. Reduction of 3+ gave the tetranuclear complex [(η5-C5Me5)Ir(μ-η4:η5-C9H7) Ir(μ-η4:η4-C5Me5C5Me5) Ir(μ-η5:η4-C9H7)Ir(η5-C5Me5)] (6).

Ruthenium phosphine complexes as catalysts of alternating copolymerization of ethylene and carbon monoxide

The properties of the ruthenium (II) phosphine complexes [Ru(dppe)2(OTs)2] and [Ru{PhP(CH2CH2CH2PPh2)2}(OTs)2] as catalysts of alternating copolymerization of ethylene and carbon monoxide were studied. The catalytic activity of these complexes in the absence of cocatalysis is low, but it is substantially increased in the presence of trifluoroacetic acid or 1,4-benzoquinone. These compounds are the first ruthenium complexes which catalyze copolymerization of ethylene and CO.

Cooperative effects of ruthenium micellar catalysts and added surfactants in transfer hydrogenation of ketones in water

The effect of various added surfactants S on the activity of surface-active ruthenium complexes RuLn (n = 8, 16) in transfer hydrogenation of ketones in water was investigated. The catalysts RuLn capable of forming mixed micelles with S showed an increase in activity. RuL16 can form mixed micelles with all types of S, while the less surface-active counterpart RuL8 strongly interacts only with anionic and zwitterionic S. The mixtures of anionic surfactants with RuL8 demonstrated strong synergic enhancement of their activities by up to two orders of magnitude in hydrogenation of hydrophobic ketones. In mixed micelles, the added surfactant lowers the cmc of RuLn, resulting in better emulsification of the substrate. It was also shown that careful choice of surfactant S allowed for better and controlled hydration of the mixed micelles RuLn/S. Both aspects concurred to achieve higher catalytic performances in hydrophobic ketone reduction. For example, in RuLn/S, the better hydrated alkane sulfonate DSS always outperforms the less hydrated alkyl sulfate SDS.