Selective hydrolytic oxidation of organohydrosilanes was achieved with water in the presence of Pt-nanoparticle catalyst. The selectivity of the process was established by NMR analysis. In addition, various Pt-based catalysts were screened to compare the activity and selectivity with Pt-nanoparticles catalysis. The method was equally applicable to hydrosilanes bearing unsaturated functional groups, which led to corresponding silanols under mild reaction conditions without formation of any side products. Pt-nanoparticle catalysis was studied in details using UV-vis, TEM and mercury poisoning experiments during the transformation.

A series of alkali and alkaline earth (Ae) metal complexes bearing 1,2-phenylene(bis-diphenylphosphinothioic/selenoic amine) [{Ph P(E)NH} C H ] (E=S (1-H2); Se (2-H2) ligands are reported. Alkali metal complexes [{Ph P(S)N} C H ]Na(THF) (3 a) [{Ph P(Se)N} C H ]Na(THF) (3 b), and [{Ph P(Se)N} C H ]K(THF) (4 b) were obtained in good yield by treating protic ligands 1-H2 or 2-H2 with metal hexamethyldisilazides [MN(SiMe ) ] (M=Na or K) at ambient temperature. The Ae metal complexes formulated as [{Ph P(E)N} C H ]M(THF) [E=S, M=Ca (5 a), Sr (6 a), Ba (7 a); E=Se, M=Ca (5 b), Sr (6 b), Ba (7 b)] can be synthesized by using two routes. The molecular structures of the free ligand 1-H2 and metal complexes 5 a,b-7 a,b in their solid states were established. Complexes 3 a and 3 b are isostructural; however, in complex 4 b, an attachment different from ligand 2 was observed. The complexes 5 a,b-7 a,b are isostructural and each metal ion exhibits a distorted pentagonal bipyramidal geometry around it. All Ae metal complexes 5 a,b-7 a,b were tested for the ring-opening polymerization (ROP) of racemic lactide (rac-LA) and ϵ-caprolactone (ϵ-CL) at room temperature. Calcium complexes 5 a and 5 b show excellent iso-selectivity, with P values of 0.78-0.87 at 298 K and with a high degree of polymerization control, whereas the corresponding strontium complexes 6 a and 6 b exhibit moderate iso-selectivity, and barium complexes 7 a and 7 b yield only atactic polylactides (PLAs). In all cases, the catalyst initiates the ROP catalytic cycle in the absence of any external initiator. Kinetic studies of the polymerization reactions indicate the relative order of polymerization rate increases with increase in the size of the metal ion: Ba>Sr>Ca.

We report the preparation of alkali and alkaline earth (Ae) metal complexes supported by 2-picolylamino-diphenylphosphane chalcogenide [(PhP(=E)NHCH(CHN)] [E = S (1-H); Se (2-H)] ligands. The treatment of the protic ligand, 1-H or 2-H, with alkali metal hexamethyldisilazides at room temperature afforded the corresponding alkali metal salts [M(THF)(PhP(=E)NCH(CHN)] [M = Li, E = S (3a), Se (3b)] and [{M(THF) (PhP(=E)NCH(CHN)}] [M = Na, E = S (4a), Se (4b); M = K, E = Se (5b)] in good yield. The homoleptic Ae metal complexes [κ-(PhP(=Se)NCH(CHN)Mg(THF)] (6b) and [κ-{(PhP(=Se)NCH(CHN)}M(THF) ] (M = Ca (7b), Sr (8b), Ba (9b)] were synthesized by the one-pot reaction of 2-H with [KN(SiMe)] and MI in a 2:2:1 molar ratio at room temperature. The molecular structures of the protic-ligands 1-H and 2-H, as well as complexes 3a,b-5a,b and 6b-9b were established using single-crystal X-ray analysis. The Ae metal complexes 6b-9b were tested for ring-opening polymerization (ROP) of racemic lactide ( rac-LA) and copolymerization of rac-LA and ε-caprolactone (ε-CL) at room temperature. In the ROP of rac-LA, the calcium complex 7b exhibited high isoselectivity, with P = 0.89, whereas both the barium and strontium complexes showed lower isoselectivity with P = 0.78-0.62. In the copolymerization of rac-LA and ε-CL, both barium and strontium complexes proved to be efficient precatalysts for the formation of the block copolymer rac-LA-CL, but the reactivity of 9b was found to be better than that of 8b. All the polymers were fully characterized using differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography analyses. Kinetic studies on the ROP reaction of LA confirmed that the rate of polymerization followed the order Ba ≫ Sr ≈ Ca.

A mild, selective and facile synthesis of vinylsilanes via a recyclable platinum nanoparticle catalysed hydrosilylation of alkynes is reported. Various functionalized alkynes are selectively hydrosilylated to furnish functional β-E vinylsilanes in high yields. The catalytic effectiveness, ease of catalyst recovery and recyclability of the polysiloxane stabilized Pt-nanoparticle catalyst are the major achievements of this work. Detailed in situ characterization using Electron Microscopy and controlled poisoning experiments supports the participation of Pt-nanoparticles as active catalysts.

The cooperativity of van der Waals interactions in biomolecules and supramolecular assemblies has drawn significant scientific attention due to its offering of seamless opportunities to generate new materials. However, the potential of such cooperativity in synthetic polymers has not yet been explored. In this study, we demonstrate a strategy to achieve cooperativity via enhancement of weak interactions in a designed siloxane copolymer. Segmentation of siloxane copolymer with specific alkyl chain length (C18) induces cooperativity in van der Waals interaction among the alkyl chains, resulting in interdigitated as well as end-to-end packing. The cooperativity of van der Waals interactions is also evident by an excess melting enthalpy of ΔH = 1.86 kJ/mol in the designed block siloxane copolymer as compared to its control counterpart, i.e., a compositionally similar random siloxane copolymer. The dynamic relationship of cooperativity and physical properties is established by various analytical tools and further substantiated by disturbing the regularity of the block segments using a trace amount (1 per 99 octadecyl units) of a dissimilar alkyl chain as “dopant”.