New cyclotetrasiloxanes bearing sila-alkyl substituted side chains and their applications as templates for gold nanowires

Abstract

New sila-alkyl substituted cyclotetrasiloxanes, [RMe₂SiCH₂CH₂(Me)SiO]₄ [R = Ph(1), 2-thienyl(2), 2-furyl(3)] have been synthesized by a hydrosilylation reaction between 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, (D₄^Vi) and dimethylphenylsilane/dimethyl-2-thienylsilane/dimethyl-2-furylsilane in the presence of Karstedt's catalyst. X-ray crystallographic studies of 1 and 2 reveal all-trans conformation of the methyl groups bonded to puckered siloxane core and formation of 3D supramolecular assemblies by virtue of intermolecular C–H⋯π interactions. These siloxanes act as potential templates for expeditious one pot synthesis of gold nanowires of varying aspect ratios which are obtained by reduction of HAuCl₄·3H₂O with triethylsilane (CHCl₃, RT). On the other hand, the use of linear polysiloxane, [2-ThMe₂SiCH₂CH₂(Me)SiO]_n (4) in lieu of the cyclosiloxane 2 affords predominant formation of polydispersed AuNPs along with a few extended structures. These results suggest that conformational confinement of the appended groups on the cyclosiloxanes, 1–3 plays an important role to impart morphological control of the gold nanowire assemblies.