Synthesis of Long, Palladium End-Capped Polyynes through the Use of Asymmetric 1-Iodopolyynes

The synthesis of a unique series of long, asymmetric 1-iodopolyynes (1-CnI and 2-CnI) with the sp-hybridized carbon chain up to a decapentayne is reported. These compounds were then used as substrates in reactions with Pd(PPh3)(4) leading to another series of palladium end-capped polyynes, which were unstable in solution. Organometallic octatetraynes 1-C-8[Pd]I, 2-C-8[Pd]I, and decapentayne 1-C-10[Pd]I are palladium end-capped polyyne compounds with the longest carbon chains reported so far. All the complexes as well as their organic precursors were fully characterized by NMR, HRMS(ESI), IR, TGA-DTA, and UV/Vis techniques, and the X-ray crystal structures of two silyl-protected precursors and one palladium complex are presented. The synthetic approach for palladium species is envisioned as a general route for the synthesis of labile organometallic polyynes.