The structure and coordinative self-assembly of films based on a palladium compound of pyridyl-acetylene platinum and its application in Suzuki and Heck coupling reactions

Abstract

The platinum complex [Pt₂(CCPy)₂(dppm)₂] (Py = 4-pyridyl, dppm = bis(diphenylphosphino)methane) 1 has been prepared and characterized. Single crystal X-ray diffraction analysis reveals that the Pt₂(CCPy)₂ fragment of 1 exhibits an approximately linear molecular geometry, in which the Pt–Pt bond may be considered as having been inserted within the delocalized π-electron system of the 1,4-bis(4′-pyridyl)buta-1,3-diyne. The ability of the two terminal pyridyl nitrogen atoms of 1 to coordinate to other metal centers has enabled the use of 1 as a linking ligand in the layer-by-layer (LbL) growth of heterometallic films. The self-assembly behavior of 1 with Pd(II), supported by chloride counter ions, on poly(ethylenimine) (PEI) functionalized solid surfaces has been investigated. The resulting multilayer films of general composition and form (PdCl₂/1)_n have been characterized using UV-vis absorption spectroscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). On the basis of the UV-vis spectroscopic data, it was shown that the (PdCl₂/1)_n multilayer films could be grown in a regular fashion, with film thickness increasing linearly with increasing deposition of the metal–ligand bilayers. Consistent with this metal ion dependent LbL growth, AFM images of the multilayer films exhibited island-shaped nanostructures with a mean diameter of about 25 nm. The catalytic properties of the (PdCl₂/1)_n multilayers were investigated, and (PdCl₂/1)_n film-loaded slides were used as a catalyst reservoir capable of liberating catalytic amounts of a highly active Pd species, which was suitable for promoting C–C bond formations. The catalyst loading was as low as 2.76 × 10⁻⁶ mol% and gave high yields. The LbL catalyst and the technology presented in this work, show distinctive features that include extraordinarily low loading and high catalytic active characteristics.