Alkyne complexes of platinum. Part 3. The synthesis and crystal structure of bis(diphenylacetylene)platinum, and studies on related compounds

Abstract

The bis(alkyne)platinum complexes [Pt(R1C2R2)2][R1= R2= Ph, CH2SiMe3, C6H4OMe-4, or C(OH)Me2; R1= But, R2= SiMe3; R1= Ph, R2= SiMe3] have been prepared by treating [Pt(cod)2](cod = cyclo-octa-1,5-diene) with excess of the alkyne. This method was unsuccessful for the synthesis of the related compounds [Pt(R1C2R2)2](R1= R2= Me, Et, But, or C6H4Me-4; R1= But, R2= Me; R1= Ph, R2= Me) but these species are readily prepared from [Pt(C2H4)3] and the respective alkynes. A single-crystal X-ray diffraction study of [Pt(PhC2Ph)2] has shown that the crystals are monoclinic, space group P2/n, with Z= 2 in a unit cell of dimensions a= 13.163(5), b= 6.062, c= 14.354(7)A, and β= 115.04(3)°. The structure has been solved by heavy-atom methods from automated diffractometer data, and refined to R 0.038 (R′ 0.046) for 3 433 reflections. The molecule adopts an essentially tetrahedral configuration, the angle between the two [graphic omitted] planes being 82°. The platinum atom lies on a crystallographic two-fold axis of rotation, at a mean distance of 2.022(5)A from the acetylenic carbon atoms which are 1.291(5)A apart. Co-ordination of the diphenylacetylene to the metal shows the expected bending of the phenyl groups away from the platinum atom [Ph–C–C 153.2(5)°]. The acetylenic stretches in the i.r. spectra of the complexes [Pt(R1C2R2)2] occur in the range 1 840–1 924 cm–1, ca. 150 cm–1 above the corresponding bands in the spectra of complexes [Pt(R1C2R2)(PR3)2], reflecting less metal–acetylene back bonding in the former. For all the complexes [Pt(R1C2R2)2] there is a downfield shift of the acetylenic-carbon resonances in the 13C n.m.r. spectra of 30–40 p.p.m. upon metal co-ordination.Equimolar amounts of [Pt(cod)2] and PhCCPh afford [Pt(PhC2Ph)(cod)], while a second mol of the acetylene yields [Pt(PhC2Ph)2]. In contrast, in the presence of excess of the alkynes 4-MeC6H4CCC6H4Me-4′, C6F5CCC6F5, and 4-MeOC6F4CCC6F4OMe-4′, [Pt(cod)2] yields monoalkyne complexes [Pt(alkyne)(cod)]. Treatment of the fluoroarylalkyne-platinum compounds with CNBut gives [Pt(R1C2R2)(CNBut)2](R1= R2= C6F5 or C6F4OMe-4). Addition of [Pt(PhC2Ph)2] to light petroleum solutions containing excess of L = CNBut, PMe3, PEt3, or PPh3 yields the complexes [Pt(PhC2Ph)L2]. By using samples containing enriched Ph13CCPh, 13C n.m.r. chemical shifts and 195Pt–13C coupling constants have been measured for these compounds, and for those species containing phosphine ligands the 13P n.m.r. spectra also recorded.