Preparation and characterisation of neutral double- and mono-alkynyl bridged diplatinum complexes

Abstract

The novel acetylide complexes [trans-Pt(CCR)₂(PPh₃)₂] [R = (Z)-CMeCHMe 2a and C(OMe)EtMe 3] have been prepared starting from [trans-Pt{CCC(OH)EtMe}₂(PPh₃)₂] 1 by dehydration (2a) and etherification (3) reactions, respectively. The analogous α-hydroxyacetylide, R = C(OH)Ph₂4, has been obtained by reaction of [cis-PtCl₂(PPh₃)₂] with HCCC(OH)Ph₂ in NEt₂H, in presence of CuI. These bis(acetylide) complexes react with [cis-Pt(C₆F₅)₂(THF)₂] leading to symmetrical diplatinum species [trans,trans-(PPh₃)(C₆F₅)Pt(μ-1κC^α:η²-CCR)(μ-2κC^α:η²-CCR)Pt(C₆F₅)(PPh₃)] [R = C(OH)EtMe 5, (Z)-CMeCHMe 6, C(OMe)EtMe 7, C(OH)Ph₂8] containing a double alkynyl bridging system. Complexes 5 and 7 have been obtained as mixtures of the corresponding RR/SS and RS/SR diastereomers (1 ∶ 1 molar ratio). Treatment of 4–8 with 2 equivalents of PPh₃ produces bridge splitting to yield the corresponding mixed mononuclear derivatives [trans-Pt(CCR)(C₆F₅)(PPh₃)₂] [R = C(OH)EtMe 9, (Z)-CMeCHMe 10, C(OMe)EtMe 11, C(OH)Ph₂12]. Treatment of the hydroxyalkynyl complex 9 with HBF₄ in Et₂O also produces the dehydrated enynyl derivative 10. The mononuclear complexes [trans-Pt(CCR)₂(PPh₃)₂] (1, 3, 4) react with [cis-Pt(C₆F₅)₂(CO)(THF)] to afford, under alkynylation of the carbonyl fragment “Pt(C₆F₅)₂(CO)”, the μ-η²-acetylide-bridged zwitterionic derivatives [cis,trans-(CO)(C₆F₅)₂Pt(μ-1κC^α:η²-CCR)Pt(CCR)(PPh₃)₂] [R = C(OH)EtMe 13, C(OMe)EtMe 14, C(OH)Ph₂15]. On the other hand, while the analogous reaction with the bis-enynyl complex 2a is not clean, the related mixed pentafluorophenyl enynyl complex 10 produces the simple displacement of THF from [cis-Pt(C₆F₅)₂(CO)(THF)] by the alkynyl fragment and formation of the adduct [trans,cis-(PPh₃)₂(C₆F₅){μ-1κC^α:η²-C^3,4-CC-(Z)-CMeCHMe}Pt(C₆F₅)₂(CO)] 16. The crystal structures of 7, 8 and 13 have also been determined. For complex 8, the dimer units are linked via unusual intermolecular hydrogen bonds (O–H⋯F–C) leading to an extended polymeric chain along the crystallographic c axis.