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-1κCα:η2-CCR)(μ-2κCα: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-1κCα: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-1κCα:η2-C3,4-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.