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

摘要

The novel acetylide complexes [trans-Pt(C ident to CR)_2(PPh_3)_2][R = (Z)-CMe=CHMe 2a and C(OMe)EtMe 3] have been prepared starting from [trans-Pt{C ident to CC(OH)EtMe}_2(PPh_3)_2] 1 by dehydration (2a) and etherification (3) reactions, respectively. The analogous #alpha#-hydroxyacetylide, R = C(OH)Ph_2 4, has been obtained by reaction of [cis-PtCl_2(PPh_3)_2] with HC ident to CC(OH)Ph_2 in NEt_2H, in presence of CuI. These bis(acetylide) complexes react with [cis-Pt(C_6F_5)_2(THF)_2] leading to symmetrical diplatinum species [trans,trans-(PPh_3)(C_6F_5)Pt(#mu#-1#kappa#C~a:#eta#~2-C ident to CR)(#mu#-2#kappa#C~a:#eta#~2-C=CR)Pt(C_6F_5)(PPh_3)][R = C(OH)EtMe 5, (Z)-CMe=CHMe 6, C(OMe)EtMe 7, C(OH)Ph_2 8] 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 PPh_3 produces bridge splitting to yield the corresponding mixed mononuclear derivatives [trans-Pt(C ident to CR)(C_6F_5)(PPh_3)_2] [R = C(OH)EtMe 9, (Z)-CMe = CHMe 10, C(OMe)EtMe 11, C(OH)Ph_2 12]. Treatment of the hydroxyalkynl complex 9 with HBF_4 in Et_2O also produces the dehydrated enynyl derivative 10. The mononuclear complexes [trans-Pt(C iddent to CR)_2(PPh_3)_2] (1,3,4) react with [cis-Pt(C_6F_5)_2(CO)z(THF)] to afaford, under alkynylation of the carbonyl fragment "Pt(C_6F_5)_2(CO)", the #mu#-#eta#~2-acetylide-bridged zwitterionic derivatives [cis,trans-(CO)(C_6F_5)_2Pt(#mu#-1#kappa#C~a:#eta#~2-C ident to CR)Pt(C ident to CR)(PPh_3)_2] [R = C(OH)EtMe 13, C(OMe)EtMe 14, C(OH)Ph_2 15]. On the other hand, while the analogous reaction with the bis-enynyl complex 2a is not clean, the related mixed pentafluoropheny enynyl complex 10 produces the simple displacement of THF from [cis-Pt(C_6F_5)_2(CO)(THF)] by the alkynyl fragment and formation of the adduct [trans,cis-(PPh_3)_2(C_6F_5){#mu#-1#kappa#C~a:#eta#~2-C~(3,4)-C ident to C-(Z)-CMe-CHMe}Pt(C_6F_5)_2(CO)] 16. The crsytal 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.