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

The novel acetylide complexes [trans-Pt(C drop CR)(2)(PPh3)(2)] [R = (Z)-CM e=CHMe 2a and C(OMe)EtMe 3] have been prepared starting from [trans-Pt{C dr op CC(OH)EtMe}(2)(PPh3)(2)] I by dehydration (2a) and etherification (3) re actions, respectively. The analogous alpha -hydroxyacetylide, R = C(OH)Ph-2 4, has been obtained by reaction of [cis-PtCl2(PPh3)(2)] with HC drop CC(O H)Ph-2 in NEt2H, in presence of CuI. These bis(acetylide) complexes react w ith [cis-Pt(C6F5)(2)(THF)(2)] leading to symmetrical diplatinum species [tr ans,trans-(PPh3)(C6F5)Pt(mu -1 kappaC(alpha):eta (2)-C drop CR)(mu -2 kappa C(alpha):eta (2)-C=CR)Pt(C6F5)-(PPh3)] [R = C(OH)EtMe 5, (Z)-CMe=CHMe 6, C( OMe)EtMe 7, C(OH)Ph-2 8] containing a double alkynyl bridging system. Compl exes 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 mononucl ear derivatives [trans-Pt(C drop CR)(C6F5)(PPh3)(2)] [R = C(OH)EtMe 9, (Z)- CMe=CHMe 10, C(OMe)-EtMe 11, C(OH)Ph-2 12]. Treatment of the hydroxyalkynyl complex 9 with HBF4 in Et2O also produces the dehydrated enynyl derivative 10. The mononuclear complexes [trans-Pt(C drop CR)(2)(PPh3)(2)] (1, 3, 4) react with [cis-Pt(C6F5),(CO)(THF)] to afford, under alkynylation of the ca rbonyl fragment "Pt(C6F5)(2)(CO)", the mu-eta (2)-acetylide-bridged zwitter ionic derivatives [cis,trans-(CO)(C6F5)(2)Pt(mu -1 kappaC(alpha):eta (2)-C drop CR)Pt(C drop CR)(PPh3)(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 co mplex 2a is not clean, the related mixed pentafluorophenyl enynyl complex 1 0 produces the simple displacement of THF from [cis-Pt(C6F5)(2)(CO)(THF)] b y the alkynyl fragment and formation of the adduct [trans,cis-(PPh3)(2)(C6F 5){mu -1 kappaC(alpha):eta (2)-C-3,C-4-C dropC-(Z)-CMe-CHMe}Pt(C6F5)(2)(CO) ] 16. The crystal structures of 7,8 and 13 have also been determined. For c omplex 8, the dimer units are linked via unusual intermolecular hydrogen bo nds (O-H . . .F-C) leading to an extended polymeric chain along the crystal lographic c axis.