Synthesis of di-, tri- and tetranuclear platinum(II) and copper(I) acetylide complexes

Abstract

Heterobimetallic { cis-[Pt](μ-σ,π-C CPh) 2}[Cu(N CMe)]BF 4 ( 3a: [Pt] = (bipy)Pt, bipy = 2,2′-bipyridine; 3b: [Pt] = (bipy′)Pt, bipy′ = 4,4′-dimethyl-2,2′-bipyridine) is accessible by the reaction of cis-[Pt](C CPh) 2 ( 1a: [Pt] = (bipy)Pt, 1b: [Pt] = (bipy′)Pt]) with [Cu(N CMe) 4]BF 4 ( 2). Substitution of N CMe by PPh 3 ( 4) can be realized by the reaction of 3a with 4, whereby [{ cis-[Pt](μ-σ,π-C CPh) 2}Cu(PPh 3)]BF 4 ( 5) is formed. On prolonged stirring of 3 and 5, respectively, N CMe and PPh 3 are eliminated and tetrametallic {[{ cis-[Pt](η 2-C CPh) 2}Cu] 2}(BF 4) 2 ( 6) is produced. Addition of an excess of N CMe to 6 gives heterobimetallic 3a. When instead of N CMe or PPh 3 chelating molecules such as bipy ( 7) are reacted with 3a then the heterobimetallic π-tweezer molecule [{ cis-[Pt](μ-σ,π-C CPh) 2}Cu(bipy)]BF 4 ( 8) is formed. Treatment of 8 with another equivalent of 7 produced [Cu(bipy 2)]BF 4 ( 9) along with [Pt](C CPh) 2. However, when 3b is reacted with 1b in a 1:1 molar ratio then 10 and 11 of general composition [{[Pt](C CPh) 2} 2Cu]BF 4 are formed. These species are isomers and only differ in the binding of the PhC C units to copper(I). A possible mechanism for the formation of 10 and 11 is presented. The solid state structures of 6, 10 and 11 are reported. In 11 the [{ cis-[Pt](μ-σ,π-C CPh) 2} 2Cu] + building block is set-up by two nearly orthogonal positioned bis(alkynyl) platinum units which are connected by a Cu(I) ion, whereby the four carbon–carbon triple bonds are unsymmetrical coordinated to Cu(I). In trimetallic 10 two cis-[Pt](C CPh) 2 units are bridged by a copper(I) center, however, only one of the two PhC C ligands of individual cis-[Pt](C CPh) 2 fragments is η 2-coordinated to Cu(I) giving rise to the formation of a [(η 2-C CPh) 2Cu] + moiety with a linear alkyne–copper–alkyne arrangement (alkyne = midpoint of the C C triple bond). In 6 two almost parallel oriented [Pt](C CPh) 2 planes are linked by two copper(I) ions, whereby two individual PhC C units, one associated with each Pt building block, are symmetrically π-coordinated to Cu.