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

Heterobimetallic {cis-[Pt](μ-σ,π-Ctriple bond; length of mdashCPh)2}[Cu(Ntriple bond; length of mdashCMe)]BF4 (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](Ctriple bond; length of mdashCPh)2 (1a: [Pt] = (bipy)Pt, 1b: [Pt] = (bipy′)Pt]) with [Cu(Ntriple bond; length of mdashCMe)4]BF4 (2). Substitution of Ntriple bond; length of mdashCMe by PPh3 (4) can be realized by the reaction of 3a with 4, whereby [{cis-[Pt](μ-σ,π-Ctriple bond; length of mdashCPh)2}Cu(PPh3)]BF4 (5) is formed. On prolonged stirring of 3 and 5, respectively, Ntriple bond; length of mdashCMe and PPh3 are eliminated and tetrametallic {[{cis-[Pt](η2-Ctriple bond; length of mdashCPh)2}Cu]2}(BF4)2 (6) is produced. Addition of an excess of Ntriple bond; length of mdashCMe to 6 gives heterobimetallic 3a. When instead of Ntriple bond; length of mdashCMe or PPh3 chelating molecules such as bipy (7) are reacted with 3a then the heterobimetallic π-tweezer molecule [{cis-[Pt](μ-σ,π-Ctriple bond; length of mdashCPh)2}Cu(bipy)]BF4 (8) is formed. Treatment of 8 with another equivalent of 7 produced [Cu(bipy2)]BF4 (9) along with [Pt](Ctriple bond; length of mdashCPh)2. However, when 3b is reacted with 1b in a 1:1 molar ratio then 10 and 11 of general composition [{[Pt](Ctriple bond; length of mdashCPh)2}2Cu]BF4 are formed. These species are isomers and only differ in the binding of the PhCtriple bond; length of mdashC 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-Ctriple bond; length of mdashCPh)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](Ctriple bond; length of mdashCPh)2 units are bridged by a copper(I) center, however, only one of the two PhCtriple bond; length of mdashC ligands of individual cis-[Pt](Ctriple bond; length of mdashCPh)2 fragments is η2-coordinated to Cu(I) giving rise to the formation of a [(η2-Ctriple bond; length of mdashCPh)2Cu]+ moiety with a linear alkyne–copper–alkyne arrangement (alkyne = midpoint of the Ctriple bond; length of mdashC triple bond). In 6 two almost parallel oriented [Pt](Ctriple bond; length of mdashCPh)2 planes are linked by two copper(I) ions, whereby two individual PhCtriple bond; length of mdashC units, one associated with each Pt building block, are symmetrically π-coordinated to Cu.