Synthesis and characterization of five-co-ordinate alkyne complexes of platinum(II). Crystal and molecular structure of [(dmphen) MePt(µ-Cl)(µ-MeC≡CMe)Pt(Cl)Me]·CH2 Cl2(dmphen = 2,9-dimethyl-1,10-phenanthroline)

Abstract

Alkynes with electron-withdrawing substituents add to square-planar platinum(II) complexes of general formula [Pt(Cl)R(N–N)](R = Me or C₆H₄OMe-4. N–N = bidentate nitrogen ligand) affording the corresponding five-co-ordinate trigonal-bipyramidal (TBPY) compounds [Pt(Cl)R(alkyne)(N–N)]. The related five-co-ordinate cationic species [PtMe(alkyne)(N–N)(MeCN)]⁺ have also been characterized in the presence of excess MeCN. Methyl insertion and formation of a β-methylvinyl dervative is instead observed by treating [PtMe(N–N)(MeCN)]⁺ with MeO₂CC ≡ CCO₂Me in the absence of free MeCN. Using a 1:2 alkyne:[Pt(Cl)Me(dmphen)] ratio (dmphen = 2,9-dimethyl-1,10-phenanthroline). binuclear species [Pt₂Cl₂Me₂(alkyne)(dmphen)] are isolated. An X-ray crystallographic study was carried out on the but-2-yne derivative. Crystals are monoclinic, space group P2₁/c, Z= 4, in a unit cell of dimensions a= 15.719(4), b= 12.307(3), c= 25.048(7)Å, β= 148.50(1)°. The structure has been refined to R 0.054 (R′ 0.064) for 3718 intensity data [I 3σ(I)]. The two platinum atoms display different co-ordination numbers [a five-(TBPY) and a four-co-ordinate square-planar arrangement of the ligands] and are held together by the but-2-yne and one chlorine bridge. The MeC≡CMe ligand transversely bridges the Pt ⋯ Pt vector (3.079 Å) and the dihedral angle between the two planes formed by the two Pt-µ-C₂ units is 102.2(5)°.