Transition metal–carbon bonds. Part XXXII. Hexamethyl Dewar benzene; dehydrohexamethyl Dewar benzene and related complexes of platinum(II)

Abstract

Na₂PtCl₄ or [Pt₂Cl₄(C₂H₄)₂] reacts with hexamethyl Dewar benzene (hmdb) to give [PtCl₂(C₁₂H₁₈)] in which C₁₂H₁₈(hmdb) is acting as a chelating diolefin. Metathesis gives the corresponding dibromide [PtBr₂(C₁₂H₁₈)] which with hydrobromic acid gives [PtBr₂(pentamethylcyclopentadiene)]. With sodium carbonate [PtCl₂(C₁₂H₁₈)] loses the elements of HCl to give [Pt₂Cl₂(µ-C₁₂H₁₇)₂] in which C₁₂H₁₇ is pentamethylbicyclo[2,2,0]hexa-2,5-dien-2-ylmethyl which bridges two platinum atoms. With lithium bromide or sodium iodide [Pt₂Cl₂(µ-C₁₂H₁₇)₂] gives [Pt₂X₂(π-C₁₂H₁₇)₂](X = Br or I) with bridging halogens and a π-allylic ligand pentamethylbicyclo [2,2,0]hexa-2,5-dien-2-ylmethyl. [Pt₂X₂(π-C₁₂H₁₇)₂] show typical bridge-splitting reactions with ligands L = pyridine, isoquinoline, PPh₃, or AsPh₃ to give [PtX(π-C₁₂H₁₇)L] or with bipyridyl to give [Pt(bipy)(π-C₁₂H₁₇]⁺I^–. With sodium cyclopentadienide or thallium acetylacetonate mononuclear species [PtQ(π-C₁₂H₁₇)](Q = C₅H₅ or acac) are formed. [Pt(acac)(π-C₁₂H₁₇)] with hydrogen chloride gives [Pt₂Cl₂(π-C₁₂H₁₇)₂]. ¹H n.m.r. and i.r. data are given and discussed.