Carbon-carbon bond formation in cationic aryl-olefin-platinum(II) complexes

Article abstract of DOI:10.1021/om00059a033

Cationic five-coordinate [Pt(3-R¹-4-R²-C₆H ₃)(MeCN)(6-Me-py-2-CH=NPh)(C₂H₄)]⁺ complexes (R¹, R² = H, Me, OMe) undergo an unexpected rearrangement at 0°C in chloroform solution, affording, after treatment with aqueous LiCl, the neutral four-coordinate species [Pt(2-Et-4-R¹-5-R²-C₆H ₂)Cl(6-Me-py-2-CH=NPh)]. Pt-C_aryl bond breaking and making is involved in the whole process, resulting in a 1,2-shift of the platinum atom to an adjacent position of the benzene ring. The same compound is obtained, together with products deriving from a typical insertion, when an equimolar amount of ethylene is added to a chloroform solution of [Pt(3-R¹-4-R²-C₆H ₃)(MeCN)(6-Me-py-2-CH=NPh)]⁺ at 0°C. When higher (>3) ethylene/Pt ratios are used, only the five-coordinate [Pt(3-R¹-4-R²-C₆H₃CH ₂CH₂)Cl(6-Me-py-2-CH= NPh)(C₂H₄)] complex is isolated. As the experimental data rule out the possibility of a (2-arylethyl)platinum to (2-ethylaryl)platinum rearrangement, different reaction paths are suggested for the two processes. When the two reactions are combined in a one-pot sequence, a regiocontrolled double alkylation of the aryl system can be obtained. The behavior of substrates containing bidentate nitrogen ligands having different five-coordination stabilizing effects is examined, and data concerning the reactions of propene and styrene are reported.