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

Cationic five-coordinate [Pt(3-R'-4-R2-C~,)(MeCN)(6-Me-py-2-CH=NPh)(C2H4)]+co mplexes (R1R,2= H, Me, OMe) undergo an unexpected rearrangement at 0 "C in chloroform solution, affording, after treatment with aqueous LiC1, the neutral four-coordinate species [Pt(2-Et-4-R1-5-R2-C6H2)C1(6-Me-py-2-CH=NPh)]. Pt4, bond breaking and making is involved in the whole process, resulting in a 1,Zshift 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-R'-4-R2-C6H3)(MeCN)(6-Me-py-2-CH=aNtP 0h )"C].+ When higher (>3) ethylene/Pt ratios are used, only the five-coordinate [Pt(3-R1-4-R2-C6H3CHzCHz)Cl(6-Me-py-2-CH=NPh)(C2H.J] complex is isolated. Aa the experimental data rule out the possibility of a (2-mylethy1)platinum to (2-ethyhryl)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.