Synthesis and reactivity of cationic (.eta.3-butadienyl)platinum complexes

(2-η 1 -Butadienyl) platinum (II) complexes can be obtained by reaction of [Pt(C 2 H 4 )(PPh 3 ) 2 ] with either chloroprene or 4-chloro-3-methylbuta-1,2-diene. Treatment of these complexes with AgPF 6 provides direct access to the cationic η 3 -butadienyl complexes [Pt{η 3 −CH 2 :C(R):C:CH 2 }(PPh 3 ) 2 ][PF 6 ] [R = H, Me), which surprisingly are attacked by the soft carbon nucleophile K- [CH(CO 2 Me) 2 ] at the central carbon atom of the allylic moiety to form methyleneplatinacyclobutanes. These are unusual molecules that on thermolysis afford Pt(O) methylenecyclopropanes complexes