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

Abstract

1-Butadienyl)platinum(11) complexes can be obtained by reaction of [Pt(C2H4)(PPh3)2] with either chloroprene or 4-chloro-3-methylbuta-1,2-diene. Treatment of these complexes with AgPF6 provides direct access to the cationic r?3-butadlenyl complexes [Ptlv3-CH2:C(R):C:CH2}(PPh3)2] [PFe] (R = H, Me), which surprisingly are attacked by the soft carbon nucleophile 2] at the central carbon atom of the allylic moiety to form methyleneplatlnacyclobutanes. These are unusual molecules that on thermolysis afford Pt(0) methylenecyclopropane complexes.

Mechanisms of the Nucleophilic Substitution of the Allyl Carbons of (π-Allyl)platinum and (π-Allyl)palladium Complexes

“…The adduct 5 is produced by the attack of the anion from the face opposite to the metal, while the adduct 5 ‘ is generated by the attack of the anion from the same face. Platinacyclo complexes have been detected by an NMR spectroscopy in solution and by X-ray analysis in solid by Ibers and co-workers. 10d,f The calculated value of the C 1 C 2 C 3 and C 1 PtC 3 dihedral angle in platinacyclobutane is 37.5° in 5a and 22.1° in 5 ‘ a , in agreement with the observed values in solution. The platinum complex 5a lies below 4a by 1.1 kcal/mol at the MP2/BS-II//RHF/BS-I level.…”

“…Soft nucleophiles attack the allyl carbons from the face opposite to the coordinated metal, whereas hard nucleophiles bind first to the metal and then attack the allyl moiety from the same face as the coordinated metal. Stereoselective syntheses by using chiral ligands have also been reported. 3c, The products of allylic alkylation, such as η 2 -complexes, η 3 -complexes, and metallacyclobutanes, , have been investigated.…”

Kinetic Addition of Nucleophiles to η3-Propargyl Rhenium Complexes Occurs at the Central Carbon to Produce Rhenacyclobutenes

“…In contrast to the predominate attack of nucleophiles at the central carbon of η 3 -propargyl complexes, the normal mode of attack on nucleophiles is at a terminal carbon of η 3 -allyl complexes . Nevertheless, a growing number of examples of nucleophilic attack at the central allyl carbon have been reported for cationic η 3 -allyl complexes of Mo, W, Rh, and Pt . In several rare cases, kinetic attack of nucleophiles at the central allyl carbon produced metallacyclobutanes that then rearranged to more stable products of net terminal allyl carbon attack.…”

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…134 A Pt π-complexed MCP 88 has been isolated by treatment of 4-chloro-3-methylbuta-1,2-diene with Pt(C 2 H 4 )(PPh 3 ) 2 followed by nucleophilic addition of potassium malonate (Scheme 25). 135 An unique synthesis of intriguing nucleobase substituted bis(formyl)MCPs 91 and 93 was obtained by treatment of nucleosides with excess of malonodialdehyde (90). The formation of ACPs occurs by elimination of water to give the final products, deriving from addition of 3 equiv of malonodialdehyde (Scheme 26).…”

“…A Pt π-complexed MCP 88 has been isolated by treatment of 4-chloro-3−methylbuta-1,2-diene with Pt(C 2 H 4 )(PPh 3 ) 2 followed by nucleophilic addition of potassium malonate (Scheme ) 25 …”