Platinacyclopentane complexes

Oxidative addition of diphenyliodonium salt, Ph2lOTf, to PtMe2(bipy) produces the Pt(iv) complex with methyl, phenyl, and triflate ligand 930, and the product reacts with Nal to form a mixture of structural isomers of octahedral Pt(iv) complexes 931 and 932 (Scheme 115). The analogous platinacyclopentane complexes also undergo the oxidative addition to afford Pt(iv) metallacycles with OTf and I ligands 933 and 934. ... 

The rearrangement of platinacyclobutanes to alkene complexes or ylide complexes is shown to involve an initial 1,3-hydride shift (a-elimina-tion), which may be preceded by skeletal isomerization. This isomerization can be used as a model for the bond shift mechanism of isomerization of alkanes by platinum metal, while the a-elimination also suggests a possible new mechanism for alkene polymerisation. New platinacyclobutanes with -CH2 0SC>2Me substituents undergo solvolysis with ring expansion to platinacyclopentane derivatives, the first examples of metallacyclobutane to metallacyclopentane ring expansion. The mechanism, which may also involve preliminary skeletal isomerization, has been elucidated by use of isotopic labelling and kinetic studies. 

As for palladium discussed above, the majority of platinacyclopentanes are based on the divalent metal. However, the structurally characterised complex [Pt(C4H8) (Ph)I(bipy)] 91 has been obtained by treating [Pt(C4H8)(bipy)] 85 with di-phenyliodonium triflate followed by triflate-iodide metathesis [Eq. (36)]. As in the palladium example 79 described above, both cis and trans oxidative addition products are observed.103 Prior to this, the structurally characterised platinum(IV) derivative [Pt(C4H8)I2(PMe2Ph)2] 92 had been obtained via trans oxidative addition of iodine to [Pt(C4H8)(PMe2Ph)2] [Eq. (37)].113... 

A detailed recent study has been made to try and elucidate whether metallacyclobutanes rearrange to alkenes by p elimination or by a elimination to give an intermediate ylide complex, which can rearrange to an alkene complex. Using deuterium-labeled platinum(IV) platinacyclobutanes it is concluded that the pathway involves a [1,3] H shift (a elimination) rather than a [1,2] H shift ()3 elimination). Platinacyclopentanes have also been formed by an alkene coupling between Pt(cod)2 and butadiene. Addition of PMcs gives complex (66 equation 2(K)). ... 

Platinacyclopentanes with heteroatoms or functional groups in the five-membered chelate ring may also be obtained as stable complexes. Single and double insertion of isonitrile into the Pt-C bond of a cyclohexyne-Pt(O)... 

The complex with triphenylphosphonium ylides 405 undergoes orthometallation of the ligand to form the complex with a five-membered platinacyclopentane 406 (Equation (102)). ... 

Oxidative addition of 1,3-dibromopropane to platinacyclopentane with a bipy ligand yields a mixture of geometrical isomers of the Pt(iv) complexes with bromo and 3-bromopropyl ligands (928 and 929, Equation (176)). ... 

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