Pallada- and platinacycles—III. Synthesis of 3,4- dialkylidene-platinacyclopentanes and their metallo-ene type reaction with dioxygen. X-ray structure of a 2,3-dioxa-platinacycloheptane (dad)CH2
التفاصيل البيبلوغرافية
العنوان:
Pallada- and platinacycles—III. Synthesis of 3,4- dialkylidene-platinacyclopentanes and their metallo-ene type reaction with dioxygen. X-ray structure of a 2,3-dioxa-platinacycloheptane (dad)CH2
The reaction of bis(dibenzylideneacetone)platinum with a diazadiene (dad = 2,6-Me2-Ph-dad, 2,6-iPr2-Ph-dad) and 1,1-dimethylallene gives the 3,4-bis(isopropylidene)platinacyclopentanes (dad PtCH 2 C(CMe 2 )C(CMe 2 )C H2 (6) and (7). The metallacyclopentane rings are non-planar and rigid. Under air or oxygen the violet complexes 6 and 7 are slowly and quantitatively converted to green complexes 8 and 9, respectively. The dioxygen does not insert directly into the PtC bond but, instead, reacts in a metallo-ene type manner to give the dioxaplatinacycloheptanes (dad) PtOOCMe 2 C(CH 2 )C(CMe 2 )C H2, as revealed by NMR and X-ray diffraction studies. In complex 8 the platinum atom shows square-planar coordination. The seven-membered ring (with an almost planar CαPtOO fragment) is folded in such a way that the two exo-alkylidene groups are not in conjugation. The conformation is also rigid in solution. The disposition of the methyl groups proves the unexpected allylic inversion which occurs with the incorporation of dioxygen.
