Stereochemistry and Mechanisms of Reactions of Dioxygen Complexes with Organic Electophiles as Studied by Use of Chiral Reagents and Isotopic Labeling

Article abstract of DOI:10.1021/ja00409a035

From reactions of PtO2L2 (L = PPh3, P(c-C6H11)3) with 1 mol of triphenylmethyl bromide or benzoyl bromide the corresponding (alkylperoxo)platinum(II) complexes L2PtBr(OOR) (1a, L = PPh3, R = CPh3; 1b, L = P(c-C6H11)3, R = CPh3; 2, L = PPh3, R = COPh) were isolated, which were well characterized by elemental analysis and IR spectroscopy.The complex 1a,b or 2 was treated with another mole of organic halides to give the corresponding dialkyl peroxides (Ph3COOCPh3, PhC(O)OOC(O)Ph) in good yields.Thus, the stepwise mechanism proposed previously for "metal-assisted peroxidations" was verified.A similar reaction of PtO2(PPh3)2 with an optically active (S)-(-)-α-phenethyl bromide produced a peroxoplatinum(II) complex, PtBr(OOCH(CH3)Ph)(PPh3)2 (3), which gave upon acidolysis (R)-(+)-α-phenethyl hydroperoxide.Reductive cleavage of 3 with NaBH4 gave (R)-(+)-α-phenethyl alcohol.Hence, it can be concluded that the reaction of PtO2L2 with organic halides proceeds via the S_N2-type transition state.From the IR 18O isotopic shifts the O-O stretching band was assigned for the products from the reactions of PtO2L2 with acetone (4), benzophenone (5), 1,1-dicyano-2-methylpropene (8), and tetracyanoethylene (9).The 18O IR study also shows that the peroxy bond involved in these products is derived from PtO2L2.The reaction product (10a, L = PPh3; 10b, L = P(c-C6H11)3) obtained from PtO2L2 and CH3OOCC<*>CCOOCH3 was also studied by 18O isotopic IR and 13C NMR spectra.Acidolysis of 10b gave dimethyl dihydroxymaleate ina good yield.Thus it was established that the reaction of an electrophilic acetylene with PtO2L2 results in the O-O bond cleavage.