| Abstrakt: |
An extension of prior protonolysis studies of platinum−carbon bonds to in situ generated Pt−C(sp2) bonds is reported. A series of (dfepe)Pt(η2-RC&tbd1;CR) complexes (R = Me, R = H; R = tert-butyl, R = H; R = Me3Si, R = Me; R = Ph, R = Me; R = R = Me; R = R = Ph) have been prepared by treatment of [(dfepe)Pt(μ-H)]2 with the corresponding alkyne in order to examine the addition of Brønsted acids to form the alkenyl complexes (dfepe)Pt(C(R)&dbd;C(H)R)(X). In the case where RC&tbd1;CR = propyne, a small (5%) amount of the propyne-bridged dimer [(dfepe)Pt]2(μ-η2:η2-MeC&tbd1;CH) was also formed which could be prepared in pure form by the thermolysis of (dfepe)Pt(η2-HC&tbd1;CMe) (1) at 90 °C. Dissolution of 1 in FSO3H at −80 °C produced the double-proton-transfer propene adduct [(dfepe)Pt(η2-H2C&dbd;C(H)Me)(X)]+, without evidence for a propenyl Pt(II) intermediate. In contrast, dissolution of 1 in FSO3D at −80 °C cleanly produced the fully deuterated propenyl complex (dfepe)Pt(C(D)&dbd;C(D)CD3)(OSO2F), which was characterized by 31P and 13C NMR. The direct observation of this initial proton-transfer intermediate in deuterated acid is ascribed to an unusually large kinetic isotope effect for the second proton-transfer step. |
