A KINETIC-STUDY OF THE REACTION OF A QUASI-AROMATIC PLATINUM(II) COMPLEX WITH AROMATIC-ALDEHYDES

A kinetic study of the reaction of PtoylH (AH), having a quasi-aromati c Pt1C3N2 ring, at the carbon para to the metal, C(12), with para-subs tituted benzaldehydes (aid) show it to be a two-step reaction producin g sequentially ACH(OH)C(6)H(4)R and A(2)CHC(6)H(4)R. In dilute HCl, 1: 4 v/v ethanol-water media, the first step follows the rate expression, rate(1) = (k(1o)+k(1h)[H+])[AH][ald] and for step 2 rate(2) = k(2)[AH ][ACh(OH)C(6)H(4)R]. The second step also has positive hydrogen ion de pendence, but lower precision in k(2) prevented a quantitative evaluat ion. In the concentration ranges used, rate(2) was about 500 x rate(1) . Both rate constants tend to decrease with increasing ethanol content of the solvent. There is a clear linear free energy relationship betw een k(1h) and the Hammett parameters for the substituted benzaldehydes . The activation parameters for k(1) showed a Delta H-double dagger of around 25 kJ mol(-1) and Delta S-double dagger of about - 170 JK(-1) mol(-1). Trends in these parameters are compared with the nickel analo gue.