Metals in organic syntheses. XIV. NMR, IR, and reactivity studies on the olefin hydroformylation catalyzed byplatinum-tin complexes

Among the several hydrides formed when trans-[PtHClL2] (L = PPh3) reacts with SnCl2, only trans-[PtH(SnCl3)L2] rapidly inserts ethylene at -80° to yield cis-[PtEt(SnCl3)L2]. At -10°, cis-[PtEt(SnCl3)L2] irreversibly rearranges to the trans isomer, thus indicating that the cis isomer is the kinetically controlled species and that the trans isomer is thermodynamically more stable. At -50°, a mixt. of trans-[PtHClL2] and trans-[PtH(SnCl3)L2] reacts with ethylene to give cis-[PtEtClL2] and cis-[PtEt(SnCl3)L2]. This result is attributed to the catalytic activity of SnCl2 which dissocs. from cis- [PtEt(SnCl3)L2] at this temp. CO promotes the cis-trans isomerization of cis-[PtEt(SnCl3)L2], which occurs rapidly even at -80°. This rearrangement is followed by a slower reaction leading to the cationic complex trans-[PtEt(CO)L2]+ SnCl3-. At -80°, this complex does not react further; when kept at room temp. Et migration to coordinated CO takes place to give several acylplatinum complexes, i.e. trans-[PtCl(COEt)L2], trans-[Pt(SnCl3)(COEt)L2], trans-[PtCl(COEt)L2•SnCl2], and trans-[Pt(COEt)(CO)L2]+ SnCl3-. This mixt. of acylplatinum complexes reacts with H2 to yield propanal and the same complex mixt. of platinum hydrides as is obtained by treating trans-[PtHClL2] with SnCl2.