Alkene isomerization catalysed with platinum hydride complexes

The mechanism of but‐1‐ene, pent‐1‐ene and 3‐methylbut‐1‐ene isomerization catalysed with trans ‐[PtH(SnX 3 )L 2 ] (I, L = PPh 3 , PMePh 2 , PEt 3 , PPr 3 ; X = Cl, Br) have been studied. Stoichiometric reactions of I with the alkenes proceed even at −90°C giving cis ‐[Pt(alkyI‐1) (SnX 3 ) L 2 ] (II). The equilibrium amounts of II are dependent on the nature of the phosphines, halogens and alkenes. The isomerization rates, determined at +20°C, change in parallel with the relative stabilities of II as a function of phosphine (PMePh 2 > PPh 3 > PAlk 3 ) and halogen (Br > Cl), and decrease with methyl substitution at γ‐ and δ‐ carbons of the alkenes. 2‐Substituted alk‐1‐enes undergo no isomerization in the reactions under investigation. When L is PPh 3 or PMePh 2 , the main platinum‐containing species in the course of the isomerization are trans ‐[Pt(alkyl‐1) (SnX 3 )L 2 ], appearing as a result of cis ‐ trans isomerization of II. The conversion of I, L = PAlk 3 into related trans ‐alkyl complexes, and oxidation of I, proceed more slowly than the isomerization of alkenes. The ratio of cis ‐ to trans ‐alk‐2‐enes is dependent on the size of L and is a maximum for L = PPh 3 .