Oxidative-addition and reductive-elimination reactions involving platinum complexes and tetraorganotin compounds

Abstract

Tetraorganotin compounds SnMe_4–nR_n(R = aryl, n= 1–3) react with [Pt(C₂H₄)(PPh₃)₂] to form cis-[PtR-(SnMe_4–nR_n–1)(PPh₃)₂][n= 1(1) or 2(2)], but with an excess of SnMe₃R (if R has no 2-substituents) the complex cis-[PtR(SnMe₂R)(PPh₃)₂](2) is also formed by insertion of (1) into an Sn–Me bond of a second molecule of SnMe₂R and elimination of SnMe₄. Complex (1) reacts with SnMe₂R₂ to form (2) and SnMe₃R and both of these reactions are reversible: (1) and SnMe₃R are formed from (2) and SnMe₄, and (1) and SnMe₂R₂ are formed from (2) and SnMe₃R. The system catalyses the redistribution 2SnMe₃R ⇌ SnMe₂R₂+ SnMe₄, and (2) catalyses redistribution of aryl groups (R,R′) between SnMe₂R₂ and SnMe₂R′₂. Mechanisms involving platinum(IV) intermediates are proposed for these and several related reactions. Reactions of (1) and (2)(R = Ph) with a number of oxidative-addition reagents are reported. With organotin chlorides SnMe₃Cl, SnMe₂Cl₂, and SnPh₂Cl₂, (1) and (2) form bis(triphenylphosphine)platinum(II) complexes in which a Pt–Ph bond is retained and in which the number of chlorine atoms on the stannio-ligand is less than or equal to that in the tin(IV) reagent. The mechanism of these processes also appears to involve platinum(IV) intermediates and to be consistent with the normal order of reactivity Sn–Cl > Sn–R > Sn–Me. Some complexes (1) and (2) have been isolated and characterised and ³¹P-{¹H} n.m.r. parameters are reported for all complexes.