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

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Abstract
Tetraorganotin compounds SnMe4–nRn(R = aryl, n= 1–3) react with [Pt(C2H4)(PPh3)2] to form cis-[PtR-(SnMe4–nRn–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.

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