Synthesis, structure, and reactivity of arylfluoro platinum(II) complexes

Complexes of the type trans-[PtPhFL2], where L = PPh3 (4), PMe2Ph (5), were synthesized. Complex 4 was characterized by X-ray crystallography. The equilibrium constant for the substitution of the fluoride trans to phenyl in 4 by Cl- and I- was determined, and the stability sequence follows the normal trend seen in "soft" metal centers: i.e., the Pt has a preference for the halide in the order I > Cl > F; the difference is, however, fairly small. The substitution kinetics follow the usual two-term rate law, and the rate constants for the solvolytic (k(1)) and the direct (k(2)) reaction pathways were determined to be k(1) = (9.7 +/- 2.4) x 10(-5) s(-1), k(2) = (11.7 +/- 0.3) x 10(-2) M-1 s(-1) and k(1) = (7.1 +/- 4.9) x 10(-5) s(-1), k(2) = (23.0 +/- 1.3) x 10(-2) M-1 s(-1) for Cl- and I-, respectively. Activation parameters for the solvolytic and direct pathways with Cl- as incoming ligand are typical for associative processes and were determined to be DeltaH(double dagger) = 77.8 +/- 5.5 kJ mol(-1), DeltaS(double dagger) = -56 +/- 18 J K(-1)mol(-1) and DeltaH(double dagger) = 67.6 +/- 1.8 kJ mol(-1), DeltaS(double dagger) = -37 +/- 6 J K(-1)mol(-1), respectively. Complexes 4 and 5 react with Me3SnPh, and within 2-15 min there is a complete conversion to products. 4 gives a single product, trans- [PtPhMe(PPh3)(2)], which was characterized by X-ray crystallography. 5 gives two products: trans-[PtPhMe(PMe2Ph)(2)] and trans-[PtPh2(PMe2Ph)(2)]. Steric effects on the reactivity speak in favor of an associative mechanism. The surprisingly high reactivity for the transmetalations, compared to the substitution reactions, can be explained in terms of an associative mechanism, where a strong, bridging Sn-F interaction stabilizes the transition state. Furthermore, only trans products are formed; i.e., we have an exclusive F-for-R (R = Me, Ph) substitution at these platinum fluoro complexes. Treatment of 4 with phenylacetylene in benzene at room temperature gives the alkynyl complex trans-[PtPh(CCPh)(PPh3)(2)] (8).