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 (k1) and the direct (k2) reaction pathways were determined to be k1 = (9.7 ± 2.4)
× 10-5 s-1, k2 = (11.7 ± 0.3) × 10-2 M-1 s-1 and k1 = (7.1 ± 4.9) × 10-5 s-1, k2 = (23.0 ± 1.3)
× 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 ΔH⧧ = 77.8 ± 5.5 kJ mol-1, ΔS⧧ = −56 ± 18 J K-1mol-1 and ΔH⧧ = 67.6
± 1.8 kJ mol-1, ΔS⧧ = −37 ± 6 J K-1mol-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).