Functionalized 2-Pyridyl-Substituted Metallo-1,2-enedithiolates. Synthesis, Characterization, and Photophysical Properties of (dppe)M{S<sub>2</sub>C<sub>2</sub>(2-pyridine(ium))(CH<sub>2</sub>CH<sub>2</sub>OR‘‘)} and (dppe)M[{S<sub>2</sub>C<sub>2</sub>(CH<sub>2</sub>CH<sub>2</sub>-<i>N</i>-2-pyridinium)}]<sup>+</sup> (R‘‘ = H, Acetyl, Lauroyl; M = Pd, Pt; dppe = 1,2-Bis(diphenylphosphino)ethane)
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The complexes (dppe)M{S2C2(2-pyridine)(CH2CH2OC(O)CH3)} (dppe = 1,2-bis(diphenylphosphino)ethane; M = Pd, Pt) were prepared from 1-(2-pyridyl)-4-acetoxy-2-bromobutan-1-one and the corresponding (dppe)M(SH)2 complexes. The acetyl group was removed from the metal complexes to yield the corresponding alcohols, (dppe)M{S2C2(2-pyridine)(CH2CH2OH)}. The lauroyl derivatives (dppe)M{S2C2(2-pyridine)(CH2CH2OC(O)(CH2)10CH3)} were prepared by esterifying the alcohols with lauroyl chloride. The alkylated pyridinium complexes [(dppe)M{S2C2(CH2CH2-N-2-pyridinium)}]+ were generated by the addition of either p-toluenesulfonyl chloride or bis(triazole) o-chloroaryl phosphate to (dppe)M{S2C2(2-pyridine)(CH2CH2OH)}. [(dppe)Pd{S2C2(CH2CH2-N-2-pyridinium)}][BPh4] crystallizes in the P1̄ space group with a = 9.1924(2) Å, b = 16.0191(2) Å, c = 17.4368(3) Å, α = 106.292(2)°, β = 96.235°, and γ = 95.183(2)°. The molecule is best described as a square planar palladium complex with a planar metallo-1,2-enedithiolate which is coplanar with the alkylated pyridinium. The pyridinium-substituted platinum 1,2-enedithiolate complexes have a 1,2-enedithiolate to heterocycle π* charge-transfer transition (ILCT) that is the lowest lying band. Like [(dppe)Pt{S2C2(2-pyridinium)(H)}]+, [(dppe)Pt{S2C2(CH2CH2-N-2-pyridinium)}]+ is luminescent in room-temperature solution with two emissive states assigned to the ILCT* singlet and triplet. The lifetime of the 1ILCT* is 0.2 ns, 1φ = 0.002, while the lifetime of the 3ILCT is 8.3 μs, 3φ = 0.01 (DMSO). While [(dppe)Pt{S2C2(CH2CH2-N-2-pyridinium)}]+ is emissive, the [(dppe)Pt{S2C2(2-pyridinium)(CH2CH2OR‘‘)}]+ complexes are weak emitters at best in solution with triplet quantum yields of <0.0001 (DMSO). These photophysical studies suggest that the heterocycle and the 1,2-enedithiolate must be coplanar in the ILCT excited states for the complexes to be emissive in room-temperature solution.
