Functionalized 2-Pyridyl-Substituted Metallo-1,2-enedithiolates. Synthesis, Characterization, and Photophysical Properties of (dppe)M{S₂C₂(2-pyridine(ium))(CH₂CH₂OR‘‘)} and (dppe)M[{S₂C₂(CH₂CH₂-<i>N</i>-2-pyridinium)}]⁺ (R‘‘ = H, Acetyl, Lauroyl; M = Pd, Pt; dppe = 1,2-Bis(diphenylphosphino)ethane)

Abstract

The complexes (dppe)M{S(2)C(2)(2-pyridine)(CH(2)CH(2)OC(O)CH(3))} (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{S(2)C(2)(2-pyridine)(CH(2)CH(2)OH)}. The lauroyl derivatives (dppe)M{S(2)C(2)(2-pyridine)(CH(2)CH(2)OC(O)(CH(2))(10)CH(3))} were prepared by esterifying the alcohols with lauroyl chloride. The alkylated pyridinium complexes [(dppe)M{S(2)C(2)(CH(2)CH(2)-N-2-pyridinium)}](+) were generated by the addition of either p-toluenesulfonyl chloride or bis(triazole) o-chloroaryl phosphate to (dppe)M{S(2)C(2)(2-pyridine)(CH(2)CH(2)OH)}. [(dppe)Pd{S(2)C(2)(CH(2)CH(2)-N-2-pyridinium)}][BPh(4)] crystallizes in the P&onemacr; space group with a = 9.1924(2) Å, b = 16.0191(2) Å, c = 17.4368(3) Å, alpha = 106.292(2) degrees, beta = 96.235 degrees, and gamma = 95.183(2) degrees. 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 pi charge-transfer transition (ILCT) that is the lowest lying band. Like [(dppe)Pt{S(2)C(2)(2-pyridinium)(H)}](+), [(dppe)Pt{S(2)C(2)(CH(2)CH(2)-N-2-pyridinium)}](+) is luminescent in room-temperature solution with two emissive states assigned to the ILCT singlet and triplet. The lifetime of the (1)ILCT is 0.2 ns, (1)phi = 0.002, while the lifetime of the (3)ILCT is 8.3 &mgr;s, (3)phi = 0.01 (DMSO). While [(dppe)Pt{S(2)C(2)(CH(2)CH(2)-N-2-pyridinium)}](+) is emissive, the [(dppe)Pt{S(2)C(2)(2-pyridinium)(CH(2)CH(2)OR")}](+) 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.