Functionalized 2-Pyridyl-Substituted Metallo-1,2-enedithiolates. Synthesis, Characterization, and Photophysical Properties of (dppe)M{S(2)C(2)(2-pyridine(ium))(CH(2)CH(2)OR")} and (dppe)M[{S(2)C(2)(CH(2)CH(2)-N-2-pyridinium)}](+) (R" = H, Acetyl, Lauroyl; M = Pd, Pt; dppe = 1,2-Bis(diphenylphosphino)ethane).
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.
Van Houten
Kelly A.
KA
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, and Department of Chemistry, University of Delaware, Newark, Delaware 19711.
Heath
Danica C.
DC
Barringer
Chris A.
CA
Rheingold
Arnold L.
AL
Pilato
Robert S.
RS