Synthesis and properties of rhenium carbonyl complexes of alpha,alpha'-bis[(1-pyrenyl)pyrazol-1-yl]alkane ligands.
The reaction between (1-acetyl)pyrene and dimethylformamide dimethylacetal followed by condensation of the resulting product mixture with hydrazine affords 3(5)-(1-pyrenyl)pyrazole (2) in good yield. The easily separable bis[(1-pyrenyl)pyrazole]methane derivatives CH(2)(3-pz(pyrene))(2) (3a, pz = pyrazolyl ring) and CH(2)(3-pz(pyrene))(5-pz(pyrene)) (3b) were prepared by metathetical reactions between pyrazole and CH(2)Cl(2), while CH((n)()Pr)(pz(pyrene))(2) (4) was prepared by transamination of 2 with butyraldehyde diethylacetal. Compounds 2-4 are luminescent under irradiation with UV light and have pyrenyl monomer-based emissions centered near 400 nm. Compounds 3a and 4 each react with Re(CO)(5)Br in a 1:1 molar ratio to form highly insoluble complexes Re(CO)(3)Br[(pz(pyrene))(2)CH(2)] (5) and Re(CO)(3)Br[(pz(pyrene))(2)CH((n)()Pr)] (6). Complex Re(CO)(3)Br[(pz)(2)CMe(2)] (7) was also prepared. X-ray structural studies of 6 show extensive pi-stacking of pyrenyl groups to form two-dimensional sheets. Pulsed field gradient spin-echo NMR (PGSE-NMR) experiments show that the complexes are monomeric in tetrachloroethane. Variable-temperature, difference NOE and 2-D NMR experiments demonstrate that isomers are present in solution that differ by restricted rotation about the pyrazolyl-pyrenyl bond. The pyrenyl-based emissions centered near 400 nm are quenched by complexation to the Re(CO)(3)Br moiety in 5 and 6.
Reger
Daniel L
DL
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, USA. reger@mail.chem.sc.edu
Gardinier
James R
JR
Pellechia
Perry J
PJ
Smith
Mark D
MD
Brown
Kenneth J
KJ