Rhenium(I) Tricarbonyl Complexes with Peripheral N‑Coordination Sites: A Foundation for Heterotrimetallic Nonlinear Optical Chromophores

The compounds 4,4′-dicyano-2,2′-bipyridyl (dcbpy), 4,4′-bis­(4-cyanophenyl)-2,2′-bipyridyl (bcpbpy), 4,4′-bis­[(E)-2-(4-cyanophenyl)­vinyl]-2,2′-bipyridyl (bcpvbpy), and 4,4′-bis­[(E)-2-(4-pyridyl)­vinyl]-2,2′-bipyridyl (bpvbpy) are used to prepare nine new complexes with fac-{ReI(CO)3(L)}n+ (L = Cl–, MeCN, pyridine (py), or 4-cyanopyridine (cpy)) centers. The cationic complexes are isolated as their OTf– salts. These new monometallic species are studied together with the known fac-ReICl­(CO)3(qpy) (qpy = 4,4′:2′,2″:4″,4‴-quaterpyridyl) (de Wolf, P.; et al. Inorg. Chim. Acta 2003, 355, 280–285). Coordination of {RuII(NH3)5}2+ centers to the peripheral N atoms of fac-ReICl­(CO)3(qpy) and fac-[ReI(CO)3(bcpbpy)­(py)]+ affords heterotrimetallic complexes that are isolated as their PF6– salts. Single-crystal X-ray structures are reported for the solvates fac-ReICl­(CO)3(dcbpy)·Me2CO, fac-[ReI(CO)3(dcbpy)­(MeCN)]­OTf·PhMe, fac-[ReI(CO)3(dcbpy)­(py)]­OTf·0.5PhMe, fac-[ReI(CO)3(dcbpy)­(cpy)]­OTf·0.5Me2CO, fac-ReICl­(CO)3(bcpbpy)·0.5PhMe, and fac-[ReI(CO)3(bcpbpy)­(MeCN)]­OTf·MeCN. Cyclic voltammetry reveals irreversible ReII/I processes in all cases, while the trimetallic compounds show a reversible two-electron RuIII/II oxidation wave. Ligand-based reductions are generally irreversible, but reversible waves are observed for the dcbpy complexes. Electronic absorption spectra show strong d → π* metal-to-ligand charge-transfer (MLCT) and intraligand π → π* absorptions. The RuII-based MLCT bands have lower energies and higher intensities than the ReI-based ones. The monometallic species emit weakly in the red/NIR region (λem = 594–732 nm; ϕ = 0.6–8.1%) when excited at 350–520 nm. Molecular first hyperpolarizabilities β for the trimetallic complex salts are measured in MeCN solutions via the hyper-Rayleigh scattering technique at 1064 nm. Stark (electroabsorption) spectroscopic studies on the low-energy MLCT bands in frozen PrCN allow the indirect estimation of static first hyperpolarizabilities β0. The trimetallic complexes have relatively large β0 values, ca. 500 × 10–30 esu or more, which are substantially greater than those of the monometallic species.