Development of Ultrafast Photochromic Organometallics and Photoinduced Linkage Isomerization of Arene Chromium Carbonyl Derivatives

Abstract

We review recent studies of processes relevant to photoinduced linkage isomerization of organometallic systems with the goal of preparing organometallics with an efficient and ultrafast photochromic response. The organometallic system thus corresponds to two linkage isomers with different electronic environments that are responsible for different optical properties. Much of this work has focused on examining processes following irradiation of cyclopentadienyl manganese tricarbonyl derivatives (compounds 3-21) including solvent coordination, thermal relaxation, solvent displacement by tethered functional groups (chelation), dissociation of tethered functional groups, and linkage isomerization. A new platform is investigated for obtaining a photochromic response in new experiments with arene chromium dicarbonyl complexes. A photochromic response is observed for arene chromium dicarbonyl complexes with tethered pyridine and olefin functional groups based on light-driven linkage isomerization on the nanosecond time scale. Irradiation at 532 nm of 23 ([Cr{eta(6)-C(6)H(5)CH(2-Py-kappaN)CH(2)CH=CH(2)}(CO)(2)]) (Py = pyridine) results in the isomerization to 22 ([Cr{eta(6)-C(6)H(5)CH(2-Py)CH(2)-eta(2)-CH=CH(2)}(CO)(2)]), and 355 nm irradiation isomerizes 22 to 23. The ultrafast linkage isomerization has been investigated at room temperature in n-heptane solution on the picosecond to microsecond time scale with UV- or visible-pump and IR-probe transient absorption spectroscopy by comparing the dynamics with model compounds containing only a tethered pyridine. Irradiation of 24 ([Cr{eta(6)-C(6)H(5)(CH(2))(3)(2-Py)}(CO)(3)]) and 25 ([Cr{eta(6)-C(6)H(5)(CH(2))(2)(2-Py)}(CO)(3)]) at 289 nm induces CO loss to immediately yield a Cr-heptane solvent coordinated intermediate of the unsaturated Cr fragment, which then converts to the kappaN(1)-pyridine chelate within 200 and 100 ns, respectively. Irradiation of 26 ([Cr{eta(6)-C(6)H(5)CH(2)(2-Py)}(CO)(3)]) also induces CO loss to immediately yield three species: the Cr-heptane solvent coordinated intermediate, a kappaN(1)-Py nitrogen chelate, and an agostic eta(2)-chelate in which the pyridine is coordinated to the metal center via a C-H agostic bond as opposed to the nitrogen lone pair. Both the transient Cr-heptane coordinated intermediate and the agostic pyridine chelate convert to the stable kappaN(1)-pyridine chelate within 50 ns. Similar reaction dynamics and transient species are observed for the chelate 33 ([Cr{eta(6)-C(6)H(5)CH(2)(2-Py)-kappaN}(CO)(2)]) where a Cr-Py bond, not a Cr-CO bond, initially cleaves.

Isomerization in Photochromic Ruthenium Sulfoxide Complexes

“…The pentacyanonitrosylmetallates show this behavior and Burkey and Heilweil have reported one such organometallic example. [75] The metal nitrosyl compounds feature phototriggered isomerization of the bound nitrosyl ligand from N-bonded to η 2 -NO to Obonded (isonitrosyl). Each isomer is observable by X-ray crystallography and infrared spectroscopy with different decay temperatures.…”

“…Alternatively, isomerization from O to S may be achieved by accessing different transition states in the two reactions. [75] The complex [Ru(bpy) 2 …”

Two‐Color Reversible Switching in a Photochromic Ruthenium Sulfoxide Complex

“…[17,18] Heilweil, Webster, Burkey and co-workers have reported one such example in their studies of ultrafast photochromic organometallic compounds. [19] Picosecond transient absorption data for the S-bonded isomer are shown in Figure 2. Initial traces from t = 0 to 10 ps yield the formation of a bleach feature centered at 372 nm, which coincides closely with the ground-state absorbance maximum.…”

Photoinduced rearrangements in transition metal compounds

“…Linkage isomerisation is also common in organometallic complexes and ultrafast processes relevant to photoinduced linkage isomerisation in organometallic systems was recently reviewed [52]. Burkey and co-workers have shown that first row organometallic complexes of manganese, ( 5 -C 5 H 4 CH 3 )Mn(CO) 2 (L) with non-chelatable bifunctional ligands (L) undergo linkage isomerisation, following irradiation as shown in Figure 16.…”