Syntheses, Structures, and Properties of New Manganese Carbonyls as Photoactive CO-Releasing Molecules: Design Strategies That Lead to CO Photolability in the Visible Region

Abstract

The unusual role of CO as a signaling molecule in several physiological pathways has spurred research in the area of synthesizing new CO-releasing molecules (CORMs) as exogenous CO donors. Auxiliary control on CO delivery can be achieved if CO can be released under the control of light. To synthesize such photoactive CORMs (photoCORMs) with the aid of smart design, a series of manganese carbonyls have been synthesized with ligands that contain extended conjugation and electron-rich donors on their frames. Five such photoCORMs, namely, [Mn(pimq)(CO)(3)(MeCN)]ClO(4) (1, where pimq = (2-phenyliminomethyl)quinoline), [Mn(qmtpm)(CO)(3)(MeCN)]ClO(4) (2, where qmtpm = 2-quinoline-N-(2'-methylthiophenyl) methyleneimine), [Mn(qmtpm)(CO)(3)Br] (3) [Mn(pmtpm)(CO)(3)(MeCN)]ClO(4) (4, where pmtpm = 2-pyridyl-N-(2'-methylthiophenyl)methyleneimine), and [Mn(pmtpm)(CO)(3)Br] (5), have been synthesized and structurally characterized. These designed carbonyls readily release CO upon exposure to light (400-550 nm). The apparent CO release rates and quantum yield values at 509 nm (φ(509)) of the photoCORMs increase steadily with rise in conjugation in the ligand frame and inclusion of a -SMe group. Addition of Br(-) as an ancillary ligand also improves the CO-donating capacity. Results of density functional theory (DFT) and time dependent DFT (TDDFT) studies indicate that low energy metal-to-ligand charge transfer (MLCT) transitions from Mn-CO bonding into ligand-π orbitals lead to reduction of M-CO(π*) back-bonding and loss of CO from these photoCORMs. Inclusion of -SMe and Br(-) in the coordination sphere attenuates the energies of the HOMO and LUMO levels and causes further enhancement of CO photorelease. Collectively, the results of this work demonstrate that new photoCORMs with excellent sensitivity to visible light can be synthesized on the basis of smart design principles.

A Photoactive Carbon‐Monoxide‐Releasing Protein Cage for Dose‐Regulated Delivery in Living Cells

“…Then umber of Mn atoms in the Fr cage (44 AE 2) was determined by inductively coupled plasma mass spectrometry (ICP-MS) and abicinchoninic acid (BCA) assay.Compound 1 has an absorption band at 365 nm which is assigned as the metal-to-ligand charge transfer (MLCT) band of the photoactive MnCO moiety as reported previously (see Figure S1 in the Supporting Information). [54] Theattenuated total reflectance infrared (ATR-IR) spectrum of 1 includes three peaks at 2028, 2011, and 1917 cm À1 in the CO-stretching vibrational region ( Figure S2a, black line). The peaks were assigned to a fac-Mn(CO) 3 structure.Although we attempted to prepare ac omposite of wild-type Fr (apo-WTrHLFr) and Mn(CO) 5 Br under the same conditions,very few Mn atoms were accumulated in the cage (3 AE 1M n/apo-WTrHLFr).…”

Design of biomaterials for intracellular delivery of carbon monoxide

“…[21][22][23][24] Most photoCORMs are transition metal complexes of Fe, [25][26][27] Mn, [28][29][30][31][32][33][34][35] Ru, 36 Re, 31,37 Mo, 38 and W. 39 Notable examples are shown in Fig. 3a.…”

Tuning coordination modes of pyridine/thioether Schiff base (NNS) ligands to mononuclear manganese carbonyls

“…27,28 We independently devised an analogous synthesis of [(NNS)Mn(CO) 3 Br] compared with a recently published report. 23 …”

“…[17][18][19][20][21][22][23] In general, the reaction of a yellow solutions of NNS and [Mn(CO) 5 Br] generated a dark red color over the course of 15 min to 1 hour. Vapor diffusion of pentane or Et 2 O afforded crystalline material that ranged from black to translucent orange.…”

“…23 Related photoactive manganese(I) tricarbonyls were also derived from diazopyridine, diimine N2, and N3 ligands. [23][24][25] Most relevant to this work are complexes derived from similar Schiff base ligands with a pendant thioether-S. In the two cases of [(L NNS )-Mn(CO) 3 ] + (L = pmtpm and qmtpm; NNS and Q NNS in our nomenclature), the thioether remained unbound.…”