This study describes the synthesis and characterization of a new class of ferrocene-containing carbon monoxide-releasing molecules (CORMs, 1–3). The ferrocenyl group is both a recognized therapeutically viable coligand and a handle for informative infrared spectroelectrochemistry. Deoxymyoglobin CO-release assays and in situ infrared spectroscopy confirm compounds 2 and 3 as photoCORMs and 1 as a thermal CORM, attributed to the increased sensitivity of the Mn–ferrocenyl bond to protonation in 1. Electrochemical and infrared spectroelectrochemical experiments confirm a single reversible redox couple associated with the ferrocenyl moiety with the Mn tetracarbonyl center showing no redox activity up to +590 mV vs Fc/Fc+, though no concomitant CO release was observed in association with the redox activity. The effects of linker length on communication between the Fe and Mn centers suggest that the incorporation of redox-active ligands into CORMs focuses on the first coordination sphere of the CORM. Redox-tagged CORMs could prove to be a useful mechanistic probe; our findings could be developed to use redox changes to trigger CO release.

NaNO3 is used in oxidative Pd-catalyzed processes as a complementary co-catalyst to common oxidants, e.g., CuII salts, in C–H bond activation and Wacker oxidation processes. NaNO3 and NaNO2 (with air or O2) assist the sp3-C–H bond acetoxylation of substrates bearing an N-directing group. It has been proposed previously that a redox couple is operative. The role played by NOx anions is examined in this investigation. Evidence for an NOx anion interaction at PdII is presented. Palladacyclic complexes containing NOx anions are competent catalysts for acetoxylation of 8-methylquinoline, with and without exogenous NaNO3. The oxidation of 8-methylquinoline to the corresponding carboxylic acid has also been noted at PdII. 18O-Labeling studies indicate that oxygen derived from nitrate appears in the acetoxylation product, the transfer of which can only occur by interaction of 18O at Pd with a coordinating-acetate ligand. Nitrated organic intermediates are formed under catalytic conditions, which are converted to acetoxylation products, a process that occurs with (50 °C) and without Pd (110 °C). A catalytically competent palladacyclic dimer intermediate has been identified. Head-space analysis measurements show that NO and NO2 gases are formed within minutes on heating catalytic mixtures to 110 °C from room temperature. Measurements by in situ infrared spectroscopy show that N2O is formed in sp3-C–H acetoxylation reactions at 80 °C. Studies confirm that cyclopalladated NO2 complexes are rapidly oxidized to the corresponding NO3 adducts on exposure to NO2(g). The investigation shows that NOx anions act as participating ligands at PdII in aerobic sp3-C–H bond acetoxylation processes and are involved in redox processes.

Reductive elimination of imidazolium salts from CuIII is extremely sensitive to the anionic ligand (X or Y) type on Cu (e.g. ΔG‡ ranges from 4.7 kcal mol−1 to 31.8 kcal mol−1, from chloride to benzyl). Weakly σ-donating ligands dramatically accelerate reductive elimination. Comparison with Ag/Au shows that the HOMO energy, strength of M–NHC and M–Y bonds and inherent stability of MIII with respect to MI are critical to governing reaction feasibility.

C–H bond functionalisation of heteroarenes, especially nucleosides, has received a lot of attention in the past few years. This review describes the state-of the art in this area with a global aspiration for possibly functionalising purine and pyrimidine moieties in more complex biomolecular systems, such as DNA/RNA in the near future.’

This feature article examines the potential of heterogeneous Pd species to mediate catalytic C–H bond functionalisation processes employing suitable substrates (e.g. aromatic/heteroaromatic compounds). A focus is placed on the reactivity of supported and non-supported Pd nanoparticle (PdNPs) catalysts, in addition to the re-appropriation of well-established heterogeneous Pd catalysts such as Pd/C. Where possible, reasonable comparisons are made between PdNPs and traditional ‘homogeneous’ Pd precatalyst sources (which form PdNPs). The involvement of higher order Pd species in traditional cross-coupling processes, such as Mizoroki–Heck, Sonogashira and Suzuki–Miyaura reactions, allows the exemplification of potential future topics for study in the area of catalytic C–H bond functionalisation processes.

Two novel succinimide-based palladium complexes, AsCat and FurCat, are highly efficient catalysts for room-temperature Stille cross-coupling of organostannanes with benzyl chlorides. The air- and moisture-stable catalysts are prepared in one step, and the coupling reactions proceed with a high selectivity for the benzyl position under mild conditions without the need for additives.

The stereoselective synthesis of a challenging macrocyclic polyene scaffold, containing a sensitive vinyl ether motif, has been accomplished using O,C-dilithiation/selective C-alkylation, Pd-catalysed etherification and Wittig reactions as key steps. An end-game macrocyclisation strategy employed a regio- and stereoselective Stille cross-coupling using Pd(Br)(N-Succ)(AsPh3)2 (AsCat) as the precatalyst.

Pd-mediated C–H bond functionalisation protocols have been designed and developed on tryptophan derivatives and tryptophan-containing peptides. The examination of different arylation reactions (three sets of different conditions A–C), all of which are notable for their low temperatures (≤40 °C), allowed identification of unified and complementary synthetic approaches toward a series of functionalised tryptophan-containing products. Tryptophan-containing peptides demonstrated to be susceptible to aromatic oxidation were successfully and selectively modified through the application of diaryliodonium salts in good yields.

C-modified 7-deazaadenosines containing a diphenylacetylene moiety have been synthesised using cross-coupling approaches. The C-modified nucleosides exhibit remarkable fluorescence properties, including high quantum yields. Solvatochromic studies show a near linear correlation between the Stokes shift and solvent polarity which is indicative of intramolecular charge transfer. DFT calculations have allowed us to correlate the experimentally observed photophysical properties with the calculated HOMO–LUMO energy gaps within a series of real and model compounds.

CuI(NHC)Br complexes (NHC = N-heterocyclic carbene) undergo a direct reaction with iodobenzene to give 2-arylated benzimidazolium products. The nature of the N-substituent on the NHC ligand influences the reactivity of the CuI(NHC)Br complex toward arylation. N-Benzyl or N-phenyl substituents facilitate arylation, whereas N-mesityl substituents hinder arylation. Density functional theory calculations show that an oxidative addition/reductive elimination pathway involving CuIII species is energetically feasible. A less hindered CuI(NHC)Br complex with N-benzyl groups is susceptible to oxidation reactions to give 1,3-dibenzylbenzimidazolium cations containing a CuIBr anion (various polymorphs). The results described herein are of relevance to C–H functionalization of (benz)azoles.

The effect of fluorine substituents on the regioselectivity of intramolecular reactions of mono- and difluorinated N,N-dimethylbenzylamines (1a–f) at palladium, to form palladacycles di-μ-acetatobis[o-dimethylaminomethyl-n-fluorophenyl-C,N)dipalladium(II) (2a–f) and di-μ-chlorobis[o-dimethylaminomethyl-n-fluorophenyl-C,N)dipalladium(II) (3a–e), has been investigated. When fluorinated substrates with two sites available for the C–H functionalization (1c and 1e) undergo cyclopalladation via a CMD mechanism (acetate-bridged palladacycles), they do not exhibit regioselectivity. In contrast, the same substrates exhibit complete regioselectivity for the C–H functionalization para to fluorine in cyclopalladation reactions that proceed via an SEAr mechanism (involving chloride-bridged palladacycles). X-ray crystal structures were obtained for all the palladacycles synthesized, and a structural analysis showed that the number and the position of the fluorine atoms on the aromatic ring have a marked effect on the “clamshell” structure of the acetate-bridged palladacycles. By contrast, there is no great variation in the structures of the planar chloride-bridged palladacycles.

A Pd-mediated direct C–H bond functionalisation of tryptophan has been developed, both as a single amino acid residue and within peptides. Important mechanistic insight into this process has been gained by characterising a Pd catalytically competent nanoparticle phase which evolves during the early stages of reaction.

Direct transmetallation between palladacyclic complexes and arylboronic acid occurs to give isolable transmetallation products. In THF, the reaction occurs <0.5 h. Prolonged reaction leads to the generation of a dinuclear Pd complex bearing bridging μ-hydroxo and μ-acetoxy ligands. Insight into precatalyst activation for Suzuki–Miyaura cross-couplings mediated by palladacycles has been gained, where acetate and N-imidate anions activate a neutral arylboronic acid.

Gold(III) catalysts mediate 1,5-enyne cycloisomerization or tandem nucleophilic substitution-1,5-enyne cycloisomerization processes in an efficient manner. This study examines the reaction kinetics of 1,5-enyne cycloisomerization, mediated by AuBr2(N-imidate)(NHC) catalysts {where N-imidate = N-tetrafluorosuccinimide (N-TFS) or N-phthalimide (N-phthal) and NHC = N,N′-di-tert-pentylimidazol-2-ylidene (ItPe)}, in the presence of AgOTf, in comparison with AuIIIBr3(NHC) and AuIBr(NHC). The nature of N-imidate anion influences catalyst efficacy. NMR spectroscopic investigations have allowed the ease of reduction of AuBr2(N-TFS)(NHC) to AuIX(NHC) (where X = N-TFS or Br) to be examined. Br2 is liberated from AuIII, which has been trapped by a sacrificial alkene. Under working catalyst conditions cationic AuIII is reduced to AuI.

Pd02(dba)3 (dba = E,E-dibenzylidene acetone) is the most widely used Pd0 source in Pd-mediated transformations. Pd02(dba-Z)3 (Z = dba aryl substituents) complexes exhibit remarkable and differential catalytic performance in an eclectic array of cross-coupling reactions. The precise structure of these types of complexes has been confounding, since early studies in 1970s to the present day. In this study the solution and solid-state structures of Pd02(dba)3 and Pd02(dba-Z)3 have been determined. Isotopic labeling (2H and 13C) has allowed the solution structures of the freely exchanging major and minor isomers of Pd02(dba)3 to be determined at high field (700 MHz). DFT calculations support the experimentally determined major and minor isomeric structures, which show that the major isomer of Pd02(dba)3 possesses bridging dba ligands found exclusively in a s-cis,s-trans conformation. For the minor isomer one of the dba ligands is found exclusively in a s-trans,s-trans conformation. Single crystal X-ray diffraction analysis of Pd02(dba)3·CHCl3 (high-quality data) shows that all three dba ligands are found over two positions. NMR spectroscopic analysis of Pd02(dba-Z)3 reveals that the aryl substituent has a profound effect on the rate of Pd-olefin exchange and the global stability of the complexes in solution. Complexes containing the aryl substituents, 4-CF3, 4-F, 4-t-Bu, 4-hexoxy, 4-OMe, exhibit well-resolved 1H NMR spectra at 298 K, whereas those containing 3,5-OMe and 3,4,5-OMe exhibit broad spectra. The solid-state structures of three Pd02(dba-Z)3 complexes (4-F, 4-OMe, 3,5-OMe) have been determined by single crystal X-ray diffraction methods, which have been compared with Goodson’s X-ray structure of Pd02(dba-4-OH)3.

The novel synthesis of macrocyclic arylketones via palladium-catalyzed cross-coupling of arylboronic acids and carboxylic acids, activated by the treatment with di(N-succinimidyl) carbonate, is disclosed. This allows the high yielding synthesis of various functionalized arylketones, which can be converted into macrocycles via a Mitsunobu protocol.

PhI(OAc)2 has previously been reported as a reagent for the direct arylation of C–H bonds in benzoxazole in a PdII/IV-mediated process. However, evidence reported here suggests this reagent degrades to iodobenzene under the literature reported reaction conditions. Further, we present evidence for the rapid formation of Pd0 nanoparticles in this reaction, leading us to question what is the active catalytic Pd phase in coupling chemistry?Iodobenzene is rapidly generated from phenyl iodonium diactate in DMSO at 150 °C, which serves as the substrate in catalytic C–H bond functionalisation of benzoxazole mediated by palladium.

The effects of substituting (pseudo)halide for anionic imidate ligands in Au(I) and Au(III) (i.e. [AuBr(NHC)] and [AuBr3(NHC)]) complexes have been investigated. [Au(N-imidate)(NHC)] and [AuBr2(N-imidate)(NHC)] complexes were prepared and the structure and bonding of the complexes examined spectroscopically and crystallographically. The [AuBr2(N-imidate)(NHC)] complexes, in combination with Ag salts, were tested for catalytic activity in the cycloisomerization of 1,5-enynes and found to be more effective than the tribromide analogues (e.g. [AuBr3(NHC)]). Subtle changes to the anionic imidate ligand structure had a pronounced effect on the catalytic activity of the Au(III) complexes.

Pd3(OAc)5NO2, an impurity in “Pd(OAc)2” {formally Pd3(OAc)6}, emerges as a serious issue in the synthesis of pure PdII complexes derived from Pd(OAc)2, for example in our C–H activation precatalyst, Pd(OAc)2(pip)2 (pip = piperidine). A previous proposal that nitrite anion can be formed by oxidation of CH3CN by metallic Pd and air, leading to cyclo(ortho)palladated complexes containing nitrite anion, e.g. Pd(NO2)(C^N)L (C^N = papaverine; L = CH3CN or DMSO) can be explained by Pd3(OAc)5NO2 acting as the nitrite source. Finally, photocrystallographic metastable linkage isomerisation and complete conversion to an oxygen-bound nitrito complex Pd(η1-ONO)(C^N)PPh3 has been observed.

A new class of photochemically-activated CO-releasing molecule (photo-CO-RM), based on a Mn(CO)4(C^N) system, is reported in this study. Three CO molecules are released per CO-RM molecule. Complex 3 is a fast releaser, thermally stable in the dark and a viable therapeutic agent.

A novel unsymmetrical dibenzylidene acetone (monothiophos-dba, compound 3), containing two chemically different alkene moieties, undergoes a selective photochemically-induced [2+2] cycloaddition solid-state transformation (single crystal and powder), as shown by X-ray diffraction methods. In the single crystal the rate constant for the cycloaddition reaction was determined {k = (2.3 ± 0.1) × 10−4 s−1}, with a 69% conversion attained, which compares well with a two-photon irradiation experiment using a Nd:YAG laser pumped dye laser at 605 nm radiation (66% conversion). Full conversion was attained using powdered 3 after 43 h. A similar conversion was noted between the single crystal and powder forms (59% and 66% conversion after 5 h irradiation). Irradiation of monothiophos-dba in solution using a 325 nm laser, and monitoring by 1H NMR spectroscopy, showed that no cycloaddition occurred, but exclusive photochemically-induced trans → cis isomerisation of the alkene bond connecting the unsubstituted aryl group (cis → trans isomerisation in these electron-deficient and polarised CC bonds occurs rapidly by thermal equilibration).

An investigation into the CO-releasing properties of a range of iron tricarbonyl and chromium and molybdenum tetracarbonyl complexes is presented. Iron tricarbonyl complexes containing the 2,5-bicyclo[2.2.1]heptene (norbornadiene) ligand are shown to be effective CO-releasing molecules, in which the rate and extent of CO release may be modulated by modification of the norbornadiene framework. Species containing the parent norbornadiene and those with a substituent at the 7-position of the organic ligand exhibit CO release; those containing ester substituents at the 2- and/or 3-positions do not. A mechanism for CO release in this species is proposed which involves initial norbornadiene dissociation, a suggestion which is supported by the spectroscopic data and the observation that the addition of excess substituted norbornadiene retards the rate of CO release. CO release from the diester-containing norbornadiene complex may be promoted photochemically, and cell viability studies indicate that in the absence of light this complex is nontoxic, making it an excellent candidate for further study as a photo-CO-RM. Both the chromium and molybdenum tetracarbonyl complexes release CO, which in the case of the molybdenum analogue is rapid.

The deoxy-myoglobin (deoxy-Mb)/carbonmonoxy-myoglobin (Mb-CO) UV-vis assay is the principal method used for quantifying the rates of CO release from CO-releasing molecules (CO-RMs) that might possess therapeutic benefits. Some issues emerge when the Mb-CO assay is utilized for testing CO-RMs with novel structures, which are comprehensively discussed here for the first time. Two methods for processing raw UV-vis spectroscopic data generated from the assay are presented in this paper.

Dinuclear palladacyclic complexes [{Pd(C∧N)(μ-NCO)}2] (C∧N = N-phenylbenzaldimine, Phbz) containing asymmetric imidato units (−NCO– = succinimidate (succ; 1), phthalimidate (phthal; 2), maleimidate (mal; 3), 2,3-dibromomaleimidate (2,3-diBrmal; 4), glutarimidate (glut; 5)) have been readily prepared by reaction between the di-μ-acetate precursor and cyclic imide ligands in a 1:2 molar ratio. Base treatment of the less acidic ligands 2-oxazolidone and δ-valerolactame with KOH/MeOH was required to give analogous −NCO– bridged complexes (6 and 7). Reactions of the dinuclear complexes with tertiary phosphines provide novel mononuclear N-bonded imidate derivatives of the general formula [Pd(Phbz)(imidate)(PR3)] (R = Ph (a), 4-F-C6H4 (b), 4-MeO-C6H4 (c), CH2CH2CN (d)). The application of these novel palladacyclic complexes as precatalysts for the Suzuki–Miyaura cross-coupling reactions of both aryl and benzyl bromides with phenylboronic acid has been examined. The acetate adducts [Pd(Phbz)(CH3COO)(PR3)] (8a,c) were prepared to assess the role of imidate ligands in catalyst performance. The mononuclear imidate derivatives possess greater activity than the parent dinuclear complexes, exhibiting comparable performance in the cross-coupling of benzyl bromide with arylboronic acids to the best examples reported in the literature. The mononuclear imidate derivatives give a common Pd0Ln intermediate, as inferred by the release of the organic fragment (first reductive elimination product). Catalyst activation occurs by reaction of phenylboronic acid with the palladacycle in the absence of exogenous base (as shown by GC-MS and ESI-MS), with implications for the reliable comparison of catalyst performance across a series of related precatalysts (e.g., how catalyst/reagents are mixed and what is their order of addition). The single-crystal X-ray structures of compounds 4, 7, 1d, 3c, and 8a have been determined.

The intermolecular Pauson–Khand (PK) reactions of sterically comparable (2-phenylethynyl)heteroaromatic compounds with norbornene, mediated by Co2(CO)8 to give cyclopentenone products, were examined in this study. A synthetic protocol utilizing focused-microwave dielectric heating proved indispensable in the efficient synthesis of the PK cyclopentenone products. “π-Deficient” heteroaromatic substrates, e.g., 2-pyrones, and some “π-excessive” heteroaromatics such as 2- and 3-thiophene and 2-furan favor the β-position in the newly formed cyclopentenone ring. Other π-excessive heteroaromatics such as 2-pyrrole or 2-indole favor the α-position. A π-excessive 3-indole derivative gave a nearly equal mixture of regioisomers. The position of the nitrogen in pyridyl-containing alkyne substrates also affects the regiochemical outcome of the PK reaction. A 2-pyridyl alkyne, possessing a proximal nitrogen, influences the regioselectivity relative to a 4-pyridyl variant quite dramatically, favoring the β-position in the newly formed cyclopentenone ring. A 2-pyrimidylalkyne exhibits similar behavior to the 2-pyridylalkyne. Compounds that do not participate in PK reactions with norbornene include (2-phenylethynyl)imidazoles and the related benzimidazoles, which promote rapid decomposition of the in situ generated (μ2-alkyne)Co2(CO)6 complexes. This stands in contrast with other nitrogen-containing heteroaromatics, e.g., pyrrole-, indole-, and pyrimidine-derived compounds, which effectively undergo PK reactions. Overall, the type of heteroaromatic group dramatically influences PK regioselectivity, which can in part be explained by rationalization of the current reaction mechanism, but not fully.

The deoxy-myoglobin (deoxy-Mb)/carbonmonoxy-myoglobin (Mb-CO) UV-vis assay is the principal method used for quantifying the rates of CO release from CO-releasing molecules (CO-RMs) that might possess therapeutic benefits. Some issues emerge when the Mb-CO assay is utilized for testing CO-RMs with novel structures, which are comprehensively discussed here for the first time. Two methods for processing raw UV-vis spectroscopic data generated from the assay are presented in this paper.

Pd-mediated C–H bond functionalisation protocols have been designed and developed on tryptophan derivatives and tryptophan-containing peptides. The examination of different arylation reactions (three sets of different conditions A–C), all of which are notable for their low temperatures (≤40 °C), allowed identification of unified and complementary synthetic approaches toward a series of functionalised tryptophan-containing products. Tryptophan-containing peptides demonstrated to be susceptible to aromatic oxidation were successfully and selectively modified through the application of diaryliodonium salts in good yields.

The stereoselective synthesis of a challenging macrocyclic polyene scaffold, containing a sensitive vinyl ether motif, has been accomplished using O,C-dilithiation/selective C-alkylation, Pd-catalysed etherification and Wittig reactions as key steps. An end-game macrocyclisation strategy employed a regio- and stereoselective Stille cross-coupling using Pd(Br)(N-Succ)(AsPh3)2 (AsCat) as the precatalyst.

Direct transmetallation between palladacyclic complexes and arylboronic acid occurs to give isolable transmetallation products. In THF, the reaction occurs <0.5 h. Prolonged reaction leads to the generation of a dinuclear Pd complex bearing bridging μ-hydroxo and μ-acetoxy ligands. Insight into precatalyst activation for Suzuki–Miyaura cross-couplings mediated by palladacycles has been gained, where acetate and N-imidate anions activate a neutral arylboronic acid.

Two novel succinimide-based palladium complexes, AsCat and FurCat, are highly efficient catalysts for room-temperature Stille cross-coupling of organostannanes with benzyl chlorides. The air- and moisture-stable catalysts are prepared in one step, and the coupling reactions proceed with a high selectivity for the benzyl position under mild conditions without the need for additives.

Reductive elimination of imidazolium salts from CuIII is extremely sensitive to the anionic ligand (X or Y) type on Cu (e.g. ΔG‡ ranges from 4.7 kcal mol−1 to 31.8 kcal mol−1, from chloride to benzyl). Weakly σ-donating ligands dramatically accelerate reductive elimination. Comparison with Ag/Au shows that the HOMO energy, strength of M–NHC and M–Y bonds and inherent stability of MIII with respect to MI are critical to governing reaction feasibility.

A Pd-mediated direct C–H bond functionalisation of tryptophan has been developed, both as a single amino acid residue and within peptides. Important mechanistic insight into this process has been gained by characterising a Pd catalytically competent nanoparticle phase which evolves during the early stages of reaction.

This feature article examines the potential of heterogeneous Pd species to mediate catalytic C–H bond functionalisation processes employing suitable substrates (e.g. aromatic/heteroaromatic compounds). A focus is placed on the reactivity of supported and non-supported Pd nanoparticle (PdNPs) catalysts, in addition to the re-appropriation of well-established heterogeneous Pd catalysts such as Pd/C. Where possible, reasonable comparisons are made between PdNPs and traditional ‘homogeneous’ Pd precatalyst sources (which form PdNPs). The involvement of higher order Pd species in traditional cross-coupling processes, such as Mizoroki–Heck, Sonogashira and Suzuki–Miyaura reactions, allows the exemplification of potential future topics for study in the area of catalytic C–H bond functionalisation processes.

Pd3(OAc)5NO2, an impurity in “Pd(OAc)2” {formally Pd3(OAc)6}, emerges as a serious issue in the synthesis of pure PdII complexes derived from Pd(OAc)2, for example in our C–H activation precatalyst, Pd(OAc)2(pip)2 (pip = piperidine). A previous proposal that nitrite anion can be formed by oxidation of CH3CN by metallic Pd and air, leading to cyclo(ortho)palladated complexes containing nitrite anion, e.g. Pd(NO2)(C^N)L (C^N = papaverine; L = CH3CN or DMSO) can be explained by Pd3(OAc)5NO2 acting as the nitrite source. Finally, photocrystallographic metastable linkage isomerisation and complete conversion to an oxygen-bound nitrito complex Pd(η1-ONO)(C^N)PPh3 has been observed.

Gold(III) catalysts mediate 1,5-enyne cycloisomerization or tandem nucleophilic substitution-1,5-enyne cycloisomerization processes in an efficient manner. This study examines the reaction kinetics of 1,5-enyne cycloisomerization, mediated by AuBr2(N-imidate)(NHC) catalysts {where N-imidate = N-tetrafluorosuccinimide (N-TFS) or N-phthalimide (N-phthal) and NHC = N,N′-di-tert-pentylimidazol-2-ylidene (ItPe)}, in the presence of AgOTf, in comparison with AuIIIBr3(NHC) and AuIBr(NHC). The nature of N-imidate anion influences catalyst efficacy. NMR spectroscopic investigations have allowed the ease of reduction of AuBr2(N-TFS)(NHC) to AuIX(NHC) (where X = N-TFS or Br) to be examined. Br2 is liberated from AuIII, which has been trapped by a sacrificial alkene. Under working catalyst conditions cationic AuIII is reduced to AuI.

A new class of photochemically-activated CO-releasing molecule (photo-CO-RM), based on a Mn(CO)4(C^N) system, is reported in this study. Three CO molecules are released per CO-RM molecule. Complex 3 is a fast releaser, thermally stable in the dark and a viable therapeutic agent.

C–H bond functionalisation of heteroarenes, especially nucleosides, has received a lot of attention in the past few years. This review describes the state-of the art in this area with a global aspiration for possibly functionalising purine and pyrimidine moieties in more complex biomolecular systems, such as DNA/RNA in the near future.’

C-modified 7-deazaadenosines containing a diphenylacetylene moiety have been synthesised using cross-coupling approaches. The C-modified nucleosides exhibit remarkable fluorescence properties, including high quantum yields. Solvatochromic studies show a near linear correlation between the Stokes shift and solvent polarity which is indicative of intramolecular charge transfer. DFT calculations have allowed us to correlate the experimentally observed photophysical properties with the calculated HOMO–LUMO energy gaps within a series of real and model compounds.