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Monoligated and bis-ligated CCC-NHC pincer Fe complexes with n-butyl substituents have been synthesized by the Zr metalation/transmetalation route. Both the direct metalation/transmetalation and transmetalation from the isolated (BuCiCiCBu)ZrNMe2Cl2, 3, yielded the octahedrally coordinated Fe(III) bis-ligated complex [(BuCiCiCBu)2Fe]Cl, 2a. Transmetalation from in situ and isolated (BuCiCiCBu)ZrCl3, 5, in the presence of excess TMSCl and 1 equiv of the Fe source yielded the monoligated (BuCiCiCBu)FeCl2, 4. Conditions that convert [(BuCiCiCBu)2Fe]+, 2, to (BuCiCiCBu)FeCl2, 4, complex have been found. Characterization included 1H NMR, UV−visible, femtosecond transient absorption spectroscopies, TDDFT computations, and mass spectroscopy along with X-ray crystallographic structure determinations. 

Cleaning symbioses on coral reefs are mutually beneficial interactions between two individuals, in which a ‘cleaner’ removes and eats parasites from the surface of a ‘client’ fish. A suite of behavioural and morphological traits of cleaners signal cooperation with co‐evolved species, thus protecting the cleaner from being eaten by otherwise predatory clients. However, it is unclear whether cooperation between cleaners and predatory clients is innate or learned, and therefore whether an introduced predator might consume, cooperate with or alter the behaviour of cleaners.

We explored the role of learning in cleaning symbioses by comparing the interactions of native cleaner fishes with both naïve and experienced, non‐native and native fish predators. In so doing, we tested the vulnerability of the predominant cleaners on Atlantic coral reefs, cleaning gobies (Elacatinusspp.), to the recent introduction of a generalist predator, the Indo‐Pacific red lionfish (Pterois volitans).

Naïve juveniles of both invasive (P. volitans) and native predators (Cephalopholisspp. groupers) initially attacked cleaning gobies and hyperventilated from a putative toxin on the gobies' skin during laboratory experiments. After one to five such encounters, invasive lionfish often approached the cleaner closely, then turned away without striking. Consistent with learned avoidance, invasive lionfish rarely interacted with cleaning gobies in the wild, either antagonistically or cooperatively, and did not affect gobies' abundance. Native predators showed little evidence of learning during early encounters; they repeatedly attacked the cleaner during laboratory experiments and hyperventilated less violently than did lionfish. However, consistent with learned cooperation, native predators rarely antagonised and were frequently cleaned by gobies in the wild.

We demonstrated that rapid, learned avoidance protects a distasteful cleaning mutualist from an invasive predator. The behavioural plasticity of this invader likely contributes to its success across its invaded range. Additionally, our results suggest that the cleaner's chemical defence most likely evolved as a way to deter predation and reinforce cooperation with naïve individuals of native species.

 

The first examples of a CNC pincer ligands with a central pyridinol derived ring were recently reported.  The differences in catalytic reactivity between CNC ligands with a central pyridine ring vs. a pyridinol derived ring are substantial and highly active and robust catalysts have been synthesized and studied.  In these pincer ligands, the 4-substituent can be OMe, OH, or O-, and these latter two options allow for altered catalyst properties as a function of proton concn.  Catalytic studies have used ruthenium(II), nickel(II), and other transition metals.  We have made metal complexes that can be protonated or deprotonated reversibly in situ to switch on or off the photocatalytic performance towards CO2 redn.  Furthermore, the methoxy group on the pyridine ring offers unique catalysis advantages not seen with the unsubstituted analog.  Our best catalysts offer selective CO formation, >300 turnover cycles, and a 40 h lifetime.  Steric and electronic ligand effects are being studied with these catalysts by exptl. and computational methods. 

A new method to synthesize complexes of the type [(CNC)Ru^II(NN)L]ⁿ⁺has been introduced, where CNC is a tridentate pincer composed of two (benz)imidazole derived NHC rings and a pyridyl ring, NN is a bidentate aromatic diimine ligand, L=bromide or acetonitrile, and n=1 or 2. Following this new method a series of six new complexes has been synthesized and characterized by spectroscopic, analytic, crystallographic, and computational methods. Their electrochemical properties have been studiedviacyclic voltammetry under both N₂and CO₂atmospheres. Photocatalytic reduction of CO₂to CO was performed using these complexes both in the presence (sensitized) and absence (self‐sensitized) of an external photosensitizer. This study evaluates the effect of different CNC, NN, and L ligands in sensitized and self‐sensitized photocatalysis. Catalysts bearing the benzimidazole derived CNC pincer show much better activity for both sensitized and self‐sensitized photocatalysis as compared to catalysts bearing the imidazole derived CNC pincer. Furthermore, self‐sensitized photocatalysis requires a diimine ligand for CO₂reduction with catalyst2_ACNbeing the most active catalyst in this series with TON=85 and TOF=22 h⁻¹with an electron donating 4,4′‐dimethyl‐2,2′‐bipyridyl (dmb) ligand and a benzimidazole derived CNC pincer.

 

We report new ruthenium complexes bearing the lipophilic bathophenanthroline (BPhen) ligand and dihydroxybipyridine (dhbp) ligands which differ in the placement of the OH groups ([(BPhen)₂Ru(n,n′‐dhbp)]Cl₂withn = 6 and 4 in 1_Aand 2_A, respectively). Full characterization data are reported for 1_Aand 2_Aand single crystal X‐ray diffraction for 1_A. Both 1_Aand 2_Aare diprotic acids. We have studied 1_A, 1_B, 2_A, and 2_B(B = deprotonated forms) by UV‐vis spectroscopy and 1 photodissociates, but 2 is light stable. Luminescence studies reveal that the basic forms have lower energy³MLCT states relative to the acidic forms. Complexes 1_Aand 2_Aproduce singlet oxygen with quantum yields of 0.05 and 0.68, respectively, in acetonitrile. Complexes 1 and 2 are both photocytotoxic toward breast cancer cells, with complex 2 showing EC₅₀light values as low as 0.50 μM with PI values as high as >200vs. MCF7. Computational studies were used to predict the energies of the³MLCT and³MC states. An inaccessible³MC state for 2_Bsuggests a rationale for why photodissociation does not occur with the 4,4′‐dhbp ligand. Low dark toxicity combined with an accessible³MLCT state for¹O₂generation explains the excellent photocytotoxicity of 2.