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  1. Abstract

    A combined synthetic and theoretical investigation of N‐heterocyclic carbene (NHC) adducts of magnesium amidoboranes is presented, which involves a rare example of reversible migratory insertion within a normal valents‐block element. The reaction of (NHC)Mg(N(SiMe3)2)2(1) and dimethylamine borane yields the tris(amide) adduct (NHC−BN)Mg(NMe2BH3)(N(SiMe3)2) (2; NHC−BN = NHC−BH2NMe2). In addition to Me2N=BH2capture at theNHCC−Mg bond, mechanistic investigations suggest the likelihood of aminoborane migratory insertion from an RMg(NMe2BH2NMe2BH3) intermediate. To elucidate these processes, the carbene complexes (NHC)Mg(NMe2BH3)2(8) and (NHC)Mg(NMe2BH2NMe2BH3)2(9) were synthesized, and a dynamic migration of Me2N=BH2between Mg−N andNHCC−Mg bonds was observed in9. This unusual reversible migratory insertion is presumably induced by dissimilar charge localization in the{NMe2BH2NMe2BH3} anion, as well as the capacity of NHCs to reversibly capture Me2N=BH2in the presence of Lewis acidic magnesium species.

     
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  2. Abstract

    A new method to synthesize complexes of the type [(CNC)RuII(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 catalyst2ACNbeing 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.

     
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  3. ABSTRACT

    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 1Aand 2A, respectively). Full characterization data are reported for 1Aand 2Aand single crystal X‐ray diffraction for 1A. Both 1Aand 2Aare diprotic acids. We have studied 1A, 1B, 2A, and 2B(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 1Aand 2Aproduce 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 2Bsuggests 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.

     
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  4. Integration of polycyclic aromatic hydrocarbon (PAH) units into semi-fluorinated polymers affords high thermal stability and excellent processability for potential applications in optoelectronic, gas-separation, and advanced composites. Base-promoted step-growth polycondensation of commercial bisphenols with new triphenylene containing bis-trifluorovinyl ether (TFVE) monomers affords semi-fluorinated arylene vinylene ether (FAVE) polymers in good yields. The solution-processable polymers form tough transparent films and produce substitution dependent blue-light emission in solution with emission quantum yields ranging from 7.2–12% (in dichloromethane). Although predominantly amorphous with high glass transition temperatures ( T g ) ranging from 176–243 °C, powder X-ray diffraction studies show typical molecular diameter and pi-stacking reflections for triphenylene polymers. The polymers exhibited excellent thermal stability, solution photostability, and remarkable thermal oxidative photostability after heating at 250 °C for 24 h in air. Further, a model post-polymerization Scholl coupling afforded a novel semi-fluorinated hexabenzocoronene polymer with new optical properties. Time-dependent density functional theory (TD-DFT) computations were also performed using SMD (dichloromethane)- ω B97XD/BS1 (BS1 = 6-31G(d′) for C, H, O and F). This work demonstrated the synthesis and characterization of processable, blue-light emitting, thermally stable triphenylene enchained semi-fluorinated aryl ether polymers. 
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