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Carbodicarbenes (CDCs) possess two lone pairs of electrons on their central carbone C atom (C carbone ). Coordination to a transition metal via a σ bond leaves one pair of electrons with appropriate symmetry for π donation to the metal. However, the high energy of the latter also renders the CDC ligand potentially redox-active. Herein, we explore these alternatives in the redox series [Cr( L ) 2 ] n + and [Co( L ) 2 ] n + ( n = 2-5), where L is a tridentate ligand comprised of a central CDC and two flanking pyridine donors. To this end, all members of both redox series were synthesized and their electronic structures were investigated by using a combination of 1 H NMR, Evans' NMR, IR, UV-vis, and EPR spectroscopies, SQUID magnetometry, X-ray crystallography, and density functional theory studies. Whereas [Co II ( L ) 2 ] 2+ is a straightforward low-spin ( S = 1 / 2 ) cobalt(II) complex, the corresponding chromium complex was found to feature an electronic structure that is intermediate between the two limiting resonance forms [Cr III ( L •- )( L )] 2+ and [Cr II ( L ) 2 ] 2+ . In the case of the tri-, tetra-, and pentacationic complexes, the qualitatively identical electronic structures [M III ( L ) 2 ] 3+ , [M III ( L •+ )( L )] 4+ , and [M III ( L •+ ) 2 ] 5+ were observed for both metals. Thus, the metal ions retain a 3+ oxidation state throughout, and the higher redox states contain oxidized ligands. The majority of the unpaired spin on the cation radical ligands was calculated to be localized in π-symmetry orbitals on the coordinated C carbone atoms. Analogous behavior was previously reported for the corresponding iron redox series and, as such, redox noninnocence in oxidized CDC and, more broadly, carbone complexes is likely widely accessible.

The development of metallogels widens the span of sensing activity as it opens new opportunities to develop chemosensors through metal-ligand interactions. Herein, a new nitrile-substituted 1,3,5-tricarboxamide-based gelator G4 has been fabricated and shows aggregate-induced enhanced emission (AIEE) after gelation in the presence of water. A dimethylformamide (DMF) solution of the gelator shows rapid crystallization, but addition of water to a DMF solution of gelator G4 leads to gelation at room temperature. In addition, gelator G4 was used for the formation of metallogels, and among them, the cobalt metallogel has been found to be effective for sensing l-tryptophan in the gel state through the quenching of AIEE. Interestingly, the gel is also effective in sensing bovine serum albumin protein at the nanomolar level, which contains an l-tryptophan residue. The limit of detection of Co(II)G4 for selective sensing of tryptophan has been found to be 2.4 × 10 -8 M. To the best of our knowledge, there have been no reports to date of a metallogel being utilized to discriminate and selectively sense an amino acid and a protein. The gelation properties of the organic gelator molecule and metallogels have been explored through various spectroscopic tools and physicochemical experiments.

Hydrogen (H 2 ) is a clean fuel that can potentially be a future solution for the storage of intermittent renewable energy. However, current H 2 production is mainly dominated by the energy intensive steam reforming reaction, which consumes a fossil fuel, methane, and emits copious amounts of carbon dioxide as one of the byproducts. To address this challenge, we report a molecular catalyst that produces H 2 from aqueous solutions, is composed of affordable, earth-abundant elements such as nickel, and has been incorporated into a system driven by visible light. Under optimized conditions, we observe a turnover number of 3880, among the best for photocatalytic H 2 evolution with nickel complexes from water-methanol solutions. Through nanosecond transient absorption, electron paramagnetic resonance, and UV-vis spectroscopic measurements, and supported by density functional theory calculations, we report a detailed study of this photocatalytic H 2 evolution cycle. We demonstrate that a one-electron reduced, predominantly ligand-centered, reactive Ni intermediate can be accessed under visible light irradiation using triethylamine as the sacrificial electron donor and reductive quencher of the initial photosensitizer excited state. In addition, the computational calculations suggest that the second coordination sphere ether arms can enhance the catalytic activity by promoting proton relay, similar to the mechanism among [FeFe] hydrogenases in nature. Our study can form the basis for future development of H 2 evolution molecular catalysts that incorporate both ligand redox noninnocence and alternative second coordination sphere effects in artificial photosynthetic systems driven by visible light.

Preparing low-dimensional perovskite materials with novel building units is highly desirable because such materials have already been demonstrated to show unusual physical properties. In this report, we first reported a new and unusual two-dimensional perovskite framework, [B(HIm) 4 ] 4 Pb 13 Br 38 (1), constructed from novel Lindqvist-type [Pb 6 Br 19 ] 7- nanoclusters. The as-prepared material shows good water resistance and chemical/heat stability. More importantly, 1 has been proven to exhibit temperature/excitation-wavelength-dependent emission. A possible mechanism has been provided.

We describe the synthesis of the ruthenacyclic carbamoyl complexes [Ru(2-NHC(O)C 5 H 3 NMe)(CO) 2 ( o,o-Me 2 -C 6 H 3 S)(L)] (L = H 2 O or MeCN), which have a labile water or acetonitrile ligand at their sixth coordination sites. Steric bulk around the ruthenium center is essential in preventing isomerization and dimerization, and embedding within papain can be achieved via coordination of its sole free cysteine residue. The observed chemistry parallels that of the natural [Fe]-hydrogenase.

Herein we describe that oxidation reactions of the dimeric cyclophosphazanes, [{P(μ-NR)} 2 (μ-NR)] 2 , R = t Bu (1), to produce a series of diagonally dioxidized products P 4 (μ-N t Bu) 6 E 2 [E = O (2), S (3), and Se (4)] and tetraoxidized frameworks. The latter display an unexpected C-N bond activation and cleavage to produce a series of novel phosphazane macrocyclic arrangements containing newly formed N-H bonds. Macromolecules P 4 (μ-N t Bu) 4 (μ-NH) 2 O 4 (5) and P 4 (μ-N t Bu) 3 (μ-NH) 3 E 4 , E = S (6) and Se (7), dicleaved and tricleaved products, respectively, are rare examples of dimeric macrocycles containing NH bridging groups. Our theoretical and experimental studies illustrate that the extent to which these C-N bonds are cleaved can be controlled by modification of steric parameters in their synthesis, by adjusting either the steric bulk of the substituents in the parent framework or the size of the chalcogen element introduced during the oxidation process. Our findings represent new synthetic pathways for the synthesis of otherwise-elusive macrocycle arrangements within the phosphazane family.

A set of structural mimics of the [Fe]-hydrogenase active site comprising all the group VIII metals, viz., [M(2-NHC(O)C 5 H 4 N)(CO) 2 (2-S-C 5 H 4 N)], has been synthesized. They exist as a mixture of isomers in solution, and the relative stability of the isomers depends on the nature of the metal and the substituent at the 6-position of the pyridine ligand.

In this work, strategic enhancement of electrophilicity of phosphenium cations for the purpose of small-molecule activation was described. Our synthetic methodology for generation of novel two-coordinate phosphorus(III)-based compounds [{C 6 H 4 (MeN) 2 C} 2 C·PR] 2+ ([2a] 2+ , R = N i Pr 2 ; [2b] 2+ , R = Ph) was based on the exceptional electron-donating properties of the carbodicarbene ligand (CDC). The effects of P-centered substituent exchange and increase in the overall positive charge on small substrate activation were comparatively determined by incorporating the bis(amino)phosphenium ion [( i Pr 2 N) 2 P] + ([1] + ) in this study. Implemented structural and electronic modifications of phosphenium salts were computationally verified and subsequently confirmed by isolation and characterization of the corresponding E-H (E = B, Si, C) bond activation products. While both phosphenium mono- and dications oxidatively inserted/cleaved the B-H bond of Lewis base stabilized boranes, the increased electrophilicity of doubly charged species also afforded the activation of significantly less hydridic Si-H and C-H bonds. The preference of [2a] 2+ and [2b] 2+ to abstract the hydride rather than to insert into the corresponding bond of silanes, as well as the formation of the carbodicarbene-stabilized parent phosphenium ion [{C 6 H 4 (MeN) 2 C} 2 C·PH 2 ] + ([2·PH 2 ] + ) were experimentally validated.

We have developed bis(N-heterocyclic olefin) derivatives 2 and demonstrated that 2 can be utilized as precursors for the synthesis of isophosphindolylium species 3. X-ray diffraction and density functional theory studies indicate the aromatic property of the PC 4 five-membered ring in 3. Despite its cationic nature, the P center in 3b exhibits nucleophilic character and thus readily forms a bond with CuCl to afford a copper phosphenium complex 4, demonstrating the potential utility of 3 as a σ-donor ligand.

Aryl bis(imino)acenaphthenes (Ar-BIANs) are well-established rigid and sterically bulky diimine ligands, which are redox-noninnocent and versatile π-acceptors due to their low-lying π* orbitals and are frequently used to bind transition metals. However, the coordination chemistry of Ar-BIAN ligands to main group elements is not as well-developed as that of their transition metal counterparts. In particular, there are no comprehensive studies describing the spectroscopic and electrochemical properties of main group Ar-BIAN complexes. Herein, we report the synthesis and full characterization of a series of new indium(III) Ar-BIAN complexes, bearing 2,6-dialkyl (1b and 2b), 4-nitro (3b), and 4-dimethylamino (4b) groups at the aryl-diimine part of the ligand. Their optical and electrochemical properties have been revealed by UV-vis spectroscopy and cyclic voltammetry, respectively. Additionally, DFT calculations were performed to gain insights into the nature of the properties displayed.

The reactivity of L 2 PhB: (1; L = oxazol-2-ylidene) as well as its transition-metal (chromium and iron) complexes toward main-group substrates have been systematically examined, which led to the construction of B-E (E = C, Ga, Cl, H, F, N) bonds. The combination of 1 and triethylborane smoothly captured carbon dioxide concomitant with the formation of B-C and B-O bonds. The soft basic boron center in 1 readily reacted with soft acidic gallium trichloride (GaCl 3 ) to afford the extremely stable adduct 4 involving a B-Ga dative bond. Electrophilic alkylation of a neutral tricoordinate organoboron was first achieved by the treatment of 1 with dichloromethane and methyl trifluoromethanesulfonate (MeOTf), both of which afforded ionic species featuring an additional B-C bond. Comparatively, redox reactions took place when halides of heavier elements such as germanium dichloride, dichlorophenylphosphine, and chlorodiphenylbismuth were employed as substrates, from which cationic species 7 bearing a B-Cl bond was obtained. In addition, reactions of metal complexes [2, Cr(1)(CO) 5 ; 8, Fe(1)(CO) 4 ] with cationic electrophiles were investigated. With HOTf and FN(SO 2 Ph) 2 , the corresponding ionic species featuring a B-H bond (9) and a B-F bond (10) were formed via a formal electrophilic substitution reaction, whereas the reaction of 1 with F·Py-BF 4 resulted in the formation of a dicationic boron species 11 with a newly formed B-N bond.

The reactivity of the 2-imino-5,6-methylenedioxylphenylgermanium(I) dimer toward group 9 metal(I) chloride and dimanganese decacarbonyl is described. [LGe:] 2 (1, L = 2-imino-5,6-methylenedioxylphenyl) underwent a disproportionation reaction with 1.5 equiv of group 9 metal(I) chloride [MCl(cod)] 2 (M = Rh, Ir) in toluene to afford a mixture of the group 9 metallogermylene-chlorometal(I) complexes [LGeμ-{M(cod)} 2 Cl] (M = Rh (2), Ir (4)) and chlorogermylene-chlorometal(I) complexes [L(Cl)GeM(cod)Cl] (M = Rh (3), Ir (5)), respectively. The disproportionation property of 1 is further evidenced by its reaction with 0.5 equiv of Mn 2 (CO) 10 in refluxing toluene to form a mixture of the manganogermylene dimer [(LGe)μ-{Mn(CO) 4 }] 2 (7) and free ligand [LH] (8). Compounds 2-5, 7, and 8 were elucidated by NMR spectroscopy, X-ray crystallography, and DFT calculations, respectively.

The reaction of the pentaphenylborole [(PhC) 4 BPh] (1) with sodium phosphaethynolate·1,4-dioxane (NaOCP(1,4-dioxane) 1.7 ) afforded the novel sodium salt of phosphaboraheterocycle 2. It comprises anionic fused tetracyclic P/B-heterocycles that arise from multiple bond activation between the borole backbone and [OCP] - anion. Density functional theory calculations indicate that the [OCP] - anion prefers the form of phosphaethynolate - O-C≡P over phosphaketenide O═C═P - to interact with two molecules of 1, along with various B-C, C-P, and C-C bond activations to form 2. The calculations were verified by experimental studies: (i) the reaction of 1 with NaOCP(1,4-dioxane) 1.7 and a Lewis base such as the N-heterocyclic carbene I Ar [:C{N(Ar)CH} 2 ] (Ar = 2,6-iPr 2 C 6 H 3 ) and amidinato amidosilylene [{PhC(NtBu) 2 }(Me 2 N)Si:] afforded the Lewis base-pentaphenylborole adducts [(PhC) 4 B(Ph)(LB)] (LB = I Ar (3), :Si(NMe 2 ){(NtBu) 2 CPh} (4)), respectively; (ii) the reaction of 1 with the carbodiimide ArN═C═NAr afforded the seven-membered B/N heterocycle [B(Ph) (CPh) 4 C(═NAr)N(Ar)] (5). Compounds 2-5 were fully characterized by NMR spectroscopy and X-ray crystallography.

The synthesis of an oligo(silanimine) is described. The reaction of the amidinato silylene [LSiN(SiMe 3 ) 2 ] (1, L = PhC(NtBu) 2 ) with SiI 4 in toluene afforded a mixture of the silanimine [LSi(I)NSiI 3 ] (2), SiMe 3 I, and Si 2 I 6 . The mechanistic studies showed that 1 reacts with SiI 4 to form the silyl ionic intermediate "{LSi(I)N(SiMe 3 ) 2 } + {SiI 3 } - ", which then eliminates SiMe 3 I and "SiI 2 " to form the silanimine intermediate "LSi(I)NSiMe 3 ". It further undergoes a substitution with another molecule of SiI 4 to form a mixture of 2 and SiMe 3 I. In addition, "SiI 2 " undergoes an oxidative addition with SiI 4 to form Si 2 I 6 . Subsequently, compound 2 reacted with [LiN(SiMe 3 )Ar] to form the silanimine [LSi(I)NSiI 2 N(SiMe 3 )Ar] (6, Ar = 2,6-iPr 2 C 6 H 3 ), which was then treated with KC 8 to give the donor-acceptor stabilized tetra(silanimine) [LSiN(SiMe 3 )SiNAr] 2 (7). It comprises four formal silanimine ">Si═N-" units, which are linked together. Compounds 2, 6, and 7 were characterized by NMR spectroscopy and X-ray crystallography.

The reaction of the N-heterocyclic-carbene-stabilized disilicon(0) complex [IPr→Si═Si←IPr] (1; IPr = :C{N(Ar)CH}2 and Ar = 2,6-iPr2C6H3) with ArN3 afforded the N-heterocyclic-carbene-stabilized siladiimide [ArNSi(IPr)NAr] (2). X-ray crystallography and theoretical studies show that the N-Si-N skeleton in compound 2 possesses considerable double-bond character and the Si atom is stabilized by the N-heterocyclic carbene.

The coordination chemistry of the amidinate-stabilized silicon(I) dimer toward group 9 metal complexes is described. The reaction of [LSi:]2 (1, L = PhC(NtBu)2) with [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) in toluene at ambient temperature afforded the base-stabilized silicon(I) dimer-iridium complex [LSi{Ir(cod)-μ-Cl-Ir(cod)}SiL][(cod)IrCl2] (2). In contrast, the reaction of 1 with [Rh(cod)Cl]2 in toluene at ambient temperature afforded a mixture of the amidinate-stabilized silicon(I) dimer-rhodium complex [LSi{Rh(cod)-μ-Cl-Rh(cod)}SiL] (3) and the dimeric amidinate-stabilized rhodosilylene [(LSi)μ-{Rh(μ-Cl)2Rh(cod)}]2 (4). Moreover, the latter reacted with PPh3 to afford a mixture of the Wilkinson's catalyst [(PPh3)3RhCl] and the dimeric rhodosilylene complex [(LSi)μ-{RhCl(PPh3)}]2 (5), which underwent a rearrangement to form the rhodosilylene-phosphidorhodium dimer (LSi)[μ-{RhCl(PPh3)}μ-{RhCl(LSiPh)}](PPh2) (6). Compounds 2-6 were characterized by NMR spectroscopy and X-ray crystallography. In addition, DFT calculations of compound 4 were performed to understand its electronic structure.

Reaction of 4-CN-PhOH with [ClP(μ-N(t)Bu)]2 (1) (2:1 ratio) in the presence of Et3N produced the functionalized cyclodiphosph(III/III)azane [(4-CN-PhO)P(μ-N(t)Bu)]2 (2). Oxidation of 2 produced cyclodiphosph(V/V)azanes [(4-CN-PhO)(E)P(μ-N(t)Bu)]2 [E = O (3), S (4), and Se (5)]. This is the first example of a series of cyclodiphosph(V/V)azane derivatives obtained from a single cyclophosph(III/III)azane precursor where all the accessible chalcogen oxidized products are air-stable over prolonged periods of time.

C-F bond cleavage by transient phosphorus(III)-based dications [RP(C(PPh3)2)](2+) (4a(2+), R = Ph; 4b(2+), R = 4-F-Ph) is reported. These dications were generated by reaction of the corresponding monocationic precursors with excess Na[BAr4(Cl)]. Evidence for the existence of transient dicationic species was obtained by trapping the dication 4a(2+) with PMe3. According to theoretical analysis, the low-lying lowest unoccupied molecular orbitals of these species were responsible for the observed activation of C-F bonds.

A novel dicationic system containing a PN fragment has been synthesized and structurally characterized. According to the solid-state analysis and theoretical investigation, the dicationic iminophosphane resonance form is the most appropriate description for the dication. However, the contribution from the phosphorus mononitride resonance form is not negligible.

The tetra- and binuclear heterometallic complexes of nickel(II)-vanadium(IV/V) combinations involving a phenol-based primary ligand, viz., N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine (H2L1), are reported in this work. Carboxylates and beta-diketonates have been used as ancillary ligands to obtain the tetranuclear complexes [Ni(II)(2)V(V)(2)(RCOO)(2)(L(1))(2)O(4)] (R = Ph, 1; R = Me(3)C, 2) and the binuclear types [(beta-diket)Ni(II)L(1)V(IV)O(beta-diket)] (3 and 4), respectively. X-ray crystallography shows that the tetranuclear complexes are constructed about an unprecedented heterometallic eight-membered Ni(2)V(2)O(4) core in which the (L(1))(2)- ligands are bound to the Ni center in a N(2)O(2) mode and simultaneously bridge a V atom via the phenoxide O atoms. The cis-N(2)O(4) coordination geometry for Ni is completed by an O atom derived from the bridging carboxylate ligand and an oxo O atom. The latter two atoms, along with a terminal oxide group, complete the O5 square-pyramidal coordination geometry for V. Each of the dinuclear compounds, [(acac)Ni(II)L(1)V(IV)O(acac)] (3) and [(dbm)Ni(II)L(1)V(IV)O(dbm)] (4) [Hdbm = dibenzoylmethane], also features a tetradentate (L(1))(2)- ligand, Ni in an octahedral cis-N(2)O(4) coordination geometry, and V in an O(5) square-pyramidal geometry. In 3 and 4, the bridges between the Ni and V atoms are provided by the (L(1))(2)- ligand. The Ni...V separations in the structures lie in the narrow range of 2.9222(4) A (3) to 2.9637(5) A (4). The paramagnetic Ni centers (S = 1) in 1 and 2 are widely separated (Ni...Ni separations are 5.423 and 5.403 A) by the double V(V)O(4) bridge that leads to weak antiferromagnetic interactions (J = -3.6 and -3.9 cm-1) and thus an ST = 0 ground state for these systems. In 3 and 4, the interactions between paramagnetic centers (Ni(II) and V(IV)) are also antiferromagnetic (J = -8.9 and -10.0 cm-1), leading to an S(T) = 1/2 ground state. Compound 4 undergoes two one-electron redox processes at E(1/2) = +0.66 and -1.34 V vs Ag/AgCl reference due to a V(IV/V) oxidation and a Ni(II)/I reduction, respectively, as indicated by cyclic and differential pulse voltammetry.