Thuwalamides A-E: Polychlorinated amides from the marine sponge Lamellodysidea herbacea collected from the Saudi Arabian Red Sea.

Thuwalamides A-E (1, 3, 5, 6 and 8), previously undescribed polychlorinated amides, along with ten previously reported related compounds (2, 4, 7 and 9-15), were isolated from the organic extract of the marine sponge Lamellodysidea herbacea (Keller), collected off the village of Thuwal in the Red Sea at Saudi Arabia. The structures of the isolated compounds have been determined through extensive analysis of their NMR and MS data, while their absolute stereochemistry was unequivocally established via single crystal X-ray diffraction. Additionally, the absolute stereochemistry of the previously reported compounds 2 and 4, whose configuration was not determined, has also been established using single-crystal X-ray crystallographic analysis.

Synthesis of N-heterocyclic carbene (NHC)-Au/Ag/Cu benzotriazolyl complexes and their catalytic activity in propargylamide cycloisomerization and carbonyl hydrosilylation reactions.

Carbene-metal-amide (CMA) complexes of gold, silver, and copper have been studied extensively for their photochemical/photocatalytic properties and as potential (pre-)catalysts in organic synthesis. Herein, the design, synthesis, and characterization of five bench-stable Au-, Ag-, and Cu-NHC complexes bearing the benzotriazolyl anion as an amide donor, are reported. All complexes are synthesized in a facile and straightforward manner, using mild conditions.

Copper-Catalyzed One-Pot Synthesis of Thiazolidin-2-imines.

The synthesis of thiazolines, thiazolidines, and thiazolidinones has been extensively studied, due to their biological activity related to neurodegenerative diseases, such as Parkinson's and Alzheimer's, as well as their antiparasitic and antihypertensive properties. The closely related thiazolidin-2-imines have been studied less, and efficient strategies for synthesizing them, mainly based on the reaction of propargylamines with isothiocyanates, have been explored less. The use of one-pot approaches, providing modular, straightforward, and sustainable access to these compounds, has also received very little attention.

New Pyridine Dicarbene Pincer Ligands with Ring Expanded NHCs and their Nickel and Chromium Complexes.

The pincer complexes [NiBr(CNC)]Br (4), [CrBr(CNC)] (5 a) and [CrBrCl(CNC)] (5 b), where CNC=3,3'-(pyridine-2,6-diyl)bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br and [NiBr(PPh)] or from [Cr{N(SiMe)}(THF)] and (CHNCH)Br by aminolysis, respectively. The tetrahedrally distorted square planar (τ≅0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone.

T-Shaped Palladium and Platinum {MNO} Nitrosyl Complexes.

The synthesis and characterization of a homologous series of T-shaped {MNO} nitrosyl complexes of the form [M(PR)(NO)] (M = Pd, Pt; R = Bu, Ad) are reported. These diamagnetic nitrosyls are obtained from monovalent or zerovalent precursors by treatment with NO and NO, respectively, and are notable for distinctly bent M-NO angles of ∼123° in the solid state. Adoption of this coordination mode in solution is also supported by the analysis of isotopically enriched samples by N NMR spectroscopy.

Secondary Metabolites with Anti-Inflammatory Activity from Collected in the Red Sea.

The chemical investigation of the organic extract of the red alga collected from Hurghada reef in the Red Sea resulted in the isolation of five C acetogenins, including four tricyclic ones of the maneonene type (-) and a 5-membered one (), 15 sesquiterpenes, including seven lauranes (-), one cuparane (), one -laurane (), one snyderane (), two chamigranes (, ), two rearranged chamigranes (, ) and one aristolane (), as well as a tricyclic diterpene () and a chlorinated fatty acid derivative (). Among them, compounds -, , , , , and are new natural products. The structures and the relative configurations of the isolated natural products have been established based on extensive analysis of their NMR and MS data, while the absolute configuration of maneonenes F () and G () was determined on the basis of single-crystal X-ray diffraction analysis.

Thorium- and Uranium-Mediated C-H Activation of a Silyl-Substituted Cyclobutadienyl Ligand.

Cyclobutadienyl complexes of the f-elements are a relatively new yet poorly understood class of sandwich and half-sandwich organometallic compounds. We now describe cyclobutadienyl transfer reactions of the magnesium reagent [(η-Cb'''')Mg(THF)] (), where Cb'''' is tetrakis(trimethylsilyl)cyclobutadienyl, toward thorium(IV) and uranium(IV) tetrachlorides. The 1:1 stoichiometric reactions between and AnCl proceed with intact transfer of Cb'''' to give the half-sandwich complexes [(η-Cb'''')AnCl(μ-Cl)Mg(THF)] (An = Th, ; An = U, ).

Synthesis, bonding properties and ether activation reactivity of cyclobutadienyl-ligated hybrid uranocenes.

A series of hybrid uranocenes consisting of uranium(iv) sandwiched between cyclobutadienyl (Cb) and cyclo-octatetraenyl (COT) ligands has been synthesized, structurally characterized and studied computationally. The dimetallic species [(η-Cb'''')(η-COT)U(μ:η:η-COT)U(THF)(η-Cb'''')] () forms concomitantly with, and can be separated from, monometallic [(η-Cb'''')U(THF)(η-COT)] () (Cb'''' = 1,2,3,4-tetrakis(trimethylsilyl)cyclobutadienyl, COT = cyclo-octatetraenyl). In toluene solution at room temperature, dissociates into and the unsolvated uranocene [(η-Cb'''')U(η-COT)] ().

Ethene Activation and Catalytic Hydrogenation by a Low-Valent Uranium Pentalene Complex.

The reaction of the uranium(III) complex [U(η-Pn)(η-Cp*)] () (Pn = CH(1,4-SiPr), Cp* = CMe) with ethene at atmospheric pressure produces the ethene-bridged diuranium complex [{(η-Pn)(η-Cp*)U}(μ-η:η-CH)] (). A computational analysis of revealed that coordination of ethene to uranium reduces the carbon-carbon bond order from 2 to a value consistent with a single bond, with a concomitant change in the formal uranium oxidation state from +3 in to +4 in . Furthermore, the uranium-ethene bonding in is of the δ type, with the dominant uranium contribution being from f-d hybrid orbitals.

Uranium(iv) cyclobutadienyl sandwich compounds: synthesis, structure and chemical bonding.

The 1 : 1 reactions of uranium(iv) tetrakis(borohydride) with the sodium and potassium salts of the cyclobutadienyl anion [C(SiMe)] (Cb'''') produce the half-sandwich complexes [Na(12-crown-4)][U(η-Cb'''')(BH)] and [U(η-Cb'''')(μ-BH){K(THF)}]. In the 1 : 2 reaction of U(BH) with NaCb'''', formation of [U(η-Cb'''')(η-CH(SiMe)-κ-(CHSiMe)(BH))] reveals that a Cb'''' ligand undergoes an intramolecular deprotonation, resulting in an allyl/tuck-in bonding mode. A computational study reveals that the uranium-Cb'''' bonding has an appreciable covalent component with contributions from the uranium 5f and 6d orbitals.

Isolation of a Perfectly Linear Uranium(II) Metallocene.

Reduction of the uranium(III) metallocene [(η -C Pr ) UI] (1) with potassium graphite produces the "second-generation" uranocene [(η -C Pr ) U] (2), which contains uranium in the formal divalent oxidation state. The geometry of 2 is that of a perfectly linear bis(cyclopentadienyl) sandwich complex, with the ground-state valence electron configuration of uranium(II) revealed by electronic spectroscopy and density functional theory to be 5f 6d . Appreciable covalent contributions to the metal-ligand bonds were determined from a computational study of 2, including participation from the uranium 5f and 6d orbitals.

Bis(pentalene)dititanium chemistry: C-H, C-X and H-H bond activation.

The reaction of the bis(pentalene)dititanium complex Ti2(μ:η5,η5-Pn†)2 (Pn† = C8H4(1,4-SiiPr3)2) (1) with the N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene results in intramolecular C-H activation of an isopropyl substituent to form a tucked-in hydride (3). Whilst pyridine will also effect this cyclometallation reaction to form (5), the pyridine analogue of (3), the bases 1,2,4,5-tetramethyl-imidazole, 2,6-lutidine, DABCO or trimethylphosphine are ineffective. The reaction of (1) with 2,6-dichloro-pyridine affords crystallographically characterised (6) which is the product of oxidative addition of one of the C-Cl bonds in 2,6-dichloro-pyridine across the Ti-Ti double bond in (1).

Activation of carbon suboxide (CO) by U(iii) to form a cyclobutane-1,3-dione ring.

The activation of C3O2 by the U(iii) complex [U(η5-Cp')3] (Cp' = C5H4SiMe3) is described. The reaction results in the reductive coupling of three C3O2 units to form a tetranuclear complex with a central cyclobutane-1,3-dione ring, with concomitant loss of CO. Careful control of reaction conditions has allowed the trapping of an intermediate, a dimeric bridging ketene complex, which undergoes insertion of C3O2 to form the final product.

Preparation and reactivity of rhodium and iridium complexes containing a methylborohydride based unit supported by two 7-azaindolyl heterocycles.

The synthesis and characterisation of a new anionic flexible scorpionate ligand, methyl(bis-7-azaindolyl)borohydride [MeBai]- is reported herein. The ligand was coordinated to a series of group nine transition metal centres forming the complexes, [Ir(MeBai)(COD)] (1), [Rh(MeBai)(COD)] (2), [Rh(MeBai)(CODMe)] (2-Me) and [Rh(MeBai)(NBD)] (3), where COD = 1,5-cyclooctadiene, CODMe = 3-methyl-1,5-cyclooctadiene and NBD = 2,5-norbornadiene. In all cases, the boron based ligand was found to bind to the metal centres via a κ3-N,N,H coordination mode.

Trimerisation of carbon suboxide at a di-titanium centre to form a pyrone ring system.

The reaction of the -bimetallic bis(pentalene)dititanium complex Ti(μ:η,η-Pn) (Pn = CH(1,4-SiPr)) with carbon suboxide (O[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]O, CO) results in trimerisation of the latter and formation of the structurally characterised complex [{Ti(μ:η,η-Pn)}{μ-CO}]. The trimeric bridging CO unit in the latter contains a 4-pyrone core, a key feature of both the hexamer and octamer of carbon suboxide which are formed in the body from trace amounts of CO and are, for example, potent inhibitors of Na/K-ATP-ase. The mechanism of this reaction has been studied in detail by DFT computational studies, which also suggest that the reaction proceeds the initial formation of a mono-adduct of with CO.

Correction: C-H and H-H activation at a di-titanium centre.

Correction for 'C-H and H-H activation at a di-titanium centre' by Nikolaos Tsoureas et al., Chem. Commun.

C-H and H-H activation at a di-titanium centre.

The reaction of the bis(pentalene)dititanium complex Ti(μ:η,η-Pn) (Pn = CH(1,4-SiPr)) with the N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene results in intramolecular C-H activation of one of the Pr methyl groups of a Pn ligand and formation of a "tucked-in" bridging hydride complex. The "tuck-in" process is reversed by the addition of hydrogen, which yields a dihydride featuring terminal and bridging hydrides.

Cu(II) Coordination Polymers as Vehicles in the A Coupling.

A family of benzotriazole based coordination compounds, obtained in two steps and good yields from commercially available materials, formulated as [Cu(L)(MeCN)]·2ClO·MeCN (1), [Cu(L)(NO)]·MeCN (2), [Zn(L)(HO)]·2ClO·2MeCN (3), [Cu(L)Cl] (4), [Cu(L)Cl] (5), [Cu(L)Br]·4MeCN·CuBr (6), [Cu(L)(MeCN)]·2BF (7), [Cu(L)(CFSO)] (8), [Zn(L)(MeCN)]·2CFSO (9), [Cu(L)(HO)]·4CFSO·4MeCO (10), and [Cu(L)(CFSO)]·2CFSO·MeCO (11), are reported. These air-stable compounds were tested as homogeneous catalysts for the A coupling synthesis of propargylamine derivatives from aldehyde, amine, and alkyne under a noninert atmosphere. Fine tuning of the catalyst resulted in a one-dimensional (1D) coordination polymer (CP) (8) with excellent catalytic activity in a wide range of substrates, avoiding any issues that would inhibit its performance.

Steric control of redox events in organo-uranium chemistry: synthesis and characterisation of U(v) oxo and nitrido complexes.

The synthesis and molecular structures of a U(v) neutral terminal oxo complex and a U(v) sodium uranium nitride contact ion pair are described. The synthesis of the former is achieved by the use of BuNCO as a mild oxygen transfer reagent, whilst that of the latter is the reduction of NaN. Both mono-uranium complexes are stabilised by the presence of bulky silyl substituents on the ligand framework that facilitate a 2e oxidation of a single U(iii) centre.

Bis(pentalene)di-titanium: a bent double-sandwich complex with a very short Ti-Ti bond.

The novel bimetallic bis(pentalene) complex Ti2(μ:η(5),η(5)-Pn(†))2 (Pn(†) = C8H4{Si(i)Pr3-1,4}2) has been synthesised and structurally characterised. Structural data show a Ti-Ti distance of 2.399(2) Å, consistent with a strong metal-metal interaction, which DFT calculations best describe as a double bond with σ and π components.

Synthesis and characterisation of group nine transition metal complexes containing new mesityl and naphthyl based azaindole scorpionate ligands.

Two novel boron-based flexible scorpionate ligands based on 7-azaindole, Li[HB(azaindolyl)(2)(1-naphthyl)] and Li[HB(azaindolyl)(2)(mesityl)] {Li[(Naphth)Bai] and Li[(Mes)Bai] respectively}, have been prepared (mesityl = 2,4,6-trimethylphenyl). These salts have been isolated in two forms, either as dimeric structures which contain bridging hydride interactions with the lithium centres or as crystalline material containing mono nuclear bis-acetonitrile solvates. The newly formed ligands have been utilised to prepare a range of group nine transition metal complexes with the general formula [M(COD){κ(3)-NNH-HB (azaindolyl)(2)(Ar)}] (where M = rhodium, iridium; Ar = 1-naphthyl, mesityl; COD = 1,5-cyclooctadiene) and [Rh(NBD){κ(3)-NNH-HB (azaindolyl)(2)(Ar)}] (where NBD = 2,5-norbornadiene; Ar = 1-naphthyl, mesityl).

Strong agostic-type interactions in ruthenium benzylidene complexes containing 7-azaindole based scorpionate ligands.

The complexes [Ru(Tai)Cl{=C(H)Ph}(PCy(3))] (4) and [Ru((Ph)Bai)Cl{=C(H)Ph}(PCy(3))] (5) [where Tai = HB(7-azaindolyl)(3) and (Ph)Bai = Ph(H)B(7-azaindolyl)(2)] have been prepared and structurally characterised. The borohydride unit is located in the coordination site trans to the chloride ligand in both complexes. The degree of interaction between the borohydride group and the metal centre was found to be significantly large in both cases.

Reversible dioxygen binding in solvent-free liquid myoglobin.

The ensemble of forces that stabilize protein structure and facilitate biological function are intimately linked with the ubiquitous aqueous environment of living systems. As a consequence, biomolecular activity is highly sensitive to the interplay of solvent-protein interactions, and deviation from the native conditions, for example by exposure to increased thermal energy or severe dehydration, results in denaturation and subsequent loss of function. Although certain enzymes can be extracted into non-aqueous solvents without significant loss of activity, there are no known examples of solvent-less (molten) liquids of functional metalloproteins.