Controlling Swing Rates in Macrocyclic Molecular Mortise Hinges.

Hinge motion is observed in macrocyclic, mortise-type molecular hinges using variable temperature NMR spectroscopy. The data is consistent with dynamic hinging from a folded-to-extended-to-folded enantiomeric state. Crystallographic and solution structures of the folded states are reported.

A Model for the Rapid Assessment of Solution Structures for 24-Atom Macrocycles: The Impact of β-Branched Amino Acids on Conformation.

Experiment and computation are used to develop a model to rapidly predict solution structures of macrocycles sharing the same Murcko framework. These 24-atom triazine macrocycles result from the quantitative dimerization of identical monomers presenting a hydrazine group and an acetal tethered to an amino acid linker. Monomers comprising glycine and the β-branched amino acids threonine, valine, and isoleucine yield macrocycles , , , and , respectively.

Syntheses, homeomorphic and configurational isomerizations, and structures of macrocyclic aliphatic dibridgehead diphosphines; molecules that turn themselves inside out.

The diphosphine complexes - or -[upper bond 1 start]PtCl(P((CH) )P[upper bond 1 end]) ( = b/12, c/14, d/16, e/18) are demetalated by MC[triple bond, length as m-dash]X nucleophiles to give the title compounds (P((CH) ))P (3b-e, 91-71%). These "empty cages" react with PdCl or PtCl sources to afford -[upper bond 1 start]MCl(P((CH) )P[upper bond 1 end]). Low temperature P NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to , (major) and , isomers.

Oxygen-atom transfer photochemistry of a molecular copper bromate complex.

We report the synthesis and oxygen-atom transfer (OAT) photochemistry of [Cu(tpa)BrO]ClO. spectroscopy and experiments indicate OAT proceeds from a Cu-O fragment generated by sequential Cu-O bond cleavage and OAT from BrO to [Cu(tpa)]. These results highlight synthetic opportunities in M-O photochemistry and demonstrate the utility of experiments to evaluating photochemical reaction mechanisms.

A High-Performance Single-Molecule Magnet Utilizing Dianionic Aminoborolide Ligands.

The first example of a homoleptic f-block borolide sandwich complex is presented and shown to be a high-performance single-molecule magnet (SMM). The bis(borolide) complex [K(2.2.

Nitrogen Atom Transfer Catalysis by Metallonitrene C-H Insertion: Photocatalytic Amidation of Aldehydes.

C-H amination and amidation by catalytic nitrene transfer are well-established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C-H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium.

Linear and Bent Nitric Oxide Ligand Binding in an Asymmetric Butterfly Complex: .

Two synthetic approaches to install metallodithiolate ligands on molybdenum centers using the synthons [Mo(CHCN)] and (NS)Co(NO) [NS = ,-bis(2-mercaptoethyl)-1,4-diazacycloheptane and NO = nitric oxide], or [Mo(NO)(CHCN)] (CHCN = acetonitrile) and [(NS)Co] lead to a bis-nitrosylated, trimetallic dication, . This unique asymmetric butterfly complex, with = 1, has a bent NO within the small {Co(NO)} wing (denoted as ), reflecting Co(NO), and is S-bridged to a linear {Mo(NO)} diamagnetic unit. The latter is further S-bridged to a pentacoordinate (NS)Co(CHCN) donor in the larger wing and is the origin of the two unpaired electrons, denoted as .

Snapshots of Rh-Catalyzed C-H Amination.

While X-ray crystallography routinely provides structural characterization of kinetically stable pre-catalysts and intermediates, elucidation of the structures of transient reactive intermediates, which are intimately engaged in bond-breaking and -making during catalysis, is generally not possible. Here, we demonstrate synthesis of Rh nitrenoids that participate in catalytic C-H amination, and we characterize these transient intermediates as triplet adducts of Rh. Further, we observe the impact of coordinating substrate, which is present in excess during catalysis, on the structure of transient Rh nitrenoids.

C-H Amination Mediated by Cobalt Organoazide Adducts and the Corresponding Cobalt Nitrenoid Intermediates.

Treatment of (L)CoBr (L = 5-mesityl-1,9-(2,4,6-PhCH)dipyrrin) with a stoichiometric amount of 1-azido-4-(-butyl)benzene N(CH--Bu) furnished the corresponding four-coordinate organoazide-bound complex (L)CoBr(N(CH--Bu)). Spectroscopic and structural characterization of the complex indicated redox innocent ligation of the organoazide. Slow expulsion of dinitrogen (N) was observed at room temperature to afford a ligand functionalized product via a [3 + 2] annulation, which can be mediated by a high-valent nitrene intermediate such as a Co iminyl (L)CoBr(N(CH--Bu)) or Co imido (L)CoBr(N(CH--Bu)) complex.

Axial Elongation of Mononuclear Lanthanide Metallocenophanes: Magnetic Properties of Dysprosium- and Terbium-[1]Ruthenocenophane Complexes.

We report the first f-block-ruthenocenophane complexes 1 (Dy) and 2 (Tb) and provide a comparative discussion of their magnetic structure with respect to earlier reported ferrocenophane analogues. While axial elongation of the rare trigonal-prismatic geometry stabilizes the magnetic ground state in the case of Dy and results in a larger barrier to magnetization reversal (U), a decrease in U is observed for the case of Tb .

Syntheses, Structures, and Spectroscopic Properties of 1,10-Phenanthroline-Based Macrocycles Threaded by PtC Pt, PtC Pt, and PtC Pt Axles: Metal-Capped Rotaxanes as Insulated Molecular Wires.

The platinum polyynyl complexes trans-(C F )(p-tol P) Pt(C≡C) H undergo oxidative homocoupling (O , CuCl/TMEDA) to diplatinum polyynediyl complexes trans, trans-(C F )(p-tol P) Pt(C≡C) Pt(Pp-tol ) (C F ) (n=4, 2; 6, 5; 8, 8; 92-97 %) as reported previously. When related reactions are conducted in the presence of CuI adducts of the 1,10-phenanthroline-based macrocycles 2,9-(1,10-phenanthrolinediyl)(p-C H O(CH ) O) (1,3-C H ) (10, 33-membered) or 2,9-(1,10-phenanthrolinediyl)(p-C H O(CH ) O) (2,7-naphthalenediyl) (11, 35-membered), excess K CO , and I (oxidant), rotaxanes are isolated that feature a Pt(C≡C) Pt axle that has been threaded through the macrocycle (2⋅10, 9 %; 5⋅10, 41 %; 5⋅11, 28 %; 8⋅10, 12 %; 8⋅11, 9 %). Their crystal structures are determined and analyzed in detail, particularly with respect to geometric perturbations and the degree of steric sp carbon chain insulation.

Characterization of a Reactive Rh Nitrenoid by Crystalline Matrix Isolation.

The fleeting lifetimes of reactive intermediates in C-H functionalization chemistry often prevent their direct characterization. For example, the critical nitrenoid intermediates that mediate Rh-catalyzed C-H amination have eluded characterization for more than 40 years. In the absence of structural characterization of these species, methodological development is often computationally guided.

Controlling O Reactivity in Synthetic Analogues of [NiFeS]- and [NiFeSe]-Hydrogenase Active Sites.

Strategies for limiting, or reversing, the degradation of air-sensitive, base metal catalysts for the hydrogen evolution/oxidation reaction on contact with adventitious O are guided by nature's design of hydrogenase active sites. The affinity of oxygen for sulfur and selenium, in [NiFeS]- and [NiFeSe]-Hase, yields oxygenated chalcogens under aerobic conditions, and delays irreversible oxygen damage at the metals by maintaining the NiFe core structures. To identify the controlling features of S-site oxygen uptake, related (μ-E)(μ-S') (E = S or Se, = (η-CH)Fe(CO)) complexes were electronically tuned by the para-substituent on μ-EPhX (X = CF, Cl, H, OMe, NMe) and compared in aspects of communication between Ni and Fe.

Oxygen uptake in complexes related to [NiFeS]- and [NiFeSe]-hydrogenase active sites.

A biomimetic study for S/Se oxygenation in Ni(μ-EPh)(μ-SN)Fe, (E = S or Se; SN = Me-diazacycloheptane-CHCHS); Fe = (η-CH)Fe(CO) complexes related to the oxygen-damaged active sites of [NiFeS]/[NiFeSe]-Hases is described. Mono- and di-oxygenates (major and minor species, respectively) of the chalcogens result from exposure of the heterobimetallics to O; one was isolated and structurally characterized to have Ni-O-Se-Fe-S connectivity within a 5-membered ring. A compositionally analogous mono-oxy species was implicated by (CO) IR spectroscopy to be the corresponding Ni-O-S-Fe-S complex; treatment with O-abstraction agents such as P(-tolyl) or PMe remediated the O damage.

A Nontemplated Route to Macrocyclic Dibridgehead Diphosphorus Compounds: Crystallographic Characterization of a "Crossed-Chain" Variant of in/out Stereoisomers.

Reactions of (O=)PH(OCH CH ) and BrMg(CH ) CH=CH (4.9-3.2 equiv; m=4 (a), 5 (b), 6 (c)) give the dialkylphosphine oxides (O=)PH[(CH ) CH=CH ] (2 a-c; 77-81 % after workup), which are treated with NaH and then α,ω-dibromides Br(CH ) Br (0.

Direct Characterization of a Reactive Lattice-Confined Ru Nitride by Photocrystallography.

Reactive metal-ligand (M-L) multiply bonded complexes are ubiquitous intermediates in redox catalysis and have thus been long-standing targets of synthetic chemistry. The intrinsic reactivity of mid-to-late M-L multiply bonded complexes renders these structures challenging to isolate and structurally characterize. Although synthetic tuning of the ancillary ligand field can stabilize M-L multiply bonded complexes and result in isolable complexes, these efforts inevitably attenuate the reactivity of the M-L multiple bond.

Discovery, Total Synthesis and Key Structural Elements for the Immunosuppressive Activity of Cocosolide, a Symmetrical Glycosylated Macrolide Dimer from Marine Cyanobacteria.

A new dimeric macrolide xylopyranoside, cocosolide (1), was isolated from the marine cyanobacterium preliminarily identified as Symploca sp. from Guam. The structure was determined by a combination of NMR spectroscopy, HRMS, X-ray diffraction studies and Mosher's analysis of the base hydrolysis product.

Gyroscope like molecules consisting of trigonal or square planar osmium rotators within three-spoked dibridgehead diphosphine stators: syntheses, substitution reactions, structures, and dynamic properties.

Reactions of (NH4)2OsX6 (X = Cl, Br) with CO and the phosphines P((CH2)mCH[double bond, length as m-dash]CH2)3 (m = 6, a; 7, b; 8, c) give cis,cis,trans-Os(CO)2(X)2(P((CH2)mCH[double bond, length as m-dash]CH2)3)2 (46-73%). These are treated with Grubbs' catalyst (7 mol%, 0.0010 M, C6H5Cl).

CB-TE2A(+)·Cl(-)·3H2O: a short intermolecular hydrogen bond between zwitterionic bicyclo[6.6.2]tetraamine macrocycles.

1,4,8,11-Tetraazabicyclo[6.6.2]hexadecane-4,11-diacetic acid (CB-TE2A) is of much interest in nuclear medicine for its ability to form copper complexes that are kinetically inert, which is beneficial in vivo to minimize the loss of radioactive copper.

Controlling the Fluorescence Response of PET Sensors via the Metal-Ion π-Contacting Ability of the Fluorophore: Coumarin, a Weaker π Contacter.

The π-contact hypothesis, that quenching of the fluorescence of complexes of photoinduced electron transfer sensors with heavy diamagnetic metal ions may be caused by π contacts between the metal ion and the fluorophore of the sensor, is examined with a study of the fluorescent properties of the sensor 4-[[bis(2-pyridinylmethyl)amino]methyl]-6,7-dimethoxy-1-benzopyran-2-one (cdpa) and the structures of its complexes with some metal ions. The coumarin-type fluorophore of cdpa is a weaker π-contact former than the anthracenyl fluorophore of the analogue adpa (Inorg. Chem.

Synthesis of Triborylalkenes from Terminal Alkynes by Iridium-Catalyzed Tandem C-H Borylation and Diboration.

A two-step reaction to convert terminal alkynes into triborylalkenes is reported. In the first step, the terminal alkyne and pinacolborane (HBpin) are converted into an alkynylboronate, which is catalyzed by an iridium complex supported by a SiNN pincer ligand. In the second step, treatment of the reaction mixture with CO generates a new catalyst which mediates dehydrogenative diboration of alkynylboronate with pinacolborane.

Steric control of the in/out sense of bridgehead substituents in macrobicyclic compounds: isolation of new "crossed chain" variants of in/out isomers.

Isomers of the cage like dibridgehead diphosphine P((CH2)14)3P (1) are treated with Ph3PAu(2,6-C6H3(Trip)2) (2 equiv.; Trip = 2,4,6-C6H2(iPr)3). With out,out-1, workup gives out,out-1·(Au(2,6-C6H3(Trip)2))2 (46%), as confirmed by a crystal structure.

The effect of π contacts between metal ions and fluorophores on the fluorescence of PET sensors: implications for sensor design for cations and anions.

The idea that M···C π contacts between diamagnetic heavy metal ions such as Pb(II), Ag(I), Pd(II), or Hg(II) and the anthracenyl fluorophore of adpa ((N-(9-anthracenylmethyl)-N-(2-pyridinylmethyl)-2-pyridinemethanamine) are responsible for quenching the fluorescence of the complexes of these metal ions with adpa is explored crystallographically. The structures of [Pb(adpa)(NO3)2] (1), [Ag(adpa)NO3] (2), [Pd(adpa)NO3]NO3 (3), [Zn(adpa)(NO3)2] (4), and [Cd(adpa)Br2] (5) are reported. The π contacts with the fluorophore are for 1 are a Pb···C π contact of 3.