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A major chemical challenge facing implementation of 225Ac in targeted alpha therapy-an emerging technology that has potential for treatment of disease-is identifying an 225Ac chelator that is compatible with in vivo applications. It is unclear how to tailor a chelator for Ac binding because Ac coordination chemistry is poorly defined. Most Ac chemistry is inferred from radiochemical experiments carried out on microscopic scales. Of the few Ac compounds that have been characterized spectroscopically, success has only been reported for simple inorganic ligands. Toward advancing understanding in Ac chelation chemistry, we have developed a method for characterizing Ac complexes that contain highly complex chelating agents using small quantities (μg) of 227Ac. We successfully characterized the chelation of Ac3+ by DOTP8- using EXAFS, NMR, and DFT techniques. To develop confidence and credibility in the Ac results, comparisons with +3 cations (Am, Cm, and La) that could be handled on the mg scale were carried out. We discovered that all M3+ cations (M = Ac, Am, Cm, La) were completely encapsulated within the binding pocket of the DOTP8- macrocycle. The computational results highlighted the stability of the M(DOTP)5- complexes.

Reaction of two equivalents of [(C 5 [e 4 Et)2U(CH3)(Cl)] (6) or [(C 5 Me 5 ) 2 Th(CH 3 )(Br)] (7) with 1,4-dicyanobenzene leads to the formation of the novel 1,4-phenylenediketimide-bridged bimetallic organoactinide complexes [{(C5Me4Et)2(Cl)U}2(μ-{N=C-(CH3)-C 6 H 4 -(CH3)C=N})] (8) and [{(C 5 Me 5 -) 2 (Br)Th} 2 ,(μ-{N=C(CH 3 )-QH4-(CH 3 )CmN))] (9), respectively. These complexes were structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. Metal-metal interactions in these isovalent bimetallic systems were assessed by means of cyclic voltammetry, UV-visible/NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. Although evidence for magnetic coupling between metal centers in the bimetallic U IV /U IV (5f 2 -5f 2 ) complex is ambiguous, the complex displays appreciable electronic communication between the metal centers through the π system of the dianionic diketimide bridging ligand, as judged by voltammetry. The transition intensities of the f-f bands for the bimetallic U IV /U IV system decrease substantially compared to the related monometallic ketimide chloride complex, [(C 5 Me 5 ) 2 U(Cl){-N= C(CH3)-(3,4,5-F 3 -C 6 H 2 ))] (11). Also reported herein are new synthetic routes to the actinide starting materials [(C5Me4Et)2U(CH3)(Cl)] (6) and [(C 5 Me 5 ) 2 Th(CH 3 )(Br)] (7) in addition to the syntheses and structures of the monometallic uranium complexes [(C 5 Me 4 Et) 2 UCl 2 ] (3), [(C 5 Me 4 Et) 2 U-(CH 3 ) 2 ) (4), [(C 5 Me 4 Et)2U(-N=C(CH3)-C 6 H 4 -C=N) 2 ) (10), and 11.

Bimetallic ytterbocene complexes with bridging N-heterocylic ligands have been studied extensively in recent years due to their potential applications ranging from molecular wires to single-molecule magnets. Herein, we review our recent results for a series of ytterbocene polypyridyl bimetallic complexes to highlight the versatility and tunability of these systems based on simple changes in bridging ligand geometry. Our work has involved structural, electrochemical, optical, and magnetic measurements with the goal of better understanding the electronic and magnetic communication between the two ytterbium metal centers in this new class of bimetallics.

A systematic study of the novel charge-transfer [(f)14-(pi)0-(f)14 --(f)13-(pi)2-(f)13] electronic state found in 2:1 metal-to-ligand adducts of the type [(Cp)2Yb](BL)[Yb(Cp)2] [BL = tetra(2-pyridyl)pyrazine (tppz) (1), 6',6' '-bis(2-pyridyl)-2,2':4',4'':2'',2'''-quaterpyridine (qtp) (2), 1,4-di(terpyridyl)-benzene (dtb) (3), Cp = (C5Me5)] has been conducted with the aim of determining the effects of increased Yb-Yb separation on the magnetic and electronic properties of these materials. The neutral [(f)13-(pi)2-(f)13], cationic [(f)13-(pi)1-(f)13] and dicationic [(f)13-(pi)0-(f)13] states of these complexes were studied by cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, NMR, X-ray crystallography, and magnetic susceptibility measurements. The spectroscopic and magnetic data for the neutral bimetallic complexes is consistent with an [(f)13(pi)2(f)13] ground-state electronic configuration in which each ytterbocene fragment donates one electron to give a singlet dianionic bridging ligand with two paramagnetic Yb(III) centers. The voltammetric data demonstrate that the electronic interaction in the neutral molecular wires 1-3, as manifested in the separation between successive metal reduction waves, is large compared to analogous transition metal systems. Electronic spectra for the neutral and monocationic bimetallic species are dominated by pi-pi and pi-pi transitions, masking the f-f bands that are expected to best reflect the electronic metal-metal interactions. However, these metal-localized transitions are observed when the electrons are removed from the bridging ligand via chemical oxidation to yield the dicationic species, and they suggest very little electronic interaction between metal centers in the absence of pi electrons on the bridging ligands. Analysis of the magnetic data reveals that the qtp complex displays antiferromagnetic coupling of the type Yb(alpha)(alphabeta)Yb(beta) at approximately 13 K.

Reaction of 2 or 3 equiv of potassium 1,3-bis(trimethylsilyl)allyl (K[1,3-(SiMe3)2C3H3] = K[A‘]) with the triflate salts of Ce, Nd, Eu, Tb, and Yb gives the corresponding neutral bis-(Yb, Eu) and tris-(Ce, Nd, Tb) allyl lanthanide complexes in yields ranging from 40 to 80%. These complexes, which have been crystallographically characterized, initiate the polymerization of methyl methacrylate (MMA), but with poor turnover frequencies when compared with the corresponding salt complexes of the type K[LnA‘3]. K[A‘] itself initiates MMA polymerization, however, and its presence as an ion-pair in the salt complexes may contribute to the activity of heterometallic lanthanide catalysts.

The structures of a series of beryllium containing complexes have been optimized at the B3LYP/6-31G(d) level and their (9)Be magnetic shielding values have been determined using B3LYP/6-311G+g(2d,p) and the gauge-including atomic orbital (GIAO) method. The calculated chemical shifts are in excellent agreement with experimental values. The performance of a variety of NMR methods (SGO, IGAIM, CSGT) were also examined but were found to be inferior to the GIAO method at the chosen level of theory employed. The theoretical method has been utilized to predict the beryllium chemical shifts of structurally characterized complexes for which no measured (9)Be NMR spectrum exists, and to investigate a literature complex with an unusual (9)Be NMR chemical shift. A new standard for beryllium NMR in nonaqueous solvents has been suggested.

Commercially available Pt(cod)Cl(2) catalyzes the diboration of alkenes, alkynes, and aldimines using bis(catecholato)diboron (cod = 1,5-cyclooctadiene). Catalyzed aldimine diboration provides the first direct route to alpha-aminoboronate esters. The diboration product from N-benzylidene-2,6-dimethylaniline is structurally characterized.

We report an investigation of complexes of the type M(2)(dmp)(4) (M = Mo, Cr; dmp = 2,6-dimethoxyphenyl) using resonance Raman (RR) spectroscopy, Cr isotopic substitution, and density functional theory (DFT) calculations. Assignment of the Mo-Mo stretching vibration in the Mo(2) species is straightforward, as evidenced by a single resonance-enhanced band at 424 cm(-1), consistent with an essentially unmixed metal-metal stretch, and overtones of this vibration. On the other hand, the Cr(2) congener has no obvious metal-metal stretching mode near 650-700 cm(-1), where empirical predictions based on the Cr-Cr distance as well as DFT calculations suggest that this vibration should appear if unmixed. Instead, three bands are observed at 345, 363, and 387 cm(-1) that (a) have relative RR intensities that are sensitive to the Raman excitation frequency, (b) exhibit overtones and combinations in the RR spectra, and (c) shift in frequency upon isotopic substitution ((50)Cr and (54)Cr). DFT calculations are used to model the vibrational data for the Mo(2) and Cr(2) systems. Both the DFT results and empirical predictions are in good agreement with experimental observations in the Mo(2) complex, but both, while mutually consistent, differ radically from experiment in the Cr(2) complex. Our experimental and theoretical results, especially the Cr isotope shifts, clearly demonstrate that the potential energy of the Cr-Cr stretching coordinate is distributed among several normal modes having both Cr-Cr and Cr-ligand character. The general significance of these results in interpreting spectroscopic observations in terms of the nature of metal-metal multiple bonding is discussed.

Reaction of tris(p-methoxyphenyl)phosphine with [Ph3C][B(ArF)4] [ArF=3,5-(CF3)2C6H3] afforded [Ph3CP(4-OMeC6H4)3][B(ArF)4], a structural analog of hexaphenylethane, which shows a very long P–C distance [1.931(3) A] in the solid state, indicating a strong steric repulsive interaction between the two parts of the phosphonium cation.

Addition of PMe3 to Mo2(allyl)4 afforded Mo2(allyl)4(PMe3)2, in which two of the allyl groups adopt an unprecedented micro2-eta1,eta3 bonding mode; theoretical studies elucidate the roles of the sigma- and pi-donor ligands in the interplay of metal-allyl and metal-metal bonding.

Modification of Beller's palladium-catalyzed cyanation procedure for simple aromatic halides leads to a versatile and rapid route to complex multi-nitrile aryl and oligopyridyl ligands that improves on known literature methods. By heating the reagents in the high boiling solvent mesitylene to reflux temperatures at ambient pressure, we have observed the conversion of halogenated precursors to the corresponding nitrile compounds. The resulting compounds can be precipitated from CH 2 Cl 2 solutions of the reaction mixtures and isolated as pure compounds in moderate to high yields. The current approach offers a safer alternative to the pressure tube method, as it does not involve the use of KCN at high pressures.

(C5Me5)2Yb x OEt2 reacts with terpyridine and tetrapyridinylpyrazine to afford new mixed-valent systems.

Novel 4f−5f complexes of U(IV) and Th(IV) with Yb have been prepared using a terpyridyl-functionalized ketimide linking group. These 4f−5f heterotrimetallic complexes (C5Me5)2An[NC(CH2C6H5)(tpyYb(C5Me5)2)]2 (where An = Th, U) exist in Yb(II/III) valence equilibria and exhibit rich electrochemical behavior consistent with electronic coupling between the actinide and Yb(II/III)tpy•- moieties. The magnetic response of the uranium complex, studied qualitatively using a subtraction method, is indicative of a coupled magnetic state between the U(IV) and Yb(III)tpy•- groups at low temperatures. Both the electrochemical and magnetic data are in agreement and are consistent with differences in participation of the actinide valence orbitals in the ketimide bonding.

While addition of phosphorus ligands such as P(OPh)3 to Rh(allyl)3 gives monovalent Rh(allyl)L2, the iridium analog gives stable mixed σ/π-tris(allyl) complexes, as evidenced by the structural characterization of mono-, bi-, and tri-dentate ligand complexes.

The metallo-diethynylbenzene complex W(CC6H4CCH-4)(dmpe)2Cl, a precursor to metal-containing poly(phenyleneethynylene)s, has been prepared using alkyne-metathesis methodology and can be coupled into unsaturated organic frameworks at both the ethynyl moiety and the tungsten center and one-electron oxidized to the open-shell cation.

Trapped by a proton: In the formation of OsII -N2 -OsII dimers, an OsV ≡N complex has been invoked as a transient intermediate but not isolated. Herein conditions are reported that allow OsV ≡N species to be trapped either in acidic, aqueous solutions as a neutral osmium(V) imido complex (OsV =NH, see structure) or in non-aqueous solvents, with high concentrations of added reductant, by N- ion transfer before coupling can occur.