H2ampa─Versatile Chelator for [203Pb]Pb2+, [213Bi]Bi3+, and [225Ac]Ac3.

A new decadentate chelator, H2ampa, was designed to be a potential radiopharmaceutical chelator component. The chelator involves both amide and picolinate functional groups on a large non-macrocyclic, ether-bridged backbone. With its large scaffold, H2ampa was paired with [nat/203Pb]Pb2+, [nat/213Bi]Bi3+, and natLa3+/[225Ac]Ac3+ ions. Nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry were used to study the non-radioactive metal complexes. A single crystal of [Bi(ampa)](NO3) was obtained; its asymmetric, 10-coordinate complex structure was revealed by X-ray diffraction. Optimal conformations of the metal complexes were assessed by density functional theory studies to provide further structural information. Solution studies providing thermodynamic insights into metal complex formation revealed H2ampa coordinated Bi3+, Pb2+, and La3+ ions to obtain pM values of 26, 14.8, and 15.1, respectively. Preliminary concentration-dependent radiolabeling experiments were carried out between H2ampa and three different radiometals to evaluate their compatibility for radiopharmaceutical applications. The chelator radiolabeled [203Pb]Pb2+, [213Bi]Bi3+, and [225Ac]Ac3+ in short reaction times (7-30 min), at dilute concentrations, and under mild conditions. Thus, H2ampa was proven to be a versatile chelator able to well coordinate a small range of radiometals frequently considered to be alpha therapeutic candidates.

Direct, Catalytic α-Alkylation of N-Heterocycles by Hydroaminoalkylation: Substrate Effects for Regiodivergent Product Formation.

Saturated N-heterocycles are prevalent in pharmaceutical and agrochemical industries, yet remain challenging to catalytically alkylate. Most strategies for C-H activation of these challenging substrates use protected amines or high loadings of precious metal catalysts. We report an early transition-metal system for the broad, robust, and direct alkylation of unprotected amine heterocycles with simple alkenes. Short reaction times are achieved using an in situ generated tantalum catalyst that avoids the use of bases, excess substrate, or additives. In most cases, this catalyst system is selective for the branched reaction product, including examples of products that are generated with excellent diastereoselectivity. Alkene electronic properties can be exploited for substrate-modified regioselectivity to access the alternative linear amine alkylation product with a group 5 catalyst. This method allows for the facile isolation of unprotected N-heterocyclic products, as useful substrates for further reactivity.

Controlling photocatalytic reduction of CO2 in Ru(II)/Re(I) dyads via linker oxidation state.

Electronic communication between the linked metal centers in Ru(ii)-Re(i) dyads is tuned using the oxidation state (S and SO2) of sulfur-bridged ligands. Higher catalytic activity is seen for the SO2-bridged dyad in the photocatalytic reduction of CO2.

Tunable Emission of Iridium(III) Complexes Bearing Sulfur-Bridged Dipyridyl Ligands.

A series of six new cyclometalated iridium(III) complexes [Ir(ppy)2(N∧N)][PF6] (ppy = 2-phenylpyridine) is reported herein. Proligands bis(pyridin-2-yl)sulfane (1a), 2,2'-sulfinyldipyridine (1b), 2,2'-sulfonyldipyridine (1c), bis(4-methylpyridin-2-yl)sulfane (2a), 2,2'-sulfinylbis(4-methylpyridine) (2b), and 2,2'-sulfonylbis(4-methylpyridine) (2c) were synthesized, characterized, and employed as the N∧N ancillary ligand. Changing the oxidation state of the sulfur atom serves as a switch to alter the emissive state from that of mainly 3LC character (blue-green emission) to one of 3MLCT/3LLCT character (yellow emission). Sulfide and sulfoxide complexes Ir(1a), Ir(1b), Ir(2a), and Ir(2b) show identical, vibrationally structured emission profiles with maxima at 478, 510, 548 nm in CH2Cl2 solutions resulting from a 3LC state. In contrast, sulfone complexes Ir(1c) and Ir(2c) show broad, red-shifted 3CT emission (552 and 537 nm, respectively).

[HL2][P(1,2-O2C6Cl4)3] (L = THF, DMF): Brønsted acid initiators for the polymerization of n-butyl vinyl ether and p-methoxystyrene.

The development of solid, weighable Brønsted acids featuring the hexacoordinated phosphorous(v) anion [TRISPHAT]- are reported. H(DMF)2[1] and H(THF)2[1] {[1]- = [P(1,2-O2C6Cl4)3]-} were synthesized and fully characterized by 1H, 31P, 13C and 2D-NOESY NMR spectroscopy, X-ray crystallography, mass spectrometry and elemental analysis. Both, H(DMF)2[1] and H(THF)2[1] are found to be suitable initiators for the polymerization of n-butyl vinyl ether and p-methoxystyrene. Optimal polymerization results for these single-component initiators were generally obtained at -50 °C where high molecular weight polymers were isolated in high yield. 1H NMR spectroscopic analysis and dynamic light scattering of solutions of the isolated polymers provide evidence for a branched structure which presumably arises from chain transfer.

Interactions of Rh(III)-dihydrido-bis(phosphine) complexes with semicarbazones.

Interaction of cis,trans,cis-[Rh(H)2(PR3)2(acetone)2]PF6 complexes (R = aryl or R3 = Ph2Me, Ph2Et) under H2 with E-semicarbazones gives the Rh(III)-dihydrido-bis(phosphine)-semicarbazone species cis,trans-[Rh(H)2(PR3)2{R'(R' ')C=N-N(H)CONH2}]PF6, where R' and R' ' are Ph, Et, or Me. The complexes are generally characterized by elemental analysis, 31P{1H} NMR, 1H NMR, and IR spectroscopies, and MS. X-ray analysis of three PPh3 complexes reveals chelation of E-semicarbazones by the imine-N atom and the carbonyl-O atom. In contrast, the corresponding reaction of [Rh(H)2(PPhMe2)2(acetone)2]PF6 with acetophenone semicarbazone gives the ortho-metalated-semicarbazone species cis-[RhH(PPhMe2)2{o-C6H4(Me)C=N-N(H)CONH2}]PF6. The X-ray structure of E-propiophenone semicarbazone is also reported. Rhodium-catalyzed, homogeneous hydrogenation of semicarbazones was not observed even at 40 atm H2.