Wurster's crowns: a comparative study of ortho- and para-phenylenediamine-containing macrocyclic receptors.

Two series of isomeric, redox-responsive azacrown ethers based on ortho- and para-phenylenediamine (Wurster's crowns) have been synthesized and their properties explored through 13C NMR spectroscopy, electrospray ionization mass spectrometry, cyclic voltammetry, and X-ray crystallography. These crowns display strong affinity for alkali metal cations while maintaining comparable selectivity profiles to the parent crown ethers from which they are derived. Like Wurster's reagent (N,N,N',N'-tetramethyl-p-phenylenediamine or para-TMPD), the para-Wurster's crowns undergo two reversible one-electron oxidations.

A bridge to coordination isomer selection in lanthanide(III) DOTA-tetraamide complexes.

Interest in macrocyclic lanthanide complexes such as DOTA is driven largely through interest in their use as contrast agents for MRI. The lanthanide tetraamide derivatives of DOTA have shown considerable promise as PARACEST agents, taking advantage of the slow water exchange kinetics of this class of complex. We postulated that water exchange in these tetraamide complexes could be slowed even further by introducing a group to sterically encumber the space above the water coordination site, thereby hindering the departure and approach of water molecules to the complex.

An efficient synthesis of the constrained peptidomimetic 2-oxo-3-(N-9-fluorenyloxycarbonylamino)-1-azabicyclo[4.3.0]nonane-9-carboxylic acid from pyroglutamic acid.

[reaction: see text] Azabicyclo[X.Y.0]alkane amino acids are rigid dipeptide mimetics that are useful tools for structure-activity studies in peptide-based drug discovery.

Aluminium alkyl and aryloxide complexes of pyrazine and bipyridines: synthesis and structure.

The reaction of AlMe(3) and [((t)Bu)(2)Al(micro-OPh)](2) with pyrazine (pyz), 4,4'-bipyridine (4-4'-bipy), 1,2-bis(4-pyridyl)ethane (bpetha) and 1,2-bis(4-pyridyl)ethylene (bpethe) yields (Me(3)Al)(2)(micro-pyz)(1), (Me(3)Al)(2)(micro-4,4'-bipy)(2), (Me(3)Al)(2)(micro-bpetha)(3), (Me(3)Al)(2)(micro-bipethe)(4), Al((t)Bu)(2)(OPh)(pyz)(5), [((t)Bu)(2)Al(OPh)](2)(micro-4,4-bipy)(6a), [((t)Bu)(2)Al(OPh)](2)(micro-bpetha)(7a), [((t)Bu)(2)Al(OPh)](2)(micro-bipethe)(8a). Compounds 1-4, 6a and 7a have been confirmed by X-ray crystallography. In solution compounds 1-4 undergo a rapid ligand-dissociation equilibrium resulting in a time-average spectrum in the (1)H NMR.

1,4-dioxobenzene compounds of gallium: reversible binding of pyridines to [[((t)Bu)(2)Ga](2)(mu-OC(6)H(4)O)](n) in the solid state.

The gallium aryloxide polymer, [[((t)Bu)(2)Ga](2)(mu-OC(6)H(4)O)](n)(1) is synthesized by the addition of Ga((t)()Bu)(3) with hydroquinone in a noncoordinating solvent, and reacts with pyridines to yield the yellow compound [((t)()Bu)(2)Ga(L)](2)(mu-OC(6)H(4)O) [L = py (2), 4-Mepy (3), and 3,5-Me(2)py (4)] via cleavage of the Ga(2)O(2) dimeric core. The analogous formation of Ga((t)()Bu)(2)(OPh)(py) (5) occurs by dissolution of [((t)Bu)(2)Ga(mu-OPh)](2) in pyridine. In solution, 2-4 undergo dissociation of one of the pyridine ligands to yield [((t)()Bu)(2)Ga(L)(mu-OC(6)H(4)O)Ga((t)Bu)(2)](2), for which the DeltaH and DeltaS have been determined.

Transition-metal complexes of a bifunctional tetradentate gallium alkoxide ligand.

The mixed gallium transition-metal complexes [FeCl[Ga(2)((t)Bu)(4)(neol)(2)]] (1) and [M[Ga(2)((t)Bu)(4)(neol)(2)]], M = Co (2), Ni (3), Cu (4), have been prepared by the reaction of [Ga(2)((t)Bu)(4)(neol-H)(2)] (neol-H(2) = 2,2-dimethyl-propane-1,3-diol) with the appropriate metal halide and Proton Sponge. Compounds 1-4 have been characterized by NMR (3), UV/vis, and IR spectroscopy and magnetic susceptibility (solution and solid state), and their molecular structures have been confirmed by X-ray crystallography. The molecular structure of compounds 1-4 consists of a tetracyclic core formed from two four-membered and two six-membered rings.

Crystal Structure of [Ru(terpy)(2)](0): A New Crystalline Material from the Reductive Electrocrystallization of [Ru(terpy)(2)](2+).

Reductive electrocrystallization of [Ru(terpy)(2)](PF(6))(2) (where terpy = 2,2':6',2' '-terpyridine) from an acetonitrile solution containing 100 mM TBAPF(6) results in the formation of black crystals. Crystal data: [Ru(terpy)(2)].(PF(6))(2)[(CH(3))(2)CO], monoclinic, space group P2(1)/c with a = 20.

Synthesis of Indium Amide Compounds.

Indium trichloride reacts with 3 equiv of lithium amide in diethyl ether to give In(NRR')(3) (R = Ph or t-Bu, R' = SiMe(3); R = t-Bu, R' = SiHMe(2)) and with 3 or 4 equiv of LiNMe(SiMe(3)) to yield Li[In{NMe(SiMe(3))}(4)]. The chloride also reacts with LiNPh(2) in THF to give the salt Li[In(NPh(2))(3)Cl] and with LiNRR' in pyridine to yield the neutral adduct In(NRR')(3)(py) (R = R' = Ph; R = Me, R' = SiMe(3)). The volatile liquids In[N(t-Bu)(SiHMe(2))](3) and In[NMe(SiMe(3))](3)(py) react with p-Me(2)Npy to form the solid compounds In[N(t-Bu)(SiHMe(2))](3)(p-Me(2)Npy) and In[NMe(SiMe(3))](3)(p-Me(2)Npy), respectively.

Formation of Ruthenium(II) Complexes with Unsymmetrical Terdentate Ligands.

Three unsymmetrical terdentate ligands, 2-(2'-quinolyl)-1,10-phenanthroline (4), 2-(1'-isoquinolyl)-1,10-phenanthroline (5), and 3,3'-dimethylene-2-(2'-quinolyl)-1,10-phenanthroline (6), have been prepared by application of the Friedländer condensation. Ligand 4 forms predominantly a pentaaza-coordinated (N5) complex with Ru(II), [Ru(4-N,N',N")(4-N,N')Cl](PF(6)), whose structure was determined by X-ray analysis (C(42)H(26)ClF(6)N(6)PRu: monoclinic, C2/c, a = 29.308(3) Å, b = 15.

Synthesis and Structure of [Tp(Bu)()t()2]In, a Highly Twisted [Tris(3,5-di-tert-butylpyrazolyl)hydroborato]indium(I) Complex: Comparison with the Re-Evaluated Ordered Structure of [Tp(Bu)()t]In.

The indium(I) complex [Tp(Bu)()t()2]In ([Tp(Bu)()t()2] = tris(3,5-di-tert-butylpyrazolyl)hydroborato), synthesized by the reaction of [Tp(Bu)()t()2]Na with InCl, exhibits a structure in which the [Tp(Bu)()t()2] ligand adopts a highly twisted configuration due to steric interactions of the tert-butyl substituents in the 5-positions of the pyrazolyl groups. In contrast, the absence of 5-tert-butyl substituents allows the pyrazolyl groups in [Tp(Bu)()t]In to be coplanar with their respective In-N-N-B planes. The structure of [Tp(Bu)()t]In has been previously reported but was noted to exhibit an unusual type of disorder in which a nitrogen atom of one molecule was coincident with the boron atom of its disordered configuration [Dias, H.