Aritra Pal

Facile access of stable divalent tin compounds with terminal methyl, amide, fluoride, and iodide substituents.

The stable beta-diketiminate tin(II) complexes LSnX [L = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3] with terminal methyl, amide, fluoride, and iodide (X = Me, N(SiMe3)2, F, I) are described. LSnMe (2) is synthesized by salt metathesis reaction of LSnCl (1) with MeLi and can be isolated in the form of yellow crystals in 88% yield. Compound LSnN(SiMe3)2 (3) was obtained by treatment of LH with 2 equiv of KN(SiMe3)2 in THF followed by adding 1 equiv of SnCl2. Reaction of 2 and 3 respectively with Me3SnF in toluene provided the tin(II)fluoride LSnF (4) with a terminal fluorine as colorless crystals in 85% yield. 4 is highly soluble in common organic solvents. The reaction of LLi(OEt2) with 1 equiv of SnI2 in diethyl ether afforded the LSnI (5). Compounds 2, 3, 4, and 5 were characterized by microanalysis, multinuclear NMR spectroscopy, and X-ray structural analysis. Single crystal X-ray structural analyses indicate that all the compounds (2, 3, 4, 5) are monomeric and the tin center resides in a trigonal-pyramidal environment.

Molecular oxygen activation by a molybdenum(IV) monooxo bis(β-ketiminato) complex

Molybdenum(IV) monooxo compound that contains bis(β-ketiminato) ligands activates molecular oxygen forming a molybdenum(VI) monooxo peroxo compound, representing a new entry into molybdenum peroxo derivatives.

Structure of Tripeptidyl-peptidase I Provides Insight into the Molecular Basis of Late Infantile Neuronal Ceroid Lipofuscinosis

Late infantile neuronal ceroid lipofuscinosis, a fatal neurodegenerative disease of childhood, is caused by mutations in the TPP1 gene that encodes tripeptidyl-peptidase I. We show that purified TPP1 requires at least partial glycosylation for in vitro autoprocessing and proteolytic activity. We crystallized the fully glycosylated TPP1 precursor under conditions that implied partial autocatalytic cleavage between the prosegment and the catalytic domain. X-ray crystallographic analysis at 2.35 Å resolution reveals a globular structure with a subtilisin-like fold, a Ser475-Glu272-Asp360 catalytic triad, and an octahedrally coordinated Ca2+-binding site that are characteristic features of the S53 sedolisin family of peptidases. In contrast to other S53 peptidases, the TPP1 structure revealed steric constraints on the P4 substrate pocket explaining its preferential cleavage of tripeptides from the unsubstituted N terminus of proteins. Two alternative conformations of the catalytic Asp276 are associated with the activation status of TPP1. 28 disease-causing missense mutations are analyzed in the light of the TPP1 structure providing insight into the molecular basis of late infantile neuronal ceroid lipofuscinosis.

A reactivity change of a strontium monohydroxide by umpolung to an acid.

Controlled hydrolysis of strontium amide LSrN(SiMe 3) 2(thf) (L = CH(CMe2,6- i-Pr 2C 6H 3N) 2) ( 1) gave an unprecedented example of a hydrocarbon-soluble strontium hydroxide, [LSr(thf)(mu-OH) 2Sr(thf) 2L] ( 2). In compound 2, the tetrahydrofuran (THF) molecules can easily replaced by benzophenone and triphenylphosphine oxide to yield [LSr(mu-OH)(OCPh 2)] 2 ( 3) and [LSr(mu-OH)(OPPh 3)] 2 ( 4) compounds. Among the two strontium atoms of 2, one is coordinated to a single THF molecule, while the other is coordinated to two THF molecules. Interestingly, strontium hydroxide complex 2 behaves as an acid in its reaction with Zr(NMe 2) 4 and results in a heterobimetallic oxide, [LSr(mu-O)Zr(NMe 2) 3] 2 ( 5). Compound 5 is dimeric in the solid state and contains a Sr 2Zr 2O 2 core.

Structures of viscotoxins A1 and B2 from European mistletoe solved using native data alone.

Crystals of the cytotoxic thionin proteins viscotoxins A1 and B2 extracted from mistletoe diffracted to high resolution (1.25 and 1.05 A, respectively) and are excellent candidates for testing crystallographic methods. Ab initio direct methods were only successful in solving the viscotoxin B2 structure, which with 861 unique non-H atoms is one of the largest unknown structures without an atom heavier than sulfur to be solved in this way, but sulfur-SAD phasing provided a convincing solution for viscotoxin A1. Both proteins form dimers in the crystal and viscotoxin B2 (net charge +4 per monomer), but not viscotoxin A1 (net charge +6), is coordinated by sulfate or phosphate anions. The viscotoxin A1 crystal has a higher solvent content than the viscotoxin B2 crystal (49% as opposed to 28%) with solvent channels along the crystallographic 4(3) axes.

From Unstable to Stable: Half-Metallocene Catalysts for Olefin Polymerization†

The reaction of LAlMeOH [L = CH(N(Ar)(CMe))2, Ar = 2,6-i-Pr2C6H3] with CpTiMe3, Cp*TiMe3, and Cp*ZrMe3 was investigated to yield LAlMe(mu-O)TiMe2Cp (2), LAlMe(mu-O)TiMe2Cp* (3), and LAlMe(mu-O)ZrMe2Cp* (4), respectively. The resulting compounds 2-4 are stable at elevated temperatures, in contrast to their precursors such as CpTiMe3 and Cp*ZrMe3, which already decompose below room temperature. Compounds 2-4 were characterized by single-crystal X-ray structural analysis. Compounds 2 and 3 were tested for ethylene polymerization in the presence of methylaluminoxane. The half-metallocene complex 3 has higher activity compared to 2. The polydispersities are in the range from 2.8 to 4.2. A copolymerization with styrene was not observed.

Soluble Molecular Dimers of CaO and SrO Stabilized by a Lewis Acid

The reaction between a β-diketiminate aluminum methyl hydroxide and [M{N(SiMe 3 ) 2 } 2 (thf) 2 ] (M=Ca, Sr) results in alkaline-earth-metal oxides such as [{LAl(Me)(μ-O)Ca(thf)}2] (see core structure; L is deprotonated β-diketiminate CH{C(CH 2 )}(CMe)(2,6-iPr 2 C 6 H 3 N) 2 ). These soluble complexes are dimeric in the solid state and contain unprecedented M 2 O 2 cores.

Synthesis and characterization of [{PhC(NBut)2}Si(S)SBut]: a silicon thioester analogue with the Si(S)–S-skeleton

A silicon thioester analogue with the Si(=S)-S-skeleton [[PhC(NBu(t))2]Si(S)SBu(t)] (3) has been prepared from the reaction of [[PhC(NBu(t))2]SiCl2SBu(t)] (2) with potassium.

Base free lithium-organoaluminate and the gallium congener: potential precursors to heterometallic assemblies

The first examples of base free lithium-organoaluminate and the corresponding gallium compound [LM(Me)OLi]3 (M = Al (3), Ga (4); L = HC{C(Me)N-2,6-iPr2C6H3}2) have been prepared by the reaction of Li[N(SiMe3)2] with the corresponding metal hydroxides LM(Me)OH (M = Al (1), Ga(2)); the oxygen atom in the M-O-Li fragment exists as oxide ion and is involved in the central Li3O3 six-membered ring formation.