Synthesis of titanium(IV) guanidinate complexes and the formation of titanium carbonitride via low-pressure chemical vapor deposition

The mono(guanidinato) complex [Ti(NMe2)2Cl{i-PrNC[N(SiMe3)2]N-i-Pr}] (1) was prepared by reaction of [Ti(NMe2)2Cl2] with 1 or 2 equiv of the lithium guanidinate salt [Li{i-PrNC[N(SiMe3)2]N-i-Pr}]. Compound 1 has been characterized by X-ray crystallography. Treatment of TiCl4 with 2 equiv of [Li{i-PrNC[N(SiMe3)2]N-i-Pr}] resulted in the formation of dark red crystals. X-ray crystallography showed that these crystals consist of a 70:30 mixture of two bis(guanidinato) complexes, namely, [TiCl2{i-PrNC[N(SiMe3)2]N-i-Pr}{i-PrNC(N=CMe2)N-i-Pr}] (2) and [TiCl2{i-PrNC[N(SiMe3)2]N-i-Pr}{i-PrNC[N(H)-i-Pr]N-i-Pr}] (3). Both compounds 2 and 3 possess a transformed guanidinate ligand. Low-pressure chemical vapor deposition of either compound 1 or [TiCl2{i-PrNC(NMe2)N-i-Pr}] (4) at 600 degrees C results in thin films of titanium carbonitride.     

Methyl, hydrochalcogenido, and phenylchalcogenolate complexes of zinc in a sulfur rich coordination environment: syntheses and structural characterization of the tris(2-mercapto-1-tert-butylimidazolyl)hydroboratozinc complexes [TmBut]ZnMe, [TmBut]ZnEH (E = S, Se) and [TmBut]ZnEPh (E = O, S, Se, Te)

A series of hydrochalcogenido and phenylchalcogenolate complexes of zinc supported by tris(2-mercapto-1-tert-butylimidazolyl)hydroborato ligation, [Tm(Bu(t))]ZnEH (E = S, Se) and [Tm(Bu(t))]ZnEPh (E = O, S, Se, Te) have been synthesized from [Tm(Bu(t))]ZnMe; structural characterization by X-ray diffraction indicates that the variation in Zn-E bonding as a function of the chalcogen is significantly different from that in other series of metal-chalcogenolate compounds.     

Towards a system for the systematic structural study of intermolecular interactions in crystals of transition metal complexes

Pseudo-macrocyclic complexes of copper(II), and in one instance nickel(II), incorporating the bidentate ligands methyl N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)imidocarbamate and N,N-dimethyl-N'-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)guanidine are reported and their X-ray structures compared with those previously reported for related complexes of two N-(4-oxo- 5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)alkanimidamides. A feature of these complexes is that they are capable of forming hydrogen bonded chains or chains in which adjacent complexes are linked by phenyl 'embraces'. Changes in supramolecular structure arising from small changes in ligand structure or on crystallisation from different solvents are also discussed.     

New cobalt(II) and zinc(II) coordination frameworks incorporating a pyridyl-pyrazole ditopic ligand

The metal-directed assembly of new molecular frameworks incorporating 4-(4-pyridyl)pyrazole (L), containing non-linear coordination vectors, is presented. Three metallo-arrays of types [Co(LH)2(NO3)4], [Co(LH)2(H2O)4][NO3]4.H2O and [Zn2(L-H)2Cl2].2EtOH are reported. The cobalt(II) in [Co(LH)2(NO3)4] displays distorted octahedral geometry, with the two protonated pyridyl-pyrazole ligands coordinated through their pyrazole nitrogen atoms in a trans-orientation; the remaining four coordination sites are occupied by nitrate anions. Two internal hydrogen bonds occur between each pyrazole NH and the oxygens of adjacent coordinated nitrato ligands. Short intermolecular hydrogen bonds also occur between the two pyridinium hydrogens and bound nitrate ligands on different molecules to yield a two-dimensional hydrogen-bonded array. Two of these arrays interpenetrate to form an extended two dimensional layer; such layers stack throughout the crystal structure. A second product of type [Co(LH)2(H2O)4][NO3]4.H2O exists as two crystallographically independent, but chemically similar, forms. In each form, the two protonated pyridyl-pyrazole ligands occupy trans positions about the cobalt, with the remaining four coordination sites being filled by water molecules to yield a distorted octahedral coordination geometry. Intramolecular hydrogen-bonding is observed between the two non-coordinated pyrazoyl nitrogen atoms and bound water oxygen atoms. The third complex, [Zn2(L-H)2Cl2].2EtOH, contains dimer units consisting of two zinc(II) ions bridged by two pyrazoylate groups in which the coordination geometry of each zinc approximates a tetrahedron. Each zinc is bound to two deprotonated pyridine-pyrazole ligands (L-H), one pyridyl group (from a different dimeric unit) and one chloro ligand. Each pyridyl nitrogen thus connects each of these zinc dimers to an adjacent dimer unit, forming a three-dimensional network containing small voids. The latter are occupied by ethanol molecules which form hydrogen bonds to the chloro ligands.     

Microscale sample deposition onto hydrophobic target plates for trace level detection of neuropeptides in brain tissue by MALDI-MS

A sample preparation method that combines a modified target plate with a nanoscale reversed-phase column (nanocolumn) was developed for detection of neuropeptides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A gold-coated MALDI plate was modified with an octadecanethiol (ODT) self-assembled monolayer to create a hydrophobic surface that could concentrate peptide samples into a approximately 200-500-microm diameter spot. The spot sizes generated were comparable to those obtained for a substrate patterned with 200-microm hydrophilic spots on a hydrophobic substrate. The sample spots on the ODT-coated plate were 100-fold smaller than those formed on an unmodified gold plate with a 1-microl sample and generated 10 to 50 times higher mass sensitivity for peptide standards by MALDI-TOF MS. When the sample was deposited on an ODT-modified plate from a nanocolumn, the detection limit for peptides was as low as 20 pM for 5-microl samples corresponding to 80 amol deposited. This technique was used to analyze extracts of microwave-fixed tissue from rat brain striatum. Ninety-eight putative peptides were detected including several that had masses matching neuropeptides expected in this brain region such as substance P, rimorphin, and neurotensin. Twenty-three peptides had masses that matched peaks detected by capillary liquid chromatography with electrospray ionization MS.     

Synthesis and Structure of Environmentally Relevant Perfluorinated Sulfonamides

Alkylated perfluorooctanesulfonamides are compounds of environmental concern. To make these compounds available for environmental and toxicological studies, a series of N-alkylated perfluorooctanesulfonamides and structurally related compounds were synthesized by reaction of the corresponding perfluoroalkanesulfonyl fluoride with a suitable primary or secondary amine. Perfluoroalkanesulfonamidoethanols were obtained from the N-alkyl perfluoroalkanesulfonamides either by direct alkylation with bromoethanol or alkylation with acetic acid 2-bromo-ethyl ester followed by hydrolysis of the acetate. N-Alkyl perfluorooctanesulfonamidoacetates were synthesized in an analogous way by alkylation of N-alkyl perfluoroalkanesulfonamides with a bromo acetic acid ester, followed by basic ester hydrolysis. Alternatively, N-alkyl perfluoroalkanesulfonamides can be alkylated with an appropriate alcohol using the Mitsunobu reaction. Perfluorooctanesulfonamide was synthesized from the perfluorooctanesulfonyl fluoride via the azide by reduction with Zn/HCl. All perfluorooctanesulfonamides contained linear as well as branched C₈F₁₇ isomers, typically in a 10:1 to 30:1 ratio. The crystal structures of N-ethyl and N,N-diethyl perfluorooctanesulfonamide show that the S-N bond has considerable double bond character. This double bond character results in a significant rotational barrier around the S-N bond (ΔG^≠ = 62-71 kJ mol⁻¹) and a preferred solid state and solution conformation in which the N-alkyl groups are oriented opposite to the perfluorooctyl group to minimize steric crowding around the S-N bond.     

Asymmetric synthesis of (1R,2S,3R)-3-methylcispentacin and (1S,2S,3R)-3-methyltranspentacin by kinetic resolution of tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate

Conjugate addition of lithium dibenzylamide to tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate occurs with high levels of stereocontrol, with preferential addition of lithium dibenzylamide to the face of the cyclic alpha,beta-unsaturated acceptor anti- to the 3-methyl substituent. High levels of enantiorecognition are observed between tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate and an excess of lithium (+/-)-N-benzyl-N-alpha-methylbenzylamide (10 eq.) (E > 140) in their mutual kinetic resolution, while the kinetic resolution of tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate with lithium (S)-N-benzyl-N-alpha-methylbenzylamide proceeds to give, at 51% conversion, tert-butyl (1R,2S,3R,alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-carboxylate consistent with E > 130, and in 39% yield and 99 +/- 0.5% de after purification. Subsequent deprotection by hydrogenolysis and ester hydrolysis gives (1R,2S,3R)-3-methylcispentacin in > 98% de and 98 +/- 1% ee. Selective epimerisation of tert-butyl (1R,2S,3R,alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-carboxylate by treatment with KO'Bu in 'BuOH gives tert-butyl (1S,2S,3R,alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-carboxylate in quantitative yield and in > 98% de, with subsequent deprotection by hydrogenolysis and ester hydrolysis giving (1S,2S,3R)-3-methyltranspentacin hydrochloride in > 98% de and 97 +/- 1% ee.