T. Stanley Cameron

Approaching the gas-phase structures of [AgS8]+ and [AgS16]+ in the solid state

Upon treating elemental sulfur with [AgSbF(6)], [AgAl(hfip)(4)], [AgAl(pftb)(4)] (hfip=OCH(CF(3))(2), pftb =OC(CF(3))(3)) the compounds [Ag(S(8))(2)][SbF(6)] (1), [AgS(8)][Al(hfip)(4)] (2), and [Ag(S(8))(2)](+)[[Al(pftb)(4)](-) (3) formed in SO(2) (1), CS(2) (2), or CH(2)Cl(2) (3). Compounds 1-3 were characterized by single-crystal X-ray structure determinations: 1 by Raman spectroscopy, 2 and 3 by solution NMR spectroscopy and elemental analyses. Single crystals of [Ag(S(8))(2)](+)[Sb(OTeF(5))(6)](-) 4 were obtained from a disproportionation reaction and only characterized by X-ray crystal structure analysis. The Ag(+) ion in 1 coordinates two monodentate SbF(6) (-) anions and two bidentate S(8) rings in the 1,3-position. Compound 2 contains an almost C(4v)-symmetric [AgS(8)](+) moiety; this is the first example of an eta(4)-coordinated S(8) ring (d(Agbond;S)=2.84-3.00 A). Compounds 3 and 4, with the least basic anions, contain undistorted, approximately centrosymmetric Ag(eta(4)-S(8))(2) (+) cations with less symmetric eta(4)-coordinated S(8) rings (d(Agbond;S)=2.68-3.35 A). The thermochemical radius and volume of the undistorted Ag(S(8))(2) (+) cation was deduced as r(therm)(Ag(S(8))(2) (+))=3.378+ 0.076/-0.120 A and V(therm)(Ag(S(8))(2) (+))=417+4/-6 A(3). AgS(8) (+) and several isomers of the Ag(S(8))(2) (+) cation were optimized at the BP86, B3LYP, and MP2 levels by using the SVP and TZVPP basis sets. An analysis of the calculated geometries showed the MP2/TZVPP level to give geometries closest to the experimental data. Neither BP86 nor B3LYP reproduced the longer weak dispersive Agbond;S interactions in Ag(eta(4)-S(8))(2) (+) but led to Ag(eta(3)-S(8))(2) (+) geometries. With the most accurate MP2/TZVPP level, the enthalpies of formation of the gaseous [AgS(8)](+) and [Ag(S(8))(2)](+) cations were established as Delta(f)H(298)([Ag(S(8))(2)](+), g)=856 kJ mol(-1) and Delta(f)H(298)([AgS(8)](+), g)=902 kJ mol(-1). It is shown that the [AgS(8)](+) moiety in 2 and the [AgS(8)](2) (+) cations in 3 and 4 are the best approximation of these ions, which were earlier observed by MS methods. Both cations reside in shallow potential-energy wells where larger structural changes only lead to small increases in the overall energy. It is shown that the covalent Agbond;S bonding contributions in both cations may be described by two components: i) the interaction of the spherical empty Ag 5s(0) acceptor orbital with the filled S 3p(2) lone-pair donor orbitals and ii) the interaction of the empty Ag 5p(0) acceptor orbitals with the filled S 3p(2) lone-pair donor orbitals. This latter contribution is responsible for the observed low symmetry of the centrosymmetric Ag(eta(4)-S(8))(2) (+) cation. The positive charge transferred from the Ag(+) ion in 1-4 to the coordinated sulfur atoms is delocalized over all the atoms in the S(8) ring by multiple 3p(2)-->3sigma* interactions that result in a small long-short-long-short Sbond;S bond-length alternation starting from S1 with the shortest Agbond;S length. The driving force for all these weak bonding interactions is positive charge delocalization from the formally fully localized charge of the Ag(+) ion.

Pacharin: a new dibenzo(2,3-6,7)oxepin derivative from bauhinia racemosa lamk

Abstract The isolation of resveratrol and a new dibenzoxepin derivative, pacharin, from the heartwood of Bauhinia racemosa Lank is reported. The structure of pacharin has been established as l,7-dlhydroxy-3-methoxy-2-methyl-dibenzo(2,3-6,7) oxepin (Va) by a study of its chemical and spectroscopic properties, including X-ray analysis.

Use of F-BODIPYs as a Protection Strategy for Dipyrrins: Optimization of BF2 Removal

We recently reported the first general method for the deprotection of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (F-BODIPYs) involving a microwave-assisted procedure for the removal of the BF(2) moiety, and liberation of the corresponding free-base dipyrrin. Further optimization of the reaction has resulted in a more convenient and accessible protocol. The availability of this new methodology enables BF(2)-complexation to be used as a dipyrrin protection strategy. Herein lies a detailed examination of the deprotection reaction, with a view to optimization and gaining mechanistic insight, and its application in facilitating a multistep synthesis of pyrrolyldipyrrins.

Synthesis and Characterization of Fluorescent Pyrrolyldipyrrinato Sn(IV) Complexes

A series of neutral, 5-coordinate pyrrolyldipyrrinato Sn(IV) complexes have been synthesized via reaction of a pyrrolyldipyrrin, or its corresponding hydrochloride salt, with dibutyltin or diphenyltin oxide. The complexes are structurally unique in that all three nitrogen atoms of the pyrrolyldipyrrinato ligand bind to the tin center, making these complexes the first examples of pyrrolyldipyrrins behaving as LX(2) ligands. The complexes are highly fluorescent, exhibiting fluorescence quantum yields between 0.28 and 0.61, and display interesting preliminary biological activity.

New Synthetic Procedures to Catena-Phosphorus Cations: Preparation and Dissociation of the First cyclo-Phosphino-halophosphonium Salts

Chlorination of 1,2,3,4-tetracyclohexyl-cyclo-tetraphosphine (2) by PhICl(2) or PCl(5) in the presence of Me(3)SiOTf or GaCl(3) provides a stepwise approach to salts of the first cyclo-phosphino-chlorophosphonium cations [Cy(4)P(4)Cl](+) ([19](+)) and [Cy(4)P(4)Cl(2)](2+) ([20](2+)). The analogous iodo derivative [Cy(4)P(4)I](+) ([17](+)) is obtained as the tetraiodogallate salt from reaction of 2 with I(2) in the presence of GaI(3). Reactions of the dication [20](2+) with PMe(3) or dmpe effect a dissociation of the cyclic framework resulting in the formation of salts containing [Me(3)PPCyPCyPMe(3)](2+) ([27](2+)), [dmpeCyP](2+) ([29](2+)), and [dmpeCyPCyP](2+) ([30](2+)), respectively. The new cations represent phosphine complexes of the [PCy](2+) and [P(2)Cy(2)](2+) cationic fragments from [20](2+), demonstrating the coordinate nature of the phosphinophosphonium bonds in cyclo-phosphino-halophosphonium cations. The compounds have been characterized by NMR spectroscopy, single crystal X-ray crystallography, and Raman spectroscopy.

What is the true space group of weberite

Abstract Analysis of X-ray diffraction evidence obtained from a single crystal of natural weberite, Na 2 MgAlF 7 , at room temperature and at −140°C rules out all space groups but two, the noncentrosymmetric Imm 2 (originally proposed by Bystrom) and I 2 1 2 1 2 1 . However, comparison of structure refinements in these two groups and in Imma shows that the departure from centrosymmetry is so slight, and the positional and thermal parameters of some of the F atoms in the Imm 2 and I 2 1 2 1 2 1 refinements are so highly correlated, that the descriptions of the weberite structure in the three space groups must be regarded as practically indistinguishable. In the absence of a proof of achirality Bystroms space group assignment is provisionally accepted as valid, and Na 2 MgAlF 7 is considered as isostructural with the recently refined Na 2 NiFeF 7 .

Investigation of phosphorus–carbon bond lengths in aromatic phosphines. Part I. Crystal and molecular structures of tri-o-tolylphosphine, -phosphine oxide, -phosphine sulphide, and -phosphine selenide

The crystal and molecular structure of the four title compounds from four circle have been determined. Tri-o-tolylphosphine (I), triclinic, a= 12.081(5), b= 10.915(5), c= 14.348(7)A; α= 91.95(5)°, β= 110.58(4)°, γ= 98.22(5)°, space group P, Z= 4; R 0.045, 4 698 independent reflections. Tri-o-tolylphosphine oxide (II), monoclinic, a= 9.039(5), b= 17.282(6), c= 35.192(12)A, β= 95.12(1)° space group P21/c, Z= 12; R 0.075, 5 428 independent reflections. Tri-o-tolylphosphine sulphide (III), triclinic, a= 15.377(4), b= 15.346(4), c= 7.979(4)A; α= 103.1(1)°, β= 86.6(1)°, γ= 96.5(1)°, space group P, Z= 4; R 0.094, 2 890 independent reflections. Tri-o-tolylphosphine selenide (IV), monoclinic, a= 33.497(10), b= 8.004(2), c= 14.701(10)A, β= 110.67(4)°, space group C2/c, Z= 8; R 0.067, 2 343 independent reflections.The differences in P–C bond lengths appear to be determined by charge density on the aromatic group and the phosphorus atom, and by steric hindrance and crystal packing forces, and not by any extension of the π system of the aromatic groups to the phosphorus atom.

Structure and electrochemistry of a tetrakis(ferrocenecarboxylato)diruthenium(II,III) diadduct: evidence for ferrocenyl–ferrocenyl communication

Abstract 1-Propanol and ethanol adducts of tetrakis(ferrocenecarboxylato)diruthenium(II,III) hexafluorophosphate have been synthesized and the 1-propanol diadduct has been characterized by X-ray crystallography. The cyclopentadienyl rings of all four ferrocenyl groups showed on average a 13° deviation from the eclipsed conformation. Cyclic voltammetry measurements in 1,2-dichloroethane show an irreversible RuIIIRuII/RuIIRuII reduction and four partially superimposed one-electron ferrocenyl-centred electron transfer processes. The existence of ferrocenyl-based mixed-valent intermediate states posessing FeIII and FeII sites are implied by the splitting of the ferrocenyl wave into two observable cathodic and anodic peaks. The first cathodic wave shows typical desorption behaviour. Osteryoung Square Wave Voltammetry (OSWV) supports the above findings.

CRYSTAL STRUCTURES AND PHYSICO-CHEMICAL PROPERTIES OF A SERIES OF RU2(O2CCH3)4L2 (PF6) ADDUCTS (L = H2O, DMF, DMSO)

Abstract The reaction of Ru 2 (O 2 CCH 3 ) 4 Cl with water in the presence of Ag 2 SO 4 and NH 4 PF 6 leads to the formation of [Ru 2 (O 2 CCH 3 ) 4 (H 2 O) 2 ](PF 6 ) (1). The subsequent reaction of complex 1 with dimethylformamide (DMF) and dimethylsulfoxide (DMSO) results in the formation of [Ru 2 (O 2 CCH 3 ) 4 (DMF) 2 ](PF 6 ) ( 2 ); [Ru 2 (O 2 CCH 3 ) 4 (DMF) 2 ](PF 6 )·DMF ( 2a ) and [Ru 2 (O 2 CCH 3 ) 4 (DMSO) 2 ](PF 6 ) ( 3 ). All complexes were characterized using single crystal X-ray crystallography, IR and UV-Vis spectroscopy, cyclic voltammetry and magnetic susceptibility. The crystallographic data for [Ru 2 (O 2 CCH 3 ) 4 (H 2 O) 2 ](PF 6 )·3H 2 O ( 1a ) are as follows: monoclinic space group C 2/ c with unit cell dimensions a = 19.552(2), b = 12.853(2), c = 8.487(2) A , β = 93.02(2)°, V = 2129.6(6) A 3 , Z = 4 . The structure was refined to R = 0.0244 ( R w = 0.266) with 1165 reflections having I > 3 σ ( I ). The RuRu distance is 2.2648(9) A; Ru distances are 2.023(4), 2.039(3), 2.018(4) and 2.026(3) A; Ru  O ( axial ) = 2.279(4) A . The relevant data for 2 are: orthorhombic, space group P 2 1 2 1 2 1 with unit cell dimensions a = 11.704(2), b = 28.452(10), c = 8.415(3) A , V = 2802(2) A 3 , Z = 4 . The structure was refined to R = 0.0597 ( wR 2 = 0.1520) with 909 reflections having I >2 σ ( I ). The RuRu distance is 2.262(3) A; RuO distances are 1.999(14), 2.003(13), 2.004(13) and 2.009(13) A; the RuO(axial) distances are both 2.22(2) A. The pertinent crystal data for 2a are: monoclinic, space group P 2 1 / c with unit cell dimensions a = 8.382(4), b = 11.918(3), c = 30.715(5) A , β = 96.84(3)°, V = 3046(1) A 3 , Z = 4 . The structure was refined to R = 0.0558 ( wR 2 = 0.1388) with 1317 reflections having I >2 σ ( I ). The RuRu distance is 2.265(2) A; RuO distances are 2.021(13), 2.052(13) and 2.023(14) A; the RuO(axial) distances are both 2.229(14) A. The data for 3 are: triclinic, space group P 1 with unit cell dimensions a = 11.45(1), b = 14.103(4), c = 8.303(3) A , α = 90.46(2), β = 110.15(4), γ = 78.93(4)°, V = 1232(1) A 3 , Z = 2 . The structure was refined to R = 0.0301 ( R w = 0.0382) with 2578 reflections having I >3 σ ( I ). The RuRu bond distances are 2.274(1) and 2.268(1) A; RuO distances range from 2.017(5) to 2.035(5) A; the RuO(axial) distances are 2.240(5) and 2.243(5) A. Increasing the donor number of the axial ligand manifests only very small changes in RuRu bond length, reduction potential and π ∗ ( Ru 2 ) → π( RuO, Ru 2 ) transition energy and no changes in μ eff implying only minor perturbation of σ ∗ and π ∗ orbital energies.

First preparation of enantiomerically pure sibutramine and its major metabolite, and determination of their absolute configuration by single crystal X-ray analysis

Abstract Racemic sibutramine was resolved with dibenzoyl- d -tartaric acid, and the absolute stereochemistry of sibutramine was determined by single crystal X-ray crystallography of its dibenzoyl d -tartrate. The major active metabolite (desmethylsibutramine) was obtained by demethylation of sibutramine with DEAD. Enantiomeric purity of sibutramine was determined by HPLC on an Ultron ES-OVM column.