Biomedical subjects

Hubert Schmidbaur

Publications and source records attributed to Hubert Schmidbaur.

At least 19 recordsLinked to original sources

PubMed2005

Isomeric mono- and bis[(phosphane)gold(I)] thiocyanate complexes.

The solid-state IR spectrum of Me(3)PAuSCN shows two signals in the range of the C-N stretching vibrations at 2075 and 2113 cm(-1). On the basis of thoroughly tested quantum chemical ab initio calculations (MP2 level of theory) these signals have been assigned to the two isomeric forms Me(3)PAuNCS and Me(3)PAuSCN. The molecular structures, the vibrational frequencies, and the relative energies of the two species have been calculated and the results compared with the experimental IR data. Treatment of Me(3)PAuSCN with equimolar quantities of [(Me(3)P)Au](+)[SbF(6)](-) in CH(2)Cl(2) at -78 degrees C gives the dinuclear reaction product [C(7)H(9)Au(2)NP(2)S](+)[SbF(6)](-) in high yields. A comparison of results of ab initio calculations and IR data suggest that at least three isomeric cationic species [(R(3)PAu)(2)NCS](+), [(R(3)PAu)(2)SCN](+) and [(R(3)PAu)SCN(AuPR(3))](+) are present, the second and third being the predominant components. The structures and vibrational frequencies of all three species have been calculated. The relative energies in the gas phase and in solution are discussed and compared with the corresponding data of the experimental IR spectra.

Crystallography, X-Ray↗

PubMed2005

The experimental gas-phase structures of 1,3,5-trisilylbenzene and hexasilylbenzene and the theoretical structures of all benzenes with three or more silyl substituents.

The structures of 1,3,5-trisilylbenzene and hexasilylbenzene in the gas phase have been determined by electron diffraction, and that of 1,3,5-trisilylbenzene by X-ray crystallography. The structures of three trisilylbenzene isomers, three tetrasilylbenzenes, pentasilylbenzene and hexasilylbenzene have been computed, ab initio and using Density Functional Theory, at levels up to MP2/6-31G*. The primary effect of silyl substituents is to narrow the ring angle at the substituted carbon atoms. Steric interactions between silyl groups on neighbouring carbon atoms lead first to displacement of these groups away from one another, and then to displacement out of the ring plane, with alternate groups moving to opposite sides of the ring. In the extreme example, hexasilylbenzene, the SiCCSi dihedral angle is 17.8(8) degrees .

Journal Article↗

PubMed2005

Bromination of (phosphine)gold(I) bromide complexes: stoichiometry and structure of products.

The course of the oxidative addition of elemental bromine to complexes of the type (L)AuBr is strongly influenced by the nature of the tertiary phosphine ligand L. Standard square planar gold(III) complexes (L)AuBr3 are obtained not only with L = PMe3 but also with P((I)Pro)3 for which the oxidative addition fails in the corresponding iodine system. Excess bromine is integrated into crystals of the products with the stoichiometry [(Me3P)AuBr3].(Br2) and {[(iPro)3P]AuBr3}.(Br2). Of the series of iodine analogues, an intercalate [(Me3P)AuI3]2.(I2) has been structurally characterized. [((t)Bu)3P]AuBr undergoes ligand redistribution upon treatment with bromine to give a complex reaction mixture, from which {[(tBu)3P]2Au}+(Br3)-.(Br2) could be crystallized. It contains polymeric anions [(Br5)-]n as zig-zag chains. [(o-Tol)3P]AuBr is readily brominated to give [(o-Tol)3P]AuBr3. Contrary to the situation in the gold(I) complex with its linear PAuBr unit, the square planar structure of the PAuBr3 unit causes steric hindering of the rotation of the tolyl groups about the P-C bonds as demonstrated by solution NMR studies. (The corresponding reaction with iodine is known to give only polyiodides with the oxidation state of the gold atom unchanged.) The even more severe congestion in [(Mes)3P]AuBr prevents oxidative addition not only of iodine but also of bromine. With the latter, P-Au cleavage occurs instead affording [(Mes)3PBr]+[AuBr4]-.

Journal Article↗

PubMed2005

A cyclic hexamer of silver trifluoroacetate supported by four triphenylphosphine sulfide template molecules.

Crystallization of silver trifluoroacetate from chloroform solutions containing triphenylphosphine sulfide affords a trigonal and a monoclinic form of a 6:4 complex {[CF3C(O)OAg]6(Ph3PS)4} of C2 symmetry with different amounts of chloroform in the crystals. With the Ph3PS components as template molecules, the CF3C(O)OAg units are assembled to form a 6-membered metallacycle codetermined by metallophilic bonding and enclosed by a 24-membered ring [AgOCO]6. A complex of the type [LAgOC(O)CF3]2, with L representing the isocyanide ligand pTolSO2CH2NC, has been shown to have a conventional bicyclic structure with three-coordinate silver atoms engaged in transannular metallophilic interactions.

Journal Article↗

PubMed2004

Insignificance of P-H...P hydrogen bonding: structural chemistry of neutral and protonated 1,8-di(phosphinyl)naphthalene.

While there is extensive information on 1,8-di(amino)naphthalene (i.e., the parent compound of the "proton sponge" series), the corresponding phosphorus compound has not been described. A high-yield synthesis of 1,8-di(phosphinyl)naphthalene (9) and the 1-naphthylphosphine reference compound (4) is now reported. Thermal decomposition of 9 leads to intramolecular dehydrogenative P-P coupling to afford 1,2-dihydro-1,2-diphosphaacenaphthene (10). Protonation of 9 and 4 with CF(3)SO(3)H gives quantitative yields of the monophosphonium salts 11 and 5, respectively. With excess acid and traces of moisture, the hydronium salt [C(10)H(6)(PH(2))(PH(3))](+)[H(3)O](+)2[CF(3)SO(3)](-) (13) is obtained. The structures of 9, 11, and 13 have been determined. Molecules of 9 have a planar naphthalene skeleton, C(10)H(6)P(2), with the two -PH(2) groups in a transoid conformation. The molecules form loose dimers in the crystal, the individual chiral enantiomers of which are related by a center of inversion. In contrast to the situation for the amino analogue, and despite the proximity of the two -PH(2) functions, there is no intra- or intermolecular hydrogen bonding. Solutions of 9 (in CD(2)Cl(2)) show equivalent P-bound hydrogen atoms due to conformational fluctionality. By analysis of the ABCD(2)XX'D'(2)C'B'A' spin system, it was shown that, in 9, there are strong through-space pericouplings [(n)J(P(X)P(X)(')) = 221.6 Hz, (n)J(P(X)H(D)(')) = 31.7 Hz, (n)J(H(D)H(D)(')) = 3.9 Hz]. In the cations of 11, the C(10)H(6)P(2) skeleton is also planar (by C(s) symmetry), with the -PH(2) and -PH(3)(+) groups in a conformation which rules out any P-H...P hydrogen bonding. The hydronium cation and the two triflate anions in 13 are associated into an anionic network through extensive hydrogen bonding surrounding stacks of the phosphonium cations. In solution, the cations of 11 and 13 show separate (31)P resonances for the two phosphorus atoms with fully resolved (1)J(PH) couplings, which indicate that there is no intra- or intercationic proton exchange. By contrast, the NMR spectra of solutions of [C(10)H(6)(NH(2))(NH(3))](+)X(-) salts show proton scrambling equilibrating all five N-bound hydrogen atoms, and in the crystal, the conformations of the cations feature intramolecular N-H...N hydrogen bonding.

Journal Article↗

PubMed2004

Synthesis and auration of primary and di-primary heteroaryl-phosphines.

Convenient high-yield syntheses of the primary and di-primary heteroaryl-phosphines R-PH2 and H2P-R'-PH2(with R = 2-thienyl, 2-furyl, and R'= 2,5-thiophenediyl, 2,5-furandiyl, respectively) are presented. The products and a set of precursor molecules have been characterized by analytical and spectral data, and the crystal structures of selected molecules have been determined: 2-C4H3O-PCl2, 2,5-(Cl2P)2C4H2O, 2,5-[(Et2N)2P]2C4H2E (with E = O, S). In the crystals, the two molecules with -PCl2 substituents adopt trans conformations, while the other two have the -P(NEt2)2 groups rotated into a twist conformation. The reaction of the thienyl compounds with tris[(tert-phosphine)gold]oxonium tetrafluoroborates gave almost quantitative yields of the tri- and hexanuclear gold complexes, respectively: {2-C4H3S-P[Au(PR3)]3}+BF4- and [2,5-{[(R3P)Au]3P}2C4H2S]2+(BF4(-)2, (R =tBu, Ph). The structures of the compounds with R3P =tBu3P ligands have been determined. In both cases the [2-C4H3/2S-P] units cap triangles of gold atoms in an array that can be described as three [Au(PR3)]+ cations bridged by a phosphido dianion (RP)2-.

Journal Article↗

PubMed2004

Governing the oxidative addition of iodine to gold(I) complexes by ligand tuning.

While several gold(I) complexes of the type (L)AuX (X = Cl, Br) are known to undergo oxidative addition of elemental chlorine and bromine (X2), respectively, to give the corresponding gold(III) complexes (L)AuX3, the addition of iodine to (iodo)gold(I) compounds is strongly ligand-dependent, suggesting a crucial threshold in the oxidation potentials. A systematic investigation of this particular oxidative addition of iodine using a large series of tertiary phosphines as ligands L has shown that both electronic and steric effects influence the course of the reaction. The reactions were followed by 31P NMR spectroscopy and the products crystallized from dichloromethane-pentane solutions. Complexes with small triakylphosphines (PMe3, PEt3) are readily oxidized, while those with more bulky ligands (PiPr3, PtBu3) are not. With L taken from the triarylphosphine series [PPh3, P(2-Tol)3, P(3-Tol3), P(4-Tol)3] no oxidation takes place at all, but mixed alkyl/aryl-phosphines [PMenPh(3-n)] induce oxidation for n = 3 and 2, but not for n = 1 and 0. However, in cases where no oxidation of the gold atoms is observed, the synthons may crystallize as adducts with molecular iodine of the polyiodide type instead, which have an iodine rich stoichiometry. This fact explains inconsistent reports in the literature. The metal atoms in (L)AuI coordination compounds with L representing a tri(heteroaryl)phosphine [P(2-C4H3E)3, E = O, S], a phosphite [P(OR)3] or a trialkenylphosphine [PVi3] are all not subject to oxidative addition of iodine. The dinuclear complex of the ditertiary phosphine Ph2PCH2PPh2, (dppm)(AuI)2, gives an iodine adduct (without oxidation of the metal atoms), but with 1,2-Ph2P(C6H4)PPh2(dppbe) an ionic complex [(dppbe)AuI2]+I3- with a chelated gold(III) centre is obtained. The gold(I) bromide complexes with tertiary phosphines are readily oxidized by bromine to give the corresponding gold(III) tribromide complexes, as demonstrated for (BzMePhP)AuBr and (Ph3P)AuBr. With (dppm)(AuBr)2 the primary product with mixed oxidation states was also isolated: (dppm)AuBr(AuBr3). The crystal structures of the following representative examples and reference compounds have been determined: (Me3P)AuI3, (Me2PhP)AuI3, (iPr3P)AuI.1.5I2, (Ph3P)AuI.I2, [[(2-Tol)3P]AuI]2.I2, [(2-Tol)3P]AuI, (dppm)(AuX)2 (with X = Br, I), (dppm)AuBr(AuBr3) and [(dppbe)AuI2]+I3-. The structures are discussed focusing on the steric effects. It appears that e.g. the reluctance of (Ph3P)AuI to add I2 is an electronic effect, while that of (iPr3P)AuI has its origin in the steric influence of the ligand.

Journal Article↗

PubMed2004

Unsuccessful/successful attempts to produce penta(heteroaryl)-phosphoranes/-arsoranes R5E (E = P, As; R = 2-furyl, 2-thienyl).

Tri(2-thienyl)phosphine (1) has been transformed into chlorotri(2-thienyl)phosphonium chloride (3) in the reaction with hexachloroethane, into tetra(2-thienyl)phosphonium bromide (4) in a NiBr2-catalyzed quaternization with 2-bromothiophene, and into the p-tolylsulfonyliminotri(2-thienyl)phosphorane (6) using "chloramine T". Attempts to generate the homoleptic penta(2-thienyl)phosphorane (2-C4H3S)5P (5) by treating 3, 4, 6 or the known (PhO)3P=NSO2C6H4-2-Me (9) with 2-thienyllithium were unsuccessful. Tri(2-furyl)phosphine (2) was converted into the related imine 7, but the reaction of 7 or of 9 with 2-furyllithium failed to give (2-C4H3O)5P (8). It was only with the strained phosphorane Ph(C12H8)P=NSO2C6H4-4-Me (C12H8= 2,2'-biphenylylene) (10) that with 2-C4H3OLi the corresponding phosphorane Ph(C12H8)P(C4H3O-2)2 (11) could be obtained (31P NMR: delta-106.7 ppm). In the arsenic series, tri(2-thienyl)- and tri(2-furyl)arsine (12, 13) were converted into the tosylimino compounds (14, 15) and successfully transformed into the homoleptic arsoranes with 2-C4H3E-Li: penta(2-thienyl)- (16) and penta(2-furyl)-arsorane (17) are stable colourless crystalline solids, the NMR spectra of which indicate rapid pseudo-rotation in solution. The single crystal structure analysis of 17 shows an only slightly distorted trigonal-bipyramidal configuration. In crystals of the phosphine 2 and the arsine 13 the molecules have a propeller configuration with approximate C3v symmetry for the former, but Cs symmetry for the latter. The crystal structures of the precursors or intermediates 3, 4, 6, 9, and 10 have also been determined.

Journal Article↗

PubMed2004

The tetra(vinyl)phosphonium cation [(CH2=CH)4P]+.

A convenient high-yield synthesis of tetra(vinyl)phosphonium salts is presented, based on the hydrophosphination of PH3 with vinyl acetate, the quaternization of the first intermediate by 2-iodoethanol, followed by its acetylation, and in the crucial final step by careful elimination of 4 equiv of acetic acid. The intermediates and products have been characterized by their analytical and spectroscopic data, and the crystal structure of the tetraphenylborate salt [Vi4P]+ [BPh4]- has been determined. The ground-state conformation of the cation is of low symmetry (point group C1, with three vinyl groups forming a propeller), as confirmed by quantum chemical calculations. This structure has now also been found for the [BVi4]- anion in its methyltriphenylphosphonium salt, or, previously, for tetravinylmethane and -silane, and appears to be general for tetravinylelement species. By contrast, tetra(ethyl)element molecules, cations or anions [Et4E] generally feature S4 symmetry. Alkyltrivinylphosphonium salts [RPVi3]+ X- are available following a similar procedure as demonstrated for the cyclohexyl series (R = Cy).

Journal Article↗

PubMed2004

Interactions of a beta-dipeptide with monovalent metal cations: crystal structures of (anthranoyl)anthranilic acid and its lithium, sodium and thallium salts.

X-ray crystal structure analyses have been performed on the beta-dipeptide (anthranoyl)anthranilic acid [HAnthAnthOH] and its lithium, sodium and thallium salts [HAnthAnthOM] to give a first set of data for this representative model ligand. Crystals of the beta-dipeptide are orthorhombic, space group Pca2(1). The unit cell contains two molecules of (anthranoyl)anthranilic acid which form a dimer via hydrogen bonds. The components of the beta-dipeptide are rotated into the trans-conformation which allows for internal hydrogen bonds. The pKS value of (anthranoyl)anthranilic acid (9.80+/-0.14) shows a slight decrease as compared to anthranilic acid; the metal salts can therefore be prepared by direct neutralization of the beta-dipeptide with metal hydroxides or carbonates. The alkali compounds crystallize as the trihydrates [HAnthAnthOM(H2O)3, M=Li, Na] in the triclinic space group p1. Both metal ions show a clear preference for water molecules over the (anthranoyl)anthranilate anions as ligands in their coordination spheres. As a consequence, the [HAnthAnthO]- anions are only partially involved in metal complexation. The cell plots of both compounds exhibit a stacking with an alternation of oppositely charged layers. The negatively charged layers are composed exclusively of (anthranoyl)anthranilate anions. The thallium compound crystallizes as the hemihydrate [HAnthAnthOTl(H2O)0.5] in the monoclinic space group C2/c. In the dinuclear units, the thallium ions accommodate one nitrogen and four oxygen atoms of the anions in their coordination sphere and in addition entertain weak Tl-arene contacts. In contrast to the alkali compounds, the water molecules are not involved in metal complexation, but contribute to a network of hydrogen bonding.

Cations, Monovalent↗

PubMed2003

Crystal structures of rubidium and cesium anthranilates and salicylates.

In an attempt to probe a potential template role of the large alkali-metal cations rubidium and cesium in the organization of biorelevant ligands, salicylate and anthranilate complexes of the two elements were prepared and structurally investigated. The studies were also expected to show the marked structural differences compared to the corresponding thallium(I) compounds. Rubidium anthranilate and cesium salicylate could be crystallized as the monohydrates Rb(Anth)(H(2)O) and Cs(Sal)(H(2)O). Both have layer structures containing the cations and the polar groups of the ligands in core domains sandwiched by the aromatic rings above and below. The metal atoms have coordination numbers 7 and 8, respectively, with an irregular coordination sphere made up exclusively of oxygen atoms. Crystalline material with a 1:2 stoichiometry, Cs[H(Anth)(2)], is obtained from aqueous solutions of Cs(Anth) upon absorption of carbon dioxide with concomitant formation of cesium bicarbonate, Cs(HCO(3)). The crystal structure of Cs(HCO(3)) was redetermined to obtain precise benchmark data for cesium carbonates and carboxylates. The cesium hydrogen bisanthranilate also has a layer structure with eight-coordinate cesium atoms. The coordination sphere includes one nitrogen donor atom. The organization of all layer structures appears to be governed mainly by steric effects and electrostatic forces with very little directional influence of the cations. This result suggests that the large alkali metals have no efficient template effect for the organization of biological substrates and can explain the low toxicity of rubidium and cesium salts.

Journal Article↗

PubMed2003

Highly asymmetric coordination in alkenes: gas-phase structures of trans-1,2-dichloro-1,2-disilylethene and 1-bromo-1-silylethene.

The molecular structures of trans-1,2-dichloro-1,2-disilylethene and 1-bromo-1-silylethene have been determined by gas-phase electron diffraction (GED) and ab initio molecular orbital calculations (MP2/6-311G). Both compounds were found to have highly asymmetric coordination around the carbon atoms with [ab initio (r(e))/GED (r(a))] C=C-Cl [117.0/117.0(2) degrees] and C=C-Si [126.2/128.1(1) degrees] in the C(2)(h) structure of trans-1,2-dichloro-1,2-disilylethene and C=C-Br [119.2/120.7(4) degrees] and C=C-Si [125.0/125.0(4) degrees] in the C(s) structure of 1-bromo-1-silylethene. Other important structural parameters for trans-1,2-dichloro-1,2-disilylethene are C=C [135.2/134.5(3) pm], C-Si [189.4/187.9(2) pm], and C-Cl [175.1/174.9(1) pm], and C=C [134.2/133.4(2) pm], C-Si [187.8/187.2(3) pm], and C-Br [191.3/191.0(3) pm] for 1-bromo-1-silylethene. Further ab initio calculations were carried out on CH(2)CRX and trans-(CRX)(2) (R = SiH(3), CH(3), or H; X = H, F, Cl, or Br) to gauge the effects of electron-withdrawing and electron-donating groups on the structures. They reveal some even more distorted structures. The asymmetric appearance of these molecules can largely be accounted for by valence shell electron pair repulsion theory.

Journal Article↗

PubMed2003

Complexity of coordinative bonding in thallium(I) anthranilates and salicylates.

An inventory of the structural chemistry of thallium(I) shows many unexpected, almost random coordination numbers and coordination geometries that appear erratic and inconsistent. This nonstandard behavior is often ascribed to the specific lone-pair characteristics originating from relativistic effects. To provide data on a set of closely related compounds from which simple general rules of coordinative bonding at Tl(+) can be established, three thallium(I) anthranilates and three thallium(I) salicylates have been prepared from Tl(2)CO(3) and the corresponding 2-amino- and 2-hydroxy-benzoic acids and crystallized from aqueous solutions. All six compounds, the simple anthranilate (1) and salicylate (4) and the 3- and 4-methyl-substituted homologues (2, 3 and 5, 6) show different structures with large variations in the coordination motif. The coordination by oxygen in a geometry which covers less than a coordination hemisphere is the only common feature, complemented (only in 1) by a nitrogen coordination and by eta(6)-coordination of one (in 1, 2, 3, 6) or two phenyl rings (in 4). Tl-Tl contacts for which "thallophilic" bonding between closed shell metal atoms could be invoked, are generally very long (close to 4.0 A) or even well beyond the limit of standard van der Waals contacts. Hydrogen bonding is only obvious for the internal contacts of the amino- or hydroxy-benzoate ligands and does not contribute significantly to the assembly of the supramolecular structure which is dominated by oxygen bridges between thallium atoms. With the exception of 5, the formula units Tl[O(2)C(2-R)(3-R')(4-R'')C(6)H(2)] are generally aggregated into dimers of various configurations depending on the relative orientation of the edge-sharing four-membered rings, and these dimers are further linked into strings or columns establishing N-Tl or Tl-O contacts and arene coordination. The drastic changes induced in the structures upon only small variations such as methyl substitution in 3- or 4-position of the ligand suggest that thallium(I) coordination is generally restricted to one hemisphere of nearest neighbors, but is extremely flexible in this realm. The open hemisphere may be partially capped by arene coordination (which is weak at a distance of ca. 3.1 A to the centroid of the ring) or feature very weak thallophilic contacts.

Journal Article↗

PubMed2003

Stability of the gold(i)-phosphine bond. A comparison with other group 11 elements.

The stability of gold phosphine complexes of the form [Au(PH(3))(n)()](+) (n = 1-4) and [AuCl(PH(3))(n)()] (n = 1-3) is analyzed in detail by applying quantum theoretical methods and compared to the coordination behavior of the lighter group 11 elements copper and silver. It is shown that, once [M(PH(3))(2)](+) or [MClPH(3)] (M = Cu, Ag, and Au) is formed, further coordination by PH(3) ligands is relatively weak; i.e., the energy gain to form [M(PH(3))(3)](+) from [M(PH(3))(2)](+) is less than 60 kJ mol(-)(1), and less than 100 kJ mol(-)(1) to form [MCl(PH(3))(2)] from [MClPH(3)]. Relativistic effects in gold significantly influence these factors and reduce the tendency for phosphine coordination beyond two-coordination. This implies that the most favored coordination number for gold is two with either a linear P-Au-P or P-Au-X arrangement (X = a strongly coordinating ligand like Cl(-)). Instead, X-Au-PH(3) units prefer to interact via close Au-Au contacts (aurophilic interactions) keeping the linear structure approximately intact, while the corresponding copper and silver compounds prefer PH(3) coordination to strongly bound M(2)Cl(2) units (M = Cu or Ag) where two chlorine atoms bridge the two metal atoms thus having the formal coordination number of three for copper or silver.

Journal Article↗

PubMed2002

Dichlorogallane (HGaCl(2))(2): its molecular structure and synthetic potential.

Dichlorogallane (HGaCl(2))(2) is readily prepared from gallium trichloride and triethylsilane in quantitative yield. Its crystal structure has been determined by single crystal X-ray diffraction. In the chlorine-bridged dimers of crystallographically imposed C(2h) symmetry, the terminal hydrogen atoms are in trans positions. In the reaction with 2 equiv of triethylphosphine, the mononuclear complex (Et(3)P)GaHCl(2) is formed. Thermal decomposition of (HGaCl(2))(2) affords hydrogen gas and quantitative yields of "GaCl(2)" as mixed-valent Ga[GaCl(4)]. Treatment of this product with triethylphosphine gives the symmetrical, Ga-Ga-bonded gallium(II) complex [GaCl(2)(PEt(3))](2) with an ethane-type structure and with the phosphine ligands in a single-trans conformation. The corresponding [GaBr(2)(PEt(3))](2) complex is prepared from Ga[GaBr(4)] and has an analogous structure. (Et(3)P)GaCl(3) has been synthesized and structurally characterized as a reference compound.

Journal Article↗

PubMed2002

Aurophilicity-based one-dimensional arrays of gold(I) phenylene-1,3- and -1,4-dithiolates.

Phenylene-1,3-dithiol is converted into a trinuclear gold complex by treatment with 1 equiv of [[(Ph(3)P)Au](3)O](+)BF(4)(-). In the product, the phenylene unit bears one gold thiolate and one di(gold)sulfonium function. These components aggregate into one-dimensional arrays through head-to-tail aurophilic contacts between the two functions. In the association process, the Au[bond]S[bond]Au angle of the sulfonium group is opened up to accommodate the incoming gold atom between its metal centers. A similar mode of aggregation is found for the triply aurated biphenylene-4,4'-dithiol obtained using the tri(gold)oxonium salt with tri(p-tolyl)phosphine ligands. Probably for steric reasons, in this oligomerization process, the gold(I) thiolate unit is attached side-on to the digold sulfonium unit with retention of the small Au[bond]S[bond]Au angle. Under similar reaction conditions, and with the same molar ratio of the components, phenylene-1,4-dithiol is converted into the bis-sulfonium salt: 1,4-[[(p-Tol)(3)PAu](2)S](2)C(6)H(4)(BF(4))(2), the dications of which also associate into chains. Along the chains, the phenylene spacers alternate with tetranuclear gold clusters which arise from intimate aggregation of pairs of gold atoms. Together with previous findings, the present results show that gold thiolate (-SAuL) and digold sulfonium functions [-S(AuL)(2)(+)] in proper orientation at an arene unit (alpha-omega) can be considered as "soldering" points which can be used for joining up the molecular units into one-dimensional arrays solely through metal-metal contacts, which appear to be operative even against Coulomb repulsion between cations. The reaction of biphenylene-4,4'-dithiol with 2 equiv of sodium methoxide and [tri(c-hexyl)phosphine]gold chloride gives only neutral digold dithiolate complex 4 which is not associated owing to the steric bulk of the tri(c-hexyl)phosphine ligands.

Journal Article↗

PubMed2002

5-Organyl-5-phosphaspiro[4.4]nonanes: a contribution to the structural chemistry of spirocyclic tetraalkylphosphonium salts and pentaalkylphosphoranes.

Spirocyclic phosphonium salts of the type [(CH(2))(4)P(CH(2))(4)](+) X(-) with X = I(3) (1a), I (1b), picrate (1c), benzoate (1d), and Cl (1e) were prepared from 1,4-diiodobutane and elemental phosphorus followed by metathesis reactions. The crystal structures of 1b and 1c and of 1d(H(2)O) have been determined by X-ray diffraction methods. In the cations of these salts the phosphorus atoms are shared by two five-membered rings in envelop conformations. In the picrate 1c the cations show an unsymmetrical ring folding pattern (point group C(1)), while the geometry of the cations of the iodide 1b and the benzoate hydrate [1d(H(2)O)] approaches the symmetry of point group C(2). These structures can be taken as models for the as yet unknown molecular geometries of the corresponding hydrocarbon (CH(2))(4)C(CH(2))(4) and silane (CH(2))(4)Si(CH(2))(4). Treatment of 1e with organolithium reagents RLi affords spirocyclic pentaorganophosphoranes RP[(CH(2))(4)](2) with R = Me, Et, n-Bu, Vi, and Ph (2a-e) in good (R = Me, Et, n-Bu) to low yields (R = Vi, Ph). The products are isolated as colorless liquids, of which only 2a, 2b, and 2d can be distilled without decomposition. Single crystals of 2a were obtained by low-temperature in situ crystal growth. The molecule has a trigonal bipyramidal configuration with the methyl group in an equatorial position and the two five-membered rings spanning axial/equatorial positions of the polyhedron. Deviations from the standard trigonal bipyramidal geometry are small. The compounds 2a-e are fluctional in solution as demonstrated by NMR spectroscopy.

Journal Article↗

PubMed2002

Cluster self-assembly of di[gold(I)]halonium cations.

Treatment of gold(I) halide complexes of the type L-Au-X [where L = PPh(3), PEt(3) with X = Cl, Br, I, or L = 2,6-(MeO)(2)C(6)H(3)PPh(2) with X = Cl] with AgSbF(6) in the molar ratio 2:1 in dichloromethane/tetrahydrofuran at -78 degrees C affords high yields of di[gold(I)]halonium salts of the formula [X[Au(PR(3))](2)](+) SbF(6)(-) (2-8). A determination of the crystal structures of the four triarylphosphine complexes (2-4, 8) revealed the presence of novel tetranuclear dications with a highly symmetrical structure (point group S(4)) that arises from self-assembly of the dinuclear monocations through a set of four equivalent aurophilic Au-Au interactions. A comparison with two reference structures of corresponding chloronium perchlorate and bromonium tetrafluoroborate salts with monomeric, dinuclear cations shows that the geometry of the latter is greatly altered on dimerization to optimize the interactions between the closed-shell metal centers (Au: 5d(10)). Weak metallophilic bonding clearly becomes significant only in crystal lattices where anions with a larger ionic radius (SbF(6)(-) vs. BF(4)(-), ClO(4)(-)) reduce the otherwise dominant role of strong interionic Coulomb forces. The results indicate that aurophilic bonding is indeed an ubiquitous, quite dependable mode of intermetallic interactions provided that the right environment is chosen to allow the weak forces to become operative.

Cations↗