Biomedical subjects
Scott R. Wilson
Publications and source records attributed to Scott R. Wilson.
Synthesis and Properties of IrRe(2)(&mgr;-H)(2)(CO)(9)(eta(5)-C(9)H(7)).
The slow addition of Re(2)(&mgr;-H)(2)(CO)(8) to a solution of Ir(CO)(eta(2)-C(8)H(14))(eta(5)-C(9)H(7)) in hexane at reflux provides IrRe(2)(&mgr;-H)(2)(CO)(9)(eta(5)-C(9)H(7)) (1) in 80% yield. The molecular structure of 1 shows an IrRe(2) triangle incorporating one Ir(CO)(eta(5)-C(9)H(7)) and two Re(CO)(4) fragments. The strongly different Ir-Re distances suggest that one hydride ligand bridges one Ir-Re edge and the other hydride bridges the Re-Re edge. Low-temperature (1)H and (13)C NMR spectra are consistent with this structure; at higher temperatures a dynamic process involving migration of one hydride ligand between the two Ir-Re edges is observed. Cluster 1 is readily deprotonated with KOH/EtOH, and the resulting anion has been isolated as the PPN salt, [PPN][IrRe(2)(&mgr;-H)(CO)(9)(eta(5)-C(9)H(7))] (2). Both the (1)H and low temperature (13)C NMR spectra of 2 are consistent with a structure in which the remaining hydride ligand bridges the Re-Re edge. Variable-temperature (13)C NMR spectra indicate that 2 undergoes CO scrambling localized on the Ir-Re edges. The reaction of 1 with PPh(3) leads to IrRe(2)(&mgr;-H)(2)(CO)(8)(PPh(3))(eta(5)-C(9)H(7)) (3), which contains the phosphine on a rhenium atom, as well as to cluster fragmentation.
Carbidoheptarhenate Complexes of Mercury Hydroxide and Arenethiolate. Crystal Structures of [NEt(3)Bz](2)[Re(7)C(CO)(21)HgOH] and [PPh(4)](2)[Re(7)C(CO)(21)HgSC(6)H(4)Br].
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Coordination Networks of 3,3'-Dicyanodiphenylacetylene and Silver(I) Salts: Structural Diversity through Changes in Ligand Conformation and Counterion.
Coordination networks of 3,3'-dicyanodiphenylacetylene (3,3'-DCPA, 1) with silver(I) salts characterized by single-crystal X-ray analysis are described. Network topology is found to depend on both the counterion and solvent employed during crystallization. The conformation adopted by the ligand varies between planar cisoid and planar transoid. With silver(I) triflate (AgCF(3)SO(3)) in benzene, a sheet structure of composition [Ag(1)CF(3)SO(3)]C(6)H(6) (2) forms in which silver(I) is five-coordinate and bonds to two nitrogen atoms of distinct 3,3'-DCPA molecules, another silver(I) ion, and two oxygen atoms of the triflate ions. Changing the solvent to toluene produces an undulating sheet structure of composition [Ag(2)(1)(CF(3)SO(3))(2)] (3) in which silver(I) is six-coordinate, bonding to a ligand nitrogen atom, to four oxygen atoms of bridging triflate ions, and to a neighboring silver(I) ion. In both triflate structures, 3,3'-DCPA adopts a transoid conformation with respect to the positioning of the nitrile groups. With silver(I) hexafluorophosphate (AgPF(6)), silver(I) hexafluoroarsenate (AgAsF(6)), or silver(I) hexafluoroantimonate (AgSbF(6)), 2-fold interpenetrated sheet structures [Ag(1)(2)]XF(6) (X = P (4), As (5), or Sb (6)) are obtained in which 3,3'-DCPA coordinates to tetrahedral silver(I) ions in a cisoid conformation. In spite of the large difference in counterion size, minimal network deformation is observed among these systems. Interestingly, with silver(I) perchlorate hydrate (AgClO(4).xH(2)O, x approximately 1), 3,3'-DCPA coordinates in a transoid conformation to tetrahedral silver(I) ions to form the 8-fold interpenetrated diamondoid network [Ag(1)(2)]ClO(4).H(2)O (7). An analysis of the packing of these networks is provided, and the results are compared to complementary systems previously reported from our study of coordination networks of dinitriles and silver(I) salts.
X-ray Crystallographic Evidence in Support of a Proposed Chiral Recognition Mechanism.
A new family of pi-basic chiral selectors has been developed and employed in the separation of enantiomers by liquid chromatography. These chiral selectors, derived from (S)-proline and designed from mechanistic considerations, show high levels of discrimination between the enantiomers of N-(3,5-dinitrobenzoyl)amino acid esters and amides. A considerable amount of chromatographic data has been assembled, all of it consistent with the proposed chiral recognition mechanism. Moreover, this mechanism is supported by induced chemical shift differences and intermolecular NOE data previously obtained in solution with an equimolar mixture of (S)-1 and (S)-2. A crystalline 1:1 complex of (S)-1 and (S)-2 has been obtained and analyzed by X-ray crystallography. The structure of this complex in the solid state illustrates the essential features of the mechanism proposed to account for chiral recognition between chiral stationary phase (CSP) 3 and the enantiomers of 2 and related analytes. In addition, the orientation of the two components in the solid state is in close agreement with the structure of the more stable diastereomeric complex deduced from solution-state NMR evidence relating to the same system.
Synthesis, Characterization, and Comparative Properties of [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] and [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)].
The reaction of [PPN](2)[Re(6)C(CO)(19)] with Mo(CO)(6) and Ru(3)(CO)(12) under sunlamp irradiation provided the new mixed-metal clusters [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] and [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)], which were isolated in yields of 85% and 61%, respectively. The compound [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] crystallizes in the monoclinic space group P2(1)/c with a = 20.190 (7) Å, b = 16.489 (7) Å, c = 27.778 (7) Å, beta = 101.48 (2) degrees, and Z = 4 (at T = -75 degrees C). The cluster anion is composed of a Re(6)C octahedral core with a face capped by a Mo(CO)(4) fragment. There are three terminal carbonyl ligands coordinated to each rhenium atom. The four carbonyl ligands on the molybdenum center are essentially terminal, with one pair of carbonyl ligands (C72-O72 and C74-O74) subtending a relatively large angle at molybdenum (C72-Mo-C74 = 147.2(9) degrees ), whereas the remaining pair of carbonyl ligands (C71-O71 and C73-O73) subtend a much smaller angle (C71-Mo-C73 = 100.5(9) degrees ). The (13)C NMR spectrum of (13)CO-enriched [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] shows signals for four sets of carbonyl ligands at -40 degrees C, consistent with the solid state structure, but the carbonyl ligands undergo complete scrambling at ambient temperature. The (13)C NMR spectrum of (13)CO-enriched [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)] at 20 degrees C is consistent with the expected structure of an octahedral Re(6)C(CO)(18) core capped by a Ru(CO)(3) fragment. The visible spectrum of [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] shows a broad, strong band at 670 nm (epsilon = 8100), whereas all of the absorptions of [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)] are at higher energy. An irreversible oxidation wave with E(p) at 0.34 V is observed for [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)], whereas two quasi-reversible oxidation waves with E(1/2) values of 0.21 and 0.61 V (vs Ag/AgCl) are observed for [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)]. The molybdenum cap in [Re(6)C(CO)(18)Mo(CO(4))](2-) is cleaved by heating in donor solvents, and by treatment with H(2), to give largely [H(2)Re(6)C(CO)(18)](2-). In contrast, [Re(6)C(CO)(18)Ru(CO)(3)](2-) shows no tendency to react under similar conditions.