Crystal structure of K[PtCl3(caffeine)] and its interactions with important nitrogen-donor ligands

The crystal structure of K[PtCl₃(caffeine)] was determined. The coordination geometry around platinum is square-planar formed by N9 of the caffeine ligand and three Cl^? ions. The bond lengths and angles of K[PtCl₃(caffeine)] were compared with those reported for [PtCl₃(caffeine)]^? and K[PtCl₃(theobromine)]. At the level of the statistical significance of the data we have compared, no differences in the bond distances and angles for any of these compounds were noticed. Weak interactions between K⁺ and Cl^? are responsible for the formation of 1-D polymeric chains in the crystal structure of the complex. The interactions of K[PtCl₃(caffeine)] with inosine (Ino) and guanosine-5′-monophosphate (5′-GMP) were studied by ¹H NMR spectroscopy at 295 K in D₂O in a molar ratio of 1 : 1. The results indicate formation of the reaction product [PtCl₃(Nu)] (Nu=Ino or 5′-GMP) with the release of caffeine from the coordination sphere of the starting complex. The higher stability of the bond between the Pt(II) ion and Ino or 5′-GMP compared to the stability of the platinum–caffeine bond is confirmed by density functional theory calculations (B3LYP/LANL2DZp) using as models 9-methylhypoxanthine and 9-methylguanine.     

Stereospecific Palladium-Catalyzed Acylation of Enantioenriched Alkylcarbastannatranes: A General Alternative to Asymmetric Enolate Reactions

We report the development of a Pd-catalyzed process for the cross coupling of unactivated primary, secondary, and tertiary alkylcarbastannatrane nucleophiles with acyl electrophiles. Reactions involving optically active alkylcarbastannatranes occur with exceptional stereofidelity and with net retention of absolute configuration. Because the stereochemistry of the resulting products is entirely reagent-controlled, this process may be viewed as a general, alternative approach to the preparation of products typically accessed via asymmetric enolate methodologies. Additionally, we report a new method for the preparation of optically active alkylcarbastannatranes, which should facilitate their future use in stereospecific reactions.     

REACTIONS OF TELLURIUM TETRAHALIDES WITH GLYCOLS

Abstract

Tellurium tetrahalides undergo reaction with glycols to yield three different products: O,O'-dioxotrihalotellurates; bis(alkoxy)dihalotellurium (IV) compounds and hexahalotellurates. The course of the reaction appears to be determined primarily by the nature of the glycol. The structure of dichlorobis(cis- 2-hydroxycyclohexyloxy)tellurium(IV) has been determined crystallographically     

THE CRYSTAL STRUCTURES OF 10,10′-BIS(PHENOXARSINE) OXIDE AND SELENIDE

Abstract

The reaction between 10,10′-bis(phenoxarsine) oxide (I) and HI gives 10-iodophenoxarsine. The latter, on treatment with H₂Se give 10,10′-bis(phenoxarsine) selenide (II). The crystal structures of I and II have been determined from single crystal X-ray data. The unit cell for I is monoclinic, P2₁/c (No. 14) with a = 15.976(3) Å, b = 10.582(2) Å, c = 12.581(2) Å, β = 111.70(1)° V = 2018.6 ų; d(calc.) = 1.65Mg/m³ at 23°C for four molecules per unit cell. From 3279 reflections for which I>0.5σ(I), F>σ(F), R = 0.041 with anisotropic thermal parameters for all non-hydrogen atoms and with fixed positions and thermal parameters for hydrogens. One of the phenoxarsina rings deviates from planarity by approximately 5° while the other deviates by more than 24°. The (As[sbnd]O) distances are 1.810(3) and 1.821(3) Å for the flat and bent ring and the (As[sbnd]O[sbnd]As) angle is 122.3(1)°. The bond distances to As and O from C are nearly the same for both rings, but the bond angles with As and the ring O as the apex are systematically larger for the flat ring. For II the unit cell is triclinic, P1 (No. 2) with a = 9.368(1) Å, b = 14.089 Å, c = 9.269(2) Å, α = 111.37(2), β = 113.11(2), γ = 74.76(1); V = 1037.5 ų, d(calc) = 1.81 Mg/m³ for two molecules per unit cell at 23°C. From 2945 reflections for which I > 0.5σ(I), F > σ(F), R = 0.055 with anisotropic thermal parameters for all non-hydrogen atoms and with fixed positions and thermal parameters for hydrogen. One of the phenoxarsina rings deviates by 3° from planarity and the other by 8°. The (As[sbnd]Se) bond distances are 2.416(1) and 2.406(1) Å. The (As[sbnd]Se[sbnd]As) bond angle is 96.66(4)° and the corresponding (As[sbnd]C) and (C[sbnd]C) distances in the two rings are nearly the same. In comparison with I, the angles with As or O as the central atoms are about the same in both rings of II.