David R. Whitcomb

Synthesis and Characterization of Silver(I) Complexes with C-Alkyl Functionalized N,N'-Diphenylamidinates: Tetrameric and Trimeric Structural Motifs

N,N′−Diphenylamidines and the silver(I) complexes of their deprotonated anions have been synthesized. Previously uncharacterized tetrameric structural motifs were produced by the inclusion of alkyl substituents at the amidinate carbon. The addition of a 2-methoxy functional group to the phenyl ring resulted in a cationic silver trimer in which hydrogen bonding links silver(I)-bound water molecules to the methoxy substituents. The thermal stabilities of the tetrameric species vary with alkyl chain length. The new complexes are: tetrakis(N,N′-diphenylpropamidinato) tetra silver(I), 1, tetrakis(N,N′-diphenylbutamidinato) tetrasilver(I) 2, tetrakis(N,N′-diphenylpentamidinato) tetra silver(I) 3, (N,N′-diphenyloctamidinato)silver(I) 4, (tetrakis(N,N′-di(4-n-butyl)phenylpropamidinato)tetrasilver(I), 5, bis(N,N′-di(2-methoxy)phenylacetamidinato)diaquatrisilver(I) nitrate 6 and tetrakis(N,N′-di(4-methoxy)phenylacetamidinato) tetrasilver(I), 7. Compounds 1, 5, 6 and 7 were structurally characterized by X-ray methods.

1H and 31P NMR spectral analysis of the cis-trans equilibria of [NiX2(Cy2PH)2] complexes: [AMY2]2 Spin Systems

Abstract Analysis of 1H and 31P NMR of cis and trans isomers of {NiI2[(C6H11)2PH]2}, {NiBr2[(C6H11)2PH]2}, and of cis-{NiCl2[(C6H11)2PH]2} is reported. Assignment of coupling constants in these compounds as [AMY2]2, spin systems and use of these assignments (particularly 2JP−P′) in distinguishing cis and trans forms are discussed. The temperature dependence of the cis-trans equilibria of the bromide and iodide complexes, followed by the 31P spectra, is used to calculate thermodynamic constants for the isomerization.

Molecular and supramolecular structure of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane, tetrahydrofuran solvate

The crystal and molecular structure of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane tetrahydrofuran solvate, C21H24O4·2(C4H8O), has been determined by single crystal X-ray analysis: the space group is monoclinic,P21/a, witha=10.77(1),b=25.357(8),c=19.009(7) Å, β-90.84(4)°,V=5190(5) Å3,Z=8,Dx=1.24 gm/cm3. The structure is abis-catechol molecule which forms layers of either (R) or (S) configurational pairs. Layers are stacked to form solvent tunnels where adjoining layers are linkedvia hydrogen bonding. One hydroxyl oxygen on each end of catechol moieties act as a hydrogen donor while the remaining hydroxyl oxygen serves as donor and acceptor. The extensive hydrogen bonding, in conjunction with the spiro linkage forcing perpendicularly arranged aromatic rings, create the conditions for supramolecular control of the crystal structure. Consequently, they are also the primary factors responsible for the unusually high melting point of this bulky, branched, spirobis-catechol compared to other alkyl derivatives of catechol molecules.

Iron(III) di(2-ethylhexyl)phosphate complexes: ligand control of co-ordination polymerization

A novel dinuclear complex comprised of H+/NO3– bridged tris[di(2-ethylhexyl)phosphate]iron(III) units, Fe(dehp)3, having the molecular formula [Fe2(dehp)5(Hdehp)(NO3)], is described which surprisingly is colourless, stable under ambient conditions, and highly soluble in cyclohexane. Solution reaction with water leads to replacement of H+/NO3– by H2O producing a highly insoluble polymer having molecular formula [{Fe(dehp)3(H2O)}n]. Interconversion between the contrasting polymeric and dinuclear species is facile and represents an example of reversible co-ordination polymerization–depolymerization with the two species differing remarkably in their properties. The preparation, characterization, and interconversion of these iron complexes are described.

Structure and properties of cis-bis(dicyclohexylphosphine)dihalogeno-nickel(II) complexes

Dicyclohexylphosphine and tetracyclohexyldiphosphane both react with anhydrous nickel(II) chloride and bromide to form the same type of complex in either case, namely cis-[NiX2{P(C6H11)2H}2](X = Cl or Br). This has been confirmed in the solid state by X-ray diffraction and in solution by 1H and 31P n.m.r. spectroscopy. Other spectro-scopic data, as well as melting points, molecular weights, and elemental analyses, are also compatible with this conclusion. Evidence for a trans isomer of the bromide in solution is also observed. No evidence for the formation of a three-membered chelate ring in the reactions with the diphosphane could be detected. The 31P chemical shifts in CH2Cl2, are 36.4 (20 °C, 0.2 mol dm–3) and –46.1 and –30.5 p.p.m. (0 °C, 0.2 mol dm–3) for cis-[NiCl2{P(C6H11)2H}2], cis-[NiBr2{P(C6H11)2H}2], and trans-[NiBr2{P(C6H11)2H}2] respectively, relative to 85% H3PO4. The complexes exhibit strong P–H coupling due to the secondary phosphine proton. X-Ray diffraction shows that cis-[NiCl2{P(C6H11)2H}2] crystallizes in the tetragonal space group /41/a(No. 88) with a= 20.69(1) and b= 25.15(2)A, and Z= 16. The structure was solved, using Weissenberg methods and the heavy-atom technique from 1400 independent reflections using Cu-Kα radiation, to R′ 0.118. The nickel atom is 0.05 A from the plane formed by the chlorine and phosphorus atoms. The average Ni–Cl distance IS 2.20(1)A and the average Ni—P distance is 2.15(l)A.