Allan H. White

Bio: Allan H. White is an academic researcher from University of Western Australia. The author has contributed to research in topics: Ligand & Triphenylstibine. The author has an hindex of 20, co-authored 79 publications receiving 1225 citations. Previous affiliations of Allan H. White include University College West & University of Wollongong.

Models for Arginine-Metal Binding. Synthesis of Guanidine and Urea Ligands through Amination and Hydration of a Cyanamide Ligand Bound to Platinum(II), Osmium(III), and Cobalt(III).

Abstract: Dimethylcyanamide (N identical withCNMe(2)) has been coordinated to both hard and soft electrophiles ((NH(3))(5)Co(3+), (NH(3))(5)Os(3+), (dien)Pt(2+)) which activate ( approximately x10(6)) the nitrile toward attack by nucleophiles such as ammonia and hydroxide. Amination with liquid ammonia gave a rare coordinated guanidine (N,N-dimethylguanidine) ligand, which NMR spectra and X-ray crystal structures show to be charge neutral rather than anionic. Crystals of [(NH(3))(5)CoNH=C(NH(2))NMe(2)](S(2)O(6))(3/2).H(2)O, CoC(3)H(26)N(8)O(10)S(3), were triclinic, space group Po, a = 11.565(2) A, b = 10.629(5) A, c = 8.026(1) A, alpha = 84.93(3) degrees, beta = 76.01(1) degrees, gamma = 73.82(3) degrees, V = 919.2(5) A(3), Z = 2, and R(F)() (R(w)(F)()) = 0.038 (0.047) for 3262 observed reflections (I > 3.0 sigma(I)). Crystals of [(dien)PtNH=C(NH(2))NMe(2)](CF(3)SO(3))(2), PtC(9)H(22)N(6)O(6) S(2)F(6), are monoclinic, space group P2(1)/c, a = 13.857(4), b = 14.748(4) A, c = 22.092(4) A, beta = 105.38(2) degrees, V = 4353(2) A(3), Z = 8, and R(F)() (R(w)(F)()) = 0.034 (0.038) for 6778 reflections. Coordination geometries around the metals are octahedral and square planar, respectively, the guanidine skeletons being planar with bond angles and lengths characteristic of the metal-imino (rather than metal-amino) tautomer. The complexes are very stable in coordinating solvents (DMSO; water, pH 3-11) indicating high affinity of guanidine ligands for metal ions. Hydration of the dimethylcyanamide ligand is base-catalyzed, and first-order in [OH(-)] (0.05-0.5 M NaOH; k = k(s) + k(OH)[OH(-)], k(OH) = 2-5 M(-)(1) s(-)(1), 25 degrees C), in each case producing coordinated N,N-dimethylurea ([dienPtNHCONMe(2)](+), [(NH(3))(5)CoNHCONMe(2)](2+), [(NH(3))(5)OsNHCONMe(2)](2+)). Hydration rates are surprizingly similar despite differing radial extensions of the metal d-orbitals, a finding consistent with their comparable polarizing powers but contrary to expectation from other work. The relevance of metal activation of nitriles to biological systems is discussed.

Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXXIII Synthesis, Spectroscopy and Structural Systematics of New 1:1 'Cubane' Tetramers of Copper(I) and Silver(I) Halides with Triphenylarsine

Abstract: Syntheses and room-temperature single-crystal X-ray structural characterization of a number of 1 : 1 ‘cube tetramer’ adducts of copper(I) and silver(I) halides, MX, with triphenylarsine, AsPh3, are recorded, being [XM(AsPh3)]4. The CuBr adduct, obtained unsolvated from toluene, orthorhombic Pbcn, a 17·844(5), b 20·778(8), c 18·430(4) A, Z = 4 tetramers, conventional R on |F| 0·058 for No 1309 independent ‘observed’ reflctions (I > 3σ(I)), is isomorphous with previously recorded [ClAg(PPh3)]4, the tetramer having crystallographically imposed 2 symmetry. The CuI adduct, previously recorded as a monobenzene solvate, has been isolated unsolvated from toluene, monoclinic, P 21/n, a 19·70(5), b 27·110(7), c 13·59(2) A, β 98·84(9)°, Z = 4 tetramers, R 0·087 for No 4359, isomorphous with previously recorded [ICu(PPh3)]4, as a 6h benzene solvate, triclinic, P-1 a 26·688(2), b 15·180(7), c 13·090(1) A, α 85·41(2), β 87·580(7), γ 77·63(2)°, Z = 2 tetramers, R 0·049 for No 11485, and as a chloroform disolvate, triclinic, P-1 a 22·584(9), b 13·979(2), c 13·892(2) A, α 68 ·99(2), β 77·31(3), γ 75·65(3)°, Z = 2, R 0·041 for No 8701. An unsolvated AgI complex, monoclinic, P 21/c, a 25·26(1), b 12·506(5), c 25·228(9) A, β 113·54(4)°, Z = 4 tetramers, R 0·054 for No 5520, isomorphous with previously recorded [IAg(PPh3)]4 (denoted ‘α’), was obtained from methanol/saturated potassium iodide solution, while a second ‘β’-form obtained from 2,4,6-trimethylpyridine, rhombohedral R3c, a 17·048(7) A, α 61·15(5)°, Z = 2 tetramers, R 0·037 for No 1622, is isomorphous with previously recorded [BrAg(PPh3)]4, for which a redetermination is described (R 0·039 for No 1289); the latter has also been obtained in the common orthorhombic Pbcnarray: a 18·10(1), b 2·08(1), c 18·39(1) A, Z = 4, R 0·041 for No 2877. A new ‘step’ form of [IAg(PPh3)]4, monoclinic, C 2/c, a 26·14(2), b 16·340(9), c 18·64(2) A, β 114·04(8)°, R 0·058 for No 2107, obtained from acetonitrile and isomorphous with [BrCu(PPh3)]4 (step), is also recorded. In the far-infrared spectra of [(Ph3As)4Cu4X4] bands which have been assigned to vibrations of the Cu4X4 core are: 166, 150, 135, 114 (X = Br); 136, 85 cm-1 (X = I; 2CHCl3 solvate). The 166, 150, 135 cm-1 bands in the bromide are only partially resolved. These, and the 136 cm-1 band in the iodide are assigned to the T2 v(CuX) mode of the Cu4X4 core; the bands at 114 and 85 cm-1 are assigned to the next highest frequency T2 mode of the cluster. The splitting of the highest frequency T2 band for the bromide is consistent with the greater degree of distortion of the Cu4X4core from ideal Td symmetry in this complex relative to the iodide.

Stereoselective Cyclopropanation Reactions

Abstract: Organic chemists have always been fascinated by the cyclopropane subunit.1 The smallest cycloalkane is found as a basic structural element in a wide range of naturally occurring compounds.2 Moreover, many cyclopropane-containing unnatural products have been prepared to test the bonding features of this class of highly strained cycloalkanes3 and to study enzyme mechanism or inhibition.4 Cyclopropanes have also been used as versatile synthetic intermediates in the synthesis of more functionalized cycloalkanes5,6 and acyclic compounds.7 In recent years, most of the synthetic efforts have focused on the enantioselective synthesis of cyclopropanes.8 This has remained a challenge ever since it was found that the members of the pyrethroid class of compounds were effective insecticides.9 New and more efficient methods for the preparation of these entities in enantiomerically pure form are still evolving, and this review will focus mainly on the new methods that have appeared in the literature since 1989. It will elaborate on only three types of stereoselective cyclopropanation reactions from olefins: the halomethylmetal-mediated cyclopropanation reactions (eq 1), the transition metal-catalyzed decomposition of diazo compounds (eq 2), and the nucleophilic addition-ring closure sequence (eqs 3 and 4). These three processes will be examined in the context of diastereoand enantiocontrol. In the last section of the review, other methods commonly used to make chiral, nonracemic cyclopropanes will be briefly outlined.

Atroposelective Synthesis of Axially Chiral Biaryl Compounds

Abstract: A rotationally hindered and thus stereogenic biaryl axis is the structurally and stereochemically decisive element of a steadily growing number of natural products, chiral auxiliaries, and catalysts. Thus, it is not surprising that significant advances have been made in the asymmetric synthesis of axially chiral biaryl compounds over the past decade. In addition to the classic approach (direct stereoselective aryl-aryl coupling), innovative concepts have been developed in which the asymmetric information is introduced into a preformed, but achiral-that is, symmetric or configurationally labile-biaryl compound, or in which an aryl--C single bond is stereoselectively transformed into an axis. This Review classifies these strategies according to their underlying concepts and critically evaluates their scope and limitations with reference to selected model reactions and applications. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed.