Near neighbour ligand hyperfine splittings in the e.p.r. spectra of copper(II) complexes

X-band e.p.r. spectra from mixed ligand complexes Cu(btc)-(Hy), Cu(TPA)(Hy) and Cu(Sal)(TPA), have been derived from the spectra of suitable reaction mixtures in CHCl₃ at 25° C (Sal⁻ = salicyladehydate, TPA⁻ = thiopicolineanilide, Hy⁻ = 8-hydroxyquinolinate and btc⁻ =N-benzoyl-N′N′-diethylcarbamide). A digital data acquisition instrument and a personal computer were used for this purpose. The¹⁴N hyperfine splittings observed in these complexes have shown that the observed increase in spin density on the coordinating atoms of one ligand, at the expense of that on the other, is unlikely to be associated with the covalent bonding involving metal d _x ²− _y ²-orbital. Covalent bonding involving metal 4s-orbital component of the unpaired electron orbital has been suggested to be responsible for the observed changes in electron delocalization. This work was carried out during the visit of Drs Z. R. Baratova and P. M. Solozhenkin to India in 1991.     

Structural and spectroscopic studies of nickel(II) complexes with a library of Bis(oxime)amine-containing ligands

A library of tripodal amine ligands with two oxime donor arms and a variable coordinating or noncoordinating third arm has been synthesized, including two chiral ligands based on l-phenylalanine. Their Ni(II) complexes have been synthesized and characterized by X-ray crystallography, UV-vis absorption, circular dichroism, and FTIR spectroscopy, mass spectrometry, and room-temperature magnetic susceptibility. At least one crystal structure is reported for all but one Ni/ligand combination. All show a six-coordinate pseudo-octahedral coordination geometry around the nickel center, with the bis(oxime)amine unit coordinating in a facial mode. Three distinct structure types are observed: (1) for tetradentate ligands, six-coordinate monomers are formed, with anions and/or solvent filling out the coordination sphere; (2) for tridentate ligands, six-coordinate monomers are formed with Ni(II)(NO(3))(2), with one monodentate and one bidentate nitrate filling the remaining coordination positions; (3) for tridentate ligands, six-coordinate, bis(mu-Cl) dimers are formed with Ni(II)Cl(2), with one terminal and two bridging chlorides filling the coordination sphere. The UV-vis absorption spectra of the complexes show that the value of 10 Dq varies according to the nature of the third arm of the ligand. The trend based on the third arm follows the order alkyl/aryl < amide < carboxylate < alcohol < pyridyl < oxime.     

Anion control over interpenetration and framework topology in coordination networks based on homoleptic six-connected scandium nodes

Reaction of ScX3 (X=NO3-, CF3SO3-, ClO4-) with 4,4'-bipyridine-N,N'-dioxide (L) affords topologically distinct six-connected three-dimensional coordination frameworks, {[Sc(L)3](NO3)3}(infinity) (1), {[Sc(L)3](CF3)SO3)3(CH3OH)2.7(H2O)3}(infinity) (2), {[Sc(L)3](ClO4)3}(infinity) (3) and {[Sc(L)4(H2O)2](ClO4)3}(infinity) (4). Compounds 1, 2 and 3 are networks based on octahedrally co-ordinated ScO6 centres bound through six oxygen atoms from six separate N-oxide ligands L. Compounds 1 and 3 are doubly interpenetrated and have alpha-polonium-type structures of 4(12)6(3) topology based upon three intersecting (4,4) nets. The structure of 2 is unusual and shows parallel, co-planar layers of (4,4) nets connected in a criss-crossed fashion to afford a new 4(8)6(6)8 topology. In 4 only four ligands L bind to each Sc(III) centre with two additional water molecules bridging metal nodes. Significantly, the bridges formed by L do not sit in a plane and if connections through L are considered alone the resultant structure is a diamondoid array typically based upon a tetrahedral connecting node at Sc. Five interpenetrating diamondoid networks are observed that are cross-bridged by water molecules to form a single three-dimensional array of 4(8)6(7) topology. Compound 4 can also be viewed as incorporating two intersecting (4,4) grids based upon two ligands L and two bridging waters. Thus, variation of anion, solvent and conditions critically affects the structures of products formed, and the series of polymers reported herein illustrates how tectons based upon (4,4) grids can be combined and distorted to form non-NaCl topologies and even cross-bridged, multiply interpenetrated diamondoid materials. Both compounds 2 and 4 represent unusual examples of self-penetrated coordination frameworks.     

Stereochemistry of cyclopropane formation involving group IV organometallic complexes

The reaction of (Z)-HDC=CHCH(OCH(3))C(6)H(5) (1) with Cp(2)Zr(D)Cl followed by BF(3).OEt(2) gave phenylcyclopropanes 3a and 3b, both having cis deuterium. This stereochemical outcome requires inversion of configuration at the carbon bound to zirconium and is consistent with a "W-shaped" transition state structure for cyclopropane formation. In a Kulinkovich hydroxycyclopropanation, trans-3-deutero-1-methyl-cis-2-phenyl-1-cyclopropanol (5) was formed stereospecifically from Ti(O-i-Pr)(4), ethyl acetate, EtMgBr, and trans-beta-deuterostyrene. This stereochemistry requires retention of configuration at the carbon bound to titanium and is consistent with frontside attack of the carbon-titanium bond on a carbonyl group coordinated to titanium. In a de Meijere cyclopropylamine synthesis, a 3:1 mixture of N,N-dimethyl-N-(trans-3-deutero-trans-2-phenylcyclopropyl)amine (6a) and N,N-dimethyl-N-(cis-3-deutero-cis-2-phenylcyclopropyl)amine (6b) was formed from Ti(O-i-Pr)(4), DMF, Grignard reagents, and trans-beta-deuterostyrene. This stereochemistry requires inversion of configuration at the carbon bound to titanium and is consistent with a W-shaped transition structure for ring closure.     

An ESR investigation of triple ions derived from 1,2,4,5-tetramesitoylbenzene

Stable triple ions were obtained in MTHF solution from the ion pairs of 1,2,4,5-tetramesitoylbenzene (TMB) radical anion and alkali metal cations by reaction with soluble alkali metal salts. Their ESR spectra are highly resolved. MO calculations with parameters which lead to spin density values as nearly as possible equal to the experimental ones allow estimates of the oxygen-metal distances. The relatively most stable triple ions are the ones with the smallest estimated oxygen metal distances.     

Synthesis of Mono- and Di-Deuterated (2S, 3S)-3-Methylaspartic Acids to Facilitate Measurement of Intrinsic Kinetic Isotope Effects in Enzymes

Kinetic isotope effects provide a powerful method to investigate the mechanisms of enzyme-catalyzed reactions, but often other slow steps in the reaction such as substrate binding or product release suppress the isotopically sensitive step. For reactions at methyl groups, this limitation may be overcomed by measuring the isotope effect by an intra-molecular competition experiment. This requires the synthesis of substrates containing regio-specifically mono- or di-deuterated methyl groups. To facilitate the mechanistic investigations of the adenosylcobalamin-dependent enzyme, glutamate mutase, we have developed a synthesis of mono- and di-deuterated (2S,3S)-3-methylaspartic acids. Key intermediates are the correspondingly labeled mesaconic acids and their dimethyl esters that potentially provide starting materials for a variety of isotopically labeled molecules.     

Macrobicyclic aminals

The synthesis of Schiff base macrocycles in the absence of templating cations and in non-protic and non-coordinating solvent media is reported. The reaction of pyridine-2,6-dicarboxaldehyde with the diamines 1,2-bis(2-aminophenoxy) ethane and 1,4-bis(2-aminophenoxy) butane has been found to give the corresponding macrobicyclic aminals. The chemical properties of the aminals are reported together with a preliminary study of their metal complexation reactions. The X-ray crystal structure of the aminal derived from pyridine-2,6-dicarboxaldehyde and 1,2-bis(2-aminophenoxy) ethane has been determined and verifies the macrobicyclic nature of the product.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Fluorocarbon derivatives of nitrogen. Part 10. Preparation of heptafluoro- and 1-chlorohexafluoro-2-nitrosopropane,and conversion on the latter to chloropentafluoroacetone oxime

Details are given for the preparation of heptafluoro-2-nitrosopropane and 1-chlorohexafluoro-2-nitrosopropane $\text{via}$ the routes CF₃CFCF₂ → [with CsFR_FCO₂Ag (R_F = CF₃, nC₃F₇)] (CF₃)₂CFAg → (with NOCl) (CF₃)₂CFNO and CF₃CFCF₂ → (with CsClNOCl) CF₃(CF₂Cl)CFNO, respectively, and for conversion of the latter nitroso-compound to chloropentafluoroacetone oxime $\text{via}$ reduction with aqueous potassium hydrogen sulphite.     

High-Resolution electron impact mass spectrometry of five novel organoiron complexes

The high resolution mass spectra of five novel η¹-R substituted Fe(II)(CO)₂ η⁵-C₅H₅ complexes are reported. Fragmentation behavior common to all the studied compounds is noted, as well as some ligand-specific fragmentation. Fragment ions associated with ligand recoordination, ligand substituent transfer and inter-ligand bond formation are noted. The role of the electron density around the metal center, and in particular the ‘18-electron’ configuration, on the fragmentation of these compounds is discussed.