Kirsty M. Anderson

A phase transition in the novel three-dimensional compound [Eu2(mal)3(H2O)6](H2mal=malonic acid)

Slow diffusion of aqueous solutions of europium(III) chloride into gel of sodium metasilicate containing malonic acid (H2mal) yields single crystals of the three-dimensional compound of formula [Eu2(mal)3(H2O)6] whose structure was determined by X-ray diffraction methods at 293 and 173 K. It crystallizes in the monoclinic system but the spatial group changes from I2/a in the high temperature range (293 ≥ nT n≥ 236 K) to Ia in the low temperature range (T < 236 K). In both cases, nine oxygen atoms forming a distorted monocapped square antiprism surround the Eu3+ ions. The structure at 293 K consists of a three-dimensional arrangement of triaquaeuropium(III) units bridged by malonate groups which result from cross-linking of the single chains running parallel to the c axis and the double zig-zag chains which grow in the ab plane. At low temperature the structure of the compound can be visualised as chains of europium(III) ions linked through two of the three crystallographically independent malonate ligands, whose chains run parallel to the b axis and a second family of chains (along the c axis) through the third independent malonate ligand forming a three-dimensional network. In both the crystal structure is stabilised through extensive hydrogen bonding involving carboxylate and water molecules. Studies of the magnetic behaviour, spectroscopic, thermogravimetric and calorimetric characteristics of [Eu2(mal)3(H2O)6] are reported. Laser-excited site selective spectroscopy shows a unique crystal-field site for EuIII ions in the crystal at room temperature and down to 236 K. However, below this temperature, two different sites are clearly identified, in agreement with a change in the crystal structure.

The Azomethine Ylid Strategy in β-Lactam Synthesis. Application to Selenapenams

Abstract Using azomethine ylid reactivity available from the β-lactam-based oxazolidinone 1 , selenoketones 6a – e react as 1,3-dipolarophiles to give racemic selenapenams 7a – e in a single step. The cycloaddition sequence proceeds with complete control of regiochemistry and the thermodynamically more stable C (3)/ C (5) relationship is observed. The selenothiocarboxylate 9a and the selenocarboxylate 9b also function as effective dipolarophiles, but attempts to convert the resulting cycloadducts 10a and 10b to the corresponding selenapenems were unsuccessful. Other selenium-containing dipolarophiles failed to give characterizable cycloadducts.

SYNTHESIS OF 3-HYDROXY AND 3-AMINO 2-SUBSTITUTED N-HETEROCYCLES VIA ENAMINE OXIDATION AND AZIRIDINATION

Reaction of the N -sulfonyl heterocyclic enamines ( 1a/b ) under asymmetric epoxidation and dihydroxylation reaction conditions leads to 2,3-dihydroxypyrrolidines and piperidines, ( 2a ) and ( 2b ). Only diols are observed under aminohydroxylation conditions, but Mn-mediated aziridination of ( 1a ) provides a route to the 3-amino-2-methoxypyrrolidine derivatives ( 6 ) and ( 7 ).

Solid state and solution structures of rhodium and iridium poly(pyrazolyl)borate diene complexes

The structures adopted by a range of poly(pyrazolyl)borate complexes [ML2Tp(x)] [M = Rh, Ir; L2 = diene; Tp(x) = Bp {dihydrobis(3,5-dimethylpyrazolyl)borate}, Tp {hydrotris(3,5-dimethylpyrazolyl)borate}, Tp {hydrotris(pyrazolyl)borate}, B(pz)4 {tetrakis(pyrazolyl)borate}] have been investigated. Low steric hindrance between ligands in [Rh(eta-nbd)Tp] (nbd = norbornadiene), [Rh(eta-cod)Tp] (cod = cycloocta-1,5-diene) and [Rh(eta-nbd)Tp] results in K3 coordination of the pyrazolylborate but [M(eta-cod)Tp] (M = Rh, Ir) are kappa2 coordinated with the free pyrazolyl ring positioned above and approximately parallel to the square plane about the metal. All but the most sterically hindered Tp(x) complexes undergo fast exchange of the coordinated and uncoordinated pyrazolyl rings on the NMR spectroscopic timescale. For [Rh(eta-cod){B(pz)4}], [Rh(eta-dmbd)Tp] (dmbd = 2,3-dimethylbuta-1,3-diene) and [Rh(eta-cod)Tp(Ph)] {Tp(Ph) = hydrotris(3-phenylpyrazolyl)borate} the fluxional process is slowed at low temperatures so that inequivalent pyrazolyl rings are observed. The bonding modes of the Tp ligand (but not of other pyrazolylborate ligands) can be determined by 11B NMR and IR spectroscopy. The 11B chemical shifts (for a series of Tp complexes) show the general pattern, kappa3 < -7.5 ppm < kappa2 and the nu(BH) stretch kappa3 > 2500 cm(-1) > kappa2. The electrochemical behaviour of the pyrazolylborate complexes is related to the degree of structural change which occurs on electron transfer. One-electron oxidation of complexes with Tp, Tp and B(pz)4 ligands is generally reversible although that of [Ir(etacod)Tp] is only reversible at higher scan rates and that of [Ir(eta-cod){B(pz)4}] is irreversible. Of the complexes with the more sterically hindered Tp(Ph) ligand, only [Rh(eta-nbd)Tp(Ph)] shows any degree of reversible oxidation. The ESR spectra of a range of Rh(II) complexes show coupling to both 14N and 103Rh nuclei in most cases but what appears to be coupling to rhodium and one hydrogen atom, possibly a hydride ligand, for the oxidation product of [Rh(eta-nbd)Tp(Ph)].

The synthesis of [FeRu(CO)2(μ-CO)2(η-C5H5)(η-C5Me5)] and convenient entries to its organometallic chemistry

The synthesis, fluxionality and reactivity of the heterobimetallic complex [FeRu(CO)2(μ-CO)2(η-C5H5)(η-C5Me5)] n (5) are described. Complex 5 exhibits enhanced photolytic reactivity towards alkynes compared to its homometallic analogues, forming the dimetallacyclopentenone complexes [FeRu(CO)(μ-CO){μ-η1:η3-C(O)CR″CR′}(η-C5H5)(η-C5Me5)] n (9, R′ n = R″ n = H; 10, R′ n = R″ n = CO2Me; 11, R′ n = H, R″ n = CMe2OH). Prolonged photolysis with diphenylethyne gives the dimetallatetrahedrane complex [FeRu(μ-CO)(μ-η2:η2-CPhCPh)(η-C5H5)(η-C5Me5)] n (17), which contains the first iron–ruthenium double bond. Complexes containing a number of organic fragments can be synthesised using 9, 10 and 11. Heating a solution of 10 gave the alkenylidene complex [FeRu(CO)2(μ-CO){μ-η1:η1-CC(CO2Me)2}(η-C5H5)(η-C5Me5)] n (23) through an unusual methylcarboxylate migration. Protonation and then addition of hydride to 9 gives the ethylidene complex [FeRu(CO)2(μ-CO)(μ-CHCH3)(η-C5H5)(η-C5Me5)] n (27) n via the ionic vinyl species [FeRu(CO)2(μ-CO)(μ-η1:η2-CHCH2)(η-C5H5)(η-C5Me5)][BF4] n (25). Compound 25 exhibits cis/trans isomerisation at room temperature. Protonation of 11 gives the allenyl species [FeRu(CO)2(μ-CO)(μ-η1:η2-CHCCMe2)(η-C5H5)(η-C5Me5)][BF4] n (30). Compound 30 exist as three isomers, two cis and one trans. The two cis isomers are shown to be interconverting by σ–π isomerisation. The solid state structures of 5, 11, 12, 17, 23, 25 and 30 were established by X-ray crystallography and are discussed.

A new synthesis of a potentially versatile ligand 2,2′-bi-(1,10-phenanthroline): crystal structure and complexation chemistry

Abstract Coupling of 2-chloro-1,10-phenanthroline with a source of Ni(0) affords the tetradentate ligand 2,2′-bi-(1,10-phenanthroline). This ligand and a resulting Ni(II) complex were characterised by X-ray crystallography.

On the relative magnitudes of cis and trans influences in metal complexes

Cis and trans influences are of similar magnitude in octahedral complexes of SnIV and SbV while the trans influence is dominant in square planar PtII (d8) and d6-ML6 cases.

Bi- and poly-metallic cyanide-bridged complexes of the redox-active cyanomanganese nitrosyl unit [Mn(CN)(PR3)(NO)(η-C5H4Me)]

Cationic nitrile complexes and neutral halide and cyanide complexes, with the general formula [MnL1L2(NO)(eta-C5H4Me)]z, undergo one-electron oxidation at a Pt electrode in CH2Cl2. Linear plots of oxidation potential, Eo, vs. nu(NO) or the Lever parameters, EL, for L1 and L2, allow Eo to be estimated for unknown analogues. In the presence of TlPF6, [MnIL(NO)(eta-C5H4Me)] reacts with [Mn(CN)L(NO)(eta-C5H4Me)] to give [(eta5-C5H4Me)(ON)LMn(mu-CN)MnL(NO)(eta5-C5H4Me)][PF6] which undergoes two reversible one-electron oxidations; DeltaE, the difference between the potentials for the two processes, differs significantly for stable cyanide-bridged linkage isomers. Novel pentametallic complexes such as [Mn[(mu-NC)Mn(CNBut)(NO)(eta5-C5H4Me)]4(OEt2)][PF6]2 and [Mn[(mu-NC)Mn(CNXyl)(NO)(eta5-C5H4Me)]4(NO3-O,O)][PF6], containing a trigonal bipyramidal and a distorted octahedral Mn(II) centre, respectively, result either from slow decomposition of the binuclear cyanide-bridged species or from the reaction of anhydrous MnI2 with four equivalents of [Mn(CN)L(NO)(eta5-C5H4Me)] in the presence of TlPF6.

Coordination complexes of the bismuth(III) thiolates Bi(SC6F5)3 and Bi(SC6Cl5)3 with pyridine ligands

The chloro-aryl bismuth thiolate Bi(SC6Cl5)3 has been prepared from the reaction between BiPh3 and the thiol HSC6Cl5 by analogy with the previously described synthesis of the fluoro-aryl species Bi(SC6F5)3. The compound Bi(SC6Cl5)3 is only sparingly soluble but can be isolated as a dmf adduct [Bi(SC6Cl5)3(dmf)2] n(dmf = nN,N-dimethylformamide) which adopts a five-coordinate square-based pyramidal geometry in which the two dmf ligands lie in the basal plane with a mutually cis configuration. Treatment of either Bi(SC6F5)3 or Bi(SC6Cl5)3 with pyridine or 2,2′-bipyridyl ligands affords the coordination complexes fac-[Bi(SC6F5)3(py)3] n(two crystalline polymorphs), fac-[Bi(SC6Cl5)3(py)3], fac-[Bi(SC6F5)3(4-pic)3] n(4-pic = 4-picoline), [Bi(SC6Cl5)3(4-pic)2], [Bi(SC6F5)3(bipy)] n(bipy = 2,2′-bipyridyl), [Bi(SC6Cl5)3(bipy)], [Bi2(SC6Cl5)6(2-pic)3] n(2-pic = 2-picoline) and [Bi(SC6F5)3(4-pic)]. Five- and four-coordinate complexes adopt square-based pyramidal and equatorially vacant, trigonal bipyramidal (disphenoidal) geometries respectively, the former having the two ligands cis to each other in the basal plane. The compound [Bi2(SC6Cl5)6(2-pic)3] contains both five- and four-coordinate mononuclear units. A salt with the formula [4-picH][(4-pic)2H][Bi3(SC6F5)11] was also isolated in which the anion contains a central bismuth bonded to five thiolate ligands with a square-based pyramidal geometry. Two cis-basal thiolates act as bridging groups to two outer bismuth centres each of which is four-coordinate with the expected disphenoidal geometry in which the bridging thiolate is in an axial position. The structure of the dinuclear arylbismuth thiolate compound [Bi2Ph2(SC6F5)4(4-pic)2] is also described. Intramolecular conformations and intermolecular associations in all structures are dominated by π–π-interactions.

Trapping highly reactive dipolarophiles. Exploiting the mechanism associated with the azomethine ylide strategy for β-lactam synthesis

Highly reactive thioaldehydes 7, which are generated transiently by thermolysis of thiosulfinates 6, are trapped using azomethine ylide (derived from the β-lactam based oxazolidinone 1) to give 2-substituted penams 8. Diethyl thioxomalonate 10 and the selenoxo analogue 13, both of which are generated transiently via a retro Diels–Alder reaction, undergo 1,3-dipolar cycloaddition reactions with 1 to give the isomeric penam 11a and isopenam 11b, and the 2,2-disubstituted selenapenam 14 respectively.