Christopher S. Frampton

An NMR spectroscopic and EHMO investigation of cationic mixed metal clusters: X-ray crystal structure of (1,7,7-trimethyl-μ2-2-propynylnorbornene)-bis(cyclopentadienyl)tetracarbonyldimolybdenum

Abstract The reaction of (C 5 H 5 ) 2 Mo 2 (CO) 4 with 2- endo -propynylborneol yields the tetrahedral cluster (R ★ Cue5fcCMe)Mo 2 (CO) 4 (C 5 H 5 ) 2 ( 7 ), where R ★ is the 2-norbornenyl group. This chiral molecule crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with a 8.938(4), b 14.074(4), c 19.510(6) A, V 2268(1) A 3 , D c 1.65 g cm −3 , D m 1.64 g cm −3 , for Z = 4, and R 1 = 0.0290 ( R 2 = 0.0276) for 4350 unique reflections ( R 1 = 0.0236, R 2 = 0.0245 for 3846 reflections with I > 2.5σ( I )). Protonation of 7 and of the related dicobalt cluster (2- endo -propynylborneol)Co 2 (CO) 6 leads to metal stabilized cations which maintain their terpenoid skeletons and are stable towards carbocationic rearrangement. Protonation of the mixed metal clusters (C 5 H 4 Me)W(CO) 2 Co(CO) 3 (HCue5fcCCH 2 OH), (C 5 H 5 )Mo(CO) 2 Co(CO) 3 (HCue5fcCCH 2 OH), and (C 5 H 5 )Mo(CO) 2 Co(CO) 3 (HCue5fcCHEtOH) yields the corresponding cationic clusters [M-Co(CO) 3 (HCue5fcCCR 2 )] + . High field NMR spectroscopy reveals that the capping vinylidene moiety leands preferentially towards one vertex and the facile antarafacial migration which is observed in the homometallic complexes [M-M(HCue5fcCCH 2 )] + (M = Co(CO) 3 , (C 5 H 5 )Mo(CO) 2 or (C 5 H 5 )W(CO) 2 ) has a very high barrier in these mixed metal systems. Variable-temperature NMR studies on the mixed trimetallic cluster cation [(C 5 H 5 )Mo(CO) 2 Co 2 (CO) 6 CC(CH 3 ) 2 ] + confirm that the carbocationic centre is better stabilized on the molybdenum vertex rather than by the tricarbonylcobalt fragment. These results are supplemented by EHMO calculations which demonstrate not only that the positive charge is better tolerated at the (C 5 H 5 )Mo(CO) 2 vertex but also that the transition state for antarafacial migration is strongly disfavored.

Blue luminescence in yttrium and gadolinium niobates caused by bismuth. The importance of non-bonding ns2 valence orbital electrons

A blue luminescent emission band (440xa0nm) has been optimised in Y1 – xBixNbO (x = 0.005) for low voltage phosphor applications. The material has useful properties when compared to a commercially available phosphor. The role of the Bi3+ ion dopant is discussed in this lattice and in the related Gd1 – xBixNbO4 lattice. The movement of the emission band with %Bi3+ is rationalised using a simple electronic band structure model. It is demonstrated that the nature (symmetry) of the chemical environment of the Bi3+ is important for the influence of the cation on the luminescent properties.

Synthesis and redox studies on ruthenium and osmium complexes with primary and secondary phosphines. Single-crystal structures of trans-[RuCl2(PPhH2)4] and trans-[OsCl2(PPh2H)4]·CH2Cl2

Reaction of RuCl3·3H2O or [NH4]2[OsCl6] with 5–7 molar equivalents of PR2H (R = Ph or C6H11) or PPhH2 in degassed refluxing EtOH solution (or EtOH–water for Os) gave [MCl2(PR2H)4] and [MCl2(PPhH2)4] in high yield as yellow solids. Ultraviolet-visible and 31P NMR spectroscopic studies confirm that these species exist as trans isomers in solution and the integrity of the PH functions. Prolonged standing of trans-[RuCl2(PPh2H)4] in CH2Cl2 solution led to partial isomerisation to the cis isomer as confirmed by 31P NMR spectroscopy. The crystal structure of trans-[RuCl2(PPhH2)4] has been determined. It confirms a trans arrangement of the Cl– ligands with the RuII occupying a crystallographic inversion centre with four precisely coplanar equatorial PPhH2 ligands. Ru–Cl 2.422(3), Ru–P(1) 2.319(3) and Ru–P(2) 2.318(3)A. The lower steric demands of the PPhH2 ligands compared to PPh2H are reflected in the more regular octahedral arrangement seen in trans-[RuCl2(PPhH2)4] compared to trans-[RuCl2(PPh2H)4]·0.5CHCl3. The crystal-structure determination of trans-[OsCl2(PPh2H)4]·CH2Cl2 showed two independent half molecules in the asymmetric unit with each OsII occupying an inversion centre and co-ordinated to a trans arrangement of two Cl– and four PPh2H ligands. Os(1)–Cl 2.448(2), Os(2)–Cl 2.443(2), Os(1)–P 2.357(2), 2.349(2), Os(2)–P 2.355(2), 2.333(2)A. With the exception of [RuCl2(PPhH2)4](irreversible), cyclic voltammetric studies on the complexes trans-[MCl2(PR2H)4] and trans-[MCl2(PPhH2)4] show a reversible oxidation in each case, which is assigned to a MII–MIII redox couple.

Synthesis, structures and redox properties of platinum metal phosphathia complexes: crystal structures of cis-[RuCl2(RSC2H4SR)]·0.75Et2O and cis-[RhCl2(RSC2H4RS)]PF6·CH2Cl2(R = Ph2PCH2CH2)

Reaction of[RuCl2(py)4](py = pyridine) with 1 molar equivalent of the new tetradentate acyclic phosphathia compound RSC2H4SR (Ph2PCH2CH2SCH2CH2SCH2CH2PPh2) or the macrocycle meso-Ph2[14]aneP2S2(4,8-diphenyl-1,11-dithia-4.18-diphosphacyclotetradecane) in refluxing toluene under a nitrogen atmosphere afforded the ruthenium(II) complexes [RuCl2(RSC2H4SR)] and [RuCl2(Ph2[14]aneP2S2)] respectively as as yellow solids. The crystal structure of [RuCl2(RSC2H4SR)]·0.75Et2O shows RSC2H4SR co-ordinated via all four donor atoms with the two P-donors occupying mutually trans co-ordination sites at RuII, and cis-dichlorides completing the overall octahedral stereochemistry, Ru–S 2.294(1), 2.292(1), Ru–P 2.339(2), 2.335(2), Ru–Cl 2.463(1), 2.463(1)A. Phosphorus-31 NMR spectroscopic studies on the macrocyclic species [RuCl2(Ph2[14]aneP2S2)] are consistent with a cis-dichloro isomer in which one Cl is trans to P and the other trans to S. Cyclic voltammetry showed a reversible one-electron oxidation occurring at E½=+0.16 and +0.32 V vs. ferrocene–ferrocenium for [RuCl2(RSC2H4SR)] and [RuCl2(Ph2[14]aneP2S2)] respectively. The complexes [MCl2(RSC2H4SR)]PF6(M = Rh or Ir) have also been prepared. The structure of [RhCl2(RSC2H4SR)]PF6·CH2Cl2 shows discrete [RhCl2(RSC2H4SR)]+ cations adopting a very similar arrangement to that in the ruthenium(II) analogue, with Rh–P 2.352(2), 2.342(2), Rh–S 2.303(2), 2.297(2), Rh–Cl 2.370(2), 2.359(2)A. Rhodium-103 NMR spectroscopy reveals a triplet at δ+ 1405 (JRhP 85 Hz).

A potential iron pharmaceutical composition for the treatment of iron-deficiency anaemia. The crystal and molecular structure of mer-tris-(3-hydroxy-2-methyl-4H-pyran-4-onato)iron(III)

mer-Tris(3-hydroxy-2-methyl-4H-pyran-4-onato)iron(III) has potential use in the treatment of iron-deficiency anaemia. It displays the ideal properties that a new iron chelation complex must possess to be an effective treatment. These properties are discussed. The crystal and molecular structure of this complex has been determined from single-crystal X-ray diffraction data and refined by least squares to R= 0.0649 for 2 735 independent reflections. The compounds crystallizes in the monoclinic space group P21/c with cell dimensions a= 7.369(1), b= 14.720(3), and c= 19.964(5)A, β= 100.41(2)°, and Z= 4. The iron atom lies in a distorted octahedral environment with the three ligands bonded through the hydroxy and ketone oxygen atoms to give the mer configuration. Variable-temperature 57Fe Mossbauer data for the complex are reported and the results are discussed in relation to the structure.

β-Hydroquinone xenon clathrate

3C 6 H 4 (OH) 2 .xXe (x=0,866) cristallise dans R 3 avec affinement jusqua 0,0242. Latome Xe est situe dans une cavite quasiment spherique constituee de six molecules dhydroquinone reliees par liaison hydrogene

The synthesis of water soluble decalin-based thiols and S-nitrosothiols—model systems for studying the reactions of nitric oxide with protein thiols

The syntheses of three decalin-based tert-thiols displaying varying degrees of solubility in aqueous milieu are described. The S-nitroso derivatives of these compounds have also been prepared and the structures of two of these determined by single crystal X-ray diffraction. These compounds have been designed for studying the interaction of nitric oxide (NO) with thiols under physiological conditions.

A new procedure for the reduction of α,β-unsaturated pyrrolidinones to 2H-pyrroles and 1H-pyrroles based on initial activation by N-nitrosation

A new two step procedure is developed for the half-reduction of lactams to cyclic imines and enamines. N-Nitrosation using dinitrogen tetroxide furnishes N-nitroso lactams, which undergo chemoselective 1,2-reduction to N-nitroso carbinolamines by one equivalent of hydride delivered from lithium triethylborohydride. The nitroso group is cleaved in a novel way using samarium(II) iodide and dehydration then generates the corresponding imine (which may tautomerise to the isomeric enamine). The reduction can be performed in the presence of esters and has proved efficient for the preparation of 2H-pyrroles (pyrrolenines) and 1H-pyrroles relevant to the study of tetrapyrrole biosynthesis.

n-Dodecylammonium Chloride

The redetermination of the structure of C 12 H 28 N + .Cl - corroborates and complements the limited data of a prior less accurate study. The structure consists of C 12 H 28 N + chains arranged head-to-tail in layers between layers of Cl- ions.

Ferrocenyl ligands-III. Bulky ferrocenyl derivatives. 1,1′-Bis(diphenylphosphino)-3,3′-bis(trimethylsilyl)ferrocene. Synthesis, metal complexation and the crystal and molecular structure

Abstract The attempted syntheses of ferrocenyl phosphines with bulky substituents are reported using N,N,N′,N′-tetramethylethylenediamine (TMED)/BuLi metallation reactions. 1,1′-3,3′-Tetrakis(trimethylsilyl)ferrocene was prepared by this route and also the title compound I. Attempts to prepare 1,1′-bis(triorganotin)3,3′-bis(trimethylsilyl)-ferrocenes failed. Only one of the two diastereomeric forms of I was obtained, indicating a regiospecific metallation of the precursor 1,1′-bis(trimethylsilyl)ferrocene. A single crystal X-ray study of this isomer is presented and its structure showed a cisoid disposition of the PPh2 groups. This results in a through-space interaction of the two phosphorus atoms as revealed by long range phosphorus-carbon coupling in the 13C NMR spectrum of I. A preliminary study of some metal complexes of I is also included together with 31P NMR and 57Fe Mossbauer spectroscopic data.