Timothy E. Burrow

The signal/noise of an HMBC spectrum can depend dramatically upon the choice of acquisition and processing parameters

The effect of various acquisition and processing parameters on the sensitivity of HMBC spectra for typical organic molecules has been systematically investigated. For molecules in the 200–600 molecular weight range, an acquisition time of 0.2 to 0.4 s, a recycle time of no more than 1.0 s, optimization for nJCH = 8 Hz and 512 time increments (with two‐ to fourfold linear prediction) are recommended. Some form of sine bell weighting along f2 and either Gaussian or sine bell weighting along f1 is suggested. The use of a 0.1‐s acquisition time and/or Gaussian or exponential weighting along f2 can result in dramatic sensitivity loss, particularly for correlation peaks involving protons with complex splitting patterns, and should be avoided. Copyright

Hydride complexes of molybdenum and tungsten in a sulphur environment

Abstract The known methods of preparation of the title complexes are reviewed. The preparation, structure and reactions of new monohydride complexes containing bulky thiolate ligands are then described: [MH(SR)3(PMe2Ph)2] (I) and [MoH(SR)3(PR′Ph2)] (II) (M = Mo or W ; R = C6H2Me3-2,4,6 or C6H2iPr3-2,4,6; R′= Me or Et). Complexes I have an unusual structure with the hydride capping a face of a distorted trigonal bipyramid defined by equatorial thiolates and axial phosphines. A significant discovery is that the hydrides of these complexes of molybdenum(IV) (II) and tungsten(IV) (I) and (II) undergo 1H/2H exchange with 2H2. Complexes I react with ligands L = py or P(OR′)3 to give [MH(SR)3(PMe2Ph)(L)], and with CO to give [M(SR)2(CO)2(PMe2Ph)2].

Cleavage of an aryl carbon–sulphur bond in hydride–thiolate complexes of molybdenum(IV); X-ray crystal structure of [{Mo(SC6H2Pri3-2,4,6)(OMe)(PMePh2)}2(µ-S)2]

The complexes [MoH(SC6H2R3-2,4,6)3(PR′Ph2)]1(R = Me or Pri; R′= Me or Et) in THF–MeOH decompose via cleavage of an aryl carbon–sulphur bond to give C6H3R3-2,4,6 and complexes [{Mo(SC6H2R3-2,4,6)(OMe)(PR′Ph2)}2(µ-S)2], 3, one of which (R = Pri, R′= Me) has been characterized by single crystal X-ray diffraction.

CRAPT: an improved version of APT with compensation for variations in JCH

A modified version of the attached proton test (APT) sequence for 13C spectral editing, which we call CRisis‐APT (CRAPT), is developed and tested on representative organic compounds. CRAPT incorporates 13C compensation for refocusing inefficiency with synchronized inversion sweeps (CRISIS) pulses in combination with 1H broadband inversion pulses to give improved compensation for variations in 1JCH along with improved refocusing efficiency. It is shown that CRAPT gives edited 13C spectra with only small losses in sensitivity (between 8% and 15% for strychnine, 1, menthol, 2, cholecalciferol, 3, and isotachysterol, 4), compared with basic 13C spectra obtained on the same compounds. CRAPT also gives significantly better signal/noise than DEPTQ for nonprotonated carbons. Therefore, we conclude that CRAPT is an improvement over APT or DEPTQ or a combination of DEPT135 with a full 13C spectrum for routine 13C spectral editing of organic compounds. Copyright

Distortions in six-co-ordinate complexes of molybdenum(II) and tungsten(II). Crystal structures of mer-[Mo(SC6H2Pri3-2,4,6)2(CO)3(PMePh2)], cis,cis,cis-[W(SC6H2Me3-2,4,6)2(CO)2-(PMe2Ph)2] and [W(SeC6H3Pri2-2,6)2(CO)2(PMe2Ph)2]

The red, diamagnetic complexes mer-[Mo(SC6H2 Pri3-2,4,6)2(CO)3(PMePh2)]1 and [Mo(SC6H2Pri3-2,4,6)2(CO)2(PMePh2)2]2 have been prepared by reaction of [MoH(SC6H2Pri3-2,4,6)3(PMePh2)] with CO in tetrahydrofuran. The crystal structure of 1 shows it to have a distorted octahedral geometry with mer-CO ligands [d(Mo–S) 2.380(1) and 2.366(1); d(Mo–C) 2.030(5), 2.026(4) and 2.066(5); d(Mo–P) 2.561(1)A; large S–Mo–S angle of 116.0°]. Reaction of CO with [WH(SC6H2Me3-2,4,6)3(PMe2Ph)2] in toluene gives green, distorted octahedral cis,cis,cis-[W(SC6H2Me3-2,4,6)2(CO)2(PMe2Ph)2]3[d(W–S) 2.379(2) and 2.385(2); d(W–C) 1.967(7) and 1.991(8); d(W–P) 2.556(2) and 2.507(2)A]. Reaction with [WH(SeC6H3Pri2-2,6)3(PMe2Ph)2] gives burgundy, trigonal prismatic [W(SeC6H3Pri2-2,6)2(CO)2(PMe2Ph)2]4[d(W–Se) 2.506(1) and 2.583(1); d(W–C) 1.942(8) and 1.943(8); d(W–P) 2.467(2) and 2.471(2)A]. The physical properties of 1–4 and the structures of 1, 3 and 4 are discussed in terms of their distortions from regular octahedral or trigonal-prismatic geometries. A method of classifying such structures is proposed.

Reactions of the hydridethiolate complexes [MH(SC6H2R3-2,4,6)3(PMe2Ph)2](M = Mo or W, R = Me or Pri): X-ray crystal structures of [M(SC6H2Pri3-2,4,6)2(CO)2(PMe2Ph)2](M = Mo or W)

Reaction of the complexes [MH(SC6H2R3-2,4,6)3(PMe2Ph)2]1(M = Mo or W, R = Me or Pri) with neutral ligands L causes phosphine displacement to give the series [MH(SC6H2R3-2,4,6)3(PMe2Ph)L]2[L = R′C5H4N, P(OR″)3 or MeCN; R′= H, 2-, 3- or 4-Me, R″= Me or Et]. Deuterido-analogues were also prepared. Reaction with CO caused hydride and thiolate displacement to give the compounds [M(SC6H2R3-2,4,6)2(CO)2(PMe2Ph)2] which have different geometries depending upon R. The X-ray crystal structure analyses of [M(SC6H2Pri3-2,4,6)2(CO)2(PMe2Ph)2]3(M = Mo or W) show them to have essentially trigonal prismatic structures with trigonal faces made from C(O), P and S atoms. The structures and fluxional properties of the carbonyl derivatives and of compounds 2 in solution have been studied by NMR spectroscopy. On treatment with 2H2 at 1 atm, compounds 1 in solution undergo H/2H exchange of the hydride ligand; the reaction is more effective for M = W than for M = Mo.

1H and 13C NMR spectra of (2′S,4′S)-lysergic acid 2,4-dimethylazetidide (LSZ)

First reported (online early view): 6 Jun 2016 in: S.D. Brandt, P.V. Kavanagh, F. Westphal, S.P. Elliott, J. Wallach, T. Colestock, T.E. Burrow, S.J. Chapman, A. Stratford, D.E. Nichols, A.L. Halberstadt. Return of the lysergamides. Part II: Analytical and behavioural characterization of N6-allyl-6-norlysergic acid diethylamide (AL-LAD) and (2′S,4′S)-lysergic acid 2,4-dimethylazetidide (LSZ). Drug Test. Analysis 2017, 9 (1), 38–50 https://doi.org/10.1002/dta.1985

Cleavage of an aryl carbon?sulfur bond in hydride?thiolate complexes of molybdenum and tungsten. Crystal structures of [{Mo(SC6H2Pri 3-2,4,6)(OMe)(PMePh2)}2(-S)2] and [{Mo(SC6H2Pri 3-2,4,6)(OEt)(PEtPh2)}2(-S)2]

The complexes [MoH(SC6H2Pri3-2,4,6)3(Pr1Ph2)]1(R1= Me or Et) in tetrahydrofuran (thf)–R2OH decomposed via cleavage of an aryl carbon–sulfur bond to give C6H3Pri3-1,3,5 and the complexes [{Mo(SC6H2Pri3-2,4,6)(OR2)(PR1Ph2)}2(µ-S)2]2(R2= Me or Et). Compounds 2a(R1= R2= Me) and 2b(R1= R2= Et) have been structurally characterised by X-ray diffraction and shown to be dimers with (µ-S)2 bridging ligands derived from the thiolate ligands of the precursor complexes. The arene produced in these reactions has been detected by 2H NMR spectroscopy and by GC–mass spectrometry; C6H2(2H)Pri3-1,3,5 was observed from [MoH(SC6H2Pri3-2,4,6)3(PR1Ph2)] in thf–MeO2H. The thermal reactivity of the complex [WH(SC6H2Me3-2,4,6)3(PMe2Ph)2]3 was studied by combined TGA–mass spectrometry. The temperature for TGA started at 50 °C and was increased at 3° min–1 until 500 °C. Three events were seen at 200, 260 and 320 °C. At each, mesitylene, the hydrodesulfurisation product, was the major species detected by mass spectrometry; PMe2Ph was also detected during the first event and HSC6H2Me3-2,4,6 during the second and third events at low levels.

Monohydride complexes of molybdenum(IV) and tungsten(IV) containing bulky thiolate ligands: X-ray crystal structures of [MH(SC6H2PrI3-2,4,6)3(PMe2Ph)2], M = Mo or W

The complexes [MH(SC6H2R3-2,4,6)3(PMe2Ph)2]1(M = Mo or W, R = Me or Pri) and their deuterio analogues have been prepared. The X-ray structures of 1(M = Mo or W, R = Pri) have been determined, showing the overall geometry in both to be based on a distorted trigonal-bipyramidal arrangement of thiolates with the phosphines essentially trans to each other. The hydride ligand could not be located by X-ray diffraction in either structure, but its presence is established by spectroscopic studies. The preparation of [MoBr(SPh)3(PMe2Ph)2] is also described.