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Aldehydes react with W2(OCH2tBu)6(py)2 to give W2(μ-CHR)(O)(OCH2tBu)6(py) compounds, where R = alkyl or aryl, which, in the presence of excess pyridine, yield W2(μ-CR)(μ-O)(OCH2tBu)5(py)2 compounds and neopentanol. A relative order of rates of reductive cleavage of the CO bond is found to be aryl > alkyl, and for p-X-C6H4CHO, the rates follow the order X = CF3 > H > F > Me > OMe. Four complexes have been structurally characterized by single-crystal X-ray crystallography: W2(μ-CHcC3H5)(O)(OCH2tBu)6(py), 1; W2(μ-CH(tolyl))−(O)(OCH2tBu)6(py), 2; W2(μ-CcC3H5)(μ-O)(OCH2tBu)5(py)2, 3, and W2(μ-C(p-MeOC6H4))(OCH2tBu)5(py)2, 4. Factors influencing the reductive cleavage of the CO bond are discussed in light of earlier studies of related reactions, and most notably comparisons are made with the development of a molecular alternative to the McMurry reagent.

The photochemical reaction between W2 (OCH2 tBu) 6 and P4 has been studied by NMRspectroscopy in toluene-d8 and those reactions have been complemented by studies on the benchtop. A complex sequence of reactions is implicated by the formation of a variety of products, oneof which has been observed previously in the thermal reaction between W2 (OCH2 tBu) 6L2 whereL = py and HNMe2 and P4, namely W3 (μ3-P) (OCH2 tBu) 9, while others must arise fromdegradation of OR ligands. A new compound W4 (μ3-P) 2 (μ-OCH2 tBu) 4 (OCH2 tBu) 6 has beenisolated and characterized. Crystal data at −165°C : a = 19.955 (4) , b = 25.222 (3) , c = 12.775 (2) A, Z = 4 and space group Pcab. The centrosymmetric structure consists of adistorted rhombus of metal atoms having two different W — W edge distances 2.6938 (8) and2.7981 (8) A and a bonding W — W distance of 2.692 (1) A between the back-bone W atomsof the planar W4 butterfly. The outer or wing-tip tungsten atoms are in a square based pyramidalenvironment with respect to the PWO4 moiety with the W — P bond in the apical position. The O4 basal plane involves two terminal and two bridging OR groups. The internal or back-bonetungsten atoms are also five coordinate, P2WO3, where two bridging OR groups occupy axial andthe two W — P bonds and one W — OR terminal group occupy equatorial sites of a trigonalbipyramid. The cluster geometry is compared with those seen for W3 (μ3-X) (OR) 9, where X = CCH3 and P, W4 (OiPr) 12 and W4 (OEt) 16. The latter contains a central centrosymmetric W16+ 4cluster as does the present compound and the presence of the distorted rhomboidal geometryobserved in both is proposed to arise from a second order Jahn-Teller distortion.

W2(OR)6 compounds where RtBu and CMe2CF3, both reversibly bind pyridine in hydrocarbon solvents to form adducts W2(OR)6L2. Pyridine binds more strongly to the fluoroalkoxide but the structural parameters of the compounds W2(OCMe2CF3)6(C6H5N)2 and W2(OtBu)6(4-CH3C6H4N)2 reveal an essentially identical W2O6N2 core with W  W = 2.39(1) A ,, W  O = 1.92–1.95 A and W  N = 2.26(1) A . Both compounds were crystallographically characterized in the space group C2/c and each molecule has rigorous C2 symmetry. Allene and 1,3-di-p-tolycarbodiimide form 1:1 adducts with W2(OCMe2CF3)6 in which the substrate is bound parallel to the M-M axis, i.e. μ-η2,η2-C3H4 and μ-η2,η2-ArNCNAr-W2(OCMe2CF3)6. Also W2(OCMe2CF3)6 and W2(OSitBuMe2)6 bind two equivalents of xylylisocyanide to afford W2(OR)6(η1-CNAr)2. For W2(OCMe2CF3)6(η1-CNAr)2, the molecular structure has been determined by X-ray crystallography and shows a nearly eclipsed central W2O6C2 skeleton with W  W = 2.44(1) A , W  O = 1.94(1) A (av.) and W  C = 2.14(1) A , whereas the WWO angles span the range of 105–114°, the WWC angles are 83(1)°. Similarly, W2(OCMe(CF3)2)4(NMe2)2 forms a bis adduct upon reaction with the isocyanide. However, the molecular structure of W2(OCMe(CF3)2)4(NMe2)2(η1-CNAr)2 shows a staggered arrangement of the two ligands about the ditungsten center where W  W = 2.382(1) A , W  O = 2.00(1) A (av.), W  N = 1.93(1) A (av.) and W  C = 2.14(1) A (av.) with a CWWC dihedral angle of 41.9°. These reactions and their products are compared for W2(OR)6 compounds where R  t Bu , t BuMe 2 Si and Cme 2 CF 3 .

The reaction between diarylthiones and [Mo2(OCH2tBu)6] in hydrocarbon solvents yielded [Mo2(OCH2tBu)6-(μ-S)(CAr2)] by cleavage of the CS double bond. The Lewis base adduct [Mo2 (OCH2tBu)6(μ-S) (CPh2) (PMe3)] (2) has been crystallographically characterized; it contains six- and five-coordinate Mo atoms linked through μ-S and μ-OR groups. The rate of the cleavage of the CS bond has been studied by variable-temperature 1H NMR in [D8]toluene. A Hammett plot shows that both electron-donating and electron-releasing substituents in the aryl groups enhance the rate relative to Ph2CS. The activation parameters for cleavage of the CS bonds in Ph2CS, (p-MeOC6H4)2CS, and (m-CF3C6H4)2CS exhibit essentially identical values for ΔS‡, while ΔH‡ is somewhat smaller for the thiones bearing electron-donating or -withdrawing substituents. We also studied the reversible binding of Et2NCN to [Mo2(OtBu)6] as a model system wherein the CN bond is reduced but not cleaved and the (MM)6+ center oxidized. Finally, the reversible binding of P(nBu)3 to [Mo2(OCH2tBu)6], wherein the product exhibits no net oxidation of the metal centers, has been similarly studied. The activation parameters for these three classes of reactions are compared with previous studies of the reversible binding of CN− to [M2(OR)6] compounds and the reaction 2[W2(OiPr)6] → [W4(OiPr)12]. We propose that the activation parameters associated with CS cleavage are associated with the formation of a μ-η1,η2-SCAr2 reactive complex similar to others described elsewhere,[23] and that they result from a) the bimolecular nature of the reaction and b) reorganizational energy. The greater facility of CX multiple-bond cleavage in reactions involving [W2(OR)6] compounds relative to [Mo2(OR)6] compounds, the substituent effects, and the dependence on R are discussed in terms of the orbital energy match between the MM and CX π and π* orbitals, and an analogy is made with neutral Diels-Alder cycloaddition reactions.

The reaction between Mo2(O2CBut)4 and [Bun4N]+[ButCO2]− in toluene yields the yellow toluene-soluble salt [Bun4N]+[Mo2(O2CBut)5]− as large yellow plates upon crystallization. The molecular struture of the anion contains the now common paddle-wheel or lantern M2(O2C)4 core, = 2.1035(7) and MoO = 2.12(2) A (av), with a monodentate pivalate ligand coordinated to one metal atom, MoO = 2.298(5) A in the axial position and MoMoO (ηl-pivalate) = 176.6(1)°. In CD2Cl2 and toluene-d8 solutions the anion shows fluxional behaviour such that exchange between all pivalates is rapid on the NMR time-scale at room temperature. At −80°C this fluxional process becomes sufficiently slow to lead to the expected 4:1 ratio for the But protons. In pyridine-d5 the exchange of pivalates is slower but still sufficiently fast to lead to coalescence at elevated temperatures. In pyridine solution the predominant species are Mo2(O2CBut)4(py)2 and [Bun4N]+[ButCO2]−. These findings complement earlier work wherein [Et4N]+[Mo2(O2CCF3)5]− was prepared (Garner and Senior, J. Chem. Soc., Dalton Trans. 1975, 1171) and the exchange of CF3CO−2 groups in the reaction between Mo2(O2CCF3)4 and NaO2CCF3 in CH3CN was studied (Sasaki et al., Bull. Chem. Soc. Japan 1979, 52, 446). The facile intramolecular exchange of pivalate ligands in the Mo2(O2CBut)−5 anion emphasizes that Mo4+2 containing compounds are kinetically labile to associative nucleophilic substitution reactions. Possible reaction pathways leading to exchange of ButCO−2 are discussed.

Reaction of M 2 (NMe 2 ) 6 (M = Mo, W) with triphenylmethanol in hexane/ether produces M 2 (OCPh 3 ) 2 (NMe 2 ) 4 ( I ) as yellow crystals in high yield (92–97%). M 2 (OCPh 3 ) 2 (NMe 2 ) 4 are air-sensitive, soluble in aromatic solvents and decompose around 160°C. The 1 H NMR of I is temperature dependent and shows a mixture of anti and gauche rotamers. The X-ray crystal structures of I reveal exclusively the gauche isomer for tungsten and the anti isomer for molybdenum. The reactions between M 2 (NMe 2 ) 6 and triphenylsilanol (2 equiv.) yield M 2 (OSiPh 3 ) 2 (NMe 2 ) 4 compounds (M = Mo, W) ( II ) as orange crystals. In the presence of ρ6 equiv. of Ph 3 SiOH the M 2 (NMe 2 ) 6 compounds react further to give yellow crystalline compounds, M 2 (OSiPh 3 ) 4 (NMe 2 ) 2 . In.compound II , where M = W, the W 2 O 2 N 4 skeleton adopted the anti conformation with WW = 2.2954(6) A, W O = 1.925(4) A, WN = 1.935(8) A, WWO = 108.1(1)°, WWN = 102(1)°. The addition of Ph 3 SiOH (6 equiv.) to W 2 (OBu t ) 6 yielded the related compound W 2 (OBu t ) 2 (OSiPh 3 ) 4 .

The title complex, tri-tert-butoxy-1κ 2 O,2κO-tri-chloro-1κCl,2κ 2 Cl-bis(N,N-dimethylamine)-1κN,2κN-ditungsten(W-W), [W 2 Cl 3 (C 4 H 9 O) 3 (C 2 H 7 N) 2 ], adopts a dinuclear structure in which two tungsten(III) atoms are united by a W≡W bond unsupported by bridging ligands. Both W atoms are coordinated to four ligand atoms that lie in a roughly square-planar arrangement. The two W atoms have different coordination environments : one is ligated by two cis-OR groups, one Cl and one HNMe 2 ligand, while the other is ligated by two trans-Cl ligands, one OR group and one HNMe 2 ligand.

Methods are reported for the preparation of mixed-carboxylate versions of the [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(4)] family of single-molecule magnets (SMMs). [Mn(12)O(12)(O(2)CCHCl(2))(8)(O(2)CCH(2)Bu(t))(8)(H(2)O)(3)] (5) and [Mn(12)O(12)(O(2)CHCl(2))(8)(O(2)CEt)(8)(H(2)O)(3)] (6) have been obtained from the 1:1 reaction of the corresponding homocarboxylate species. Complex 5.CH(2)Cl(2).H(2)O crystallizes in the triclinic space group P1 with, at -165 degrees C, a = 15.762(1), b = 16.246(1), c = 23.822(1) A, alpha = 103.92(1), beta = 104.50(1), gamma = 94.23(1) degrees, Z = 2, and V = 5674(2) A(3). Complex 6.CH(2)Cl(2) crystallizes in the triclinic space group P1 with, at -158 degrees C, a = 13.4635(3), b = 13.5162(3), c = 23.2609(5) A, alpha = 84.9796(6), beta = 89.0063(8), gamma = 86.2375(6) degrees, Z = 2, and V = 4207.3(3) A(3). Complexes 5 and 6 both contain a [Mn(12)O(12)] core with the CHCl(2)CO(2-) ligands ordered in the axial positions and the RCO(2-) ligands (R = CH(2)Bu(t) (5) or Et (6)) in equatorial positions. There is, thus, a preference for the CHCl(2)CO(2-) to occupy the sites lying on the Mn(III) Jahn-Teller axes, and this is rationalized on the basis of the relative basicities of the carboxylate groups. Direct current magnetic susceptibility studies in a 10.0 kG field in the 2.00-300 K range indicate a large ground-state spin, and fitting of magnetization data collected in the 10.0-70.0 kG field and 1.80-4.00 K temperature range gave S = 10, g = 1.89, and D = -0.65 K for 5, and S = 10, g = 1.83, and D = -0.60 K for 6. These values are typical of [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(4)] complexes. Alternating current susceptibility studies show the out-of-phase susceptibility (chi(M)' ') signals characteristic of the slow relaxation in the millisecond time scale of single-molecule magnets. Arrhenius plots obtained from chi(M)' ' versus T data gave effective barriers to relaxation (U(eff)) of 71 and 72 K for 5 and 6, respectively. (1)H NMR spectra in CD(2)Cl(2) show that 5 and 6 are the main species present on dissolution, but there is evidence for some ligand distribution between axial and equatorial sites, by intra- and/or intermolecular exchange processes.

Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4-7 K region and the other in the 2-3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two magnetization relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]. 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P2(1)/c, which at -170 degrees C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(9) A, beta = 103.85(2) degrees, and Z = 4. The arrangements of H2O and carboxylate ligands on the Mn12 molecule are different in the two crystal forms. The complex [Mn12O12-(O2)CC6H4-p-Cl)16(H2O)4].8CH2Cl2 (5) crystallizes in the monoclinic space group C2/c, which at -172 degrees C has a = 29.697(9) A, b = 17.708(4) A, c = 30.204(8) A, beta = 102.12(2) degrees, and Z = 4. The ac susceptibility data for complex 5 show that it has out-of-phase signals in both the 2-3 K and the 4-7 K ranges. X-ray structures are also reported for two isomeric forms of the p-methylbenzoate complex. [Mn12O12(O2CC6H4-p-Me)16(H2O)4]. (HO2CC6H4-p-Me) (6) crystallizes in the monoclinic space group C2/c, which at 193 K has a = 40.4589(5) A, b = 18.2288(2) A, c = 26.5882(4) A, beta = 125.8359(2) degrees, and Z = 4. [Mn12O12(O2CC6H4-p-Me)16(H2O)4].3(H2O) (7) crystallizes in the monoclinic space group I2/a, which at 223 K has a = 29.2794(4) A, b = 32.2371(4) A, c = 29.8738(6) A, beta = 99.2650(10) degrees, and Z = 8. The Mn12 molecules in complexes 6 and 7 differ in their arrangements of the four bound H2O ligands. Complex 6 exhibits an out-of-phase ac peak (chi(M)' ') in the 2-3 K region, whereas the hydrate complex 7 has a chi(M)' ' signal in the 4-7 K region. In addition, however, in complex 6, one Mn(III) ion has an abnormal Jahn-Teller distortion axis oriented at an oxide ion, and thus 6 and 7 are Jahn-Teller isomers. This reduces the symmetry of the core of complex 6 compared with complex 7. Thus, complex 6 likely has a larger tunneling matrix element and this explains why this complex shows a chi(M)' ' signal in the 2-3 K region, whereas complex 7 has its chi(M)' ' peak in the 4-7 K region, i.e., the rate of tunneling of magnetization is greater in complex 6 than complex 7. Detailed 1H NMR experiments (2-D COSY and TOCSY) lead to the assignment of all proton resonances for the benzoate and p-methyl-benzoate Mn12 complexes and confirm the structural integrity of the (Mn12O12) complexes upon dissolution. In solution there is rapid ligand exchange and no evidence for the different isomeric forms of Mn12 complexes seen in the solid state.

The reaction of IrH 5 (P i Pr 3 ) 2 (1) with [Cu(MeCN) 4 ]BF 4 (2:1) in acetone yields [IrH 2 (MeCN) 2 (P i Pr 3 ) 2 ]BF 4 , characterized by spectroscopic methods and X-ray diffraction, in 46% yield. A similar reaction with CuCF 3 SO 3 in CH 2 Cl 2 yield [IrH 5 -(P i Pr 3 ) 2 CuCF 3 SO 3 in 91% yield

Reaction of M(2)(O(t)Bu)(6) (M = Mo, W) with 3 equiv of 2,5-dimethylhexane-2,5-diol (LH(2)) in hexane/THF produces orange crystals of M(2)(mgr;-L(3))(2), Ia (M = Mo), Ib (M = W), in high yield (80%). Treatment of M(2)(NMe(2))(6) with excess (8 fold) LH(2) in THF/hexane solution at -20 degrees C produces exclusively green crystals of M(2)(mgr;-L)(eta(2)-L)(2)(HNMe(2))(2), IIa (M = Mo), IIb (M = W), in high yield (75%). Dissolving IIa and IIb in toluene at room temperature slowly produces Ia and Ib, respectively, the process being accelerated by heat (t(1/2) = 10 min at 60 degrees C). Compounds Ia, Ib, IIa, and IIb were characterized by (1)H NMR, IR, melting point, and microanalysis, and Ib and IIb were also characterized by X-ray crystallography. Addition of excess HNMe(2) to a solution of Ia or Ib at -50 degrees C does not produce any IIa or IIb after 2 months, but at +25 degrees C, 40% IIa and IIb are produced with HNMe(2) after 2 days. Crystal data for Ib: W(2)(mgr;-L)(3) at -171 degrees C, a = 12.568(2) Å, b = 12.568(3) Å, c = 37.075(8) Å, Z = 8, d(calcd) = 1.822 g/cm(3), space group I4(1)/a. The molecule Ib adopts an "ethane-like" staggered conformation with three eight-membered diolate rings spanning the W-W triple bond: Wtbd1;W = 2.3628(11) Å; W-O = 1.87 Å (average). Crystal data for compound IIb: W(2)(mgr;-L)(eta(2)-L)(2)(HNMe(2))(2) at -170 degrees C, a = b = 20.198(3) Å, c = 17.819(3) Å, Z = 8, d(calcd) = 1.629 g/cm(3), space group P4/ncc. IIb has two essentially square planar WO(3)N units connected by a W-W triple bond, Wtbd1;W = 2.3196(12) Å, W-O = 1.95 Å (average), and W-N = 2.294(11) Å, and one bridging eight-membered diolate ring. The other two diolate ligands chelate at opposite ends of the molecule forming two seven-membered rings.

Addition of 1,2-W 2 Cl 2 (NMe 2 ) 4 (W≡W) to a toluene slurry of LiCH(SiMe 3 ) 2 (2 equiv) results in the formation of 1,2-W 2 [CH(SiMe 3 ) 2 ] 2 (NMe 2 ) 4 (W≡W) ( I ) in 79% isolated yield. Compound I has been characterized by 1 H and 13 C NMR, IR, elemental analysis and single-crystal X-ray diffraction. The molecule exists exclusively in the gauche conformation in solution and in the solid state with WW = 2.320(1) A. Compound I is very sterically encumbered as evidenced by: (1) large WWC angles, 110°, at the disyl ligand; (2) skewing of the NC 2 planes of the NMe 2 ligands off the WW vector; (3) anomalously large barriers to WNM 2 bond rotation in solution; (4) the inertness of I towards CO 2 and alcohols. However, compound I reacts with acetic anhydride to form 1,2-W 2 [CH(SiMe 3 ) 2 ] 2 (O 2 CMe) 4 (W≡W) ( II ) in 31% isolated yield. Compound II has been characterized by 1 H and 13 C NMR, IR, and elemental analysis. The mechanistic implications of these studies with regard to alcoholysis and CO 2 insertion reactions of other 1,2-W 2 R 2 (NMe 2 ) 4 compounds are discussed. Crystal data for 1,2-W 2 [CH(SiMe 3 ) 2 ] 2 (NMe 2 ) 4 at −140°C: space group P 2 1 / n , a = 12.555(3), b = 18.699(5), c = 15.214(4) A, β = 95.24(1)° and Z = 4.

Isolement de complexes W 2 Cl 2 (NMe 2 ) 4 (μ−C 2 RR')(py) 2 a partir des reactions des alcynes avec W 2 Cl 2 (NMe 2 ) 4 en presence de pyridine. Structure cristalline de W 2 Cl 2 (NMe 2 ) 4 (μ-C 2 H 2 )(py) 2 et W 2 Cl 3 (NMe 2 ) 3 (μ-PhC 2 H)(py) 2 •1/2C 7 H 8

We survey recent results from our efforts in vanadium sulphur and oxygen chemistry. A unifying theme for most of the discussion is the reactivity characteristics of vanadyl (VO 2+ ) complexes, and it is shown how such complexes are capable of a variety of transformations leading to products with oxidation states in the range III–V and nuclearities in the range 1–5. Also described are mononuclear non-oxo vanadium sulphur complexes, including the structural characterization of both V(SBu t ) 4 and V(SBu t ) 4 − . The relevance of this work to our understanding of the fate of crude oil vanadyl impurities during hydrotreating processes is discussed.

Addition of primary alcohols, RCH{sub 2}OH (> 6 equiv), to hydrocarbon solutions of M{sub 2}(O-t-Bu){sub 6} compounds has led to the isolation of the first homoleptic series of cluster alkoxides M{sub 4}(OCH{sub 2}R){sub 12} for both M = Mo and W where R = i-Pr, Cy (Cy = cyclohexyl), Cp (Cp = cyclopentyl), and c-Bu (c-Bu = cyclobutyl). The NMR data ({sup 1}H and {sup 13}C) indicate a common structural unit for this class of compounds containing a molecular mirror plane. For each M{sub 4}(OCH{sub 2}R){sub 12} compound there are eight types of alkoxide ligands in the integral intensity 2:2:2:2:1:1:1:1. Those having integral intensity two possess diastereotopic methylene protons, indicating that they do not lie on the mirror plane, whereas the other four alkoxides (1:1:1:1) are contained within the mirror plane. Though these compounds yield crystals from 1,2-dimethoxyethane, they failed to diffract beyond 10{degree} indicating a molecular disorder within hexagonal packing of M{sub 4} units. However, the cyclobutylmethoxide derivatives crystallize with an additional molecule of alcohol, M{sub 4}(CH{sub 2}-c-Bu){sub 12}(HOCH{sub 2}-c-Bu), and the molecular structure of the molybdenum compound was determined by an X-ray study. Crystal data for Mo{sub 4}(OCH{sub 2}-c-Bu){sub 12}(HOCH{sub 2}-c-Bu) at {minus}156{degree}C: a = b = 19.952more » (7) {angstrom}, c = 34.755 (16) {angstrom}, Z = 8, d{sub calcd} = 1.43 g cm{sup {minus}3}, and space group Pr{sub 1}. The unit cell contains two crystallographically independent molecules that are essentially equivalent with respect to M-M and M-O distances and angles. In each there is a central Mo{sub 4} butterfly with a dihedral angle between the Mo{sub 3} triangles of 132.5{degree}.« less

1,2-M{sub 2}(NMe{sub 2}){sub 4}(P(t-Bu){sub 2}){sub 2} compounds react with CO{sub 2} (> 4 equiv) to yield initially M{sub 2}(O{sub 2}CNMe{sub 2}){sub 2}(O{sub 2}CP(t-Bu){sub 2}){sub 2}(NMe{sub 2}){sub 2}, where M = Mo and W. The reaction occurs rapidly at room temperature in solution and even as a gas/solid heterogeneous reaction. Mechanistic studies employing the use of {sup 13}CO{sub 2} have established that at low temperatures CO{sub 2} preferentially attacks the phosphido ligand (with respect to the amido ligands) giving an initially P-bound phosphinecarboxylate that then rearranges to the O-bound form of the ligand. Comparisons are made with earlier work involving the reactions between metal amides and CO{sub 2}.

Ethyl 4-chloroacetoacetate condenses with 4-amino-6-hydroxy-2-pyrimidinethiol to yield ethyl 3-hydroxy-5-oxo-7-aminothiazolino[3,2-a]pyrimidin-3-acetate (3), and not ethyl 3-hydroxy-5-amino-7-oxothiazolino[3,2-a]-pyrimidin-3-acetate, as previously reported. This compound reacts with ammonia to produce ethyl 4-(6′-amino-4′-oxo-2′-pyrimidinethiol)-3-aminocrotonate (8), the open chain structure of which accounts for the cyclization of 3 to the poly-cyclic lactam, 6a-hydroxy-5,6,6a,7-tetrahydro-8-thia-1,4-diazacycl[3.3.2]azine-2,5-dione, rather than the sterically more favorable lactone, when 3 was treated with triethylamine. Some other reactions of 3 are described, and the structures of 3 and 8 were comfirmed by single crystal X-ray diffraction analysis.

From the addition of Na/Hg (1 equiv) to a WCl/sub 4/ slurry in THF (THF = tetrahydrofuran) was obtained the green crystalline compound NaW/sub 2/Cl/sub 7/(THF)/sub 5/ in 60-70% recrystallized yields. The compound has been shown to involve a confacial bioctahedral W/sub 2/Cl/sub 7/(THF)/sub 2//sup -/ anion coordinated to a (THF)/sub 3/Na/sup +/ cation via two chloride ligands that are terminally bonded to W atoms. The W-W distance 2.4028 (15) A is essentially identical with that seen in other W/sub 2/X/sub 9//sup 3 -/ anions (X = Cl or Br) and is indicative of strong t/sub 2g//sup 3/-t/sub 2g//sup 3/ M-M bonding. The compound provides a useful synthetic starting material for metathetic reactions involving Li-X leading to the known X/sub 3/W identical with WX/sub 3/ compounds where X = CH/sub 2/-t-Bu, NMe/sub 2/, and O-t-Bu. The latter are obtained in 60-80% yield based on W by either sublimation or crystallization. The compound NaW/sub 2/Cl/sub 7/(THF)/sub 5/ bears a striking similarity in terms of both its preparation and its reactivity to the compound formulated as W/sub 2/Cl/sub 6/(THF)/sub 4/ by Schrock, Sturgeoff, and Sharp, though it is not presently known how the two are related. Crystal data for NaW/sub 2/Cl/sub 7/(THF)/submore » 5/ at -151/sup 0/C: a = 18.817 (7) A, b = 8.397 (3) A, c = 20.964 (10) A, ..beta.. = 107.09 (3)/sup 0/, Z = 4, V = 3166.2 (1) A/sup 3/, d/sub calcd/ = 2.097 g cm/sup -3/, space group P2/sub 1//c. 20 references, 4 figures, 6 tables.« less

During their studies of the early d-block metal chemistry associated with aryloxide ligation they have examined the reactivity of a series of mixed alkyl, aryloxide compounds toward CO and the isoelectronic organic isocyanide molecule. This has allowed them to isolate and study in detail a series of compounds containing a number of eta/sup 2/-iminoacyl functions. Furthermore they have demonstrated that intramolecular coupling of iminoacyl groups to produce enediamido ligands can take place, as well as the related coupling of iminoacyl and acyl groups. They report here in detail the synthesis of a number of enamidolate and enediamido complexes using this synthetic method and also report in detail on the coordination properties of the resulting metallacycles, an area that has received recent theoretical interest. In a subsequent paper they report a kinetic investigation of these carbon-carbon bond-forming processes.

Le complexe cristallise dans le systeme triclinique, groupe P1 et sa structure est affinee jusqu'a R=0,063. Coordination octaedrique deformee autour des atomes Mo, les coordinats dithiophosphate etant monodentes

Observation of 2M≡M⇄M 4 equilibrium reaction (M=transition metal), synthesis and structure of hexaisopropoxyditungsten and its dimer Observation de la reaction 2M≡M⇄M 4 a l'equilibre (M=metal de transition); synthese et structure de l'hexaisopropoxyditungstene et de son dimere