Volume 52, Issue 6

Starting from tris(dialkylamino)phosphonium methylides(R 2 N) 3 PCH 2 [1a: R = Me; 1b: R = Et] a series of silylated ylides with functional groups at the silicon substituents have been prepared (2 - 8 ). In the general formula X 3 Si-CH = P(NR 2 ) 3 the group SiX 3 represents examples for X = Me, Cl, Br, OMe, iPrO, NMe 2 , but also for X 3 = PhH 2 , etc. The compounds are prepared either via the transylidation reaction of 1a, b with reaction components X 3 SiY [Y = Cl, OTf], or through action of a base on the corresponding silylated phosphonium salts, following methods of preparation for non-functional silylated ylides. Bis(ylides) (9 - 12) are available along the same sequence of reactions, but employing difunctional silanes X 2 SiY 2 . Products of the type X 2 Si[CH = P(NR 2 ) 3 ] 2 were investigated with X = Me, OMe, OEt, and NMe2. All ylides are thermally stable, distillable liquids, which have been identified via conventional spectroscopic methods. The ylides are versatile synthons in trans-silylation, trans-ylidation, and de-silylation reactions.

Treatment of (Me 2 N) 3 PCHSiMe 3 with Me 3 SiOTf (OTf = triflate) affords the phosphonium salt [(Me 2 N) 3 PCH(SiMe 3 ) 2 ]OTf (2a), which can be converted into the correspond­ing ylide (Me 2 N) 3 PC(SiMe 3 ) 2 (3a) in high yield using NaN(SiMe 3 ) 2 . The compounds with SiMe 2 Ph substituents (2, 3b) are obtained following an analogous procedure. The ylide (Me 2 N) 3 PC[Si(OMe) 3 ] 2 (3c) is available in 50% yield by direct transylidation of (MeO) 3 SiOTf with (Me 2 N) 3 PCH 2 in the molar ratio 2:3, with [(Me 2 N) 3 PMe]OTf as the by-product. Com­pound 3c is a distillable liquid, but 3a,b are crystalline solids the structure of which has been determined by single crystal X-ray diffraction. Both compounds feature a trigonal planar ylidic carbon atom and short ylidic P-C and Si-C bonds. The nitrogen atoms are also in a planar configuration with non-standard orientations of the NMe 2 groups at the phosphorus atoms. These data are in agreement with the results of recent quantum chemical calculations of simple prototypes which show very flat energy profiles for internal motions (rotation, inversion) of dimethylamino groups at the phosphorus atoms in phosphines and phosphoranes.

A metal-assisted ring expansion from the preferred solution species (EtAsO) n , n = 3,4, to the hexameric ligand (EtAsO) 6 is observed for the reactions of [ReBr(CO) 5 ], [RuCL 2 (Ph 3 P) 3 ], RhCl 3 ·3H 2 O and [Cu 2 CF 3 SO 3 ) 2 (C 6 H 6 )] with ethylcycloarsoxane. Whereas two metal frag­ments are facially coordinated by the upper and lower three As atoms of a flattened As 6 O 6 cuboctahedron in both [{ReBr(CO) 2 } 2 {μ-[cyclo-(EtAsO) 6 ]}] (1) and [Cu 2 {μ-[cyclo-(EtAsO) 6 ]}(Me 2 PhP) 2 ](CF 3 SO 3 )2 (4), potential ring strain restricts the reaction with the other compounds to the formation of mononuclear complexes [RuCl 2 {cyvclo-(EtAsO) 6 }(Ph 3 P)] (2)and [RhCl 3 {cyclo-(EtAsO) 6 }] (3) with k 3 As 1,3,5 coordination. The structures of 1 - 4 were established by X-ray structure analysis. A shift in the ν(As-O) IR absorption bands to higher wavenumbers (830 - 788 cm -1 ) is characteristic for (EtAsO) 6 complexes in comparison to those of the cyclic tetramer (781-747 cm -1 ).

Hydrothermal reaction of Ge and Se with Ag(CH 3 COO) in the presence of alkali metal carbonates affords the open framework selenidogermanates(IV) A 3 [AgGe 4 Se 10 ]·2H 2 O (A = Rb, Cs), 1 and 2, which contain corner linked adamantane-like Ge 4 Se 10 cages and AgSe 4 tetrahedra. The analogous reaction with Mn(CH 3 COO) 2 yields the isostructural tetragonal compounds A 2 [MnGe 4 Se 10 ]·3H 2 O (A = Rb, Cs), 3 and 4. The cations are sited at a general position in the channels of the silver bridged anionic framework of 1 and 2 and exhibit a disordered pattern of occupation (s.o.f. = 0.75) with one of the two crystallographically independent water oxygen atoms O(2) (s.o.f. = 0.25). In contrast, the Rb + cations in 3 are disordered over all three cation/oxygen sites, and the cation/water occupation pattern is fully reversed for the larger Cs + cations in 4 in comparison to 1 and 2.

A new binuclear vanadium( V) complex was synthesized by reaction of an aqueous oxovanadium(IV) sulfate solution with 2-(2′-hydroxyphenyl)-8-quinolinol dissolved in methanol. The molecular structure of the complex was determined by X-ray structure analysis. Crystal data: a = 10.004(3), b = 9.325(2), c = 15.089(3) Å; β = 91.95(2)°; space group P2 1 /n, Z = 4.

The decomposition equilibria of Ammonium Lanthanum Halides (NH 4 ) 2 LaX 5 were determined by total pressure measurements in a membrane zero manometer. The phases (NH 4 ) 2 LaX 5 decompose in one step to give solid LaX 3 and gaseous NH 3 and HX. From the decomposition functions the enthalpies of formation and the standard entropies of the phases are derived. ΔH° B (NH 4 ) 2 LaCl 5 ,f,298) = -411 ,7 ± 2,2 kcal/mol; S°((NH 4 ) 2 LaCl 5 ,f,298) = 86,7 ± 2,3cal/Kmol; ΔH° B (NH 4 ) 2 LaBr 5 ,f,298) = -351,6 ± 3,8 kcal/mol; S°((NH 4 ) 2 LaBr 5 ,f,298) = 101,1 ± 1,8 cal/Kmol; ΔH° B (NH 4 ) 2 LaI 5 ,f,298)= -268 ,9 ± 3,9 kcal/mol; S°((NH 4 ) 2 LaI 5 ,f,298) = 115,5 ± 4,3 cal/Kmol.

Bis[tris(methylamino)silyl]methane (1) and bis[tris(phenylamino)silyl]methane (2) have been synthesized as potential precursors of porous oxygen-free solids by the reaction of bis(trichlorsilyl)methane with methylamine and with lithiated aniline, respectively. Compound 2 was characterized by a crystal structure analysis. It crystallizes in the monoclinic space group P 2 1 ,/c with the unit cell parameters a= 10.963(2),b= 17.801(2), c = 17.557(2) Å, β = 97.96(2)° and Z = 4 (R 1 , = 4,4 %, wR 2 = 9,8 %, 5950 independent reflections).

In order to determine the structure parameters of the reaction intermediate formed during the reduction process of chromate(VI) ion by hydrogen peroxide, a laboratory stopped-flow X-ray absorption fine structure (XAFS ) apparatus, which was constructed by a rotating anode X-ray generator, an energy scanning spectrometer, a stopped-flow assembly, and X-ray detectors, was newly developed. Using the apparatus, the Cr K -edge XAFS spectrum of the reaction intermediate was measured. One oxo group, two peroxo groups, and one water molecule are coordinated to the Cr(VI) center in the intermediate, CrO(O 2 ) 2 (H 2 O ) , with Cr - O bond lengths of 157, 168, and 193 pm, respectively. The geometry around the Cr(VI) center is probably 6-coordinate pentagonal pyramidal.

The crystal structures of two binuclear iron(III) complexes with linear μ-oxo bridge, Fe 2 OCl 2 (tfpy) 2 (ClO 4 ) 2 ·2CH 3 CN and Fe 2 OCl 2 (epy) 2 (ClO 4 ) 2 were determined, where (tfpy) and (epy) represent N,N-bis(2-pyridylmethyl)-tetrahydrofurfurylamine and N,N-bis(2-pyridylmethyl)-2-ethoxyethylamine, respectively. Their structural features are essentially the same as that of the corresponding linear binuclear complex with (tpa)-complex, Fe 2 OCl 2 (tpa) 2 (ClO 4 ) 2 , where (tpa) is tris(2-pyridylmethyl)amine; the ligands (tfpy) and (epy) act as a tetradentate tripod-like ligand, and Fe-O (ethereal oxygen atom; these are located at the trans-position of bridging oxo-oxygen atom) distances are 2.209(4) and 2.264(2) Å for (tfpy) and (epy) compounds, respectively. These two (tfpy) and (epy) complexes exhibited much higher activity for the oxygenation of cyclohexane in the presence of hydrogen peroxide than that of the (tpa) complex. In contrast to this, the former two complexes exhibit negligible activity for the decomposition of hydrogen peroxide, whereas the catalase-like function of the (tpa) compound is remarkable. These are indicating that an active species for oxygenation of cyclohexane, which is assumed to be an iron(III)-hydroperoxide adduct with η 1 -coordina­tion mode, should be different from that is operating for decomposition of hydrogen perox­ide; for the latter case formation of a (μ-η 1 :η 1 -peroxo)diiron(III) species being stressed. The EHMO calculation showed that electronic interaction between the monodentate hydroperox­ide adduct of the binuclear iron(IIl)-(tfpy) compound and the tetrahydrofuran ring of the ligand system may lead to facile peroxide-tetrahydrofuran linkage formation, and the interac­tion described above should promote the O-O cleavage of the peroxide ion heterolytically. Based on these discussions, it was concluded that heterolytic O-O bond cleavage of the iron(III)-hydroperoxide adduct caused by electronic interaction with organic moiety contain­ing an ethereal-oxygen and by approach of the substrate which donates electron to the perox­ide adduct should play an important role in producing a high-valent iron-oxo species in these systems. In the case of (tpa) complex, formation of a hydroperoxide adduct linking with the ligand system seems to be unfavorable because of both the steric and electronic reasons.

Successive oxidation of bis[pyridine-phthalocyaninato(2-)iridium(II)] with iodine first yields mixed-valent bis[pyridine-phthalocyaninato(1,5-)iridium(II)] iodide ([(Ir(py)pc 1.5- } 2 ]I) and then pyridine-iodo-phthalocyaninato(2-)iridium(III)-pyridine ([Ir(py)(I)pc 2- ]·py). The latter crystallizes monoclinically with the following cell parameters: a = 10.258(1) Å, b = 17.589(3) Å, c = 19.723(2) Å, β = 92.95(1)°, space group P2 1 /n, Z = 4. Ir III is in the centre of a slightly distorted pc 2- ligand and coordinates pyridine and iodide in a trans-arrangement. The average Ir-N iso distance is 1.995(5) Å (N iso : isoindole N atom), the Ir-N py and Ir-I distan­ces are 2.102(5) and 2.657(1)Å, respectively. By a similar oxidation of [{Rh(py)pc 2- } 2 ] only [Rh(py)(I)pc 2- ]·py is obtained. Solid state spectral properties with diagnostic absorption bands at 1360. 1456, 5620 and 19800 cm -1 confirm the mixed-valent diphthalocyaninate(1.5-).

Dipotassium aryl(alkyl)sulfonylcarboniminodithioates (1a-c) crystallize with one or two molecules of water. In aqueous solution, they are protonated to form sulfonylcarbamodithioates (1”a-c). Aryl(alkyl)sulfonylcarboniminodithioates (1a-c) react with cyclooctate­traene dibromides (2a,b) to yield a mixture of 10-aryl(alkyl)sulfonylimino-9,11-dithiabicyclo-[6.3.0]undeca-2,4,6-trienes (3a-c) and 11-aryl(alkyl)sulfonyl-9,11-thiazabicyclo[6.3.0]-undeca-2.4.6-triene-10-thiones (4a-c). Structure (4a) was confirmed by X-ray analysis.

Electrolysis of acetic acid/sodium acetate solutions of N-methylated uracils results in the formation of 5-substituted methyl and acethoxy derivatives. Electrolysis of trifluoroacetic acid/potassium trifluoroacetate solutions of N-1-and N-3-methylated uracils provided, be­ sides 5-trifluoromethyl derivatives, novel N-C uracil dimers. In the case of 1,3-dimethyluracil in trifluoroacetic acid. N-l demethylathion was also observed.

The cryoscopic measurements show that title compounds are strongly associated in CHCl 3 solutions. The association of the 20 R epimer is distinctly less pronounced than that of the 20 S epipmer. Self-association of the 20 S epimer leads to the formation of very large com­plexes. The 20 R epimer forms associates via water molecules. The dissimilarity may be ex­plained in terms of different accessibility of the lactam carbonyl groups in the two epimers for the association. It is proposed that the association process is controlled by the configura­tion at the carbon atom C(20) and conformation around the C(20)-C(22) bond. Populations of side chain conformations of both epimers were determined by means of proton nuclear magnetic resonance. It was found for the 20 R epimer that the t and the -g rotamers are almost equally populated, and the rotamer +g is excluded. For the 20 S epimer the +g rotamer predominates over the t one, and the -g rotamer is excluded. The NMR data are fully consistent with the results of the molecular modelling studies.

The 13 C NMR chemical shifts of 19 2-substituted 1,3-dithian-2-ylium-tetrafluorborates 1a-1s are discussed in comparison to known analogous 1,3-dithianes and 2-lithio-1,3-dithianes. The unusual γ-effects (up to 9 ppm), which can also observed in other six-membered ring systems, are explained by the electric field effect (σ-polarisation effect). The electron density distribution can be estimated qualitatively by comparison with the 1,3-dioxan-2-ylium-and cyclohexylcations.

The reaction of [{Cp*(OC) 2 Re} 2 ](Re = Re) (1), Cp* = C 5 Me 5 , with CH 2 Cl 2 yields the dinuclear rhenium complexes [{Cp*(Cl)Re} 2 (μ-CO) 2 ](Re ≡ Re) (2) with cis orientation of the Cl atoms, [{Cp*(OC) 2 Re} 2 (μ-CH 2 )](Re-Re) (3), a complex with a bridging CH 2 -carbene ligand, and [{Cp*(OC) 2 Re} 2 (μ-C=CH 2 )]( Re-Re) (4), a μ-vinylidene( alkenylidene) compound. The structure of 2 has been confirmed by a single crystal X-ray structure determination. Starting with [Cp*Re- (CO)2(thf)] (6) instead of 1 the reaction with CH 2 Cl 2 affords cis-[Cp*Re(CO) 2 (Cl)(CH 2 Cl)] (7) by oxidative addition of dichloromethane.

Single crystals of PbCu 2 I 4· 2(CH 3 CN) are formed by reaction of Pbl 2 with Cul in acetonitril. The compound crystallizes in the mono­clinic space group C2/m; a = 1625.8(3), b = 436.6(1), c = 1025.8(2)pm; β = 94.77(3)°; V = 725.7 pm 3 10 6 ; Z = 2. The crystal structure is built up by chains of trans-edge sharing 1 ∞ [PbI 6/3 ] octahedra and corner sharing 1 ∞ [CuI 3/3 CH 3 CN)] tetra­hedra connected by common I-I edges.

Treatment of bis(diphenylphosphino)amine (dppa) with (dimethylsulfide)gold(I) chloride in the molar ratio 1:2 leads to the dinuclear complex (dppa)Au 2 Cl 2 in 95% yield. The compound was crystallized from diethyl ether/dimethylformamide as the 1:1 solvate with dmf, the crystal structure of which has been determined. The complex features an intramolecular Au--Au contact [3.121(1) Å] and an intermolecular hydrogen bond NH--O=C.

The donor-acceptor complex [Cl-I-C≡C-Ph] - has been prepared as the methyl-triphenyl-phosphonium salt from 1-iodo-2-phenylacetylene and [PMePh 3 ]N 3 in CH 2 Cl 2 solution. It forms co­lourless single crystals which were characterized by a crystal structure determination. Space group Pbca, Z = 8, lattice dimensions at -80 °C: a = 1047.1(1), b = 1700.3(1), c = 2793.2(1) pm, R = 0.035. The chloride ion is coordinated at the io­dine atom of the 1-iodo-2-phenylacetylene molecule in a nearly linear arrangement [CI-I-C≡C-Ph] - with bond lengths I-Cl of 302.4 pm and I-C of 203.1(5) pm.