Main Group Chemistry

The antimony(III) complex with the α-hydroxy acid glycolic acid (hydroxyacetic acid), ammonium bis(hydroxyacetato) antimony(III), has been prepared and its structure determined by X-ray diffraction. The novel monomeric complex anion involves two glycolato(2-) ligands in bidentate coordination with the typical distorted pseudo trigonal bipyramidal stereochemistry about Sb. Bond lengths are Sb—O(axial = carboxyl), 2.136(4), 2.200(5) Å and Sb—O(equatorial = hydroxyl), 1.980(5), 1.985(4) Å.

The reaction of hexaethyldigermane with allylic halides proceeded regioselectively in the presence of a catalytic amount of Pd₂(dba)₃ at temperatures of 120 °C ∼ 170 °C and gave allylgermanes in 42 ∼ 95% yields. The results indicate that the present reaction proceeds predominately through an S_N2-type mechanism over an S_N2′-type one.

Reaction of elemental zinc, cadmium, or mercury with sulfur in liquid ammonia at room temperature produces X-ray amorphous metal sulfide MS (M = Zn, Cd, Hg). Thermolysis of this material at 250–300°C produced crystalline MS (α-ZnS (wurtzite), α-CdS (greenockite), α-HgS (cinnabar), and β-HgS (metacinnabar). Products were characterised by microanalysis, FT-IR and Raman spectroscopy, SEM/EDAX, X-ray powder diffraction, magnetic moment measurements, and X-ray photoelectron spectroscopy.

The recently formulated second-order state-selective quasidegenerate perturbation theory (QDPT2) is compared with quadratic configuration interaction singles and doubles (QCISD) calculations for the molecules in this study. The results of calculations using nondegenerate perturbation theory (MP2) are also reported. The molecules in this study are of current or potential experimental interest; furthermore, the molecules studied are difficult to characterize theoretically and so are useful examples on which to assess newly developed formalisms. The equilibrium geometries and vibrational frequencies of five structural isomers of phosphaazarine, HNPCH, that have the phosphorus located between the nitrogen and the carbon have been determined using a split valence one-electron basis set with polarization functions on the heavy atoms and a complete active space self-consistent field (CASSCF) description of the active space. Both QDPT2 and QCISD calculations have been performed at the equilibrium geometries using a larger basis set to accurately determine the relative energies of the various structural isomers. The calculations predict that NPCH₂ is the lowest-lying isomer, being between 2.6 and 3.7 kcal/mol lower in energy than the energetically closest isomer, NPHCH.

Reaction of either LiPPh₂ or LiAsMes₂ with the diborane(4) compound (Me₂N) BrBBBr (NMe₂) affords the compounds (Me₂N) (Ph₂P)BB(PPh₂) (NMe₂), 1, and (Me₂N) (Mes₂As)BB(AsMes₂)(NMe₂)·0.5 PhMe, 2·0.5PhMe (Mes = 2,4,6-Me₃C₆H₂-). Both 1 and 2 feature normal B–B single bond lengths; however, the empty boron p-orbitals display strong π-interactions with the dimethylamino substituents. The B–P and B–As distances and the pyramidal phosphorus and arsenic geometries are consistent with single bonding. Furthermore, the stereochemical activity of the phosphorus and arsenic lone pairs is demonstrated by the ready formation of the complex cis-[Cr(CO)₄(Me₂N) (Ph₂P)BB(PPh₂)(NMe₂)]·C₆H₆, 3·C₆H₆, by treatment of 1 with [Cr(CO)₄(2,5-norbornadiene)]. Compounds 1–3 were characterized by X-ray crystallography, ¹¹B and ³¹P NMR spectroscopy, and by IR spectroscopy in the case of 3.

We recently reported on the neat synthesis of 3-dimensional, 6-functional cyclophosphazenic cores through a regiospecific peraminolysis of N₃P₃C1₆ by long-chain diamines on suitable solid supports. Preparation of spherical dendrimers (up to the eighth generation) from such cores was achieved through alternate additions of N₃P₃Cl₅ flagstones (5-fold multiplier) and of diamino tentacles (linker). The eighth generation possesses 2,343,750 terminal (P-C1) functions (M 228,977,179), which are suitable for further nucleophilic substitutions. Molecular modeling shows that the compactness of these dendrimers is extremely low, conferring to these huge monomers a noticeable vacuity for accomodation of host moieties.

Thermolysis of six acylpolysilanes, acetyl-, isopropionyl-, pivaloyl-, adamantoyl-, benzoyl-, and mesitoyltris(trimethylsily1)silane (1–6), in the presence or absence of a trapping agent has been examined. Thermolysis of 1 in benzene at 150 °C gave 1,1,1,4,4,4-hexamethyl-2-[1-(trimethylsiloxy)ethenyl]-3-[l-(trimethylsiloxy)ethyl]-2,3-bis(trimethylsilyl)tetrasilane (7). Similar treatment of 2 at 140 °C produced 1,1,1,3,3,3-hexamethyl-2-[l-isopropyl-3-methyl-2-(trimethylsiloxyl)-l-butenyl]-2-(trimethylsiloxy)trisilane (9), along with a dimer (8), analogous to 7. Thermolysis of 3 and 4 under the same conditions afforded no products, but the starting compounds were recovered quantitatively, while 5 and 6 yielded mainly nonvolatile substances. The thermolysis of 1–4 in the presence of 2,3-dimethyl-1,3-butadiene produced both [2 + 4] cycloadducts and ene adducts arising from the reaction of silenes generated thermally from 1–4 with butadiene, while 5 and 6 gave only [2 + 4] cycloadducts. With α-methylstyrene, 1–6 afforded only adducts derived from the ene reaction of the silenes with olefin. The thermolysis of 1–4 with styrene produced the respective [2 + 2] cycloadducts composed of a mixture of cis and trans isomers. Similar reactions of 5 and 6 with styrene gave only [2 + 2] cycloadducts with cis configuration.

A series of anhydrous calcium dithiocarbamates, Ca(S₂CNR₂)₂ (NR₂ = NEt₂, N(CHMe₂)₂, NBu₂, N(CH₂)₄, N(H)CMe₃, N(H)(CH₂)₃NMe₂), and one strontium dithiocarbamate (Sr(S₂CNBu₂)₂) were synthesized. All compounds were characterized by NMR, IR, and elemental analysis. Thermogravimetric analysis shows the dialkyldithiocarbamates to decompose around 350–400°C and the monoalkyl derivatives to decompose at a lower temperature, 100–150 °C. Only the diisopropyl and the two monoalkyl derivatives decompose cleanly to CaS; all the other dialkyldithiocarbamates decompose to a highly carbonized product. The crystal structures of two dithiocarbamates, Ca(S₂CN(CH₂)₄)₂ ((CH₂)₄NH)₂ (3a) and Ca(S₂CN(H)(CH₂)₃NMe₂)₂ (THF)₂·H₂O (7a), and a calcium thiocyanate byproduct Ca(NCS)₂ (THF)₂ (8a) were determined. Crystal data: 3a; Pccn, a = 15.074(5), b = 11.924(4), c = 13.662(5), d(ca1c) = 1.284, Z = 4, 2845 unique data, R = 0.107; 7a, P2₁2₁2₁, a = 10.471(4), b = 15.065(6), c = 18.736(11), d(ca1c) = 1.252, Z = 4, 2291 unique data, R = 0.062; 8a, P2₁/n, a = 7.675(3), b = 10.274(3), c = 15.658(6), β = 96.42(3), d(calc) = 1.204, Z = 2, 2169 unique data, R = 0.126.

Chalcogen ring molecules are known to undergo facile interconversion reactions in organic solvents and in the melts, e.g. polymerization of liquid sulfur or the formation of Se₆ and Se₇ upon dissolving Se₈ in CS₂. These interconversion reactions have been suggested to proceed via the homolytic cleavage of the chalcogen-chalcogen bonds or through the formation of hypervalent intermediates. The experimental evidence on the actual mechanism, however, is rather sparse. The energetics of the various suggested interconversion pathways have been studied by ab initio MO techniques using suitable model reactions involving sulfur and selenium hydrides. Full geometry optimization has been performed for hypervalent chalcogen hydrides H₂EE and H₂E(EH)₂ as well as for the radicals HE and HEE (E = S or Se in the case of each chalcogen atom) utilizing the MIDI-4* basis sets. The energy changes in their formation from appropriate unbranched chalcogen hydrides HE_nH(n = 1,2 or 4) and HE_nE′_mH (m, n = 0–4; n + m = 2,4; E, E′ = S or Se) have been calculated including the corrections for the electron correlation by the second-order Møller-Plesset perturbation theory and for the zero-point vibrational energy. The formation of hypervalent interconversion intermediates is seen as an energetically plausible alternative for the homolytic cleavage of the chalcogen-chalcogen bonds. The present calculations help to understand why the interconversion of heterocyclic selenium sulfides proceeds principally with selenium-atom transfer.

The ¹⁹⁹Hg NMR spectra of three series of 37 ortho–mercurated ferrocenylimines, (η⁵–C₅H₅)Fe [(η⁵–C₅H₃)(HgCl)C(R)= NAr] (R = H(l),CH₃(2), C₆H₅(3); Ar = substituted phenyl groups, 1–naphthyl and 2–naphthyl), have been recorded. The ¹⁹⁹Hg chemical shifts are regularly disturbed by the substituents in the N–phenyl rings, and excellent linear relationships are found to exist between the ¹⁹⁹Hg shifts (δ) and Hammett substituent constants in all three series. The directions of the substituent effect on δ are the same in the three series, i.e. electron-donating substituents cause shifts to lower field, but the sensitivities of the ¹⁹⁹Hg shift toward the substituent effect are different, ascending in the order of 1,2, and 3. These ^l99Hg NMR features support the intramolecular secondary interaction between the n-electrons of the imino nitrogen atom and the unoccupied 6p orbital of the mercury atom and the n–π conjugation between the nitrogen and the N–phenyl ring.

The microdynamics of a 2:1 A1C1₃-1-ethyl-3-methylimidazoliumc chloride (MEICI) room-temperature melt are studied using ¹³C and ²⁷Al NMR relaxation methods. The ¹³C and ²⁷Al NMR correlation times for MEI⁺ and A1₂CI₇⁻ are compared with viscosity measurements corrected for temperature. The Dual Spin Probe (DSP) method is used to calculate an ²⁷Al nuclear quadrupole coupling constant (χ) of 4.86 MHZ for A1₂C1₇⁻ in the 2:1 melt. Theoretical (ab initio-gas phase) calculations at the HF/3–21 G(d) and HF/6–31 (d) levels yield ²⁷Al nuclear quadrupole coupling constants of 8.015 and 11.211 MHZ for A1₂Cl₇⁻. Finally, a linear relationship between ²⁷Al correlation times of A1₂C1₇⁻ and reciprocal conductivity is reported.

The synthesis of poly(diphenylsilylene-co-methylene) of the general composition [SiPh₂(CH₂)₁,₁]_x was afforded by the reaction of diphenyldichlorosilane and dibromomethane with sodium. The product obtained was characterized by elemental analysis and by ¹H, ¹³C, ²⁹Si NMR, IR spectroscopy, and gel permeation chromatography. The pyrolysis process of the oligomeric poly(diphenylsilylene-co-methylene) was investigated up to 1700 °C, and the gaseous, liquid, and viscous decomposition products were mainly identified by GC-MS coupling method. The ceramic residues were determined and analyzed, and the state of β-SiC crystallization was examined by XRD analysis.

YbI₂(thf)₂ reacts with two equiv of KPPh₂ in tetrahydrofuran to give Yb[PPh₂]₂ (thf)₄, 1.1 can also be obtained from the reaction of YbI₃(thf)₃ with KPPh₂ in tetrahydrofuran in a 1:3 ratio with half an equiv of Ph₂P-PPh₂ as a byproduct as well as from Yb[N(SiMe₃)₂]₂ (thf)₂ and two equiv of Ph₂PH in tetrahydrofuran. 1 can be converted to Yb [PPh₂]₂(N-MeIm)₄, 2, in tetrahydrofuran using four equiv of the strong donor ligand N-methylimidazole (N-MeIm). 2 crystallizes in space group P2₁/n. Crystal data for 2 at 217 K: a = 9.881 (l) Å, b = 17.717 (2) Å, c = 11.153 (2) Å, β = 95.61 (1)°; V = 1943.1 (5) ų; Z = 2; D_calcd = 1.490 g cm⁻³; R_F = 2.01%. The structure of 2 shows the hexacoordinate ytterbium atom, which lies on an inversion center, in a slightly distorted octahedral environment with two phosphido ligands in trans positions. A significant feature of the molecular structure of 2 is the only slightly pyramidal configuration of the metal-coordinated phosphorus atoms (sum of angles: 343.9°).

The isosteric phosphonic acid analogue of tyrosine O-phosphate has been prepared in good yield via a three-step sequence. In addition, the nominally isosteric α-hydroxyphosphonic acid analogue of the natural phosphate has also been prepared using a direct oxidation of an intermediate in the aforementioned reaction sequence