The Preparation and X-Ray Structure of [AsPh4][Ph2P(S)NSiMe3] · 0.5 THF

The reaction of Ph₂P(S)N(SiMe₃)₂ with potassium tert-butoxide in a 1:1 molar ratio produces K[Ph₂P(S)NSiMe₃], which was converted to the AsPh₄⁺ salt by metathesis with [AsPh₄]Cl. The X-ray crystal structure of [AsPh₄][Ph₂P(S)NSiMe₃] · 0.5 THF consists of noninteracting AsPh₄⁺ and Ph₂P(S)NSiMe₃^? ions with d(P? S) = 1.980(4) Å and d(P? N) = 1.555(8) Å. The PNSi bite angle in the anion is 136.3(5)°. Electrophilic attack by Ph₂P(S)Cl occurs at the sulfur atom of Ph₂P(S)NSiMe₃^?. The oxidation of the anion with iodine produces a disulfide which regenerates K[Ph₂P(S)NSiMe₂] upon treatment with potassium tert-butoxide.     

Syntheses and structures of an unsolvated tetrakisimidophosphate (Li3(P(NBut)3(NSiMe3))2 and the face-sharing double-cubane (Li2(THF)[P(O)(NBut)2(NHBut)])2

The treatment of Me3SiN=P(NHBut)3 with three equivalents of LiBun in toluene produces (Li3(P(NBut)3(NSiMe3)))2 comprised of a Li6N6 cyclic ladder capped on the two hexagonal faces by mu 3-PNSiMe3 groups; the corresponding reaction of O=P(NHBut)3 yields the face-sharing double-cubane (Li2(THF)P(O)(NBut)2(NHBut))2 with a central Li2O2 ring.     

Investigations of the TeCl(4)-(t)BuNHLi Reaction: Synthesis, X-ray Structures, and Fluxional Behavior of the Tellurium-Nitrogen Compounds [Li(2)Te(N(t)Bu)(3)](2), {[LiTe(N(t)Bu)(2)(NH(t)Bu)](2)LiCl}(2), and {Te(2)(N(t)Bu)(4)[LiTe(N(t)Bu)(2)(NH(t)Bu)]LiCl}(2)

The reaction of (t)BuNHLi with TeCl(4) in toluene at -78 degrees C produces (t)BuNTe(&mgr;-N(t)Bu)(2)TeN(t)Bu (1) (55%) or [((t)BuNH)Te(&mgr;-N(t)Bu)(2)TeN(t)Bu]Cl (2) (65%) for 4:1 or 7:2 molar ratios, respectively. The complex {Te(2)(N(t)Bu)(4)[LiTe(N(t)Bu)(2)(NH(t)Bu)]LiCl}(2) (5) is obtained as a minor product (23%) from the 4:1 reaction. It is a centrosymmetric dimer in which each half consists of the tellurium diimide dimer 1 bonded through an exocyclic nitrogen atom to a molecule of LiTe(N(t)Bu)(2)(NH(t)Bu) which, in turn, is linked to a LiCl molecule. Crystals of 5 are monoclinic, of space group C2/c, with a = 27.680(6) ?, b = 23.662(3) ?, c = 12.989(2) ?, beta = 96.32(2) degrees, V = 8455(2) ?(3), and Z = 4. The final R and R(w) values were 0.046 and 0.047. At 65 degrees C in toluene solution, 5 dissociates into 1, LiCl, and {[LiTe(N(t)Bu)(2)(NH(t)Bu)](2)LiCl}(2) (4), which may also be prepared by treatment of [Li(2)Te(N(t)Bu)(3)](2) (6) with 2 equiv of HCl gas. The centrosymmetric structure of 6 consists of a distorted hexagonal prism involving two pyramidal Te(N(t)Bu)(3)(2)(-) anions linked by four Li atoms to give a Te(2)N(6)Li(4) cluster. Crystals of 6 are monoclinic, of space group P2(1)/c, with a = 10.194(2) ?, b = 17.135(3) ?, c = 10.482(2) ?, beta = 109.21(1) degrees, V = 1729.0(5) ?(3), and Z = 2. The final R and R(w) values were 0.026 and 0.023. VT (1)H and (7)Li NMR studies reveal that, unlike 1, compounds 2, 4, and 6 are fluxional molecules. Possible mechanisms for these fluxional processes are discussed.     

Conformations and energetics of sulfur and selenium diimides

The geometries and energetics of different conformations of sulfur and selenium diimides E(NR)(2) (E = S, Se; R = H, Me, (t)Bu, C(6)H(3)Me(2)-2,6, SiMe(3)) have been studied by using various ab initio and DFT molecular orbital techniques. The syn,syn conformation is found to be most stable for parent E(NH)(2), but in general, the preferred molecular conformation for substituted chalcogen diimides is syn,anti. In the case of E(NH)(2) the present calculations further confirm that syn,syn and syn,anti conformations lie energetically close to each other. From the three different theoretical methods used, B3PW91/6-31G proved to be the most suitable method for predicting the geometries of chalcogen diimides. The optimized geometrical parameters are in a good agreement with all available experimental data. While qualitative energy ordering of the different conformations is independent of the level of theory, the quantitative energy differences are dependent on the method used. The performance and reliability of higher level ab initio calculations and DFT methods using large basis sets were tested and compared with experimental information where available. All of the higher level ab inito methods give very similar results, but the use of large basis sets with the B3PW91 method does not increase the reliability of the results. The combination of CCSD(T)/cc-pVDZ with the B3PW91/6-31G-optimized geometries is found to be the method of choice to study energetic properties of chalcogen diimides.     

Synthetic applications of (Me3SiNSN)2E (E = S, Se) in chalcogen-nitrogen chemistry: formation and structural characterization of Cl2TeESN2 (E = S, Se) and [PPh4]2[Pd2(mu-Se2N2S)X4] (X = Cl, Br)

The reaction of (Me3SiNSN)2S with TeCl4 in CH2Cl2 affords Cl2TeS2N2 (1) and that of (Me3SiNSN)2Se with TeCl4 produces Cl2TeSeSN2 (2) in good yields. The products were characterized by X-ray crystallography, as well as by NMR and vibrational spectroscopy and EI mass spectrometry. The Raman spectra were assigned by utilizing DFT molecular orbital calculations. The pathway of the formation of five-membered Cl2TeESN2 rings by the reactions of (Me3SiNSN)2E with TeCl4 (E = S, Se) is discussed. The reaction of (Me3SiNSN)2Se with [PPh4]2[Pd2X6] yields [PPh4]2[Pd2(mu-Se2N2S)X4] (X = Cl, 4a; Br, 4b), the first examples of complexes of the (Se2N2S)2- ligand. In both cases, this ligand bridges the two palladium centers through the selenium atoms.     

Preparation and structure of a ruthenium dicarbonyl derivative of the P2N4S2 ring

The reaction of Ru(CO)₄(C₂H₄) or Ru(CO)₅ with 1,5-Ph₄P₂N₄S₂ in CH₂Cl₂/hexane at 23°C produces the dimer [Ru(CO)₂(Ph₄ P₂N₄S₂)]₂ (2), which was shown by X-ray crystallography to have a centrosymmetric structure in which the P₂N₄S₂ ring is attached to one ruthenium atom through two (geminal) nitrogen atoms and the remote sulfur atom and serves as a bridge to the other ruthenium atom via the second sulfur atom. Crystals of 2 ·2(CH₂Cl₂) are triclinic, space group P (No. 2), a = 12.901(1) Å, b = 13.072(1) Å, c = 10.123(1) Å, = 100.88(1)°, β = 98.90(1)°, γ = 67.50(1)°, V = 1542.4(3) Å, Z = 1 with final R and R_w values of 0.040 and 0.027, respectively.     

Synthesis and structures of aluminum and magnesium complexes of tetraimidophosphates and trisamidothiophosphates: EPR and DFT investigations of the persistent neutral radicals {Me2Al[(mu-NR)(mu-NtBu)P(mu-NtBu)2]Li(THF)2}(*) (R = SiMe3, tBu)

Reactions of (RNH)(3)PNSiMe(3) (3a, R = (t)()Bu; 3b, R = Cy) with trimethylaluminum result in the formation of {Me(2)Al(mu-N(t)Bu)(mu-NSiMe(3))P(NH(t)()Bu)(2)]} (4) and the dimeric trisimidometaphosphate {Me(2)Al[(mu-NCy)(mu-NSiMe(3))P(mu-NCy)(2)P(mu-NCy)(mu-NSiMe(3))]AlMe(2)} (5a), respectively. The reaction of SP(NH(t)Bu)(3) (2a) with 1 or 2 equiv of AlMe(3) yields {Me(2)Al[(mu-S)(mu-N(t)Bu)P(NH(t)()Bu)(2)]} (7) and {Me(2)Al[(mu-S)(mu-N(t)()Bu)P(mu-NH(t)Bu)(mu-N(t)Bu)]AlMe(2)} (8), respectively. Metalation of 4 with (n)()BuLi produces the heterobimetallic species {Me(2)Al[(mu-N(t)Bu)(mu-NSiMe(3))P(mu-NH(t)()Bu)(mu-N(t)()Bu)]Li(THF)(2)} (9a) and {[Me(2)Al][Li](2)[P(N(t)Bu)(3)(NSiMe(3))]} (10) sequentially; in THF solutions, solvation of 10 yields an ion pair containing a spirocyclic tetraimidophosphate monoanion. Similarly, the reaction of ((t)BuNH)(3)PN(t)()Bu with AlMe(3) followed by 2 equiv of (n)BuLi generates {Me(2)Al[(mu-N(t)Bu)(2)P(mu(2)-N(t)Bu)(2)(mu(2)-THF)[Li(THF)](2)} (11a). Stoichiometric oxidations of 10 and 11a with iodine yield the neutral spirocyclic radicals {Me(2)Al[(mu-NR)(mu-N(t)Bu)P(mu-N(t)Bu)(2)]Li(THF)(2)}(*) (13a, R = SiMe(3); 14a, R = (t)Bu), which have been characterized by electron paramagnetic resonance spectroscopy. Density functional theory calculations confirm the retention of the spirocyclic structure and indicate that the spin density in these radicals is concentrated on the nitrogen atoms of the PN(2)Li ring. When 3a or 3b is treated with 0.5 equiv of dibutylmagnesium, the complexes {Mg[(mu-N(t)()Bu)(mu-NH(t)()Bu)P(NH(t)Bu)(NSiMe(3))](2)} (15) and {Mg[(mu-NCy)(mu-NSiMe(3))P(NHCy)(2)](2)} (16) are obtained, respectively. The addition of 0.5 equiv of MgBu(2) to 2a results in the formation of {Mg[(mu-S)(mu-N(t)()Bu)P(NH(t)Bu)(2)](2)} (17), which produces the hexameric species {[MgOH][(mu-S)(mu-N(t)()Bu)P(NH(t)Bu)(2)]}(6) (18) upon hydrolysis. Compounds 4, 5a, 7-11a, and 15-17 have been characterized by multinuclear ((1)H, (13)C, and (31)P) NMR spectroscopy and, in the case of 5a, 9a.2THF, 11a, and 18, by X-ray crystallography.     

Electronic structures and electronic spectra of the linkage isomers NSO and SNO

The relative stabilities and electronic structures of the linkage isomers NSO⁻ and SNO⁻ have been determined by the MNDO and ab initio Hartree—Fock—Slater methods. Both approaches predict a higher stability for SNO⁻ by ca. 100 kcal mol⁻¹, but an overlap population analysis indicates substantially higher bond orders for NSO⁻ compared to SNO⁻. The calculations also reveal a low energy pathway with a barrier of ca. 6 kcal mol⁻¹ for the isomerization process NSO⁻ → SNO⁻. Good agreement was found between the observed UV-visible absorption bands for NSO⁻ (λ_max 379 nm) and SNO⁻ (λ_max 340 nm) and calculated values of the electronic transition energies.     

Student-Designed Experiment: Preparation and Mass Spectrum of Cyclohexasulfur

The teaching laboratory is an ideal environment for fostering active learning; yet, it is often criticized for being too cookbook. In introductory courses, the high student population often dictates that many students perform the same experiment simultaneously. By working in discussion groups, with individual bench work, we are able to turn this communal effort into a strength. This article describes the revision of a recipe-style experiment into a student-designed procedure.     

A sulfur(II) complex of a dithioimidodiphosphinate

The structure of bis[P,P‐di‐tert‐butyl‐N‐(di‐tert‐butylphosphorothioyl)phosphinimidothioato‐κS]sulfur(II) toluene solvate (systematic name: 5,13‐dibutyl‐7,7,11,11‐tetramethyl‐8,9,10‐trithia‐6,12‐diaza‐5λ⁵,7λ⁵,11λ⁵,13λ⁵‐tetraphosphaheptadeca‐6,11‐diene‐5,13‐dithione toluene solvate), C₃₂H₇₂N₂P₄S₅·C₇H₈, at 173 K has monoclinic (C2/c) symmetry. The S^II centre of (SP^tBu₂NP^tBu₂PS–)₂S is coordinated in an S‐monodentate fashion to two [(SP^tBu₂)₂N]⁻ monoanions. The molecule resides on a twofold axis which bisects the central S atom. The internal P—S distance is ca 0.19 Å longer than the terminal P=S bond and there is a compensating alternation in P—N bond distances. The central S—S—S angle is 106.79 (8)°. The toluene solvent molecule is disordered about a twofold axis.