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Tristram Chivers

Publications and source records attributed to Tristram Chivers.

53 records · Page 3Linked to original sources
PubMed2002

Redox chemistry of tellurium bis(tert-butylamido)cyclodiphosph(V)azane disulfide and diselenide systems: a spectroscopic and structural study.

The redox chemistry of tellurium-chalcogenide systems is examined via reactions of tellurium(IV) tetrachloride with Li[(t)()BuN(E)P(mu-N(t)Bu)(2)P(E)N(H)(t)Bu] (3a, E = S; 3b, E = Se). Reaction of TeCl(4) with 2 equiv of 3a in THF generates the tellurium(IV) species TeCl(3)[HcddS(2)][H(2)cddS(2)] 4a [cddS(2) = (t)BuN(S)P(mu-N(t)Bu)(2)P(S)N(t)Bu] at short reaction times, while reduction to the tellurium(II) complex TeCl(2)[H(2)cddS(2)](2) 5a is observed at longer reaction times. The analogous reaction of TeCl(4) and 3b yields only the tellurium(II) complex TeCl(2)[H(2)cddSe(2)](2) 5b. The use of 4 equiv of 3a or 3b produces Te[HcddE(2)](2) (6a (E = S) or 6b (E = Se)). NMR and EPR studies of the 5:1 reaction of 3a and TeCl(4) in THF or C(6)D(6) indicate that the formation of the Te(II) complex 6a via decomposition of a Te(IV) precursor occurs via a radical process to generate H(2)cddS(2). Abstraction of hydrogen from THF solvent is proposed to account for the formation of 2a. These results are discussed in the context of known tellurium-sulfur and tellurium-nitrogen redox systems. The X-ray crystal structures of 4a.[C(7)H(8)](0.5), 5a, 5b, 6a.[C(6)H(14)](0.5), and 6b.[C(6)H(14)](0.5) have been determined. The cyclodiphosph(V)azane dichalcogenide ligand chelates the tellurium center in an E,N (E = S, Se) manner in 4a.[C(7)H(8)](0.5), 6a.[C(6)H(14)](0.5), and 6b.[C(6)H(14)](0.5) with long Te-N bond distances in each case. Further, a neutral H(2)cddS(2) ligand weakly coordinates the tellurium center in 4a small middle dot[C(7)H(8)](0.5) via a single chalcogen atom. A similar monodentate interaction of two neutral ligands with a TeCl(2) unit is observed in the case of 5a and 5b, giving a trans square planar arrangement at tellurium.

Journal Article↗
PubMed2002

Preparation and structural characterization of (Me(3)SiNSN)(2)Se, a new synthon for sulfur-selenium nitrides.

The reaction of (Me(3)SiN)(2)S with SeCl(2) (2:1 ratio) in CH(2)Cl(2) at -70 degrees C provides a route to the novel mixed selenium-sulfur-nitrogen compound (Me(3)SiNSN)(2)Se (1). Crystals of 1 are monoclinic and belong the space group P2(1)/c, with a = 7.236(1) A, b = 19.260(4) A, c = 11.436(2) A, beta = 92.05(3) degrees, V = 1592.7(5) A(3), Z = 4, and T = -155(2) degrees C. The NSNSeNSN chain in 1 consists of Se-N single bonds (1.844(3) A) and S=N double bonds (1.521(3)-1.548(3) A) with syn and anti geometry at the N=S=N units. The N-Se-N bond angle is 91.8(1) degrees. The EI mass spectrum shows a molecular ion with good agreement between the observed and calculated isotopic distributions. The (14)N NMR spectrum exhibits two resonances at -65 and -77 ppm. Both (13)C and (77)Se NMR spectra show single resonances at 0.83 and 1433 ppm, respectively. The reaction of 1 with an equimolar amount of SeCl(2) produces 1,5-Se(2)S(2)N(4) (2) in a good yield, and that of (Me(3)SiNSN)(2)S with SCl(2) affords S(4)N(4) (3), but the reactions of (Me(3)SiNSN)(2)Se with SCl(2) and (Me(3)SiNSN)(2)S with SeCl(2) result in the formation of a mixture of 2 and 3. A likely reaction pathway involves the intermediate formation of E(2)N(2) fragments (E = S, Se).

Journal Article↗
PubMed2001

Imido Analogues of Common Oxo Anions: A New Episode in the Chemistry of Cluster Compounds.

Oxo anions of p- and d-block elements, for example, SiO(4)(4-), PO(4)(3-), SO(4)(2-), and CrO(4)(2-), are commonly encountered species. The full or partial replacement of the oxo ligands by isoelectronic imido (NR) groups generates homoleptic polyimido anions of the type [E(NR)(x)](z-) or heteroleptic imidooxo anions with the general formula [O(y)E(NR)(x-y)](z-) (where E=main group element or transition metal). The alkali metal derivatives of this new class of anions form ternary or quaternary cluster systems, respectively. The structures of these clusters can be rationalized in terms of the self-assembly of fundamental building blocks. An understanding of the factors that control this process may allow the design of functional materials with specific properties. In addition, these anions are attracting attention as multidentate ligands with unique electronic and stereochemical properties that may engender novel metal-centered chemistry.

Journal Article↗
PubMed1999

Template Effects of Lithium Salts on the Crystallization of Diazasulfates: X-ray Structures of {THF.Li(2)[O(2)S(N(t)Bu)(2)]}(8).2LiOH.2LiCl and {(THF.Li)(2)[O(2)S(N(t)Bu)(2)].(THF)LiCl}(2).

The addition of 2 equiv of (n)BuLi to solutions of O(2)S[N(H)R](2) (R = (i)Pr, (t)Bu) produces the dilithium diazasulfates {Li(2)[O(2)S(N(i)Pr)(2)]}(n)() (2) and {THF.Li(2)[O(2)S(N(t)Bu)(2)]}(n)() (3), which were characterized by solid-state (7)Li and (13)C NMR spectroscopy. Crystals were obtained from a THF/n-hexane solution of 3 and determined by X-ray crystallography to be {THF.Li(2)[O(2)S(N(t)Bu)(2)]}(8).2LiOH.2LiCl (4), which consists of a 64-atom (Li(20)S(8)N(16)O(18)Cl(2)) cluster composed of two Li(4)O(4) cubes and a central Li(4)O(4) step-shaped ladder. The eight [O(2)S(N(t)Bu)(2)](2)(-) dianions in 4 exhibit three distinct modes of bonding to the Li(+) cations: (a) bis-(N,O),(N',O')-chelate, (b) N,O-chelate, bis-N',O'-monodentate, and (c) bis-(N,O),(N,N')-chelate, O'-monodentate. The synthesis of 3 in the presence of 1 equiv of LiCl produces the dimer {(THF.Li)(2)[O(2)S(N(t)Bu)(2)].(THF)LiCl}(2) (5). The structure of 5 incorporates an 18-atom (Li(6)S(2)N(4)O(4)Cl(2)) quinary cluster in which two {[THF.Li(&mgr;-O)(&mgr;-N(t)Bu)](2)S} molecules are held together by two (THF.LiCl) units. The mean Li-Cl distance (2.348 Å) linking the {[THF.Li(&mgr;-O)(&mgr;-N(t)Bu)](2)S} molecules to the (THF.LiCl) units is significantly shorter than the corresponding value of 2.483 Å within these units. Crystal data: 4, monoclinic, P2(1)/n, a = 18.557(1) Å, b = 15.731(1) Å, c = 28.063(2) Å, beta = 107.381(1) degrees, V = 7817.9(9) Å(3), and Z = 2; 5, monoclinic, P2(1)/n, a = 11.583(3) Å, b = 17.126(5) Å, c = 13.891(4) Å, beta = 94.613(4) degrees, V = 2747(1) Å(3), and Z = 2.

Journal Article↗
PubMed1999

Steric and Solvation Effects on the Aggregation of Lithium Thioamidates: Single-Strand Polymers with (LiS)(n)() and (LiNCS)(n)() Backbones.

The addition of methyllithium or n-butyllithium to alkyl isothiocyanates produces lithium thioamidates {Li[RCS(NR')]}(n)(). Three such compounds were structurally characterized after recrystallization from THF. When R = n-Bu and R' = t-Bu, an unsolvated hexamer {Li[n-BuCS(N-t-Bu)]}(6) (1) is obtained. By contrast, the solvated derivatives {Li.THF[MeCS(N-t-Bu)]}(infinity) (2.THF) and {Li.2THF[MeCS(NMe)]}(infinity) (3.2THF) form single-strand polymers. The monosolvated complex 2.THF involves four-membered rings with an (LiS)(n)() backbone whereas the disolvate 3.2THF is comprised of LiNCS repeating units. The structures of all three aggregates can be generated via sterically directed solvation of a common dimeric precursor. Crystal data for 2.THF: C(10)H(20)NLiOS, monoclinic, P2(1)/a (#14), a = 9.129(2) Å, b = 11.099(2) Å, c = 12.537(2) Å, beta = 94.14(2) degrees, V = 1267.0(4) Å(3), Z = 4. Crystal data for 3.2THF: C(11)H(22)NLiSO(2), monoclinic, P2(1)/a (#14), a = 10.974(3) Å, b = 8.575(5) Å, c = 14.898(5) Å, beta = 91.33(3) degrees, V = 1401.6(10) Å(3), Z = 4.

Journal Article↗
PubMed1999

Reactions of cis-[(t)BuNTe(&mgr;-N(t)Bu)](2) with CF(3)SO(3)Me and M[O(3)SCF(3)] (M = Ag, Cu): Chelation, Cis --> Trans Isomerization, and the Spirocyclic Ligand [(t)BuNTe(&mgr;-N(t)Bu)(2)Te(&mgr;-O)](2).

The first investigations of coordination complexes of the tellurium diimide dimer [(t)BuNTe(&mgr;-N(t)Bu)](2) (1a) are presented. The coinage metals Ag(+) and Cu(+) were chosen to evaluate the ability of 1a to function as a chelating or bridging ligand. Reaction of 1a with Ag[O(3)SCF(3)] in toluene produces [Ag(2)L(2)][O(3)SCF(3)](2) (5, L = 1a) or, in the presence of LiCl, [Ag(2)L(2)(&mgr;-Cl)][O(3)SCF(3)] (3). In 4 the two Ag(+) ions bridge two molecules of cis-1a and engage in a weak Ag.Ag bonding interaction. In 3 the Cl(-) ion bridges two Ag(+) ions, which are each chelated to the terminal N(t)Bu groups of 1a. Treatment of 1a with Cu[O(3)SCF(3)] in toluene yields {[CuL][CF(3)SO(3)]}(n)() (5) which, in turn, reacts with 1a to form [Cu(2)L(3)][CF(3)SO(3)](2) (6). In 6 the two Cu(+) ions bridge cis and trans forms of 1a. The hydrolysis products {[(t)BuNTe(&mgr;-N(t)Bu)(2)Te(&mgr;-O)](2)[M(H(2)N(t)Bu)](2)}[O(3)SCF(3)](2) (7a, M = Ag; 7b, M = Cu) and [Cu(2)L((t)BuNH(2))(2)][O(3)SCF(3)](2) (8) were also structurally characterized. The complexes 7a,b contain the dimer [(t)BuNTe(&mgr;-N(t)Bu)(2)(&mgr;-O)](2) in which one of the terminal N(t)Bu ligands in 1a is replaced by an O atom. The central Te(2)O(2) ring in this spirocyclic ligand is planar with unsymmetrical oxygen bridging [d(Te-O) = 1.885(7) and 2.170(7) Å in 7b]. The ligand 1a in 8 is in the trans conformation. Mono- or dimethylation of 1a with CF(3)SO(3)Me was shown to occur at the terminal nitrogens by (1)H and (125)Te NMR spectroscopy.

Journal Article↗
PubMed1999

Preparation, X-ray Structure, and Spectroscopic Characterization of 1,5-Se(2)S(2)N(4).

The reaction of [(Me(3)Si)(2)N](2)S with equimolar amounts of SCl(2) and SO(2)Cl(2) produces S(4)N(4) in a good yield. The new chalcogen nitride 1,5-Se(2)S(2)N(4) has been prepared in high yield by two different reactions: (a) from [(Me(3)Si)(2)N](2)S and SeCl(4) and (b) from [(Me(3)Si)(2)N](2)Se with equimolar amounts of SCl(2) and SO(2)Cl(2). 1,5-Se(2)S(2)N(4) has a cage structure similar to those of S(4)N(4) and Se(4)N(4). The crystal structure is disordered with site occupation factors ca. 50% for selenium in each chalcogen atom position. The 12 eV EI mass spectrum shows Se(2)SN(2)(+) as the fragment with highest mass. Both the (14)N and (77)Se NMR spectra show a single resonance (-238 and 1418 ppm, respectively). These data rule out the possibility that the crystalline sample is a solid solution of S(4)N(4) and Se(4)N(4) and imply the presence of 1,5-Se(2)S(2)N(4). This deduction was further verified by Raman spectroscopy and vibrational analysis.

Journal Article↗
PubMed1998

ESR Investigations of the Radicals {Li(3)[E(N(t)Bu)(3)](2)}(*) (E = S, Se) and the Radical Anions SO(x)()(N(t)Bu)(3)(-)(x)()(*)(-) (x = 1, 2).

The air oxidation of the cluster compounds [Li(2)E(N(t)Bu)(3)](2) (E = S, Se) in toluene produces deep blue (E = S) or green (E = Se) solutions. The ESR spectra of these solutions consist of a septet (1:3:6:7:6:3:1) of decuplets. The simulation of these spectra shows that the secondary hyperfine splitting results from interaction of the unpaired electron with three equivalent (7)Li ions consistent with the formation of the neutral radicals {Li(3)[E(N(t)Bu)(3)](2)}(*) (4a, E = S, g = 2.0039, a((14)N) = 5.69 G, a((7)Li) = 0.82 G; 4b, E = Se, g = 2.00652, a((14)N) = 5.41 G, a((7)Li) = 0.79 G). Over a period of 25 h the seven line pattern of 4b is replaced first by a five line (1:2:3:2:1) spectrum (g = 2.009, a((14)N) = 13.4 G) and, subsequently, by a three line (1:1:1) spectrum (g = 2.00946, a((14)N) = 15.4 G, a((77)Se) = 4.3 G), neither of which exhibit (7)Li hyperfine splitting. These spectra are tentatively assigned to the radical anions SeO(N(t)Bu)(2)(*)(-) and SeO(2)(N(t)Bu)(*)(-), respectively. The cluster {Li(2)[O(2)S(N(t)Bu)]}(n)() (3) is prepared by the reaction of sulfur dioxide with 2 equiv of LiNH(t)Bu in toluene. The air oxidation of toluene solutions of {Li(2)[OS(N(t)Bu)(2)]}(6) (2a) or 3 produces deep blue species. In the former case the initial ESR spectrum is a 1:2:3:2:1 quintet (g = 2.009, a((14)N) = 13.3 G) which, after 16 h, evolves into a 1:1:1 triplet (g = 2.0088, a((14)N) = 15.9 G). The same triplet is observed in the ESR spectrum of oxidized solutions of 3 leading to the assignments OS(N(t)Bu)(2)(*)(-) and O(2)S(N(t)Bu)(*)(-) for the quintet and triplet, respectively. The disproportionation 2OS(N(t)Bu)(2)(*)(-) --> O(2)S(N(t)Bu)(*)(-) + S(N(t)Bu)(3)(*)(-) is indicated by the changes observed for the ESR spectra of oxidized solutions of 2a.

Journal Article↗
PubMed1997

Experimental and Theoretical Studies on 1,4,5,7-Dithiadiazepinyl Radicals: Preparation and X-ray Structure of 5-(Trimethylsilyl)tetrachlorobenzo-1,4,5,7-dithiadiazepine.

1,4,5,7-Dithiadiazepinyl radicals and their selenium analogs have been studied by density functional theory calculations. Compared to 1,2,3,5-dithiadiazolyls, this novel family of 9 pi-electron radicals is predicted to have low disproportionation and dimerization energies, properties that are advantageous for the preparation of molecular conductors. The radical [CH(3)C(6)H(3)S(2)N(2)C(C(6)H(4)CH(3)-4)](*)() (5a) was generated in solution by the cyclocondensation reaction of CH(3)C(6)H(3)(SCl)(2) with 4-CH(3)C(6)H(4)CN(2)(SiMe(3))(3) followed by treatment with PhSeCl. The ESR spectrum of 5a consists of a slightly asymmetric quintet (g = 2.0070 and A(N)(iso) = 4.9 G). The N-(trimethylsilyl)-substituted was characterized by X-ray crystallography: monoclinic, P2(1)/a, a = 12.585(3) Å, b = 12.211(2) Å, c = 14.003(2) Å, beta = 101.86(2) degrees, V = 2106.0(7) Å(3), and Z = 4. Polycyclocondensation reactions and thermal instability toward elimination of nitriles hamper the isolation of pure samples of the radicals.

Journal Article↗
PubMed1997

Theoretical and Experimental Studies of Six-Membered Selenium-Sulfur Nitrides Se(x)()S(4)(-)(x)()N(2) (x = 0-4). Preparation of S(4)N(2) and SeS(3)N(2) by the Reaction of Bis[bis(trimethylsilyl)amino]sulfane with Chalcogen Chlorides.

The reaction of [(Me(3)Si)(2)N](2)S with equimolar amounts of SCl(2) and S(2)Cl(2) produces S(4)N(2) in a good yield. The reaction of [(Me(3)Si)(2)N](2)S with a 3:1:1 mixture of S(2)Cl(2), Se(2)Cl(2), and SeCl(4) yields a dark brown-red insoluble material that was inferred to be mainly SSeSNSN on the basis of the elemental analysis, mass spectroscopy, vibrational analysis, and NMR spectroscopy. Attempts to prepare selenium-rich species resulted in the formation of elemental selenium or Se(3)N(2)Cl(2). The experimental work was supported by ab initio MO calculations which establish the structural and stability relationships of the different members of the series 1,3-Se(x)()S(4)(-)(x)()N(2) (x = 0-4). Full geometry optimization was carried out for each molecular species using the polarized split-valence MIDI-4 basis sets. The effects of electron correlation were taken into account involving the second-order Møler-Plessett perturbation theory. Each molecule was found to lie in an approximate half-chair conformation that is well established for 1,3-S(4)N(2) (i.e., interacting planar NEN and EEE fragments; E = S, Se). The bond parameters agree well with experimental information where available. Whereas the lengths of the bonds in the NEEEN fragment approach those of the single bonds, the bonds in the NEN fragment show marked double bond character. The stabilities of the molecules decrease expectedly with increasing selenium content as judged by the total binding energy at the MP2 level of theory. Within a given chemical composition, isomers containing a N=Se=N unit lie higher in energy than those containing a N=S=N unit. These results may explain why selenium-rich Se(x)()S(4)(-)(x)()N(2) molecules have not been isolated.

Journal Article↗
PubMed1997

Formation and X-ray Structures of Eight- and Sixteen-Membered Rings (ArC)(n)()N(2)(n)()(SPh)(n)() [n = 2, Ar = 4-XC(6)H(4) (X = Br, CF(3)); n = 4, Ar = 4-BrC(6)H(4)] and the Electronic Structures of (HC)(2)N(4)(SH)(2) and (HC)(2)N(4)(SH)(2)(2)(-).

Optimum yields of heterocyclic products are obtained when the reaction of 4-XC(6)H(4)CN(2)(SiMe(3))(3) (X = Br, CF(3)) with PhSCl in a 1:3 molar ratio in CH(2)Cl(2) is carried out at -100 degrees C followed by the mixture being warmed to -70 degrees C for 16 h. Under these conditions the eight-membered rings (4-XC(6)H(4))(2)C(2)N(4)S(2)Ph(2) (1b, X = Br; 1c, X = CF(3)) are obtained in 64 and 80% yields, respectively, in addition to the purple diazenes Z,E,Z-PhSN(4-XC(6)H(4))CN=NC(C(6)H(4)X-4)NSPh (2b, 8%; 2c, 19%) and, in the case of X = Br, the sixteen-membered ring (4-BrC(6)H(4))(4)C(4)N(8)S(4)Ph(4) (3) (8%). With a reaction time of 40 h the yield of 3 is increased to 25%. By contrast, the reaction of 3-BrC(6)H(4)CN(2)(SiMe(3))(3) with 3 equiv of PhSCl at -70 degrees C gives Z,E,Z-PhSN(3-BrC(6)H(4))CN=NC(3-BrC(6)H(4))NSPh in 75% yield. A possible pathway for the formation of cyclic products is proposed. The solid-state structures of 1b, 1c, and 3 were determined by X-ray crystallography. The eight-membered rings 1b and 1c adopt long boat conformations with the phenyl groups (attached to S) in equatorial positions. Density functional theory (DFT) calculations for the model ring system (HC)(2)N(4)(SH)(2) reveal that the observed C(2)(v)() geometry is the result of a second-order Jahn-Teller distortion of the planar (D(2)(h)()) structure. The chair conformer (C(2)(h)()) is only ca. 10 kJ mol(-)(1) higher in energy than the boat conformer. The hypothetical dianion (HC)(2)N(4)(SH)(2)(2)(-) is predicted to have a transannular S.S contact of about 2.5 Å. The sixteen-membered ring 3 has a cradle-like structure with S(4) symmetry.

Journal Article↗
PubMed1996

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) Å, b = 23.662(3) Å, c = 12.989(2) Å, beta = 96.32(2) degrees, V = 8455(2) Å(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) Å, b = 17.135(3) Å, c = 10.482(2) Å, beta = 109.21(1) degrees, V = 1729.0(5) Å(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.

Journal Article↗
PubMed1996

Experimental and Theoretical Investigations of the Formation of the Diazene PhSN=C(H)N=NC(H)=NSPh from HCN(2)(SPh)(3) by a Thiyl-Radical-Catalyzed Mechanism: Identification of the HC(NSPh)(2)(*) Radical and X-ray Structures of HCN(2)(SPh)(3) and PhSN=C(H)N=NC(H)=NSPh.

The reaction of HCN(2)(SiMe(3))(3) with benzenesulfenyl chloride in a 1:3 molar ratio produces HCN(2)(SPh)(3) (4) as thermally unstable, colorless crystals. The decomposition of (4) in toluene at 95 degrees C was monitored by UV-visible, (1)H NMR and ESR spectroscopy. The major final products of the decomposition were identified as PhSN=C(H)N=NC(H)=NSPh (5) and PhSSPh. The structures of 4 and 5 were determined by X-ray crystallography. The crystals of 4 are monoclinic, space group P2(1)/a, with a = 9.874(2) Å, b = 19.133(2) Å, c = 10.280(2) Å, beta = 113.37(1) degrees, V = 1782.8(5) Å(3), and Z = 4. The final R and R(w) values were 0.042 and 0.049, respectively. The crystals of 5 are monoclinic, space group P2(1)/n, with a = 5.897(6) Å, b = 18.458(10) Å, c = 7.050(8) Å, beta = 110.97(5) degrees, V = 716(1) Å(3), and Z = 2. The final R and R(w) values were 0.075 and 0.085, respectively. The diazene 5 adopts a Z,E,Z structure with weak intramolecular S.N contacts of 2.83 Å, giving rise to four-membered NCNS rings. During the thermolysis of 4 at 95 degrees C in toluene a transient species (lambda(max) 820 nm) was detected. It decomposes with second-order kinetics to give 5 (lambda(max) 450 nm). The ESR spectrum of the reaction mixture consisted of the superposition of a three-line 1:1:1 spectrum (g = 2.0074, A(N) = 11.45 G), attributed to (PhS)(2)N(*), upon a doublet of quintets (1:2:3:2:1) with g = 2.0070, A(N) = 6.14 G, A(H) = 2.1 G assigned to the radical HCN(2)(SPh)(2)(*). Density functional theory (DFT) calculations for the models of the radical showed the E,Z isomer to have the lowest energy. Thermochemical calculations indicate that the decomposition of HCN(2)(SH)(3) into the diazene (Z,E,Z)-HSN=C(H)N=NC(H)=NSH (and 2 HSSH) is substantially more exothermic (DeltaH = -176.1 kJ mol(-)(1)) than the corresponding formation of the isomeric eight-membered ring (HC)(2)N(4)(SH)(2) (DeltaH = -40.6 kJ mol(-)(1)). These calculations also indicate that the diazene is formed by a mechanism in which the RS(*) radical acts as a catalyst.

Journal Article↗
PubMed1996

Preparation, Crystal Structures, and Isomerization of the Tellurium Diimide Dimers RNTe(&mgr;-NR')(2)TeNR (R = R' = (t)Bu; R = PPh(2)NSiMe(3), R' = (t)Bu, (t)Oct): X-ray Structure of the Telluradiazole Dimer [(t)Bu(2)C(6)H(2)N(2)Te](2).

The reaction of R'NHLi (R = (t)Bu, (t)Oct) with Ph(2)P(NSiMe(3))(2)Te(Cl)NPPh(2)NSiMe(3) in toluene at -78 degrees C, followed by warming to 23 degrees C, produces the tellurium diimide dimers RNTe(&mgr;-NR')(2)TeNR (2a, R' = (t)Bu, R = NPPh(2)NSiMe(3); 2b, R' = (t)Oct, R = NPPh(2)NSiMe(3)) and Ph(2)P(NHSiMe(3))(NSiMe(3)). X-ray analyses revealed that 2a and 2b have centrosymmetric structures containing a planar four-membered Te(2)N(2) ring and short exocyclic tellurium-nitrogen bond lengths (d(Te-N) = 1.900(5) and 1.897(4) or 1.905(4) Å for 2a and 2b, respectively). The exocyclic imido substituents adopt a trans arrangement with respect to the Te(2)N(2) ring. By contrast, the reaction of 2,4,6-(t)Bu(3)C(6)H(2)NHLi with Ph(2)P(NSiMe(3))(2)Te(Cl)NPPh(2)NSiMe(3) in toluene under similar conditions produces the telluradiazole ((t)Bu(2)C(6)H(2)N(2)Te)(2) (3), which exists as a weakly associated dimer in the solid state with intramolecular Te-N distances of 2.628(4) Å. The tellurium diimide dimer (t)BuNTe(&mgr;-N(t)Bu)(2)TeN(t)Bu (2c'), prepared by the reaction of TeCl(4) with (t)BuNHLi in a 1:4 molar ratio, consists of a folded Te(2)N(2) ring with exocyclic N(t)Bu groups in a cis orientation. The (1)H, (31)P, and (125)Te NMR spectra of 2a and 2b indicate that the trans isomers slowly transform into the corresponding cis isomers in solution. Crystals of 2b are triclinic, space group P&onemacr; (No. 2), with a = 13.304(3) Å, b = 16.927(3) Å, c = 13.292(5) Å, alpha = 98.94(2), beta = 109.27(2), gamma = 69.04(2) degrees, V = 2636(1) Å(3), and Z = 4. The final R and R(w) values were 0.034 and 0.033, respectively. Crystals of 2c' are orthorhombic, space group Pnma (No. 62), with a = 9.535(3) Å, b = 14.264(3) Å, c = 16.963(4) Å, V = 2307.1(9) Å(3), and Z = 4. The final R and R(w) values were 0.040 and 0.040, respectively. Crystals of 3 are monoclinic, space group P2(1)/n (No. 14), with a = 9.117(3) Å, b = 11.481(4) Å, c = 16.550(4) Å, beta = 97.76(2) degrees, V = 1716.5(8) Å(3), and Z = 4. The final R and R(w) values were 0.031 and 0.034, respectively.

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