NMR-spektroskopische Untersuchungen an Mercaptophosphazenen. II. NMR-spektroskopische Untersuchungen an 15N-markierten Mercaptophosphazenen

N.M.R. Spectroscopic Investigations of Thiophosphazenes. II. N.M.R. Spectroscopic Investigations of ¹⁵N Labelled Thiophosphazenes Completely ¹⁵N labelled compounds of the type ¹⁵N₃P₃Cl_6?n(SR)_n, R = Et or Ph; n = 0, 2, 4, or 6, and of the type ¹⁵N₄P₄Cl_8?n(SR)_n, R = Et; n = 0, 4, or 8, were prepared and investigated by means of both ³¹P n.m.r. spectroscopy and ¹⁵N n.m.r. spectroscopy respectively. The coupling constants ²J_PP, in some cases only found by simulating the spectra, and the coupling constants ¹J_PN are given. The values of these coupling constants and their relation are discussed. The general tendency is visible, that with increasing coupling constant ¹J_PN the coupling constant ²J_PP decreases. With increasing grade of substitution n the ¹⁵N chemical shifts are changed to higher fields.     

Darstellung,Kristallstrukturen und Schwingungsspektren von [Pt(N3)6]2– und [Pt(N3)Cl5]2–, 195Pt‐ und 15N‐NMR‐Spektren von [Pt(N3)nCl6–n]2– und [Pt(15NN2)n(N215N)6–n]2–, n = 0–6

Synthesis, Crystal Structures, and Vibrational Spectra of [Pt(N₃)₆]^2– and [Pt(N₃)Cl₅]^2–, ¹⁹⁵Pt and ¹⁵N NMR Spectra of [Pt(N₃)_nCl_6–n]^2– and [Pt(¹⁵NN₂)_n(N₂¹⁵N)_6–n]^2–, n = 0–6 By ligand exchange of [PtCl₆]^2– with sodium azide mixed complexes of the series [Pt(N₃)_nCl_6–n]^2– and with ¹⁵N‐labelled sodium azide (Na¹⁵NN₂) mixtures of the isotopomeres [Pt(¹⁵NN₂)_n(N₂¹⁵N)_6–n]^2–, n = 0–6 and the pair [Pt(¹⁵NN₂)Cl₅]^2–/[Pt(N₂¹⁵N)Cl₅]^2– are formed. X‐ray structure determinations on single crystals of (Ph₄P)₂[Pt(N₃)₆] ( 1 ) (triclinic, space group P1, a = 10.175(1), b = 10.516(1), c = 12.380(2) Å, α = 87.822(9), β = 73.822(9), γ = 67.987(8)°, Z = 1) and (Ph₄As)₂[Pt(N₃)Cl₅] · HCON(CH₃)₂ ( 2 ) (triclinic, space group P1, a = 10.068(2), b = 11.001(2), c = 23.658(5) Å, α = 101.196(14), β = 93.977(15), γ = 101.484(13)°, Z = 2) have been performed. The bond lengths are Pt–N = 2.088 ( 1 ), 2.105 ( 2 ) and Pt–Cl = 2.318 Å ( 2 ). The approximate linear azido ligands with N^α–N^β–N^γ‐angles = 173.5–174.6° are bonded with Pt–N^α–N^β‐angles = 116.4–121.0°. In the vibrational spectra the PtCl stretching vibrations of (n‐Bu₄N)₂[Pt(N₃)Cl₅] are observed at 318–345, the PtN stretching modes of (n‐Bu₄N)₂[Pt(N₃)₆] at 401–428 and of (n‐Bu₄N)₂[Pt(N₃)Cl₅] at 408–413 cm^–1. The mixtures (n‐Bu₄N)₂[Pt(¹⁵NN₂)_n(N₂¹⁵N)_6–n], n = 0–6 and (n‐Bu₄N)₂[Pt(¹⁵NN₂)Cl₅]/(n‐Bu₄N)₂[Pt(N₂¹⁵N)Cl₅] exhibit ¹⁵N‐isotopic shifts up to 20 cm^–1. Based on the molecular parameters of the X‐ray determinations the vibrational spectra are assigned by normal coordinate analysis. The average valence force constants are f_d(PtCl) = 1.93, f_d(PtN^α) = 2.38 and f_d(N^αN^β, N^βN^γ) = 12.39 mdyn/Å. In the ¹⁹⁵Pt NMR spectrum of [Pt(N₃)_nCl_6–n]^2–, n = 0–6 downfield shifts with the increasing number of azido ligands are observed in the range 4766–5067 ppm. The ¹⁵N NMR spectrum of (n‐Bu₄N)₂[Pt(¹⁵NN₂)_n(N₂¹⁵N)_6–n], n = 0–6 exhibits by ¹⁵N–¹⁹⁵Pt coupling a pseudotriplett at –307.5 ppm. Due to the isotopomeres n = 0–5 for terminal ¹⁵N six well‐resolved signals with distances of 0.03 ppm are observed in the low field region at –201 to –199 ppm.     

14/15N-NMR und 11B-NMR-Daten von Trifluormethylthioaminoboranen mit natürlicher Isotopenhäufigkeit

^14/15N N.M.R. and ¹¹B N.M.R. Data of Trifluoromethylthioamino-boranes with Natural Isotope Abundance (Part 2) ^14/15N as well as ¹¹B-NMR data for trifluoromethylthioabminoboranes of the types XnB[N(SCF₃)₂], with X = F, Cl, Br, N₃, or NHSCF₃, n = 0, 1 or 2, and Cl_3?nB(NHSCF₃)n with n = 1, 2 or 3, as well as for the amine-borne Me₃NBCl₂N(SCF₃)₂ and the cyclic borazene (CF₃SNHBNH)₃ are reported. These data are used, together with a qualitative analysis of the bonding situation based on observed rotational barriers and known structures, to analyse for B ← N back donation in these compounds. Relatively small variations in δ^14/15N compared to those observed for alkylaminoboranes as well as large variations in δ¹¹B are suggestive of small contributions only from back bonding. In addition the ?halogene like”? nature of the (CF₃S)₂N group is confirmed. For the series X₂BN(SCF₃)₂ (X = F, Cl, Br on N₃), XB[N(SCF₃)₂]₂ (X = Cl, Br, N₃ or N(SCF₃)₂) and Cl_n?3B(NHSCF₃)_n (n = 1, 2 or 3) a linear relationship for δ¹¹B and δ^14/15N is observed. It is furtheron demonstrated that hitherto known δ^14/15N/¹¹B correlations are valid only in case of strong B ← N back donation.     

Bildung und NMR-spektroskopische Charakterisierung von Alk-(ar-)oxyderivaten von Trichlorphosphazen-N-phosphoryldichlorid,Cl3PN?P(O)Cl2, Imido- und N-Methylimidodiphosphoryltetrachlord,Cl2P(O)NHP(O)Cl2 bzw. Cl2P(O)N(CH3)P(O)Cl2

Formation and N.M.R.-Spectroscopic Characterization of Alk-(ar-)oxy Derivatives of Trichlorophosphazene-N-phosphoryldichloride, Cl₃P?N? P(O)Cl₂, Imido- and N-Methylimidodiphosphoryltetrachloride, Cl₂P(O)NHP(O)Cl₂ and Cl₂P(O)N(CH₃)P(O)Cl₂ The ester chlorides and esters P₂NOCl_5?x(OR)_x (x = 1?5), P₂(NH)O₂Cl_4?x(OR)_x (x = 1–4) and P₂(NCH₃)O₂Cl_4–x(OR)_x (x = 1–4) derived from the title compounds by substitution of chlorine atoms by alk- or aroxy groups are characterized by their ³¹P-n.m.r. data. The possibilities for forming these compounds by alcoholysis, chloridolysis, dealkylation and P? N-bond formation are discussed.     

‘Anomalous’ 2J(Sn?H) coupling in mono– and dichloromethyltin compounds

The linear relationship between the coupling constants ¹J(Sn? ¹³C) and ²J(Sn? H), observed for a number of organotin compounds, does not hold for coupling in the Sn? CH_nCl_3?n group of mono- and dichloromethyltin compounds. A complete determination of all NMR parameters of the compounds Me₃Sn-CH_nCl_3?n (n = 0 to 3) shows no further anomalies, indicating that steric factors must be responsible for the unusually low values of ²J(Sn? H) in the SnCH_nCl_3?n group. Molecular weight measurements support this theory, showing that the chlorine-containing compounds are associated.     

Preparation and properties of perfluorochloromethyl-mercaptophosphoryldichlorides and -chlorophosphanes

In Arbuzov-type reactions CF_nCl_3?nSCl reacts with ROPCl₂ (R = CH₃, C₂H₅) to give CF_nCl_3?nSP(O)Cl₂ (n = 3,2,1,0). The corresponding reaction with CF₃SeX (X = Cl, Br) produces CF₃SeP(O)Cl₂ in good yields only in the presence of catalysts such as SbCl₅ or BCl₃. Reactions between P₄ and the sulfenylchlorides produce (CF_nCl_3?nS)_xPCl_3?n (n = 3,2,1 and x = 1,2). On heating CF_n′ Cl_3?n′ SP(O)Cl₂ (n′ = 2,1,0) decompose to P(O)Cl₃ and SCF_n′ Cl_2?n′. During this process fluorination of P(O)Cl₃ to P(O)F₃ by SCF₂ is observed. A Cl/Br exchange between CF_nCl_3?nSP(O)Cl₂ (n = 3,2) and PBr₃ was proved ¹⁹F? and ³¹P-NMR-spectroscopically.Chemical and physical properties of the newly synthesized compounds will be discussed.     

Beitrag zur Chemie der Phosphor-Stickstoff-Verbindungen. Reaktion von Cl2(O)P?NH?P(O)Cl2 mit Tetrahydrofuran

Contribution to the Chemistry of Phosphorus-Nitrogen Compounds. Reaction of Cl₂(O)P? NH? P(O)Cl₂ with Tetrahydrofuran As well as many phosphorus compounds, the imidodiphosphoryl tetrachloride HN(P(O)Cl₂)₂ reacts with a large excess of tetrahydrofuran to give the polytetrahydrofuran. Otherwise, if we use smaller molecular ratios THF/HN(P(O)Cl₂)₂ (1/2 to 3) a polytetrahydrofuran with short chains and N(ω-hydroxypolytetramethylenoxy)imidodiphosphoryl tetrachloride R? N(P(O)Cl₂)₂; R = H(O(CH₂)₄)_n- are obtained at 22° or 30°C. The ¹H and ³¹P n.m.r. spectra show that oxonium ions are formed with progressive additions of THF to HN(POCl₂)₂/CCl₄ solution. Then two mechanisms have been considered by nucleophilic attack on carbon α of oxonium ion coming from: the free electronic dublett on oxygen of THF to give polytetrahydrofuran or (and) from the nitrogen of imido diphosphoryl tetra chloride anion ((Cl₂OP)₂N)^? to obtain N(ω-hydroxypolytetramethylenoxy)imidodiphosphoryl tetrachloride.     

1H and 31P nuclear magnetic resonance spectra of compounds containing the PIII?N?PV skeleton

The ¹H and ³¹P NMR spectra of a series of compounds containing the P^III-N-P^V skeleton including Cl₂PNMeP(Z)Cl₂ (Z?O or S), Cl₂P·NMe·P(O)CINMe₂, P₄(NMe)₆Z_n (Z?S, n = 1?3; Z?Se, n = 1), XP(NBu^t)₂P(Z)X (X?Cl, Z?O or S; X?OMe, Z?S or Se; X?NMe₂, Z?S or Se; X?NEt₂, Z?Se), (X?O or S), and Ph₂PNRP(S)Ph₂ (R?Me, Et) have been obtained. ¹H-{³¹P} double resonance, and in selected cases, ³¹P-{¹H, ⁷⁷Se} and ³¹P-{¹H, ³¹P} triple resonance experiments, indicate that ²J(P^III NP^V) is positive in acyclic compounds, negative in most cyclic or cage compounds, and furthermore, is related to the conformation adopted by the P^III-N bond.     

Darstellung und Charakterisierung von bindungsisomeren Hexakis-(thiocyanato-isothiocyanato)-rhodaten(III) und Di-μ-thiocyanato-N,S-octathiocyanatodirhodat(III)

Preparation and Characterization of Bond-Isomeric Hexakis-(thiocyanato-isothiocyanato)rhodates(III) and Di-μ-thiocyanato-N, S-octathiocyanatodirhodate (III) The reaction of RhCl₃ with an aqueous solution of KSCN does not yield pure [Rh(SCN)₆]^3? as is supposed until now but a mixture of the bond isomers [Rh(NCS)_n(SCN)_6?n]^3?, n = 0–3. By heating the tetrabutylammonium salts N coordination of the ambident SCN^? is favoured forming mixtures with n = 0–4. The pure bond isomers are separated by ion exchange chromatography on diethylaminoethyl cellulose. Extracting the mixture (n = 0–3) with triphenylphosphiniminiumchloride from water into CH₂Cl₂ [Rh₂(SCN)₁₀]^4? is formed, containing two Rh? SCN? Rh bridges and exclusively S-coordinated terminal ligands. Depending on S or N bonding the IR and Raman spectra show typical vibrations: ν_CN(N) and ν_CN(S): 2095–2170, ν_CS(N): 810–835, ν_CS(S): 695–710, δ_NCS: 460–470, δ_SCN: 425–465, ν_RhN: 300–340, ν_RhS: 265–306 cm^?1. The application of group theory indicates that for n = 2 and 4 the cis-, for n = 3 the mer-compound exists. Except the inner ligand vibrations the Rh? N and Rh? S valence vibrations are assigned according to the supposed point symmetries. By interaction of trans-positioned ligands characteristic shifts are caused. The isolated complexes may also be distinguished and identified by their electronic spectra.     

The B–N Bond in Some Aminoboranes and an Iminoborane,Studied by 11B and 15N NMR Spectroscopy and DFT Methods

¹⁵N NMR spectra of several aminoboranes (Me₂B–NMe₂, Cl₂B–NMe₂, Br₂B–NMe₂, OCH₂CH₂OB–NMe₂), three N‐pyrrolylboranes, and an iminoborane (tBu–B≡N–tBu) was measured. The spin‐spin coupling constants ¹J(¹⁵N, ¹¹B) were resolved at elevated temperatures. In the case of the iminoborane at 105 °C, the coupling constant ¹J(¹⁴N,¹¹B) = 57 Hz could also be determined from the ¹¹B NMR spectrum [from ¹⁵N NMR ¹J(¹⁵N,¹¹B) = 81 Hz]. Generally, there is no correlation between the magnitude of ¹J(¹⁵N,¹¹B) and the bond length d_BN. The values ¹J(¹⁵N,¹¹B) indicate that changes in σ bonding affect their magnitude, and the nature of the lone pair of electrons at nitrogen is of great importance. The calculated NMR parameters of an adduct of the iminoborane with an N‐heterocyclic carbene, show that the bonding situation around the BN double bond in the adduct is comparable with imines.     

13C, 15N and 29Si nuclear magnetic resonance studies of some aminosilanes and aminodisilanes

¹³C, ¹⁵N (at natural abundance) and ²⁹Si NMR data (chemical shifts and coupling constants) are reported for aminosilanes R₂R′SiNHR¹ (1), bis(silyl)amines Me₂R′SiNHSiMe₃ (2), 1,2-bis(amino)-ethanes (3), bis(amino)silanes RR′Si(NHR¹)₂ (4), 1,2-bis(amino)tetramethyldisilanes (5) and 1,1,2,2-tetrakis(amino)dimethyldisilanes (6). The δ¹⁵N values depend more on the nature of the substituents R¹(H, alkyl, aryl) at the nitrogen atom (in the same way as for other amines) than on different substituents at the silicon atom. A linear correlation between ¹J(²⁹Si¹⁵N) and ¹J(²⁹Si¹³C) is proposed for silanes in which the SiN unit is replaced by the SiCH unit. This correlation comprises all ¹J(²⁹Si¹⁵N) values for aminosilanes R_4-nSi(N)n (n = 1–4) and—most likely—also for aminodisilanes, and it predicts ¹J(²⁹Si¹⁵N)>0 if the corresponding value |¹J(²⁹Si¹³C)|>25 Hz. For the first time a two-bond coupling across Si, ²J(²⁹Si ¹⁵N) = 6.9 Hz, has been observed for 6a. In the case of 6b (R¹ = ^sBu) all resonances for the diastereomers are resolved in the ¹⁵N and ²⁹Si NMR spectra in contrast to the ¹H and ¹³C NMR spectra.     

Synthese und Eigenschaften linearer Phosphorylchlorphosphazene

Synthesis and Properties of Lineary Phosphorylchlorphosphazenes The phosphorylchlorphosphazenes, Cl₂(O)P—[N?PCl₂]_n—Cl, (n = 1, 2, 3) react like POCl₃ with hexamethyldisilazan forming silylamides, Cl₂(O)P—[N ? PCl₂]_n—NHSi(CH₃)₃, (n = 0, 1, 2, 3). From these are obtained the phosphorylchlorphosphazenes by reaction with PCl₅ containing one group —N ? PCl₂ more.     

Derivatives of cis-NPCl2(NSOCl)2 and (NPCl2)2NSOCl. Part XIV—synthesis and nuclear magnetic resonance study of dimethylamino derivatives of NPCl2(NSOPh)2 and (NPCl2)2NSOPh

The compounds trans-NPCl_2?n(NMe₂)_n(NSOPh)₂(n=0-2iNPCl_2?n NMe₂)_n (NSOPh)₂ (n=0-2) and N₂P₂Cl_4?nl_4?n(NMe₂)_nNSOP₂P₂Cl_4?n(NMe₂)_nNSOPh(n=0-4), were prepared from their chloro-precursors. The substitution follows a completely non-geminal pathway, and all possible isomers are formed. The observed relative abundance of these isomers shows that the phenyl group exhibits a strong directing effect on the incoming amine. The ¹H, ³¹P and ¹³C NMR spectra of the most abundant isomers are reported. ²J(CP) couplings within the PNMe₂ grouping are affected by the number of substituents at the phosphorus atom. Almost linear relationships exist between the degree of substitution and the chemical shift of C-1 and C-4 of the phenyl groups. The effect of substitution on the ¹³C chemical shifts of these groups is ascribed to inductive effects.     

Intramolecular Antiferromagnetism in μ-Oxo-bis[(5,15-dimethyl-2,3,7,8,12,13,17,18-octaethylporphyrinato)iron(III)]

The magnetism of μ-oxo-bis[(5,15-dimethyl-2,3,7,8,12,13,17,18-octaethylporphyrinato)iron(III)] with bridge geometry d(Fe? O) = 1.752 Å and ?(Fe? O? Fe) = 178.6° can be explained in terms of antiferromagnetically exchange coupled iron(III)-3d⁵ pairs. The magnetochemical analysis in the temperature range 6K–295K on the basis of the isotropic Heisenberg model (spin Hamiltonian: ? = ?2J?₁ · ?₂ S₁ = S₂ = 5/2) leads to the exchange parameter J = ?125 cm^?1. With regard to the Fe? O bond length the J value corresponds to the series of data observed for other μ-oxodiiron-porphyrins and -porphycenes. Compared to the spin-spin coupling in [Fe₂Cl₆O]^2?, |J| is enhanced by ≈ 10%.     

Die Darstellung der Methylthio(trihalogen)phosphonium-Salze ClnBr3−nPSCH3+MF6−(n = 0–3; M = As,Sb) und Hal3PSCH3+SbCl6−(Hal = Br,Cl)

The Preparation of Methylthio(trihalogeno)phosphonium Salts Cl_nBr_3?nPSCH₃⁺MF₆^?(n = 0–3; M = As, Sb) and Hal₃PSCH₃⁺SbCl₆^?(Hal = Br, Cl) The methylthio(trihalogeno) phosphonium salts Br_nCl_3?nPSCH₃⁺MF₆^? (n = 0–3; M = As, Sb) are prepared by methylation of the corresponding thiophosphorylhalides Br_nCl_3?nPS in the system SO₂/CH₃F/MF₅. The hexachloroantimonates Hal₃PSCH₃⁺SbCl₆^?(Hal = Br, Cl) are synthesized by thiomethylation of PBr₃ and PCl₃ with CH₃SCl/SbCl₅. All salts are characterized by vibrational and NMR spectroscopy.     

1H, 13C, 15N and 195Pt NMR studies of Au(III) and Pt(II) chloride organometallics with 2‐phenylpyridine

¹H, ¹³C, ¹⁵N and ¹⁹⁵Pt NMR studies of gold(III) and platinum(II) chloride organometallics with N(1),C(2′)‐chelated, deprotonated 2‐phenylpyridine (2ppy*) of the formulae [Au(2ppy*)Cl₂], trans(N,N)‐[Pt(2ppy*)(2ppy)Cl] and trans(S,N)‐[Pt(2ppy*)(DMSO‐d₆)Cl] (formed in situ upon dissolving [Pt(2ppy*)(µ‐Cl)]₂ in DMSO‐d₆) were performed. All signals were unambiguously assigned by HMBC/HSQC methods and the respective ¹H, ¹³C and ¹⁵N coordination shifts (i.e. differences between chemical shifts of the same atom in the complex and ligand molecules: Δ^1H_coord = δ^1H_complex ? δ^1H_ligand, Δ^13C_coord = δ^13C_complex ? δ^13C_ligand, Δ^15N_coord = δ^15N_complex ? δ^15N_ligand), as well as ¹⁹⁵Pt chemical shifts and ¹H‐¹⁹⁵Pt coupling constants discussed in relation to the known molecular structures. Characteristic deshielding of nitrogen‐adjacent H(6) protons and metallated C(2′) atoms as well as significant shielding of coordinated N(1) nitrogens is discussed in respect to a large set of literature NMR data available for related cyclometallated compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Additions- und SubstitutionsReaktionen an Tetrafluor- und Tetrachlordiboran(4)

Addition and Substitution Reactions at Tetrafluoro- and Tetrachlorodiborane(4) From equimolar mixtures of B₂F₄ and Me_nN(SiMe₃)_3-n (n = 0–3) the mono-addition products 1–4 are formed at low temperatures. By elimination of Me₃SiF the adduct 2 gives the dimeric monosubstituted diborane 8 , which slowly decomposes at room temperature to the aminoborane 6 and (BF)_n. The course of the reactions was studied by means of ¹¹B and ¹⁹F NMR spectroscopy and by measuring the vapor pressures. According to the ¹¹B and ³¹P NMR spectra the reaction of B₂Cl₄ with PCl₅ or [Me₄N]Cl in liquid hydrogen chloride at 0°C does not yield [PCl₄]₂⁺[B₂Cl₆]^2? or [Me₄N]₂⁺[B₂Cl₆]^2? but gives [PCl₄]⁺[BCl₄]^?, PCl₃ and BCl₃ or [Me₄N]⁺[BCl₄]^? and BCl₃ besides (BCl)_n.     

103Rh-NMR-spektroskopischer Nachweis der gemischten Nonahalogenodirhodate(III), [Rh2ClnBr9–n]3−, n = 0–9

¹⁰³Rh NMR Spectroscopic Evidence of Mixed Nonahalogenodirhodates(III), [Rh₂Cl_nBr_9–n]^3?, n = 0–9 On heating a mixture of the tetrabutylammonium salts (TBA)₃[Rh₂Cl₉] and (TBA)₃[Rh₂Br₉] at 60°C in propylenecarbonate the complete system of the mixed nonahalogenodirhodates(III) [Rh₂Cl_nBr_9–n]^3?, n = 0–9 is formed. In the ¹⁰³Rh nmr spectra 40 different species have been detected, 16 with two equivalent ¹⁰³Rh atoms each resulting in one singlet and 24 with inequivalent ¹⁰³Rh atoms each pair giving two resonances. The signals of the geometric isomeres are not resolved. All 64 expected resonances are really observed. By additional measuring of the ¹⁰³Rh nmr spectra of the fractions n = 0–4 separable by ion exchange chromatography on DEAE cellulose, and utilizing characteristic increments of chemical shifts the complete and unambiguous assignment of all signals is achieved.     

15N- und 19F-NMR-spektroskopischer Nachweis und Xa-Austauschreaktionen der Clusteranionen [(Mo6Cl)(15NCS) X]2−, Xa = F,Cl, Br,I; n = 1–6

¹⁵N and ¹⁹F NMR Spectra and X^a-Exchange Reactions of the Cluster Anions [(Mo₆Clⁱ₈)(¹⁵NCS)^a_nX^a_6?n]^2?, X^a = F, Cl, Br, I; n = 1–6 By intermolecular ligand exchange reaction of the new compound [(Mo₆Clⁱ₈)(¹⁵NCS)^a₆] ^2? with [(Mo₆Clⁱ₆)X^a₆]^2?, X^a = F, Cl, Br, I, in acetone, the outersphere mixed cluster ions [(Mo₆Clⁱ₈)(¹⁵NCS)^a₆X^a_6?n]^2?, n = 1–6, are formed and characterized by their distinct ¹⁵N nmr chemical shifts. The ambident SCN^? is exclusively N-bonded, indicated by ¹⁵N nmr and vibrational spectra. The mixed cluster ions containing X^a = F are identified in acetonitrile by ¹⁹F nmr measurement as well. The kinetic analysis reveals equilibration at room temperature within 10 hours to statistical distribution of all compounds, inclusive the ratios for the geometric isomers for each system at any time with n = 2,4 cis:trans = 4 : 1 and n = 3 fac:mer = 2 : 3, indicating the equivalence of all X^a positions with respect to exchange reactions. For [(Mo₆Clⁱ₈)X^a₆]^2? the reaction rates increase in the series X^a = Cl < Br < I < SCN < F. The ¹⁵N nmr chemical shifts are depending on the electronegativity and the number of the X^a ligands. Furthermore an antipodal influence working on ¹⁵N trans-positioned to X^a effects an additional highfield shift for X^a = F and an additional downfield shift for X^a = Cl, Br, I.     

Influence of methyl‐modified silyl groups on the properties of polymers and Si/B/N/C ceramics derived from N‐silylated borazine derivatives

Thermal silazane cleavage of dichloroboryldisilylamines (SiCl_mMe_3?m)N(SiMe₃)(BCl₂) (1: m = 1; 2: m = 2) at 196 °C leads to the borazine derivates [(SiCl_mMe_3?m)NB(Cl_nMe_1?n)]₃ (3: m = 1, n = 0.185; 4: m = 2, n = 0.111) characterized by NMR and IR spectroscopy and mass spectrometry. Single‐crystal X‐ray diffraction structure analyses reveal (BN)₃ units with unusual twisted boat conformations in both compounds. Additionally, more detailed studies are done to clear up the function of the by‐products (SiCl_mMe_3?m)N(SiClMe₂)(BClMe) formed during the cyclization step leading to asymmetrically boron substituted borazine derivatives. The single‐source precursors 3 and 4 were cross‐linked with methylamine producing polymers 3P and 4P, which were transformed into black amorphous materials with ceramic yields of 20.8 % and 50.3 %, respectively. Ceramic 4C (Si_1.00B_0.98 N_2.55 C_1.37O_0.05) was further investigated by ¹¹B and ²⁹Si magic angle spinning (MAS) NMR spectroscopy. A combined study of high‐temperature TG analyses and X‐ray powder diffraction analyses confirms the thermal stability of 4C up to 1670 °C. Copyright © 2012 John Wiley & Sons, Ltd.