NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

Photo-degradation studies on Di-η5-Cyclopentadienyldimethylvanadium,Di-η5-Cyclopentadienylmethylvanadium,Di-η5-Cyclopentadienyldimethylniobium,and some deuterated analogs

The photolysis of alkyl metallocene derivatives of vanadium and niobium in hydrocarbon solvents results in cleavage of the carbon—metal σ-bond. In the cases of (η⁵-C₅H₅)₂VCH₃ and (η⁵-C₅H₅)₂Nb(CH₃)₂, only methane (>99%) is produced photochemically. (η⁵-C₅H₅)₂V(CH₃)₂, prepared on a convenient new synthesis from (η⁵-C₅H₅)₂VCl₂ and methyllithium in toluene, degrades under photochemical conditions to yield both methane and ethane in a 2 : 1 ratio. The ethane arises from intra- and intermolecular methyl dimerization. Deuterium labeling studies have shown that the methyl group, the cyclopentadienyl ring, and the solvent are all sources of hydrogen in the formation of methane in these photolyses. The extent to which each source participates in the hydrogen abstraction process cannot be quantitatively determined because of the influence of an isotope effect. Chemical reactions with carbon monoxide during the photolyses give low yields of (η⁵-C₅H₅)V(CO)₄ from (η⁵-C₅H₅)₂VCH₃ or (η⁵-C₅H₅)₂V(CH₃)₂, and of (η⁵-C₅H₅)₂Nb(CO)CH₃ from (η⁵-C₅H₅)₂Nb(CH₃)₂.     

CNDO/2 study of 29Si NMR chemical shifts

A CNDO-2 study of ²⁹Si NMR chemical shifts for compounds of the type (CH₃)_nSiX_4-n (X = H, F, Cl) is reported. The paramagnetic screening constants σ_p are given. The general variation in σ_p with n agrees fairly well with the variation of the observed chemical shifts for X = H and F, but the correlation is not so good for X = Cl.     

Actinide-centered cyclometalation chemistry. An unusually distorted thorium bishydrocarbyl: Thp[η5-(CH3)5C5]2CH2Si(CH3)3]2

The crystal and molecular structure of the complex Th[η⁵-(CH₃)₅C₅]₂[CH₂-Si(CH₃)₃]₂, which undergoes facile intramolecular cyclometalation to the thoracyclobutane Th[η⁵-(CH₃)₅C₅]₂(CH₂)₂Si(CH₃)₂, is reported. While the Th[η⁵-(CH₃)₅C₅]₂ ligation is unexceptional, the Th[CH₂Si(CH₃)₃]₂ fragment is highly unsymmetrical having Th-C (corresponding angle Th-C-Si) 2.51(1) Å (132.0(6)°) and 2.46(1) Å (148.0(7)°). This conformation, which appears to result from severe intramolecular non-bonded contacts, allows a methyl hydrogen atom of one CH₂Si(CH₃)₃ ligand to approach within ca. 2.3 Å of the α-carbon atom of the other CH₂Si(CH₃)₃ ligand.     

Darstellung und charakterisierung von verbindungen des typs (CH3)3ME(CF3)2 (M = Si,Ge, Sn; E = P,As)

Various preparative routes for the synthesis of (CH₃)₃SiP(CF₃)₂ are discussed. The most favourable method, reaction of (CH₃)₃MPH₂ with HE(CF₃)₂, provides a good yield of (CH₃)₃ME(CF₃)₂ compounds (M = Si, Ge, Sn; E = P, As). The reaction rate is dependent on M (Si < Ge <Sn) und E (P < As). The stability and reactivity of the (CH₃)₃ME(CF₃)₂ compounds are discussed. The new compounds were characterized by NMR and IR spectra and by cleavage reactions of the M-E bond. ¹H, ¹⁹F NMR and IR spectral data are reported.     

Carbene tetrel-bonded complexes

An ab initio calculation has been carried for the carbene tetrel bonded complexes CH₃Y???CH₂ (Y = F, CN, NC, and NO₂), CH₃F???CZ₂ (Z = Cl and CH₃), XH₃F???CF₂ (X = C, Si, Ge, and Sn), SiF₄???CF₂, and XH₃F???NHC (N-heterocyclic carbene), where carbene is treated as a Lewis base and XH₃Y is a Lewis acid. Formation of the tetrel bond is mainly attributed to charge transfer from the lone pair on the C atom in the carbene toward the σ* X–Y orbital and also the σ* X–H one in the strong tetrel bond. The carbene tetrel bond is strengthened/weakened by the electron-withdrawing group in the tetrel donor/acceptor and enhanced by the methyl group in C(CH₃)₂. NHC forms a stronger carbene tetrel bond in XH₃F???NHC (X = Si, Ge, and Sn) where it exceeds that of the majority of H-bonds. Interestingly, the tetrel bond becomes stronger in the order of X = C < Ge < Sn < Si in XH₃F???NHC and the largest interaction energy occurs in SiH₃F???NHC, amounting to ?103 kJ/mol. The carbene tetrel bond can be strengthened by cooperative effect with the N???M interaction in trimers H₂C???CH₃CN???M (M = CH₃CN, HCN, ICN, SbH₂F, LiCN, and BeH₂) and has doubled in H₂C???CH₃CN???BeH₂.

     

Threshold energies for production of CH2(3B1) and CH2(1A1) from ketene photolysis. The CH2(3B1) ↔ CH2(1A1) energy splitting

By measuring the relative CO quantum yields from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25° for CH₂CO(¹A₁) → CH₂(³B₁) + CO(¹Σ⁺) to be 75.7 ± 1.0 kcal/mole. This corresponds to a value of 90.7 ± 1.0 kcal/mole for ΔH_f298⁰[CH₂(³B₁)]. By measuring the relative ratio of CH₂(¹A₁)/CH₂(³B₁) from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25°C for CH₂CO(¹A₁) → CH₂(¹A₁) + CO(¹Σ⁺) to be 84.0 ± 0.6 kcal/mole. This corresponds to a value of 99.0 ± 0.6 kcal/mole for ΔH_f298⁰[CH₂(¹A₁)]. Thus a value for the CH₂(³B₁) ? CH₂(¹A₁) energy splitting of 8.3 ± 1 kcal/mole is determined, which agrees with three other recent independent experimental estimates and the most recent quantum theoretical calculations.     

Branched and dendritic metallo-carbosiloxanes with OCH2PPh2MLn end-grafted units

A straightforward method for the preparation of metallo carbosiloxanes of type Si(OCH₂CH₂CH₂SiMe₂[OCH₂PPh₂M(CO)_n])₄ (n = 3, M = Ni, 7a; n = 4, M = Fe, 7b; n = 5: M = Mo, 7c; M = W, 7d), Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₄ (8) and Me₂Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₂ (11) is described. The reaction of Si(OCH₂CH₂CH₂SiMeXCl)₄ (1: X = Me, 2: X = Cl) or Me₂Si(OCH₂CH₂CH₂SiMeCl₂)₂ (9) with HOCH₂PPh₂ (3) produces Si(OCH₂CH₂CH₂SiMe₂(OCH₂PPh₂))₄ (4), Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₄ (5) or Me₂Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₂ (10) in presence of DABCO. Treatment of the latter molecules with Ni(CO)₄ (6a), Fe₂(CO)₉ (6b), M(CO)₅(Thf) (6c: M = Mo; 6d: M = W), respectively, gives the title compounds 7a-7d, 8 and 11 in which the PPh₂ groups are datively bound to a 16-valence-electron metal carbonyl fragment.The formation of analytical pure and uniform branched and dendritic metallo carbosiloxanes is based on elemental analysis, and IR, ¹H, ¹³C{¹H}, ²⁹Si{¹H} and ³¹P{¹H} NMR spectroscopic studies. In addition, ESI-TOF mass spectrometric studies were carried out.     

2,2-diphenyl-2λ5-phospha-phenalenyl-und 2,2-dimethyl-2λ5-phospha-indenyl-lithium

From the reaction of 1,8-bis(bromomethyl)naphthalene with diphenyl(trimethylsilyl)phosphine a cyclic phosphonium salt IX is formed which can be rearranged with (CH₃)₃PCH₂ to yield the cyclic ylide X. Its metallation with t-butyllithium gives 2,2-diphenyl-2λ⁵-phospha-phenalenyl-lithium XI. The anion of XI cannot be seen as a delocalized phospha-phenalenyl π-system but rather as a phosphonium-bis-ylide similar to the diphenylphosphonium-bis-benzylide.From 1,2-bis(chloromethyl)benzene and (C₆H₅)₂PSi(CH₃)₃ or from 1,2-bis(chloromagnesiummethyl)benzene and CH₃PCl₂, followed by quaternization using CH₃Br, cyclic phosphonium salts (XII and XV, respectively) can also be obtained, which may again be rearranged to form the ylides XIII or XVI. XVI gives with (CH₃)₃CLi 2,2-dimethyl-2λ⁵-phospha-indenyl-lithium XVII, containing a dimethyl-phosphonium-bis-ylide anion (“isophosphindolyl-lithium”).     

Preparation and Ir, 31P,and 93Nb NMR spectroscopic investigation of phosphine derivatives of η5-C5H5Nb(CO)4

UV irradiation of η⁵-C₅H₅Nb(CO)₄ in the presence of the phosphine ligands L (L = 2 PEt₃, Ph₂P(CH₂)₂PPh₂ (p₂(n), n = 1–5), cis-Ph₂PCH=CHPPh₂ (c-dpe)), and the mixed arsine-phosphine ligands Ph₂AsCH₂CH₂PPh₂ (arphos) and o-C₆H₄(AsPh₂)(PPh₂) (pab) yields the well defined complexes cis-[η⁵-C₅H₅Nb(CO)₂L]. The monosubstituted species η⁵-C₅H₅Nb(CO)₃L have been characterized spectroscopically. P₂Ph₄ forms mono- and dinuclear, mono- and biligate carbonylniobium complexes.Shielding of the ⁹³Nb nucleus increases in the sequences (i) Ph₂As- < Ph₂P-, (ii) chelate 4-ring < chelate 5-ring and (iii) η⁵-C₅H₅Nb(CO)₂L < η⁵-C₅H₅Nb(CO)₃L < η⁵-C₅H₅Nb(CO)₄, and ³¹P coordination shifts decrease in the order c-dpe > pab > arphos > p₂(2) > p₂(5) > p₂(4) ～ PEt₃ > p₂(3) > p₂(1). The trends generally parallel those for the corresponding NMR parameters of the vanadium complexes. Paramagnetic contributions to the overall shielding are smaller for the ⁹³Nb than for the ⁵¹V nucleus, and this is explained in terms of increased covalency and decreased π-interaction in the niobium complexes.     

New stable germylenes, stannylenes, and related compounds: 6. Heteroleptic germanium(II) and tin(II) compounds [(SiMe3)2N-E-OCH2CH2NMe2]n (E = Ge, n = 1; Sn, n = 2): synthesis and structure

New stable heteroleptic germanium(II) and tin(II) compounds [(SiMe₃)₂N-E¹⁴-OCH₂CH₂NMe₂]_n (E¹⁴ = Ge, n = 1 (1), Sn, n = 2 (2)) have been synthesized and their crystal structures have been determined by X-ray diffraction analysis. While compound 1 is monomer stabilized by intramolecular Ge ← N coordination, compound 2 is associated to dimer via intermolecular dative Sn ← O interactions.     

The reaction of trimethylchlorosilane with phenyltelluromagnesium bromide in tetrahydrofuran: Characterisation of the products by 29Si and 125Te NMR spectroscopy

The products of the reaction of Me₃SiCl with PhTeMgBr in THF have been identified with the aid of high resolution ²⁹Si and ¹²⁹Te NMR spectroscopy. In addition to the expected product Me₂SiTePh (40%), the symmetrical telluride (Me₃Si)₂Te (10%) and the ether Me₃SiO(CH₂)₄TePh (45%) are also formed. The latter results from ring-opening of the solvent THF by Me₃SiCl followed by reaction of the product with PhTeMgBr.     

The influence of the steric properties of the ligands PR2Ph and L on the formation and properties of the complexes Mo(η6-PhPR2)(L)(PPh2CH2CH2PPh2), R = Et,L = PPhEt2 and R = Ph,L = PPh3, PR′3, CO,CNR, N2, H2

The reduction of MoCl₄(DPPE) (DPPE = PPh₂CH₂CH₂PPh₂) with Mg or Na/Hg in the presence of 2 PPhR₂ under Ar results in the formation of the new complexes Mo(η⁶-PhPR₂)(PPhR₂)(DPPE) when R is Ph (Ia) or Et(II). No η⁶-PhPR₂ complex is obtained when R is Me because this small ligand forms strong MoP σ-bonds; nor is one obtained for R = Cy because of too much steric crowding. The limits for η⁶-complexation can be quantified in terms of cone angle sums.Complex Ia is very similar to Mo(η⁶-PhPMePh)(PMePh₂)₃ (IIIa) in that both react at similar rates with a variety of small ligands L = PMePh₂, PMe₂Ph, PMe₃, P(OMe)₃, N₂, CO, CNBu^t and H₂ via dissociation of a labile σ-bonded ligand. Several other less crowded η⁶-arylphosphinemolybdenum complexes including II do not have labile ligands at 25°C. The new complexes Mo(η⁶-PhPPh₂)(L)(DPPE) have been characterized by ³¹P and ¹H NMR, IR and gas uptake measurements, Ia has a higher affinity for H₂ than IIIa possibly because Mo(η⁶-PhPPh₂)(H)₂(DPPE) adopts a non-fluxional trans-configuration. The ³¹P chemical shift of the σ-bonded ligand in 8 derivatives of Ia and 12 of IIIa correlate with the sum of the cone angles of the three σ-bonded ligands in each complex.     

Protolyses of (CH3)3SnM(CH3)3 (M = Sn,Ge, Si,C)

Product and kinetic studies on the reactions of hydrogen chloride in methanol solution with the substrates (CH₃)₃SnM(CH₃)₃ (M = Sn; Ge and Si) show that both SnM and SnCH₃ cleavage reactions occur, at similar rates, and are followed by other reactions giving complex but explicable mixtures of products. Similar behaviour is observed for trifluoroacetolysis in carbon tetrachloride solution, and some intermediates are observable. Trifluoroacetolysis of (CH₃)₃SnC(CH₃)₃ results in exclusive SnCH₃ cleavage. The very slow apparent solvolysis in acetic acid solution is thought to involve reaction with dissolved oxygen.     

Synthesis, characterization and structural studies of dithiocarbamate derivatives of 2,2,6,6-tetramethyl-1-oxa-4,4-diiodo-4-tellura-2,6-disilacyclohexane,O[Si(CH3)2CH2]2TeI(dtc)

Five new hetero-organotellurium (IV) dithiocarbamates O[Si(CH₃)₂CH₂]₂TeIS₂CN(CH₂CH₂)₂ (1), O[Si(CH₃)₂CH₂]₂TeIS₂CN(CH₂CH)₂ (2), O[Si(CH₃)₂CH₂]₂TeIS₂CN(CH₂CH₂)₂O (3), O[Si(CH₃)₂CH₂]₂-TeIS₂CN(CH₂CH₂)₂S (4) and O[Si(CH₃)₂CH₂]₂TeIS₂CN(CH₂CH₂)₂CH₂ (5) were prepared from the 2,2,6,6-tetramethyl-1-oxa-4,4-diiodo-4-tellura-2,6-disilacyclohexane and the corresponding dithiocarbamate (dtc) sodium salts in ethanol. The compounds were characterized by means of Elemental Analyses, FAB MS, IR, ¹H, ¹³C, ¹²⁵Te NMR spectroscopy. The crystal structures of 1, 3 and 4 were determined. Dithiocarbamate ligands display an anisobidentate chelating coordination mode on interacting with the tellurium center in all compounds. The Te(IV) immediate environment can be described as that of a sawhorse structure in which the lone pair is apparently stereochemically active and occupying an equatorial position in a distorted trigonal bipyramid. The two methylene groups occupy the other equatorial positions with a sulfur atom of the dithiocarbamate group and the iodine atom occupying the axial positions. The solid state structures of 3 and 4 exhibit important intermolecular interaction Te?S(2B). This interaction results in the formation of a dimer, which is better described as a distorted octahedron with an apparently inactive lone pair.     

Trioxaphosphocanes-1,3,6,2, etude par R.M.N. (13C, 1H, 31P et stereochimie

The stereochemistry of several 2-R-1,3,6,2-trioxaphosphocanes (R = Cl, OCH₃, CH₃, N(CH₃)₃ has been investigated by ¹H, ¹³C and ³¹P n m r spectroscopy.     

Synthesis, 119Sn, 13C and 195Pt NMR studies of five-coordinate rhodium(I), iridium(I) and platinum(II) complexes containing three trichlorostannate ligands

The synthesis and ¹¹⁹Sn NMR characteristics of new five-coordinate tris(trichlorostannato) complexes of Rh^I, Ir^I and Pt^II are reported. The Rh^I and Ir^I complexes are complex dianions of the form (PPN)₂[M(SnCl₃)₃L₂] where L can be CO, CN (cyclohexyl) or L₂, a diolefin such as 1,5-COD or NBD (norbornadiene). The anionic platinum complexes (PPN)[Pt(SnCl₃)₃L₂] contain similar L ligands. A number of neutral monotrichlorostannato complexes of type [M(SnCl₃)L₄] including [Ir(SnCl₃)(NBD)(1,5-COD)] have been prepared and characterized. Their δ(¹¹⁹Sn), δ(¹³C), δ(¹⁹⁵Pt) as well as ¹J(¹⁰³Rh, ¹¹⁹Sn), ¹J(¹⁹⁵Pt, ¹¹⁹Sn), ²J(¹¹⁹Sn, ¹¹⁷Sn) and ²J(¹¹⁹Sn, ¹³C) data are given. A trans influence series, based on ¹J(¹⁹⁵Pt, ¹¹⁹Sn), reveals the following sequence: H^? > PR₃ > AsR₃ > SnCl₃^? > olefin > Cl^?.     

Preparation and reactivity of the new cyclopentadienyl-bridged complex (Me2SiCH2CH2SiMe2)(C5H4Fe(CO)2)2

A new metal-metal bonded binuclear iron system [Me₂SiCH₂CH₂SiMe₂][η⁵-C₅H₄Fe(CO)₂]₂ (2) has been prepared by treating two equivalents of NaCp with one equivalent of ClSi(Me)₂CH₂CH₂SiClMe₂ obtaining the intermediate (C₅H₅)Si(Me)₂CH₂CH₂Si(Me)₂(C₅H₅) which then is directly allowed to react with Fe(CO)₅ given 2 in 30% yield. From this cyclopentadienyldisilyl linked system three new binuclear irom complexes are formed. Treatment of 2 with Na/Hg in THF produced the dianion [Me₂SiCH₂CH₂SiMe₂][η⁵-C₅H₄Fe(CO)₂^?]₂ which is quenched with CH₃I giving [Me₂SiCH₂CH₂SiMe₂][η⁵-C₄H₄Fe(CO)₂CH₃]₂ (4) in 76% yield. Complex 2 is oxidized with 1.2 equivalent of I₂ to give [Me₂SiCH₂CH₂SiMe₂][η⁵-C₅H₄Fe(CO)₂I]₂ (5) in 85% yield. Photolysis of 5 (1 equiv.) and PPh₃ (3 equiv.) results in the formation of the bis-substituted compound [Me₂SiCH₂CH₂SiMe₂][η⁵-C₅H₄Fe(CO)(PPh₃)I]₂ (6). These four new binuclear iron complexes are characterized by ¹H, ¹³C, and ³¹P NMR and IR spectroscopy.     

Synthesis and characterization of new silicon-centred tin-dendrimers Si[CH2CH2SnR3]4. Single-crystal X-ray structure of the tetrahydrofuran adduct of tetrakis[2-(tribromostannyl)ethyl]silane

A series of novel first-generation silicon-centred tin dendrimers Si(CH₂CH₂SnR₃)₄ [R = CH₃ (3), ⁱBu (4), CCCH₃ (5), C₆H₄CH₃-4 (6), C₆H₄OCH₃-4 (7), (CH₂)₄OCH₂CH₂OCH₃ (8), CH₂SiMe₃ (9)] was prepared by the reaction of Si(CH₂CH₂SnBr₃)₄ (2) with the appropriate Grignard reagent or LiCH₂SiMe₃ in tetrahydrofuran. The new compounds were characterized by multinuclear NMR studies (¹H, ¹³C, ¹¹⁹Sn), mass spectrometry (MALDI-TOF, EI) and elemental analyses. The molecular structure of Si[CH₂CH₂SnBr₃(THF)₂]₂[CH₂-CH₂SnBr₃(THF)]₂ (2a) was determined by single-crystal X-ray diffraction.     

SO (B3σ−,A 3Π—X3σ−) Emission from low temperature rare gas—sulfur dioxide afterglows

The emission systems produced in He(2 ³S)/SO₂, Ne(³P_0,2)/SO₂ and Ar(³P_0,2)/SO₂, afterglows have been investigated in the ultraviolet and visible spectral ranges. In all three afterglows we have identified previously unknown long—wavelenght progressions in the SO(A³Π → X ³ σ^?) system and have assigned several new bands in the SO(B ³σ^? → X ³σ^?)system. Reducing the temperature of the helium gas flowing through a hollow cathode discharge source to 118K effectively removes helium ions from the stream, thus facilitating spectral studies in uncontaminated metastable afterglows. A further effect of cooling the rare gases He, Ne, and Ar is an improvement in the resolution of the emission spectra and an enhanced signal-to-noise ratio. bl