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.     

Preparation and characterization of M(CH3)5 (M = Nb or Ta) and Ta(CH2C6H5)5 and evidence for decomposition by α-hydrogen atom abstraction

The preparations of Nb(CH₃)₅, Ta(CH₃)₅, and Ta(CH₂C₆H₅)₅ are reported in detail. The M(CH₃)₅ complexes decompose autocatalytically to give 3.4 ± 0.1 mol of methane and a non-hyclrolyzable residue with approximate composition MC_1–5H while Ta(CH₂C₆H₅)₅ decomposes in a non-autocatalytic manner to give ca. 2.6 mol of toluene per Ta. Decomposition of Nb(CD₃)₅ gave 96% CD₄ in diethyl ether while the toluene produced on decomposition of Ta(CD₂C₆H₅)₅ was at least 90%-d₃. An observed kinetic deuterium isotope effect of 2–3 in each case is evidence that an α-CH(D) bond is broken in a slow step of the decomposition. It is postulated that M(CH₃)₅ and Ta(CH₂C₆H₅)₅ decompose primarily by α-hydrogen atom abstraction though almost certainly in a complex, possibly intermolecular fashion in the case of M(CH₃)₅. In neither case (R = CH₃ or CH₂C₆H₅) was there evidence for significant homolytic cleavage of the metalcarbon bond to give free alkyl radicals.     

Platinumolefin bond strength in Pt(PPh3)2(CH2CH2) and Pt(PPh3)2 {C(CN)2C(CN)2}

The enthalpy of the reaction: Pt(PPh₃)₂ (CH₂CH₂)(cryst.) + C(CN)₂C(CN)₂ (g) → Pt(PPh₃)₂ {C(CN)₂C(CN)₂}(cryst.) + CH₂ CH₂ (g) has been determined as ΔH₂₉₈=?155.8±8.0 kJ·mol^?1, from solution calorimetry. The interpretation, that the platinumethylene bond is much weaker than the platinumtetracyanoethylene bond, is contrary to conclusions drawn recently from electron emission spectroscopic studies, but in agreement with available structural data.     

Multiparameter equations of state for siloxanes: [(CH3)3-Si-O1/2]2-[O-Si-(CH3)2]i=1,…,3, and [O-Si-(CH3)2]6

This article presents the continuation of the work on the development of technical equations of state for linear and cyclic siloxanes already documented in this journal. The fluids considered herewith are octamethyltrisiloxane (MDM, C₈H₂₄Si₃O₂), decamethyltetrasiloxane (MD₂M, C₁₀H₃₀Si₄O₃), dodecamethylpentasiloxane (MD₃M, C₁₂H₃₆Si₅O₄), dodecamethylcyclohexasiloxane (D₆, C₁₂H₃₆Si₆O₆). The 12-parameter functional form proposed by Span and Wagner has been selected because of its positive characteristics. Siloxanes are produced in bulk quantities and are mostly utilized in the cosmetics industry and, mixed, as high-temperature heat transfer fluids. Furthermore, they are used as working fluids in high-temperature organic Rankine cycle power plants. The available property measurements are carefully evaluated and selected for the optimization of equation of state parameters. For some of the fluids, experimental values are scarce, therefore ad hoc estimation methods have been used to supply more information to the procedure for the optimization of the parameters of the equation of state. In addition, saturated liquid density and vapor pressure measurements are correlated with the equations proposed by Daubert and Wagner–Ambrose, respectively, to provide short, simple, and accurate equations for the computation of these properties. The recently developed isobaric ideal-gas heat capacity correlation for the selected siloxanes is included in the thermodynamic models. The performance of the newly developed equations of state is tested by comparison with experimental data and also with predictions calculated with the Peng–Robinson–Stryjek–Vera cubic EoS, as this model was adopted in previous technical studies. The new thermodynamic models perform significantly better than cubic equations of state. T–s and P  – v$v$ diagrams for all the substances are also reported.     

Reactions of the carbonyl complexes M(CO)3(L)3 (L = py,M = Mo,W; L = NH3, M = Mo) and M(CO)4(2-Mepy)2 (M = Mo,W) with HgX2 (X = Cl,CN, SCN)

The reactions of the substituted Group VI metal carbonyls of the type M(CO)₄(2-Mepy)₂ (M = Mo, w) and M(CO)₃(L)₃ (L = py, M = Mo, W; L = NH₃, M = Mo) with mercuric derivatives HgX₂ (X = Cl, CN, SCN) have given rise to three series of tricarbonyl complexes: M(CO)₃(py)HgCl₂ · 1/2HgCl₂ (M = Mo, W); 2[M(CO)₃(L)]Hg(CN)·nHg(CN)_x (L = py, M = Mo, W, n = $\text{1}\text{2}$, × = 2; L = 2- Mepy, × = 1; M = Mo, n = 3; M = W, n = 1); and [M(CO)₃(L)Hg(SCN)₂ · nHg(SCN)₂] (L = py, M = Mo,W, n = 0; L = 2-Mepy, M = Mo, W, n = $\text{1}\text{2}$; L = NH₃, M = Mo, n = 0) depending on which mercuric compound is employed. All the reactions with Hg(SCN)₂ give isolable products whereas those with Hg(CN)₂ and HgCl₂ did so far only the reactions with [M(CO)₄(2-Mepy)₂] and M(CO)₃(py)₃. The greater reactivity of Hg(SCN)₂ than of Hg(CN)₂ and HgCl₂ is consistent with the various acceptor capacities of the groups bonded to the mercury atom.The reactions studied always involve displacement of the N-donor ligand of the original complex and partial or total displacement of the halide or pseudohalide groups of the mercury compound to give in all cases compounds containing MHg bonds. In addition, elimination of a CO group in the tetracarbonyl complexes M(CO)₄(2-Mepy)₂occurs.     

Synthesis and X-ray diffraction study of R[UO2(CH3COO)3] (R = H3O+ or NH(C2H5) 3+ )

Single crystals of (H₃O)[UO₂(CH₃COO)₃] (I) and (NH(C₂H₅)₃)[UO₂(CH₃COO)₃] (II) are synthesized, and their structures are studied by X-ray crystallography. Compound I crystallizes in the tetragonal crystal system with the unit cell parameters a = 13.70640(10) ?, c = 27.5258(5) ?, V = 5171.14(11) ?³, space group I4₁/a, Z = 16, R = 0.0238. The crystals of compound II are orthorhombic with the parameters a = 13.3685(3) ?, b = 10.6990(3) ?, c = 12.2616(3) ?, V = 1753.77(8) ?³, space group Pna2₁, Z = 4, R = 0.0228. The uranium-containing structural units of crystals I and II are [UO₂(CH₃COO)₃]⁻ island mononuclear groups belonging to the A B₃⁰¹(A = UO₂²⁺, B⁰¹ = CH₃COO⁻) crystal-chemical group of uranyl complexes. [UO₂(CH₃COO)₃]⁻ complexes are linked into a three-dimensional framework by electrostatic interactions with the outer-sphere cations and by hydrogen bonds involving the hydrogen atoms of hydroxonium (I) or triethylammonium (II) with the oxygen atoms of the acetato groups.     

DFT studies of structural preference of coordinated ethylene in W(CO)3(PX3)2(CH2CH2) (X=H, CH3, F, Cl, Br, and I)

A set of phosphine complexes of the type W(CO)₃(PX₃)₂(CH₂CH₂) (X=H, CH₃, F, Cl, Br, and I) were investigated by density functional theory method (BP86) to examine the effect of the substituent X on the orientation of C-C vector of the ethylene ligand with respect to one of the metal-ligand bonds as well as the donation and the backdonation in the bonding ligands of phosphine and ethylene. When X=CH₃, H, F, and Cl, the ethylene C-C vector prefers to be coplanar with metal-phosphine bonds, while for the ethylene complexes containing PBr₃ and PI₃ ligands, the structural preference is coplanarity of the ethylene and the metal-carbonyl bonds. The molecular orbital calculations and natural bond orbital analysis were used to examine the structural consequences derived from these complexes. It can be concluded that the structural preferences in the complexes have a clear relation to electronic effects of phosphine ligands. Our calculations for halide phosphine complexes, particularly for PBr₃ and PI₃, allow us to conclude that in addition to electronic effects, steric factors can also affect the orientation of the ethylene ligand in complexes.     

Nuclear quadrupole resonances of α-(CH3)2 TeX2 (X=Cl, Br, I) and (CH3)2 TeI4

NQR spectra were observed for α-(CH₃)₂ TeX₂ (X=Cl, Br, I) and (CH₃)₂ TeI₄ at various temperatures. The two ⁸¹Br NQR lines were observed above 110 K in α-(CH₃)₂TeBr₂. The characteristic temperature dependence of the ¹²⁷I NQR line in α-(CH₃)₂ TeI. can be explained by the 3c—4e bond of the linear I---Te---I group. The positive temperatures dependence of the lowest ¹²⁷I NQR line in (CH₃)₂TeI₄ is discussed on the basis of the electron population calculated from Townes—Dailey treatment.     

Carbonylvanadium complexes of the tripod ligands MeC(CH2PPh2)3 and P(CH2CH2PPh2)3

UV irradiation of [Et₄N] [V(CO)₆] in the presence of the tripod ligands (L) MeC(CH₂PPh₂)₃ (cp₃) and P(CH₂CH₂PPh₂)₃ (pp₃) yields [Et₄N] [V(CO)₅L], cis-[Et₄N] [V(CO)₄L] and mer-[Et₄N] [V(CO)₃L] (where the meridional configuration for L = cp₃ is uncertain). Except for [Et₄N] [V(CO)₅cp₃], all these species were isolated. The complexes are characterized by their IR, ³¹P and ⁵¹V NMR spectra.     

Preparation and structural characterization of [RuCl2(CO)2{Te(CH2SiMe3)2}2] and [RuCl2(CO){Te(CH2SiMe3)2}3]

The objective of the present work was to synthesize mononuclear ruthenium complex [RuCl₂(CO)₂{Te(CH₂SiMe₃)₂}₂] (1) by the reaction of Te(CH₂SiMe₃)₂ and [RuCl₂(CO)₃]₂. However, the stoichiometric reaction affords a mixture of 1 and [RuCl₂(CO){Te(CH₂SiMe₃)₂}₃] (2). The X-ray structures show the formation of the cis(Cl), cis(C), trans(Te) isomer of 1 and the cis(Cl), mer(Te) isomer of 2. The ¹²⁵Te NMR spectra of the complexes are reported. The complex distribution depends on the initial molar ratio of the reactants. With an excess of [RuCl₂(CO)₃]₂ only 1 is formed. In addition to the stoichiometric reaction, a mixture of 1 and 2 is observed even when using an excess of Te(CH₂SiMe₃)₂. Complex 1 is, however, always the main product. In these cases the ¹²⁵Te NMR spectra of the reaction solution also indicates the presence of unreacted ligand.     

Selective formation of trans and cis(CH3CN) isomers of [Ru(bpy)(CO)2(CH3CN)2] (bpy=2,2-bipyridine) from [Ru(CO)2(CH3CN)3]2(PF6)2 using an electrochemical oxidation step

The selective in situ synthesis of trans and cis(CH₃CN)-[Ru(bpy)(CO)₂ (CH₃CN)₂]²⁺ isomers from the same [Ru(CO)₂ (CH₃CN)₃]₂²⁺ dimer precursor but using either an electrochemical-chemical or chemical-electrochemical process is described.     

Density functional studies of influences of Ni triad metals and solvents on oxidative addition of MeI to [M(CH3)2(NH3)2] complexes and C-C reductive elimination from [M(CH3)3(NH3)2I] complexes

Three metal square planar complexes of the type [M(CH₃)₂(NH₃)₂] (M = Ni, Pd, Pt), with a systematic variation in the metals, are chosen to investigating their S_N2-type oxidative addition reactions with methyl iodide by using the B3LYP levels of theory. The oxidative addition was found to take place via a transition state with a nearly linear arrangement of the I-CH₃-M moiety. Solvation effects in these oxidative addition reactions were also investigated. Considering the nature of the metal centre and solvation effects, the following conclusions emerge: (i) addition of MeI is exothermic for all three metals, and Pt is predicted to react with a much lower barrier than either Pd or Ni. The results describe that the MeI addition would be expected to be more favourable with the complex bearing the third-row metal (platinum) as compared to the other triad metals, nickel or palladium, in which case a more strongly bound MeI adduct is formed with a lower activation barriers and the reaction being more exothermic; (ii) the reaction is very difficult to occur in low polar solvents, such as benzene, due to the high barrier which is induced by dissociation of iodide anion from methyl group, but the reaction easily occurs in polar solvents, such as acetonitrile; this is attributed to the ability of polar solvents to solvate and therefore stabilize the related polar intermediate ion pair. Ethane reductive elimination from the M(VI) complexes fac-[M(CH₃)₃(NH₃)₂I] were also studied, indicating that the Ni(IV) and Pd(IV) complexes are very prone to undergo the reductive elimination while the Pt(IV) analogous is less reactive towards the reductive elimination. The results indicate that in contrast to the Me-Me reductive elimination, the S_N2 oxidative addition reaction of MeI to M(II) is much less sensitive to the nature of the metal centre, suggesting that the nucleophilicity of M(II) in [M(CH₃)₂(NH₃)₂] does not change significantly as one moves from M = Ni to Pt.     

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.     

Rate constant of unimolecular decomposition of the radical (CH3)2juvyCCH(CH3)2

The energy of activation of CH ₃ ^. radical rupture from the radical (CH₃)₂juvyCCH(CH₃)₂ is 142.2 kJ mol^–1; the selfcombination rate constant is k_c {(CH₃)₂juvyCCH(CH₃)₂}=10^7.3 dm³ mol^–1 s^–1.

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CH ₃ ^. (CH₃)₂juvyCCH(CH₃)₂ 142,2 /, k_c {(CH₃)₂juvyCCH(CH₃)₂}=10^{7,3 3–1 –1}.

     

X-ray crystal analysis of tricyclohexyltin trifluoroacetate and Mössbauer data for (cyclo-C6H11)3SnO2CR′ (R′ = CH3, CH2CL,CHCL2, CCl3 and CF3)

The halogenocarboxylates (cyclo-C₆H₁₁)₃SnO₂CR′, (R′ = CH₃, CH₂Cl, CHCl₂, CCl₃ and CF₃) have been prepared, and characterized by Mössbauer and IR spectroscopy. The crystal structure of (cyclo-C₆H₁₁)₃SnO₂CCF₃ has been determined by X-ray analysis. The crystals are orthorhombic, space group Pcmn, with unit cell parameters a 14.390 ± 0.004, b, 13.427 ± 0.004, c 11.516 ± 0.003 Å. The structure was resolved by Patterson methods and refined to an R value of 0.147. The coordination about the tin atom can be considered distorted trigonal-pyramidal or distorted tetrahedral. Mössbauer data are explained in terms of distortions of bond angles about the tin atom.     

1,2-Eliminations from (CH3)2NH+CH2CH3 and (CH3)2NH 2+ : Guided dissociations

1,2-Eliminations are a varied and extensive set of dissociations of ions in the gas phase. To understand better such dissociations, elimination of CH₂=CH₂ and CH₃CH₃ from (CH₃)₂NH⁺CH₂CH₃ (1) and of CH₄ from (CH₃)₂NH₂⁺ are characterized by quantum chemical calculations. Stretching of the CN bond to ethyl is followed by shift of an H from methyl to the bridging position in ethyl and then to N to reach (CH₃)₂NH₂⁺ + CH₂=CH₂ from 1. CH₃CH₃ elimination by H-transfer to C₂H₅⁺ to form CH₃NH⁺=CH₂ + CH₃CH₃ also takes place. (CH₃)₂NH₂⁺ eliminates methane by CN bond extension followed by β-H-transfer to give CH₂=NH⁺ + CH₄. Low-energy reactions resembling complex-mediated 1,2-eliminations occur and constitute a hitherto largely unrecognized type of reaction. As in many complex-mediated reactions, these reactions transfer H between incipient fragments. They are distinguished from complex-mediated processes by the fragments not being able to rotate freely relative to each other near the transition state for reaction, as they do in complexes. Most 1,2-eliminations are ion-neutral complex-mediated, occur by the just described lower energy reactions, have 1,1-like transition states, or utilize highly asynchronous 1,2 transition states. All of these avoid synchronized 1,2-transition states that would violate conservation of orbital symmetry.     

On the molecular structure of (CH3)2NSO2N(CH3)2 as studied by gas electron diffraction

The following bond lengths and bond angles have been deduced from a vapour phase electron diffraction study of (CH₃)₂NSO₂N(CH₃)₂: r(C-H) 1.114 ± 0.005 Å, r(S-O) 1.432 ± 0.010 Å, r(N-C) 1.475 ± 0.013 Å, r(S-N) 1.651 ± 0.003 Å, ∠N-C-H 109.3 ± 2.0°, ∠C-N-C 118.0 ± 302°, ∠S-N-C 115.2 ± 1.1°, ∠N-S-N 110.5±1.3° and ∠O-S-O 114.7±2.5°. The sulphur bond configuration and the prevailing conformation, which was identical to that in the crystal, are discussed in relation to analogous sulphide and sulphoxide derivatives.     

Structure, 31P and 13C chemical shift anisotrophy of (CH3)3P, (CH3)3PO, (CH3)3PS and (CH3)3PSe as determined by liquid crystal NMR spectroscopy

The ¹³P and ¹³C spectra of the triply ¹³C labelled molecules (CH₃)₃P, (CH₃)₃PO, (CH₃)₃PS and (CH₃)₃PSe oriented in a nematic phase are reported. The CPC bond angles have been measured. The ¹³P chemical shift tensor shows a large anisotropy except in the case of (CH₃)₃P. The abnormal large value observed for the PSe bond length suggests a large anisotropy of the ¹J(PSe) spin coupling.     

Λ-doublet populations in CH(A2Δ) produced in the 193 nm multiphoton dissociation of (CH3)2CO, (CD3)2CO, (CH3)2S and CH3NO2

Unequal intensities of the Λ-doublet components were observed in the CH(A²Δ-X²Π) emission following the multiphoton dissociation of (CH₃)₂CO, (CH₃)₂S and CH₃NO₂ by an ArF laser (193 nm). The power dependence of the emission intensity was estimated to be cubic (3.1±0.2) when the laser power was below ≈ 8×10¹⁷ photons cm^?2 pulse^?1. The Λ-doublet populations depended on the rotational quantum number N′ and the preferred level changed at N′ = 20. A similar behavior was observed for the CD(A²Δ) from (CD₃)₂CO. Rotational distributions show bimodal behavior, having a hump around N′ = 13 in CH(A²Δ) and N′ = 11 in CD(A²Δ). These trends indicate that the CH(A²Δ) is produced through multiple processes where stepwise mechanisms are operative via either CH₂ or CH₃, or both radicals as intermediates.     

Internally coordinated organozinc-transition metal compounds. Crystal structure of (CH3)2N(CH2)3ZnW(ν-C5H5)(CO)3

The stabilities of simple and internally coordinated organozinc-transition metal compounds towards disproportionation have been investigated by the microwave titration technique. Simple alkyl- and aryl-derivatives disproportionate to such an extent as to preclude isolation. Internal coordination was found to stabilize the asymmetric compounds, and several derivatives containing the dimethylaminopropyl group were isolated. The crystal structure of one of them, Me₂N(CH₂)₃-ZnW(Cp)(CO)₃, was determined by a single-crystal X-ray study. The crystals are orthorhombic, space group P2₁2₁2₁, with four molecular units in a cell with parameters a 8.406(1), b 12.179(2) and c 16.642(2) Å. The structure was solved by standard Patterson and Fourier techniques. The refinement, with anisotropic temperature factors for the two heavy atoms, converged at R_F = 0.092 (R_wF = 0.089) for 1536 observed reflections with I>2.5σ(I). The molecule consists of a central tungsten atom, surrounded in a tetragonal pyramidal fashion by a cyclopentadienyl group in the apical position and three carbon monoxyde molecules and a zinc atom occupying the basal positions. The zinc atom is three-coordinate, being surrounded by the tungsten atom and the chelating dimethylaminopropyl group; there is, however, a short intermolecular contact between zinc and a carbonyl oxygen atom at 2.61(3) Å.