Oligosilanylated Silocanes

A number of mono- and dioligosilanylated silocanes were prepared. Compounds included silocanes with 1-methyl-1-tris(trimethylsilyl)silyl, 1,1-bis[tris(trimethylsilyl)silyl], and 1,1-bis[tris(trimethylsilyl)germyl] substitution pattern as well as two examples where the silocane silicon atom is part of a cyclosilane or oxacyclosilane ring. The mono-tris(trimethylsilyl)silylated compound could be converted to the respective silocanylbis(trimethylsilyl)silanides by reaction with KO^tBu and in similar reactions the cyclosilanes were transformed to oligosilane-1,3-diides. However, the reaction of the 1,1-bis[tris(trimethylsilyl)silylated] silocane with two equivalents of KO^tBu leads to the replacement of one tris(trimethylsilyl)silyl unit with a tert-butoxy substituent followed by silanide formation via KO^tBu attack at one of the SiMe₃ units of remaining tris(trimethylsilyl)silyl group. For none of the silylated silocanes, signs of hypercoordinative interaction between the nitrogen and silicon silocane atoms were detected either in the solid state. by single crystal XRD analysis, nor in solution by ²⁹Si-NMR spectroscopy. This was further confirmed by cyclic voltammetry and a DFT study, which demonstrated that the N-Si distance in silocanes is not only dependent on the energy of a potential N-Si interaction, but also on steric factors and through-space interactions of the neighboring groups at Si and N, imposing the orientation of the p_z(N) orbital relative to the N-Si-X axis.     

Formation of two isomeric closo-[(eta5-C5H5)FePC2B8H10] phosphadicarbaborane analogues of ferrocene via isolable eta1-bonded complexes of the [7-[(eta5-C5H5)Fe(CO)2]-(eta1-nido-PC2B8H10)] type

The reaction of nido-[7,8,9-PC(2)B(8)H(11)] (1) with [[CpFe(CO)(2)](2)] (Cp=eta(5)-C(5)H(5) (-)) in benzene (reflux, 3 days) gave an eta(1)-bonded complex [7-Fp-(eta(1)-nido-7,8,9,-PC(2)B(8)H(10))] (2; Fp=CpFe(CO)(2); yield 38 %). A similar reaction at elevated temperatures (xylene, reflux 24 h) gave the isomeric complex [7-Fp-(eta(1)-nido-7,9,10-PC(2)B(8)H(10))] (3; yield 28 %) together with the fully sandwiched complexes [1-Cp-closo-1,2,4,5-FePC(2)B(8)H(10)] 4 a (yield 30%) and [1-Cp-closo-1,2,4,8-FePC(2)B(8)H(10)] 4 b (yield 5%). Compounds 2 and 3 are isolable intermediates along the full eta(5)-complexation pathway of the phosphadicarbaborane cage; their heating (xylene, reflux, 24 h) leads finally to the isolation of compounds 4 a (yields 46 and 52%, respectively) and 4 b (yields 4 and 5%, respectively). Moreover, compound 3 is isolated as a side product from the heating of 2 (yield 10%). The structure of compound 4 a was determined by an X-ray structural analysis and the constitution of all compounds is consistent with the results of mass spectrometry and IR spectroscopy. Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B]-COSY, and (1)H[(11)B(selective)] magnetic resonance measurements led to complete assignments of all resonances and are in excellent agreement with the structures proposed.     

Ozonization: An Efficient Method for the Oxidation of Halophosphines

Abstract

The ozonization of various halophosphines 1a-j leads with quantitative yields to the corresponding phosphine oxides 2a-j.

Ozonization is a convenient method of oxidation, in particular of compounds with bulky ligands (1c, 1d, 1e).     

Electron Capture,Collision-Induced,and Electron Capture-Collision Induced Dissociation in Q-TOF

Recently, we demonstrated that a radio-frequency-free electromagnetostatic (rf-free EMS) cell could be retrofitted into a triple quad mass spectrometer to allow electron-capture dissociation (ECD) without the aid of cooling gas or phase-specific electron injection into the cell (Voinov et al., Rapid Commun Mass Spectrom 22, 3087–3088, 2008; Voinov et al., Anal Chem 81, 1238–1243, 2009). Subsequently, we used our rf-free EMS cell in the same instrument platform to demonstrate ECD occurring in the same space and at the same time with collision-induced dissociation (CID) to produce golden pairs and even triplets from peptides (Voinov et al., Rapid Commun Mass Spectrom 23, 3028–3030, 2009). In this report, we demonstrate that ECD and CID product-ion mass spectra can be recorded at high resolution with flexible control of fragmentation processes using a newly designed cell installed in a hybrid Q-TOF tandem mass spectrometer.     

A new route to vinyltributyltin compounds by flash pyrolysis of alkyltributyltin acetates

Flash pyrolysis of alkyltributyltin acetates, at high temperatures (600–850° C) under a moderate vacuum provides a convenient route to vinyltin derivatives.     

Nouveaux heterocycles tricycliques synthese de derives de l'aza-2 pyrrolo[1,2-a]indole

The synthesis of aza-2 pyrrolo[1,2-a]indole derivatives was achieved by a 1,3-dipolar cycloaddition reaction of dimethylacetylenedicarboxylate with a mesoionic ion.     

Solvolysen von 4-Alkylidenbicyclo[3.2.0]hept-2-en-6-olen. Synthese von 1-Vinylfulvenen und 8,8-Diphenylheptafulven

Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-Diphenylheptafulvene Four 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2–5 , obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’- 6 to ‘endo’- 9 (68–73%) and ‘exo’- 6 to ‘exo’- 9 (3–20%). Treatment of some of these alcohols with (CF₃SO₂)₂O in CH₂Cl₂/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10–12 or 1-vinylfulvenes 13 and 14 , a new class of reactive tetraenes: Both ‘endo’- 9 and ‘exo’- 9 , having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’- 6 to ‘endo’- 8 afforded only the corresponding 7-membered-ring pyridinium salts 10–12 (66–79%), while ‘exo’- 6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’- B and ‘endo’– 6 -‘endo’- 8 , as well as the C(1), C(7)-bond cleavage with ‘exo’- B , ‘exo’- 6 , and with both ‘endo’- and ‘exo’- 9 . Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19 , respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene ( 23 , 86%) was obtained.     

The first 1,2-dibora-[2]ferrocenophane and its dynamic behaviour in solution

1,2-Bis(dimethylamino)-1,2-dibora-[2]ferrocenophane (1) was prepared by the reaction of 1,1′-dilithioferrocene with 1,2-dichlorobis(dimethylamino)diborane(4). In addition to hindered rotation about the B-N bond (ΔG^‡ > 80 kJ mol⁻¹), another dynamic process was revealed by ¹H and ¹³C NMR in solution at low temperature, and interpreted as motion of the cyclopentadienyl rings between staggered and eclipsed conformations (ΔG_{(233 K)}^‡ = 44 ± 1 kJ mol⁻¹).