A. V. Kisin

Nuclear magnetic resonance spectroscopy of metal cyclopentadienyls V. Metallotropic rearrangement in silicon cyclopentadienyls: 1,2 shift and spectral regularities in σ-cyclopentadienyls

The saturation transfer technique, INDOR, and related computations have been used to provide a complete analysis of the PMR spectra of isomeric (trimethylsilyl)cyclopentadienes whilst the spectra of C5H5Si(CH3)2Cl and C5H5SiCl3 have been partially analysed. The main vinylic isomer in the series C5H5Si(CH3)nCl3-n (n is 0, 1, 2, 3) is the 1-substituted species while the 5-substituted isomers are subject to a metallotropic rearrangement. From the assumption that 3J(HH) > 0 and 4J(HH) < 0, it follows that the upfield olefinic signal of the 5-substituted isomers is related to the 1,4 protons. Unsymmetrical broadening shows that in all the compounds the migration proceeds predominantly through the 1,2 shift with a free energy of activation of 15 to 16 kcal/mole. As the electronegativity of the substituents attached to the silicon atom increases, the equilibrium associated with the prototropic rearrangement is shifted towards formation of the vinylic isomers while the corresponding metal migration rate decreases. A thorough analysis of the coupling constants, J(HH), and chemical shifts, δ(H), associated with the protons of σ-cyclopentadienyl compounds shows that the constant 3J15 is always positive and equal to 1.2±0.2 Hz while 4J25 is, as a rule, negative and variable within the range −1.6 to +0.2 Hz. In the absence of electron-withdrawing groups (e.g. as in carbonyls) at the metal, the condition δ14 < δ23 invariably applies.

Nuclear magnetic resonance spectroscopy of metal cyclopentadienyls X. Proton magnetic resonance spectra of, and dynamic behaviour in, bis(trimethylsilyl)cyclopentadiene☆

Abstract The PMR spectra of bis(trimethylsilyl)cyclopentadiene (I) have been studied at −30° to + 220° indicating that (I) is a mixture of the 5,5-(Ia), 2,5-(Ib), 1,4-(Ic), and 1,3-(Id) isomers, the ratio being 132/3.6/2.2/1 at −30°. The structures have been proved using INDOR and spin-decoupling techniques and through Diels-Alder reactions with dienophiles or metallation with an aminostannane. (Ib) has been shown to exhibit a degenerate metallotropic rearrangement which proceeds via the 1,2 shift of the 5- positioned (CH 3 ) 3 Si group ( E a 14.5 ± 1.8 kcal/mole, Δ S ≠ −1.5 ± 4 e.u.). The inter- conversion of (Ia) and (Ib) proceeds via the 1,3 shift of the (CH 3 ) 3 Si group. The methyl chemical shifts have been processed using a MINIMAX 1 program to yield the thermodynamic characteristics of the (Ia) ⇄ (Ib) metallotropic tautometic equili- brium, i.e. Δ H 2.73 kcal/mole and Δ S ≠ 4.99 e.u. The values of the activation parameters have been obtained for the metallotropic rearrangement of (Ib) into (Ia) (E a 15.8 ± 1.0 kcal/mole, Δ S ≠ − 4.7 ± 4 e.u.) and (Ia) into (Ib) (E a 18.6 ± 1.0 kcal/mole, Δ S ≠ 0.3 ± 4 e.u.). Above + 120° (Ic) ⇄ (lb) ⇄ (Id) hydrogen migration has been observed, the process being fast relative to the NMR time scale. The activation energy has been estimated as 21 kcal/mole for the rearrangement of (Ic) to (Ib).

Nuclear magnetic resonance spectroscopy of metal cyclopentadienyls VI. Metallotropic rearrangement in the group IVB cyclopentadienyls

Abstract The 1 H NMR spectra of the fluxional C 5 H 5 Ge(CH 3 ) 3 and C 5 H 5 Sn(CH 3 ) 3 molecules have been studied at 100 MHz over a wide temperature range. The AA′BB′X spectrum has been analysed to show that the BB′ signal (δ A > δ B ) corresponds to the 1,4 protons. The metal in the cyclopentadienylgermane migrates through a 1,2 shift, as indicated by the unsymmetrical collapse of the olefin multiplets in such a way that a rapid broadening of the high-field side of the spectrum occurs. The AA′BB′X spectrum has been recorded for C 5 H 5 Sn(CH 3 ) 3 at −150° but its complete analysis proved to be impossible. The thermodynamic characteristics of metallotropic migration in the Group IVB C 5 H 5 M(CH 3 ) 3 derivatives have been found. The free energy of activation for migration, Δ G 300 , increases in the series Sn, Ge, Si, C. Essential features of the metallotropic rearrangement are discussed. The migration has been shown to proceed through a 1,2 shift in all cases (Si, Ge, Fe, Ru, H) where reliable data are available. An attempt is made to extend the concept of metallotropism to embrace both quasi-degenerate (indenyl) and non-degenerate (ring-substituted cyclopentadienyl) compounds.

NMR spectroscopy of metal cyclopentadienyls IX. Non-degenerate metallotropic rearrangement in bis(trimethylgermyl)- and bis(trimethylstannyl)-cyclopentadienes

Abstract The PMR spectra of C 5 H 4 [Ge(CH 3 ) 3 ] 2 and C 5 H 4 [Sn(CH 3 ) 3 ] 2 have been studied at temperatures over the range −130 to +190°. A non-degenerate metallotropic rearrangement has been found to occur in both compounds. The 5,5 isomers are transformed to the 2,5 isomers via a 1,3 metallic shift. The 5,5 isomers are the most stable in both cases. Chemical shifts of the ring and methyl protons have been studied for the germanium derivative as a function of temperature. The results have been processed by means of a MINIMAX 1 program (an improved version of the relaxation method) on a BESM-6 large computer. The C 5 H 4 [Ge(CH 3 ) 3 ] 2 metallotropic rearrangement has the thermodynamic constants Δ H = 4.8±0.3 kcal/mole, Δ S = 11.5± e.u. The metallotropic equilibrium lies well towards the 5,5 isomer for the tin compound, irrespective of the temperature. The metallotropism in this case has been demonstrated by the use of an aminostannane.

Reactions of chlorinated vinylsilanes with hydrogen chloride

Catalytic hydrochlorination of a series of chloro(chlorovinyl)methylsilanes was studied. The course of the reaction depends on the number and position of the chlorine atoms in the initial monomers.

Intercyclic haptotropic rearrangements in chromium tricarbonyl complexes of 1,1-dimethyl-1-silaacenaphthene

Conclusions1.The reaction of 1,1-dimethyl-l-silaacenaphthene with chromium carbonyl complexes L3Cr(CO)3, where L=CO, NH3, and C6H5N leads to a mixture of isomeric complexes differing in the position of the Cr(CQ)3 group.2.The interconversion of these isomeric chromium tricarbonyl complexes occurs in benzene, toluene, cyclohexane and decane at from 80 to 115°C due to reversible transfer of the Cr(CO)3 group between the six-membered rings. The thermodynamic and kinetic parameters of this isomerization were established.