Yu. A. Ustynyuk

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.

Proton magnetic resonance spectra and structure of iron π-allyl complexes

Abstract 1. The proton magnetic resonance spectra of a series of π-allylirontricarbonyl compounds have been studied. π-allylirontricarbonyl halides have been shown to exist in the form of two rotation isomers and their structure has been discussed. 2. Temperature-dependence of the di(π-allyl)irondicarbonyl NMR spectrum has been investigated and the energy barriers for hindered internal rotation of the allyl groups have been estimated to be 4.6±0.8 kcal/mole.

Indenyl-and flourenyl-transition metal complexesss : I. Synthesis, structures, and reactions of ν5-and ν6-derivatives of chromium group metals

Abstract The reaction leading to the ν5-fluorenyl-and ν-indenyl-tricarbonylmetallate anions, ν5-C13H9(CO)3Cr- and ν5-C9H7(CO)3M- where M stands for Cr, Mo, W have been studied. Deprotonation of (ν6-fluorene)Cr(CO)3 with t-BuOK seemingly proceeds via the corresponding ν6-anionic intermediate which is transformed into the ν5-isomer with a conversion halftime of several minutes. Chromium and molydenum ν5-anions rearrage on treatment with CH3COOH to the corresponding ν6-indene and fluorene complexes. Protonation of ν5-C9H7- (CO)3W- leads to the stable hyride ν5-C9H7(CO)3WH. All the anions studied react with Hg(CN)2 to give symmetric organomercury derivatives containing M–Hg bonds (M=Cr, Mo, W). The reaction of ν5-C9H7(CO)3Cr- and ν5-C13H9 structure and containing a Cr–CH3 bond: the product ν5-C9H7(CO)3CrCH3 has undergo thermal rearrangement to the ν6-compounds via transfer of the CH3 group to the five-membered ring and of the Cr(CO)3 group to the benzene nucleus. The molybdenum and tungsten anions form stable σ-methyl derivatives in reactions with CH3I. The possible reversible isomerization processes involving anionic and neutral compounds are considered form mechanic and stereo-chemical points view.

Determination of the activation parameters of permanent allylic rearrangement in allyl- and methallylboranes and in 1,1-bis(dipropylborylmethyl)ethylene by dynamic NMR spectroscopy

Abstract The activation parameters were determined for the permanent allylic rearrangement (PAR) in five organoboranes of allylic type by means of complete line shape analysis for the dynamic NMR spectra. The introduction of the second boron atom into the allylborane molecule leads to a significant decrease in the activation barrier of the PAR.

Reactions of nickelocene with benzylmagnesium compounds phenyltris(π-cyclopentadienylnickel)methane

Abstract Nickelocene reacts with benzylmagnesium compounds to form phenyltris(π-cyclopentadienylnickel)methane derivatives whose structures have been verified by IR, PMR, and mass spectra. Alkylation of the cyclopentadienyl ring occurs in the presence of excess Grignard reagent.

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.

Activation of CH4 and H2 by zirconium(IV) and titanium(IV) cationic complexes. Theoretical DFT study

Abstract The reactions of methane and dihydrogen molecules with the cations [(η 5 -C 5 H 5 ) 2 MCH 3 ] + ( 1 ) and [(η 5 -C 5 H 5 ) 2 MH] + ( 3 ) (M=Zr, Ti) have been investigated by gradient-corrected density functional calculations. In the case of CH 4 , the active cationic center of 1 or 3 attracts the substrate molecule first to form an agostic complex in which its CH bond is already somewhat weakened. The σ-bonded ligand exchange reaction in the system 1 +CH 4 proceeds through a symmetric transition state with an activation barrier of 15.0 kcal mol −1 (11.6 kcal mol −1 ) for the Zr (Ti) complex. Hydrogen reacts with 1 exothermally, Δ H 0 =−7.1 kcal mol −1 (−8.6 kcal mol −1 ) for Zr (Ti), yielding 3 and CH 4 without an activation barrier. These theoretical results give insight into the mechanism of H/D exchange in methane in the presence of Ziegler–Natta-type catalysts observed experimentally by Grigoryan et al. It is shown that organometallic cationic complexes of Zr(IV) and Ti(IV) may prove to be promising systems for CH and HH bond activation under mild conditions.

Electron diffraction study of the molecular structure of trimethylcyclopentadienylsilane

Abstract The molecular structure of trimethylcyclopentadienylsilane, C 5 H 5 Si(CH 3 ) 3 , has been studied by electron diffraction in the vapour phase. The Si atom is found to be bonded by the localized σ-bond with one of the cyclopentadienyl carbon atoms. The SiC bond distances are 1.90±0.01 A. The cyclopentadienyl ring has an “envelope” conformation, the dihedral angle between planar four- and three-membered fragments of the ring being 22±4°. The SiC bond makes an angle of 56±4° with the plane of the bent-out “envelope flap”. Assuming the equality of all CH bond lengths and also of three CC bond lengths within the planar four-membered fragment of the cyclopentadienyl ring, the following values are obtained: r (C-H) = 1.11± 0.02, r (CC) = 1.53±0.03, r (CC) = 1.40±0.02 A

Indenyl and flourenyl transition metal complexes : III. Some new reactions of flourenyl- and indenyl-metal tricarbonyl anions

Abstract Deprotonation of η 6 -flourenechromium tricarbonyl (III) with excess t-BuOK in THF at70°C yields [η 6 -C 13 H 9 Cr(CO) 3 ] − K + (Ia), which isomerizes to η 5 -C 13 H 9 Cr(CO) 3 Cr − K + (II) at temperatures above −20°C. [η 6 -C 13 H 9 Cr(CO) 3 ] − Li + (Ib) may be obtained in the solid state by treatment of III with BuLi in absolute ether followed by precipitation with n-hexane. Methylation of Ib and II with methyl iodide goes stereospecifically to give η 6 - exo - (IX) and η 6 -(9- endo -methylfuorene)chromium tricarbonyl (XII) from Ib and II, respectively. Acylation of Ia with CH 3 COCl yields the acetate of 9-acetylfluorenechromium tricarbonyl (VII) in its enol form. Treatment of III with excess t-BuOK and CH 3 I in THF at −30°C leads to the derivative (XI), which is fully methylated at C(9). Phenyldiazonium borofluoride, diphenyliodonium iodide, ferrocenium borofluoride, trimethylchlorostannane and triethylbromogermane react with η 5 -C 9 H 7 (CO) 3 M − K + in THF to give compounds of the η 5 -series: η 5 -C 9 H 7 (CO) 2 MN 2 C 6 H 5 (M  Cr, Mo, W), η 5 -C 9 H 7 (CO) 3 WC 6 H 5 , [η 5 -C 9 H 7 (CO) 3 M] 2 (M  Mo, W), η 5 -C 9 H 7 (CO) 3 MSnMe 3 (M  Cr, Mo, W) and η 5 -C 9 H 7 (CO) 3 MGeEt 3 (M  Cr, Mo, W), respectively.