The thermal isomerizations of η1‐vinylidene complexes [(η5‐C5H5)(CO)(NO)W=C=CHR] [5a, R = Si(CH3)2C(CH3)3; 5c, R = C(CH3)3] as well as [(η5‐C5H5)(CO)(NO)Mo=C=CHC(CH3)3] (8), to the corresponding η2‐1‐alkyne complexes [(η5‐C5H5)(CO)(NO)W(η2‐H−C≡C−R)] [7a, R = Si(CH3)2C(CH3)3; 7c, R = C(CH3)3] and [(η5‐C5H5)(CO)(NO)Mo{η2‐H−C≡C−CHC(CH3)3}] (9) has been investigated. Activation parameters for the isomerization of 5a in [D6]benzene and 8 in [D8]toluene and [D5]ethanol were determined. In [D8]toluene η1‐vinylidene complex 5a undergoes a single step 1,2‐shift of the silyl group from Cβ to Cα. However, complex 8 shows dichotomous behavior. The isomerization 8 ⇄ 9, dependent upon the solvent applied, occurs by means of two different pathways: in a nonpolar solvent, 8 tautomerizes via the 1,2‐migration of the hydrogen atom to 9 and in ethanol this tautomerization proceeds by a multi‐step process via deprotonation‐protonation and subsequent reductive elimination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Starting from a silicon dichloro substituted silole and a silacyclobutene, a series of new organosilicon-based spiro compounds was synthesized by using standard organometallic reaction procedures. The spiro compounds that combine two organic photoactive subunits at one silicon center were fully characterized by the usual analytical and spectroscopic methods, which include molecular structure determination by single-crystal X-ray analysis. Photoluminescence spectra of the compounds were recorded in the solid state and also as dilute solutions in THF. Interpretation of the spectra revealed that photoluminescence in this series of compounds originated from the stilbene or its vinylogue subunits. Different linkages of these groups to the silicon atoms (cyclic or open structures, four- or five-membered cycles) strongly affected both the excitation and the emission spectra, which show different emission maxima depending on the state of the sample (solid state or in solution) and the wavelength of light used for excitation. Thus, owing to their optoelectronic properties these compounds might be useful tools for the design of sensitive sensor materials and of optical switches.
The reaction of alkynyltungsten complexes [(CO)(NO)(Cp)W-CtC-R]Li (R ) H, C 6 H 5 , C(CH 3 ) 3 ) with differently substituted iminium ions is investigated. Due to the relative high acidity of the hydrogen atoms on the -carbon atom of the η 1 -vinylidene complex [(CO)(NO)-(Cp)WdCdCH 2 )] (1), the parent η 1 -acetylide complex [(CO)(NO)(Cp)W-CtC-H)] -is generated in situ simultaneously with the iminium ion by the reaction of η 1 -vinylidene complex 1 with an enamine. The reaction of 1 with enamines 2a-e leads to vinylcarbene complexes 3a-e in good yield. The first step of this transformation is a Mannich reaction on the -carbon atom of alkynyltungsten complexes, generating the expected -aminoalkylated η 1 -vinylidene complexes 6. This intermediate reacts further to 3a-e by migration of the hydrogen atom adjacent to the nitrogen atom to the R-carbon atom of the η 1 -vinylidene moiety. The appearance of a η 1 -vinylidene complex as an intermediate is supported by NMR experiments, and the postulated retro-imino-ene reaction is confirmed by the reaction of deuterated η 1 -vinylidene complex 1-D with enamine 2b to the vinylcarbene complex 8. The scope of the reaction is demonstrated by the reaction of alkynyltungsten complexes 9, 16, and 17 with a series of differently substituted iminium ions to the corresponding vinylcarbene complexes. Activation parameters for the retro-imino-ene reaction of η 1 -vinylidene complex 6a to vinylcarbene 3a in THF-d 8 were determined using 1 H NMR spectroscopy. On the basis of this experiment ∆H q , ∆S q , and ∆G q (at -1°C) were found to be 20.5 ( 1.4 kcal/mol, -1.4 ( 0.6 cal/mol, and 20.9 ( 1.4 kcal/mol, respectively. The profile of the postulated retroimino-ene reaction is calculated on the model compound [(CO)(NO)(Cp)WdCdCH-CH 2 -NH-CH 3 ] (6M), yielding [(CO)(NO)(Cp)WdCH-CHdCH 2 ] using density functional theory at the B3LYP level. The calculation shows the process is more likely a single-step reaction where the hydrogen migration and carbon-nitrogen bond breaking are two consecutive reactions without formation of a true intermediate. Single-crystal X-ray diffraction data of 3a and 4 are reported.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.