Journal article

Publication year: 2005

Pages: 977-989

Journal: Organometallics

Volume number: 24

Issue number: 5

ISSN: 0276-7333

eISSN: 1520-6041

DOI Link: https://doi.org/10.1021/om0491185

Publisher: American Chemical Society

Abstract: 
The reaction of alkynyltungsten complexes [(CO)(NO)(Cp)W-CdropC-R]Li (R = H, C6H5, C(CH3)(3)) with differently substituted iminium ions is investigated. Due to the relative high acidity of the hydrogen atoms on the beta-carbon atom of the eta(1)-vinylidene complex [(CO)(NO)-(Cp)W=C=CH2)] (1), the parent eta(1)-acetylide complex [(CO)(NO)(Cp)W-CdropC-H)](-) is generated in situ simultaneously with the iminium ion by the reaction of eta(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 P-carbon atom of alkynyltungsten complexes, generating the expected beta-aminoalkylated eta(1)-vinylidene complexes 6. This intermediate reacts further to 3a-e by migration of the hydrogen atom adjacent to the nitrogen atom to the alpha-carbon atom of the eta(1)-vinylidene moiety. The appearance of a eta(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 eta(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 eta(1)-vinylidene complex 6a to vinylcarbene 3a in THF-d(8) were determined using H-1 NMR spectroscopy. On the basis of this experiment DeltaH(+), DeltaS(+), and DeltaG(+) (at -1degreesC) 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 retro-imino-ene reaction is calculated on the model compound [(CO)(NO)(Cp)W=C=CH-CH2-NH-CH3] (6M), yielding [(CO)(NO)(Cp)W=CH-CH=CH2] 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.

Harvard Citation style: Ipaktschi, J., Mohsseni-Ala, J., Dülmer, A., Loschen, C. and Frenking, G. (2005) Reaction of tungsten η¹-acetylide complexes [(η⁵-C₅H₅)(NO)(CO)W-C≡C-R]Li with iminium ions, Organometallics, 24(5), pp. 977-989. https://doi.org/10.1021/om0491185

APA Citation style: Ipaktschi, J., Mohsseni-Ala, J., Dülmer, A., Loschen, C., & Frenking, G. (2005). Reaction of tungsten η¹-acetylide complexes [(η⁵-C₅H₅)(NO)(CO)W-C≡C-R]Li with iminium ions. Organometallics. 24(5), 977-989. https://doi.org/10.1021/om0491185