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The diverse chemistry of some tungsten nitrosyl complexes

University of British Columbia

The η⁵-C₅H₄iPr ligand imparts unprecedented effects on the physical and chemical properties of (η⁵-C₅H₄iPr)W(NO)(CH₂CMe₃)(η³-CH₂CHCMe₂) (2.3) and its precursors. Specifically, the reaction of (η⁵-C₅H₄iPr)W(NO)(CO)₂ (2.1) with PCl₅ results in the formation of the PCl₃ adduct of the (η⁵-C₅H₄iPr)W(NO)Cl₂ complex. Moreover, the subsequent metathesis reaction with the Mg(CH₂CH=CMe₂)₂ binary reagent occurs at the P-Cl bond of the adduct affording (η⁵-C₅H₄iPr)W(NO)(PCl₂CMe₂CH=CH₂)Cl₂ (2.4). The investigation of the unique effects of the η⁵-C₅H₄iPr ligand on the chemistry of tungsten-nitrosyl complexes has been extended to encompass (η⁵-C₅H₄iPr)W(NO)(H)(η³-CH₂CHCMe₂) (3.1), (η⁵-C₅H₄iPr)W(NO)(CH₂CMe₃)₂ (3.7), and trans-(η⁵-C₅H₄iPr)W(NO)(H)(κ²-PPh₂C₆H₄) (3.9). Results of these studies are summarized in following paragraphs. Trapping reactions of the coordinatively unsaturated reactive intermediates, formed via intramolecular isomerization of 3.1, using PMe₃ show a preferential isomerization to the η¹ intermediate (η⁵-C₅H₄iPr)W(NO)(H)(η¹-CH₂CH=CMe₂), isolable as its PMe₃ adduct. Increasing the temperature facilitates the intramolecular rearrangement to the desired η²-alkene intermediate, but due to the thermal instability of the starting material, the C-H activation of alkanes cannot be carried out at very high temperatures. The reaction of 3.7 with H₂ and PPh₃ shows instantaneous cis to trans isomerization of the generated ortho-metallated complex to form an inert trans-(η⁵-C₅H₄iPr)W(NO)(H)(κ²-PPh₂C₆H₄) (3.9). In this case, the faster rate of cis to trans isomerization hinders the C-H activation potential of the ortho-metallated product. In addition, results of the investigation of the multiple C-H activation chemistry of (η5-C5Me5)W(NO)(CH₂CMe₃)2 (4.1) are presented. Thermolysis of 4.1 in neat hydrocarbons results in elimination of neopentane and formation of the transient (η⁵-C₅Me₅)W(NO)(=CHCMe₃) complex, which subsequently effects the multiple C-H activations of linear n-alkanes. The corresponding (η⁵-C₅Me₅)W(NO)(H)(η³-allyl) complexes obtained from the reactions with various n-alkanes have been isolated and characterized. These thermolysis reactions are accompanied by the generation of alkenes. Attempts to improve the production of olefins by varying different experimental factors have been investigated. The preliminary results of the investigation of the C-C coupling reactivity of (η⁵-C₅Me₅)W(NO)(H)(η³-allyl) complexes with aldehydes and phenylacetylene are presented. Thermolysis reactions of (η⁵-C₅Me₅)W(NO)(H)(η³-allyl) complexes with aldehydes under aerobic conditions result in the formation of the corresponding coupled alcohol product. Also, thermolysis reactions of (η⁵-C₅Me₅)W(NO)(H)(η³-CH₂CHCMe₂) with phenylacetylene reveal incorporation of phenylacetylene molecules into the (η⁵-C₅Me₅)W(NO) and (η⁵-C₅Me₅)W(NO)(H)(η³-CH₂CHCMe₂) fragments.

Text

2017-03-15

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/60905

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/