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Chemistry of bis(alkyl) nitrosyl and related complexes of molybdenum and tungsten

University of British Columbia

The reactions of (ɳ⁵-C₅R₅)M(NO)(CO)₂ (R = H, Me; M = Mo, W) with PCl₅ result in the formation of the corresponding (ɳ⁵-C₅R₅)M(NO)(Cl)₂ products in high isolated yields (85-95%). These products have been fully characterized by conventional analytical and spectroscopic techniques including an X-ray crystallographic study of [ɳ⁵-C₅Me₅)Mo(NO)(Cl)₂]₂. Alkylation of the (ɳ⁵-C₅R₅)W(NO)(Cl)₂ compounds with Grignard reagents results in the formation of the corresponding complexes, (ɳ⁵-C₅R₅)W(NO)(R')₂ (R = H, Me; R' = CH₂CM₃, CH₂CM₂Ph: R = Me; R' = p-C₆H₄Me, Ph). An electrochemical study of (ɳ⁵-C₅H₅)W(NO)(CH₂CMe₃)₂, (ɳ⁵-C₅H₅)W(NO)(CH₂CMe₂Ph)₂, and (ɳ⁵-C₅Me₅)W(NO)(p-C₆H₄Me)₂ shows 2 successive, chemically reversible, one electron reductions in THF for each complex. The complexes (ɳ⁵-C₅R₅)W(NO)(R')₂ (R = H; R' = CH₂CMe₃, CH₂CMe₂Ph: R = Me; R' = CH₂CMe₂Ph,p-C₆H₄Me) react with 1 atm of CO resulting in the formation of the singly inserted products (ɳ⁵-C₅R₅)W(NO){C(O)R'}(R') in good yields, presumably via initial CO coordination. These acyl complexes have been completely characterized by conventional techniques. The IR and NMR spectroscopic properties of these complexes are indicative of an ɳ²-acyl coordination mode for all of the acylalkyl and acylaryl products. Under 6 atm of CO the (ɳ⁵-C₅H₅)W(NO)(R')₂ (R' = CH₂CMe₃, CH₂CM₂Ph) complexes are doubly carbonylated to form the corresponding (ɳ⁵-C₅H₅)W(NO){C(O)R'}₂ products. Furthermore, (ɳ⁵-C₅Me₅)W(NO){C(O)p-C₆H₄Me}(p-C₆H₄Me) reacts to form (ɳ⁵-C₅Me₅)W(NO)(CO){C(O)p-C₆H₄Me}(p-C₆H₄Me) under 6 atm of CO, but there is no evidence for the formation of a bis(acyl) product. A preliminary X-ray crystallographic investigation of (ɳ⁵-C₅H₅)W(NO){C(O)CH₂CMe₂Ph}₂ reveals the presence of one ɳ²-acyl ligand and one ɳ¹acyl ligand. The ¹H and ¹³C{¹H} NMR spectra of the (ɳ⁵-C₅H₅)W(NO){C(O)R'}₂ compounds exhibit signals for only one type of acyl ligand, indicating that the complexes are stereochemically non-rigid in solution through a process which averages the signals for the ɳ¹and ɳ³- acyl ligands. The bis(benzyl) complexes, (ɳ⁵-C₅R₅)M(NO)(CH₂Ar)₂ (R = H, Me; M = Mo, W; Ar = Ph, p-Tol), react with HCl to form (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ar)(Cl) complexes. These complexes have been reacted with Grignard reagents, R'MgCl, to form the corresponding (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ar)(R') (R' = CH₂SiMe₃, CH₂CMe₃, p-Tol) products. The benzyl ligand in all of these complexes is coordinated in an ɳ²-fashion, similar to that seen in the solid-state molecular structures of the bis(benzyl) precursors. The coordination mode of the benzyl ligands has been confirmed by solid-state molecular structure determinations of the representative examples (ɳ⁵-C₅Me₅)Mo(NO)(CH₂Ph)(Cl) and (ɳ⁵-C₅Me₅)Mo(NO)(CH₂Ph)(CH₂SiMe₃). The ¹H and ¹³C{¹H} NMR spectroscopic data for all of the complexes are discussed, with focus on the diagnostic characteristics for the ɳ²-benzyl ligand. A possible qualitative interpretation for the symmetric ɳ²-bonding mode in these complexes is presented. The (ɳ⁵-C₅Me₅)M(NO)( ɳ²-CH₂Ph)(Cl) (M = Mo, W) complexes react with AgBF₄ in CH₃CN to form electrophilic complexes of the type [(ɳ⁵-C₅Me₅)M(NO)( ɳ²-CH₂Ph)(NCCH₃)]BF₄. The solid-state molecular structures of these complexes are discussed and contrasted with those found for the neutral ɳ²-benzyl complexes. The reaction of racemic AgO₂CCH(Et)(Ph) with the (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ph)(Cl) (R = H, Me; M = Mo, W: R = H; M = Mo) compounds forms the corresponding diastereomeric (ɳ⁵-C₅R₅)M(NO)( ɳ¹-CH₂Ph)(O₂CCH(Et)(Ph)) products. The ɳ¹ coordination of the benzyl ligand and bidentate coordination of the carboxylate ligand are established by the IR, ¹H, and ¹³C{¹H} NMR spectroscopic data for these products. A mixture of two diasteromeric products is demonstrated by the ¹H and ¹³C{¹H} NMR spectroscopic data and initial attempts to separate these diastereomers by crystallization are described.

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2011-01-19

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http://hdl.handle.net/2429/30694

Chemistry

University of British Columbia

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