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Pi-bonding and reactivity in transition metal nitrosyl complexes

University of British Columbia

This Thesis investigates the effect of π-bonding interactions on the electronic configuration and reactivity of Cr and Mo organometallic complexes that contain Cp' (C₅R₅ ; R = H (Cp), CH₃ (Cp*)) and NO ligands. From metrical parameters obtained from X-ray crystallographic studies and geometry optimization computations, the orbitals of CpCr-containing compounds in a variety of spin states are examined using Extended Hiickel molecular-orbital calculations. The ligand effects are evaluated in the context of Spectrochemical and Nephelauxetic effects. Reaction of Cp'Cr(NO)₂Cl with AgOTf yields Cp'Cr(NO)₂OTf. The covalentlybound trifiate ligand in CpCf(NO)₂(OTf) can be displaced by amines to afford [CpCr(NO)₂(NHR₂)][OTfj salts (NHR₂ = NH₃ , NHMe₂ , NH₂’Bu, NH₂Ph). Treatment of basic, aqueous solutions of CpCr(NO)₂OTf with HXL reagents (HXL = acetylacetone, salicylaldehyde, picolinic acid) results in the precipitation o f CpCr(NO)(LX) complexes. These mononitrosyl complexes may be independently synthesized from [CpCr(NO)(μ- I)]₂ and the appropriate chelating ligand in either anhydrous organic solvents or aqueous solution. CpMo(NO)(CH₂Ph)Cl reacts with R₂Mg (R = Me, Ph) or L i R (R = C=CPh) reagents to form CpMo(NO)(CH₂Ph)R complexes. These products are stabilized by the ƞ²] -benzyl ligand; the corresponding 16e CpMo(NO)R₂ species are too thermally unstable to be isolated. The ƞ²-CH₂Ph interaction is disrupted by introducing other ligands capable of multihapto-bonding, as evidenced by the synthesis of Cp₂Mo(NO)(CH₂Ph). Reaction of CpMo(NO)(CH₂Ph)Cl with AgOTf yields CpMo(NO)(CH₂Ph)OTf, which reacts with PPh₃ or pyridine to afford [CpMo(NO)(CH₂Ph)L][OTfJ salts. Cp*Cr(NO)(CO)₂ reacts with PCl₅ or I₂ in NCMe to form [Cp*Cr(NO)(M--X)]₂ dimers via the Cp*Cr(NO)(NCMe)X adducts (X = CI, I). The coordinating solvent is required in order to avoid overoxidation and subsequent decomposition via NO loss. Cr(NO)(N'Pr₂)(02CPh)₂ reacts with Mg(CH₂SiMe₃)₂ to afford Cr(NO)(N'Pr₂)(CH₂SiMe₃)₂ . The unusual nature o f this 14e, pseudo-tetrahedral, monomeric, diamagnetic bis(alkyl) compound is in part accounted for by the π-bonding properties of the ancillary amide and nitrosyl ligands.

Thesis/Dissertation

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2009-06-02

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http://hdl.handle.net/2429/8558

Chemistry

University of British Columbia

UBCV

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