Synthetic and Structural Studies of Permethylscandocene and Permethyltantalocene Derivatives

Citation

St. Clair, Martin A. (1989) Synthetic and Structural Studies of Permethylscandocene and Permethyltantalocene Derivatives. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/192V-TK10. https://resolver.caltech.edu/CaltechTHESIS:08262013-094527536

Abstract

Cp^*₂Sc-H reacts with H₂ and CO at -78°C to yield Cp^*₂ScOCH₃. A stepwise reduction of CO to an alkoxide is observed when CO reacts with Cp^*₂ScC₆H₄CH₃-p to give the η²-acyl Cp^*₂Sc(CO)C₆H₄CH₃-p, which then reacts with H₂ to produce Cp^*₂ScOCH₂C₆H₄CH₃-p. Cp^*₂ScCH₃ and Cp^*₂ScH(THF) react with CO to give uncharuncharacterizable products. Cp^*₂ScH and Cp^*₂ScCH₃ react with Cp₂MCO (M = Mo, W) to give scandoxycarbenes, Cp₂M=C(CH₃)OScCp^*₂, while a wide variety of Cp^*₂ScX (X = H, CH₃, N(CH₃)₂, CH₂CH₂C₆H₅) reacts with CpM(CO)₂ (M = Co, Rh) to yield similar carbene complexes. An x-ray crystal structure determination of Cp(CO)Co=C(CH₃)-OScCp^*₂ revealed a µ²: η¹, η¹ carbonyl interaction between the Co-CO and Sc.

CO₂ inserts cleanly into Sc-phenyl bonds at -78°C to produce a carboxylate complex, Cp^*₂Sc(O₂C)C₆H₄CH₃-p. The structure of this compound was determined by x-ray crystallographic techniques.

Excess C₂H₂ reacts with Cp^*₂ScR (R = H, alkyl, aryl, alkenyl, alkynyl, amide) at temperatures below -78°C to form the alkynyl species Cp^*₂Sc-C≡C-H, which then reacts with the remaining acetylene to form polyacetylene. Cp^*₂Sc-C≡C-H further reacts to yield Cp^*₂Sc-C≡C-ScCp^*₂. This unusual C₂ bridged dimer was characterized by x-ray crystallography.

Attempts were made to model the C-N bond breaking step of hydrodenitrogenation by synthesizing Cp^*₂TaH(η²-H₂C=N(C₆H₄X)) and studying its rearrangement to Cp^*₂Ta(=N(C₆H₄X))(CH₃). The 1,2 addition/elimination reactions of Cp^*₂Ta(η²-H₂C=N(CH₃)H and Cp^*₂Ta(=X)H (X=O, S, NH, N(C₆H₅)) were investigated. Cp^*₂Ta(=NH)H was found to react with D₂ to give Cp^*₂Ta(=ND)H, implying a nonsymmetric amide-dihydride intermediate for the addition/elimination process. Cp^*₂Ta(=S)H and H₂O equilibrate with Cp^*₂Ta(=O)H and H₂S, which allowed determination of the difference in bond strengths for Ta=O and Ta=S. Ta=O was found to be approximately 41 kcals/mole stronger than Ta=S.

Thesis Files