Chemistry of high-oxidation-state groups V and VI complexes: Novel silyl and imido complexes and the reactions of silyl and alkyl alkylidyne complexes with oxygen

This dissertation describes the synthesis and characterization of the novel early transition metal (especially group VI metals) complexes free of anionic π-ligands such as cyclopentadienyl (Cp) and studies of their reactions with oxygen and silanes.; Our study of Cp-free tungsten silyl chemistry is reported. A novel d 0 tungsten silyl complex 2 [(ButCH ₂)W(=CHBut)₂(SiButPh₂ ) (2a) (ButCH₂)₂W(≡CBu t)(SiButPh₂) (2b)] and an equilibrium between 2a and 2b are described in Chapter 2. The thermodynamics of this equilibrium [ΔH° = −0.9(0.2) kcal/mol, ΔS° = −0.6(0.8) eu] was investigated by 1H NMR. The studies of the α-hydrogen exchange between 2a and 2b by 2-D EXSY experiments gave kinetic parameters of the exchange: ΔH≠ = 17.9(1.1) kcal/mol, ΔS≠ = 1.9(5.7) eu for the forward reaction (2a → 2b) and Δ H≠ = 18.6 (1.1) kcal/mol, ΔS ≠ = 1.9(5.7) eu for the back reaction (2b → 2a).; The reaction of O₂ with silyl alkylidyne 2b [(Bu tCH₂)W(=CHBut)₂(SiBut Ph₂) (2a) (ButCH₂)₂W(≡CBu t)(SiButPh₂) (2b)] is described in Chapter 3. A silyl migration product (ButCH₂) ₂W(=O)[=C(But)(SiButPh₂)] ( 5) was characterized. A siloxy analog of 2b, (Bu tCH₂)₂W≡CBut(OSiBu tPh₂) (6), was prepared and excluded as a possible intermediate in the formation of 5. Ab initio calculations suggested a pathway involving silyl migration in 2b to give a tungsten (IV) intermediate (ButCH ₂)₂W=C(But)(SiButPh₂) (7) prior to the reaction with O₂. A crystal structure of (Me₃SiCH₂)₂W(=O)(=CHSiMe₃)(O=PMe ₃)•(Me₃SiCH₂)₃W≡CSiMe ₃ (12) was obtained from the reaction of alkyl alkylidyne (Me₃SiCH₂)₃W≡CSiMe₃ with O₂ in the presence of PMe₃.; In Chapter 4, preparation and characterization of bis(2,6-diisopropylphenylimido)molybdenum(VI) amide and silyl complexes (ArN=)₂Mo(NMe₂)₂ (14), (ArN=)₂Mo(NMe₂)[Si(SiMe₃) ₃] (15), (ArN=)₂MoCl[N(SiMe₃) ₂] (16), (ArN=)₂Mo(NMe₂)[N(SiMe ₃)₂] (17), and (ArN=)₂Mo(NHAr) ₂ (18) are reported. In addition, new bis(imido)molybdenum(VI) amine adducts (ArN=)₂MoCl₂(NHMe₂) ( 19), (ArN=)₂MoCl₂(NHEt₂) (20 ), (ArN=)₂MoCl₂(NHMe₂)₂ (21), and (ArN=)₂MoCl₂(NHMe₂)•(ArN=) ₂MoCl₂(DME) (22) and their X-ray structures are reported. ^ Prepar...