The synthesis, reactivity, and structural study of multiple imido complexes of group 6.
AuthorMorrison, Donald Lee.
Committee ChairWigley, David E.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe first reported tris(imido) complexes of group 6, (Li(THF)₄) (M(NAr)₃Cl) (M = W (4) or Mo (9)), are formed upon treatment of M(NAr)₂Cl₂(THF)₂ complexes with two equiv of LiNHAr. Tris(imido) complexes constitute the kinetic products of reaction between M(NAr)₂Cl₂(THF)₂ and 2 equiv of LiNHAr. [(Li(THF)₄) (M(NAr)₃Cl)] can back react with the H₂NAr formed in the reaction to give the thermodynamic products M(NAr)₂(NHAr)₂ (M = W (29), Mo (11)) irreversibly. Mechanistic evidence for the formation of the bis(imide) complex W(NAr)₂Cl₂(THF)₂ (2) from W(NAr)Cl₄(THF) (1) show the reaction proceeds by an α-H abstraction of nascent W(NAr)(NHAr)₂Cl₂(THF)ₓ. Thus treatment of W(NAr)(NEt₂)Cl₂ (8) with LiNHAr yields 2 and Et₂NH. Mechanistic evidence shows that the formation of tris(imide) complexes 4 and 9 proceeds through an intermolecular α-H deprotonation. In support of this, no 4 is formed upon treatment of W(NAr)₂(NEt₂)Cl (3) with LiNHAr. It is possible to displace the chloride with a variety of nucleophiles to form analogs to complexes 4 and 9. For example, treatment of complex 4 with PMe₃ yields W(NAr)₃(PMe₃) (5), whereas reaction of complex 9 with pyridine yields Mo(NAr)₃(pyr) (16). Alkyl analogs [Li(THF)₄][W(NAr)₃Me] (19) and [Li(THF)₄][(Mo(NAr)₃Me) (17) are formed upon reaction of 4 and 9 with MeLi, respectively. Construction of an orbital interaction diagram for tris(imido) complexes (M(NAr)₃L), as well as related CpM(NAr)₂Cl complexes, reveals that the HOMO is a three-fold symmetric ligand-based non-bonding orbital. This makes these complexes highly reactive with a variety of electrophiles. Thus protonation of 17 with [HNMe₃][BPh₄] yields Mo(NAr)₂(NHAr)Me (23), methylation of 4 with methyl iodide yields W(NAr)₂[N(Me)Ar]I (33), and reaction of CO₂ with 5 yields W(NAr)₂ [N(C(O)O)Ar](PMe₃) (38). M(NAr)₃L and CpM(NAr)₂Cl complexes catalyze the metathesis of carbodiimides and olefins. The rate of ring opening metathesis polymerization (ROMP) of cyclic olefins is greatly enhanced in the presence of Lewis acid activators.