Two-sided Amido Ligands

An important recent development in the area of the monodentate amido metal chemistry has come from the group of Cummins who introduced ligands of the type —N(R)Ar (for example, R = Bu , 1-adamantyl (I-Ad), 2-adamantyl (2-Ad), —C(CD3)2(CH3) Ar = Ph, C6H3Me2-3,5, C6H4F-4).These allowed the isolation of an Mo N(R)Ar 3 species having three-coordinate molybdenum as well as three-coordinate derivatives of several other metals. Apart from [M N(SiMe3)2 3] (M = Y, La), the molybdenum compounds are the only examples of structurally characterized open shell, three-coordinate homoleptic amides 

C 03 (p-t-B u -calix [4] are b eOS iSMejJ flJif) Co4(t-Bit2Cfllh Ehf 5j t-BuiCal = 5,5Bij 2calecl lartje 

Numerous studies involving similar amido derivatives of metals such as Ti (e.g. heterometallic cross-coupling of benzonitrile with carbon dioxide, pyridine, and benzophenone with mixed [Ti N(Bu )Ar 3] and [Mo N(Bu )Ar 3] systems), V (e.g. denitrogenation of a vanadium nitride by carbon disulfide and dioxide), Nb (e.g. the 

This transformation is in contrast to the corresponding more sterically crowded [Mo N (Bu )Ar 3] which does not exhibit this type of behaviour. Initially it was assumed that the cyclometallated structure would inhibit the type of reactions (e.g. with N2 or N2O) shown by the t-Bu substituted tris-amido complex. Investigation of the chemistry, however, showed that this is not the case and the imine-hydrido product behaves as an effective source of [Mo N(Pr )Ar 3] which, because of its less sterically encumbered nature, exhibits reactivity not observed for its more hindered [Mo N(Bu )Ar 3] counterpart. A simple example is provided by complex formation with benzophenone to give [Mo N(Pr )Ar 3(r 2-OCPh2)], whereas the Bu analogue did not react with this reagent.  

A more recent application, involving the nobium system, concerns the reaction of NaPNbN 3 with [Cl(0)W N(Pr )Ar 3] to afford [P=W N(P )Ar 3] with elimination of [ONbN 3] and NaCl. °  

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