Tri-chlorido, 2-methylallyl and 2-butenyl tert-butylimido niobium and tantalum complexes: Synthesis, multinuclear NMR spectroscopy and reactivityThis paper is dedicated to the memory of Dr Amelio Vázquez de Miguel who died April 20, 2010 and whom we remember with affection.

Pseudooctahedral complexes [MCl3(NtBu)L2] (M = Nb, L = py 1, ½ tmeda 3; M = Ta, L = py 2, ½ tmeda 4) have been studied by spectroscopic methods. By a VT 1H NMR experiment a mutual exchange process between the pyaxand pyfreein the complexes 1–2was observed, whereas 13C and 15N NMR studies showed in the complexes 3–4a tmeda ligand with an axial/equatorial coordination mode. The reaction of 2with 3 equiv of Grignard reagent produces the methathesis products [TaR3(NtBu)] (R = CH2CMeCH25, CH2CHCHCH36) in which 2-methylallyl and 2-butenyl groups appear with a η3- and σ-coordination mode, respectively. When, toluene solutions of the compounds 5–6were treated with 2 equiv of 2,6-dimethylphenylisocyanide the imido bisiminoacyl compounds [TaR(NtBu){C(R)NAr-κ1C}2] (Ar = 2,6-Me2C6H3; R = CH2CMeCH27, CH2CHCHCH38) can be isolated, viaan imido iminoacyl intermediate [TaR2(NtBu){C(R)NAr-κ1C}] (Ar = 2,6-Me2C6H3; R = CH2CMeCH29) as we have observed in the treatment of 5with 1 equiv of isocyanide; however, the analogous reaction between 5and COPh2leads to the formation of the trisalkoxo imido compound [Ta(OCPh2R)3(NtBu)] (R = CH2CMeCH210). All new complexes were studied by IR and multinuclear NMR spectroscopy. [ABSTRACT FROM AUTHOR]