Tri-chlorido, 2-methylallyl and 2-butenyl tert-butylimido niobium and tantalum complexes: Synthesis, multinuclear NMR spectroscopy and reactivity

摘要

Pseudooctahedral complexes [MCl_3(NtBu)L_2] (M = Nb, L = py 1, tmeda 3; M = Ta, L = py 2, tmeda 4) have been studied by spectroscopic methods. By a VT ~1H NMR experiment a mutual exchange process between the py_(ax) and py_(free) in the complexes 1-2 was observed, whereas ~(13)C and ~(15)N NMR studies showed in the complexes 3-4 a tmeda ligand with an axial/equatorial coordination mode. The reaction of 2 with 3 equiv of Grignard reagent produces the methathesis products [TaR _3(NtBu)] (R = CH_2CMeCH_25, CH _2CHCHCH_36) in which 2-methylallyl and 2-butenyl groups appear with a η~3- and σ-coordination mode, respectively. When, toluene solutions of the compounds 5-6 were treated with 2 equiv of 2,6-dimethylphenylisocyanide the imido bisiminoacyl compounds [TaR(NtBu){C(R)NAr-κ~1C}_2] (Ar = 2,6-Me _2C_6H_3; R = CH_2CMeCH_27, CH_2CHCHCH_38) can be isolated, via an imido iminoacyl intermediate [TaR_2(NtBu){C(R)NAr-κ~1C}] (Ar = 2,6-Me_2C_6H_3; R = CH_2CMeCH _29) as we have observed in the treatment of 5 with 1 equiv of isocyanide; however, the analogous reaction between 5 and COPh_2 leads to the formation of the trisalkoxo imido compound [Ta(OCPh_2R) _3(NtBu)] (R = CH_2CMeCH_210). All new complexes were studied by IR and multinuclear NMR spectroscopy.