1050359-30-2Relevant academic research and scientific papers
Synthesis and reactivity of cationic niobium and tantalum methyl complexes supported by imido and β-diketiminato ligands
Tomson, Neil C.,Arnold, John,Bergman, Robert G.
, p. 7718 - 7729 (2011/09/19)
The synthesis and reactivity of the cationic niobium and tantalum monomethyl complexes [(BDI)MeM(NtBu)][X] (BDI = [Ar]NC(CH 3)CHC(CH3)N[Ar], Ar = 2,6-iPr2C 6H3; M = Nb, Ta; X = MeB(C6F5) 3, B(C6F5)4] was investigated. The cationic alkyl complexes failed to irreversibly bind CO but formed phosphine-trapped acyl complexes [(BDI)(R3PC(O)Me)M(N tBu)][B(C6F5)4] (R = Et, Cy) in the presence of a combination of trialkylphosphines and CO. Treatment of the monoalkyl cationic Nb complex with XylNC (Xyl = 2,6-Me2-C 6H3) resulted in irreversible formation of the iminoacyl complex [(BDI)(XylNC(Me))Nb(NtBu)][B(C6F5) 4], which did not bind phosphines but would add a methide group to the iminoacyl carbon to provide the known ketimine complex (BDI)(XylNCMe 2)Nb(NtBu). Further stoichiometric chemistry explored i) migratory insertion reactions to form new alkoxide, amidinate, and ketimide complexes; ii) protonolysis reactions with Ph3SiOH to form thermally robust cationic siloxide complexes; and iii) catalytic high-density polyethylene formation mediated by the cationic Nb methyl complex.
Halo, alkyl, aryl, and bis(imido) complexes of niobium supported by the β-diketiminato ligand
Tomson, Neil C.,Arnold, John,Bergman, Robert G.
, p. 2926 - 2942 (2010/10/04)
Synthesis of the complex (BDI)Nb(NtBu)Cl2py (BDI=HC[C(Me)N(2,6-iPr2-C6H3)] 2) was achieved in high yield following the treatment of Nb(N tBu)Cl3py2 with Li(BDI)(OEt2). Substitution of the chlorides for fluorides was effected by introducing 2.0 equiv of Me3SnF in toluene, providing the pyridine-coordinated difluoride complex (BDI)Nb(NtBu)F2py in modest yield. The pyridine ligands from both halide compounds were removed by treatment with B(C6F5)3, affording the Lewis base-free complexes (BDI)Nb-(NtBu)X2 (X=Cl, F). Additionally, the Lewis base-free dichlorides of the tBu-imido and Ar-imido (Ar= 2,6-iPr2-C6H3) complexes were obtained following treatment of Nb(NR)Cl3(dme) (R = tBu, Ar) with Li(BDI)(OEt2). The pyridine-coordinated dichloride was alkylated and arylated to form the dimethyl complex (BDI)Nb(N tBu)Me2 (described previously, see text) and the mono(p-tolyl) complex (BDI)Nb-(NtBu)Cl(p-tol), the latter of which was methylated with MeMgBr to yield the mixed alkyl/aryl complex (BDI)Nb(N tBu)Me(p-tol) in good yield. A rare example of a group 5 bis( tBu-imido) species was synthesized in good yield via treatment of (BDI)Nb(NtBu)Cl2py with 2.0 equiv of LiNHtBu to form (BDI)Nb(NtBu)2py. Exchange of the coordinated pyridine ligand for either pyridine-d5 or dmap (p-(dimethylamino) pyridine) was shown to occur through a dissociative mechanism, allowing for removal of the coordinated Lewis base by treatment with B(C6F 5)3. The resulting average C2v-symmetric tetracoordinate bis(imido) complex (BDI)Nb(NtBu)2 was characterized in solution by NMR spectroscopy and observed to undergo clean thermal decomposition to yield (BDI#)Nb(NtBu)(NH tBu) (BDI#=H2Cd C(NAr)CH=C(NAr)Me) over several hours at room temperature. Treatment of the four-coordinate bis(imido) with tBuNCO resulted in clean [2 + 2] cycloaddition to yield an oxaazametallacyclobutane complex, which was further observed to extrude tBuNdCdNtBu over 12 h at room temperature. The molecular structures of (BDI)Nb(NtBu)Cl2py, (BDI)Nb(NAr)Cl 2, (BDI)Nb(NtBu)Me2, (BDI)Nb-(N tBu)Cl(p-tol), (BDI)Nb(NtBu)2py, and (BDI)Nb(NtBu)2(dmap) were determined crystallographically. Finally, DFT (BP86) geometry optimization calculations on a model complex of the thermally unstable four-coordinate bis(imido) species allowed for identification of the orbital interactions leading to activation of the imido groups through mixing with the BDI frontier orbitals.
