Tomson Neil C, Arnold John, Bergman Robert G
Department of Chemistry, University of California, Berkeley, California 94720.
Organometallics. 2010 Jun 7;29(13):2926-2942. doi: 10.1021/om1001827.
Synthesis of the complex (BDI)Nb(N(t)Bu)Cl(2)py (BDI = HCC(Me)N(2,6-iPr(2)-C(6)H(3))) was achieved in high yield following the treatment of Nb(N(t)Bu)Cl(3)py(2) with Li(BDI)(OEt(2)). Substitution of the chlorides for fluorides was effected by introducing 2.0 equiv of Me(3)SnF in toluene, providing the pyridine-coordinated difluoride complex (BDI)Nb(N(t)Bu)F(2)py in modest yield. The pyridine ligands from both halide compounds were removed by treatment of the pyridine adducts with B(C(6)F(5))(3), affording the Lewis base-free complexes (BDI)Nb(NtBu)X(2) (X = Cl, F). Additionally, the Lewis base-free dichlorides of the (t)Bu-imido and Ar-imido (Ar = 2,6-(i)Pr(2)-C(6)H(3)) complexes were obtained following treatment of Nb(NR)Cl(3)(dme) (R = tBu, Ar) with Li(BDI)(OEt(2)). The pyridine-coordinated dichloride was alkylated and arylated to form the dimethyl complex (BDI)Nb(N(t)Bu)Me(2) (described previously, see text) and the mono(p-tolyl) complex (BDI)Nb(N(t)Bu)Cl(p-tol), the latter of which was methylated with MeMgBr to yield the mixed alkyl/aryl complex (BDI)Nb(N(t)Bu)Me(p-tol) in good yield. A rare example of a Group 5 bis((t)Bu-imido) species was synthesized in good yield via treatment of (BDI)Nb(N(t)Bu)Cl(2)py with 2.0 equiv of LiNHtBu to form (BDI)Nb(NtBu)(2)py. Exchange of the coordinated pyridine ligand for either pyridine-d(5) 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(C(6)F(5))(3). The resulting average C(2v)-symmetric tetracoordinate bis(imido) complex (BDI)Nb(N(t)Bu)(2) was characterized in solution by NMR spectroscopy and observed to undergo clean thermal decomposition to yield (BDI(#))Nb(N(t)Bu)(NH(t)Bu) (BDI(#) = H(2)C=C(NAr)CH=C(NAr)Me) over several hours at room temperature. Treatment of the four-coordinate bis(imido) with (t)BuNCO resulted in clean [2 + 2] cycloaddition to yield an oxaazametallacyclobutane complex, which was further observed to extrude (t)BuN=C=N(t)Bu over 12 h at room temperature. The molecular structures of (BDI)Nb(N(t)Bu)Cl(2)py, (BDI)Nb(NAr)Cl(2), (BDI)Nb(N(t)Bu)Me(2), (BDI)Nb(N(t)Bu)Cl(p-tol), (BDI)Nb(N(t)Bu)(2)py, 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.
用Li(BDI)(OEt₂)处理Nb(N(t)Bu)Cl₃py₂后，以高产率合成了配合物(BDI)Nb(N(t)Bu)Cl₂py（BDI = HC[C(Me)N(2,6-iPr₂-C₆H₃)]₂）。通过在甲苯中引入2.0当量的Me₃SnF将氯化物替换为氟化物，以适度的产率得到吡啶配位的二氟化物配合物(BDI)Nb(N(t)Bu)F₂py。用B(C₆F₅)₃处理吡啶加合物可除去两种卤化物化合物中的吡啶配体，得到无路易斯碱的配合物(BDI)Nb(NtBu)X₂（X = Cl，F）。此外，用Li(BDI)(OEt₂)处理Nb(NR)Cl₃(dme)（R = tBu，Ar）后，得到了(t)Bu-亚氨基和Ar-亚氨基（Ar = 2,6-(i)Pr₂-C₆H₃）配合物的无路易斯碱二氯化物。吡啶配位的二氯化物经烷基化和芳基化反应分别形成二甲基配合物(BDI)Nb(N(t)Bu)Me₂（先前已描述，见正文）和单(对甲苯基)配合物(BDI)Nb(N(t)Bu)Cl(p-tol)，后者用MeMgBr甲基化，以良好的产率得到混合烷基/芳基配合物(BDI)Nb(N(t)Bu)Me(p-tol)。通过用2.0当量的LiNHtBu处理(BDI)Nb(N(t)Bu)Cl₂py，以高产率合成了一个罕见的第5族双((t)Bu-亚氨基)物种的例子，形成(BDI)Nb(NtBu)₂py。已表明，通过解离机制，配位的吡啶配体可被吡啶-d₅或dmap（对-(二甲氨基)吡啶）取代，从而通过用B(C₆F₅)₃处理除去配位的路易斯碱。所得的平均C₂v对称四配位双(亚氨基)配合物(BDI)Nb(N(t)Bu)₂在溶液中通过核磁共振光谱进行了表征，并观察到在室温下经过数小时会发生完全热分解，生成(BDI(#))Nb(N(t)Bu)(NH(t)Bu)（BDI(#) = H₂C=C(NAr)CH=C(NAr)Me）。用(t)BuNCO处理四配位双(亚氨基)会发生完全的[2 + 2]环加成反应，生成一个氧杂氮杂金属环丁烷配合物，进一步观察到在室温下经过12小时会挤出(t)BuN=C=N(t)Bu。通过晶体学确定了(BDI)Nb(N(t)Bu)Cl₂py、(BDI)Nb(NAr)Cl₂、(BDI)Nb(N(t)Bu)Me₂、(BDI)Nb(N(t)Bu)Cl(p-tol)、(BDI)Nb(N(t)Bu)₂py和(BDI)Nb(NtBu)₂(dmap)的分子结构。最后，对热不稳定的四配位双(亚氨基)物种的模型配合物进行DFT（BP86）几何优化计算，从而确定了通过与BDI前沿轨道混合导致亚氨基基团活化的轨道相互作用。
