New Group 5 and 6 transition metal imido complexes with monodeprotonated triazacyclononane ligands

摘要

The 1, 4-dialkyl-1, 4, 7-triazacyclononanes HR_2[9]aneN_3 (R = Me or Pr~i) were smoothly deprotonated with n-butyllithium to give corresponding lithiated amides {li[R_2[9]aneN_3]}_x 1, 2 which are in turn useful precursors to new transition metal complees. Reaction of 1 or 2 with the mono(imido) or bis(imido) complexes [M(NBu~t)Cl_3(py)_2] (M = Nb or Ta) or [MO_2(NC_6H_3R'-2, 6)_2Cl_2(dme)] gave [M(NBu~t)(R_2[9]aneN_3)Cl_2] (M = Nb, R = Me 3 or Pr~i 4; M = Ta, R = Me 5 or Pr~i 6) or [Mo(NC_6H_3R'_2-2, 6)(R_2[9]aneN_3)Cl] (R = Me, R' = Pr~i 8; R = Pr~i, R' = H 9, Me 10 or Pr~i 11). The compounds 3-6 are relatives of the d~0 metallocene dichlorides [M(#eta#-C_5R_5)_2] (M = Group 4 metal). The titanium imido anglogue [Ti(NBu~t)(HPr_2~i[9]aneN_3)Cl_2] 7 has been prepared for purposes of comparison and exists as a mixture of isomers in solution. The crystal structure of the bis(imido) compound 11 has been determined and shows that the co-ordination of the amido N-donor of Pr_2~i[9]aneN_3 is not greatly distorted from planarity. Examination of the molecular structure suggests that in this compound the Pr_2~i[9]aneN_3 ligand acts effectively as a 5-electron donor with the molybdenum d_(#pi#)-acceptor orbitals dominated by the strongly #pi#-donating arylimido ligands. Extrapolation to the mono(imido) complexes [M(NBu~t)(R_2[9]aneN_3Cl_2] 3-6, in which the amido N-donor of Pr_2~i[9]aneN_3 lies trans to one of the Cl ligands and cis to NBu~t, suggests that the amido N-donor should be able at least partly to #pi#-donate to the metal centres. Hence in 3-6 the pr_2~i[9]aneN_3 ligand can in primciple act as up to a 7-electron donor.