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

The 1,4-dialkyl-1,4,7-triazacyclononanes HR2[9]aneN(3) (R=Me or Pr-i) were smoothly deprotonated with n-butyllithium to give corresponding lithiated a mides {Li[R-2[9]aneN(3)]}(x) 1, 2 which are in turn useful precursors to ne w transition metal complexes. Reaction of 1 or 2 with the mono(imido) or bi s(imido) complexes [M(NBut)Cl-3(py)(2)] (M=Nb or Ta) or [Mo-2(NC6H3R'-2,6)( 2)Cl-2(dme)] gave [M(NBut)(R-2[9]aneN(3))Cl-2] (M=Nb, R=Me 3 or Pr-i 4; M=T a, R=Me 5 or Pr-i 6) or [Mo(NC6H3R'(2)-2,6)(2)(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 -C5R5)(2)Cl-2] (M=Group 4 metal) . The titanium imido analogue [Ti(NBut)(HPr2i[9]aneN(3))Cl-2] 7 has been pr epared for purposes of comparison and exists as a mixture of isomers in sol ution. The crystal structure of the bis(imido) compound 11 has been determi ned 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 s tructure suggests that in this compound the Pr-2(i)[9]aneN(3) ligand acts e ffectively as a 5-electron donor with the molybdenum d(pi)-acceptor orbital s dominated by the strongly pi -donating arylimido ligands. Extrapolation t o the mono(imido) complexes [M(NBut)(R-2[9]aneN(3))Cl-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 NBut, 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) lig and can in principle act as up to a 7-electron donor.