Synthesis of Titanium CCC-NHC Pincer Complexes and Catalytic Hydroamination of Unactivated Alkenes
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The previously reported amine elimination methodology using group 4 tetrakis(dimethylamido) starting materials for the synthesis of CCC-NHC pincer Zr and Hf complexes has been extended to include Ti. Use of excess Ti(NMe2)4 with 1,3-bis(3-butylimidazol-1-yl)benzene diiodide (1) yielded (1,3-bis(3-butylimidazol-1-yl-2-idene)-2-phenylene)bis(dimethylamido)iodotitanium(IV) (2), which subsequently reacted with CH2Cl2 to afford (1,3-bis(3-butylimidazol-1-yl-2-idene)-2-phenylene)trichlorotitanium(IV) (3). Combining complex 2 with TMSCl yielded complex 3 along with the geometric isomers of (1,3-bis(3-butylimidazol-1-yl-2-idene)-2-phenylene)dichloroiodotitanium(IV) (4a,e). The salt, 1,3-bis(3-butylimidazol-1-yl)benzene dichloride (5), was reacted with Ti(NMe2)4 in a stoichiometric amount to yield (1,3-bis(3-butylimidazol-1-yl-2-idene)-2-phenylene)dichloro(dimethylamido)titanium(IV) (6), while use of excess Ti(NMe2)4 yielded (1,3-bis(3-butylimidazol-1-yl-2-idene)-2-phenylene)chlorobis(dimethylamido)titanium(IV) (7). An efficient direct synthesis of trichloro complex 3 was accomplished by reacting the chlorobis(dimethylamido)titanium complex 7 with TMSCl. The catalytic activity of the bis(dimethylamido)iodotitanium complex 2 and chlorobis(dimethylamido)titanium complex 7 toward the hydroamination/cyclization of unactivated alkene-amines was also evaluated.
