Unsymmetrical Tren-Based Ligands: Synthesis and Reactivity of Rhenium Complexes

Reaction of bis(2-aminoethyl)(3-aminopropyl)amine with C6F6 and K2CO3 in DMSO yields unsymmetrical
{(C6F5)HNCH2CH2}2NCH2CH2CH2NH(C6F5) ([N3N]H3). The tetraamine acts as a tridentate ligand in complexes of
the type H[N3N]Re(O)X (X = Cl 1, Br 2) prepared by reacting Re(O)X3(PPh3)2 with [N3N]H3 and an excess of NEt3
in THF. Addition of 1 equiv of TaCH(CMe2Ph)Br3(THF)2 to 1 gives the dimeric compound H[N3N]ClReOReBrCl[N3N]H (3) in quantitative yield that contains a Re(V)ORe(IV) core with uncoordinated aminopropyl groups in
each ligand. Addition of 2 equiv of TaCH(CMe2Ph)Cl3(THF)2 to 1 leads to the chloro complex [N3N]ReCl (4) with
all three amido groups coordinated to the metal, whereas by addition of 2 equiv of TaCH(CMe2Ph)Br3(THF)2 to 2
the dibromo species H[N3N]ReBr2 (5) with one uncoordinated amino group is isolated. Reduction of 4 under an
atmosphere of dinitrogen with sodium amalgam gives the dinitrogen complex [N3N]Re(N2) (6). Single-crystal X-ray
structure determinations have been carried out on complexes 1, 3, 5, and 6.