Bifunctional chelates with aliphatic amine donors for labeling of biomolecules with the {Tc(CO)3}+ and {Re(CO)3}+ cores: the crystal and molecular structure of [Re(CO)3{(H2NCH2CH2)2 N(CH2)4CO2Me}]Br

A general synthetic approach to the design of bis(ethylamine) derivatives of single amino acid chelates has been developed. In general, protection of diethylenetriamine as the phthalimide, followed by reaction with the appropriate bromoalkylcarboxylate and deprotection, yields the bifunctional reagents (H2NCH2CH2)2N–R–CO2H. Reaction of the bis(aminoethyl)aminovaleric acid derivative with (NEt4)2[Re(CO)3Br3] in methanol yields [Re(CO)3{(H2NCH2CH2)2N(CH2)4CO2Me}]Br (1Br), the first example of the {Re(CO)3}+ core ligated to exclusively aliphatic amine donors. Crystal data: C13H23BrN3O5Re (1Br), monoclinic P21/c, a=8.3419(5) Å, b=9.4018(6) Å, c=23.569(1) Å, β=99.165(1)°, V=1824.9(2) Å3, Z=4, Dcalc=2.065 g cm−3.