Bifunctional Single Amino Acid Chelates for Labeling of Biomolecules with the {Tc(CO)3}+ and {Re(CO)3}+ Cores. Crystal and Molecular Structures of [ReBr(CO)3(H2NCH2C5H4N)], [Re(CO)3{(C5H4NCH2)2NH}]Br, [Re(CO)3{(C5H4NCH2)2NCH2CO2H}]Br, [Re(CO)3{X(Y)NCH2CO2CH2CH3}]Br (X = Y = 2-pyridylmethyl; X = 2-pyridylmethyl, Y = 2-(1-methylimidazolyl)methyl; X = Y = 2-(1-methylimidazolyl)methyl), [ReBr(CO)3{(C5H4NCH2)NH(CH2C4H3S)}], and [Re(CO)3{(C5H4NCH2)N(CH2C4H3S)(CH2CO2)}]

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Abstract
The reactions of a series of potentially tridentate ligands, derived from single amino acids or amino acid analogues, with [NEt4]2[ReBr3(CO)3] have been investigated. The model compounds [Re(CO)3Br{(2-pyridylmethyl)NH2}] (1) and [Re(CO)3{(2-pyridylmethyl)2NH}]Br (2) were also prepared and structurally characterized. With ligands possessing two pyridyl appendages, (2-pyridylmethyl)2NX (X = −CH2CO2H, −CH2CO2Et, −CH2CH2CO2H, −CH2CH2CO2Et, −CH2CH2CH2CH2CH(NHCO2tBu)CO2H), complexes of the type [Re(CO)3(ligand)]Br (3−6) were isolated. All possess the fac-{Re(CO)3N3} coordination geometry in the cationic molecular unit. Similarly, the ligands with the imidazolyl arms (2-pyridylmethyl){2-(1-methylimidazolyl)methyl}NCH2CO2Et and {2-(1-methylimidazolyl)methyl}2NCH2CO2Et, complexes 7 and 8 of the same [Re(CO)3(ligand)]Br type, were prepared. Replacement of one pyridyl arm with a thiophene group yielded the complex [Re(CO)3{(2-pyridylmethyl)N(CH2CO2)(2-thiophenemethyl)}] (9), while additional substitution of X = −H for −CH2CO2H yielded [Re(CO)3Br{(2-pyridylmethyl)NH(2-thiophenemethyl)}] (10). In both 9 and 10, the thiophene is uncoordinated and pendant, and the derivatives display fac-{Re(CO)3N2O} and fac-{Re(CO)3N2Br} coordination geometries, respectively. Crystal data: C9H8BrN2O3Re (1), triclinic P1̄, a = 8.156(1) Å, b = 12.077(1) Å, c = 12.945(2) Å, α = 92.183(3)°, β = 107.848(3)°, γ = 100.955(7)°, V = 1185.1(3) Å, Z = 4; C15H13BrN3O3Re (2), tetragonal P41, a = 8.6095(3) Å, c = 22.228(1) Å, V = 1646.9(1) Å3, Z = 4; C17H14BrN3O5Re·CH3OH (3), monoclinic P21/m, a = 7.4425(3) Å, b = 9.7596(4) Å, c = 14.0646(6) Å, β = 97.753(1)°, V = 1012.26(7) Å3, Z = 2; C19H19BrN3O5Re (4), tetragonal P4̄21c, a = 16.895(3) Å, c = 15.042(3) Å, V = 4293.7(13) Å3, Z = 8; C18H20BrN4O5Re·CH3OH·H2O (7), monoclinic P21/c, a = 10.2816(4) Å, b = 30.386(1) Å, c = 14.5810(6) Å, β = 99.868(1)°, V = 4488.03(3) Å3, Z = 8; C17H21BrN5O5Re·0.5CH2Cl2·0.5H2O (8), triclinic P1̄, a = 11.5363(6) Å, b = 13.1898(6) Å, c = 16.4933(8) Å, α = 89.356(1)°, β = 74.907(1)°, γ = 76.216(1)°, V = 2349.8(2) Å3, Z = 4; C16H13N2O5ReS (9), monoclinic P21/c, a = 17.2072(7) Å, b = 8.5853(4) Å, c = 11.5607(5) Å, β = 101.73(1)°, V = 1672.2(1) Å3, Z = 4; and C14H12N2O3BrReS (10), triclinic P1̄, a = 7.5585(3) Å, b = 9.7713(4) Å, c = 11.7103(4) Å, α = 109.566(1)°, β = 98.298(1)°, γ = 100.925(1)°, V = 779.73(5) Å3, Z = 2.

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