We report the design and synthesis of a novel N2S2 ligand system for the formation of Re(V) oxo and 99Tc(V) oxo complexes. An S,S′-bis(trityl) N-benzyl monoamine-monoamide (Bn-MAMA′-Tr2) complex was prepared in four steps from commercially available cysteamine hydrochloride. S-Trityl protection of cysteamine hydrochloride followed by N-acylation of the amine function with bromoacetyl bromide provided the corresponding primary bromide, which was then reacted with additional S-trityl-protected cysteamine to provide the S,S′-bis(trityl) monoamine-monoamide ligand (MAMA′-Tr2). N-Alkylation by nucleophilic displacement with the methanesulfonate of benzyl alcohol gave the N-benzyl MAMA′ ligand in the thiol-protected form. Metal incorporation to provide the title compounds consisted of deprotection of the sulfur atoms with Hg(OAc)2 followed by H2S to provide free bis (thiol) which could then be reacted with the corresponding metals in basic methanolic medium to provide a mixture of syn-and anti-substituted metal(V) oxo products (Bn-MAMA′-M=0, metal = Re, 99Tc). The two diastereomers could be differentiated by proton NMR due to the upfield shifts of the methylene protons on the endo (anti) phenylmethyl substitutent (2.7 and 3.4 ppm) relative to those of the exo-(syn-) substituted isomer (4.7 and 5.1 ppm). An unambiguous structural assignment of the N-benzyl-MAMA-metal(V)-oxo compounds was established by an X-ray diffraction study on the rhenium compounds 8a-Re (syn) and 8b-Re (anti). Crystal data for 8a-Re (syn): C13H17N2O2S2Re.1/6C2H6O, trigonal, R3 a = b = 25.961(7) Å, c = 12.392(4) Å,α = β = 90°, γ = 120°, V = 7233(12) Å3, Z=18, R = 2.7%. Crystal data for 8b-Re (anti): C13H17N2O2S2Re, triclinic, Pl = 6.696(2)Å, b = 8.494(1) Å, c = 13.981(3) Å, α= 104.25(2)°, β = 103.19(2)°, γ = 93.38(2)°, V = 744.8(6) Å3, Z = 2, R = 1.6%.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry