Ligand exchange reactions starting from [Re(CO)3Br3]2−. Synthesis, characterization and structures of rhenium(I) tricarbonyl complexes with thiourea and thiourea derivatives

Abstract

The anionic rhenium(I) complex fac-[Re(CO)3Br3]2− has been reacted with thiourea (tu), N,N-dialkylbenzoylthioureas (HR2btu) and N,N-dialkylthiocarbamoylbenzamidines (HR12tcbR2) to give novel mono- and binuclear rhenium(I) complexes. All new compounds are air-stable and non-sensitive against aqueous media. Fac-[Re(CO)3(tu)3] (NO3) is formed from the bromo complex by precipitation of AgBr after addition of AgNO3 and subsequent reaction with thiourea. The compound co-crystallizes with one molecule of (Et4N) NO3 in the monoclinic space group P21/n,a = 143675(3), b = 13.372(1), c = 28.841 (7) Å, ß = 102.53(1)°, Z = 8. The mean ReS bond length is 2.529 Å. N,N-Dialkylbenzoylthioureas react with (Et4N)2[Re(CO)3)Br3] to form neutral [Re(CO)3Br(HR2btu)] complexes. With the rhenium(I) centers under study they coordinate bidentately, but without deprotonation, which is unusual for this class of chelate ligands. [Re(CO)3Br(HEt2btu)] crystallizes in the triclinic space group P1, a = 8.080(2), b = 9.254(3), c = 13.761(5) Åα = 76.60(2), ß = 88.66(2), γ = 70.92(3)°, Z = 2. The chelate ring shows significant deviations from planarity which underline the absence of an extended π-system. Complexes of different composition are formed with thiocarbamoylbenzamidines depending on the sterical requirements of the individual ligands. A binuclear compound could be isolated with N,N-diethylthiocarbamoylbenzamidinate (Et2tcbH−). [Re2(CO)6−(Et2tcbH)2] crystallizes in the monoclinic space group P21/c, a = 10.859(4), b = 17.409(2), c = 9.159(5) Å, ß = 79.15(2)°, Z = 2. Both rhenium atoms are coordinated by three facially arranged carbonyls and a singly deprotonated Et2tcbH− ligand. The sulfur atoms of these ligands act as bridges between the metal centers forming a four-membered Re2S2 ring. Two slightly different ReS bond lengths are observed in this ring system (2.507(2) and 2.545(2) Å). Only a mononuclear, anionic complex is formed with the more bulky benzamidine ligand N(N-morpholinylthiocarbonyl)-N′-phenylbenzamidine (Hmorphtcbph). (Et4N) [Re(CO)3Br(morphtcbph)] crystallizes in the triclinic space group P1, a = 10.018(4), b = 10.065(4), c = 16.720(7) Å, α = 80.90(3), ß = 79.82(3), γ = 70.81(4)°, Z = 2. The rheniumsulfur distance is 2.476(2) Å.