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

Article abstract of DOI:10.1016/0020-1693(96)05014-1

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 = 14.675(3), b = 13.372(1), c = 28.841 (7) A, β= 102.53(1)°, Z= 8. The mean Re-S bond length is 2.529 A. 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) A, α=76.60(2), β = 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) A, β= 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) A). 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) A, α=80.90(3), β=79.82(3), γ=70.81(4)°, Z=2. The rhenium-sulfur distance is 2.476(2) A.