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

The anionic rhenium(I) complex fac-[Re(CO)(3)Br-3](2-) has been reacted with thiourea (tu), N,N-dialkylbenzoylthioureas (HR(2)btu) and N,N-dialkylthiocarbamoylbenzamidines (HR(2)(1)tcbR(2)) 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 (Et(4)N)NO3 in the monoclinic space group P2(1)/n, a=14.675(3), b=13.372(1), c=28.841(7) Angstrom, beta=102.53(1)degrees, Z=8. The mean Re-S bond length is 2.529 Angstrom. N,N-Dialkylbenzoylthioureas react with (Et(4)N)(2)[Re(CO)(3))Br-3] to form neutral [Re(CO)(3)Br(HR(2)btu)] 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)(3)Br(HEt(2)btu)] crystallizes in the triclinic space group <P(1)over bar>, a=8.080(2), b=9.254(3), c=13.761(5) Angstrom, alpha=76.60(2), beta=88.66(2), gamma=70.92(3)degrees, Z=2. The chelate ring shows significant deviations from planarity which underline the absence of an extended pi-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 (Et(2)tcbH(-)). [Re-2(CO)(6)-(Et(2)tcbH)(2)] crystallizes in the monoclinic space group P2(1)/c, a=10.859(4), b=17.409(2), c=9.159(5) Angstrom, beta=79.15(2)degrees, Z=2. Both rhenium atoms are coordinated by three facially arranged carbonyls and a singly deprotonated Et(2)tcbH(-) 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) Angstrom). Only a mononuclear, anionic complex is formed with the more bulky benzamidine ligand N(N-morpholinylthiocarbonyl)-N'-phenylbenzamidine (Hmorphtcbph). (Et(4)N)[Re(CO)(3)Br(morphtcbph)] crystallizes in the triclinic space group <P(1)over bar>, a=10.018(4), b=10.065(4), c=16.720(7) Angstrom, alpha=80.90(3), beta=79.82(3), gamma=70.81(4)degrees, Z=2. The rhenium-sulfur distance is 2.476(2) Angstrom.