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Novel Coordination Behavior of fac-[ReBr3(CO)3]2- with 1,3,5-Triaza-7-phosphaadamantane (PTA). Systematic Investigation on Stepwise Replacement of the Halides by PTA Ligand. Phase Transfer Studies and X-ray Crystal Structure of [NEt4][ReBr2((PTA)(CO)3], [ReBr(PTA)2(CO)3], and [Re(PTA)3(CO)3]PF6

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posted on 05.09.1998, 00:00 by Roger Schibli, Kattesh V. Katti, Wynn A. Volkert, Charles L. Barnes
Starting originally from [NEt4]2[ReBr3(CO)3] (1), the three novel complexes [NEt4][ReBr2(PTA)(CO)3] (2), [ReBr(PTA)2(CO)3] (3a), and [Re(PTA)3(CO)3]PF6 (4) (PTA = 1,3,5-triaza-7-phosphaadamantane) were prepared and characterized by IR, 1H, 13C, and 31P NMR spectroscopy and X-ray crystallography. These complexes are the first representatives of mixed carbonyl/PTA complexes of an element of the manganese row. All substitution reactions have been performed under aerobic conditions at ambient temperature and the yields were in all the cases high. The disubstituted complex was isolated as the neutral species 3a and as the dicationic species [ReBr(PTAH)2(CO)3]Br2, 3b, which is protonated at one amine group of each of the two PTA ligands. The substitution reaction leading to the formation of 3a was performed in H2O, methanol and DMSO/methanol (4:1) and the reaction was followed using 31P NMR techniques. These experiments revealed that the number and concentration of intermediate species during the substitution reaction are strongly dependent on the solvent system. Furthermore due to a completely different solubility behavior of 3a and 3b, a fully reversible phase transfer of the disubstituted complex from the organic (THF) to the aqueous layer (2 M NaBr) and back could be induced by simply changing the pH of the aqueous phase. In the 31P NMR experiment, the existence of the monoprotonated species [ReBr(PTA)(PTAH)(CO)3]Br (3c) could also be detected. X-ray data for complex 2:  monoclinic P21/n, a = 8.6889(4) Å, b = 29.3089(14) Å, c = 9.3017(5) Å, β = 97.1520(10)°, Z = 4, R/Rw = 0.048/0.079. X-ray data for complex 3a:  monoclinic P21/c, a = 6.8581(40 Å, b = 21.9499(12) Å, c = 13.9526(8) Å, β = 94.6650(10)°, Z = 4, R/Rw = 0.036/0.042. X-ray data for complex 3b:  triclinic P1̄ , a = 8.7051(5) Å, b = 11.9307(7) Å, c = 14.7458(8) Å, α = 78.9450(10)°, β = 87.2340(10)°, γ = 76.4770(10)°, Z = 2, R/Rw = 0.034/0.042. X-ray data for complex 4:  triclinic P1̄, a = 9.3842(50) Å, b = 13.5797(7) Å, c = 13.9499(7) Å, α = 105.5910(10)°, β = 91.8560(10)°, γ = 107.0190(10)°, Z = 2, R/Rw = 0.051/0.062.