Relevance of the Ligand Exchange Rate and Mechanism of fac-[(CO)3M(H2O)3]+ (M = Mn, Tc, Re) Complexes for New Radiopharmaceuticals
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- 作者：Pascal V. Grundler ; Lothar Helm ; Roger Alberto ; André ; E. Merbach
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：December 11, 2006
- 年：2006
- 卷：45
- 期：25
- 页码：10378 - 10390
- 全文大小：160K
- 年卷期：v.45,no.25(December 11, 2006)
- ISSN：1520-510X
文摘
The water exchange process on fac-[(CO)3Mn(H2O)3]+ and fac-[(CO)3Tc(H2O)3]+ was kinetically investigated by 17ONMR as a function of the acidity, temperature, and pressure. Up to pH 6.3 and 4.4, respectively, the exchange rateis not affected by the acidity, thus demonstrating that the contribution of the monohydroxo species fac-[(CO)3M(OH)(H2O)2] is not significant, which correlates well with a higher pKa for these complexes compared to the homologuefac-[(CO)3Re(H2O)3]+ complex. The water exchange rate 
/s-1 (
Hex
/kJ mol-1; Sex/J mol-1 K-1; V/cm3mol-1) decreases down group 7 from Mn to Tc and Re: 23 (72.5; +24.4; +7.1) > 0.49 (78.3; +11.7; +3.8) > 5.4× 10-3 (90.3; +14.5; -). For the Mn complex only, an O exchange on the carbonyl ligand could be measured (
= 4.3 × 10-6 s-1), which is several orders of magnitude slower than the water exchange. In the case of the Tccomplex, the coupling between 17O (I = 5/2) and 99Tc (I = 9/2) nuclear spins has been observed (1J99Tc,17O = 80 ± 5Hz). The substitution of water in fac-[(CO)3M(H2O)3]+ by dimethyl sulfide (DMS) is slightly faster than that byCH3CN: 3 times faster for Mn, 1.5 times faster for Tc, and 1.2 times faster for Re. The pressure dependencebehavior is different for Mn and Re. For Mn, the change in volume to reach the transition state is always clearlypositive (water exchange, CH3CN, DMS), indicating an Id mechanism. In the case of Re, an Id/Ia changeover isassigned on the basis of reaction profiles with a strong volume maximum for pyrazine and a minimum for DMS asthe entering ligand.
/s-1 (Hex/kJ mol-1; Sex/J mol-1 K-1; V/cm3mol-1) decreases down group 7 from Mn to Tc and Re: 23 (72.5; +24.4; +7.1) > 0.49 (78.3; +11.7; +3.8) > 5.4× 10-3 (90.3; +14.5; -). For the Mn complex only, an O exchange on the carbonyl ligand could be measured (= 4.3 × 10-6 s-1), which is several orders of magnitude slower than the water exchange. In the case of the Tccomplex, the coupling between 17O (I = 5/2) and 99Tc (I = 9/2) nuclear spins has been observed (1J99Tc,17O = 80 ± 5Hz). The substitution of water in fac-[(CO)3M(H2O)3]+ by dimethyl sulfide (DMS) is slightly faster than that byCH3CN: 3 times faster for Mn, 1.5 times faster for Tc, and 1.2 times faster for Re. The pressure dependencebehavior is different for Mn and Re. For Mn, the change in volume to reach the transition state is always clearlypositive (water exchange, CH3CN, DMS), indicating an Id mechanism. In the case of Re, an Id/Ia changeover isassigned on the basis of reaction profiles with a strong volume maximum for pyrazine and a minimum for DMS asthe entering ligand.