η5-Pentamethylcyclopentadienyliridium(III) and -rhodium(III) Labeling of Amino Acids with Aromatic Side Chains – The Importance of Relativistic Effects for the Stability of Cp*Irııı Sandwich Complexes
✍ Scribed by Diran Agaid Herebian; Claudia S. Schmidt; William S. Sheldrick; Christoph van Wüllen
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 225 KB
- Volume
- 1998
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
η 5 -Pentamethylcyclopentadienyliridium(III) and -rhodiumθ = 12.9°from that of the remaining ring atoms. Facial isomers are present in an effective 1:1 ratio for all tryptophan (III) sandwich complexes of the type [(η 5 -Cp*)M(η 6 -aa)]-(CF 3 SO 3 ) 2 (M = Ir, Rh; 3-14) containing L-tyrosine, L-trypto-derivatives. Whereas the Cp*Ir III sandwich complexes of aromatic α-amino acids are stable in polar solvents, rapid phan and L-phenylalanine derivatives (aa) can be prepared by treatment of [(η 5 -Cp*)ML 3 ] (CF 3 SO 3 ) 2 [L = thf, (CH 3 ) 2 CO, decay is observed for analogous Cp*Rh III complexes of Nunprotected derivatives in polar solvents. Comparative CH 3 CN] with the appropriate bioligand in thf for N-protected compounds and in CF 3 COOH for α-amino acids with nonrelativistic and relativistic all-electron density functional calculations on the cationic sandwich complexes [Cp*M(η 6 -unprotected amino groups. Coordination to the Cp*M III fragments stabilizes the ketonic form of the tyrosine aromatic C 6 H 5 Me)] n+ (n = 2, M = Ir, Rh; n = 1, M = Ru) confirm that all three metals bind more tightly to Cp* than to toluene as side chains, leading to a marked enhancement in the acidity of the p-hydroxy function. The crystal structure of [Cp* gauged by the respective force constants (k 1 Ͼ k 2 ). A much larger relativistic enhancement of k 2 for M = Ir (279 vs 207 Ir(ActyrOMe)] (CF 3 SO 3 ) 2 (3b, ActyrOMe = N-acetyltyrosine methyl ester) confirms a marked distortion towards an η 5 -Nm -1 ) could be responsible for the greater stability of Cp*Ir III complexes in solution. oxohexadienyl coordination mode as may be gauged from the tilting of the p-OH plane C13/C14/C15 by no less than