Reactivity of Rhodium(I) Complexes Bearing Nitrogen-Containing Ligands toward CH3I: Synthesis and Full Characterization of Neutral cis-[RhX(CO)2(L)] and Acetyl [RhI(μ-I)(C

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• 作者：Romain J. Adcock ; Duc Hanh Nguyen ; Sonia Ladeira ; Carole Le Berre ; Philippe Serp ; Philippe Kalck
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：August 20, 2012
• 年：2012
• 卷：51
• 期：16
• 页码：8670-8685
• 全文大小：615K
• 年卷期：v.51,no.16(August 20, 2012)
• ISSN：1520-510X

文摘

The neutral rhodium(I) square-planar complexes [RhX(CO)₂(L)] [X = Cl (3), I (4)] bearing a nitrogen-containing ligand L [diethylamine (a), triethylamine (b), imidazole (c), 1-methylimidazole (d), pyrazole (e), 1-methylpyrazole (f), 3,5-dimethylpyrazole (g)] are straightforwardly obtained from L and [Rh(渭-X)(CO)₂]₂ [X = Cl (1), I (2)] precursors. The synthesis is extended to the diethylsulfide ligand h for 3h and 4h. According to the CO stretching frequency of 3 and 4, the ranking of the electronic density on the rhodium center follows the order b > a 鈮?d > c > g > f 鈮?h > e. The X-ray molecular structures of 3a, 3d鈥?b>3f, 4a, and 4d鈥?b>4f were determined. Results from variable-temperature ¹H and ¹³C{¹H} NMR experiments suggest a fluxional associative ligand exchange for 4c鈥?b>4h and a supplementary hydrogen-exchange process in 4e and 4g. The oxidative addition reaction of CH₃I to complexes 4c鈥?b>4g affords the neutral dimeric iodo-bridged acetylrhodium(III) complexes [RhI(渭-I)(COCH₃)(CO)(L)]₂ (6c鈥?b>6g) in very good isolated yields, whereas 4a gives a mixture of neutral 6a and dianionic [RhI₂(渭-I)(COCH₃)(CO)][NHMeEt₂]₂ and 4h exclusively provides the analogue dianionic complex with [SMeEt₂]⁺ as the counterion. X-ray molecular structures for 6d₂ and 6e reveal that the two apical CO ligands are in mutual cis positions, as are the two apical d and e ligands, whereas isomer 6d₁ is centrosymmetric. Further reactions of 6d and 6e with CO or ligand e gave quantitatively the monomeric complexes [RhI₂(COCH₃)(CO)₂(d)] (7d) and [RhI₂(COCH₃)(CO)(e)₂] (8e), respectively, as confirmed by their X-ray structures. The initial rate of CH₃I oxidative addition to 4 as determined by IR monitoring is dependent on the nature of the nitrogen-containing ligand. For 4a and 4h, reaction rates similar to those of the well-known rhodium anionic [RhI₂(CO)₂]^{鈭?/sup> species are observed and are consistent with the formation of this intermediate species through methylation of the a and h ligands. The reaction rates are reduced significantly when using imidazole and pyrazole ligands and involve the direct oxidative addition of CH₃I to the neutral complexes 4c鈥?b>4g. Complexes 4c and 4d react around 5鈥?0 times faster than 4e鈥?b>4g mainly because of electronic effects. The lowest reactivity of 4f toward CH₃I is attributed to the steric effect of the coordinated ligand, as supported by the X-ray structure.}