Ferrocene-Based Bis(guanidines): Superbases for Tridentate N,Fe,N-Coordination

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• 作者：Lutz R. R. Klapp ; Clemens Bruhn ; Michael Leibold ; Ulrich Siemeling
• 刊名：Organometallics
• 出版年：2013
• 出版时间：October 28, 2013
• 年：2013
• 卷：32
• 期：20
• 页码：5862-5872
• 全文大小：614K
• 年卷期：v.32,no.20(October 28, 2013)
• ISSN：1520-6041

文摘

The condensation of 1,1鈥?diaminoferrocene (1) with a range of chloroformamidinium salts [(R鈥睷N)₂CCl]X (2) afforded the corresponding bis(guanidines) [Fe{(畏⁵-C₅H₄)鈥揘鈺怌(NRR鈥?₂}₂] (3; five examples). The two guanidine units present in 3 are able to chelate a proton or a water molecule. The structures of 3 and of the corresponding hydrates were determined by single-crystal X-ray diffraction. Cyclic voltammetry revealed that the ferrocene moiety of 3 is exceptionally electron rich, with E_1/2 values down to 鈭?.90 V vs the ferrocenium/ferrocene couple. According to the results of DFT calculations, these bis(guanidines) are superbases with proton affinities considerably higher than that of the classic 鈥淧roton Sponge鈥?1,8-bis(dimethylamino)naphthalene. Furthermore, they are able to act as tridentate ligands, giving rise to Fe鈫扢 dative bonds, as is shown by chelates of the type [PdCl(3-魏Fe,魏²N)]⁺, which were obtained by reaction of 3 with [PdCl₂(MeCN)₂]. The unusual N,Fe,N-chelating mode leads to exceptionally short Fe鈥揚d bonds (ca. 2.69 脜) and causes an enormous coordination-induced anodic shift of the half-wave potential of ca. 0.6 V.