Cationic Terminal Gallylene Complexes by Halide Abstraction: Coordination Chemistry of a Valence Isoelectronic Analogue of CO and N2

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• 作者：Natalie D. Coombs ; Dragoslav Vidovic ; Joanna K. Day ; Amber L. Thompson ; Delphine D. Le Pevelen ; Andreas Stasch ; William Clegg ; Luca Russo ; Louise Male ; Michael B. Hursthouse ; David J. Willock ; Simon Al
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：November 26, 2008
• 年：2008
• 卷：130
• 期：47
• 页码：16111-16124
• 全文大小：449K
• 年卷期：v.130,no.47(November 26, 2008)
• ISSN：1520-5126

文摘

While N₂ and CO have played central roles in developing models of electronic structure, and their interactions with transition metals have been widely investigated, the valence isoelectronic diatomic molecules EX (E = group 13 element, X = group 17 element) have yet to be isolated under ambient conditions, either as the “free” molecule or as a ligand in a simple metal complex. As part of a program designed to address this deficiency, together with wider issues of the chemistry of cationic systems [L_nM(ER)]⁺ (E = B, Al, Ga; R = aryl, amido, halide), we have targeted complexes of the type [L_nM(GaX)]⁺. Halide abstraction is shown to be a viable method for the generation of mononuclear cationic complexes containing gallium donor ligands. The ability to isolate tractable two-coordinate products, however, is strongly dependent on the steric and electronic properties of the metal/ligand fragment. In the case of complexes containing ancillary π-acceptor ligands such as CO, cationic complexes can only be isolated as base-trapped adducts, even with bulky aryl substituents at gallium. Base-free gallylene species such as [Cp*Fe(CO)₂(GaMes)]⁺ can be identified only in the vapor phase by electrospray mass spectrometry experiments. With bis(phosphine) donor sets at the metal, the more favorable steric/electronic environment allows for the isolation of two-coordinate ligand systems, even with halide substituents at gallium. Thus, [Cp*Fe(dppe)(GaI)]⁺[BAr^f₄]⁻ (9) can be synthesized and shown crystallographically to feature a terminally bound GaI ligand; 9 represents the first experimental realization of a complex containing a valence isoelectronic group 13/group 17 analogue of CO and N₂. DFT calculations reveal a relatively weakly bound GaI ligand, which is confirmed experimentally by the reaction of 9 with CO to give [Cp*Fe(dppe)(CO)]⁺[BAr^f₄]⁻. In the absence of such reagents, 9 is stable for weeks in fluorobenzene solution, presumably reflecting (i) effective steric shielding of the gallium center by the ancillary phosphine and Cp* ligands; (ii) a net cationic charge which retards the tendency toward dimerization found for putative charge neutral systems; and (iii) (albeit relatively minor) population of the LUMOs of the GaI molecule through π overlap with the HOMO and HOMO-2 of the [Cp*Fe(dppe)]⁺ fragment.