Synthesis, Structure, and Reactivity of a Stabilized Calcium Carbene: R2CCa
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- 作者：Lars Orzechowski ; Georg Jansen ; Sjoerd Harder
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：November 15, 2006
- 年：2006
- 卷：128
- 期：45
- 页码：14676 - 14684
- 全文大小：357K
- 年卷期：v.128,no.45(November 15, 2006)
- ISSN：1520-5126
文摘
Attempted 2-fold deprotonation of the bis(iminophosphorano)methane ligand, H2C(Ph2P=NSiMe3)2(4-H2), with a calcium amide led only to mono-deprotonation. The crystal structure of (4-H)2Ca showstwo tridentate ligands with short Ca-N and a rather long Ca-C bond. Reaction of 4-H2 with adibenzylcalcium complex gave the desired 2-fold deprotonation and formation of 4-Ca, which crystallizedas a dimeric complex. Analysis of the calculated atomic and group charges in 4-H2, (4-H)2Ca, and [4-Ca]2showed that the negative charge at the imine nitrogens only slightly increases upon successive deprotonationof 4-H2. The electron density at the central carbon, however, increases considerably: the charge on thecarbene carbon in [4-Ca]2 is ca. -1.8. The negative charge in 42- is therefore mainly located on thecarbon. Reaction of [4-Ca]2 with benzophenone in benzene gave the remarkably stable adduct[4-Ca]2·O=CPh2, which was characterized by X-ray diffraction. Reaction of [4-Ca]2 with adamantylcyanidegave exclusive formation of the adduct [4-Ca]2·(N
CR)2, which did not react further, even at highertemperatures. Addition of cyclohexyl isocyanate to a benzene solution of [4-Ca]2 gave immediate [2 + 2]-cycloaddition and formation of a dianionic tetradentate ligand that binds to Ca2+ through two nitrogens, thecentral carbon, and an oxygen. This product crystallized as a dimer with bridging oxygen atoms.
CR)2, which did not react further, even at highertemperatures. Addition of cyclohexyl isocyanate to a benzene solution of [4-Ca]2 gave immediate [2 + 2]-cycloaddition and formation of a dianionic tetradentate ligand that binds to Ca2+ through two nitrogens, thecentral carbon, and an oxygen. This product crystallized as a dimer with bridging oxygen atoms.