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Issue 4, 2008
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Prototropic rearrangements in cycloheptatrienyl PCP pincer iridium complexes

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Abstract

When the cycloheptatriene iridium(III) pincer complex (PCP)Ir(CO)(H)(Cl) (3) (PCP = 2,7-(CH2PtBu2)2C7H5) is treated with the bases NaH, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and lithium 2,2,6,6-tetramethylpiperidide (LiTMP) under various conditions different products are obtained. At elevated temperatures and with DBU or LiTMP as a base the transdihydride (PCP′)Ir(CO)(H)2 (PCP′ = 2-(CHPtBu2)-7-(CH2PtBu2)C7H4) (5) is formed where the π-system extends into one of the phosphine bridges. This compound loses H2 to give the square-planar iridium(I) carbonyl complex 7 (PCP′IrCO). The dihydride 5 can also rearrange to the new isomeric iridium(I) carbonyl 6 (PCP″IrCO, PCP″ = 2,7-(CH2PtBu2)2C7H5). Thus the two hydrides have moved into the ligand backbone creating a methylene group in the 3-position of the cycloheptatriene ring. Alternatively, 6 is formed by a rearrangement from 6a which differs from 6 by having the methylene group in the 4-position of the cycloheptatriene ring. The iridium(I) carbonyl 6a in turn is made from 3 by treatment with DBU at room temperature. Interestingly, when compound 3 is heated to reflux in THF the hydrogen bound at the metal carbon is shifted to a carbon atom in the cycloheptatriene ring generating a ring methylene group (3a). From this complex HCl is eliminated upon chromatography forming 6 as the final product. Quantum chemical calculations at various levels of theory illustrate the relative energetic stabilities of all iridium complexes.

Graphical abstract: Prototropic rearrangements in cycloheptatrienyl PCP pincer iridium complexes

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Publication details

The article was received on 17 Aug 2007, accepted on 25 Oct 2007 and first published on 09 Nov 2007


Article type: Paper
DOI: 10.1039/B712712J
Citation: Dalton Trans., 2008,0, 527-532
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    Prototropic rearrangements in cycloheptatrienyl PCP pincer iridium complexes

    A. M. Winter, K. Eichele, H. Mack, W. C. Kaska and H. A. Mayer, Dalton Trans., 2008, 0, 527
    DOI: 10.1039/B712712J

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