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Issue 12, 2013
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Understanding intermolecular C–F bond activation by a transient titanium neopentylidyne: experimental and theoretical studies on the competition between 1,2-CF bond addition and [2 + 2]-cycloaddition/β-fluoride elimination

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Abstract

Complex (PNP)Ti[double bond, length as m-dash]CHtBu(CH2tBu) (PNP = N[2-P(CHMe2)2-4-methylphenyl]2) eliminates H3CtBu to form transient (PNP)Ti[triple bond, length as m-dash]CtBu, which activates the C–F bond of ortho-difluoropyridine and ortho-fluoropyridine to form the alkylidene–fluoride complexes, (PNP)Ti[double bond, length as m-dash]C[tBu(NC5H3F)](F) (1) and (PNP)Ti[double bond, length as m-dash]C[tBu(NC5H4)](F) (2), respectively. When (PNP)Ti[double bond, length as m-dash]CHtBu(CH2tBu) is treated with meta-fluoropyridine, the ring-opened product (PNP)Ti(C(tBu)CC4H3-3-FNH) (3) is the only recognizable titanium metal complex formed. Theoretical studies reveal that pyridine binding disfavors 1,2-CF bond addition across the alkylidyne ligand in the case of ortho-fluoride pyridines, while sequential [2 + 2]-cycloaddition/β-fluoride elimination is a lower energy pathway. In the case of meta-fluoropyridine, [2 + 2]-cycloaddition and subsequent ring-opening metathesis is favored as opposed to C–H bond addition or sequential [2 + 2]-cycloaddition/β-hydride elimination. In all cases, C–H bond addition of ortho-fluoropyridines or meta-fluoropyridine is discouraged because such substrate must bind to titanium via its C–H bond, which is rather weak compared to the titanium–pyridine binding.

Graphical abstract: Understanding intermolecular C–F bond activation by a transient titanium neopentylidyne: experimental and theoretical studies on the competition between 1,2-CF bond addition and [2 + 2]-cycloaddition/β-fluoride elimination

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Publication details

The article was received on 26 Oct 2012, accepted on 14 Jan 2013, published on 16 Jan 2013 and first published online on 16 Jan 2013


Article type: Paper
DOI: 10.1039/C3DT32570A
Citation: Dalton Trans., 2013,42, 4163-4174
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    Understanding intermolecular C–F bond activation by a transient titanium neopentylidyne: experimental and theoretical studies on the competition between 1,2-CF bond addition and [2 + 2]-cycloaddition/β-fluoride elimination

    H. Fan, A. R. Fout, B. C. Bailey, M. Pink, M. Baik and D. J. Mindiola, Dalton Trans., 2013, 42, 4163
    DOI: 10.1039/C3DT32570A

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