Synthesis and Structure of Amido- and Imido(pentafluorophenyl)borane Zirconocene and Hafnocene Complexes: N[BOND]H and B[BOND]H Activation

Authors

  • Elizabeth A. Jacobs,

    1. Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK), Fax: (+44) 1603-592003
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  • Anna Fuller,

    1. Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK), Fax: (+44) 1603-592003
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  • Simon J. Coles,

    1. EPSRC National Crystallography Service, School of Chemistry, University of Southampton, University Road, Southampton, SO17 1BJ (UK)
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  • Garth A. Jones,

    1. Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK), Fax: (+44) 1603-592003
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    • Computational queries should be addressed to Garth A. Jones.

  • Graham J. Tizzard,

    1. EPSRC National Crystallography Service, School of Chemistry, University of Southampton, University Road, Southampton, SO17 1BJ (UK)
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  • Joseph A. Wright,

    1. Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK), Fax: (+44) 1603-592003
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  • Simon J. Lancaster

    Corresponding author
    1. Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK), Fax: (+44) 1603-592003
    • Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ (UK), Fax: (+44) 1603-592003
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Abstract

Treatment of Me2SB(C6F5)nH3−n (n=1 or 2) with ammonia yields the corresponding adducts. H3NB(C6F5)H2 dimerises in the solid state through N[BOND]H⋅⋅⋅H[BOND]B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH2B(C6F5)nH3−n]. Reaction of the n=2 reagent with [Cp2ZrCl2] leads to disubstitution, but [Cp2Zr{NH2B(C6F5)2H}2] is in equilibrium with the product of β-hydride elimination [Cp2Zr(H){NH2B(C6F5)2H}], which proves to be the major isolated solid. The analogous reaction with [Cp2HfCl2] gives a mixture of [Cp2Hf{NH2B(C6F5)2H}2] and the N[BOND]H activation product [Cp2Hf{NHB(C6F5)2H}]. [Cp2Zr{NH2B(C6F5)2H}2]PhMe and [Cp2Hf{NH2B(C6F5)2H}2]4(thf) exhibit β-B-agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp2Hf{NH2B(C6F5)2H}2]PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp2Hf{NHB(C6F5)2H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond-length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp2MMe(μ-Me)B(C6F5)3] (M=Zr, Hf) with Li[NH2B(C6F5)nH3−n] (n=2) results in [Cp2MMe{NH2B(C6F5)2H}] complexes, for which the spectroscopic data, particularly 1J(B,H), again suggest β-B-agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp′′2ZrMe(μ-Me)B(C6F5)3] precursor (Cp′′=1,3-C5H3(SiMe3)2, n=1 or 2) to give [Cp′′2ZrMe{NH2B(C6F5)nH3−n}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp′′2HfMe2] and the formation of Li[HB(C6F5)3] through hydride abstraction.

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