the amido and anilido derivates show evidence for ligand-to-metal
p-donation from nitrogen to zirconium, but P and As congeners do
not.4,7 Amido derivatives also exhibit stronger Zr–X bonds accord-
ing to computations.7c Thus, it was unclear with these substrates
whether p-donation, which is likely present in both Zr–Cl and
Zr–N bonds, or bond strength is the cause for this reactivity.
To test the whether p-bonding may or may not be causal for
this unusual reactivity, another (N3N)ZrX (5) complex with a
s-only donor was explored. Treatment of (N3N)ZrMe12 with one
equiv. of N,N0-diisopropylcarbodiimide in benzene solution
exclusively reacted at the Zr–N bond to afford [N,N,N,N,N,N-
N(CH2CH2NSiMe3)2{CH2CH2NC(NiPr)(NiPrSiMe3)}]ZrMe (6)
in 63% yield [eqn (3)]. The same C1 symmetry and as well as
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1
similar H and 13C NMR spectroscopic features allow for the
ready identification of 6 in comparison to complexes 2 and 4.
ð3Þ
The solid state structure of 5 is that of the expected s-donor
methyl ligand,13 and according to computational studies,
complex 5 has a stronger Z–X bond than related Zr-phosphide
complexes.7c A similar trend was noted for the amido complexes
relative to the phosphide complexes.
These observations lead to the conclusion that while there is
a driving force for insertion into M–X bonds for these
triamidoamine-supported zirconium complexes, other factors
can thwart the expected Zr–X insertion and activate M–Namido
bonds of the triamidoamine ligand. Current evidence supports
the notion that the relative Zr–X bond strength allows for this
previously unseen reactivity at the M–Namido bonds of the
triamidoamine ligand. This somewhat unusual transformation
with carbodiimides represents a mild and facile route to
guanidinate-substituted triamidoamine ligands.
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Commun., 2007, 4172–4174; (b) A. J. Roering, S. N. MacMillan,
J. M. Tanski and R. Waterman, Inorg. Chem., 2007, 46,
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S. M. Chan, M. B. Ghebreab, K. L. Donovan, J. J. Davidson,
R. P. Hughes, T. Shalumova, S. N. MacMillan, J. M. Tanski and
This work was supported by the U. S. National Science
Foundation (CHE-0747612) and the Vermont Space Grant
Consortium (NASA grant NNG05GH16H). X-ray facilities
were provided by the U. S. National Science Foundation
(CHE-0521237 to J.M.T. and CHE-1039436 to R.W.). R.W.
is a Sloan Research Fellow and a Cottrell Scholar. The authors
thank the reviewers for providing invaluable suggestions to
improve this study.
R.
Waterman,
Organometallics,
2009,
28,
573–581;
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Notes and references
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13 S. N. MacMillan, J. M. Tanski and R. Waterman, Acta Crystallogr.,
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c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 11769–11771 11771