C-H activation of acetonitrile at nickel: Ligand flip and conversion of N-bound acetonitrile into a C-bound cyanomethyl ligand

Article abstract of DOI:10.1021/ja105368p

Nickel joins the fairly exclusive list of metals that can activate nitrile C-H bonds. We report the first example of the C-H activation of an acetonitrile ligand on a nickel center. The acetonitrile ligand formally loses a proton and undergoes a sharp flip to give a cyanomethyl ligand that is coordinated to the nickel atom. Structures of an initial N-bound acetonitrile-nickel complex and of a final cyanomethyl-nickel complex are both presented.

Full text of DOI:10.1021/ja105368p

Published on Web 09/10/2010
C-H Activation of Acetonitrile at Nickel: Ligand Flip and Conversion of
N-Bound Acetonitrile into a C-Bound Cyanomethyl Ligand
Anna Magdalena Oertel,† Vincent Ritleng,*,† Michael J. Chetcuti,*,† and Luis F. Veiros‡
Laboratoire de Chimie Organome´tallique Applique´e, UMR CNRS 7509, Ecole Europe´enne de Chimie, Polyme`res et
Mate´riaux, UniVersite´ de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France, and Centro de Qu´ımica
Estrutural, Complexo I, Instituto Superior Te´cnico, AV. RoVisco Pais, 1049-001 Lisboa, Portugal
Received June 18, 2010; E-mail: vritleng@unistra.fr; michael.chetcuti@unistra.fr
X-ray data are also very limited for cyanomethyl complexes, and
to our knowledge, no structural data for a CH3CN complex and its
corresponding cyanomethyl derivative have been reported.
Abstract: Nickel joins the fairly exclusive list of metals that can
activate nitrile C-H bonds. We report the first example of the
C-H activation of an acetonitrile ligand on a nickel center. The
acetonitrile ligand formally loses a proton and undergoes a sharp
We have shown that when CH3CN solutions of the neutral
complexes [Ni{(Mes2)NHC}ClCp†] are treated with KPF6, chloride
flip to give a cyanomethyl ligand that is coordinated to the nickel
abstraction affords the cationic complexes [Ni{(Mes2)NHC}-
atom. Structures of an initial N-bound acetonitrile-nickel complex
(NCCH3)Cp†]+[PF6-] [Cp† ) Cp (2), Cp* (2*)] in high yield. The
and of a final cyanomethyl-nickel complex are both presented.
CH3CN ligands in complexes 2 and 2* are labile.3c An X-ray
diffraction study of the cation of 2, which is presented here (Figure
1), shows that the CH3CN ligand is essentially linear but that the
Ni-N bond is not perfectly collinear with this axis.
The activation of C-H bonds has emerged as a potent tool for
the functionalization of organic molecules.1 As sp3-hybridized C-H
bonds are much less reactive than most other bonds, their activation
when they are proximal to other functional groups is nontrivial.
Herein, we describe the first example of the C-H activation of a
labile acetonitrile ligand on a nickel center. The ligand formally
loses a proton and does a sharp flip to give a cyanomethyl-nickel
complex. Structural data for an initial CpNi N-bound acetonitrile
species, a final CpNi-CH2CN complex,2 and some DFT calcula-
tions are presented.
Our recent research has focused on nickel Cp and Cp*
complexes with N-heterocyclic carbene (NHC) ligands. We have
described the chemistry and some aspects of the catalytic
behavior of [Ni(NHC)XCp†] (X ) Cl, I) complexes.3 In this
context, we now report a [Ni(NHC)ClCp] complex in which the
NHC ligand bears a -(CH2)3CN side-chain group on one
nitrogen atom and a mesityl group on the other. Upon treatment
with KOtBu, a C-H bond R to the nitrile group underwent an
intramolecular activation to give the nickelacyclic species 1
(Scheme 1; see the Supporting Information).
Figure 1. Molecular structure of the cation of 2. Key atoms are labeled.
Only H atoms of acetonitrile are shown (as isotropic spheres). Selected
distances (Å) and angles (deg): Ni-C1, 1.902(2); Ni-N1, 1.8685(19);
C2-N1, 1.138(3); Ni-N1-C2, 174.52(19); N1-C2-C3, 177.9(2);
N1-Ni-C1, 96.93(8).
1
When 2 was reacted with KOtBu, H NMR data indicated the
rapid, quantitative deprotonation of the CH3CN ligand. The resulting
cyanomethyl group coordinated to the nickel atom, leading to the
isolation of the neutral species [Ni{(Mes)2NHC}(CH2CN)Cp] (3).
The Cp* species 2* similarly generated complex 3* (Scheme 2).
Scheme 1. Formation of Nickelacycle 1 by Activation of a C-H Bond
R to a Nitrile Group in a Side Chain Linked to the NHC Ligand
Scheme 2. Base-Promoted C-H Activation of Coordinated CH3CN
The extension of this reaction to CH3CN was of interest, as
acetonitrile metalation to M-CH2CN complexes is not only rare
in general (it is a challenge to selectively cleave C-H bonds in
the presence of other functional groups) but also completely
unknown for nickel species.4 Such activation has been observed
virtually exclusively for group 8 and group 9 metal complexes.5
Spectroscopic data for 3 and 3* (see the Supporting Information)
are in accord with their proposed structures. The structure of 3 was
confirmed by X-ray diffraction (Figure 2). The transformation of
† Universite´ de Strasbourg.
‡ Instituto Superior Te´cnico.
9
13588 J. AM. CHEM. SOC. 2010, 132, 13588–13589
10.1021/ja105368p  2010 American Chemical Society

C O M M U N I C A T I O N S
more expensive palladium or ruthenium species) in transition-metal-
catalyzed C-H bond functionalization.
C-H bonds R to other functional groups can also be activated
at Cp†Ni(NHC) centers. Our recent results show that R-C-H bonds
of ketones are activated to give [Ni(NHC){CH2C(O)R}Cp] spe-
cies.11 We continue to investigate the scope and breadth of these
activation reactions.
Acknowledgment. We thank the CNRS and the Universite´ de
Strasbourgforsupport.A.M.O.thankstheMiniste`redel’Enseignement
Supe´rieur et de la Recherche for a Ph.D. research scholarship.
Supporting Information Available: Full details of the synthesis
and characterization of all new compounds; X-ray data (CIF) for 1, 2,
and 3; and full DFT computational details. This material is available
free of charge via the Internet at http://pubs.acs.org.
Figure 2. Molecular structure of 3. Key atoms are labeled. Only H atoms
of the cyanomethyl ligand are shown (as isotropic spheres). Selected
distances (Å) and angles (deg): Ni-C1, 1.877(2); Ni-C3, 1.961(2); C2-C3,
1.429(3); C2-N1, 1.147(3); Ni-C3-C2, 112.5(2); C3-C2-N1, 178.5(6);
C1-Ni-C3, 91.9(1).
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