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Nickel(I) Monomers and Dimers with Cyclopentadienyl and Indenyl Ligands

Wu, Jianguo and Nova, Ainara and Balcells, David and Brudvig, Gary W. and Dai, Wei and Guard, Louise M. and Hazari, Nilay and Lin, Po-Heng and Pokhrel, Ravi and Takase, Michael K. (2014) Nickel(I) Monomers and Dimers with Cyclopentadienyl and Indenyl Ligands. Chemistry: a European Journal, 20 (18). pp. 5327-5337. ISSN 0947-6539.

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The reaction of (μ-Cl)_2Ni_2(NHC)_2 (NHC=1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene (IPr) or 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr)) with either one equivalent of sodium cyclopentadienyl (NaCp) or lithium indenyl (LiInd) results in the formation of diamagnetic NHC supported Ni^I dimers of the form (μ-Cp)(μ-Cl)Ni_2(NHC)_2 (NHC=IPr (1 a) or SIPr (1 b); Cp=C_5H_5) or (μ-Ind)(μ-Cl)Ni_2(NHC)_2 (NHC=IPr (2 a) or SIPr (2 b); Ind=C_7H_9), which contain bridging Cp and indenyl ligands. The corresponding reaction between two equivalents of NaCp or LiInd and (μ-Cl)_2Ni_2(NHC)_2 (NHC=IPr or SIPr) generates unusual 17 valence electron NiI monomers of the form (η5-Cp)Ni(NHC) (NHC=IPr (3 a) or SIPr (3 b)) or (η5-Ind)Ni(NHC) (NHC=IPr (4 a) or SIPr (4 b)), which have nonlinear geometries. A combination of DFT calculations and NBO analysis suggests that the NiI monomers are more strongly stabilized by the Cp ligand than by the indenyl ligand, which is consistent with experimental results. These calculations also show that the monomers have a lone unpaired-single-electron in their valence shell, which is the reason for the nonlinear structures. At room temperature the Cp bridged dimer (μ-Cp)(μ-Cl)Ni_2(NHC)_2 undergoes homolytic cleavage of the Ni[BOND]Ni bond and is in equilibrium with (η^5-Cp)Ni(NHC) and (μ-Cl)_2Ni_2(NHC)_2. There is no evidence that this equilibrium occurs for (μ-Ind)(μ-Cl)Ni_2(NHC)_2. DFT calculations suggest that a thermally accessible triplet state facilitates the homolytic dissociation of the Cp bridged dimers, whereas for bridging indenyl species this excited triplet state is significantly higher in energy. In stoichiometric reactions, the Ni^I monomers (η^5-Cp)Ni(NHC) or (η^5-Ind)Ni(NHC) undergo both oxidative and reductive processes with mild reagents. Furthermore, they are rare examples of active NiI precatalysts for the Suzuki–Miyaura reaction. Complexes 1 a, 2 b, 3 a, 4 a and 4 b have been characterized by X-ray crystallography.

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Takase, Michael K.0000-0001-8365-3645
Additional Information:© 2014 Wiley-VCH Verlag GmbH & Co. Article first published online: 24 Mar 2014. Received: December 24, 2013. Revised: January 28, 2014. Published online on March 24, 2014. N.H. gratefully acknowledges support through a Doctoral New Investigator Grant from the ACS Petroleum Research Fund (51009-DNI3). D.B. and A.N. thank the Research Council of Norway for the funding provided through the Center of Excellence for Theoretical and Computational Chemistry (CTCC; Grant 179568V30) and the Norwegian Metacenter for Computational Science (NOTUR; Grant nn4654k). The EPR spectroscopy work was supported by the Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences grant DEFG02-05ER15646 (R.P. and G.W.B.). We are grateful to Professor Theo Agapie (Caltech) for assistance with SQUID measurements.
Funding AgencyGrant Number
American Chemical Society Petroleum Research Fund51009-DNI3
Center of Excellence for Theoretical and Computational Chemistry (CTCC)179568V30
Norwegian Metacenter for Computational Sciencenn4654k
Department of Energy (DOE)DE-FG02-05ER15646
Subject Keywords:cross-coupling catalysis; electronic structure; metal–metal bonding; NiI complexes; organometallic chemistry
Issue or Number:18
Record Number:CaltechAUTHORS:20140610-105007742
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Official Citation:Wu, J., Nova, A., Balcells, D., Brudvig, G. W., Dai, W., Guard, L. M., Hazari, N., Lin, P.-H., Pokhrel, R. and Takase, M. K. (2014), Nickel(I) Monomers and Dimers with Cyclopentadienyl and Indenyl Ligands. Chem. Eur. J., 20: 5327–5337. doi: 10.1002/chem.201305021
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46178
Deposited By: Ruth Sustaita
Deposited On:10 Jun 2014 20:52
Last Modified:09 Mar 2020 13:19

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