J. Am. Chem. Soc., 129 (46), 14162 -14163, 2007. 10.1021/ja076356t S0002-7863(07)06356-1
Web Release Date: October 30, 2007

Copyright © 2007 American Chemical Society

The Shortest Metal-Metal Bond Yet: Molecular and Electronic Structure of a Dinuclear Chromium Diazadiene Complex

Kevin A. Kreisel, Glenn P. A. Yap, Olga Dmitrenko, Clark R. Landis,* and Klaus H. Theopold*

Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, and Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706

landis@chem.wisc.edu; theopold@udel.edu

Received August 23, 2007

Abstract:

Reduction of a diazadiene chromium halide complex, [(HLiPr)Cr(-Cl)]2 (1, HLiPr = bis(2,6-diisopropylphenyl)diazadiene), with KC8 gave a diamagnetic, bimetallic complex, (HLiPr)2Cr2 (2). Complex 2 has been structurally characterized by X-ray crystallography and consists of a Cr2 unit spanned by two diazadiene ligands. The very short Cr-Cr distance (1.8028(9) Å) and low formal oxidation state of the Cr atoms suggest that the Cr-Cr bond order may be greater than 4. Spin-restricted and spin-unrestricted DFT calculations on a model complex both converge on a singlet spin state and accurately reproduce the metric parameters of 2. The calculations show high-order metal-metal bonding along with extensive delocalization over the diazadiene ligands. Natural resonance theory analysis shows population of resonance structures that contain quintuple bonds, and natural bond order analysis gives a bond order of 4.28 for the Cr-Cr bond.

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