Jump to main content
Jump to site search

Issue 24, 2016
Previous Article Next Article

Synthesis of a mononuclear, non-square-planar chromium(ii) bis(alkoxide) complex and its reactivity toward organic carbonyls and CO2

Author affiliations

Abstract

In this paper, we report the synthesis and reactivity of a rare mononuclear chromium(II) bis(alkoxide) complex, Cr(OR′)2(THF)2, that is supported by a new bulky alkoxide ligand (OR′ = di-t-butyl-(3,5-diphenylphenyl)methoxide). The complex is prepared by protonolysis of square-planar Cr(N(SiMe3)2)2(THF)2 with HOR′. X-ray structure determination disclosed that Cr(OR′)2(THF)2 features a distorted seesaw geometry, in contrast to nearly all other tetra-coordinate Cr(II) complexes, which are square-planar. The reactivity of Cr(OR′)2(THF)2 with aldehydes, ketones, and carbon dioxide was investigated. Treatment of Cr(OR′)2(THF)2 with two equivalents of aromatic aldehydes ArCHO (ArCHO = benzaldehyde, 4-anisaldehyde, 4-trifluorbenzaldehyde, and 2,4,6-trimethylbenzaldehyde) leads cleanly to the formation of Cr(IV) diolate complexes Cr(OR′)2(O2C2H2Ar2) that were characterized by UV-vis and IR spectroscopies and elemental analysis; the representative complex Cr(OR′)2(O2C2H2Ph2) was characterized by X-ray crystallography. In contrast, no reductive coupling was observed for ketones: treatment of Cr(OR′)2(THF)2 with one or two equivalents of benzophenone forms invariably a single ketone adduct Cr(OR′)2(OCPh2) which does not react further. QM/MM calculations suggest the steric demands prevent ketone coupling, and demonstrate that a mononuclear Cr(III) bis-aldehyde complex with partially reduced aldehydes is sufficient for C–C bond formation. The reaction of Cr(OR′)2(THF)2 with CO2 leads to the insertion of CO2 into a Cr–OR′ bond, followed by complex rearrangement to form a diamagnetic dinuclear paddlewheel complex Cr2(O2COR′)4(THF)2, that was characterized by NMR, UV-vis, and IR spectroscopy, and X-ray crystallography.

Graphical abstract: Synthesis of a mononuclear, non-square-planar chromium(ii) bis(alkoxide) complex and its reactivity toward organic carbonyls and CO2

Back to tab navigation

Supplementary files

Article information


Submitted
20 Jan 2016
Accepted
05 Apr 2016
First published
05 Apr 2016

Dalton Trans., 2016,45, 9794-9804
Article type
Paper

Synthesis of a mononuclear, non-square-planar chromium(II) bis(alkoxide) complex and its reactivity toward organic carbonyls and CO2

M. Yousif, A. C. Cabelof, P. D. Martin, R. L. Lord and S. Groysman, Dalton Trans., 2016, 45, 9794
DOI: 10.1039/C6DT00279J

Social activity

Search articles by author

Spotlight

Advertisements