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

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