A restricted polyhedral rearrangement of an amino substituted 12-vertex ferratricarbollide

摘要

The oxidation of anion [7,8-CH2OCH2-7,8-C2B9H10](-) with aqueous FeCl3 gives the 10-vertex nido-carborane 5,6-CH2OCH2-5,6-C2B8H10 in 23% yield. Its interaction with BuNC in the presence of proton sponge gives the tricarbollide anion [7,8-CH2OCH2-9Bu(t)NH-7,8,9-C3B8H8](-) (44% yield) having a short linkage between carbon atoms. Further photochemical reaction of this anion with [CpFe(C6H6)](+) is accompanied by room-temperature polyhedral rearrangement giving ferratricarbollide 1-Cp-2,3-CH2OCH2-9-(BuNH)-N-t-1,2,3,9-FeC3B8H8 (5) in 89% yield. The process involves the migration of the amino-substituted carbon atom, while the separation of two other carbons (observed for the non-linked analogue) is restricted by the CH2OCH2 bridge. DFT calculations of the hypothetical non-rearranged isomer 1-Cp-2-(BuNH)-N-t-1,2,3,4-FeC3B8H10 revealed its strongly distorted geometry with the C2-C3 distance (2.347 angstrom) being clearly non-bonding, thus explaining the mild conditions of the polyhedral rearrangement. The structure of 5 was confirmed by X-ray diffraction. (c) 2006 Elsevier B.V. All rights reserved.