Frozen-Out Rotamers of Mixed Cobaltacarborane Complexes
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- 作者：Jordi Llop ; Clara Viñ ; as ; Francesc Teixidor ; Lluí ; s Victori ; Raikko Kivekä ; s ; and Reijo Sillanpä ; ä
- 刊名：Organometallics
- 出版年：2002
- 出版时间：January 21, 2002
- 年：2002
- 卷：21
- 期：2
- 页码：355 - 361
- 全文大小：109K
- 年卷期：v.21,no.2(January 21, 2002)
- ISSN：1520-6041
文摘
Although the existence of frozen-out rotamers in solution had been shown for mixedcobaltacarborane complexes forming adducts with BF3 at low temperature. The existence ofeither one or more frozen-out conformations of these complexes in solution at roomtemperature, or otherwise the presence of free rotation of the pyrrolyl unit showing anaverage behavior, is still obscure. The reaction of 1,2-C2B10H12 and 1-C6H5-1,2-C2B10H11 witha suspension of K[NC4(CH3)2H2] in THF and anhydrous CoCl2 in 1:12:5 ratio yielded,respectively, closo-[3-Co(
5-NC4(CH3)2H2)-1,2-C2B9H11] (2) and closo-[3-Co(5-NC4(CH3)2H2)-1-C6H5-1,2-C2B9H10] (3). 1H NMR studies performed on 2, 3, and other mixed complexesincorporating one pyrrolyl and one dicarbollide unit (closo-[3-Co(5-NC4(CH3)2H2)-1-CH3-1,2-C2B9H10] (4), closo-[3-Co(5-NC4H4)-1,2-C2B9H11] (1), closo-[3-Co(5-NC4H4)-1-C6H5-1,2-C2B9H10] (5), and closo-[3-Co(5-NC4H4)-1-CH3-1,2-C2B9H10] (6)) showed the presence ofresonances with atypical chemical shifts that suggested the existence of stable frozen-outconformations. This abnormal displacement of 1H NMR resonances was assigned to electronicring effects due to the presence of the phenyl unit; this electronic ring effect of the electronsof the phenyl ring on neighboring hydrogen atoms has been seen in mixed complexes for thevery first time. ZINDO semiempirical calculations have been used to calculate the theoreticalenergy profile of the different rotamers. The obtained profiles furnish an explanation forexperimental results with good qualitative concordance in all cases.
5-NC4(CH3)2H2)-1,2-C2B9H11] (2) and closo-[3-Co(5-NC4(CH3)2H2)-1-C6H5-1,2-C2B9H10] (3). 1H NMR studies performed on 2, 3, and other mixed complexesincorporating one pyrrolyl and one dicarbollide unit (closo-[3-Co(5-NC4(CH3)2H2)-1-CH3-1,2-C2B9H10] (4), closo-[3-Co(5-NC4H4)-1,2-C2B9H11] (1), closo-[3-Co(5-NC4H4)-1-C6H5-1,2-C2B9H10] (5), and closo-[3-Co(5-NC4H4)-1-CH3-1,2-C2B9H10] (6)) showed the presence ofresonances with atypical chemical shifts that suggested the existence of stable frozen-outconformations. This abnormal displacement of 1H NMR resonances was assigned to electronicring effects due to the presence of the phenyl unit; this electronic ring effect of the electronsof the phenyl ring on neighboring hydrogen atoms has been seen in mixed complexes for thevery first time. ZINDO semiempirical calculations have been used to calculate the theoreticalenergy profile of the different rotamers. The obtained profiles furnish an explanation forexperimental results with good qualitative concordance in all cases.