SPECTROELECTROCHEMICAL (IR, UV/VIS) DETERMINATION OF THE REDUCTION PATHWAYS FOR A SERIES OF [RE(CO)(3)(ALPHA-DIIMINE)L'](0/+) (L'=HALIDE, OTF(-), THF, MECN, N-PRCN, PPH(3), P(OME)(3)) COMPLEXES

被引:213
作者
STOR, GJ [1 ]
HARTL, F [1 ]
VANOUTERSTERP, JWM [1 ]
STUFKENS, DJ [1 ]
机构
[1] UNIV AMSTERDAM,ANORGAN CHEM LAB,1018 WV AMSTERDAM,NETHERLANDS
关键词
D O I
10.1021/om00003a013
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
The reduction pathways were investigated for a series of [Re(CO)3(a-diimine)L'](0'+) (L' = Cl-, Br-, I-, Otf(-), THF, MeCN, n-PrCN, PPh(3), P(OMe)(3); alpha-diimine = bpy, i-Pr-PyCa, dapa, dpp, abpy) complexes. The individual one-electron reduction steps were studied mainly in THF, by a combination of cyclic voltammetry and in situ FTIR and UV/vis spectroscopy. The stability of the reduced [Re(CO)(3)(alpha-diimine)L'](.-/.) complexes depends on the ability of the alpha-diimine radical ligand to accommodate the unpaired electron in its lowest empty pi* orbital, which increases in the order bpy < i-Pr-PyCa < dapa < dpp < abpy. The higher the energy of this pi* orbital, the more pronounced is the donor character of the alpha-diimine radical. Concomitant polarization of the radical complex and increased electron density within the Re-(alpha-diimine) chelate ring labilize the Re-L' bond and may cause dissociation of L' and dimerization of the Re radicals, or substitution of L' by a better pi acceptor. The kinetic stability of the Re-L' bond increases in the order halide << THF < PPh(3), n-PrCN < P(OMe)(3). The labilizing effect of the strong donating power of the reduced cl-diimine ligand on the Re-L' bond becomes much more apparent upon the second one-electron reduction step. For alpha-diimine = bpy, i-Pr-PyCa, dpp, the products of the first one-electron reduction were converted in this step into the five-coordinated anionic [Re(CO)(3)(alpha-diimine)](-) complexes, in which the pi-electron density is largely delocalized over the Re-(alpha-diimine) chelate bond, as indicated by their low v(CO) frequencies and average C=O force constants. For alpha-diimine dapa, the anionic [Re(CO)(3)(N,N(N)-dapa)](-) species was produced, in which the third imine nitrogen atom interacts only weakly with the Re center. Importantly, for L' = P(OMe)(3), the strongest n acceptor employed, the stable six-coordinated [Re(CO)(3)(N,N-dapa)(P(OMe)(3))](-) anion was formed. The only stable six-coordinated [Re(CO)(3)(alpha-diimine)L'](-) anions with L' = THF or PPh(3) in the axial position were obtained for alpha-diimine = abpy. The abpy ligand is a strong pi acceptor due to its very low-lying pi* LUMO of the azo bond character. In this case, even a third one-electron reduction step was observed, which is probably more localized on the aromatic rings of abpy and converted the abpy ligand into a strong donor. As a result, the interaction of the ligand L' = THF, PPh(3) with the Re center in the dianionic product {[Re(CO)(3)(abpy)](2-)...L'} is very weak.
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页码:1115 / 1131
页数:17
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