RATE AND MECHANISM OF THE REDUCTIONS OF IRON PENTACARBONYL AND CHROMIUM HEXACARBONYL TO THEIR METALATE COMPLEXES

被引:22
作者
AMATORE, C
KRUSIC, PJ
PEDERSEN, SU
VERPEAUX, JN
机构
[1] DUPONT CO INC, DEPT CENT RES & DEV, EXPTL STN, WILMINGTON, DE 19898 USA
[2] AARHUS UNIV, DEPT CHEM, DK-8000 AARHUS, DENMARK
关键词
D O I
10.1021/om00002a011
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
The electrochemical reductions of Fe(CO)(5) and Cr(CO)(6) in THF were shown to proceed by an ECE mechanism leading to the electrogenerated dianions Fe(CO)(4)(2-) and Cr(CO)(5)(2-), respectively. The initial 19-electron anion radical Fe(CO)(5)(-) could not be observed by the fastest direct electrochemical methods but was shown to have an approximate lifetime of 10 ns. Cr(CO)(6)(-) also could not be observed by fast scan cyclic voltammetry, and its lifetime was estimated to lie in the range 50 mu s to 10 ns. In the absence of an electrophile, the electrogenerated dianions further react slowly via a nucleophilic substitution reaction with the parent Fe(CO)(5) and Cr(CO)(6) to yield the dimers Fe-2(CO)(8)(2-) and Cr-2(CO)(10)(2-), respectively. The corresponding rate constants were estimated at 120 (Fe(CO)(4)(2-) + Fe(CO)(5)) and 0.95 M(-1) s(-1) (Cr(CO)(5)(2-) + Cr(CO)(6)). Although these rate constants are rather modest, their magnitudes are sufficient to explain why Fe-2(CO)(8)(2-) and Cr-2(CO)(10)(2-) are the major products of the electroreductions of Fe(CO)(5) and Cr(CO)(6) when the electrolyses are performed under classical conditions (viz., batch electrolyses; t(elec) greater than or equal to 0.5 h). Conversely, when generated by fast exhaustive electrolysis in a percolating flow cell (t(elec) less than a few seconds), Fe(CO)(4)(2-) is the single electrolysis product that remains stable for minutes in the dry electrochemical medium in the absence of Fe(CO)(5).
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页码:640 / 649
页数:10
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