In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 101, No. 36 ( 2004-09-07), p. 13138-13141
Abstract:
The kinetics of reduction of benzoquinone (Q) to hydroquinone (H 2 Q) by the Os(IV) hydrazido ( trans -[Os IV (tpy)(Cl) 2 (N(H)N(CH 2 ) 4 O)]-PF 6 = [1]PF 6 , tpy = 2,2′:6′,2″-terpyridine), sulfilimido ( trans -[Os IV -(tpy)(Cl) 2 (NS(H)-4-C 6 H 4 Me)]PF 6 = [2]PF 6 ), and phosphoraniminato ( trans -[Os IV (Tp)(Cl) 2 (NP(H)(Et) 2 )] = [3] , Tp – = tris(pyrazolyl)-borate) complexes have been studied in 1:1 (vol/vol) CH 3 CN/H 2 O and CH 3 CN/D 2 O (1.0 M in NH 4 PF 6 /KNO 3 at 25.0 ± 0.1°C). The reactions are first order in both [Q] and Os(IV) complex and occur by parallel pH-independent ( k 1 ) and pH-dependent ( k 2 ) pathways that can be separated by pH-dependent measurements. Saturation kinetics are observed for the acid-independent pathway, consistent with formation of a H-bonded intermediate ( K A ) followed by a redox step ( k red ). For the pH-independent pathway, k 1 (H 2 O)/ k 1 (D 2 O) kinetic isotope effects are 455 ± 8 for [1 + ], 198 ± 6 for [2 + ], and 178 ± 5 for [3] . These results provide an example of colossal kinetic isotope effects for proton-coupled electron transfer reactions involving nitrogen, sulfur, and phosphorus as proton-donor atoms.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.0405086101
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2004
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
