Kinetic evidence for intramolecular proton transfer between nickel and coordinated thiolate

被引:38
作者
Clegg, W [1 ]
Henderson, RA [1 ]
机构
[1] Univ Newcastle Upon Tyne, Dept Chem, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England
关键词
D O I
10.1021/ic0104306
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
The complexes [Ni(YR)(triphos)]BPh4 {Y = S, R = Ph or Et or Y = Se, R = Ph; triphos = (Ph2PCH2CH2)(2)PPh} have been prepared and characterized, and the X-ray crystal structure of [Ni(SPh)(triphos)]BPh4 has been solved. In MeCN, [Ni(YR)(triphos)](+) are protonated by [lutH](+) (lut = 2,6-dimethylpyridine) to give [Ni(YHR)(triphos)](2+), Studies on the kinetics of these equilibrium reactions reveal an unexpected difference in the reactivities of [Ni(SPh)(triphos)](+) and [Ni(SEt)(triphos)](+). In both cases, the reactions exhibit a first-order dependence on the concentration of complex. When R = Ph, the dependence on the concentrations of [lutH(+)] and lut is given by k(obs) = k(1)(Ph)[lutH(+)] + k(-1)Ph[lut], which is typical of an equilibrium reaction where k(1)(Ph) and k(-1)(Ph) correspond to the forward and back reactions, respectively, Analogous behavior is observed for [Ni(SePh)(triphos)](+). However, for [Ni(SEt)(triphos)](+), the kinetics are more complicated, and k(obs) = {k(1)k(2)[lutH(+)] + (k(-2) + k(2))}/(k(1)[lutH(+)] + k(-1)[lut]), which is indicative of a mechanism involving two coupled equilibria in which the initial protonation of the thiolate is followed by a unimolecular equilibrium reaction that is assumed to involve the formation of an eta(2)-EtS-H ligand. The difference in reactivity between the complexes with alkyl and aryl thiolate ligands is a consequence of the {Ni(triphos)}(2+) site "leveling" the basicities of these ligands. The pK(a)'s of the PhSH and EtSH constituents coordinated to the {Ni(triphos)}(2+) are 16.0 and 14.6, respectively, whereas the difference in pK(a)'s of free PhSH and EtSH differ by ca, 4 units, The pK(a) of [Ni(SeHPh)(triphos)](+) is 14.4. The more strongly sigma-donating EtS ligand makes the {Ni(triphos)}2+ core sufficiently electron-rich that the basicities of the sulfur and nickel in [Ni(SEt)(triphos)](+) are very similar; therefore, the proton serves as a bridge between the two sites. The relevance of these observations to the proposed mechanisms of nickel-based hydrogenases is discussed.
引用
收藏
页码:1128 / 1135
页数:8
相关论文
共 32 条
[1]  
[Anonymous], ANGEW CHEM INT EDIT
[2]  
BIGELEISEN J, 1964, PURE APPL CHEM, V8, P217
[3]   MONOHYDRIDE COMPLEXES OF MOLYBDENUM(IV) AND TUNGSTEN(IV) CONTAINING BULKY THIOLATE LIGANDS - X-RAY CRYSTAL-STRUCTURES OF [MH(SC6H2PRI3-2,4,6)3(PME2PH)2], M = MO OR W [J].
BURROW, TE ;
HILLS, A ;
HUGHES, DL ;
LANE, JD ;
MORRIS, RH ;
RICHARDS, RL .
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, 1991, (07) :1813-1820
[4]  
CAMMACK R, 1989, BIOINORGANIC CHEM NI, pCH8
[5]  
CRABTREE RH, 1994, ORGANOMETALLIC CHEM, P161
[6]   Understanding structure and reactivity of new fundamental inorganic molecules: metal sulfides, metallocarbohedrenes, and nitrogenase [J].
Dance, I .
CHEMICAL COMMUNICATIONS, 1998, (05) :523-530
[7]   PROTONATION SITES IN THIOLATO IRON CARBONYLATES - EVIDENCE FOR AN ARRESTED FE(RS-H) OXIDATIVE ADDITION [J].
DARENSBOURG, MY ;
LIAW, WF ;
RIORDAN, CG .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1989, 111 (20) :8051-8052
[8]   Synthesis and structure of a thiolate-bridged nickel-iron complex: towards a mimic of the active site of NiFe-hydrogenase [J].
Davies, SC ;
Evans, DJ ;
Hughes, DL ;
Longhurst, S ;
Sanders, JR .
CHEMICAL COMMUNICATIONS, 1999, (19) :1935-1936
[9]   Ni-Fe hydrogenases: A density functional theory study of active site models [J].
De Gioia, L ;
Fantucci, P ;
Guigliarelli, B ;
Bertrand, P .
INORGANIC CHEMISTRY, 1999, 38 (11) :2658-2662
[10]  
EIGEN M, 1964, ANGEW CHEM INT EDIT, V1, P3