168:
278:
of cobalt(III) ammine halide complexes are deceptive, appearing to be associative but proceeding by an alternative pathway. The hydrolysis of follows second order kinetics: the rate increases linearly with concentration of hydroxide as well as the starting complex. Based on this information, the
311:
and R. G. Wilkins, is a mechanism and rate law in coordination chemistry governing associative substitution reactions of octahedral complexes. It was discovered for substitution by ammonia of a chromium-(III) hexaaqua complex. The key feature of the mechanism is an initial rate-determining
262:(η to η). Nitric oxide typically binds to metals to make a linear MNO arrangement, wherein the nitrogen oxide is said to donate 3e to the metal. In the course of substitution reactions, the MNO unit can bend, converting the 3e linear NO ligand to a 1e bent NO ligand.
241:
In special situations, some ligands participate in substitution reactions leading to associative pathways. These ligands can adopt multiple motifs for binding to the metal, each of which involves a different number of electrons "donated." A classic case is the
179:
In many substitution reactions, well-defined intermediates are not observed, when the rate of such processes are influenced by the nature of the entering ligand, the pathway is called associative interchange, abbreviated
128:
Y that in a subsequent step dissociates one of their ligands. Dissociation of Y results in no detectable net reaction, but dissociation of X results in net substitution, giving the 16e complex MX
209:
pathway. The electrostatically held nucleophile can exchange positions with a ligand in the first coordination sphere, resulting in net substitution. An illustrative process comes from the "
637:
M. Eigen, R. G. Wilkins: Mechanisms of
Inorganic Reactions. In: Advances in Chemistry Series. Nr. 49, 1965, S. 55. American Chemical Society, Washington, D. C.
484:
is 0.0202 dmmol for neutral particles at a distance of 200 pm. The result of the rate law is that at high concentrations of Y, the rate approximates k
279:
reactions would appear to proceed via nucleophilic attack of hydroxide at cobalt. Studies show, however, that the hydroxide deprotonates one NH
187:. Representative is the interchange of bulk and coordinated water in . In contrast, the slightly more compact ion exchanges water via the
54:. Intermediate pathways exist between the pure associative and pure dissociative pathways, these are called interchange mechanisms.
716:
683:
667:
662:
R. G. Wilkins "Kinetics and
Mechanism of Reactions of Transition Metal Complexes," 2nd Edition, VCH, Weinheim, 1991.
587:
558:
529:
105:
721:
711:
651:
450:
113:
202:
Polycationic complexes tend to form ion pairs with anions and these ion pairs often undergo reactions via the
731:
726:
695:
Atkins, P. W. (2006). Shriver & Atkins inorganic chemistry. 4th ed. Oxford: Oxford
University Press
70:
47:
646:
Basolo, F.; Pearson, R. G. "Mechanisms of
Inorganic Reactions." John Wiley and Son: New York: 1967.
254:"slips' from pentahapto (η) coordination to trihapto (η). Other pi-ligands behave in this way, e.g.
141:
89:, the associative pathway is desirable because the binding event, and hence the selectivity of the
31:
603:
Helm, Lothar; Merbach, André E. (2005). "Inorganic and
Bioinorganic Solvent Exchange Mechanisms".
499:(and thus a faster pre-equilibrium) are obtained for large, oppositely-charged ions in solution.
255:
69:
followed by loss of another ligand. Complexes that undergo associative substitution are either
385:
Leading to the final form of the rate law, using the steady-state approximation (d / dt = 0),
678:
G. L. Miessler and D. A. Tarr “Inorganic
Chemistry” 3rd Ed, Pearson/Prentice Hall publisher,
437:
represents the minimum distance of approach between complex and ligand in solution (in cm), N
137:
133:
98:
86:
66:
35:
8:
474:
251:
145:
140:
is negative, which indicates an increase in order in the system. These reactions follow
576:
547:
518:
109:
679:
663:
647:
620:
583:
554:
525:
442:
413:
comes from the Fuoss-Eigen equation proposed independently by Eigen and R. M. Fuoss:
90:
58:
43:
23:
612:
292:
284:
243:
121:
82:
409:
A further insight into the pre-equilibrium step and its equilibrium constant K
340:
The subsequent dissociation to form product is governed by a rate constant k:
104:
Examples of associative mechanisms are commonly found in the chemistry of 16e
705:
308:
149:
74:
288:
624:
446:
51:
39:
259:
220:
62:
320:
and incoming ligand Y. This equilibrium is represented by the constant K
275:
616:
291:, the chloride spontaneously dissociates. This pathway is called the
94:
78:
157:
549:
Kinetics and
Mechanism of Reactions of Transition Metal Complexes
210:
247:
27:
213:" (reaction with an anion) of chromium(III) hexaaquo complex:
16:
Process of exchange of ligands between coordination compounds
356:
A simple derivation of the Eigen-Wilkins rate law follows:
167:
473:
Where z is the charge number of each species and ε is the
495:. The Eigen-Fuoss equation shows that higher values of K
287:
of the starting complex, i.e., . In this monovalent
120:) bind the incoming (substituting) ligand Y to form
575:
546:
517:
307:The Eigen-Wilkins mechanism, named after chemists
174:
703:
312:pre-equilibrium to form an encounter complex ML
93:, depends not only on the nature of the metal
515:
573:
488:while at low concentrations the result is kK
449:and T is the reaction temperature. V is the
161:
602:
302:
57:Associative pathways are characterized by
30:. The terminology is typically applied to
236:
197:
73:or contain a ligand that can change its
582:(3rd ed.). Pearson/Prentice Hall.
544:
404:
704:
574:Miessler, G. L.; Tarr, D. A. (2004).
516:Basolo, F.; Pearson, R. G. (1967).
13:
265:
166:
14:
743:
520:Mechanisms of Inorganic Reactions
524:. New York: John Wiley and Son.
144:: the rate of the appearance of
132:Y. The first step is typically
553:(2nd ed.). Weinheim: VCH.
175:Associative interchange pathway
65:to give a discrete, detectable
689:
672:
656:
640:
631:
596:
567:
538:
509:
453:of the ions at that distance:
451:electrostatic potential energy
1:
502:
77:to the metal, e.g. change in
22:describes a pathway by which
7:
46:. The opposite pathway is
10:
748:
71:coordinatively unsaturated
50:, being analogous to the
48:dissociative substitution
717:Organometallic chemistry
20:Associative substitution
545:Wilkins, R. G. (1991).
303:Eigen-Wilkins mechanism
162:Eigen–Wilkins Mechanism
116:. These compounds (MX
722:Coordination chemistry
712:Substitution reactions
237:Special ligand effects
198:Effects of ion pairing
171:
108:metal complexes, e.g.
36:coordination complexes
480:A typical value for K
170:
142:second order kinetics
138:entropy of activation
87:homogeneous catalysis
405:Eigen-Fuoss equation
114:tetrachloroplatinate
38:, but resembles the
732:Reaction mechanisms
578:Inorganic Chemistry
475:vacuum permittivity
316:-Y from reactant ML
283:ligand to give the
226:{, NCS} ⇌ + H
160:is governed by the
727:Chemical reactions
172:
617:10.1021/cr030726o
443:Avogadro constant
274:The rate for the
61:of the attacking
44:organic chemistry
739:
696:
693:
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629:
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611:(6): 1923–1959.
600:
594:
593:
581:
571:
565:
564:
552:
542:
536:
535:
523:
513:
134:rate determining
124:intermediates MX
97:but also on the
85:ligand (NO). In
81:or bending of a
747:
746:
742:
741:
740:
738:
737:
736:
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229:
208:
200:
193:
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148:depends on the
131:
127:
122:pentacoordinate
119:
110:Vaska's complex
17:
12:
11:
5:
745:
735:
734:
729:
724:
719:
714:
698:
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688:
671:
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566:
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401:
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361:
354:
353:
349:
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338:
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333:
329:
321:
317:
313:
304:
301:
294:
285:conjugate base
280:
271:
267:
264:
244:indenyl effect
238:
235:
234:
233:
232:
231:
227:
224:
206:
199:
196:
191:
184:
176:
173:
153:
129:
125:
117:
83:nitrogen oxide
32:organometallic
15:
9:
6:
4:
3:
2:
744:
733:
730:
728:
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723:
720:
718:
715:
713:
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684:0-13-035471-6
681:
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669:
668:1-56081-125-0
665:
659:
653:
649:
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634:
626:
622:
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591:
589:0-13-035471-6
585:
580:
579:
570:
562:
560:1-56081-125-0
556:
551:
550:
541:
533:
531:0-471-05545-X
527:
522:
521:
512:
508:
500:
478:
476:
468:
456:
455:
454:
452:
448:
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388:
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386:
377:
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365:
359:
358:
357:
343:
342:
341:
327:
326:
325:
310:
309:Manfred Eigen
300:
298:
297:1cB mechanism
290:
286:
277:
270:1cB mechanism
263:
261:
258:(η to η) and
257:
253:
249:
245:
225:
222:
218:
217:
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205:
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169:
165:
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150:concentration
147:
143:
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135:
123:
115:
111:
107:
106:square planar
102:
100:
96:
92:
88:
84:
80:
76:
72:
68:
64:
60:
55:
53:
49:
45:
41:
40:Sn2 mechanism
37:
33:
29:
25:
21:
691:
674:
658:
642:
633:
608:
604:
598:
577:
569:
548:
540:
519:
511:
479:
472:
466:
447:gas constant
434:
432:
422:
408:
384:
355:
339:
306:
273:
246:in which an
240:
203:
201:
188:
181:
178:
136:. Thus, the
103:
67:intermediate
56:
26:interchange
19:
18:
445:, R is the
260:naphthalene
156:and Y. The
63:nucleophile
52:Sn1 pathway
706:Categories
652:047105545X
503:References
429:exp(-V/RT)
425:/3000) x N
276:hydrolysis
252:reversibly
223:⇌ {, NCS}
605:Chem. Rev
389:rate = kK
378:rate = kK
348:-Y → ML
99:substrate
79:hapticity
24:compounds
625:15941206
396:/ (1 + K
375:rate = k
332:+ Y ⇌ ML
158:rate law
95:catalyst
91:reaction
441:is the
352:Y + L
250:ligand
248:indenyl
211:anation
146:product
75:bonding
59:binding
28:ligands
682:
666:
650:
623:
586:
557:
528:
433:Where
289:cation
457:V = z
421:= (4Ď€
256:allyl
152:of MX
680:ISBN
664:ISBN
648:ISBN
621:PMID
584:ISBN
555:ISBN
526:ISBN
465:e/4Ď€
112:and
34:and
613:doi
609:105
493:tot
486:tot
394:tot
368:tot
360:= K
221:SCN
219:+
42:in
708::
619:.
607:.
477:.
370:-
366:=
344:ML
336:-Y
328:ML
324::
299:.
194:.
101:.
686:.
627:.
615::
592:.
563:.
534:.
497:E
490:E
482:E
469:ε
467:a
463:2
461:z
459:1
439:A
435:a
427:A
423:a
419:E
417:K
411:E
400:)
398:E
391:E
380:E
362:E
350:5
346:6
334:6
330:6
322:E
318:6
314:6
295:N
293:S
281:3
268:N
266:S
230:O
228:2
207:a
204:I
192:d
189:I
185:a
182:I
164:.
154:4
130:3
126:4
118:4
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