Intermediate Octahedral Ligand Fields and Substitution Reaction

30

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on November 20, 2015 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0062.ch030

Intermediate Octahedral Ligand Fields and Substitution Reaction Stereomobility R O N A L D D. A R C H E R Department of Chemistry, University of Massachusetts, Amherst, Mass.

Alfred Werner discovered the concept of octahedral coor dination and coordination sphere rigidity in substitution reactions. On the other hand, he also noted reactions in volving stereomobility. A generalized scheme for deter mining potential reaction products in octahedral substitu tion reactions is given and used to discuss species known to exhibit stereomobility. The availability of a thermally accessible, spin-free, excited state is shown for complexes which undergo interesting stereochemical changes. A correlation of this ligand field strength concept with πdonor, steric, solvent, and charge effects allows a rather comprehensive understanding of d octahedral substitution reactions. Extension to other configurations is possible. 6

A lfred Werner and his students studied the stereochemistry of numerous substitution reactions with octahedral complexes. Often the products of a substitution reaction appeared capable of existing i n more than one isomeric form, but no evidence of their configurations could be obtained by the methods available at that time. Werner would assume that the product has the same configuration as the reactant—and he was correct more often than not. Crystal field calculations (Table I) also imply that the d and spin-paired d species studied b y Werner should give retained configurations. The dissociative tetragonal pyramid and the associative 1:4:2 intermediates, which yield all of the product with retained configura tion, have lower activation energies than the other intermediates which can give changes i n configuration. Hence, the concept of coordination sphere rigidity has become a useful concept i n octahedral coordination chemistry. z

6

452 In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

30.

ARCHER

Octahedral Ligand

Table I.

453

Fields

Octahedral Crystal Field Activation Energies

0

(t2 y(e y 0

ff

Dissociative

Tetragonal pyramid (C ») Trigonal bipyramid (T>ZH)

6

4

C

0.20 0.57

0.40 1.14

0 0

0.18 0.43

0.36 0.85

0 0


Associative

1:4:2 Intermediate of C » symmetry* Pentagonal bipyramid (D /0 2

6

6

In units of A. » 080). Calculated from the d-orbital energy levels (19). Based on the calculations by Hush (45).

a

e

d

On the other hand, Werner was aware of and did investigate substitu tion reactions of octahedral complexes which yield isomer mixtures (97102). Furthermore, he knew that isomerization sometimes occurred with out apparent reaction. In fact, his contemporary, S. M . J0rgensen, ob served the isomerization of [CoCl (en) ] before the turn of the century (52). Therefore, the stereomobility of substitution reactions of inert, octahedral species has long been of interest to coordination chemists. 2

General Substitution

Reaction

2

+

Stereomobility

Before considering the results of previously studied complexes, i t would seem wise to consider a general scheme for classifying the products of octahedral substitution reactions i n general. The products of the substitution of a ligand G for ligand A of the species [ M A B C D E F ] (in which M is a metal ion and A , B , C, D , E , and F are monodentate ligands or donor atoms of chelating ligands of an octa hedral complex) are shown i n Figure 1. Letters under the arrows indicate positions made adjacent by the loss of A , or the insertion position of G . The products are based on the principle that minimal atomic motion accompanies the attainment of the transition state, the reaction inter mediates (if any), and the products. The results of a large number of studies support this principle, which was assumed by Werner, and which recently has been used by Pearson and Basolo (81) and by K y u n o , Boucher, and Bailar (67). Although the product isomers are shown as resulting v i a a dissociation process, the products are equally valid for associative mechanistic con siderations, as indicated by Figure 2. Attachment of G anywhere on the top half of [ M A B C D E F ] prior to the release of A will result i n isomer G . (The designation "isomer G " is based on the ligand atom which is trans to atom F i n the octahedron and is the atom at the top of the octahedron as drawn. The other isomers can be similarly differentiated.) Isomer G n

n

In Werner Centennial; Kauffman, G.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.


WERNER

CENTENNIAL

Figure 1. A general scheme for octahedral substitution reaction products assuming a dissociative mechanism

Figure 2. A general scheme assuming an associative mechanism



30.

ARCHER

Octahedral Ligand

Fields

455

will result irrespective of whether a 1:4:2 intermediate (45), an approxima tion of a pentagonal bipyramid (16), or related interchange process (68) occurs, provided the principle of minimal atomic motion for the atoms not directly involved in the reaction is valid. On the other hand, attachment of G on the bottom side of the complex prior to release of A will result i n isomers E , C, D , and B being formed. This is true either by a considera tion of face attack, edge displacement (28), or edge shift (21, 48). Application of this general product prediction to real situations is straightforward. Figures 3 and 4 show the application to cis and trans

Figure 3.

Product expectations for an octahedral reactant with two bidentate and two cis monodentate ligands

complexes with two bidentate groups and two monodentate groups. The D * and L * cis isomer designations represent right- and lefthandedness with respect to the C axis of complexes with symmetrical bidentate ligands (7, 67) and are based on the absolute configuration of (+)-[Co(en) ] (86). However, the diagrams are applicable to unsymmetrical ligands as well. Note that the chelate ring structure eliminates one potential product for the cis reactant because normal size chelate rings (five or six atoms) cannot span the trans positions. Therefore, G cannot end up between D and F either by a dissociative or by an associative mechanism. Another point of interest, to which we will return later, is the nature of the postulated trigonal bipyramids necessary for dissociative stereomobility sans scrambling. 2

3


+3

456

WERNER

CENTENNIAL


Considering the related D*-cis ion i n which B C = D F = unsymmetri cal chelating ligands, we note that only three of the six geometrically pos sible isomers would be produced. The expected products are the sym metrical trans isomer, the retained D*-a cis isomer, and a L * - £ cis isomer in which the identical ends B and D are cis to each rather than trans.

Extension to the triethylenetetramine complexes shows that the cis isomer labeled D * - a (Figure 5) should give only D * - a and L*-# cis isomers, as previously suggested by K y u n o , Boucher, and Bailar (67). A l l D * designations are D*-a-cis and the L * is L*-0-cis. The corresponding D*-/3 diagram (not shown) would show the possibility of obtaining products with D*-0, L * - a , and trans configurations. Similarly, a trans isomer might give trans, D*-0, and L*-/3 products. One last example, the racemization of a tris (bidentate) ion by an intramolecular mechanism i n which one end is temporarily uncoordinated is shown in Figure 6, where A = G . The bond rupture mechanism is con sidered the probable mechanism for racemization of unsymmetrical #-diketone complexes based on the nuclear magnetic resonance studies by F a y and Piper (89). Extension of the scheme shown i n Figures 1 and 2 to other systems is almost limitless.



30.

ARCHER

Octahedral Ligand

457

Fields

L*

Figure 5.

Cobalt(III)

Product expectations for a complex similar to a D*-a-triethylenetetramine complex with two cis monodentate ligands

Stereomobility

The semiquantitative stereochemical observations of Alfred Werner and his students, as well as later contributions by J . C. Bailar, J r . , J . P . Mathieu, P . Pfeiffer, M . Delephine, and others, have been ably reviewed by Fred Basolo (16, 17, 21, 22). Reviews emphasizing more recent i n vestigations have also appeared (18, 68, 108), as have short reviews em phasizing aquation (acid hydrolysis) (47) and base hydrolysis (48, 90), both i n terms of stereochemistry and kinetics. Since the reviews have stressed the numerous stereochemical studies which have been conducted on the octahedral bis (ethylenediamine) com plexes of cobalt(III), those results will be reiterated only briefly. Aquation (acid hydrolysis) of m-[CoXY(en) ] complexes 2

[CoXY(en) ]° + H 0 ;=± [CoY(H 0)(en) ] 2

2

2

2

n+1

n

+ X"

(1)

takes place with apparently 100% retention of configuration, where en = ethylenediamine, X ~ = B r " , C l ~ , or N O r , and Y = N ~ , C l ~ , O H ~ , H 0 , N C S ~ , N H , or N 0 ~ , and n = the charge on the cobalt (III) complex. Although not all combinations of the above have been studied, enough have been investigated to suggest a generality. The corresponding trans ions aquate with complete retention of configuration, if Y = N H or N02~, 3

3

2

2

3



458

WERNER CENTENNIAL

Figure 6.

An intramolecular bond rupture racemization mechanism; A = G

but not if Y = N r , C I " , O H " , or N C S " This definite ligand field correla tion is considered to be due to w donation by the low field ligands into an empty orbital in a dissociative intermediate. Overlap for this w interaction is obtained only if a trigonal bipyramidal type intermediate is generated (80). Stronger field ligands lack this 7r-donating ability. A duality of mechanisms is indicated even i n these relatively simple aquations since water exchange and racemization of cis- and ^rans-[Co(H 0)(NH )(en) ] occur at different rates (73). 2

Table n. Reactant

ciN0 NCSNH, OH2

2

+3

One-step Base Hydrolysis

% { reactant % trans reactant —> cis product —> cis product c s

A

E

3

cicicicici-

6

h

37 66 80 84 97

5 6 76 76 95

° Figure 3 shows the general reaction sequence for the cis complexes where G = O H The first three percentage columns are based on experimental observations. b


ARCHER

30.

Octahedral Ligand

Base hydrolysis of [CoXY(en) ] complexes normally involves con siderable stereomobility during the substitution process. Illustrative studies for which both the optical and geometrical isomer composition of the products are known are given i n Table I I . A tabulation of the cis and trans product ratios for a large number of such reactions has been made by Ingold, Nyholm, and Tobe (48) and by Jordan and Sargeson (50). The latter have noted a similarity i n product ratios for the same E ligand i n a cis reactant or F ligand in a trans reactant (Figures 3 and 4, respectively), even though A may vary somewhat ( N ~ , C l ~ , B r ~ , N C S ~ ) . A n almost general agreement has been reached that the reacting species in these hydrolyses is the conjugate base [CoXY(en-H)(en)] ~ (68, 82). However, Green and Taube (43) have noted that the moleeularity of the conjugate base reaction appears to vary. Competition from an interchange process between the first and second coordination spheres with a unimolecular conjugate base mechanism (80-83, 68, 89) merits consideration. n

2


459

Fields

3

n

1

A comparison of these base hydrolysis results with the trigonal bipyramidal intermediates postulated for dissociative stereomobility is interesting. The two trigonal bipyramidal intermediates for the trans reactant (Figure 4) are mirror image optical isomers of the same geo metrical isomer. One of the trigonal bipyramids of the cis reactant (Figure 3) is identical to one of the optical isomers of the trans reactant, but the other bipyramidal intermediate is different and only yields cis products of D * and L * chirality. If the D F chelating group is asymmetric, Pearson and Basolo (81) suggest that any isomer ratio can be explained in terms of a dissociative type mechanism, provided (1) the cis reactant yields more cis product than the trans reactant, and (2) provided the per cent retention of configuration by the cis reactant is greater than or at least equal to the per cent of the top intermediate (Figure 3) necessary to obtain a product balance times the fraction of cis product obtained from the trans reactant, all of which must go through that intermediate and its mirror image. However, i n order to make a postulated unimolecular conjugate Products of [CoEA(en)2] Complexes n

% cis reactant —* inverted cis product*

16 20 24 24 36

0

% cis reactant thru lower intermediate DB:BF attack** 6

34 64 16 33 50

18:16 44:20 -8:24 9:24 14:36

9:8 11:5 l:oo 3:8 7:18

These columns are based on the same treatment as above but with Figure 3 nomenclature. This ratio should be related to the relative acidity of the two types of amine nitrogens in the complexes. c

d


460

WERNER

CENTENNIAL

base (SATICB) mechanism include the five cobalt(III) bis (ethylenediamine) complexes for which isomer data are available, the acidity of the N H groups at the opposite ends of the ethylenediamine molecules must vary from a factor of about 2:1 in one direction to 1: L * inversions similar to the tetrahedral Walden inversions) have been noted for [CoCl (en) ]+ and the corresponding chlorobromo (14) and d i bromo (14) species. Dwyer, Sargeson, and Reid (38) found that hydroxide rather than carbonate is responsible for the aqueous inversion. Subse quently, Boucher, K y u n o , and Bailar (26) have shown that Ag+ is not necessary for the reaction. The cis to trans ratios of the products in the inversion compared to the same ratios for dilute solution would be enlightening. Stronger field ligands, such as fluoro (74), hydroxo (26, 38), ammine (78), or nitro (38), show no such inversion. Again, this ligand field correlation may be due to low ir donation by the higher field ligands. 2


2

2

y

2

2

The closely related triethylenetetramine complexes show a D * - a to inversion (66, 67) similar to that expected (Figure 5). Although the investigators suggested complete inversion i n the second step (67)—the opposite of the ethylenediamine complexes—their data on direct hydrolysis suggest considerably more inversion for the two-step reaction than for the second step alone. N o configurational change was noted for the P isomer reaction (65). None of the substitution reactions of the bis(dimethylglyoximato) complexes of cobalt (III) have been found to exhibit configurational changes (1). A l l reactants and products possess the strongly hydrogen-bonded trans configuration. Cobalt (III) stereomobility has been noted i n complexes other than those with four nitrogen donors. For example, the base hydrolysis of 2rans-[Co(acac) (N0 )(H 0)] (acac = acetylacetonato ligand) appears to give some czs-dihydroxo products (37), even though the first step gives retention (10, 25). Another ligand field correlation is that although [ C o ( C 0 ) ( H 0 ) ] ~ decomposes easily, even i n water at 0°C. (5), [ C o ( C 0 ) ( N 0 ) ] ~ is quite stable when isolated (69). B o t h cis- and £rans-[Co(C0 ) (NH ) ]~ react with two moles of acetylacetone to give only m - [ C o ( a e a e ) ( N H ) ] (8). R i n g strain appears to determine the intermediate for this reaction. A series of synthetic and stereochemical studies by K y u n o (55-64) also has indicated stereomobility for sev eral cobalt (III) complexes, including the dicarbonatodiamminecobaltate(III) isomers, both of which yield £ratts-[Co(N0 )( (NH ) ]- upon reaction with nitrite (58, 85). K y u n o assumed stereorigidity i n some of the aquations, which might be questionable for species such as the 2

2

4

2

2

4

2

2

2

2

2

2

3

2

3

2

3

2

2

3

2

+

2

4

3

2


30.

ARCHER

Octahedral Ligand Fields

461

two [Co(N0 )2(C204)(en)] isomers (61). In fact, anation of the corresponding nitroaquo species was found to involve isomerization. Isomerization had previously been noted for the dicarbonato complexes of cobalt (III) (75-77), some of which appear sterically impossible (e.g., trans2

[Co(C0 ) (en)]-)


3

2

(76).

The bimolecular racemization of ethylenedinitrilotetraacetatocobaltate(III) (29,36) should be noted. This racemization suggests that bimolecularity should not be excluded in mechanistic considerations of octahedral complexes. Base hydrolysis studies of other complexes without ionizable protons would be of considerable value, provided they are of intermediate field strength. Other d Complexes 6

Rhodium (III) acid and base hydrolyses appear to go with almost complete retention of configuration (49). Furthermore, base hydrolysis rates are not much greater than the corresponding acid hydrolysis rates. This lack of stereomobility can be correlated with the larger A (or Dq) values for rhodium (III) (15, 51). Nuoleophilic reactions of the spin-paired tris(o-phenanthroline) iron(II) ion are bimolecular (70-72). The tris complex is close to the spin-free complex i n energy since dithiocyanatobis(o-phenanthroline) iron (II) exists in a spin-free ;=± spin-paired equilibrium (53). The corresponding tris (o-phenanthroline) nickel (II) ion is unaffected by the same nucleophile, which probably rules out S#2 attack on the organic ring as the predominant factor. Studies with platinum (IV) complexes are complicated by platinum (II) catalysis (18). Some of the recent Russian work has considered this aspect (44), but correlations are still being made without consideration of the catalytic problem (104). The recent isolation of several optically active platinum (IV) complexes with all inorganic, monodentate ligands (35) should allow substantiation for older work which has always suggested retention, i n agreement with the high A values for platinum (IV). Spin-free

Intermediate

Although a large number of electronic and steric factors appears to be important in determining the rates and stereomobility for reactions of the inert, octahedral complexes which have been studied (19-22, 68, 87), the simple ligand field parameters are quite useful i n ascertaining both rates and stereochemistry. This correlation is related to the ligand field activation parameter (Table I) and to the ^-donating ability of the lower field ligands. Several factors suggest another possibility — a spin-free intermediate — advanced previously (19, 85) to explain the bimolecular base hydrolysis of tris (o-phenanthroline) iron (II).


462

WERNER CENTENNIAL

Whereas the ligand field activation energy of the spin-paired paths allowing configurational change have very high activation energies (Table I), spin-free d complexes can undergo dissociative or associative rearrange ments without any ligand field activation energy. Therefore, the spin-free state might function as a precursor to a stereomobile substitution reaction provided the energy of the spin-free state is not greater than the ligand field activation energy of an alternate spin-paired path. This concept allows competition by the spin-free state to about 0.4 A i n d systems. The results of calculated A values and spin-free activation energies for the extremely stereomobile conjugate base of [CoCl (en) ] and some related ions are given in Table I I I . The average A values for spin-paired cobalt (III) species and some related rhodium (III) complexes necessary for the calculations in Table I I I are tabulated in Table I V . The energy values in both tables have been calculated from spectra of known species using the average environment approximation and values of B and C , based on the method of Wentworth and Piper (94, 96). The calculations of A for the cobalt(III) conjugate base are based on related rhodium (III) species. The spectrochemical position of the nitro gen conjugate base ligand can be estimated from A, B , and C values for known rhodium (III) complexes (51) and the recent observations that [Rh(en-H) ] is diamagnetic (91), whereas [Rh(en-H) (en-2H)]~ is para magnetic (92). Since the magnetic crossover occurs at 2A = 5 B + 8 C for d species, and B and C values for known rhodium (III) complexes are about 310 and 3000 c m . , respectively, the conjugate base ends of the ethylenediamine ligands must have a A of only about 1200 cm." to account


6

6

2

3

2

+

2

6

-1

1

Table III.

Estimated Spin-free Activation Energies for Selected Cobalt(ni) Species Spin-free E (kcal./mole)

a

A(kK)*

[CoCl (en) ]+ [Co(H 0) ] * (observed) * [CoCl (en-H)(en)]« [Co(H 0)«]+ (calculated)[CoCl (en-H)(en)]/ Spin-paired [CoF ]-» ° Estimated crossover" Spin-free [CoF ] (observed) 2

21.7 20.4 19.2 18.8 17.7 16.8 16.5 13.0

2

2

8

+

2

2

3

2

6

6

(95).

_3

b

Spin-paireda (kcal./mole)

31 23 16 14 7

e

25 23 22 22 20

° The A values are based on Dq' values of Wentworth and Piper, kK = 1000 c m r Spin-free E - E( !T ) - E 0 A i ) = 2A —5 B — 8 C ; 1 kcal./mole - 350 cm." Spin-paired E = 0.4A. Reference (51). • The A for the conjugate base donor estimated as 10 kK. The A for the conjugate base donor estimated as 1.2 kK. « Crossover based o n B = 0.5 kK; C = 3.8 kK (95).

b c

6

a

2a

a

0

d

f


1

1

30.

ARCHER

Octahedral Ligand

Table IV.

463

Fields

Average A Values for Cobalt(III) and Rhodium(III) Complexes 0


Co(III) Rh(III)

/-

Nr

Br~

CI-

F~

OH-

C0 "

10

11

13 21

15 22

17-18

18 27

19

edta

Co(III) Rh(III)

NH

Z

22 31

25 36

3

en

N0 ~

25 36

31

2

H0

C ^

19-20 28

20 28

2

2

CN'

36

° For the complexes which have been measured, the corresponding iridium (III) and platinum(IV) complexes have A values approximately double the cobalt(III) values, whereas the iron(II) species have slightly lower A values than the cobalt (III species. A Values are in kK units of 1000 cm." , edta = ethylenedinitrilotetraacetate 1

for the diamagnetic to paramagnetic transition i n the rhodium conjugate base series. A higher value would require that both complexes be dia magnetic. Considering the dearth of B and C data for rhodium (III) com plexes, this estimate could be somewhat low. E v e n so, the A value for N H ~ is undoubtedly considerably less than the iodide ion value given i n Table I V . B o t h extreme values (1200 and 10,000 c m . ) have been used to calculate the maximum range of A values for the cobalt(III) conjugate base species (Table III). Cobalt(III) complexes appear to have B and C values of about 500 and 3800 c m . , respectively. These typical values give a crossover point of 16,500 c m . , which has been used in Table I I I to estimate the spin-free activation energies of the other species, the spin-free activation energies being the amount by which 2A exceeds 5 B + 8 C. That the position of the spin-free crossover is not too low is indicated by the fact that the hypotheti cal spin-paired [Co F ] ion has a A value (Table IV) about equal to the crossover point estimated from the Racah parameters, B and C. The spin-paired activation energies, estimated at 0.4A, are also given i n Table I I I for comparison purposes. The A value of the hexaaquocobalt(III) ion is important since spinfree activation estimates of only 4 or 5 kcal./mole have been made to account for the rapid ligand exchange rate observed for this complex (23, 40, 41, 88). Unfortunately, two A values must be given for the hexaaquo ion since the spectrum reported for the metastable complex (51) gives a re sult which differs somewhat from the calculated value (95). A l l of the values in the spin-free column could be lowered by 9 to 18 kcal./mole, depending on the proper hexaaquo A value, if the 5 kcal./mole spin-free activation assumption were correct. In any case, the spin-free state of the conjugate base i n question is low enough in energy to provide competition for the spin-paired paths. 2

-1

- 1

-1

6

- 3



464

WERNER

CENTENNIAL

Similarly, the dichlorotriethylenetetraminecobalt(III) isomers, which possess almost identical ligand field parameters, show marked stereo mobility. A l l isomers yield primarily the 0 isomer during base hydrolysis. On the other hand, bis (ethylenediamine) complexes having higher field monodentate ligands show less stereomobility during base hydrolysis, i n agreement with the spin-free concept. E v e n though the activation energy of this process may be less than that for other paths, a low frequency factor would allow other paths to compete at higher temperatures. This postulate would also explain the temperature dependence of the Bailar inversions. A n alternate, oriented ion-pair mechanism has been suggested previously (9, 26, 69), but the observations with [CoCl (en) ]+ in methanol (24) make this less probable because both the ion pair and the solvated ion appear to give trans and racemic cis isomers under the conditions studied. Some orientation effects would be expected for the ion-pair reaction if i t were operative i n the inversion reactions. The availability of a spin-free state at the right energy does not mean that the species use that path. The frequency factor may be too low, either as a result of the A\ —> T transition rate being too slow to com pete with other paths, or because the lifetime in the T state is too short to allow the requisite atomic motion for substitution. A long lifetime would facilitate reduction of cobalt (III) to cobalt (II). I n fact, cobalt (II) species are often found i n cobalt (III) products when low ligand field ligands are involved i n substitution reactions. It appears possible that only the conjugate bases of the bis(ethylenediamine) and triethylenetetramine cobalt (III) ions have low enough ener gies for competition b y this mechanism. A consideration of the acid hydrolysis of [CoCl (en) ]+ shows no competition b y the spin-free path if Wentworth and Piper's B and C values are right. The observation of re tention for this and the related triethylenetetramine aquation reactions is i n agreement with a lack of competition. On the other hand, if the lower activation energy suggested b y the hexaaquo species were correct, competition could exist. M a r t i n and Tobe (73) found that the water ex change of the [Co(H 0)(NH )(en) ]+ isomers proceeds at less than a hundred times the rate of racemization — suggesting similar activation parameters. Since these ions have A values of about 24 kK, the spin-free state could not compete unless the lowest hexaaquo value were correct. Hence, no definite conclusions can be drawn for the acid hydrolyses at this time. Extension of the spin-free idea to other species is also possible. Of the rhodium (III) amine species, only a multiple conjugate base species would be suitable, since A values are larger and the B and C parameters are lower (15). Spin-paired iron (II) species and certain cobalt (III) com plexes with several ligands lower than the amines might also use the spin2

l

2

b

g

2g

5

2

2g

2

2

3

2

3



30.

ARCHER

Octahedral Ligand

465

Fields

free path. Bis(oxalato) complexes of rhodium(III) isomerize (54), also i n agreement with their relatively lower ligand field, whereas configurational changes are difficult with higher field rhodium complexes. Bimolecular processes are apparently more important in rhodium (III) reactions (49, 83). The racemization of tris (ethylenediamine) ions may also need a bimolecular path (42, 84)Caution should be suggested against using this or any other effect as a cure-all for octahedral kinetics and mechanisms. For example, steric hindrance can change a planar d* system, which normally reacts by a bimolecular path (18) to unimolecular reactivity (11, 93). (On the other hand, even the concept of molecularity in complex ion reactions has been questioned by Adamson (3) who initiated and made good use of the S;y2FS path (2, 4)- Some of the manifestations of this problem have been discussed by others as well (68, 90).) Other Electronic

Configurations

The correlation of rates with ligand field strength can also be made for other electronic configurations. For example, whereas C r C l ~ hydrolyzes almost instantaneously, M o C l ~ has a specific rate constant of less-than 10~ at 0°C. (6), i n keeping with the 5 0 % greater A values of the second transition series (51). In fact, the rate is about the same as for chromium (III) species about that much higher i n the series. The lack of a strong conjugate base effect (17, 68) in d systems can also be related to the unavailability of a state with lower ligand field activation. On the other hand, d species racemize more readily than the corresponding d complexes, in agreement with the ligand field parameters. (See Table I.) The d ruthenium (III) species exhibit intermediate behavior (27). The interelectronic repulsions for a d system (15B + 10C vs. 2A) are greater than those of a a! system (5B + 8C vs. 2A), suggesting a greater ligand field effect for ruthenium (III) than for rhodium (III). B u t the greater A values and lower B and C values relative to those of cobalt (III) are insufficient to compensate fully for the 10B and 2C differences. Other relationships could also be mentioned, but the preceding should give an indication of general relationships which exist among ligand field strength, reaction rates, and stereomobility. 6

3

3

6

3

z

z

%

5

b

6

Acknowledgment The author wishes to acknowledge the support of the National Science Foundation for the unpublished work reported herein which was conducted at Tulane University, New Orleans, L a . The constructive criticism of a referee with respect to Table I I I is also humbly acknowledged.


466

WERNER

Literature

CENTENNIAL

Cited

(1) Ablov, A. V., Syrtsova, G. P., Russ. J. Inorg. Chem. 10, 1079 (1965).


(2) Adamson, A. W., ADVAN. CHEM. SER. 49, 237 (1965).

(3) Ibid., p. 248. (4) Ablov, A. V., Syrtsova, G. P., J. Am. Chem. Soc. 80, 3183 (1958). (5) Ablov, A. V., Syrtsova, G. P., J. Inorg. Nucl. Chem. 6, 319 (1958). (6) Andruchow, W., Archer, R. D., unpublished results. (7) Archer, R. D., Bailar, J. C., Jr., J. Am. Chem. Soc. 83, 812 (1961). (8) Archer, R. D., Catsikis, B., J. Am. Chem. Soc., in press. (9) Archer, R. D., Chung, D. C., paper presented at Am. Chem. Soc. meeting, Washington, D. C., March, 1962. (10) Archer, R. D., Cotsoradis, B. P., Inorg. Chem. 4, 1584 (1965). (11) Baddley, W. H., Basolo, F., J. Am. Chem. Soc. 86, 2075 (1964). (12) Bailar, J. C., Jr., Auten, W., J. Am. Chem. Soc. 56, 774 (1934). (13) Bailar, J. C., Jr., Haslam, J. H., Jones, E. M., J. Am. Chem. Soc. 58, 2226 (1936). (14) Bailar, J. C., Jr., Peppard, D. F., J. Am. Chem. Soc. 62, 820 (1940). (15) Ballhausen, C. J., "Introduction to Ligand Field Theory," Chapter 10, McGraw-Hill, New York, 1962. (16) Basolo, F., Chem. Rev. 52, 459 (1953). (17) Basolo, F., "The Chemistry of the Coordination Compounds," Bailar,J.C., Jr., ed., Chapter 8, Reinhold, New York, 1956. (18) Basolo, F., Pearson, R. G., Advances in Inorg. Chem. Radiochem. 3, 1 (1961). (19) Basolo, F., Pearson, R. G., "Mechanisms of Inorganic Reactions," Chapter 2, Wiley, New York, 1958. (20) Ibid., Chapter 3. (21) Ibid., Chapter 5. (22) Ibid., Chapter 6. (23) Bonner, N. A., Hunt, J. P., J. Am. Chem. Soc. 74, 1886 (1952). (24) Bosnich, B., Ingold, C. K., Tobe, M. L., J. Chem. Soc. 1965, 4074. (25) Boucher, L. J., Bailar, J. C., Jr., J. Inorg. Nucl. Chem. 27, 1093 (1965). (26) Boucher, L. J., Kyuno, E., Bailar, J. C., Jr., J. Am. Chem. Soc. 86, 3658 (1964). (27) Broomhead, J. A., Basolo, F., Pearson, R. G., Inorg. Chem. 3, 826 (1964). (28) Brown, D. D., Ingold, C. K., Nyholm, R. S., J. Chem. Soc. 1953, 2674. (29) Busch, D. H., Cooke, D. W., Swaminathan, K., Im, Y. A., "Advances in the Chemistry of the Coordination Compounds," p. 139, Kirshner, S., ed., Mac millan, New York, 1961. (30) Chan, S. C., Leh, F., J. Chem. Soc. 1966, 126. (31) Ibid., p. 129. (32) Ibid., p. 134. (33) Ibid., p. 138. (34) Chan, S. C., Tobe, M. L., J. Chem. Soc. 1963, 5700. (35) Chernyyaev, I. I., Korablina, L. S., Muraveiskaya, G. S., Russ. J. Inorg. Chem. 10, 567 (1965). (36) Cooke, D. W., Im, Y. A., Busch, D. H., Inorg. Chem. 1, 13 (1962). (37) Cotsoradis, B. P., Ph.D. Dissertation, Tulane University, New Orleans, La., 1965. (38) Dwyer, F. P., Sargeson, A. M., Reid, I. K., J. Am. Chem. Soc. 85, 1215 (1963). (39) Fay, R. C., Piper, T. S., Inorg. Chem. 3, 348 (1964). (40) Friedman, H. L., Hunt, J. P., Plane, R. A., Taube, H., J. Am. Chem. Soc. 73, 4028 (1951). (41) Friedman, H. L., Hunt, J. P., Taube, H., J. Chem. Phys. 18, 759 (1950). (42) Gehman, W. G., Fernelius, W. C., J. Inorg. Nucl. Chem. 9, 71 (1959). (43) Green, M., Taube, H., Inorg. Chem. 2, 948 (1963). (44) Grinberg, A. A., Korableva, A. A., Russ. J. Inorg. Chem. 9, 1253 (1964). (45) Hush, N. S., Australian J. Chem. 15, 378 (1962).



30.

ARCHER

Octahedral Ligand Fields

467

(46) Ingold, C. K., "Substitution at Elements Other Than Carbon," Weizmann, Jerusalem, 1959 (47) Ingold, C. K., Nyholm, R. S., Tobe, M. L., Nature 187, 477 (1960). (48) Ibid. 194, 344 (1962). (49) Johnson, S. A., Basolo, F., Pearson, R. G., J. Am. Chem. Soc. 85, 1741 (1963). (50) Jordan, R. B., Sargeson, A. M., Inorg. Chem. 4, 433 (1965). (51) Jørgensen, C. K., "Absorption Spectra and Chemical Bonding in Complexes," Chapter 15, Pergamon Press, Oxford, 1962. (52) Jørgensen, S.M.,J.Prakt. Chem. 39, 16 (1889). (53) König, E., Madeja, K., Chem. Commun. 1966, 61. (54) Krishnamurty, K. V., Harris, G. M., Chem. Rev. 61, 213 (1961). (55) Kyuno, E., Nippon Kagaku Zasshi 78, 1494 (1957); Chem. Abstr. 53, 21349 (1959). (56) Ibid. 80, 722 (1959); Chem. Abstr. 55, 206 (1961). (57) Ibid. 80, 724 (1959); Chem. Abstr. 55, 206 (1961). (58) Ibid. 80, 849 (1959); Chem. Abstr. 55, 206 (1961). (59) Ibid. 80, 852 (1959); Chem. Abstr. 55, 206 (1961). (60) Ibid. 80, 981 (1959); Chem. Abstr. 55, 206 (1961). (61) Ibid. 80, 984 (1959); Chem. Abstr. 55, 6235 (1961). (62) Ibid. 80, 987 (1959); Chem. Abstr. 55, 6236 (1961). (63) Ibid. 81, 724 (1960); Chem. Abstr. 55, 20749 (1961). (64) Ibid. 81, 728 (1960); Chem. Abstr. 55, 20749 (1961). (65) Kyuno, E., Bailar, J. C., Jr., J. Am. Chem. Soc. 88, 1120 (1966). (66) Ibid., p. 1125. (67) Kyuno, E., Boucher, L. J., Bailar, J. C., Jr., J. Am. Chem. Soc. 87, 4458 (1965). (68) Langford, C. H., Gray, H. B., "Ligand Substitution Processes," Chapter 3, Benjamin, New York, 1966. (69) Moffitt, M. G., Archer, R. D., unpublished results. (70) Margerum, D. W., J. Am. Chem. Soc. 79, 2728 (1957). (71) Margerum, D. W., Morgenthaler, L. P., "Advances in the Chemistry of Coor dination Compounds," Kirshner, S., ed., p. 481, Macmillan, New York, 1961. (72) Margerum, D. W., Morgenthaler, L. P., J. Am. Chem. Soc. 84, 706 (1962). (73) Martin, D. F., Tobe, M. L., J. Chem. Soc. 1961, 4637. (74) Matoush, W. K., Basolo, F., Am. Chem. Soc. 78, 3972 (1956). (75) Mori, M., Shibata, M., Kyuno, E., Adachi, T., Bull. Chem. Soc. Japan 29, 883 (1956). (76) Mori, M., Shibata, M., Kyuno, E., Hoshiyama, K., Bull. Chem. Soc. Japan 31, 291 (1958). (77) Mori, M., Shibata, M., Kyuno, E., Maruyama, F., Bull. Chem. Soc. Japan 35, 75 (1962). (78) Nyholm, R. S., Tobe, M. L., J. Chem. Soc. 1956, 1707. (79) Pearson, R. G., Record Chem. Progr. 23, 53 (1962). (80) Pearson, R. G., Basolo, F., J. Am. Chem. Soc. 78, 3878 (1956). (81) Pearson, R. G., Basolo, F., Inorg. Chem. 4, 433 (1965). (82) Pearson, R. G., Schmidtke, H. H., Basolo, F., J. Am. Chem. Soc. 82, 4434 (1960). (83) Robb, W., Harris, G. M., J. Am. Chem. Soc. 87, 4472 (1965). (84) Sen, D., Fernelius, W. C., J. Inorg. Nucl. Chem. 10, 269 (1959). (85) Shibata, M., Mori, M., Kyuno, E., Inorg. Chem. 3, 1573 (1964). (86) Siato, Y., Nakatsu, K., Shiro, M., Kuroyo, H., Bull. Chem. Soc. Japan 30, 795 (1957). (87) Stranks, D. R., "Modern Coordination Chemistry," Lewis, J., Wilkins, R. G., eds., Chapter 2, Interscience, New York, 1960. (88) Taube, H., Chem. Rev. 50, 69 (1952). (89) Taube, H., ADVAN. CHEM. SER. 49, 7 (1965).

(90) Tobe, M. L., Sci. Progr. 48, 483 (1960). (91) Watt, G. W., Crum, J. K., J. Am. Chem. Soc. 87, 5366 (1965).



468

WERNER CENTENNIAL

(92) Watt, G. W., Crum, J. K., Summers,J.T., J. Am. Chem. Soc. 87, 4641 (1965). (93) Weick, C. F., Basolo, F., Inorg. Chem. 5, 576 (1966). (94) Wentworth, R. A.D.,Inorg. Chem. 5, 496 (1966). (95) Wentworth, R. A.D.,Piper, T. S., Inorg. Chem. 4, 709 (1965). (96) Ibid. 4, 1524 (1965). (97) Werner, A., Ann. 386, 1 (1912). (98) Werner, A., Ber. 44, 3272 (1911). (99) Ibid. 47, 1961 (1914). (100) Werner, A., Cutcheon, Mc., Ber. 45, 3281 (1912). (101) Werner, A., Shibata, Y., Ber. 45, 3287 (1912). (102) Werner, A., Tschernoff, G., Ber. 45, 3294 (1912). (103) Wilkins, R . G., Williams, M. J. G., "Modern Coordination Chemistry," Lewis, J., Wilkins, R. G., eds., Chapter 3, Interscience, New York, 1960. (104) Zvyagintsev, O. E., Shubochkina, E. F., Peshchevitskii, B. I., Russ. J. Inorg. Chem. 10, 560 (1965). RECEIVED June 30, 1966.


Intermediate Octahedral Ligand Fields and Substitution Reaction

Recommend Documents