4200
FREDBASOLO, HARRYB. GRAY.\ND RALPHG . PEARSON
1.01, 82
the free base and not with a protonated species such mium(II1) to coordinate to oxygen, this is the most as the aniliniurn ion. X similar difference woulcl reasonable explanation of the conductivity data. probably be found for ligands which are anions, Herwig and Zeiss” found anhydrous chromium i.e., benzoate ion. Here the comparison required (111) chloride to react with tetrahydrofuran to would be that between the benzoate ion (not ben- give [CrC13(C4Hs0)3],a compound which indicates zoic acid) and the coardinated benzoate. the avidity with which Cr(II1) coordinates even to h final point which emerged from this work was ethereal oxygen. The tetrahydrofuran molecules an indication of a considerable degree of variation are not lost when the compound is heated to 100’ of the inertness of the inert complexes used. Thus at 20 min. the pyridine complex was very stable, the aniline Summary complex less so, and the bromoaniline complexes 1. Preparative methods which give good yields even less stable. Thus for inert complexes, the of trichlorotripyridinechromium(II1) and trichlodegree of inertness of the complex may sometimes rotrianilinechromium( 111) were developed. depend on the base strength of the ligand. The 2. The reactivities of pyridine or aniline coreactivity of the trichlorotripyridinechromium( 111) ordinated to a metal do not differ greatly from and the trichlorotrianilinechromium(II1) toward those of the free ligands insofar as typical electromethanol was also quite unexpected as inetha- philic reactions are considered. no1 frequently is used as a solvent in studying 3. Pauling’s principle of electroneutrality pruthe reactions of such complexes. The conductivity vides a satisfactory qualitative theoretical explanadata indicate unambiguously that a rapid reaction tion for the effect of coordination on the reactivity occurs with methanol to produce conducting species. of simple neutral monodentate aromatic ligands. Measurements taken even a few minutes after the 4. Both of the chromium complexes examined solutions were prepared indicated essentially com- reacted very readily with methanol to give conductplete reaction. The reaction which occurs is pre- ing species. sumably one in which a chloride ion in the coorThis work was supported in part by a National dination sphere is replaced by a methyl alcohol Science Foundation Research Grant (No. 099 19). molecule. In view of the great tendency of chro(17) \V, Herwig and H. 13. Zeiss. J . O T E .Chrm., as, 1404 (1928).
[CONTRIBUTION FROM THE CHEMlSTKY DEPARThlENT O F xOKTH\VESTERS UXIVERSITY,
EVASSTO?;, ILLISOIS]
Mechanism of Substitution Reactions of Complex Ions. XVII.’ Rates of Reaction of Some Platinum(I1) and Palladium(I1) Complexes with Pyridine2 BY FREDBASOLO,HARRYB. GRAY3 AND RALPHG. PEARSON RECEIVEDDECEMBER 31, 1059 The relative reactivities of replaceable ligands in planar complexes rrf plaliuum(I1) foll(i\r the order: SO3- > CI- > Br- > I - > SCS- > S O : - . This is i h e same order 3 s for octahedral conlpleses of cobalt(II1) escept for a n inversion in the reactivities of the halides. 111 both systems labilities parallel instabilities. hnalogous palladium( 11) complexes of the t > p e Pd(dien)S+ react 106 to 106 times faster than corresponding platiiiurn(I1) cmnplexes.i Sickel complexes are again somewhat more reactive than palladiuni complexes.
Although there have been several kinetic studies5 on substitution reactions of square complexes, there is as yet little quantitative comparison of the reactivities of analogous platinum(I1) and palladium (11) complexes. There is also very little information on the relative rates of displacement of different ligands from similar complexes of the same metal. This paper reports a kinetic study of the replacement of a ligand X in platinum(I1) and palladium (1) Previ(,us paper in this series. R. C. F e u s o n , H. Ii. i;ruy ; ~ n d F. Basolo. THISJ O U K N A I . . 82, 787 (1960).
(2) T h i s invegtigation w a s partly supported b y ii y r a n t from the U. S. Atomic Energy Commission under contract AT(ll-l)-8Y-project h-0. 2. (3) D o w Chemical Company I’elloa. 1RBS-IF5,H. (4) Symbols used: dien = diethylenetriamine, tripy = 2.2‘,2”tripyridyl, p p = pyridine. ( 5 ) (a) F. Basolo a n d R.G . Pearsim. “hlechanismsof In(nx:inir Heact i o n s , ” John Wiley a n d Sons.I n c . , S e w York. N . Y , 1958, p p 172-212: ( h ) 0. R. Z r y n g i n t q e v a n d E 1:. Shuhochkina. 7 h u r . .Vmre. Khi?n,, 3 , 1139-1148 (195X); ( c ) I). Hanerje:t ;+nd K . K. T r i p a t h i , J . I n o r g . ?f S u r l r o r Chrm., 7 , 7X (1!15b); ( d ) T . S Iilleman, J . W. Rrishue onrl D. S. Martin. Jr , ’his J O r l K N h L , 81, 10 (195%); ( e ) A . A . GrinkiW4 , u d Y.N. Kukushkin. Xrsa’iun 1.I n o r g . C h e m . . 4, 2 . 13U (lW9).
(11) complexes of the types M(dien)X+ and 11(tripy)X+ by pyridine in aqueous solution. Experimental and Results Preparation of Compounds .-The known compounds were prepared by essentially the same methods as those described in the literature. This was the case for the halogen complexes of the types [Pt(dien)SjX,6[Pt(tripy)XIS’ :ml [Pti(tripy)X]X.* The Pd(dien)S IS conlpounds were prepared by almost the same procedure as that used for the corresponding platinum coinpounds. .\ reaction mixture containing 5 p. of PdCI?, D g . of tlieri,3HCi, 5 g. (if dien and 100 cc. o f H 2 0 was nilowed t o reflux for 8 h i . During this time a11 orange solution is formed arid some metallic palladium deposits. The solution was passed through a filter mid the filtrate was concentrated to 30 cc. on a steam-bath. To a 10 cc. portion of this solution was added 2 g . of solid NHICl and a yellow crystalline precipitate slowly separated. The yellow product was collected and washed with a sinall amount of cold water. I t was recrystallized from a small amount.of water, air dried at 50’ and found to weigh 1.7 g. (65Yc yield). Addition of 1 g. of NaBr to a second portion of the original filtrate yielded [Pd(dien)Br]Br and the addition of I g. of S a 1 to the third portion gave [Pd(dien)I]I. ( t i ) F. G . h l a n n , J . C h r m . So< , 4tiC (1VR4). ( 7 ) G . T. Slorgim and F. H. Burstall. i h i d . , 1498 ( l t 4 3 4 ) . ( 8 ) G. T. Morgan a n d F. H.Burstall, ibid., 1649 (1937).
Aug. 20, 1960
420 1
PLATINUM AND PALLADIUM COMPLEXES WITH PYRIDINE TABLE I ANALYSES OF Pt(I1) AND Pd(I1) COMPOUNDS
Compound
Pt, calcd. Pt, found
52.9 52.4 [Pt(dien)Cl]Cl 42.9 42.9 [Pt(dien)Br]Br' 38.4 35 G [Pt(dien)I]I 46.0 46.U [Pt(dieu)SCK ] XOab 47.2 48.0 [Pt(dieri)NO~]S03h -16.3 4 5 .0 [Pt(dien)NOz1x0: 50.5 49.2 [Pt(dien)CX]SO?b 48,G 48 . O [Pt(dien)Sa]SOk 36.7 36,4 [Pt(dien)py ]Br? [Pt(tripy)Cl ]C13H?O 36.4 35.6 31.3 ; < I7, iPt( tripy)Br]Br,2HzO 27.2 27.5 [Pt(tripy)I ]I.2H?0 34.1 34.0 [Pt(tripy)SOzIS02.3HaO [Pt(tripy)SCX]CSS 35.0 36. B Calcd.: C. 10.5; H , 2.81. Found: C. 10.6: complexes to explode on ignition.
Compound
[Pd(dien)Cl]Cl [Pd(dien)Br ]Br [Pd(dien)I]I [Pd(dien)NOz]SO:~ [Pd(dirn)SCS]CSS [Pd(dien)(py)[ B ( C ~ H K 12 ) ~ [Pd(tripy)Cl]Cl.I LO [Pd(tripy)Br[Br jPd( tripy)I ]I [Pd(tripy)NOplNO~.H%O [Pd(tripy)SCS]CNS [Pd(tripy)(py)][B(caH~)r]z [Pt(tripy)(py)][B(C6H6)4]~
H.2.77.
Pd, calcd.
C, 17.1; H , 4 . 6 3 C, 13.0; H , 3 52 C, 10.4; H , 2.80 s,22.0 9,21.2 s,6 . 1 8 C, 41.6; €I, 3 . 0 0 C, 3 6 . 0 ; H , 2.20 C, 3 0 . 4 ; H, 1.86 C, 4 0 . 0 ; H , 2.89 C, 44.7; H , 2 . 4 1 s,5.34 s,4 . 9 4
Pd, found
C, 17.1; H, 4.44 C, 13.1; H, 3 . 4 8 C, 10.5; H, 2 . 7 2 N, 21.6 ii-, 20.7 X, 6.42 C, 41.4;H , 3.45 C, 3 5 . 6 ; H, 2.35 C, 31.2; H, 2.18 C, 3 9 . 4 ; H , 2 . 7 7 C, 4 4 . 2 ; H , 2 . 3 5 s,5 . 6 8 s.5 . 2 6
Analysis of P t is low because of loss due t o tendelicy of nitrate
Compounds of the type [M(dien)T]h'Os were all preTABLE I1 pared by the reaction of the halogen compound [M(dien)RATES OF THE REACTION OF SOME PLATISUM(II) COMPLEXES X ] X with two equivalents of AgSO,. After removal of WITH PYRIDINE IN WATERAT 25.1" AgX, the resulting aqueous soiution, presumably [M(dien)(H,O)]( SO3)2, was a,lowed to react with one equivapy -c Pt(dien)(py)+2 XPt(dien)X+ lent o f IiaT. For example, a reaction mixture containing hobad. X min.Complex Pyridine, M 2 g. of [Pt(dien)Br]Br, 1.5 g. uf A g S 0 3 and 30 cc. of water [Pt (dien )SOa]i';Oa . . . . . Aquates, fast was heated on ii steam-bath and occasionally stirred for a period of 30 min. The AgBr was removed on a filter and 0 00090 4 23 x lo-'" [Pt(dien)Cl]Cl washed with a small amount of water. The filtrate plus .00592 2 09 x 10-3 washings was divided into four equal portions. T o one of ,0096 3.i i x 10-3 these was added 0.07 g. of Na& and the solution was concentrated to 5 cc. on a steam-bath. The white crystalline 2 . 4 x 10-4 [R(dien)Br]Br .0006product then separated upon cooling the solution in an ice.00090 3 . 0 3 x 10-4* salt bath. The crystals were collected on a filter, washed 2 94 x 10-4 .00090" with a minimum amount of ice-mater followed b\- acetone. 1 . 0 3 x 10-3 ,00372After air drying a t 50", the salt, jPt(dien)Xi]SOi, weighed 0.3 E. f87% vield). 1.38 X .00592 Cknpo&hs of'the type [M(tripy)l']Y were prepared by 2.10 x 10-3 ,0096the reaction between the halogen compound and an excess 2.56 X ,0126 of Sa\'. For example, 0.2 g. of [Pd(tripy)C1]C1.H20 7.95 x 10-3 ,0372was dissolved in 5 cc. of hot water and 0.7 g. of NahT02was added. -411 immediate precipitate separated and was col,0621.29 X lected on a filter. After water and acetone washes, the 1 . 4 7 X lo-' [Pt(dien)I]I .00090 solid was dried a t 50" and found t o weigh 0.2 g. (95% 6.02 X lo-' ,00592 ).ield of [Pd(tripy)SOp]SO~.HtO). The pyridine derivatives, [M(dien)py]X? and [M(tripy),0096 9 . 3 x 10-4 py]X*, were prepared by the reaction of the corresponding .00090 1 . 2 x 10-6 [Pt(dien)Na]NOa halogen compound with an e x e s s of pyridine. The com,00592 5.0 X pound [Pt(dien)py]Brz was isolated by evaporating a n aqueous reaction mixture of [Pt(dien)Br]Br and excess .00090 3 . 7 x 10-6d [Pt(dien)SCN]NOs pyridine to dryness at 50'. Under similar conditions the .00592 1.82 X other compounds yielded only starting material. They were prepared by allowing the parent compound to react with [Pt(dien)N02]NOs .00090 Slow excess pyridine a t room temperature for 30 min. Then the 3.0 X .00592 desired complex was precipitated by the addition of excess .OS92 1 . 5 X lo-& NaB( C C H ~ ) ~ . Analyses for all of the compounds are reported in Table I. [Pt(dien)C1;]NOs .00090 Slow The platinum analysis was performed by ignition of the ,00592 1 . 0 x 10-6 compound and weighing the residue. This method usually k is 9.13 X lO-'at 33.3' and 3.33 X 10i3a t 50". k i g gave low results for the nitrate salts which tend to explode on a t 50 . iidded subignition. The infrared spectra of all of the compounds were 6.16 X 10-4 a t 33.3" and 2.39 X a t 33.3' a n d k is 1.02 X determined by the KBr wafer technique. All of the M(dien)- stance, 0.00080 AI, NaBr. S spectra are very similar as are also all of the M(tripy)X + 5.36 X 10-6at50 . e k i s 3 . 7 3 X 10-4at500. spectra. Conductivity measurements on aqueous solutions Standard aqueous solutions of the complex and of pyridine of these compounds showed them to be univalent electrowere placed in separate compartments of a Y-shaped conlytes. ductance cell and thermostated. After reaction temperaDetermination of Rates of Reaction.-The reactions with ture was reached, the reactants were mixed by tipping the pyridine were followed by measuring changes in electrical conductivity of the solution under investigation. The cell. In this way it was possible to take a resistance reading within about 10 seconds after mixing. The conductconcentration of the complex was in the range between 0.0004 and 0.001M and the pyridine concentration was ance data were analyzed as described earlier9 and the obvaried as shown in the Tables. Before adding pyridine, the served first order rate constants calculated are given in Tables 11, 111 and IV. Figure 1 shows that good first order conductances of the solutions of the complexes corresponded t o one to one electrolytes and did not chnrlge with time. plots were obtained through one half-life although in some Thus no hydrolysis occurred. The change in conductance cases the pyridine concentration was not very much greater o n adding pyridine corresponded to the reaction, e . ~ . (g) D. Banerjea. 1'. Bamulu and R . G . Perrsun. THIS JUORNAL, 79, Pt(dien)X' 4 py --+ Pt(dien)py+* S - (1) 4066 (1957).
+
+
+
+
Vol. 82
FREDBASOLO, HARRY B. GRAYAND RALPHG. PEARSON
4202
1.0
0.2
c
/
1
1000 2000 3000 Minutes. Fig. l.--First order rate analysis a t different pyridine 0.01 0.02 0.03 0.04 0.05 0.06 concentrations a t 25" : concn. [Pt(dien)Br]Br, 0.0004 M; Concentration py, X. concn. py: A,0.0009 M ; D,0.003T2 ill; 0,0.00592 M ; -, Fig. 8.-Dependence of k o a . on concentration of pyridine calculated limiting slope (kl). for its reaction with [Pt(dien)Br]Br a t 25". than the complex concentration. The reason for this is discussed later. Reactions in which the calculated infinity important a t low pyridine concentrations and kobsd. resistance was reached a t the first reading (10 sec.) are approaches kl which means that k o w . resembles labelled "Fast" in the Tables. Duplicate runs were made more closely a true first order rate constant. This in many cases with reproducibility being about 5%.
is supported by the observation that good first order plots are obtained (Fig. 1) a t low pyridine From the rate data in Table I1 and I11 i t may be concentrations when its concentration is only seen that the reactions are not of simple order with slightly greater than that of the complex. Estimates respect to pyridine. A more comprehensive study indicate that the second order process must not contribute over 20% to the total rate a t 0.0009 M TABLE 111 RATES OF THE REACTIONOF SOME PALLADIUM(II) COM- pyridine and 0.0004 M [Pt(dien)Br]Br.
Discussion
PLEXES WITH
Pd(dien)X+
PYRIDINE IN WATER
+ py +Pd(dien)(py)+2+ XPyridine,
ko:d
M [Pd(dien)Cl]Cl 0.00124 [Pd(dien)Br ]Br ,00124 ,00124" [Pd(dien)I ]I ,00062 ,00124 ,00248 [Pd(dien)SCX]N03 ,00124 ,00124 ,00248 0124
0
Complex
X mh-1
25.10
Fast .. Complete in 15 Fast sec. Fast 1.53 Fast 1.95 .. 3.35 .. (1) 3 . 9 2 X 10-' 2.52b (2) 3 . 9 8 X lo-' 2.68" 4 . 9 2 X lo-' .. 1.53 .. [Pd(dien)NOz]NOs ,00124 2 . 0 X lo-' 1.98 ,00248 2 . 2 2 x 10-1 .. ,0124 3.22 X 10-l .. Added substance, 0.00080 M NaBr. k is 4.36 at 33.3". kis4.57at33.3".
of the reaction order in these systems has been made and will be published elsewhere. These studies indicate that a general rate law for square complexes reacting with such a reagent is kabsd =
kl
+ kl[Y]
(2)
where k o b d is the observed first order constant. The data collected here all seem to conform to such an equation and it is possible to extract rate constants kl, presumably involving the solvent as nucleophilic agent and k2 with pyridine as the reagent. For example, a straight line is obtained by plotting kobsd. versus pyridine concentration for the reaction between [Pt(dien)Br]Br and pyridine (Fig. 2), with k2 the slope and kl the intercept. Furthermore the second order process becomes less
TABLE IV RATESOF REACTION OF SOMEPLATINUM( I I ) ASD PALLADIUM (11) COMPLEXES WITH PYRIDINE IN WATER M(tripy)X+ 4-py +M(tripy)(py)+*-I-XPyridine, Complex
[Pt(tripy)Cl]Cl [Pt(tripy)Br ]Br [Pt(tripy)I]I
[Pt(tripy)SCN]CNS
24
kobd
00
X min.-' 25.10
0.00124 .. ,0124 6 . 9 X IO-' ,00124 .. ,00062 5.0 X lo-' ,00124 5 . 5 X lo-' ,00258 1.4 ,0124 Fast ,00124 .0124
..
..
Fast' 4.0 Fast" . . . :3.9 ...
...
6.15 8.90
x x x
10-3
10-2
[ P t ( t r i p y ) N O ~ ] N O ~ .00090 .. 3.06 10-3 ,00124 .. 3.50 X ,00592 .. 5.30 X l W Z ,0296 .. 1.01 x l o r 3 Fast ... [Pd(tripy)Cl]Cl ,00124 Fast ... [Pd(tripy)Br]Br ,00124 Fast , . . [Pd(tripy)I]I ,00124 Fast ... [Pd(tripy)SCN]CNS ,00124 Fast ... [Pd(tripy)NO~]NOp ,00124 a Reaction complicated by a slower secondary process.
A "dissociation" mechanism6" in which groups such as water or pyridine are added above and below the plane of the complex and which move into the metal atom to displace the group X may be used to visualize the course of the reaction. A five coordinated intermediate, probably a square pyramid, is formed which rapidly reacts with various potential ligands in the solution. An intermediate
PLATINUM AND PALLADIUM COMPLEXES WITH PEWDINE:
Aug. 20, 1960
aqua complex would be reactive and rapidly convert to the pyridine complex. Adding NaBr had no effect on the rate of reaction of [Pt(dien)Br]Br or [Pd(dien)Br]Br with pyridine. This may seem surprising since i t should be possible to inhibit “dissociative” type reactions by adding other reagents which would compete for the active Intermediate. However, it is likely that pyridine is much more efficient than the bromide ion in capturing the intermediate, since pyridine binds more strongly.1° These reactions go to completion even when excess bromide ion is added. Using either kl or kr as a measure, the order of decreasing reactivity of different X groups in the Pt(dien)X+ series is S O : { - > C1- > Br- > I - > S a - > S C S - > S O ? - > CNThis nicely parallels both the order of increasing bond strength1”>l1 and the position of these ligands in the trans effect series.& Thus, a t least in these examples, strongly trans activating groups are difficult groups to dislodge. The total separation in rate is about 2000 in going from Pt(dien)Cl’ to Pt(dien)CN+. This is approximately the same spread as is found for octahedral cobalt(II1) complexes where the order of reactivity is12 NOs- > I- > Br- > Cl- > SCX- > S O ? It is of considerable interest that the order of reactivity for halide complexes is reversed in going from cobalt(II1) to platinum(I1). Thus, the changes in stability paiallel the changes in lability in both cases since from equilibrium datal2 cobalt(II1) holds the halogens in the order C1- > Br- > I-. This indicates that a-bonding is more important for platinum(I1) than for cobalt(II1). For Pd(dien)X+ the general order of reactivity seems to be the same as for platinum but the rates are much closer together. For example, there is only a i-fold difference in rate between Pd(dien)I+ and Pd(dien)NOz+, whereas for platinum the factor is 200. This supports the view that a-bonding is less important for palladium(I1) than for platinurn(11) complexes.13 Comparing the results in Tables I1 and I11 reveals a great difference in reactivity between analogous Pt(I1) and Pd(I1) complexes. For example, Pd(dien)SCN+ reacts 700,000 times faster than Pt(dien)SCN+. This is a t variance with some of the results reported by Banerjea and T r i ~ a t h i . ~These ‘ workers found most reactions of palladium(I1) complexes too fast to measure a t 36”, but occasionally they report rate constants which indicate about the same reactivity for corresponding platinum and palladium complexes. As a comparison, they give data on the reaction tmns-Pd(NHa)sp)-CI’ ~~
~
+ pv d
Pd(NHa)s(py)s+*
+ C1-
(3)
(10) S Ahrland. J. C h a t t and Ii. Davies, Quart. Rev., Vol. XII. No. 3 (1958). (11) J. Chatt, L. A. Duncanson, R. L. Shaw and L. M. Venanzi, Discussi072s Faraday Soc., 26, 131 (1958). (12) Reference sa, page 121-122. (13) J. C h a t t , L . A. Duncanson and L. M. Venanzi, J. C h e v . SOL., 4466 (195.5).
4203
from which a half-life of 280 min. a t 36’ can be calculated. We find the very similar reaction
4-py d Pd(dien)pyLz+ C1- (4) is complete in 10 sec. a t 0’. It is unlikely that the pyridine substituent in ( 3 ) can make such a Pd(dien)Cl+
difference in rate. For example, the rates of acid hydrolysis of Pt(bipy)Cl* and Pt(en)Clz are 0.7 X and 3.2 X X min.-’ l 4 a t 25’. The rates of reaction of analogous nickel(I1) complexes are much too fast to study by our method. However, recent studies15on some sterically hindered systems such as M(PEt~)z(o-tolyl)CI show relative rates of reaction with pyridine of 5,000,000:100,000: 1 for Ni(II), Pd(I1) and Pt (11), respectively. For comparison the relative rates of acid hydrolysis of Yf(NH3)6Br2+complexes are about 4,000: 100: 1 for Co(III), Rh(III), Ir(III), respectively.12 This much larger spread in rates for the nickel triad may be due to the greater ease with which Ni(I1) and Pd(I1) are known to add a fifth and sixth group relative to Pt(I1). Thus the observed results are in agreement with a “dissociation” mechanismbain which groups are added above and below the plane of the complex. This process is not involved in the six-coordinated complexes of the cobalt triad and the differences in their rates of reaction are found to be much smaller. Table IV gives the rates of the reactions of Pt(tripy)X+ and Pd(tripy)X+ with pyridine. The Pt(tripy)X+ complexes react 1000 to 10,000 times faster than corresponding Pt(dien)X+ complexes. This is probably also the case with palladium(I1) but no good comparisons can be made, since the Pd(tripy)X+ complexes are all too reactive to measure. This result is somewhat surprising in view of the fact that Pt(bipy)Cl, and Pt(en)Cls do not differ appreciably in their reactivity. Since 2,2‘-bipyridine shows no great trans labilizing effect, i t is unlikely that the more rapid reactions of the 2,2’,2”-tripyridyl complexes are the result of a trans-eff ect. The structures of some 2,2”2”-tripyridyl complexes of bivalent metals have been determined by Corbridge and COX.'^ They found that Zn(tripy) Cl2 is five-coordinated and has a distorted trigonal bipyramid structure. The tripyridyl rings remained coplanar, but the N-Zn-N bond angles were less than 90” (72 and 79”). However, conductivity measurements in nitrobenzene made by us indicate that [Pt(tripy)X]X and [Pd(tripy)X]X complexes are 1: 1 electrolyte^,^^ so i t is likely that they have strained planar structures. This strain could render the complexes unstable and explain their high reactivity. An attractive mechanism, consisting of a M-N bond breaking in a slow step, also has been suggested to explain these rapid reactions. (14) See reference Sa, p. 194. (15) Detailed kinetic studies on these compounds will he published
in J . Chem. S O L . (16) D. E. C. Corbridge and E. G. Cox, i b i d . , 594 (1956). (17) Molar conductance of jPt(tripy)IlI is 22.2 cm.:mole-‘ ohm-’. of [Pd(tripy)SCS]CXS is 20.0 a t 2 5 O . (18) L. hl. Venanzi, private communication.
