59

Journal of OrganometalIic Chemistry, 212 (1981) 59-70 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands

LEWIS ACIDITY OF CARBOXYETHYLTIN CHLORIDES, Cl,SnCH,CH,CO,R AND C12Sn(CH,CH2C02R)2

DOUGLAS MAUGHAN, JAMES L. WARDELL *,

Department of Chemistry, University of Aberdeen, Meston Walalk, OId Aberdeen A B9 2 UE

(Great Britairz)

and JOSEPH W. BURLEY

Akzo Chemie UK_ Ltd., HoIIingwood Road, Littleborough. Lanes. (Great Britain)

(Received November 25th, 1980)

Summary

The Lewis acidity of estertin chlorides, C13SnCH2CH2C02R (R i Me, PI?, Ph and H) and C12Sn(CH2CH2C02R)2 (R = Me and Pr’) has been investigated. Stability constants (K,, K2 and KS) for adducts of these Lewis acids with nitrogen donors, e.g. D = bipy, phen, py, quinoline and aniline, have been determined in CHzClz solution at 25 f 1°C by UV and IR methods. From com-

RSnCls + D ZRSnCl, - D

RSnC&, - D + D zRSnC13 - 2 D

parisons of stability constants, the following conclusions can be made: (i)

C13SnCH2CH&02Me appears as strong a Lewis acid as MeSn% towards bidentate ligands and a single py molecule (from K1 values); (ii) C13SnCH&H2- COzMe - D (D = monodentate ligand) is a poorer acceptor than MeSnCls - D but comparable to Me#nCl, (using K2 and K3 values) towards D, and (iii) C12Sn(CH2(=H&02R)2 is a weaker acceptor than ClzSnMez towards phen and bipy (from K3 values). Qualitatively it was established that for C13SnCH&H2- CO*R, the sequence of acidity is R = Ph > Me > Pr’ > H towards bipy. Adducts of Cl,SnCH&H2C02Me and Cl,Sn(CH,CH,CO,Me), with phen and bipy have similar MSssbauer parameters to those for other phen and bipy adducts of organotin trichloride and diorganotin dichloride.

0022-328X/81/0000-0000/$02_50, @ 1981, Elsevier Sequoia S-A.

60

Introduction

The Lewis acidity of. organotin halides has been frequently and variously studied [I]. The majority of the studies have been concerned with complex formation with donor molecules. The dominant concern in these studies has been the investigation of structural and spectroscopic properties of solid adducts. Less attention has been paid to the determination of formation constants of the complexes in solution [l-4]. These data are of value since they are quantitative measures of acceptor strengths and have been used to derive sequences of acceptor ability; e.g. PhSnC13 > PhtSnClz > Ph$nCl towards ar,a-bipyridyl (bipy) and also Bu,P in PhH solution [a], PhSnCl, > MeSnCl, > BuSnCl, towards aniline donors in diethyl ether solution 1.5’1 and Ph,Sn& > Me,SnCl, > Bu,SnCl, towards pyridine (py) in PhH solution [a]. As exemplified, all these sequences involve simple alkyl- and aryl-tin halides.

While there are many known functionally-substituted organotin halides, few have been studied in regards to their Lewis acidity. When the functional substi- tuent is itself a donor group, e.g. an amine or a carbonyl group, there exists the possibility of intramolecular complexation tvithin the organotin halide. Crystal structure determination have in fact indcated such intramolecular com- plexations, e.g. in 2-[I-(S)-Me2NCH(Me)]CsH,SnMePhBr [6] and the carbonyl- substituted ethyltin chlorides, C13SnCH2CH2C02Me (I), C&Sn(CH,CH&O,Me), (II), and C12Sn(CH2CH2CONH2)2 [7] _ Compound I is a distorted trigonal bipyramid with one chlorine and the coordinated carbonyl oxygen axial while the organic residue and the remaining two chlorines are equatorial; compound II is a distorted octahedron with the two chlorines occupying c&sites and the two organic groups mutually trans.

The intramolecular carbonyl coordination is also indicated by the v(C0) values, e.g. for I, v(C0) is ca. 1660 cm-’ and for II Y(CO) is ca. 1680 cm-‘, compared to v(C0) = ca. 1740 cm-’ for simple esters, such as MeCO*Me [7-91. For all carboxyethyltin trichlorides and bis(carboxyethyl)tin dichlorides [8,9] as well as C12Sn(CH2CH&ONH,)2 [?I, X2Sn(CH,CH2COR)2, X = Cl, Br or I; R = Ph or alkyl [lo], Me2CISn(CH2),COR, n = 2 or 3; R = Me or Ph [ll] and Ph,ClSn(CH,),C(Me)=X (X = 0 or NOH) 1121, these is compelling spectral evidence for intramolecular coordination_

Kuivila et al. [11] have shown that an external donor, pyridine, can compete with the carbonyl coordination to the tin centre in Me,ClSn(C&),COR (III). Pyridine coordination to III results in an increase in the v(C0) value. Although there appeared to be equilibria involving III and pyridine, no attempt was made to determine the equilibrium constants, nor even the stoichiometry of the adducts.

Poller and Abbas [12] isolated adducts of X2Sn[(CH2)sCOMe]2 with bipy; bipy complexation led to increases in the Y(CO) values (e.g. to 1703 from 1675 cm-’ for X = Br). MGssbauer parameters for these adducts suggest similar struc- tures to those of simple dialkyltin dichloride-bipy adducts [13].

We have been studying how such intramolecular coordination affects the Lewis acidity of carboxyethyltin chlorides. As well as the preparation of representative solid adducts, we have looked at equilibria in solution and now report our findings.

Experimental

Carboxyethyltin chlorides, Cl$nCH,CH2C0,R, R = Me, Ph, Pr’ or H, and C12Sn(CH&H2C02R)2, R = Pr’ or Me, were prepared as published [S] _ Me-LSnClz was a commercial sample. Analytical data was as expected for all the tin chlorides. Solvents were dried over CaH, and distilled before use. Donors were all recrystallised or redistilled commercial samples.

Mbssbauer spectra were recorded as previously reported [ 14]_

Determination of equilibrium constants These were determined from IR or UV data, obtained at 25 f l°C in CH,Cl,.

Solutions were made up and optical cells filled within a dry-box. Absorptions were measured at suitable wavelengths for a number of solutions containing different compositions of a particular accep tar-donor pair; see Table 1 for the wavelengths used. Figs. 1 and 2 illustrate the spectral changes for the bipy-Cl,SnCHzCH2COzMe system and in Fig. 3 is shown the IR spectral changes for the C1,SnCH,CH,COzMe-py interaction. Concentrations of each donor/ acceptor pair were taken to give as great a range of complexation as possible. However for the weaker donors (e.g. anilines) complete complexation could not be achieved_ The equilibrium constants were calculated from the absorp- tion data using standard equations ]3,5] _ In -Table I z.re listed the equilibrium constants.

Solid adducts

Solid adducts were prepared by adding hexane dropwise to CH,C& solu- ._ tions containing appropriate molar ratios of the acceptor and donor until

TABLE 1

STABILITY CONSTANTS FOR ADDUCTS OF C13SnCH2CH_ 7202Me AND DOSORS. D; IN CH2C12 SOLUTION AT 25 * l°C

DOllOZ log ICI log R2 Wavelength used for measurement (cm-l)

Pyridine Quinoline

4-MeOCgHqNH2

4MeC6HqNH2 PhNHz

Bipy

5.28 4.90

5.36

5.08 4.60

>.5 2.15 + 0.1 2.27 ? 0.1 2.45 i 0.1

1.85 f 0.1 1.50 + 0.1

>5 c.d

cY.d-Biquinolinyl 2.G5 +_ 0.1 =

0.8 2 0.1 Y(CO) 1500

-

-

- -

a hmax_ of donor and adduct (in UV); ’ A,,_ of donor (in UV) _ c Chelate complex: d Data did not completely satisfy a simple 1/l equilibrium.

K1 = [C13SnCH+H2CO2Me - D]/[D][C13SnCH2CH$02Me]

K2 = [Cl$SnCH2CH2C02Me - 2D]/[D][Cl$nCH2CH2CO2Me - Dl

KA = dissociation constants of DH+ in water at 25OC.

62

_ 0.0

.[ 0.1

w z” 2 $cj 0.2- u-3 m a

0.4-

I I I , , I I I ,

1750 1650 ’ 1750 1650 ’ 1750 1650 ’ 1750 1650

CM-’

Fig. 1. I&a-red’spectra in the carbony region for bipy-ClgSnCHpCH2C02Me interaction in CHzC12 solution at 25 * 1°C. [C&WCH2CH+02Me] = 1.44 X 101 M: [bipyl = 0. (A). 0.288 X lo-3 M (B): 0.86 X lO-3 fir (C); 1.44 X 10” lW (D).

1.01 1 0

250 300 “nl

Fig. 2. UV spectra for the bipy-C13SnCH2CH2CO2Me interac+on.&.C&C!z sqlution at 25 i l°Ct [bipyl = 5 X lo* M; [C1~SnCH~CH~CO~hkl = 0. (A); 2.5 X lo* 11-I. (B); 5 X lo+ AM, (C); 10 X lo* fir

CD).

TABLE 2

ANALYTICAL AND OTHER DATA FOR CARBOXYETHYLTIN CHLORIDE COMPLEXES

Compound Analysis talc. (Found) (%)

C H Cl N

MeO2CCH2CH2SnCl3 - bipy 35.9 3.2 22.7 6.0 (35.7) (3.1) (23.0) (5.8)

hIe02CCH2CH2SnCl3 - phen 39.1 3.1 21.6 5.7

(39.5) (3‘1) (21.3) (5.5)

<Me02CCH2CH~)~SnC12 - bipy 41.6 13.6 5.4

(41.9) ,t::,

(13.4) (5.2) <MeO+CH2CH2)2SnCI2 - phen 44.2 .4.1 13.0 5.2

<44_4) (S-9) (12.9) (5.3)

ma. (“Cl v(C0) (KBr) (cm-‘)

203-206 1728

198-200 1725.1735. o 1745 1728

139-142 1720 = 1730 1750

a S~nples recrystaBised from CH+l+exane solutions.

63

1 I

l&O I

1750 1650 CM-’ 1600

Fig. 3. Infra-red spectra in the carbonyl region for pyridine--C13SnCH2CH2CO2Me interaction in

CH2CI2 solution at 25 i l°C. [CI$nCH2CH2C02Me] = 1.55 X 10-2 M. [pyridine] = 0 (A): 0.389 X 10m3 fi2 (B); 0.778 X 10m3 M (C) and 1.55 X 10M2 M (D). [CI$nCH2CH2C02Me] = 2.64 X 10-2 I)f;

[pyridine] 2.64 X low3 M (E); 10.6 X 10s3 M (F); 16.0 X 10m3 df (G).

precipitation resulted_ Recrystallisations were attempted from hexane/CH2C1,. Analytical and other data for bipy and phen complexes are given in Table 2.

Results and discussion

Solid complexes of I and II with bide&ate ligands, such as bipy and phen, were the easiest to prepare. Mbssbauer data for these compounds are given in Table 3. Also included in Table 3 are published data for BuSnC13 [X5,16], 0ct&nC12 1151 and Br2Sn(CH2CH2CH2COMe)_2 [12] complexes. For all the RSnC13 complexes [R = Bu and Me02CH&H2 as well as Phi, a common structure is suggested from the similar MSssbauer parameters. Mullins 1161 proposed octahedral structures with two chlorides mutually tram for

TA

BL

E 3

TIN

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1.46

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cn

1.60

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Oct

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59

Oct

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l2 *

phen

I,

56

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ha(C

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* blp

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66

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3.93

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65

RSnCls - L-L (IV), R = Bu or Ph, L:L = phen or bipy, and this must be considered also for IV, R = CH2CH2C02Me. All R2SnX2 - L-L (V) (R, X = Me, Cl [4,17] Ott, Cl [15] and MeCOCH2CH,CH,, Br 1121) have similar Mijssbauer parameters (and hence structures) to those of V, (R, X = Me0&CH,CH2, Cl). The quadrupole splittings values ca. 4 mm/set, are those expected, from point- charge calculations [18], for octahedral complexes with trans-R,Sn groups.

Complexation of I and II by these chelating ligands frees the carbonyl groups and results in the expected increases in v(C0) (Table 2). The phen adducts of both I and II, when obtained from CH2C12/hexane solutions, gave three car- bony1 maxima as indicated in Table 2, yet only one v(C0) was found for the adducts obtained from PhH/CH2C12 solution [e.g. for phen-I, v(C0) 1738 cm-‘]. We assume that these carbonyl absorptions are due to different conforma- tions. The bipy adducts, on the other hand, consistently gave just one absorption.

Adducts of II and related diestertin dichlorides with monodentate ligands could not be isolated. Even adducts of monodentate ligands with I proved difficult to isolate in a pure state, e.g. attempts to crystallise crude Cl,SnCH,CH,- CO,Me - py (initially precipitated from a CII,Cl, solution containing a l/l mole ratio of components by addition of hexane) led to the breakdown of the complex and recovery of I.

IR spectra in CH2CL2 solutions For many donors, there were IR spectral indications for interactions with I

and II in CH2C12 solution, even if solid adducts could not be obtained, see Table 4.

The chelating ligand, Ph,P(O)CH,(O)PPh,, as well as bipy and phen, clearly complexes strongly and practically completely with I. This is borne .out by v(C0) for solutions containing equimolar donor and I, being at ca. 1730 cm-’ with negligible-absorption at 1670 cm-‘. Several monodentate ligands, e.g., pyridine, quinoline, (MeO),P and MerSO, also coordinate to I strongly, if not all completely at a l/l ratio of components, to give hexacoordinate tin, e.g. VI and VII. The carbonyl group is still coordinated to tin as shown by the v(C0) values. The l/l complexation by these monodentate ligands causes slight shifts (decreases) in Y(CO) as well as decreases in EA as compared to values in I. Such changes, albeit small, can be used diagnostically for l/l complexa- tion *. The small shifts in v(C0) indicate little changes in the character of the

* Confirmation of complexation can be gained Tom other spectral changes. e.g. for the quinoline interaction. decrease in tbe absorption at 1500 cm-l and for the Me2SO inteI;lction development of new absorption at 990 cm-l [complexed v(SO)].

66

TABLE 4

C_4RBONYL FREQUENCIES AND INTENSITIES FOR MIXTURES OF C13SnC!H2CH2~OZMe (A) AND

DOh’ORS (D) IN CH$Iz SOLUTION AT 25 + 1%

Donor

-

Ph3P (Me0)3P

CAIICDI Y<CO) <cm-‘) EA X 10-Z a C0mmelltS -__- ___.-__

l/O 1668 5.6 -

111 1667 5.3 No interaction

111.5 1668 4.3 l/l Complexation; carbonyl group stilI coordiated

Ph+sO Me2CO Me2SO

QuinoIine phen

bipy

PY

111

l/l 111.4 l/5

l/l 111 l!l

l/l l/l4

1730

1665 4.85

1670 5.4

1660 3.7

1725 0.6 1665 4.3 1733 4.35 1730 4.65

1648 a_3 1730 4.5

4.3 Chelate complex. carbonyl free Slight interaction

No interaction l/l and l/2 compkxes l!l complex

Chelate complex Chelate complex l/l complex l/2 complex

=E A = apparent molecuk%t absorption coefficient.

C=O bond as the additional ligand complexes with the tin centre. In going from the five-coordinate I to the six-coordinate adduct, e-g_ VI and VII, one might assume, in the absence of other effects, that v(C0) should increase [towards the v(C0) value for a free carbonyl group], since the :C=O + Sn interaction should be reduced and as a consequence greater double bond character in the carbonyl bond would result. However this is not so and some compensating effect must operate. This compensating effect could be back bonding from tin to oxygen (using the carbonyl anti-bonding orbital) as the additional ligand complexes. An additional cause could be the structural change in going from I (trigonal bipyramidal) to VI and VII (octahedral).

For the more powerful monodentate donors (D), e.g. pyridine and Me$O, addition of donor beyond a l/l mole ratio leads to adducts of 2(D)/l(I) stoichiometies and development of v(C0) at ca. 1730 cm-‘.

Equilibrium constrrnts Equilibrium constants are listed in Table 1. The major study was made with

I. Complexation by pyridine, as discussed earlier, occurs in two stages (Scheme

1). However the first pyridine complexes too strongly for accurate measure- ment. A lower estimate for log K, would be 5. The second equilibrium con&u-&

. K2 was more accessible_ In Table 5, are listed published equilibrium constants for organotin chloride-

pyridine interactions. Prom the data, it is possible to compare the relative acidities of I, RSn& (R = Bu or Ph) and R$nCl* (R = Me or Bu) towards pyridine. The data has been gathered in different solvents, namely PhH, Ccl4 and CH,Cl,. However little differences are to be expected for log Ki values

67

SCHEME 1

PY

ct-12 CH2

/ ‘C-OMe K1 J /C"2c"2 Cl$n

Fi/

C13Sn

\ o /IC--OMe

PY

-l. Cl3 Sn CH2CH2C02Me

t PY

(5, vtco1 1730 cm -1

obtained in these non-coordinating solvents. The temperature differences can also be ignored and so the log K1 values can be compared without amendment.

Satchel1 and coworkers [19] reported that the log KI for the l/l 3,5-dichloro- pyridine/PhSnCl, complex in E&O solution was 0.92. From the pK, values of 3,5dichloropyridine (0.76) and pyridine (5.28), one can estimate the log KL value for PhSnCls-py to be at least 5 in E&O and certainly also in CH,Cl,.

The intramolecular coordination in I cannot increase the electron density too much on tin as this would lead to a very significant difference in the Lewis acidities of I and PhSnC13 towards a monodentate donor. Different reorganisa- tion energies for PhSnCl, and I on complexation (i.e. due to changes in hybridisation and structures) could have some influence. That no intramolecular complexation has to be undone in I on order to accommodate the first pyridine moJecule also must be important. When such intramolecular complexation has to be removed, as happens when the second pyridine complexes to I, the log K, value is considerably reduced. From the data, the acidity of MeOz-

TABLE 5

COMPARISON OF STABILITY CONSTANTS FOR PYRIDINE-ORGANOTIN CHLORIDE <A) ADDUCTS

RnSnC4-t, log KI log K2 log Ii Solvent/Temp (“C)

Me3SnCl 0.28 PhH/BO cC14/2i’

MezSnCl2 1.23 1.11 PhH/BO BuZSnClp 0.80 0.70 PhHl30 Me02CCH+H$nC13 >5 0.85 CHzCl2/25 BuSnCl3 25.6 PhH130

KI = CA ~PY~~CPYI[AI~~~ = CA *PY~I/CA .PYICPYI:K= CA*PY&CA~[PYI~

Ref.

25 26

2 2

This work 2

66

CCH&H,SnCls - py appears only comparable to that of R2SnC12 - py (R = Me or Bu).

The log K1 values for the aniline adducts enabled comparison of acidities of I and PhSnC13 towards another type of monodentate ligand, anilines, to be made. The aniline interactions were followed by UV spectroscopy. As observed for other tin halideaniline interactions [ 5,211 weak long-wavelength charge- transfer absorption was observed for the adducts. Complete l/l complexation was not achieved even with the maximum concentration of I used and hence x mar_ for the charge-transfer absorption could not be determined with any accuracy; under the conditions used, [I] > [D], adducts of stoichiometries 2D/lI were not expected.

Correlations have been established between pK, for anilines and log K1 for aniline-PhSnC& complexes in ether at 23°C [5] (eq. 1) and in dioxane at

log K, = 0.80 pKa - 1.40 (1)

log K, = 0.79 pKa - 0.94 (2)

25°C [ZO] (eq. 2). Satchell and coworkers 1201 actually measured the log K, value (= 2.68) for the PhSnCl,-PhNH, complex in dioxane at 25°C. This value and those calculated from the correlations are listed below:

PhNH*-PhSnCl, 2.28 (Et*O) 2.68 (dioxane) 4-MeC6H4NH2-PhSnCl, 2.66 (EbO) 3.09 (dioxane) 4-MeOC&NH2-PhSnCl, 2.89 (EbO) 3.29 (dioxane)

Some differences in log K1 values in ether and in non- or weakly coordinating solvents such as CH2C12 are generally to be expected. For example, for SnC14 complexes, K, values in Et,0 are ca_ 40 times less than in o-dichlorobenzene. For the weaker acceptor, SnBr,, the difference reduces to 3 times 1221. It is anticipated that for the still weaker Lewis acid, PhSnCl, [5] the differences between K, values in E&O and non-coordinating solvents (e.g. CH&l,) should be small. With this in mind, we conclude that the acidity difference between PhSnC13 and I towards aniline bases is between 2-5 times. Furthermore, the relative acidity sequence of PhSnClJMeSnClJBuSnCl, was established as 12/3/l [5] d an so, for example, I has a comparable acidity to that of MeSnCl, towards anilines.

The quinoline-I interaction (eq. 3) was studied both by UV and IR spectro-

cc) 08 + (I> K1 1 ,CHzC?z C13Sn

\ O//C-OMe (3)

x max 279nm II (CO) 1668 cm-’ A,,, 324 nm

-1 V(CO) 1660 cm

69

scopies. Similar UV spectral changes as reported by Satchell [19] for other quinoline-Lewis acid systems were observed. Only the l/l adduct was indicated. Despite the quite different concentrations used - for the UV study [quinoline] 2.11 X 10m4 M and [I] O-75-75 X lo4 M and for the IR study [quinoline]

4.22 X 10” M and [I] 4.24-42.4 X 10m3 M -- consistent log R1 values were calculated.

It has been reported [19] that pyridines are 30-50 fold and quinolines Z-20 fold more basic towards Lewis acids such as SnC14 and ZnC12, than expected compared with an aniline of similar pKa value_ Towards I, the relative basicities of pyridine (pKa 5.28), quinoline (pKa 4.90) and aniline (pKa 4.60) are 3000/5/l. Thus for I, a fairly elaborate Lewis acid, a similar trend is found for aniline and quinoline, although pyridine appears to be much more basic.

Bipy proved to be a considerably stronger chelating ligand than Q ,cu-biquinolyl. Unfortunately the log K, value for bipy-I was too great (>5) to &ow accurate calculation. In addition, it appears as if a simple l/l equilibrium did not com- pletely satisfy the data. On a qualitative basis, a sequence of acceptor ability of Cl$nCH,CH,CO,R towards bipy [R = Ph > Me > & > H] was obtained. This sequence was established from the amounts of uncomplexed donor in solutions containing equimolar donor and acceptor. The UV spectral changes on complexation of bipy (see Fig. 2) are similar to those recorded for complexa- tion by other organotin halides [3,23,24]. Various bipy-organotin halide formation constants have been reported (Table 6) and hence comparison of acidity towards bipy can be made. These data show that even to a chelating donor, I has a comparable acidity to RSnCL.

Equilibrium constants for C12Sn(CH2CH2C02R)2 adducts. Comparison of the Lewis acidities of Cl$!jn(CH2CH2C02R)2 and MezSnC1,

can be made towards two donors. From data in Table 6, MezSnClz is ca. 200 times more acidic than C12Sn(CH2CH2C02Pr’)2 towards bipy and from data

TABLE 6

COMPARISON OF STABILITY CONSTANTS FOR (r,(r-BIPYRIDYL ADDUCTS WITH ORGANOTIN HALIDES

R,SnC!l~, log KI Solvent/Temp <OC) Ref.

Me2SnCl2

BuzSnClz

PhSnClg Me02CCH2CH2SnC13

2.09 PhH130 2 3.42. 3.30 M&N/25 4.83 3.55 CH2CI2/25 This work 1.60 PhHl30 2

3.03 MeCNl25 23 1.43 PhH/BO 3 3.80 PhH/BO 2 1.2 CHzCI2/25 This work 5.0 PhHl30 2

>7.O MeCN/25 23 >5.0 PhHJ30 2 >5.0 CH+I2/25 This work

ICI = CiRnSnCI+& - bipyl/CRnSnC14_,l[bipy]

70

TABLE 7

STABILITY CONSTANTS FOR R$%rClyphen COMPLEXES __--

log KI SolventlTemp <OC) Ref.

CI+,n<CH2CH2CO2Pri)-phen 2.10 = 0.10 CH2C12/25 This work MezSnC&-phen 5.67 CH3CN/25 4

KI = ~R~SnC1~phenl/CR~SnCl~l~phenl.

in Table 7, a greater factor (>3 X 103) can be estimated for the difference between MezSnC12 and C12Sn(CH2CH2C02Me)2 towards phen.

Acknowledgement

We thank the SRC for a CASE Award to D.M.

References

1

2 3 4

R.C. Poller. The Chemistry of Organotin Compounds. Logos Press. Plainfield. NJ. 1970. Y_ Farhangi and D.P. Graddon, J. Orggome’&. Chem.. 7 (1975) 67. J.L. Wardell. J. Chem. Sot. A. (1971) 2628 and references therein. W.D. Honnick. MC. Hughes. C-D. Schaeffer. and J.J. Zuckermann. Inorg. Chem.. 15 <1976) 1391

and references therein. 5 6

7 8

9 10 11

12

J.L. Wardell. J. Organometal. Chem.. 9 (1967) 89_ G. van Koten, J.T.B.H. Jastrzebski. J.G. Noltes. W.M.F.G. Pontenagel. J. Kroon and A-L. Spek, J. Amer. Chem. Sot.. 100 (1978) 5021: see also G. van Koten and J-G. No&s. J. Amer. Chem. Sot.. 38 (1976) 5393; Ad\-_ Chem. Ser.. No. 157 (1976) 275: G. van Roten. J-T-B-H. Jastrzebski, J.G. Noltes. -4-L. Spek. and J-C!. Schoone. J. Organometal. Chem.. 148 (1978) 233. P-G. Harrison. T-J. King and hl.A. Healey. J. OrganometaL Chem.. 182 <1878) 17. R-E. Hutton, J-W. Burley and V. Oakes, J. Organometal. Chem.. 156 (1978) 369: J.W_ Burley. P. Hope and C.J. Gronenboom. J. Organometal_ Chem.. 170 (1979) 21. R.M. Ha&h, A.G. Davies and MW. Tse. J. OrganometaL Chem.. 174 (1979) 163.

S. Matsuda. S. Kikkawa and N. Kashiwa. Kosyo Kabaku Zasshi. 69 (1966) 1036. H-G. Kuivila, J-E. Dixon. P-L. Maxfield N.hl. Scarpa, TM. To&a. K-H. Tsai and K.R. Wuxsthorn, J. Organometal. Chem., 86 (1975) 89. S.Z. Abbss and R.C. Poller. J. Chem. Sot_ Dalton, (1974) 1769; J. Organometal. Chem.. 104 (1976) 187.

13 14 15 16 17 18

J.N.R. Ruddick Rev. Silicon. Germanium. Tin and Lead Compounds, 2 (1976) 115. P-L. Clarke. R.A. Howie and J.L. Wardell. J. Inorg. Nucl. Chem.. 36 (1974) 2449. A-G. Davies. L. Smith and P. Smith. J. OrganometaL Chem.. 23 (1970) 135. F-P. Mullins. Can. J. Chem.. 48 (1970) 1677_ H.A. Stockier. H. Sand and R-H_ Herber. J. Chem. Phys.. 47 (1967) 1567. B-W. Fitzsirnmons, N.J. Seeley and A-W_ Smith. Chem. Commun.. (1968) 390; J. Chem. Sot. A. . (1969) 143.

19 D. Bert-y. K. Bukka and R.S. SatchelI. J. Chem. Sot. Perkin II. (1975) 89. 20 K. Bukka and R-S. SatchelI. J. Chem. Sot. Perkin II. (1976) 1058. 21 D-P-N. SaccheR and J.L. Wardell, J. Chem. Sot.. (1964) 4134.4296.4300. 22 D-P-N. Sztchell and R.S. Satchell, Chem. Rev.. 69 (1969) 251. 23 M- Komua, Y. Ka==eaki. T. Tanaka and R. 0kawar-a. J. Organometal. Chem.. 4 (1965) 308. 24 G. -Matsu:~ayaabi. Y. Kawasaki. T. Tanaka and R. Okawara. J. Inorg. Nucl. Chem.. 28 <1966) 2937. 25 D-P_ Graddon and B.A. Rana. J. Organometal. Chem.. 105 (1976) 51. 26 T.F. Bollss and R-S. Drago. J_ Amex Chem. Sot.. 88 (1966) 3921.