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Neighbouring group participation in reactions between iodine and Ph3Sn(CH2)nS(O)mC6H4Me-p
C24 Journal
of Organometallic
preliminary
205 (1981) C24426 Printed in The Netherlands
Chemistry,
Ekevier Sequoia S.A., Lausanne -
communication
NEIGHBOURING GROUP PARTiCIPATION IODINE AND Ph,Sn(CH,),S(O), C6 H,Me-p
JAMES L. WARDELL* Department of (Great Britain)
IN REACTIONS
BETWEEN
and JOHN McM. WIGZELL
Chemistv,
University
of Aberdeen,
Meston
Walk,
Old Aberdeen
AB9
2iJE
(Received October ZOth, 1980)
Summary Reactions of Ph,Sn(CH,),S(O),C,HJMe-p (t2 = 2, 3 or 4; m = 0, 1 or 2) with- iodine in CCI, result in phenyl-tin bond cleavage. The relative reactivities indicate intramolecular nucleophilic catalysis by the sulphur-containing substituents. ______ ---_ ..There have been few indications in carbon-tin bond cleavage reactions for enhancement of reactivity arising from assistance by a group not directly bonded to tin. One such report came from Kuivila’s group [I], who showed that the rate of the forward reaction (k,) in equilibrium 1 is considerably larger than that for the analogous reaction involving lMe,SnBu and Me,SnCl. Me,SnCl + Me,Sn(CH,),
COR
k,
Me,Sn(Cl)(CH,),COR
+ Me,Sn
(1)
R = Me or Ph; n = 2 or 3. The rate enhancement was attributed to the carbonyl group providing intramolecular nucleophilic catalysis or neighbouring group participation. We have observed appreciable rate differences in the reactions of iodine with Ph,Sn(CH,),S(O), C,H,Me-p (I; n = 2, 3 or 4; m = 0, 1 or 2) in CCl, solution at 30°C (eq. 2). All the reactions lead to phenyl-tin cleavage. I2 f Ph$n(CH,
tnS(O), C,H,Me-p
--f Phi + Phz (I)Sn(CIL),S(O),
C,H,Me-p (2)
The relative reactivities were obtained from competitive reactions of compound I and @-lMeC,H,),Sn for a deficiency of iodine; typical concentrations were ca. lo-* &Z each for the organotins and [Iz] = ca 2 X 10s3 M. The 0022-328X/81/0000-0000/‘$
02.50,
o 1981,
Elsevier Sequoia S.A.
c25
TABLE
1
RELATIVE REACTIVITIES CCI, SOLUTION n
2 3 4
= OF
Ph,Sn(CH2),S(0),C,H,Me-P
TOWARDS
IODINE
AT
30 i 0.2OC IN
m= 0
1
2
0.25 + 0.04 1.20 f 0.06 0.23 f 0.03
2300 fr 100 2.15 2 0.10
3.6 + 0.1
aV~ues
are averages
PhsSnBu = 0.16
from
2.6 f 0.1 0.49 2 0.04
4 experiments. Reactivity of (p-MeC,H,),Sn
= 1: relative reactivity of
i 0.02.
ratios [PhI] :Ip-MeC,&J] were determined by GLC. The quoted reactivities (Table 1) are each averages of four experiments and are calculated from compound I] Ip-MeC,HJ]. C@-aleC6H4 LSnl CPhIJ/C The rate differences reflect differences in participation by the functional substituent. As shown by the substituent effects on cleavage by I, of aryl-tin bonds [ZJ, a substantial degree of positive charge is developed on the aromatic ring in the transition state. Additional electron release from the tin centre to the phenyl ring, such as would result from coordination of the substituent, S(O), to the tin, will increase the rate. As it is unlikely that free ions, I- and Ph,Sn+(CH,),S(O), C,H?Me-p, will be formed in CC14, some interaction between the tin centre and the developing iodide ion is envisaged. A simpli_ fied scheme is shown in Scheme l*. -
Ph3Sn
(W2),,
S(O),
C6H4Me-p
+ I2
z?
-
\
L
C6b+Me-p
-Phi 7 K
Php
Sn(X)(CW~)nS(0),C6H~Me--p
ml,,X=I
_
; Ph2Sn \ i ,(W” (01,s \
SCHEME 1
‘C6H4Me
-p
(D)X=I
of carbon-tin bonds. including aryl-tin [21, alkenyl-tin. alkynyl-tin and benzyl-tin bon& 131 by iodine in CCI, ax third order processes (first order in organotin and second order in iodine). Scheme 1 ignores the extra molecule of iodine, which is considered to be involved either in a n-complex with the organotin or in formation of I, [2.3] _
*Cleavas?e
C26
As expected from other findings on donor abilities, the greatest effect is found with the sulphoxide substituent. As well as the type of the particular functional group, another important factor is the size of the potential chelate ring formed during the reaction. It is worth remembering that for the sulphoxides and sulphones, any coordination will be via oxygen and thus the potential chelate ring size is (rc + 3) from compound I (m = 1 or 2) in contrast to a (n + 2) membered ring from sulphide I (m = 0). Evidence was obtained to support the basis of intramolecular complexation for halodiphenyl derivatives, such as II. The hmax_value for charge-transfer adducts of Ph,Sn(CH,),SC,H,Me-p (n = 2, 3 and 4) and (CN),C=C(CN), in CH,Cl, solution were at 610 f 1 nm (an indication of similar donor abilities adducts for all these sulphides) while A,,_ for the Ph,Sn(X)(CHz)3SC6H,Me-p were at 598 + 1 (X = Cl) and 602 f 1 (X = I) nm; these are small but significant differences. The v(SO) frequencies for Ph2Sn(Cl)(CH,),SOC,H,Me-p in CH& solution appear at ca. 1040 (free SO) and 980 cm-’ (complexed SO). Equilibrium constants (K = [II, X = Cl] /[III, X = Cl]) were calculated (at 25°C) to be 10 t 1 and 0.9 t 1 for n = 3 and 4, respectively. Thus the greater intramoIecuIar complexation is found for the compound, n = 3, which compliments the reactivity finding. References 1 2 3
H.G. Ruivila, J-E. Dixon. P.L. Maxfield. N.M. Scarpa. TX. Topka. K.H. Tsai and K-R. Wursthom. J. Organometal. Chem.. 86 (1972) 89. R-W. Bott. C. Eabom. and J-A. Waters, J. Chem. Sot., (1963) 681. A.K. Kashin, LP. Beletskaya. A.T.S. Malkhasyan, A.A. Solov’yanov and O.A. Reutov, J. 0~. Chem. U.S.S.R.. 10 (1974) 2257.
of Organometallic
preliminary
205 (1981) C24426 Printed in The Netherlands
Chemistry,
Ekevier Sequoia S.A., Lausanne -
communication
NEIGHBOURING GROUP PARTiCIPATION IODINE AND Ph,Sn(CH,),S(O), C6 H,Me-p
JAMES L. WARDELL* Department of (Great Britain)
IN REACTIONS
BETWEEN
and JOHN McM. WIGZELL
Chemistv,
University
of Aberdeen,
Meston
Walk,
Old Aberdeen
AB9
2iJE
(Received October ZOth, 1980)
Summary Reactions of Ph,Sn(CH,),S(O),C,HJMe-p (t2 = 2, 3 or 4; m = 0, 1 or 2) with- iodine in CCI, result in phenyl-tin bond cleavage. The relative reactivities indicate intramolecular nucleophilic catalysis by the sulphur-containing substituents. ______ ---_ ..There have been few indications in carbon-tin bond cleavage reactions for enhancement of reactivity arising from assistance by a group not directly bonded to tin. One such report came from Kuivila’s group [I], who showed that the rate of the forward reaction (k,) in equilibrium 1 is considerably larger than that for the analogous reaction involving lMe,SnBu and Me,SnCl. Me,SnCl + Me,Sn(CH,),
COR
k,
Me,Sn(Cl)(CH,),COR
+ Me,Sn
(1)
R = Me or Ph; n = 2 or 3. The rate enhancement was attributed to the carbonyl group providing intramolecular nucleophilic catalysis or neighbouring group participation. We have observed appreciable rate differences in the reactions of iodine with Ph,Sn(CH,),S(O), C,H,Me-p (I; n = 2, 3 or 4; m = 0, 1 or 2) in CCl, solution at 30°C (eq. 2). All the reactions lead to phenyl-tin cleavage. I2 f Ph$n(CH,
tnS(O), C,H,Me-p
--f Phi + Phz (I)Sn(CIL),S(O),
C,H,Me-p (2)
The relative reactivities were obtained from competitive reactions of compound I and @-lMeC,H,),Sn for a deficiency of iodine; typical concentrations were ca. lo-* &Z each for the organotins and [Iz] = ca 2 X 10s3 M. The 0022-328X/81/0000-0000/‘$
02.50,
o 1981,
Elsevier Sequoia S.A.
c25
TABLE
1
RELATIVE REACTIVITIES CCI, SOLUTION n
2 3 4
= OF
Ph,Sn(CH2),S(0),C,H,Me-P
TOWARDS
IODINE
AT
30 i 0.2OC IN
m= 0
1
2
0.25 + 0.04 1.20 f 0.06 0.23 f 0.03
2300 fr 100 2.15 2 0.10
3.6 + 0.1
aV~ues
are averages
PhsSnBu = 0.16
from
2.6 f 0.1 0.49 2 0.04
4 experiments. Reactivity of (p-MeC,H,),Sn
= 1: relative reactivity of
i 0.02.
ratios [PhI] :Ip-MeC,&J] were determined by GLC. The quoted reactivities (Table 1) are each averages of four experiments and are calculated from compound I] Ip-MeC,HJ]. C@-aleC6H4 LSnl CPhIJ/C The rate differences reflect differences in participation by the functional substituent. As shown by the substituent effects on cleavage by I, of aryl-tin bonds [ZJ, a substantial degree of positive charge is developed on the aromatic ring in the transition state. Additional electron release from the tin centre to the phenyl ring, such as would result from coordination of the substituent, S(O), to the tin, will increase the rate. As it is unlikely that free ions, I- and Ph,Sn+(CH,),S(O), C,H?Me-p, will be formed in CC14, some interaction between the tin centre and the developing iodide ion is envisaged. A simpli_ fied scheme is shown in Scheme l*. -
Ph3Sn
(W2),,
S(O),
C6H4Me-p
+ I2
z?
-
\
L
C6b+Me-p
-Phi 7 K
Php
Sn(X)(CW~)nS(0),C6H~Me--p
ml,,X=I
_
; Ph2Sn \ i ,(W” (01,s \
SCHEME 1
‘C6H4Me
-p
(D)X=I
of carbon-tin bonds. including aryl-tin [21, alkenyl-tin. alkynyl-tin and benzyl-tin bon& 131 by iodine in CCI, ax third order processes (first order in organotin and second order in iodine). Scheme 1 ignores the extra molecule of iodine, which is considered to be involved either in a n-complex with the organotin or in formation of I, [2.3] _
*Cleavas?e
C26
As expected from other findings on donor abilities, the greatest effect is found with the sulphoxide substituent. As well as the type of the particular functional group, another important factor is the size of the potential chelate ring formed during the reaction. It is worth remembering that for the sulphoxides and sulphones, any coordination will be via oxygen and thus the potential chelate ring size is (rc + 3) from compound I (m = 1 or 2) in contrast to a (n + 2) membered ring from sulphide I (m = 0). Evidence was obtained to support the basis of intramolecular complexation for halodiphenyl derivatives, such as II. The hmax_value for charge-transfer adducts of Ph,Sn(CH,),SC,H,Me-p (n = 2, 3 and 4) and (CN),C=C(CN), in CH,Cl, solution were at 610 f 1 nm (an indication of similar donor abilities adducts for all these sulphides) while A,,_ for the Ph,Sn(X)(CHz)3SC6H,Me-p were at 598 + 1 (X = Cl) and 602 f 1 (X = I) nm; these are small but significant differences. The v(SO) frequencies for Ph2Sn(Cl)(CH,),SOC,H,Me-p in CH& solution appear at ca. 1040 (free SO) and 980 cm-’ (complexed SO). Equilibrium constants (K = [II, X = Cl] /[III, X = Cl]) were calculated (at 25°C) to be 10 t 1 and 0.9 t 1 for n = 3 and 4, respectively. Thus the greater intramoIecuIar complexation is found for the compound, n = 3, which compliments the reactivity finding. References 1 2 3
H.G. Ruivila, J-E. Dixon. P.L. Maxfield. N.M. Scarpa. TX. Topka. K.H. Tsai and K-R. Wursthom. J. Organometal. Chem.. 86 (1972) 89. R-W. Bott. C. Eabom. and J-A. Waters, J. Chem. Sot., (1963) 681. A.K. Kashin, LP. Beletskaya. A.T.S. Malkhasyan, A.A. Solov’yanov and O.A. Reutov, J. 0~. Chem. U.S.S.R.. 10 (1974) 2257.