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Interaction of distannanes with substitutedo-quinones
47
Journal of Organometallic Chemistry, 174 (1979) 47--55
© Elsevier Sequoia S.A., Lausanne -- Printed in The Netherlands
INTERACTION OF DISTANNANES WITH SUBSTITUTED o-QUINONES
G.A. RAZUVAEV *, V.A. TSARJAPKIN, L.V. GORBUNOVA, V.K. CHERKASOV, G.A. ABAKUMOV and E.S. KLIMOV Institute of Chemistry, Academy of Sciences of the U.S.S.R., Gorky (U.S.S.R.) (Received January 8th, 1979)
Summary The reactions of distannanes with 3,5- and 3,6-di-t-butyl-l,2-benzoquinone have been investigated. It has been shown that the primary.step of the process is a one-electron transfer from distannane to quinone. The main reaction products are formed from tin-containing semiquinones by elimination o f the organic substituent (R) from the tin atom. Elimination of radical R is the result of intramolecular coordination of oxygen with the tin atom in semiquinone and it occurs with the participation of the second moiety without the removal of the kinetically independent R" into solution.
Introduction It was shown earlier t h a t the reactions of bimetallic organometallic compounds containing Si--Hg or Ge--Hg bonds with o-quinones proceed by a radical mechanism: electron transfer taking place during the primary step of the reaction [ 1--3]. Recombination of the ion--radical pair formed there from in the solvent cage results in the formation of the corresponding bis(triorganoelementoxy)benzenes. Partial removal of R3M radicals from the cage causes dimerization products to be generated and ESR signals for the corresponding semiquinones are observed. Harrison et al. [4,5] have shown that electron transfer from a bimetallic organometallic c o m p o u n d to the acceptor molecule takes place in the reactions of distannanes with tetrachloro-l,4-benzoquinone (TCBQ) as well. They proved that the interaction of TCBQ with distannanes was a radical reaction resulting in the formation of 1,4-bis(triorganostannyloxy)-2,3,5,6-tetrachlorobenzenes in the case of hexabutyl- and hexaphenyl-distannanes. The reaction o f TCBQ
48
with hexamethyldistannane affords a c o m p o u n d identified as Me3Sn--TCBQ'. The tin atom of tin-containing semiquinones, o-quinones and semidiones is known [6--8] to have a pentacoordinated structure due to intramolecular oxygen coordination with the tin atom. Taking the above into account we considered t h a t it would be of interest to check whether one-electron transfer is applied in the reaction of distannanes with 3,5- (I) and 3,6-di-t-butyl-l,2-benzoquinones (II) and to investigate the products of their reaction. Results and discussions It is known [9] that the electric current in a galvanic cell modelling the reagent system is the most direct estimation of the possible occurrence of electron transfer in the reactions. We observed the current in a closed external circuit when performing the process in the electrochemical cell: Pt Ihexaethyldistannane(HEDS), LiBr, DMF II DMF, LiBr, o-quinone(I)l Pt ÷. The current density was apnroximately 5 X 10 -4 A/dm 2 and the cell e.m.f. was equal to 0.56 V. This proves unequivocally t h a t electron transfer takes place in the primary step of the process. An investigation of the products formed in the reaction of distannanes with I and II and an ESR study of the reaction run showed that it was a complex process comprising several distinct steps. In hexane, benzene and cumene interaction of the reagents begins as soon as the reaction mixture is melted. The reaction with alkyldistannanes is complete within 10--15 min at room temperature but 5--7 days are required to complete the reaction with hexaphenyldistannane. One mole of distannane reacts with four moles of quinone in all cases (R - Et, n-Bu) regardless of solvent, reagent character and their ratio. The interaction of hexaethyldistannane with I leads to the formation of a 3--5% ethane ethylene mixture (in terms of distannane reacted). The a m o u n t of the above mixture increases slightly (to 7%) in cumene. The reaction of I with hexaphenyldistannane in hexane and cumene does not afford benzene. White crystalline compounds which were stable in air, but which changed slowly in solvents, were obtained in 80--85% yields (based on distannane reacted) in the reactions investigated instead of the expected 1,2-bis(triorganostannyloxy)di-t-butylbenzenes (III). Structure IV may be assigned to these compounds judging by elemental analysis data, however, cryoscopic molecular weight measurements indicate a dimeric structure (V) for alkyl derivatives.
I'
o\
'l
o
o_o
/\ R (l-n)
(a)
R
(T~7)
=
Me
:
(b)
IR :
Et
~ (c)
R CV)
IR :
n-Bu;
( d ) !R :
Ph
49 IR spectra of the compounds investigated contain the bands: 1210m, 1260s, 1360m, 1380m cm -1 (t-Bu group); 680--710s and 1560--1580s cm -1 {aromatic ring); and vibrations corresponding to Sn--C bonds [10] and the Sn--O fragment. Moreover, one and the same strong band at 970--980 cm -1 corresponds to both Sn--O bond vibrations of c o m p o u n d Vb and those o f compound IIIb obtained in accordance with eq. 1.
( "T1-1" b )
Preparation of Vb in 85% yield according to eq. 2 confirms the suggested structure V.
+ v
"
l?q
°-
°-q-(q- I
~- 2 NaCl
(2)
~0 N~
Et
Et (Vb)
A monomer--dimer equilibrium is observed for similar organosilicon derivatives of non-substituted catechol [ 11] and it apparently results from the intramolecular coordination of oxygen with an atom of a group IVB element to form a less-strained ring. The initial ESR spectra observed for reactions of o-quinones with R3SnSnR3 are analogous to the signals of tin-containing semiquinones formed according eq. 3.
Na +
+
R3SnCI
_---
SnR 3 +
NaCI
(3)
The high frequency coupling constants in the ESR spectra are essentially independent of the substituent adjacent to the tin atom. The ESR spectra in R3SnSnR3/o-quinone/I are doublets. Satellites caused by the magnetic isotopes of tin are observed at the sides of the signal. The parameters of the spectrum for R = Ph are: g 2.0026; a(H) 2.60, a(Sn) 9.79 Oe (Fig. la). Triplet ESR spectrum with intensity ratio 1/2/1 (a(Sn) 11.6, a(H) 3 . 6 0 e ; g 2.0041) is observed during the reaction of II with Rh3SnSnPh3 (Fig. lb). The triplet spectrum (a(H) 3.4, a(Sn) 1 2 . 4 0 e when R = Et) observed at the beginning of the reactions with alkyldistannanes graduallv transforms into a quartet spectrum with intensity ratio 1/1/1/1 (a(H1) 2.60, a(H2) 5.20 Oe when R = Et).
50
50e
(a)
(b)
(c)
Fig. I . (a) T h e E S R s p e c t r u m o f the s y s t e m h e x a o r g a n o d i s t a n n a n e / I ; Co) the initial E S R s p e c t r u m o f t h e s y s t e m h e x a o r g a n o d i s t a n n a n e / I I ; (c) the E S R s p e c t r u m in the r e a c t i o n s o f a l k y l d i s t a n n a n e s w i t h II a f t e r disappearance o f t h e t r i p l e t .
The quartet spectrum becomes more complex with time b u t the initial signal can be maintained provided that the reaction is carried o u t in a great excess o f distannane. The latter allows the quartet spectrum to be ascribed to secondary reactions of II with the organotin c o m p o u n d s formed. Indeed, the interaction of II with Vb results in a spectrum with the above parameters. The quartet spectrum can be explained by the reduced rate of exchange (on the ESR time scale) o f heavy organotin fragment in semiquinone (VII) [6] forme formed b y the substitution of an alkyl group for the semiquinone ligand adjacent to the tin atom (eq. 4).
A +
___
.L ; -..
.
O
This results in the non-equivalence of ring protons at the 4- and 5-positions. The reaction with quinones is n o t observed until the temperature reaches 70°C in the case of Vd and accounts for the fact that the triplet spectrum remains unaltered into II/hexaphenyldistannane system. The form of the ESR spectra of dimers suggests that dimers of structure V are formed as a result of the transformation of tin-containing semiquinones VI.
(4)
51 (Tin-containing semiquinones prepared according to eq. 3 appeared to be unstable: they disproportionate at room temperature to give V in 40--45% yield.) The complete absence of gas formation during the disproportionation o f VIb is worthy of note. Together with the stoichiometry of the Et3SnSnEt3 o-quinone/I reaction in cumene this fact proves that radicals are n o t formed as kinetically independent moieties. Perhaps the Sn--C bond of semiquinone with a pentacoordinated tin atom is weakened by intramolecular coordination but it does remain strong enough to prevent the elimination of an organic radical. Radical elimination becomes possible when the semiquinone is attacked by a second acceptor molecule such as quinone or a second molecule of semiquinolate. The stoichiometric ratio of o-quinone/distannane {4/1) is explained by the interaction of semiquinolate with quinones (eq. 5). A small a m o u n t of gases released in the reaction of I with HEDS may be associated with secondary processes (eq. 5).
SnR 3
+
o/Snl~z+
~
(5) O.
(r~o-]3Zd) IVa and IVb are further dimerized (eq. 6).
2
O\
~
I ~ ( ~ ] - - - - 0 - - Sn - - 0 - ~ ( ~ l
o~ s ~ R 2
~>~___.>--o--sn--o~
(6)
/\
R
The addition of t-nitrosobutane as a spin trap in reaction 3 (R = Et) leads to the formation of ethyl t-butyl nitroxide, and this is confirmed unequivocally by the ESR method. However, the above facts make it possible to ascribe the formation of the nitroxide radical to the reaction of a tin-containing semiquinone with t-nitrosobutane, but it does n o t explain the interaction of spin trap with ethyl radical {eq. 7).
I ~
0~.
~.~_.j____o/SnE±3
+
t-BuNO
~-
~
[ /~
2,SnEt 0
+
Et
t-BuNO •
(7)
When R = Et the disproportionation of VI mainly follows eq. 8.
2
SnEt 3 ~
SnEt 2
+
(8) ;~
v
-OSnEts
52 As far as we k n o w similar transformations of semiquinones have n o t been observed previously. We identified VIII in reaction 8 by its hydrolysis products. A chromatographic analysis carried out after the hydrolysis o f the reaction m i xt ure indicated the presence of 0.2 mole of hexaethyldistannane and 0.25 mole of 2-ethoxy-3,5-di-t-butylphenol per mole of semiquinone. Apart from VIII the main reaction p r o d u c t is Vb (0.43 mole per mole o f semiquinone). As is men tio n e d above, c o m p o u n d s having structure III were not isolated in the reactions o f I with distannanes. This is due to the rapid interaction of III with quinones u n d e r the conditions o f the experiment. Thus IIIb p r o d u c e d in reaction 3 reacts immediately with I and II according to eq. 9.
~OSnE%3
+ [~'0
o/SOEt3
OSnEt3
(97
A p pr o x imately 3 moles of quinone per mole of IIIb is used in this case which is associated with the transformation of tin-containing semiquinone according to eq. 5. Stoichiometric ratios in the reactions of IIIb and distannanes with I lead us to conclude that the reaction of tin-containing semiquinone with I predominates when processes 5 and 8 are competing. The p r o d u c t o f reaction 9 is a dimer of diethyltin catecholate produced in 83% yield based on initial IIIb. The results obtained and the above facts allow us to draw the conclusion that the interaction of I and II with distannanes proceeds in several steps, with electron transfer and the form at i on of an ion--radical pair (IX) taking place in the primary step. The probability of removing R3M" from the cage determines the t r ans f or m at i on of the latter. Compounds III and
],
SnR 3
Jr 1~3Sn--Snl~3~ 0
( ~
I SnIq3
(10) OSnR 3 OSnl~
53
VI prepared according to eq. 10 then react with quinone as in reactions 5 and 9. R3Sn" leaving the cage then either is dimerized or reacts with quinone forming the corresponding semiquinone (eq. 11).
4- R3Sn
/SnR 3
(11)
Experimental 3,5- and 3,6-di-t-butylbenzoquinones were prepared in accordance with well known methods [12,13]. Na-semiquinones of I and II were produced by the interaction of disodium salts of the corresponding catechols with equivalent amounts of I and II in ether. Disodium salts were prepared by treating I and II with metallic sodium in ether [14]. All reactions were carried out in evacuated ampoules.
ESR spectra Measurements were performed on an X-region radiospectrometer RE-13-1. Reagent solutions of 1--5 × 10 -2 mol/1 concentration were used to obtain ESR spectra. The temperature of the sample placed in the resonator was thermostatically controlled with the help of a TC-IKhF thermoblock. Mn 2÷ ions in the MnO crystal lattice were used as a standard for magnetic field calibration. Reaction o f 3,5-di-t-butylpyrocatechol disodium salt with Et3SnCl The disodium salt (2.66 g (0.01 mol)) in 30 ml of ether was mixed with 4.82 g (0.02 mol) of EtSnC1. The mixture was kept at room temperature for 3 h after which the ether was replaced with hexane. NaC1 was separated by centrifuging: yield 1.12 g (96%). The c o m p o u n d was recrystallized from hexane in vacuo. 1.22 g (19%) of IIIb was isolated, M.p. 54--56°C. Anal.: found: C, 48.97; H, 7.31; Sn, 36.81. C26Hs00~Sn2 calcd.: C, 49.41; H, 7.91; Sn, 37.51%. Reaction of sodium semiquinolate with triethyltin chloride Et3SnC1 (4.82 g (0.02 mol)) was added to 4.86 g (0.02 mol) of sodium semiquinolate. The disappearance of the sodium semiquinolate colour indicates the termination of the reaction. The ether was the substituted for hexane and the residual NaC1 was removed from the reaction mixture by dissolving in water. 3.86 g (86%) of Vb was isolated, M.p. 274--276°C Anal.: found: C, 54.27; H, 7.64; Sn, 29.88. C18H3002Sn calcd.: C, 54.54; H, 7.75; Sn, 29.97%. Mol. wt. (cryosc.) 770). GLC analysis carried out after the hydrolysis revealed the presence of 1.75 g (40%) of hexaethyldistannoxane and 1.24 g (25%) of 2-ethoxy3,5-di-t-butylphenol. The reactions of sodium semiquinolate with other R3SnX compounds were carried out in a similar manner. The characteristics of the various organotin compounds are presented below.
54 R = Me (Va). Va was recrystallized from a hexane/toluene mixture (1/2) (yield ~41%). Va decomposes above 350°C. Anal.: found: C, 52.05; H, 6.66; Sn, 32.74. CI,,H2~,O2Sn calcd.: C, 52.07; H, 7.05; Sn, 32.19%. Mol. wt. (cryosc.) 670. R -- Bu (Vc). Vc was recrystallized from hexane (yield ~40%). M.P. 183-185°C. Anal.: found: C, 58.60; H, 8.43; Sn, 25.96. CnH3802Sn calcd.: C, 58.31; H, 8.39; Sn, 26.22%. Mol. wt. found, 830; calcd. (dimer) 905.4. R = Ph (Vd). Vd was recrystallized from toluene (yield ~45%). M.P. 2 1 6 218°C. Anal.: found: C, 63.55; H, 5.60; Sn, 24.39. C.~,H3002Sn calcd.: C, 63.32; H, 6.08; Sn, 24.09%. Reaction o f hexaethyldistannane with (I) in benzene
(4.11 g (0.01 mol)) Hexaethyldistannane was added to 2.20 g (0.01 mol) of I in benzene. The solution became green in colour. The reaction terminated after 15 min at room temperature: the colour of the solution becoming orange. 4 mol of gas were formed in the process. GLC analysis of the gas revealed the presence of ethane and ethylene. 2.92 g (71%) of unreacted distannane was found in the reaction mixture by GLC method. When benzene was substituted for hexane, 1.92 g of Vb was isolated (83% yield based on reacted distannane). Reaction o f 3,5-di-t-butylcatechol disodium salt with Et2SnCl2
Disodium salt (0.01 mol) in 30 ml of ether was added to 2.46 g (0.01 mol) of Et2SnC12 in 10 ml of ether. The solution was kept for 3 h at room temperature. The ether was than replaced by hexane and the residue of NaC1 was removed from the reaction mixture b y dissolving it in water 1.13 g (.97%) of NaCl was isolated. 3.36 g (85%) of Vb was isolated u p o n cooling. Reaction o f IIIb with 1,2-bis(triethylstannyloxy)-3,5-dit-butylbenzene
IIIb (0.80 g (0.00127 tool)) in 10 ml of ether was mixed with 0.84 g (0.0038 mol) of I at room temperature. The colour of quinone rapidly disappeared. After the reaction terminated the ether was replaced by hexane and 0.84 g (83%) of Vb was isolated upon cooling. Initial quinone was not present in the reaction mixture according to chromatographie analysis data. References 1 G.A. A b a k u m o v , N.S. V y a z a n k i n , E.N. G l a d y s h e v , G.A. Razuvaev, P.Ya. B a y s h k i n a n d V.A. Muraev, J. O r g a n o m e t a l . C h e m . , 64 ( 1 9 7 4 ) 3 2 7 . 2 G.A. Razuvaev, E.N. G l a d y s h e v , P.Ya. B a y s h k i n , G.A. A b a k u m o v a n d E.S. Klimov, Izv. A k a d . N a u k SSSR, Set. K h i m . , ( 1 9 7 6 ) 2 7 6 2 . 3 G. N e u m a n n a n d W.P. N e u m a n n , J. O r g a n o m e t a l . Chem., 42 ( 1 9 7 2 ) 2 7 7 . 4 A.B. Cornwell, P.G. H a r r i s o n a n d T.A. R i c h a r d s , J. O r g a n o m e t a l . Chem., 67 ( 1 9 7 4 ) C43. 5 A.B. Cornwell, P.G. H a r r i s o n a n d J.A. R i c h a r d s , J. O r g a n o m e t a l . C h e m . , 1 4 0 ( 1 9 7 7 ) 2 7 3 . 6 B. S c h r o e d e r , W.P. N e u m a n n a n d H. Hillgartner, Chem. Bet., ( 1 9 7 4 ) 3 4 9 3 . 7 S.G. Kukes, A.I. P r o k o f ' e v , N.N. B u b n o v , S.P. Solodovnikov0 E.D. K o r n i e t s , D.N. K r a v t s o v a n d M.I. K a b a c h n i k , Dokl. A k a d . N a u k SSSR, 2 2 9 ( 1 9 7 6 ) 8 7 7 . 8 A.I. P r o k o f ' e v , T.I. P r o k o f ' e v a , N.N. B u b n o v , S.P. S o l o d o v n i k o v , I.S. B e l o s t o t s k a y a , V.V. Ershov a n d M.I. K a b a c h n i k , DokL A k a d . N a u k SSSR, 2 3 9 ( 1 9 7 8 ) 1 3 6 7 . 9 G.A. A b a k u m o v , V.A. Muraev, G.A. Razuvaev, V.D. T i k h o n o v , Yu.V. C h e c h e t and A.I. Nechuev, Dokl. A k a d . N a u k SSSR, 2 3 0 ( 1 9 7 6 ) 589.
55 10 N . A . C h u m a e v s k i 0 T h e V i b r a t i o n s p e c t r a o f O r g a n o e l e m e n t C o m p o u n d s of I V B a n d V B G r o u p s , Mir, M o s c o w , 1 9 7 1 (in R u s s i a n ) . 11 A. N a g a t a a n d I. I g o d a , J. C h e m . Soc. J a p . , 9 ( 1 9 7 5 ) 1 5 4 5 . 12 H . H . S c h u l z e a n d W. Tlaig, J u s t u s Liebigs A n n . C h e m . , 5 7 5 ( 1 9 7 2 ) 2 3 1 . 13 I.S. B e l o s t o t s k a y a , N.L. K o m i s s a r o v a , E.V. D s k u a r y a n a n d V . V . E r s h o v , Izv. A k a d . N a u k S S S R , SE Ser. K h i m . , ( 1 9 7 2 ) 1 5 9 4 . 14 E. Muller, A. R i e e k e r , K. S c h e f f l e r a n d A. H o o m a y e r , A n g e w . C h e m . , 7 8 ( 1 9 6 6 ) 9 8 .
Journal of Organometallic Chemistry, 174 (1979) 47--55
© Elsevier Sequoia S.A., Lausanne -- Printed in The Netherlands
INTERACTION OF DISTANNANES WITH SUBSTITUTED o-QUINONES
G.A. RAZUVAEV *, V.A. TSARJAPKIN, L.V. GORBUNOVA, V.K. CHERKASOV, G.A. ABAKUMOV and E.S. KLIMOV Institute of Chemistry, Academy of Sciences of the U.S.S.R., Gorky (U.S.S.R.) (Received January 8th, 1979)
Summary The reactions of distannanes with 3,5- and 3,6-di-t-butyl-l,2-benzoquinone have been investigated. It has been shown that the primary.step of the process is a one-electron transfer from distannane to quinone. The main reaction products are formed from tin-containing semiquinones by elimination o f the organic substituent (R) from the tin atom. Elimination of radical R is the result of intramolecular coordination of oxygen with the tin atom in semiquinone and it occurs with the participation of the second moiety without the removal of the kinetically independent R" into solution.
Introduction It was shown earlier t h a t the reactions of bimetallic organometallic compounds containing Si--Hg or Ge--Hg bonds with o-quinones proceed by a radical mechanism: electron transfer taking place during the primary step of the reaction [ 1--3]. Recombination of the ion--radical pair formed there from in the solvent cage results in the formation of the corresponding bis(triorganoelementoxy)benzenes. Partial removal of R3M radicals from the cage causes dimerization products to be generated and ESR signals for the corresponding semiquinones are observed. Harrison et al. [4,5] have shown that electron transfer from a bimetallic organometallic c o m p o u n d to the acceptor molecule takes place in the reactions of distannanes with tetrachloro-l,4-benzoquinone (TCBQ) as well. They proved that the interaction of TCBQ with distannanes was a radical reaction resulting in the formation of 1,4-bis(triorganostannyloxy)-2,3,5,6-tetrachlorobenzenes in the case of hexabutyl- and hexaphenyl-distannanes. The reaction o f TCBQ
48
with hexamethyldistannane affords a c o m p o u n d identified as Me3Sn--TCBQ'. The tin atom of tin-containing semiquinones, o-quinones and semidiones is known [6--8] to have a pentacoordinated structure due to intramolecular oxygen coordination with the tin atom. Taking the above into account we considered t h a t it would be of interest to check whether one-electron transfer is applied in the reaction of distannanes with 3,5- (I) and 3,6-di-t-butyl-l,2-benzoquinones (II) and to investigate the products of their reaction. Results and discussions It is known [9] that the electric current in a galvanic cell modelling the reagent system is the most direct estimation of the possible occurrence of electron transfer in the reactions. We observed the current in a closed external circuit when performing the process in the electrochemical cell: Pt Ihexaethyldistannane(HEDS), LiBr, DMF II DMF, LiBr, o-quinone(I)l Pt ÷. The current density was apnroximately 5 X 10 -4 A/dm 2 and the cell e.m.f. was equal to 0.56 V. This proves unequivocally t h a t electron transfer takes place in the primary step of the process. An investigation of the products formed in the reaction of distannanes with I and II and an ESR study of the reaction run showed that it was a complex process comprising several distinct steps. In hexane, benzene and cumene interaction of the reagents begins as soon as the reaction mixture is melted. The reaction with alkyldistannanes is complete within 10--15 min at room temperature but 5--7 days are required to complete the reaction with hexaphenyldistannane. One mole of distannane reacts with four moles of quinone in all cases (R - Et, n-Bu) regardless of solvent, reagent character and their ratio. The interaction of hexaethyldistannane with I leads to the formation of a 3--5% ethane ethylene mixture (in terms of distannane reacted). The a m o u n t of the above mixture increases slightly (to 7%) in cumene. The reaction of I with hexaphenyldistannane in hexane and cumene does not afford benzene. White crystalline compounds which were stable in air, but which changed slowly in solvents, were obtained in 80--85% yields (based on distannane reacted) in the reactions investigated instead of the expected 1,2-bis(triorganostannyloxy)di-t-butylbenzenes (III). Structure IV may be assigned to these compounds judging by elemental analysis data, however, cryoscopic molecular weight measurements indicate a dimeric structure (V) for alkyl derivatives.
I'
o\
'l
o
o_o
/\ R (l-n)
(a)
R
(T~7)
=
Me
:
(b)
IR :
Et
~ (c)
R CV)
IR :
n-Bu;
( d ) !R :
Ph
49 IR spectra of the compounds investigated contain the bands: 1210m, 1260s, 1360m, 1380m cm -1 (t-Bu group); 680--710s and 1560--1580s cm -1 {aromatic ring); and vibrations corresponding to Sn--C bonds [10] and the Sn--O fragment. Moreover, one and the same strong band at 970--980 cm -1 corresponds to both Sn--O bond vibrations of c o m p o u n d Vb and those o f compound IIIb obtained in accordance with eq. 1.
( "T1-1" b )
Preparation of Vb in 85% yield according to eq. 2 confirms the suggested structure V.
+ v
"
l?q
°-
°-q-(q- I
~- 2 NaCl
(2)
~0 N~
Et
Et (Vb)
A monomer--dimer equilibrium is observed for similar organosilicon derivatives of non-substituted catechol [ 11] and it apparently results from the intramolecular coordination of oxygen with an atom of a group IVB element to form a less-strained ring. The initial ESR spectra observed for reactions of o-quinones with R3SnSnR3 are analogous to the signals of tin-containing semiquinones formed according eq. 3.
Na +
+
R3SnCI
_---
SnR 3 +
NaCI
(3)
The high frequency coupling constants in the ESR spectra are essentially independent of the substituent adjacent to the tin atom. The ESR spectra in R3SnSnR3/o-quinone/I are doublets. Satellites caused by the magnetic isotopes of tin are observed at the sides of the signal. The parameters of the spectrum for R = Ph are: g 2.0026; a(H) 2.60, a(Sn) 9.79 Oe (Fig. la). Triplet ESR spectrum with intensity ratio 1/2/1 (a(Sn) 11.6, a(H) 3 . 6 0 e ; g 2.0041) is observed during the reaction of II with Rh3SnSnPh3 (Fig. lb). The triplet spectrum (a(H) 3.4, a(Sn) 1 2 . 4 0 e when R = Et) observed at the beginning of the reactions with alkyldistannanes graduallv transforms into a quartet spectrum with intensity ratio 1/1/1/1 (a(H1) 2.60, a(H2) 5.20 Oe when R = Et).
50
50e
(a)
(b)
(c)
Fig. I . (a) T h e E S R s p e c t r u m o f the s y s t e m h e x a o r g a n o d i s t a n n a n e / I ; Co) the initial E S R s p e c t r u m o f t h e s y s t e m h e x a o r g a n o d i s t a n n a n e / I I ; (c) the E S R s p e c t r u m in the r e a c t i o n s o f a l k y l d i s t a n n a n e s w i t h II a f t e r disappearance o f t h e t r i p l e t .
The quartet spectrum becomes more complex with time b u t the initial signal can be maintained provided that the reaction is carried o u t in a great excess o f distannane. The latter allows the quartet spectrum to be ascribed to secondary reactions of II with the organotin c o m p o u n d s formed. Indeed, the interaction of II with Vb results in a spectrum with the above parameters. The quartet spectrum can be explained by the reduced rate of exchange (on the ESR time scale) o f heavy organotin fragment in semiquinone (VII) [6] forme formed b y the substitution of an alkyl group for the semiquinone ligand adjacent to the tin atom (eq. 4).
A +
___
.L ; -..
.
O
This results in the non-equivalence of ring protons at the 4- and 5-positions. The reaction with quinones is n o t observed until the temperature reaches 70°C in the case of Vd and accounts for the fact that the triplet spectrum remains unaltered into II/hexaphenyldistannane system. The form of the ESR spectra of dimers suggests that dimers of structure V are formed as a result of the transformation of tin-containing semiquinones VI.
(4)
51 (Tin-containing semiquinones prepared according to eq. 3 appeared to be unstable: they disproportionate at room temperature to give V in 40--45% yield.) The complete absence of gas formation during the disproportionation o f VIb is worthy of note. Together with the stoichiometry of the Et3SnSnEt3 o-quinone/I reaction in cumene this fact proves that radicals are n o t formed as kinetically independent moieties. Perhaps the Sn--C bond of semiquinone with a pentacoordinated tin atom is weakened by intramolecular coordination but it does remain strong enough to prevent the elimination of an organic radical. Radical elimination becomes possible when the semiquinone is attacked by a second acceptor molecule such as quinone or a second molecule of semiquinolate. The stoichiometric ratio of o-quinone/distannane {4/1) is explained by the interaction of semiquinolate with quinones (eq. 5). A small a m o u n t of gases released in the reaction of I with HEDS may be associated with secondary processes (eq. 5).
SnR 3
+
o/Snl~z+
~
(5) O.
(r~o-]3Zd) IVa and IVb are further dimerized (eq. 6).
2
O\
~
I ~ ( ~ ] - - - - 0 - - Sn - - 0 - ~ ( ~ l
o~ s ~ R 2
~>~___.>--o--sn--o~
(6)
/\
R
The addition of t-nitrosobutane as a spin trap in reaction 3 (R = Et) leads to the formation of ethyl t-butyl nitroxide, and this is confirmed unequivocally by the ESR method. However, the above facts make it possible to ascribe the formation of the nitroxide radical to the reaction of a tin-containing semiquinone with t-nitrosobutane, but it does n o t explain the interaction of spin trap with ethyl radical {eq. 7).
I ~
0~.
~.~_.j____o/SnE±3
+
t-BuNO
~-
~
[ /~
2,SnEt 0
+
Et
t-BuNO •
(7)
When R = Et the disproportionation of VI mainly follows eq. 8.
2
SnEt 3 ~
SnEt 2
+
(8) ;~
v
-OSnEts
52 As far as we k n o w similar transformations of semiquinones have n o t been observed previously. We identified VIII in reaction 8 by its hydrolysis products. A chromatographic analysis carried out after the hydrolysis o f the reaction m i xt ure indicated the presence of 0.2 mole of hexaethyldistannane and 0.25 mole of 2-ethoxy-3,5-di-t-butylphenol per mole of semiquinone. Apart from VIII the main reaction p r o d u c t is Vb (0.43 mole per mole o f semiquinone). As is men tio n e d above, c o m p o u n d s having structure III were not isolated in the reactions o f I with distannanes. This is due to the rapid interaction of III with quinones u n d e r the conditions o f the experiment. Thus IIIb p r o d u c e d in reaction 3 reacts immediately with I and II according to eq. 9.
~OSnE%3
+ [~'0
o/SOEt3
OSnEt3
(97
A p pr o x imately 3 moles of quinone per mole of IIIb is used in this case which is associated with the transformation of tin-containing semiquinone according to eq. 5. Stoichiometric ratios in the reactions of IIIb and distannanes with I lead us to conclude that the reaction of tin-containing semiquinone with I predominates when processes 5 and 8 are competing. The p r o d u c t o f reaction 9 is a dimer of diethyltin catecholate produced in 83% yield based on initial IIIb. The results obtained and the above facts allow us to draw the conclusion that the interaction of I and II with distannanes proceeds in several steps, with electron transfer and the form at i on of an ion--radical pair (IX) taking place in the primary step. The probability of removing R3M" from the cage determines the t r ans f or m at i on of the latter. Compounds III and
],
SnR 3
Jr 1~3Sn--Snl~3~ 0
( ~
I SnIq3
(10) OSnR 3 OSnl~
53
VI prepared according to eq. 10 then react with quinone as in reactions 5 and 9. R3Sn" leaving the cage then either is dimerized or reacts with quinone forming the corresponding semiquinone (eq. 11).
4- R3Sn
/SnR 3
(11)
Experimental 3,5- and 3,6-di-t-butylbenzoquinones were prepared in accordance with well known methods [12,13]. Na-semiquinones of I and II were produced by the interaction of disodium salts of the corresponding catechols with equivalent amounts of I and II in ether. Disodium salts were prepared by treating I and II with metallic sodium in ether [14]. All reactions were carried out in evacuated ampoules.
ESR spectra Measurements were performed on an X-region radiospectrometer RE-13-1. Reagent solutions of 1--5 × 10 -2 mol/1 concentration were used to obtain ESR spectra. The temperature of the sample placed in the resonator was thermostatically controlled with the help of a TC-IKhF thermoblock. Mn 2÷ ions in the MnO crystal lattice were used as a standard for magnetic field calibration. Reaction o f 3,5-di-t-butylpyrocatechol disodium salt with Et3SnCl The disodium salt (2.66 g (0.01 mol)) in 30 ml of ether was mixed with 4.82 g (0.02 mol) of EtSnC1. The mixture was kept at room temperature for 3 h after which the ether was replaced with hexane. NaC1 was separated by centrifuging: yield 1.12 g (96%). The c o m p o u n d was recrystallized from hexane in vacuo. 1.22 g (19%) of IIIb was isolated, M.p. 54--56°C. Anal.: found: C, 48.97; H, 7.31; Sn, 36.81. C26Hs00~Sn2 calcd.: C, 49.41; H, 7.91; Sn, 37.51%. Reaction of sodium semiquinolate with triethyltin chloride Et3SnC1 (4.82 g (0.02 mol)) was added to 4.86 g (0.02 mol) of sodium semiquinolate. The disappearance of the sodium semiquinolate colour indicates the termination of the reaction. The ether was the substituted for hexane and the residual NaC1 was removed from the reaction mixture by dissolving in water. 3.86 g (86%) of Vb was isolated, M.p. 274--276°C Anal.: found: C, 54.27; H, 7.64; Sn, 29.88. C18H3002Sn calcd.: C, 54.54; H, 7.75; Sn, 29.97%. Mol. wt. (cryosc.) 770). GLC analysis carried out after the hydrolysis revealed the presence of 1.75 g (40%) of hexaethyldistannoxane and 1.24 g (25%) of 2-ethoxy3,5-di-t-butylphenol. The reactions of sodium semiquinolate with other R3SnX compounds were carried out in a similar manner. The characteristics of the various organotin compounds are presented below.
54 R = Me (Va). Va was recrystallized from a hexane/toluene mixture (1/2) (yield ~41%). Va decomposes above 350°C. Anal.: found: C, 52.05; H, 6.66; Sn, 32.74. CI,,H2~,O2Sn calcd.: C, 52.07; H, 7.05; Sn, 32.19%. Mol. wt. (cryosc.) 670. R -- Bu (Vc). Vc was recrystallized from hexane (yield ~40%). M.P. 183-185°C. Anal.: found: C, 58.60; H, 8.43; Sn, 25.96. CnH3802Sn calcd.: C, 58.31; H, 8.39; Sn, 26.22%. Mol. wt. found, 830; calcd. (dimer) 905.4. R = Ph (Vd). Vd was recrystallized from toluene (yield ~45%). M.P. 2 1 6 218°C. Anal.: found: C, 63.55; H, 5.60; Sn, 24.39. C.~,H3002Sn calcd.: C, 63.32; H, 6.08; Sn, 24.09%. Reaction o f hexaethyldistannane with (I) in benzene
(4.11 g (0.01 mol)) Hexaethyldistannane was added to 2.20 g (0.01 mol) of I in benzene. The solution became green in colour. The reaction terminated after 15 min at room temperature: the colour of the solution becoming orange. 4 mol of gas were formed in the process. GLC analysis of the gas revealed the presence of ethane and ethylene. 2.92 g (71%) of unreacted distannane was found in the reaction mixture by GLC method. When benzene was substituted for hexane, 1.92 g of Vb was isolated (83% yield based on reacted distannane). Reaction o f 3,5-di-t-butylcatechol disodium salt with Et2SnCl2
Disodium salt (0.01 mol) in 30 ml of ether was added to 2.46 g (0.01 mol) of Et2SnC12 in 10 ml of ether. The solution was kept for 3 h at room temperature. The ether was than replaced by hexane and the residue of NaC1 was removed from the reaction mixture b y dissolving it in water 1.13 g (.97%) of NaCl was isolated. 3.36 g (85%) of Vb was isolated u p o n cooling. Reaction o f IIIb with 1,2-bis(triethylstannyloxy)-3,5-dit-butylbenzene
IIIb (0.80 g (0.00127 tool)) in 10 ml of ether was mixed with 0.84 g (0.0038 mol) of I at room temperature. The colour of quinone rapidly disappeared. After the reaction terminated the ether was replaced by hexane and 0.84 g (83%) of Vb was isolated upon cooling. Initial quinone was not present in the reaction mixture according to chromatographie analysis data. References 1 G.A. A b a k u m o v , N.S. V y a z a n k i n , E.N. G l a d y s h e v , G.A. Razuvaev, P.Ya. B a y s h k i n a n d V.A. Muraev, J. O r g a n o m e t a l . C h e m . , 64 ( 1 9 7 4 ) 3 2 7 . 2 G.A. Razuvaev, E.N. G l a d y s h e v , P.Ya. B a y s h k i n , G.A. A b a k u m o v a n d E.S. Klimov, Izv. A k a d . N a u k SSSR, Set. K h i m . , ( 1 9 7 6 ) 2 7 6 2 . 3 G. N e u m a n n a n d W.P. N e u m a n n , J. O r g a n o m e t a l . Chem., 42 ( 1 9 7 2 ) 2 7 7 . 4 A.B. Cornwell, P.G. H a r r i s o n a n d T.A. R i c h a r d s , J. O r g a n o m e t a l . Chem., 67 ( 1 9 7 4 ) C43. 5 A.B. Cornwell, P.G. H a r r i s o n a n d J.A. R i c h a r d s , J. O r g a n o m e t a l . C h e m . , 1 4 0 ( 1 9 7 7 ) 2 7 3 . 6 B. S c h r o e d e r , W.P. N e u m a n n a n d H. Hillgartner, Chem. Bet., ( 1 9 7 4 ) 3 4 9 3 . 7 S.G. Kukes, A.I. P r o k o f ' e v , N.N. B u b n o v , S.P. Solodovnikov0 E.D. K o r n i e t s , D.N. K r a v t s o v a n d M.I. K a b a c h n i k , Dokl. A k a d . N a u k SSSR, 2 2 9 ( 1 9 7 6 ) 8 7 7 . 8 A.I. P r o k o f ' e v , T.I. P r o k o f ' e v a , N.N. B u b n o v , S.P. S o l o d o v n i k o v , I.S. B e l o s t o t s k a y a , V.V. Ershov a n d M.I. K a b a c h n i k , DokL A k a d . N a u k SSSR, 2 3 9 ( 1 9 7 8 ) 1 3 6 7 . 9 G.A. A b a k u m o v , V.A. Muraev, G.A. Razuvaev, V.D. T i k h o n o v , Yu.V. C h e c h e t and A.I. Nechuev, Dokl. A k a d . N a u k SSSR, 2 3 0 ( 1 9 7 6 ) 589.
55 10 N . A . C h u m a e v s k i 0 T h e V i b r a t i o n s p e c t r a o f O r g a n o e l e m e n t C o m p o u n d s of I V B a n d V B G r o u p s , Mir, M o s c o w , 1 9 7 1 (in R u s s i a n ) . 11 A. N a g a t a a n d I. I g o d a , J. C h e m . Soc. J a p . , 9 ( 1 9 7 5 ) 1 5 4 5 . 12 H . H . S c h u l z e a n d W. Tlaig, J u s t u s Liebigs A n n . C h e m . , 5 7 5 ( 1 9 7 2 ) 2 3 1 . 13 I.S. B e l o s t o t s k a y a , N.L. K o m i s s a r o v a , E.V. D s k u a r y a n a n d V . V . E r s h o v , Izv. A k a d . N a u k S S S R , SE Ser. K h i m . , ( 1 9 7 2 ) 1 5 9 4 . 14 E. Muller, A. R i e e k e r , K. S c h e f f l e r a n d A. H o o m a y e r , A n g e w . C h e m . , 7 8 ( 1 9 6 6 ) 9 8 .