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Desulfurization of Benzo[b]thiophene by SRu Exchange Formation and Structure of the Cluster [Ru3(CO)8(C8H6)].

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ed. however, that the isomerization rate for trans-3 is half that
for rrcins-2 (Scheme 2). This observation nicely supplements the
former structural analysis (Fig. 1) which also suggests that trans-2,
(Fig. 1 a) being significantly more strained than /rum-3 (Fig. 1 c).
would. given the opportunity, undergo a faster conformational
change. Therefore, the present combination of structural and
kinetic studies demonstrates that one driving force for the isomerization of such redox cage molecules is to achieve the less
constrained planar configuration for their TTF” cores. that is.
the c i ~configuration, even for the longer bridge. The first event
of the EC mechanism now involves the creation of the oxidized
/Y(II?.S cages T” ; one expects therefore that the subsequent lengthening of the inner T T F central double bond will result in an
increase of the steric constraints within the cages in their trans
configuration. Thus. the electron transfer also increases the tension within the /runs cages, while at the same time weakening the
central double bond. These combined events appear quite effective at driving the trans to cis isomerization even in the case of
the somewhat less constrained /runs cage 3. Indeed, while the
aliphatic fragment of the -S(CH,), zS- bridge is properly locked
in within the crystal structure of trims-3 (Fig. 1 c). it is found
highly disordered within the structure of (cis-3);+[Re6S,C1,]
which indicates that the cage in the cis configuration is unconstrained and fairly flexible (Fig. 1 d).
Future reports on this unique system will focus on the design
and properties of molecular solid-state assemblies based on
such redox-active nonplanar molecules whose molecular shape
switches upon electron transfer.
Received. February 19. 1994 [Z 6700 IE]
German version’ Aiigcii.. Clim?. 1994. 106. 1448
[I] W. Huber. K. Mullen, Ace. Chmi. Rcs. 1986. I Y . 300 306.
[2] M . Jorgensen, K. Lerstrup, P. Frederiksen. T. Bjarnholm. P. Sommer-Larsen,
I
Org. Chcrn. 1993. 58, 2785. and references
K. Schaumburg. K. Bechgaard. .
therein.
131 Only few cagelike n-donor molecules exhibiting reversible redox processes have
been described so far: a ) A. Renault. D. Talham. J. Canceill. P. Batail. A.
Collet, J. Lajzcrowicz. Airgcu. Clieni. 1989. /Of. 1251 ; .4iigeii. Cliiwi. / / i f . Ed.
Eiigl. 1989. 28, 1249. h) M. Adam. V. Enkelmann, H.-J. Rider. J Riirich. K.
Milllen. rhid I9Y2. 104. 331 and 1992. .?I. 309: c) M. Adam. K . Miillen. 4d1’.
M u r i ~ r 1994.
.
6. 439.
[4] F. Bertho-Thoraval. A . Robert, A . Souizi. K. Bouhekeor, P. Batail, J. C h i n .
So1 Clwn~.Coiiim~iii 1991, 843.
[i] K. Boubekeur. P. Batail. F. Bertho-Thoraval, A. Robert. Acro Cr!,.clu/logr.
.%/. C. 1991. 47. 1109.
[h] As nbsxvcd recently for other cage donor inolecules with strongly bent redox
unit: a ) T. Jorgensen. J. Becher. T K Hansen. K. Christiansen. P. Roepstorff.
rd. Adv M a i e r . 1991, 3, 486: b) R. Gasiorou,ski. T. Jorgeiisen. _I Mollei-. T. K. Hansen. M. Pietrasrkiewicr, J. Becher, ibid. 1992. 4,
568
[7] /ruii\-Z:M.p. 358-159 C,correctelementalanalysis(C.H. S ) . ‘ H N M R ( C D CI,. 300 M H r ) : 0 = 3.07 (dtt. 2H. S-CH,,).2.52 (dt, 2 H , S-CH,). 2.17 ( s , 6H,
Me). 1.66 (m.4 H ) . 1.33 (m. XH). 1.02 (m. 4H): MS: n ; : . 434037 (calcd
334.0358)
[8] triiirs-3. M.p. 115 116 C. correct elemental analysis (C. H. S). ’ H NMR
(CDCI,. 80 MHz): d = 3.62 (m, 4 H ) . 2.05 (s, 6H. Me). 1.20 (m, 2OH); MS:
i i i ; : : 462.066 (calcd 462.067).
[Y] Cry$tiil structure for rruiic-2: C,,H,,S,.
M = 434.79. yellow flat crystals.
moiiocliiiic space group P l n . (I =11.874(2), h =7.745(2). c =12.996(2) A.
/{ = 116 99(2)
V = 1065.0 A’. Z = 2. Q,.,,,, = 1 36 g ~ m - Mo,,
~ ; radiation:
iibwrptioii corrections by Y-scan: 1902 independent reflections with 0 - 2 8
scans were measured tip to H = 25 at 293 K on an Enraf-Nonius CAD4 diffriictometer The structure was solved by direct methods. The fullmatrix leastsquares refinements of 109 parameters from 1519 reflections with I > 3 (i(/)
convci-gcd at R = 0.035 and R, = 0.056 [12].
[lo] Shiny, black paralellepiped singlecrystals of(cis-2”),[Re,S,C1,]2~ . 2CH,CN
were hui-vested after five days of anodic oxidation under constant low current
(1.5 pAmp) at a platinuin wire electrode of /runs-2 (0.025 mmol) in a 7:l
acetonitrile.dichloromethane solution of (Bu,N)Z(Re,S,CI,) (0.022 mmol).
The latter was prepared according to published procedures 1141. Crystal strucM =
ture for (ci\-2”),[Re,S,,CI,]’~ . 2CH,CN: C,,,H,,CI,N,Re,S,,.
2.072.44. triclinic. space group P-1. u =12.010(6). b =13.795(7). L‘ =
i n 6 ’ ) 7 ( 1 ) j \ . ~ = 9 ~ . 9 L ) ( 2 ) . / ~ = 1 0 2 . ~ 8 ( 2 ) . ~ = 7 j . v6 =1 i( 6j )7. 2 . 7 A 3 , z = i ,
.
Q
~ = 2.06
~
,gcm-’:
~
~ Mo,, radiation; absorption corrections by Y-scan: 7598
independent reflections with u)-2 Oscans were measured up to (I = 38 at 293 K
on an Enraf-Nonius CAD4 diffractometer. The structure MI?, solved by the
Patterson method. The fullmatrix least-squares refinement5 of 334 parameters
from 4244 reflections with I > 3 ~ ( 1converged
)
at R = 0.034 and R , = 0.043.
The cation radical cores of the 1,;s cage molecules form strong. discrete fully
oxidized diamagnetic dimers in the crystal in agreement with the absence of an
ESR signal.
[ I l l Crystal structure for rrur~s-3:C,,H,,S,, M = 462.85. yellou flat cryst?ls, triclinic. space group PT. u = 9.633(2). h =10.308(2). ~ ‘ = 1 3 . 3 5 0 ( 2A.
) a=
110.16(1). /j = 98.04(1). y =105.74(2)’. C’=1157.1 LA.Z = 2. pirlid =
1.33 g c m - A ,Mo,, radiation: absorption corrections by Y-scan: 4503 independent reflections with o - 2 0 scans were measured up to 0 = 26 at 293 K on an
Enraf-Nonius CAD4 diffractometer. The structure was solved by direct methods. The full-matrix least squares refinements of 235 p~rainctcrsfrom 2956
reflections with I > 3 a(/) converged at R = 0.029 and R, = 0.034.
[I 21 Brittle. black paralellepiped single crystals of (cu-3); ’ [Re,S,CI.,] were harvested after five days of anodic oxidation under constiint low current
(1.5 {‘Amp) at a platinum wire electrode of /runs-3 (0.021 mind) i n ii 7:1
acetonitri1e;dichloromethane solution of (BU,N)~[R~,S,(’I.,J(0.026 miiiol).
The latter was prepared according to published procediirca 1141. C‘i-ystd structure for (~i.~-3);*[Re,S,CI,]~
: C,,H,,CI,Re,S,,,
IM = ?.S?2.3S, triclinic.
space group Pi. (I = 12.086(6). h =13.939(8), c = I 1.306(?) A. 1 = 90.690).
8=103.67(3). ; . = 7 5 . 5 3 ( 5 ) , C’=1790A3. % = I . p , , , ,‘,, = 3 4 g c m - ’ . Mo,,
radiation; absorption corrections by Y-scan; 8278 independent rellections w t h
w 2 B scans were measured up to H = 28 at 293 K on an Enriif-Noniur CAD4
diffractometer. The structure was solved by the Patterson method. Note that.
not only was the thermal motion for all atoms of the u.\-3 c‘ition found to he
significantly larger than for the other three structures but also the located
carbon atoms of the -S(CH,),,S- fragment. which are consistently found all on
one side of the molecule only, exhibited considerable instability uhen treated
as independent atoms in the refinement procedure. Icadin@ to unrealistic
geometries. Therefore the final refinement stages were conducted imposing
restraints on bond lengths and angles for this fragment using the program
XTAL3.2 [IS]. Thus. the full-matrix least-squares refinement\ of 253 parameters from 3950 reflections with / > 3 u(/) converged a t R = 0.1 15 and
R, = 0.161. Further details of the crystal structure investigiitions may he ohteined from the Fachinformationszentrum Karlsruhe. D-76344 EggenrtciiiLeopoldshafen (FRG) on quoting the depository number CSD-58143. A single. quasi-isotropic ESR line (temperature independent linewidth o f 4 3 Gauss
with g values extremes of 2.0065 and 2.010) is observed on a Fingle crystal of
(cis-3)Z+[Re6S?CIU]-.
The spin susceptibility shows a Curic-type behavior in
agreement with the presencc of discrete. noninteracting m i x e d - v h v x dimers
in the structure.
[I31 C. P. Andrieux. J.-M. Savint in Elecfrocliemicul R ~ u c r i o i i si i i 1ii1~~~11gufron.c
of
R u m und Mechunisms of Reucliuns. Tcchniqries uf C h o i i i . t r r ) . . L ’ d V 1 4 6 .
Purr 2 (Ed.: C. F. Bernasconi). Wiley. New York, 1986, pp. j0.5 390.
[I41 J.-C. Gabriel. K. Boubekeur. P. Batail. lnorg. C1iviii. 1993. 32. 1x94.
[is] S. R. Hall. H . D. Flack. J. M . Stewart, X T A L 3.7 R
ties of Western Australia, Geneva and Maryland. 1992.
Desulfurization of Benzo[b]thiophene by S/Ru
Exchange: Formation and Structure of the
Cluster [Ru,( CO),( C,H,)J * *
Alejandro J. Arce,* Ysaura De Sanctis,
Arquimedes Karam, and Antony J. Deeming*
The organometallic chemistry of thiophenes has been developed extensively during the past few years.“ - 31 The cleavage of
C-S bonds in thiophenes is required for metals to abstract
[*I Dr. A. J. Arce, Y. De Sanctis, A. Karam
Centro de Quimica. lnstituto Venezolano de Investigaciones Cientifica? (IVIC)
Apartado 21827. Caracas 1020-A (Venezuela)
Telefax. Int. code + (2)501-1350
[**I
Prof. A. J. Deeming
Department of Chemistry. University College London
20 Gordon Street. GB-London WCIH OAJ ( U K )
Telefax: Int. code + (713380-7463
This work was supported by the Sciencc and Engineering Research Council
(SERC). by the Consejo Nacional de Investigaciones Cientificns y Tecnologicas (CONICIT) (Venezuela). and the University of London Central Research Fund.
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sulfur from the heterocycle, and the homogeneous desulfurization of thiophenes with transition-metal compounds has provided models for the catalytic heterogeneous dehydrosulfurization
of thiophenic components of crude oil.
The cluster [Fe,(CO),,] reacts with thiophene with loss of the
sulfur atom to give the ferrole compound [Fe2(p-C,H,)(CO),],[41
while [Fe,(p-C,H,MeS)(CO)J as well as the sulfur-free species
[Fez(/(-C,H,Me)(CO),] are formed from 2-methylthiophene.['- 61
Similarly the reaction of [Ru,(CO),,] with thiophene['] gives the
sulfur-free species [Ru,(p-C,H,)(CO),] derived by C-S bond
cleavage as in the iron case. but in addition the tetranuclear
cluster [Ru,(p,-S)(p-C,H,)(CO), 1], which contains separate S
and C,H, ligands within the same molecule. Better yields were
obtained from 2-rnethylthiophene. and in this case. products of
both C- S and C-H bond cleavage were obtained: [Ru,(p-H)(pC,H,MeS)(CO),,] (em and mdo isomers) and [Ru4(p3-S)(pC,H,Me)(CO), I]. With osmium, C - H rather than C - S bonds
are cleaved exclusively, and [Os,(CO),,] o r [Os,(CO),,(MeCN),]
react with thiophene to give the thienyl isomers [Os,(p-H)(pC,H,S)(CO),,] (eso and endo isomers in rapid equilibrium),
which decarbonylate to the "thiophyne" cluster [Os3(p-H),(p3C,H,S)(CO),].[*- "I
Benzo[h]thiophene I and dibenzothiophene more closely correspond to the major sulfur components in fossil fuels than
thiophene, and these compounds are difficult to activate." 21 The
first example of metal-assisted opening and hydrogenation of 1
was described by Rauchfuss et al.,'61 who treated 1 with
[Fe,(CO),,] to obtain the benzothiaferrole [Fe,(C,H,S)(CO),],
which was hydrogenated to give ethylbenzene together with
some 2-ethylbenzenethiol, bis(2-ethylphenyl) sulfide, and bis(2ethylphenyl) disulfide. Also oxidative addition of the C --Sbond
of I with [(C,Me,)Rh(PMe,)(Ph)H] was reported.['31 Recently
oxidative addition of 1 to iridium(1) gave an iridium(ii1) complex
that could be selectively hydrogenated to give the 2-ethylbenzenethiolate ligand at iridium(rr~).['~~
We now report the synthesis of the clusters [Ru,(C,H,)(CO),] (2), [Ru,(C,H,S)(CO),]
( 3 ) . and [Ru2(C,H,)(CO),] (4),obtained from the reaction of
[Ru,(CO),,] with 1 under relatively mild conditions.
The reaction of [Ru,(CO),,] with 1 under reflux in T H F gave,
compounds 2.3,and 4 in 28.17, and 10 % yield. respectively. after
TLC work-up (Scheme 1). The clusters were characterized by
' H N M R and IR spectroscopy. and the X-ray structure of 2 was
determined." 'I
Compounds 2 and 4 are formed by C-S bond cleavage and
extrusion of the sulfur atom. Compound 3 is closely related to
that obtained by Rauchfuss from the reaction of benzo[b]thiophene and [Fe,(C0)l,];[6] their ' H N M R spectra correspond.
The dinuclear compound 3 was isolated and heated in cyclohexane for 20 min to afford an insoluble black by-product, which
suggests the formation of RuS, , and the sulfur-free compound
4,since the spectroscopic data of 4 resemble those of the product
obtained from the debromination of 1,4-dibromocyclooctatetraene with [Ru,(CO),,] in hydrocarbon solvent (the
metallaindene complex [Ru,(C,H,)(CO),]), the most likely
structure is that shown in Scheme 1 . The X-ray structure of the
osmium analogue was reported.["]
Although 4 was obtained in low yield (10%). this can be
increased considerably if the reaction is carried out under carbon monoxide. ' H N M R (CDCI, solution) and IR monitoring
(showing the presence of Ru(CO),) confirmed that 2 can be
converted quantitatively into 4 at room temperature under 1
atm of CO over a period of 24 h (Fig. 1 ) .
Under our reaction conditions, no decacarbonyl or nonacarbony1 clusters such as the eso and endo isomers [Ru,(p-H)(pC,H,S)(CO),,] or their expected decarbonylation products
1
I
A
(PA\ D..
4
Scheme I . Synthesis of 2, 3. and 4.
[Ru3(p-H),(p-C,H,S)(CO),1 were obtained on treating 1 with
[Ru,(CO),,] . Probably compound A containing a ring-opened
benzo[h]thiophene ligand bonded to an opened Ru, triangle is
formed in the early stages of the reaction (Scheme 1) and con-
I
I
9
E
I
I
I
7
6
5
6 [PP~]
Fig. 1 Monitoring of the conversion 2 + 4 (CDCI,. CO 1 atrn) by 'HN M R spectroscopy. A: Initial spectrum; B: after 70 min; C : after 5 h: and D : after 24 h.
showing the clean. almost quantitative. conversion to compound 4.
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verts readily to the dinuclear ring-opened compound 3, or is
desulfurized to afford cluster 4. A single-crystal X-ray structure
for 2 (see Fig. 2) was needed to establish the mode of bonding.
The desulfurized ligand is bonded to three metal atoms as a n
10-electron donor to give a 50-electron cluster with only two
Ru-Ru bonds.
T
O(311
Fig. 2 Molecular structure of 2: selected bond lengths [A] and angles [ 1: Ru(1)Rui2). 1.946(2): Ru(Z)-Ru(3), 2.781(2): Ru(2)-C(7), 2.257(5j; Ru(2)-C(8), 2.237;
R u ( l ) - [ . ( I ) , 2.322(5); Ru(1) C(4). 2.294(6): Ru(3)-C(l). 2.088(6); Ru(3)-C(X).
2.058i6). ~ ( 1 -C(X
)
1.41xx): c(2) ~ ( 3 1 ,1 . 4 3 ~ 9 ) ;c ( 3 ) ~ ~ ( 4i.40(1);
) .
~(4)C ( 5 ) . l . 4 l i l ) ; C(5)-C(6), 1.424(8): C(6)-C(7). 1.45XiX); C(7)-C(8). 1.400(9);
C(1) ~ C i 6 ) . 1.454(8); R u ( l ) . . . R u ( 3 )
3.815(2): R u ( 2 ) . . . C ( l ) 2.934(6):
Ru(2) . C(6). 2.657(6): Ru(l)-Ru(2)-Ru(3). 83.5(1): Ru(l)-C(l)-Ru(3). 119.6(2);
Ru(3)-CIl)-C(6). 113.9(4); Ru(l)-C(l)-C(6), 72.9(3); Ru(3)-C(X)-C(7), 116.8(4);
Ru(3)-CiX)-C(7), 72.7(3): C(2)-Ru(l)-C(5). 76.0(2); C(3)-Ru(l)-C(6). 75.6(2);
Ru(l )-Ci6)-C(7). 128.3(3): Ru(2)-C(7)-C(6). XX.6(3).
.
.
[Ru,(C,H,)(CO),] (2) is the first example of a fully characterized trinuclear Ru complex containing a I-ruthenaindene system.
The nine atoms of the bicyclic metallaindene system are substantially coplanar; the C,H,Ru(CO), unit can thus be regarded as an 8-electron-donor ligand n-complexed to the Ru,(CO),
group.
[I] R. J. Angelici, Acr. Clieni. Res. 1988. 21, 387
[2] T. B. Rauchfuss, Prog. Inorg. Chrm. 1991. 39, 259.
[3] T. Frejd in Heterocyclic Compounds, Voi44 (Ed.: S. Gronowtta). Wiley. New
York, 1992. Part 5. pp. 257-754.
[4] H. D . Kaesz, R. B. King, T. A. Manuel. L. D. Nichols, F. G . A. Stone. J. Am.
Cliem. Sor. 1960, 82, 4750.
[5] P. Huberer. E. Weiss. J. Orgunorner. Chrm. 1977. 129. 105.
[6] A. E. Ogilvy. M. Draganjac. T. B. Rauchfuss, F. R. Wilson, Orgununirtu//ic.s
1988. 7, 1171.
[7] A. J. Arce. P. Arrojo. A. J. Deeming. Y. De Sanctis. J. C/icvn So(..Dulmi Truns.
1992. 2413.
[8] A. J. Arce. A. J. Deeming, Y. De Sanctis. R. Machado, J. Manrur. C. Rivas. J.
Chwr Soc. Chrm. Coinmun. 1990, 1568.
[9] A. J. Arce. J. Manzur, M. Marquez. Y. De Sanctis. A. J. Deeming. J.
Orgunom@/.Ckrni. 1991, 412. 177.
[lo] A. J. Deeming. A. J. Arce. Y. De Sanctis, M. W. Day. I<. I. Hardcastle,
OrganomctaUics 1989, H. 1408.
[ l l ] M. W. Day, K. 1. Hardcastle, A. J. Deeming. A. J. Arce. Y. De Sanctir.
Orgunoiiictu//it.s 1990, 9, 6.
[12] R . Bartsch. C . Tanelian. J. C u d . 1974.35.353; D. R. Kilanowski. B. C. Gates.
;hit/. 1980, 62. 70.
1991. 113, 559.
[13} W. D. Jones. L. Dong. J. Am. C/ierii. SJC.
[14] C. Bianchini. A. Meli. M. Peruzzini. F. Vizza. P. Frediani, V. Herrera. R. A.
Shchez-Delgado. J A m . Climi. Sor. 1993. 115. 7505.
1151 Ci-ystal structure of 2: C,,H,O,Ru,. M = 629.43. monoclinic, space group
P2,lii. ~ = 9 . 4 4 7 ( 4 ) , h=16.426(8), c=ll.X57(8),&, /j=102.81(5) , J'=
1794(2)A3.Z= 4.7. = 0.71073,&,p(Mok,) = 14.9cm-'.F(000) =1192.Solution with direct methods (SHELXTL-PLUS),4101 unique absorption-corrected data between 5 < 2 H s 55 and with f, I 1.5 u(fJ used. 244 parameters ( a l l
non-H atoms anisotropic), final R = 0.041X and R , = 0.00469. with
R,. = [ ~ w ( l F O-l ~ F c ~ ) 2 ~ ~ i ~and
~ ~ usF o=l:[uz(Fo)
~2]'~+
z 0.001221;3. H atoms
in calculated positions (C-H 0.96 A. c',,, = 0.08 A'). Further details of the
crystal structure investigation are available on request from the Director of the
Cambridge Crystallographic Data Centre, 12 Union Road. GB-Cambridge,
C B 2 l E Z ( U K ) on quoting the full journal citation.
[I61 P. J Harris. J. A. K. Howard, S. A. R. Knox. R. P. Phillips, F. G. A. Stone. P.
Woodward. J. Clicni. So<,.D u h n Truns. 1976, 377.
Samarium Iodide Induced Intramolecular
C-Glycoside Formation : Efficient Radical
Formation in the Absence of an Additive
Daniel Mazkas, Troels Skrydstrup,* Olivier Doumeix,
and Jean-Marie Beau*
E.xprrinwntal Procrdzrrr
[ R U , [ C O ) ~(0.200
~ ] g) and 1 (0.200g) were heated at reflux in tetrahydrofuran
(50 cni') for 24 h under N,.The orange-brown solution was evaporated to dryness
under reduced pressure. and the residue separated by TLC on silica with n-hexane
'IS eluent into three bands. which yielded 2 (yellow, 2X%). 3 (yellow-orange, 17%).
a n d 4 ( y e l l o w . 10%).Asolutionof2(0.020g)inCDCI,(0.5 cm3) underCO(1 atm)
showed complete conversion to compound 4 in 24 h at room temperature (monitored by ' H N M R spectroscopy). Crystals ofcompound 2 for structure determination
were obtained fi-om cyclohexane. 2: IR (cyclohexane): 17(CO)[cm-'1 = 2077 s.
2045 1's. 2017 bs. 2003 s. 1980 m. 1963 m: ' H N M R (CDCI,. 300 MHz, 296 K. J i n
HL):0 = 8.89 (d. HI). 5.45 (d. H'j. 4.44 (dd. H'). 5.96 (ddd. HI). 6.36 (ddd, H'),
5.11 (dd. HI') [J(H'H2) = 6.3. J(H'H4) = 6.7, J(H3H5) = 1.1. J(H4H5)= 6.0,
JiH'H') = 1.3. J ( H S H h )5.81.3:IR(cyc1ohexane): 17(CO)[cm-'1 = 20x8 m. 2061 s.
2021 s. 2 0 1 4 ~ s .2000m. ' H N M R (CD,COCD,. 300MHr. 296K. J in Hz):
ii = 9.04(d. HI). h.OX(dd. H'). 7.18 (dddd. H'),6.91 (ddd. H"), 7.05(ddd. H'). 7.22
(dd. hr. H"j [ J ( H ' H ' ) = 10.0. J ( H z H 3 j= 0.6. J(H3H4) = 7.6. J ( H 3 H 5 )= 1.2,
J(H'H-) = 0.5. J(H"Hi) = 7.5. J ( H 4 H b )= 1.4. J(H5Hh)= 7.51. [Fe,(C,H,S)(CO),] [h]: IR (cyclohexane): ?(CO) [cm-'1 = 2077 m, 2044 vs, 2005 s, 1993 w.
' H N M R (CD,COCD,. 300 MHz. 296 K, J i n Hz): h = 9.04 (d, HI), 5.67 id. H'),
7 06 (dd. H'). 6.X1 (ddd, H4), 6.99 (ddd, H'), 7.12 (dd, He) [J(H'H'): 9.1.
J(H3H*) = 76.J(H'Hs) = I.2.J(H4HS) = 7.5,J(H4H") = I.2,J(HSHb) = 751.4:
IR (cyclohexane)' i ( C 0 ) [cni-'] = 2082m. 2051 vs. 2010vs, 1992 m, 19x4s.
'H NMR (CD,COCD,. 300 MHz. 296 K. J in Hz): d = 7.53 (d. H'). 7.45 (d. H').
8-04 (ddd. H'). 7.35 (ddd. H4]. 7.05 (ddd. H'). 7.89 (d. hi-. Hh) [J(H'H') = 6.5.
J(H-'HJ) = X.5. .J(H'H'j = 1.1, J(H'H6) = 1.0, J(H"Hi) = 6.7, J(H4Hb) = 1.2,
J(HsHHh)
= 8.31.
Received. January 28, 1994 [ Z 6653 IE]
German version: Angew. Chriii. 1994. 106. 1459
Of the numerous existing methods for C-glycoside construction,['] the intramolecular free radical cyclization employing the
temporary silicon connection reported by Stork et al. lends itself
as the most attractive.[21The reaction conditions are mild and
complete stereochemical control at the anomeric center may be
achieved by the judicious choice of the linking hydroxy group
(i. e. the oxygen of the substrate which carries the silicon tether).
Only a few examples of this reaction are known, however, and
in each case the tin hydride based procedure coupled with
phenylselenoglycosides has been applied for radical generation
at the anomeric center.[2-41
In the last few years samarium(i1) iodide has not only emerged
as a unique alternative for carrying out reductive radical cyclization reactions of unsaturated haloalkanes, but has shown greater
versatility as
However, for efficient single-electron transfer with concomitant radical formation, the reducing potential
of Sml, has to be augmented by the addition of a cosolvent such
as hexamethylphoshoramide (HMPA) .['I Reductive desulfonyl-
[*I
Dr. T. Skrydstrup, Prof. Dr. J.-M. Beau. D. Mazeas. 0. Doumeix
Universite d'Orleans, Laboratoire de Biochimie Structurale
URA 499. BP 6759. F-45067 Orleans CCdex 2 (France)
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exchanger, benz, structure, ru3, c8h6, clusters, sru, thiophene, formation, desulfurization
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