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Highly Coordinated LanthanoidЦPhosphane Complexes.

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E.xprrinwntal Procedure
In the preparative-scale reaction. 1.50 mmol hydroperoxide ( f ) - l and
1 .50 mmol guaiiicol were dissolved in 10 mL 0.1 M phosphate buffer (pH 6) and
subsequently 0.25- 1.25 x
mrnol HRP was added. The reaction mixture
was allowed to stand at 20 C for 2 h and then extracted with CH,CI,
( 3 x 20 niL) The combined organic phases were dried over Na,SO, and the
bolvent rcrnoved on the rotary evaporator (ca. 20 C 17 Torr). Hydroperoxide
(S)-1 a n d ,ilcohol (R)-2were separated by column chromatography (silica gel.
0.032 0 62 mmol eluting with petroleum etherldiethyl ether (4.1).
Received: September 7. 1993 [Z 6346 I E ]
German version: Arrgeiv. ('hrrn. 1993. 1115. 1x00
pletely different. This can be attributed at least in part to the
exocyclic carbanion substituent (Me,Si in 11, H in 111). which
in 11 markedly reduces the nucleophilic nature of the carbanion. We have now succeeded in synthesizing highly coordiMe,Si
,"-P
R2
MP-
-
6'O
' P '
\
[ I ] a ) H L Holland. Orguriic Sjnr/i&! w 1 / 7 O.\.if/uriw € n x r i i e . \ , VCH. New
York. 1992: b) S. M. Roberts. K Wiggins, G . Casy. P r q ~ u r [ i i i wBiorrrmsf(nmrr;orr.s
Wliole Cell u r i c / 1,solrrtrd Enzjriie! r n O r p i i c S~nrhasi,s.Wiley,
Chichester. 1992.
[2] .I.H. Dawson. .%~i<~nce
1988. 2411. 433 439.
[3] a ) S. Colonnn. N. Gaggero. A. Manfredi, L. Casella, M Gullotti, G. Carrea.
P. Pasta. Brocfieriiirtri. 1990. 29, 10465-10468; h) S. Colonna. N. Gaggero,
L. Casella, G . Carrea. P. Pasta, T e r r u h d w . A.?jriimrtrJ 1992. 3, 95- 106:
c) H Fu. H. Kondo. Y Ichikawa. G . C. Look. C.-H. Wong, L Org. C/iem
1992. 57. 7265- 7270.
14) E. J Alliiin. L. P. Hager. Li Deng. E. N. Jacohsen. .I A m . C'hen?.Soc. 1993.
115. 4415 4416.
IS] a ) S. Colonna. N. Gaggero. G. Carrea. P. Pasta. J. C h m . So(.. C/ierii. Cornn i i i r i . 1992. 357 358: h) R. Z. Harris. S. L. Newinyer. P. R. Ortiz de Montellano. L Brol. Clicvii. 1993, 268. 1637- 1645.
161 A. Kunnth. E. HBft. H.-J. Hamann. J. Wagner. J. Chronirrrr~gr.1991. 588.
352 355.
[7] a ) A. G Davies. R. V. Foster. A. M. White, J Clzwn. Sw. 1953. 1541 1547:
h) W. Adam. A. Griesbeck. S~nrhe.si.s1986. 1050-1051.
[8] a ) P. Dussault, N. A. Porter. J. Ani. Chcni. So(..1988, /10.6276-6277; h) P.
Dussault. I. Q. Lee. S. Kreifels. L 0 r ~C/im?.
.
1991. 56, 4087-4089.
[9] J. Putter. R. Becker. M<>r/iods
€nzi.rii. Ariul. 3rd ed. i983-19K6, 1983. 3,
286- 193.
p
"'22
C'Me,
RZ
Me,Si
I
111
I1
nated lanthanoid-phosphane complexes in which the ligands are bound as in 11. The methanide 1 acts as a source of
anionic diphosphinomethanide ligands. For the syntheses of
these complexes metal halides are not appropriate starting
materials, since only mixtures containing substantial
amounts of lithium halide are formed. Evidently addition
and only partial substitution occurs, as is established by the
isolation and structural characterization of 2 (violet crystals
from pentane) [Eq. (l)].
-
Ybl,
2 Li[C(PMe,),(SiMe,)]
,I.
cP ---
L'
---
U
1
Highly Coordinated Lanthanoid- Phosphane
Complexes**
By Hans H. Karscli,* Gunter Ferazin. Oliver Steigelmann,
Huub Kooijman. and Wolfgang Hiller
Dedicarsd IO Profiissor Ernst Otto Fischer
on the occnsion of his 75th birthday
Phosphane ligands are almost indispensible in transition
metal chemistry. Complexes with high numbers of coordinated phosphanes are known and are very important in
many catalytic processes. Although lanthanoid complexes
also have notable catalytic properties, there are only few
structurally characterized examples of compounds in which
the metal center is coordinated by a number of phosphane
ligands. Only with heteroatom-phosphane chelating ligands, for example [N(SiMe,CH,PR,),]-,
can up to four
lanthanoid -phosphorus bonds be formed.['] The electrophilicity of lanthanoid centers generally resembles that of
"hard" main group metal centers such as A13+.[*]With
diphosphinomethanides as chelating ligands, metal centers
can attain high phosphane coordination numbers by forming covalent and ionic bonds (I), as in the case of A13 (II).f31
In fact the corresponding lanthanum diphosphinomethanide complex 111 could also be synthesized;[4f however, the coordination modes in I1 (0)
and 111 (x)are com-
2
In 2 (Fig. 1) a YbI, . THF moiety has been inserted into
the framework of 1 . T H E which exists as the dimer
[(THF)Li{C(PMe,),(SiMe,)J1, ,I5] whereby all Li-P bonds
are broken and replaced by four Yb-P bonds. This results in
a seven-coordinate Yb2' ion and the formation of Li-I
bonds.[61
c22
+
[*] Prof. Dr. H. H. Karsch. Dr. G. Ferazin. Dr. 0. Steigelmann.
Dr. H Kooijman. Prof. Dr. W. Hiller
Anorgaiiisch-cliemisches lnstltut der Technischen Universltit Miinchen
Lichtcnhergstrasse 4, D-85747 Garching (FRG)
Telefax: Int. code (89)3209-3125
+
[**I
This work was funded by the Fonds der Chemischen Industrie.
Fig. I . Crystal structure of 2. Important distances [A] and angles [ 1: Yh-I1
3.131(5). Yh-I2 3.114(3), Yb-PI 3.08(1). Yb-P2 2.99(2). Yb-P3 3.03(2). Yh-P4
2.96(1). Yh-01 2.44(4). Lil-I2 2.67(7). Lil-Cl 2.22(8), Lil-01 1.9318). Li2-I2
2 87(1O). Li2-CY 2.20(10). Li2-03 1.72(10)i 11-Yb-I2 176.5(2), Pl-Cl-P2 103(2).
Yh-P2-CI YS(1). PI-Yh-P2 55.7(3), Yh-PI-C1 96(1). P3-C9-P4 101(2). P3-YhC4 54.9(4), Yb-P4-C9 YX(1). Yb-P3-C9 lOO(2).
In order to achieve complete substitution, lanthanoid
complexes containing a better leaving group are needed.
Lanthanoid triflates[’] have now been shown to be successful
reagents. Complex 3 was obtained according to Equation (2)
as yellow crystals (pentane).[’]
Not less than four diphosphinomethanide chelating ligands (regardless of the stoichiometry) are arranged around
the lanthanum ion such that the eight P atoms form one
almost square-planar and one tetrahedral P4 ligand arrangement (Fig. 3). The resulting distorted dodecahedra1 coordi-
I
SiMe,
3
In 3 (Fig. 2) the lanthanoid center is also seven-coordinate: one T H F and three planar diphosphinomethanide ligands surround the lutetium ion in a distorted pentagonalbipyramidal arrangement. Thus the ion is coordinated by six
phosphane donor units. The four-membered chelate rings
are also planar. The T H F ligand can be removed in vacuo;
however, the resulting yellow solid could not be recrystallized.
C27
P2
c 32
P7
C92
P6
p5
c21
6
a
C4’
S12h
C81
Fig. 2. Crystal structure of 3. Important distances [A] and angles [ 1: Lu-P
2.814(2)-2.92212). L u - 0 2.271(5): PI-CI-PZ 106.1(3).Cl-Pi-Lu 99.4(2). Cl-P2Lu 96.8(2), Pl-Lu-P2 57.7(1). P3-C2-P4 107.5(3). C2-P4-Lu 96.3(2). P3-Lu-P4
59.8(1). Lu-P3-C2 95.0(2), P5-C3-P6 104.3(3). C3-P6-Lu 97.3(2). PS-Lu-P6
57.7(1). Lu-P5-C3 95.9(2).
Lutetium, the smallest lanthanoid, is obviously coordinatively saturated in 3. Even in the complexes with the only
slightly larger
as well as with yttrium[”] or lanthanum, the coordination changes dramatically. The lanthanum complex4. which was formed as orange crystals
according to Equation (3),[’01is a representative example.
Me,Si
+ 4 1
TI+
(3)
Fig. 3. Top: crystal structure of 4. Important distances[A] and angles [ 1: La-PI
3.105(2), La-P2 3.068(2), La-P3 3.051(2). Ld-P4 3.145(2). La-PS 3.039(2). La-P6
3.121(2), Ld-P7 3.046(2). La-P8 3.234(2). Lil-C13 2.243(9), Lil-P4 2.879(8),
Lil-C29 1.208(8). Lll-P8 2.814(7). Lil-Si2 2.946(8). Lil-C16 2.541(9). LilH121 2 419(8). Lil-H161 2.339(9). Lil-H163 2.386(9), Si2-Cl6 1.889(6); La-P3C13 90.1(1). P3-C13-P4 102.6(2). C14-P4-La 87.2(1). P3-La-P4 53.75(3). P4C13-Si2 123.3(2). P3-Cl3-Si2 125.7(2), La-P8-C29 90.6(1). P7-C29-P8 100.9(2),
La-P7-C29 96.8( I ) , P7-La-P8 52.14(3). P7-C29-Si4 120.8(2), P8-C29-Si4
126.9(2). La-PS-CZl 9 8 3 1 ) . P5-C21-P6 107.1(2),La-P6-C21 95.6(1), P5-Ld-P6
54.41(5). La-Pl-CS 97.8(1). PI-C5-P2 107.5(2). Ld-P2-C5 99.5(1), PI-Ld-P2
54.62(5). La-P3-C13-P430.3(1), La-P7-C29-P8 27.01(1). La-PS-CZl-P6 13.0(1).
La-Pi-CS-P2 4.55(1). Bottom: structure of the Ld(PIC), fragment in 4.
nation is sterically favorable. The centers of the four chelating ligands are at the corners of a tetrahedron, such that the
two sets of four phosphorus atoms form together with the
lanthanum center two mutually orthogonal planes. The resulting complex has “ate” character; in other words, an excess anionic charge must be compensated for. This is
achieved intramolecularly by the inclusion of a lithium ion
between the carbanionic atoms of two diphosphinomethanide ligands which results in a significant folding of
the four-membered chelate rings. The lithium ion shows additional contacts to two P atoms and also to a PCH, and
SiCH, group ( L i . . . H . . . C ) , so that on the one hand it is
coordinatively saturated and on the other hand so well protected. especially by the SiCH, group, that it neither coordinates additional T H F nor is it released from its “basket” by,
for example, crown ethers. Consider going from the largest
to the smallest metal: if the lighter homologue scandium is
used (i(Sc3+): 0.75 A) instead of lanthanum (r(La3+):
1.03 A), the coordination number changes again. Compound 5 is obtained as yellow needles'"] according to Equation (4).
into a marked affinity by an appropriate choice of ligands,
namely phosphinomethanides.
Experimental Procedure
All reactions were carried out under purified and dried nitrogen using conventional vacuum techniques. The glassware was dried by heating. evacuated several times, and flushed with inert gas. NMR spectra in [D,]toluene; standards:
'H, "C. TMS; "P: H,PO,.
2: To 50mL YbI, ( 3 6 . 7 m ~in T H E 1.84mmol) was added 1 (0.84g.
3.92 mmol) at - 78 "C. The mixture was allowed to warm to room temperature,
and after 12 h stirring the solvent was removed in vacuo. The remaining solid
was extracted twice with 40 mL pentane. On evaporation of the pentane in
vacuo violet crystals formed (1.31 g, yield 97.2%). Correct C,H.I analysis.
Me,Si
Le2
5
Unlike the arrangement in 3, but similar to that in 111 the
scandium center in 5 is not coordinated by a solvent molecule, and. just as in I11 the M-P-C-P four-membered rings are
not planar. The CP, and ScP, planes form an angle of 121
which is intermediate between that in TI and 3 (180") and in
111(80' ) (Fig. 4). As a result of the trigonal symmetry in 5 the
O,
3 1 P ( 1 H )NMR (109 MHz): 6 -24.27 (s), -24.20 (d, 'J("P. '"Yb) =
497.3Hz); ' H N M R (270MHz): 6 =1.38 (s, 24H; PMe,). 0.32 (s. 1 8 H .
SiMe,), 3.28 (s, br. 1 2 H ; THF); "C('H) NMR (67.8 MHz). 6 = 20.21 ("t".
N (separation of the outermost signals) = 21.3 Hz, PMe,), 7.54 (s, SiMe,),
25 19 (s, THF), 68.23 (s, THF).
3: Lu(O,SCF,), (0.65 g, 1.05 mmol) and 1 (0.75 g, 3.50 mmol) were added
together, and 4 0 m L T H F was condensed into the mixture at -78°C. The
solution was allowed to warm to room temperature and stirred for 12 h. Afler
removal of the solvent the residue was dried in vacuo and extracted three times
with pentane. During evaporation of the solvent from the combined filtrates in
vdcuo 3 precipitated as a yellow. crystalline solid (0.49 g, yield: 60.3 %). Correct
C.H analysis.
'*P( ' H NMR (109.4 MHz, 25 C ) :6 = - 26.60 (br). ( - 1 10 C): two AB patterns(2:1):6P,,=-25,41,6P,,
=-31.72.J,,,,,
=245.2Hz.sP,,=-27.78.
6P,, = - 30.13. &,,= 240.0 Hz; ' H NMR (270 MHz): 6 = 1.35 (s, br. 36H;
PMe,), 0.37 (s, 27H; SiMe,), 3.62 (s, br. 4 H ; T H F ) , 1.45 (s, br. 4 H : T H F ) ;
I3 ,I
C, H ] NMR (67.8 MHz): 6 = 22.29 ("1". N = 25.3 Hz. PMe,). 6.43 (s.
SiMe,). 68.48 (s. THF). 25.66 (s, THF).
i
4: To a mixture of La(O,SCF,), (0.78 g, 1.33 mmol) and 1 (0.96 g. 4.48 mmol)
at - 78 ' C was added 40 mL T H F by condensation. After warming to room
temperature the mixture was stirred for 3 d. The solvent wasevaporated and the
residue dried in vacuo and extracted with pentane (3 x 30 mL). When the solvent from the combined pentane extracts was removed under vacuum. the
product precipitated as an orange, crystalline solid. (0.71 g, yield: 65 0 % ) .
Correct C,H analysis.
"Pi'H; NMR (109.4 MHz, 2 5 T ) : b = 29.0 (s, br), -30.8 (s. br),
(-100'C): 6 = - 2 2 to -48 (m); ' H N M R (270MHz): 6=1.31 (s, br.
48H: PMe,), 0.32 (s. 36H; SiMe,): "C('H: NMR (67.8 MHz): 6 = 22.95
("t". N = 25.9 Hz. PMe,), 7.10 (s, SiMe,).
~
Fig. 4. Crystal structure of 5. Important distances [A] and angles [ I: Sc-P
2.617(1). Sc-CI 2.908(2); Sc-P-Cl 80.8(2), P-C1-P 105.4(3). P-Sc-P 94.13(3).
P-C1-Si 126.5(1).
P atoms are arranged in a trigonal-prismatic fashion. The
planar carbanionic C atoms approach the scandium center
without forming a bond (Sc...C: 2.908 A). The coordination mode of the diphosphinomethanide ligands in 5, intermediate between a o-chelating (as in 3) and a n coordination
mode (as in III), appears almost like a snapshot of the mutual conversion of either type of coordination into the other.
This accounts for the facile change in hapticity and for rearrangement reactions as, for example in silicon[l2I and zirconium[' 'I disphosphinomethanide compounds; here we have
observed this structurally for the first time. The folding of
the four-membered chelates in the scandium complex can be
attributed to the additional Sc ... C d-orbital interactions.
The reduced nucleophilicity of the Me&-protected carbanion compared to that in 111 and the steric hindrance at the
small Sc3+ ion prevents a closer approach of the carbanions
to the coordination center. The four-, six-, and especially
eight-coordinate phosphane-lanthanoid complexes presented here demonstrate that the disinclination of lanthanoids to
coordinate phosphanes can be reversed and even transposed
5 : To a mixture of Sc(O,SCF,), (0.85 g. 1.73 mmol) and 1 (1.17 g. 5.46 mmol)
at - 78 "C was added 40 mL T H F by condensation. The resulting solution was
allowed to warm to room temperature and stirred for 3 h before the solvent was
evaporated. The residue was dried in vacuo and extracted with pentane
(3 x 30 mL). During evaporation of the pentane from the combined extracts
orange needles precipitated (0.91 g, yield: 79.3%). Correct C.H analysis.
" P i ' H ) NMR (109.4MHr. 25°C): 6 = -11 to -23 (br). (-100'C): 6 =
-12.82 (s), (+70'C): 6 = -17 to -23 (br); ' H N M R (270 MHz): 6 =1.25
(s. br. 36H; PMe,), 0.33 (s, 27H; &Me,), "C('HJ NMR (67.8 MHz):
6 = 20.36 ("t", N = 30.2Hz. PMe,), 6.11 (s, SiMe,).
Received: July 20, 1993 [Z 6220 IE]
German version: Angew. Chrm. 1993, 105. 1814
[I] M. D. Fryzuk, T. S. Haddad, S. J. Rettig, Orgunomerullics 1991, 10,20262036.
[2] H. Schumann. Angrit. Chem. 1984. 96. 475-493; Angrx. Chem. Int. Ed.
Engl. 1984. 23,474-493.
[3] H. H. Karsch. A. Appelt. J. Riede, G. Muller, Orgnnomrfullic~1987. 6,
316-323.
141 H. H. Karsch. A. Appelt. G. Muller, Angen.. C h m . 1986. YN, 832-834;
Angeu. Chem. In!. Ed. Engl. 1986. 25. 823-824.
[ 5 ] H. H. Karsch. B. Deubejly, G. Miiller. J Orgunornet. C / w m 1988, 352,
47-59.
(61 Crystdilographic data (141 of 2 at 293 K (Mo,, radiation. i.
= 0.71073 A):
P2,jn. n = 23.497(2). h = 24.864(5), c = 24.470(3) A. /l = 95.33(1) , V =
14234(4) A', 2 = 4,
= 1.500 gem-', p(MoKJ = 34.6 cm-'. 6928 reflections with I > 2.5 u(I), 352 parameters. R = 0.084.
171 a) R. D. Howells, J. D. McCown, Chem. Rev. 1977,77,69-92; b) H. Schumann, J. A. Meese-Marktschrffel, A. Dietrich. J Organornet. C h m . 1989,
377, C5SC8.
[8] CryStdlographic data [I41 o f 3 at 293 K (Mar, radiation. i.= 0.71073 A):
P2,/n.0=10.089(1), h=12.026(2). c=36.693(4)& /l=94.55(1)', V =
4438(2) A', Z = 4, Q , , , , ~ = 1.30 gcm-'. p(MoKJ = 25.4 c m - I . 5649 reflections with F > 4u(F), 352 parameters. R = 0.033.
[9] Analogues of 4 have been obtained; however, the crystals are disordered.
[lo] Crystallographic data [14] of 4 at 293 K (Mo,, radiation .; = 0.71073 A):
pi,
=17.9?2(2), h =18.099(3), =i9.241(3) A,
=70.71(1),
=
?8.09(1). ;.=69.76(1), V = 5 5 1 2 ( 2 ) A 3 , Z = 4 , gcdird
=1.196gc1~-~,
~(Mo,,) = I 1 1 cm-'. 14705 reflections with I > 2 S d l ) . 1011 pardmeters, R = 0.0291
I1 I] Crystallographic data 1141 of 5 at 293 K (Mo,, radiation. i = 0.71073 A):
P6,/ni, u = 13.146(2). c =14.965(2), V = 2239.7(7) A'. Z = 2 , Q ~ = ~
0.989 gem-', p(MoK,) = 4 7 Em-'. 908 reflections with f > 4o(F).
60 parameters, R = 0.058.
1121 H. H. Karsch. R. Richter. A. Schier, Z. Nartrrforscli. B. in press.
[13] a) H. H . Karsch, G. Grauvogl. B. Deubelly, G. Muller, Orgunonielul1;c.s
1992, I / , 4238-4245: b) H. H. Karsch. G. GYduVOgl, M. Kawecki, P.
Bissinger. 0rgunonietull;c.s. 1993. 12. 2757-2766.
(141 a) Further details on the crystal structure determinations can be obtained
form the Fdchinformationszentrum Karlsruhe. Gesellschaft fur wissenschaftlich-technische Information mbH. D-76344 Eggenstein-Leopoldshafen (FRG). on quoting the deposition number CSD-56536, the
authors and the journal citation: b) program used: SHELXS-86. G. M.
Sheldrick, Aclu Cr,i~.ctullugr.Sec 1. A 1990, 46, 467L473; SHELXL-93.
G . M. Sheldrick, J. Appl. Cri.stu/lugr. 1993, submitted.
Table 1. Influence of the solvent and the alkyl substituent R of the leaving
group (RO),PO; on the competition constant !ir!k,, of radical 5 a at 30-C.
The Mechanism of Anaerobic, Radical-Induced
DNA Strand Scission""
Solvent
By Bernd Giese,* Xenia Be.yrich-GraL Jutta Burger,
Christoph Kesselheim, Martin Senn, and Thomas Schayer
C,H,0H:H20
(4:l)
Radicals generated either radiolytically o r chemically may
cleave the DNA strand by H abstraction. An important intermediate in this process is the 4'-deoxyribonucleotide radical 1111 (Scheme 1). This reactive intermediate can lead to
strand breakage either by direct fragmentation or by reaction with 0,. In order to account for the cleavage products
that are observed under anaerobic conditions, SchulteFrohlinde et al. have DroDosed that the radical cation 2 is an
intermediate, and have demonstrated analogous heterolytic
p-bond cleavage in simple radicak12.31
By selective generation of 4-nucleotide radicals, we have
now been
to prove that nucleot,de radical cations are
produced and have studied their reactivity. Alkene 3a and
6ovb
6owb
-
DNA H abstraction
1
,
selenide 4 b were both utilized as precursors of the 4-nucleotide radical 5. As we recently showed, radical addition of
PhSH to alkene 3a leads via the 4-nucleotide radical 5a to
the cyclic enol ether 7a.[41
If the radical cation 6a is indeed an intermediate, then
~
~
breakage
of the C - 0 bond ought to be strongly accelerated
by increasing either the polarity of the solvent or the acidity
of the phosphoric dialkylester which is released as an anion.[51We measured the ratio of the rate constants for H
abstraction (k,) and for C - 0 bond cleavage ( k E )under
pseudo-first-order conditions, using thiophenol as the source
of the radical X' and as H donor.[6] Since k , ought to be
largely independent of both the nature of the solvent['] and
the type of substituent R on the phosphate group, the change
in the ratio k J k , is a measure of the change of the rate of
C - 0 bond cleavage.
The data in Table 1 show that the rate of cleavage of the
C - 0 bond (5a -7a) increases by a factor of about 100 on
changing from toluene to ethanol/water (4: 1) as solvent.
C,H,CH,
Me
Et
nPr
iPr
Me
Et
nPr
iPr
9.77 x
7.08 x
5.13 x
2.19 x
14.2
7.7
6.5
1.7
0.17
0.077
0.056
0.021
10-4
1W4
10-4
lo-'
When the selectivity Igk,/k, was plotted against the acidity
k K , of the phosphoric dialkylester in the two solvents, a
linear correlation was observed with a gradient p of about
1.3 (Fig. 1). The solvent effect, which is unusually large for
'1
-
h
CzH50HIH20 = 4:1
1
2
X
k,jk,,
[a] Vdlues in E t O H / H 2 0 (4 1) at 25 C
cleavage products
yo-
K , of (RO),P02H [a]
Me
kE l : /
0kH
LWb
X
Et
lg-
n Pr
7
8
-3.8
1
-11
[*I
1")
=
-3.0
-
-2.8
Fig. I . Dependence of the C - 0 bond breakage in radical 5 a (Ig k F / k , , )on the
acidity (Ig K , ) of the phosphoric dialkylester (RO),PO,H.
6-N-benzoyladenin-9-yl
VCH Verlug.~ge.sr~llscliu~~
m h H , D-69451 Weinlicnn. 1993
-3.2
IgKa
Prof. Dr. B. Giese. Dip].-Chem. X. Beyrich-Graf, Dr. J. Burger.
Dip1.-Eng. C . Kesselheim, DipLChem. M. Senn, Dipl.-Eng. T. Schdfer
Depdrtement Chemie der Universitdt
St.-Johanns-Ring 19, CH-4056 Basel (Switzerland)
Telefax: Int. code + (61)-3226017
This work was supported by the Schweizerische Nationalfonds zur
Forderung wissenschaftlichen Forschung.
1742
-3.4
b: X = (EtO),PO,,b = T
0 4b
Scheme 1. ABz
-3.6
a: X = PhS, b = ABz
O-f(OR)z
0
neutral radicals, and the high value for the slope of the
Bronsted relationship are clear indications of heterolytic
C-0 bond cleavage in the reaction 5a 6a.
Interestingly, radical cation 6 a is not trapped nucleophilically in the presence of thiophenol, because electron transfer
-
+
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Angeic. Chem. I n / .
Ed. EngI. 1993. 32, N o . I2
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lanthanoidцphosphane, coordinated, complexes, highly
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