The first example of linkage-isomeric ketene metal complexes

Full text of DOI:10.1002/(SICI)1521-3773(19990115)38:1/2<156::AID-ANIE156>3.0.CO;2-I

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[3] For a recent comprehensive review of lattice interpenetration see: S. R.
Batten, R. Robson, Angew. Chem. 1998, 110, 1558 ± 1595; Angew.
Chem. Int. Ed. 1998, 37, 1460 ± 1494.
[4] Crystal data for 1: C18H12N14O2Zn.6C3H7NO, Mr ˆ 960.36, clear octa-
hedron, 0.30  0.23  0.20 mm, orthorhombic, space group Fddd, a ˆ
16.638(5), b ˆ 20.198(3), c ˆ 26.273(3) Š3, Vˆ 8829(3) Š3, Z ˆ 8,
1calcd ˆ 1.445 gcm 3, m(CuKa) ˆ 1.400 mm 1, F(000) ˆ 4032. Siemens P4
diffractometer, graphite-monochromated CuKa radiation, w scans, Tˆ
293 K. Of 1650 independent reflections measured (2q < 1208), 1156 had
Io > 2s(Io) and were considered observed. The structure was solved by
direct methods and the non-hydrogen atoms were refined anisotropi-
cally. The hydrogen atoms were placed in calculated positions, assigned
isotropic thermal parameters U(H) ˆ 1.2Ueq(C) and allowed to ride on
their parent carbon atoms. Refinement was by full-matrix least-squares
based on F 2 to give R1 ˆ 0.0767, and wR2 ˆ 0.2143. Computations were
carried out with the SHELXTL 5.03 program package. The included
DMF solvent was distributed randomly throughout the channels in the
structure and no realistic atom positions could be fitted to the weak
diffuse areas of residual electron density. The value of about six DMF
molecules per zinc atom given in the empirical formula was deduced
from the TGA measurements and the corresponding values of
calculated density, m, and F(000) reflect this figure. Crystallographic
data (excluding structure factors) for the structures reported in this
paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-102315. Copies of the
data can be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
Scheme 1. L ˆ PiPr3.
ested to find out whether the metal-assisted formation of
ˆ ˆ
Ph2C C O from 1 and CO occurs via the intermediate trans-
ˆ ˆ
[RhCl(Ph2C C O)(PiPr3)2]. Attempts to detect such a com-
pound by controlled addition of CO to a solution of 1 in C6D6
or CDCl3 failed. Therefore we chose a different synthetic
route for our target, the square-planar ketenerhodium com-
plex, and treated the chloro-bridged binuclear compound 4[4]
with diphenylketene. In benzene at room temperature com-
plex 5 (Scheme 2) is readily formed and, after removal of the
[5] A search of the April 1998 release of the Cambridge Crystallographic
Database revealed only three other examples of a linear M-O-C
arrangement out of a total of 1787 hits.
[6] A substantial portion of the powder pattern of the heated sample
comprises an amorphous ªhumpº but with the principal lines of the
host structure clearly visible.
Scheme 2. L ˆ PiPr3.
solvent, is isolated as a red-brown solid in almost quantitative
The First Example of Linkage-Isomeric Ketene
Metal Complexes**
ˆ
yield. The coordination of diphenylketene through the C O
ˆ
and not the C C bond, which was already indicated by the
Elke Bleuel, Matthias Laubender,
Birgit Weberndörfer, and Helmut Werner*
spectroscopic data,[3c] was confirmed by an X-ray crystal
structure analysis (Figure 1).[5] The coordination geometry
around the rhodium atom is distorted square-planar, the bond
angle P1-Rh-P2 of 168.41(4)8 thereby deviates considerably
from the ideal value of 1808. We assume that this is due to the
repulsion between the isopropyl and phenyl groups. More-
over, a remarkable feature is that in contrast to Cl-Rh-C1
(146.32(1)8) the axis Cl-Rh-O (177.25(9)8) is nearly linear and
Dedicated to Professor Otto J. Scherer
on the occasion of his 65th birthday
In the course of investigations on the reactivity of
ˆ
carbenerhodium complexes trans-[RhCl( CR')(L)2] (R' ˆ
2
aryl; L ˆ PR3, AsR3, SbR3) we recently observed[1] that these
compounds react smoothly with olefins, CO, and isocyanides
by C ± C coupling. While the reaction of 1 with ethene affords
besides 2 exclusively 1.1-diphenylpropene (and not 1.1-
diphenylcyclopropane), treatment of 1 with CO forms the
carbonyl complex 3 and diphenylketene (Scheme 1).[1, 2]
Since it is known from the work by the groups of Herrmann,
Cutler, Roper, and others that reactions of both metal
carbonyls with diazoalkanes and of metal carbenes with CO
under pressure lead to ketene complexes,[3] we were inter-
ˆ
thus unsymmetrical bonding of the C O unit to the metal
center results. Compared to other h2(C,O)-diphenylketene
complexes,[6] the distance O ± C1 in 5 is significantly shorter
which points to a reduced degree of p-back bonding from the
ˆ
rhodium center to the p* orbital of the C O moiety. In view of
the presence of the electron-rich [RhCl(PiPr3)2] fragment this
observation is really surprising.
The ketene complex 5, which is thermally remarkably
stable, reacts with CO under normal pressure to yield
quantitatively the rhodium carbonyl compound trans-
[RhCl(CO)(PiPr3)2][7] and diphenylketene. Upon treatment
of 5 with C9H7K in THF a substitution of chloride for indenyl
does not occur. However, the desired ligand exchange can be
carried out if compound 5 is transformed in the initial step
with one equivalent of AgPF6 to an intermediate with the
ˆ ˆ
[*] Prof. Dr. H. Werner, Dipl.-Chem. E. Bleuel,
Dipl.-Chem. M. Laubender, Dipl.-Chem. B. Weberndörfer
Institut für Anorganische Chemie der Universität
Am Hubland, D-97074 Würzburg (Germany)
Fax: (‡49)931-888-4605
E-mail: helmut.werner@mail.uni-wuerzburg.de
supposed
composition
trans-[Rh(Ph2C C O)(PiPr3)2-
[**] This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 347), the Fonds der Chemischen Industrie, and the BASF AG.
ˆ
(O CMe2)]PF6, which subsequently reacts in situ with
156
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Figure 2. Molecular structure of 6 (thermal elipsoids with 50% proba-
bility). Selected bond lengths [Š] and angles [8]: Rh ± C1 1.936(5), Rh ± C2
2.180(5), Rh ± P 2.321(1), Rh ± C30 2.461(5), Rh ± C31 2.263(5), Rh ± C32
2.242(4), Rh ± C33 2.271(5), Rh ± C34 2.451(5), O ± C1 1.208(4), C1 ± C2
1.467(5); P-Rh-C1 98.1(2), P-Rh-C2 103.9(1), Rh-C1-O 139.6(4), Rh-C2-C1
60.4(2), C1-Rh-C2 41.2(2), O-C1-C2 142.0(5).
Figure 1. Molecular structure of 5 (thermal elipsoids with 50% proba-
bility). Selected bond lengths [Š] and angles [8]: Rh ± O 2.090(3), Rh ± C1
1.971(4), Rh ± Cl 2.298(1), Rh ± P1 2.382(1), Rh ± P2 2.369(1), C1 ± O
1.264(5), C1 ± C2 1.349(6); P1-Rh-P2 168.41(4), Cl-Rh-O 177.25(9), Cl-
Rh-C1 146.32(1), P1-Rh-Cl 90.02(4), P2-Rh-Cl 90.28(4), P1-Rh-O 88.37(8),
P2-Rh-O 90.85(8), Rh-O-C1 66.8(2), Rh-C1-C2 144.0(3), O-C1-C2
138.9(4).
The C1 ± C2 bond is longer and the C1 ± O bond shorter than
in 5. The difference of the Rh ± C1 bond length in 5 and 6 is
quite small and also the bond angle O-C1-C2 is almost
identical in both complexes. The indenyl ligand in 6 is
unsymmetrically linked (i.e. approaching h3 coordination) to
the metal, as was also found in other rhodium complexes of
the general composition [(C9H7)RhL2] and [(C9H7)-
RhL(L')].[8]
Although compound 6 is thermally stable up to 1378C,
upon treatment with acidic Al2O3 or with a solution of HCl in
benzene it rapidly rearranges to the isomeric complex 7. The
isomerization, which can be monitored by the change of color
from orange-red to orange, is confirmed by the spectroscopic
data. Characteristic features for 7 are the position of the
1
ˆ
nÄ(C O) stretching frequency at 1598 cm (see for compar-
ison the data for 5 and 6) and the chemical shift of the signals
ˆ ˆ
for the carbon atoms of the C C O unit at d ˆ 223.0 and
130.2. With regard to the reactivity, compounds 6 and 7 differ
insofar as the h2(C,C)-bonded isomer reacts instantaneously
with CO to yield the carbonylrhodium complex 8 (plus
diphenylketene), while the h2(C,O)-bonded isomer is com-
pletely inert toward carbon monoxide (C6H6, 258C, 1 bar,
5 days).
The attempt to generate either compound 6 or 7 by metal-
assisted C ± C coupling from the carbene complex 9 (recently
prepared in our laboratory)[8d] and CO led to a surprising
result. Instead of a coupling of the CPh2 moiety with CO, after
attack of CO at the metal center a migration of the carbene to
the indenyl ligand takes place, which is accompanied by an
insertion of CPh2 into one of the C ± H bonds of the five-
membered ring of C9H7. The structure of 10 (Scheme 4) has
been confirmed by X-ray crystallography.[9] Complex 9 thus
behaves differently to the corresponding cyclopentadienyl
Scheme 3. L ˆ PiPr3.
C9H7 K to give the indenyl complex 6 (Scheme 3). By using
this method, 6 can be isolated in 86% yield. Spectroscopic
data reveal that the conversion of 5 to 6 is accompanied by a
change of the coordination mode of the ketene ligand from
h2(C,O) to h2(C,C). The IR spectrum of 6 displays an
1
ˆ
ˆ
absorption at 1777 cm for the C O stretch (5: nÄ(C O) ˆ
1
1590 cm ) and the 13C NMR spectrum a doublet of doublets
ˆ ˆ
at d ˆ 227.7 for the C C O and a doublet at d ˆ 19.5 for the
ˆ ˆ
C C O carbon atom (5: d ˆ 167.4 (dt) and 123.9 (s)). The
X-ray crystal stucture analysis of 6 confirms the proposed
linkage isomerization of the metal-bound ketene (Figure 2).
Angew. Chem. Int. Ed. 1999, 38, No. 1/2
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1
PCHCH3), 19.5 (d, J(Rh,C) ˆ 3.8 Hz, C C O); 31P NMR (81.0 MHz,
ˆ ˆ
1
C6D6): d ˆ 52.8 (d, J(Rh,P) ˆ 197.1 Hz).
7: A solution of 6 (74 mg, 0.13 mmol) in benzene (5 mL) was treated with a
0.36m solution of HCl (833 mL, 0.30 mmol) in benzene and stirred for 5 min
at room temperature. The solvent was removed in vacuo, the residue was
dissolved in pentane (5 mL), and the solution stored for 24 h at 08C.
Orange crystals were formed which were washed with small quantities of
pentane and dried in vacuo; yield 69 mg (93%); m.p. 1228C (decomp); IR
(C6H6): nÄ(C C O) ˆ 1598 cm 1; 1H NMR (400 MHz, C6D6): d ˆ 7.89, 7.45 ±
ˆ ˆ
6.66 (both m, C6H5 and H4-7 of indenyl), 5.85 (m, H2 of indenyl), 5.28, 5.00
(both m, H1, 3 of indenyl), 2.23 (m, PCHCH3), 0.86 (dd, 3J(P,H) ˆ 13.1,
3J(H,H) ˆ 7.2 Hz, PCHCH3), 0.82 (dd, 3J(P,H) ˆ 14.4, 3J(H,H) ˆ 7.3 Hz,
Scheme 4.
PCHCH3); 13C{1H} NMR (100.6 MHz, C6D6): d ˆ 223.0 (dd, 1J(Rh,C) ˆ
2
ˆ ˆ
32.6, J(P,C) ˆ 7.1 Hz, C C O), 141.1, 140.5 (both s, C6H5), 130.2 (s,
5
ˆ
8, 9
analogue [(h -C5H5)Rh( CPh2)(PiPr3)] which reacts with CO
ˆ ˆ
C C O), 129.4, 129.2, 129.0, 128.3 (all s, C6H5), 128.2 (s, C of indenyl),
to give [(h5-C5H5)Rh(CO)(PiPr3)] and diphenylketene.[1b]
With the synthesis and the characterization of compounds 6
and 7 we have shown for the first time that linkage isomerism
exists also among ketene transition metal complexes. Up to
now examples for this type of isomerism were known mainly
for metal compounds containing NO2 , NCS , and triazole
derivatives as ligands,[10] the stability of the respective isomers
could usually be predicted by the hard/soft acid/base (HSAB)
concept.[11] Since only a conversion of 6 to 7 but not in the
reverse direction takes place, we assume that the h2(C,O)-
bonded isomer is thermodynamically more stable. We are now
attempting to prepare rhodium and iridium complexes with
different configurations as well as oxidation states of the
127.6, 127.4, 126.7, 126.6 (all s, C6H5), 123.2, 120.5 (both s, C4, 7 of indenyl),
104.7 (d, J(Rh,C) ˆ 5.7 Hz, C5 or C6 of indenyl), 82.0 (m, C2 of indenyl),
3
77.4 (s, C5 or C6 of indenyl), 62.9 (d, 1J(Rh,C) ˆ 9.5 Hz, C1, 3 of indenyl), 25.0
(d, 2J(P,C) ˆ 19.1 Hz, PCHCH3), 19.6, 19.1 (both s, PCHCH3); 31P NMR
1
(162.0 MHz, C6D6): d ˆ 49.8 (d, J(Rh,P) ˆ 162.8 Hz).
10: A slow stream of CO was passed through a solution of 9 (98 mg,
0.18 mmol) in pentane (10 mL) for 30 s at 788C. Upon warming the
mixture to room temperature, the color of the deep green solution
brightened. The solution was stirred for 30 min, the solvent was removed,
and the residue was dissolved in pentane (3 mL), which was saturated with
CO. After the solution had been stored for 3 d at 188C, an orange-yellow
solid precipitated which was washed with small quantities of pentane
(
108C) and dried in vacuo; yield 81 mg (79%); m.p. 568C; IR (C6H14):
1
nÄ(CO) ˆ 1944 cm
;
1H NMR (400 MHz, C6D6): d ˆ 7.69, 7.24 ± 6.89 (both
m, C6H5 and H4±7 of indenyl), 6.06 (d, 3J(Rh,H) ˆ 3.2 Hz, CHPh2), 5.83 (m,
H2 of indenyl), 4.82 (d, J(Rh,H) ˆ 3.2 Hz, H3 of indenyl), 1.72 (sept (br),
2
ˆ ˆ
metal using not only Ph2C C O but also other ketenes as
3J(H,H) ˆ 7.2 Hz, PCHCH3), 0.84 (dd, 3J(P,H) ˆ 14.4, 3J(H,H) ˆ 7.2 Hz,
PCHCH3), 0.81 (dd, 3J(P,H) ˆ 14.0, 3J(H,H) ˆ 7.2 Hz, PCHCH3); 13C{1H}
NMR (100.6 MHz, C6D6): d ˆ 196.0 (dd, 1J(Rh,C) ˆ 89.0, 2J(P,C) ˆ 21.6 Hz,
Rh ± CO), 144.3, 144.0, 130.4, 128.9, 128.5, 128.1, 126.5, 126.4 (all s, C6H5),
122.9, 121.2 (both s, C4, 7 of indenyl), 119.3 (s, C8 or C9 of indenyl), 118.6 (s,
C5 or C6 of indenyl), 117.6 (s, C8 or C9 of indenyl), 117.3 (s, C5 or C6 of
indenyl), 98.5 (dd, 2J(Rh,C) ˆ 5.2, 3J(P,C) ˆ 1.7 Hz, CHPh2), 97.3 (dd,
1J(Rh,C) ˆ 13.0, 2J(P,C) ˆ 3.8 Hz, C1 of indenyl), 72.3 (d, 1J(Rh,C) ˆ 3.3 Hz,
C2 of indenyl), 51.0 (d, 1J(Rh,C) ˆ 1.5 Hz, C3 of indenyl), 28.0 (d, 1J(P,C) ˆ
21.2 Hz, PCHCH3), 19.8, 19.7 (both s, PCHCH3); 31P NMR (162.0 MHz,
ligands in an effort to establish under which circumstances the
h2(C,O)- or the h2(C,C)-coordination mode of a particular
ketene is preferred.
Experimental Section
5: A solution of 4 (238 mg, 0.26 mmol) in benzene (5 mL) was treated with
diphenylketene (88 mL, 0.52 mmol) and stirred for 5 min at room temper-
ature. The solvent was removed in vacuo, the red-brown solid was washed
1
C6D6): d ˆ 74.3 (d, J(Rh,P) ˆ 194.7 Hz).
twice with pentane (10 mL) and dried; yield 296 mg (87%); m.p. 1108C
1
(decomp); IR (C6H6): nÄ(C C O) ˆ 1590 cm
;
1H NMR (200 MHz,
ˆ ˆ
Received: August 31, 1998 [Z12352IE]
German version: Angew. Chem. 1999, 111, 222 ± 225
C6D6):[12] d ˆ 8.76, 7.66, 7.39 ± 6.98 (all m, C6H5), 2.33 (m, PCHCH3), 1.19
(dvt, N ˆ 13.5, 3J(H,H) ˆ 6.8 Hz, PCHCH3); 13C{1H} NMR (50.3 MHz,
C6D6): d ˆ 167.4 (dt, 1J(Rh,C) ˆ 19.5, J(P,C) ˆ 4.9 Hz, C C O), 138.4,
2
ˆ ˆ
Keywords: carbene complexes ´ indenyl complexes ´ ketene
complexes ´ linkage isomerism ´ rhodium
137.6, 130.2, 129.4, 129.1, 128.9, 128.7, 128.3, 127.8, 127.6 (all s, C6H5), 123.9
ˆ ˆ
(s, C C O), 22.2 (vt, N ˆ 19.5 Hz, PCHCH3), 19.6, 19.3 (both s, PCHCH3);
31P NMR (81.0 MHz, C6D6): d ˆ 32.5 (d, J(Rh,P) ˆ 108.3 Hz).
1
6: A solution of 5 (117 mg, 0.18 mmol) in acetone (10 mL) was treated
dropwise with a solution of AgPF6 (45 mg, 0.18 mmol) in acetone (10 mL).
A change of color from red-brown to orange occurred and a white flocky
precipitate of AgCl was formed. After the reaction mixture had been
stirred for 5 min at room temperature, the solution was filtered. The filtrate
was dried in vacuo and the residue was dissolved in THF (10 mL). The
solution was treated with C9H7K (139 mg, 0.90 mmol) and stirred for
30 min. After the solvent had been removed, the residue was extracted with
pentane (50 mL). The extract was filtered, the filtrate was concentrated to
about 10 mL and then stored for 12 h at 08C. Orange-red crystals were
formed which were washed with small quantities of pentane and dried in
[1] a) P. Schwab, N. Mahr, J. Wolf, H. Werner, Angew. Chem. 1993, 105,
1498 ± 1500; Angew. Chem. Int. Ed. Engl. 1993, 32, 1480 ± 1482; b) H.
Werner, J. Organomet. Chem. 1995, 500, 331 ± 336.
[2] H. Werner, P. Schwab, E. Bleuel, N. Mahr, P. Steinert, J. Wolf, Chem.
Eur. J. 1997, 3, 1375 ± 1384.
[3] Übersichten: a) W. A. Herrmann, Angew. Chem. 1978, 90, 855 ± 868;
Angew. Chem. Int. Ed. Engl. 1978, 17, 800 ± 813; b) M. A. Gallop,
W. R. Roper, Adv. Organomet. Chem. 1986, 25, 121 ± 198; c) G. L.
Geoffroy, S. L. Bassner, Adv. Organomet. Chem. 1988, 28, 1 ± 83.
[4] a) Isolation: H. Werner, J. Wolf, A. Höhn, J. Organomet. Chem. 1985,
287, 395 ± 407; b) Strukturanalyse: P. Binger, J. Haas, G. Glaser, R.
Goddard, C. Krüger, Chem. Ber. 1994, 127, 1927 ± 1929.
ˆ ˆ
vacuo; yield 89 mg (86%); m.p. 1378C (decomp); IR (C6H6): nÄ(C C O) ˆ
1777 cm 1; 1H NMR (200 MHz, C6D6):[13] d ˆ 7.59, 7.12 ± 6.75 (both m, C6H5
and H4-7 of indenyl), 6.07 (dt, 2J(Rh,H) ˆ 3J(H,H) ˆ 2.8 Hz, H2 of indenyl),
4.58 (m, H1, 3 of indenyl), 1.23 (sept (br), 3J(H,H) ˆ 7.2 Hz, PCHCH3), 0.85
(dd, 3J(P,H) ˆ 13.4, 3J(H,H) ˆ 7.2 Hz, PCHCH3); 13C{1H} NMR
(100.6 MHz, C6D6): d ˆ 227.7 (dd, 1J(Rh,C) ˆ 22.9, 2J(P,C) ˆ 5.1 Hz,
[5] Data for the X-ray structure analyses: 5: Crystals from pentane at 08C,
C32H52ClOP2Rh (653.04); crystal size 0.2 Â 0.15 Â 0.1 mm; triclinic,
Å
space group P1 (no. 2), a ˆ 8.7233(4), b ˆ 11.0994(8), c ˆ 18.725(1) Š,
a ˆ 93.249(5), b ˆ 103.280(5), g ˆ 107.901(6)8, Z ˆ 2, Vˆ 1663.2(2) Š3,
1calcd ˆ 1.304 gcm 3; Tˆ 293(2) K; 2Vˆ 488; 5595 reflections meas-
ured, 5207 were unique (Rint ˆ 0.0227) and 4037 observed (I > 2s(I));
Enraf-Nonius CAD4 diffractometer, MoKa radiation (l ˆ 0.71073 Š),
graphite-monochromated, zirconium filter (factor 15.4); Lp and
ˆ ˆ
C C O), 142.3, 140.3, 133.1, 128.4, 128.3, 128.1, 128.0, 127.2, 126.0, 125.4,
124.9, 123.8 (all s, C6H5), 122.3, 122.2, 119.9, 119.0 (all s, C4±7 of indenyl),
115.8 (s, C8, 9 of indenyl), 99.4 (d, 1J(Rh,C) ˆ 6.4 Hz, C2 of indenyl), 68.5 (s
(br), C1, C3 of indenyl), 27.1 (d, 1J(P,C) ˆ 19.1 Hz, PCHCH3), 20.2 (s,
158
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empirical absorption corrections (Y scan, min. transmission 94.56%).
The structure was solved by direct methods and refined with the full-
matrix, least-squares method; R1 ˆ 0.0398, wR2 ˆ 0.0729 (for 4037
reflections with I > 2s(I)), R1 ˆ 0.0626, wR2 ˆ 0.0859 (for all 5207
data); data-to-parameter ratio 15.04; residual electron density
‡0.349/ 0.343 eŠ 3. 6: crystals from pentane at 08C, C32H38OPRh
(572.50); crystal size 0.4 Â 0.3 Â 0.2 mm; monoclinic, space group
Functionalization of Hydrocarbons by a New
Free Radical Based Condensation Reaction**
James. M. Tanko* and Mitra Sadeghipour
There is increased awareness of the need to develop new
chemical reactions and processes which avoid the use or
generation of toxic and/or environmentally threatening ma-
terials. Herein we report a newly developed reaction in which
a C H bond of a hydrocarbon is converted into a C C bond
P21/c (no. 14), a ˆ 9.753(3), b ˆ 13.384(4), c ˆ 20.914(6) Š, b ˆ
3
95.998(14)8, Z ˆ 4, Vˆ 2714.9(14) Š3, 1calcd. ˆ 1.401 gcm
;
Tˆ
173(2) K; 2Vˆ 508; 3569 reflections measured, 3473 were unique
(Rint ˆ 0.0328) and 2619 observed (I > 2s(I)); Enraf-Nonius CAD4
diffractometer, MoKa radiation (l ˆ 0.71073 Š), graphite-monochro-
mated, zirconium filter (factor 16.4); Lp and empirical absorption
corrections (Y scan, min. transmission 96.85%). The structure was
solved by direct methods and refined with the full-matrix, least-
squares method; R1 ˆ 0.0348, wR2 ˆ 0.0604 (for 2619 reflections with
ˆ
by transfer of an allyl group (R H !R C C C). This
process is especially attractive because (unlike other proce-
dures which effect this conversion) the transformation is
accomplished in a single step and does not require strongly
acidic or basic reaction conditions, or the use of heavy metals.
The proposed mechanism of this reaction is depicted in
I > 2s(I)), R1 ˆ 0.0602, wR2 ˆ 0.0683 (for all 3473 data); data-to-
3
parameter ratio 10.24; residual electron density ‡0.239/ 0.240 eŠ
.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-102818 (5) and CCDC-102919 (6). Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: depos-
it@ccdc.cam.ac.uk).
.
Scheme 1. Abstraction of hydrogen from R H (by Br ) yields
.
ˆ
R , which subsequently adds to the C C bond of a substituted
allyl bromide (1). Adduct radical 2 undergoes b cleavage to
yield product 3 and regenerate Br . Each step depicted in
.
Scheme 1 is well documented in the literature: A bromine
atom exhibits high selectivity in hydrogen atom abstractions
(step 1),[1] and is especially reactive towards benzylic hydro-
gen atoms (for example in the Ziegler bromination).[2] Allyl
bromides have been shown to be effective chain transfer
reagents in free radical polymerizations, essentially by steps
identical to 2 and 3.[3]
[6] a) S. Gambarotta, M. Pasquali, C. Floriani, A. Chiesi-Villa, C.
Guastini, Inorg. Chem. 1981, 20, 1173 ± 1178; b) R. Birk, H. Berke, H.-
U. Hund, G. Huttner, L. Zsolnai, L. Dahlenburg, U. Behrens, T.
Sielisch, J. Organomet. Chem. 1989, 372, 397 ± 410; c) P. Hofmann,
L. A. Perez-Moya, O. Steigelmann, J. Riede, Organometallics 1992, 11,
1167 ± 1176; d) A. AntinÄolo, A. Otero, M. Fajardo, C. Lopez-
Mardomingo, D. Lucas, Y. Mugnier, M. Lanfranchi, M. A. Pellinghelli,
J. Organomet. Chem. 1992, 435, 55 ± 72; e) D. B. Grotjahn, H. C. Lo,
Organometallics 1995, 14, 5463 ± 5465; f) R. Flügel, O. Gevert, H.
Werner, Chem. Ber. 1996, 129, 405 ± 410.
[7] a) C. Busetto, A. DꢁAlfonso, F. Maspero, G. Perego, A. Zazzetta, J.
Chem. Soc. Dalton Trans. 1977, 1828 ± 1834; b) K. Wang, G. P. Rosini,
S. P. Nolan, A. S. Goldman, J. Am. Chem. Soc. 1995, 117, 5082 ± 5088.
[8] a) G. G. Aleksandrov, Y. T. Struchkov, V. S. Khandkarova, S. P. Gubin,
J. Organomet. Chem. 1970, 25, 243 ± 247; b) P. Caddy, M. Green, E.
OꢁBrien, L. E. Smart, P. Woodward, Angew. Chem. 1977, 89, 671 ± 672;
Angew. Chem. Int. Ed. Engl. 1977, 16, 648 ± 649; c) T. B. Marder, J. C.
Calabrese, D. C. Roe, T. H. Tulip, Organometallics 1987, 6, 2012 ±
2014; d) E. Bleuel, Diplomarbeit, Universität Würzburg, 1996.
[9] M. Laubender, Dissertation, Universität Würzburg, unpublished.
[10] L. H. Gade, Koordinationschemie, WILEY-VCH, Weinheim, 1998,
chapter 7.
[11] a) R. G. Pearson, J. Am. Chem. Soc. 1963, 85, 3533 ± 3539; b) H.
Werner, Chem. Unserer Zeit 1967, 1, 135 ± 139; c) R. G. Pearson, J.
Chem. Educ. 1968, 45, 581 ± 587; R. G. Pearson, J. Chem. Educ. 1968,
45, 643 ± 648.
Scheme 1. Mechanism of the proposed allyl transfer reaction.
[12] Abbreviations used: vt ˆ virtual triplet, dvt ˆ doublet of virtual
To test whether this chemistry could be coupled as shown in
Scheme 1 to ªinventº a viable synthetic process, we examined
the reaction of several allyl bromides with toluene and
cumene (Table 1). Overall, mass balances for these reactions
were high, and good to excellent yields were obtained,
especially when the allyl bromide possesses a radical-stabiliz-
ing substituent (e.g., Z ˆ Ph, CO2Et, or CN). To confirm the
1
triplets, N ˆ 3J(P,H) ‡ 5J(P,H) or J(P,C) ‡ 3J(P,C).
[13] For the numbering of the indenyl carbon (and corresponding hydro-
gen) atoms see formula A.
.
role of Br as the chain carrier in this reaction, a series of
competition experiments were performed pitting PhCH3
[*] Prof. J. M. Tanko, M. Sadeghipour
Department of Chemistry
Virginia Polytechnic Institute and State University
Blacksburg, VA 24061-0212 (USA)
Fax: (‡1)540-231-3255
E-mail: jtanko@vt.edu
[**] Financial support from the National Science Foundation (CHE-
9524986) is acknowledged and appreciated.
Angew. Chem. Int. Ed. 1999, 38, No. 1/2
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