Reaction of ketenylidenetriphenylphosphorane (Ph3P=C=C=O) with platinum(II) and palladium(II) complexes. Synthesis, characterization, and molecular structure of [Pt(η3-C3H5){η1-C(PPh 3)(CO)

Article abstract of DOI:10.1021/om9602668

Ketenylidenetriphenylphosphorane, Ph₃P= C=C=O, reacts with Pt(II) and Pd(II) η³-allyl complexes (allyl = C₃H₅, 2-MeC₃H₄) to give neutral or cationic mononuclear η¹-ketenyl deriva

Full text of DOI:10.1021/om9602668

3250
Organometallics 1996, 15, 3250-3252
Rea ction of Keten ylid en etr ip h en ylp h osp h or a n e
(P h 3P dCdCdO) w ith P la tin u m (II) a n d P a lla d iu m (II)
Com p lexes. Syn th esis, Ch a r a cter iza tion , a n d Molecu la r
Str u ctu r e of [P t(η3-C3H5){η1-C(P P h 3)(CO)}(P P h 3)]BF 4
Luciano Pandolfo,*,† Gastone Paiaro,† Luana K. Dragani,† Chiara Maccato,†
Roberta Bertani,*,‡ Giacomo Facchin,‡ Livio Zanotto,‡ Paolo Ganis,*,§ and
Giovanni Valle|
Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Universita` di Padova,
Via Marzolo 1, I-35131 Padova, Italy, Centro di Studio per la Chimica e Tecnologia dei
Composti Metallorganici degli Elementi di Transizione del CNR, Istituto di Chimica
Industriale, Universita` di Padova, Via Marzolo 9, I-35131 Padova, Italy, Dipartimento di
Chimica, Universita` di Napoli, Via Mezzocannone 4, I-80134 Napoli, Italy, and Centro di
Studio sui Biopolimeri (CNR), Via Marzolo 1, I-35131 Padova, Italy
Received April 4, 1996X
Ch a r t 1
Summary: Ketenylidenetriphenylphosphorane, Ph3Pd
CdCdO, reacts with Pt(II) and Pd(II) η3-allyl complexes
(allyl ) C3H5, 2-MeC3H4) to give neutral or cationic
mononuclear η1-ketenyl derivatives [M(η3-allyl){(η1-
C(PPh3)(CO)}L]m+ (L ) Cl, m ) 0; L ) PPh3, m ) 1)
that have been characterized by elemental analysis, IR,
and multinuclear NMR. The X-ray molecular structure
determination performed on a single crystal of the air-
stable derivative [Pt(η3-C3H5){η1-C(PPh3)(CO)}(PPh3)]-
BF4 furnishes the first crystallographic evidence of an
η1-ketenyl derivative in which the ketene moiety is also
involved in an ylide grouping.
Ketenes, a (Chart 1), are known from the beginning
of the century,1 and their organic chemistry is well-
known and reviewed.2 In the last years even the
organometallic chemistry of ketenes has been more
intensively studied,3 since metal-ketene derivatives
were reported to be involved in important catalytic and
stoichiometric processes.4 The first platinum-ketene
derivative has been obtained by substitution of ethylene
in [Pt(PPh3)2(C2H4)] with diphenylketene,5 and nowa-
days a large number of ketene and η2-ketenyl deriva-
tives are known.3a Despite their potentiality as useful
synthetic reagents η1-ketenyl derivatives, b, in which
a metal center is one of the ketene substituents, are
less studied. They are typically obtained by ligand-
induced CO migration to a carbyne ligand.6 Other
syntheses involve the coordination of carbon suboxide,
OdCdCdCdO, on Pt and Ni7 with formation of η1-
ketenyl, η 2-(C,C)-ketene derivatives, c, or the insertion
of carbon suboxide in transition metal-hydride bonds8
giving η1-ketenyl formyl derivatives, d . Peculiar η1-
ketenyl derivatives, in which the second substituent of
the ketene moiety is SiMe3, have been obtained by
reaction of Me3PdCHSiMe3 with [FeCp(CO)2]I followed
by rearrangements9 and, more recently, by Wolff rear-
rangement of a Rh diazolkane complex.10 Moreover it
has been reported that ketenylidenetriphenylphospho-
rane, Ph3PdCdCdO, 1,11 substitutes CO or MeCN from
some early or medium transition metal complexes giving
η1-ketenyl derivatives, e.12
Continuing our interest in metal-ketene deriva-
tives3b,7a,b,8b,c and in the reactivity of Ph3PdCdCdO,13
we started a systematic research on the use of 1 as a
synthon for new ketenyl complexes of late transition
metals. Actually the relevant negative charge on the â
* To whom correspondence should be addressed. E-mail:
pandolfo@chim02.chin.unipd.it.
(7) (a) Paiaro, G.; Pandolfo, L. Angew. Chem., Int. Ed. Engl. 1981,
20, 288. (b) Pandolfo, L.; Morandini, F.; Paiaro, G. Gazz. Chim. Ital.
1985, 115, 711. (c) List, A. K.; Smith, M. R., II; Hillhouse, G. L.
Organometallics 1991, 10, 361.
(8) (a) Hillhouse, G. L. J . Am. Chem. Soc. 1985, 107, 7772. (b)
Pandolfo, L.; Paiaro, G. Gazz. Chim. Ital. 1990, 120, 531. (c) Ganis,
P.; Paiaro, G.; Pandolfo, L.; Valle, G. Gazz. Chim. Ital. 1990, 120, 541.
(9) Voran, S.; Malisch, W. Angew. Chem., Int. Ed. Engl. 1983, 22,
151.
† Dipartimento di Chimica Inorganica, Metallorganica e Analitica,
Universita` di Padova.
‡ Istituto di Chimica Industriale, Universita` di Padova.
§ Universita` di Napoli.
| Centro di Studio sui Biopolimeri.
X Abstract published in Advance ACS Abstracts, J uly 1, 1996.
(1) Staudinger, H. Chem. Ber. 1906, 90, 689.
(2) (a) Tidwell, T. T. Acc. Chem. Res. 1990, 23, 273. (b) Allen, A. D.;
Ma, J .; McAllister, M. A.; Tidwell, T. T.; Zhao, D. Acc. Chem. Res. 1995,
28, 265. (c) Tidwell, T. T. Ketenes; Wiley: New York, 1995.
(3) (a) Geoffroy, G. I.; Bassner, S. L. Adv. Organomet. Chem. 1988,
28, 1. (b) Paiaro, G.; Pandolfo, L. Comments Inorg. Chem. 1991, 12,
213.
(10) Deydier, E.; Menu, M.-J .; Dartiguenave, M.; Dartiguenave, Y.
J . Organomet. Chem. 1993, 458, 225.
(11) (a) Mattews, C. N.; Birum, G. H. Tetrahedron Lett. 1966, 46,
5707. (b) Bestmann, H. J . Angew. Chem., Int. Ed. Engl. 1977, 16, 349.
(c) Bestmann, H. J .; Sandmeier, D. Chem. Ber. 1980, 113, 274.
(12) (a) Berke, H.; Lindner, E. Angew. Chem., Int. Ed. Engl. 1973,
12, 667. (b) Lindenberger, H.; Birk, R.; Orama, O.; Huttner, G.; Berke,
H. Z. Naturfosch. 1988, 43b, 749.
(4) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1982, 21, 117
and references therein.
(5) Schorpp, K.; Beck,W. Z. Naturforsch. 1973, B28, 738.
(6) Hedelhoven, W.; Eberl, K.; Kreissl, F. R. Chem. Ber. 1979, 113,
3376.
(13) Pandolfo, L.; Facchin, G.; Bertani, R.; Ganis, P.; Valle, G.
Angew. Chem., Int. Ed. Engl. 1996, 35, 83.
S0276-7333(96)00266-X CCC: $12.00 © 1996 American Chemical Society
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Communications
Organometallics, Vol. 15, No. 15, 1996 3251
carbon atom of Ph3PdCdCdO14 makes possible, in
principle, a nucleophilic attack of this carbon to an
electron-deficient metal center.
NMR spectra show signals at 22-25 ppm, a zone far
from that of free Ph3PdCdCdO,21 attributable to the
phosphonium group. The 13C{1H} NMR spectrum re-
corded for the most stable compound 2a shows, together
with the typical signals of the allyl moiety,22 the
Cationic η1-ketenyl derivatives [M(η3-2-R-C3H4){η1-
C(PPh3)(CO)}(PPh3)]+ (M ) Pt, R ) H, 2a ;15 M ) Pd, R
) Me, 2b16) have been obtained by treating the corre-
sponding solvate complexes17 with 1 equiv of 1 at room
temperature for 2a and at -30 °C for 2b, according to
eq 1. Pd(II) η3-allyl dimers [Pd(η3-2-R-C3H4)Cl]2 (R )
carbonylic carbon as a doublet at 156.73 ppm (2J CP
)
18.9 Hz), in the range observed for other η1-ketenyl
derivatives.3a,7c A doublet at 9.26 ppm (1J CP ) 59.0 Hz),
with 195Pt satellites covered by instrumental noise, is
assigned to the ylidic carbon; the high-field shift and
the decrease of 1J CP with respect to free Ph3PdCdCdO21
are in agreement with the reduction of the charge
density on the C-P bond by coordination to the metal.
For compound 2a it was possible to obtain pale-yellow
crystals, suitable for a X-ray structure determination,23
by slow evaporation of a CH2Cl2/toluene solution. The
structure of 2a is shown in Figure 1 with the atom
(1)
(2)
-
labeling (the counterion BF4 is omitted). The coordi-
nation about Pt is consistent with a slightly distorted
square planar geometry assuming the allyl group as a
bidentate ligand bonded to the metal through C(37) and
C(39). The allyl group exhibits a structural disorder
deriving from down- or upward orientation of the carbon
atom C(38) with respect to the coordination plane of Pt.
Only a few structures of η1-ketenyls have been
reported,8c,24,25 but this is a quite new example in which
the CdCdO moiety is bonded to Pt and is involved also
H, Me) have been reacted with 1 to give the neutral
compounds [Pd(η3-2-R-C3H4){η1-C(PPh3)(CO)}Cl]18 (R )
H, 2c; R ) Me, 2d ) (eq 2). The reaction of 1 with [Pt-
(C3H5)Cl]4 gave [Pt(η3-C3H5){(η1-C(PPh3)(CO)}Cl], 2e,19
in very low yield.
The IR spectra of compounds 2a -e clearly indicate
the presence of the η1-ketenyl moiety,3a showing an
intense absorption in the region 2060-2080 cm-1. The
1H NMR spectra point out the maintenance of the η3-
allylic moiety in the coordination sphere of the metal.20
Besides the signals due to coordinated PPh3 (2a ,b) 31P
(18) 2c: To a -50 °C CH2Cl2 (5 mL) solution of [Pd(η3-C3H5)Cl]2
(0.060 g, 0.165 mmol) was added a cooled CH2Cl2 (5 mL) solution of 1
(0.100 g, 0.33 mmol). The solution was concentrated at -50 °C under
vacuum to ca. 3 mL, and by adding 10 mL of cooled n-hexane, a green
yellow solid precipitated, which decomposes rapidly at room temper-
ature even in the solid state. IR (Nujol, cm-1): νCO 2077 (s). 1H NMR
(200 MHz, CD2Cl2, -50 °C, TMS ext.): 3.90, 2.70, 2.10 (3 m, br, 4H);
4.70 (m, Hc). 31P{1H} NMR (81 MHz, CD2Cl2, -50 °C, H3PO4 ext.):
22.16 (s). 2d : The compound has been prepared similarly to 2c starting
from [Pd(η3-2-Me-C3H4)Cl]2 (0.098 g, 0.25 mmol) and 1 (0.150 g, 0.5
mmol). The compound can be handled at room temperature in the solid
state. Yield: 0.162 g (65%). Anal. Calcd for C24H22ClOPPd: C, 57.73,
H, 4.45. Found: C, 56.55, H, 4.30. IR (Nujol, cm-1): νCO 2075 (s), νPdCl
275 (m). 1H NMR (200 MHz, CD2Cl2, -50 °C, TMS ext.): 3.90, 2.86,
2.24, 1.75 (4 m, br, 4H); 1.61 (s, Me). 31P{1H} NMR (81 MHz, CD2Cl2,
-50 °C, H3PO4 ext.): 24.39 (s).
(14) Mulliken’s charge density analysis (Mulliken, R. S. J . Chem.
Phys. 1955, 23, 1833) relative to density functional calculations carried
out by using the DMOL method (Delley, B. J . Chem. Phys. 1990, 92,
508. Delley, B. J . Chem. Phys. 1991, 94, 7245) on the model molecule
H3PCCO gives the following charge distribution on the PCâCRO
moiety: P (0.436), Câ (-0.568), CR (0.212), O (-0.282).
(19) 2e: A toluene suspension (15 mL) of [Pt(C3H5)Cl]4 (0.090 g, 0.08
mmol) was treated with a toluene solution (10 mL) of 1 (0.100 g, 0.33
mmol), and the mixture was stirred for 3 h. The yellow solid was
extracted with CH2Cl2, and from the resulting solution a yellow solid
was obtained by addition of ethyl ether. The compound was filtered
out, washed with ethyl ether, and dried under vacuum. Yield: 0.045
g, 24%. Anal. Calcd for C23H20OPPt: C, 48.13, H, 3.51. Found: C, 46.56,
H, 3.45. IR (Nujol, cm-1): νCO 2065 (s). 1H NMR (200 MHz, CD2Cl2,
(15) 2a : To a THF (40 mL) solution of [Pt(η3-C3H5)(Cl)(PPh3)] (0.533
g, 1.00 mmol) was added a 0.24 M solution of AgBF4 in acetone (1.05
mmol). AgCl was filtered off and the solution treated with 1 (0.302 g,
1.00 mmol) at room temperature. After 10 min a white solid started
to precipitate. The mixture was stirred for 24 h, and the precipitate
was filtered out and washed with THF. After drying, a white-yellow
powder was obtained (0.540 g, 61%). Anal. Calcd for C41H35OP2PtBF4:
C, 55.48, H, 3.97. Found: C, 54.73, H, 3.86. IR (Nujol, cm-1): νCO 2073
(s). 1H NMR (200 MHz, CD2Cl2, 25 °C, TMS ext.): 3.43, 2.38, 2.32 (3
3
2
-50 °C, TMS ext.): 3.79 (d, J HHc ) 7.7 Hz, J HPt ) 90.4 Hz, 1H); 1.04
(d, 3J HH ) 11.0 Hz, 2J HPt ) 77.9 Hz, 1H); 2.11 (d, 3J HH ) 11.0 Hz, 2J HPt
) 58.8 Hz, 2 H), 4.15 (m, Hc). 31P{1H} NMR (81 MHz, CD2Cl2, -50 °C,
2
H3PO4 ext.): 22.92 (s, J PPt ) 216 Hz).
(20) Carturan, G.; Belluco, U.; Del Pra, A.; Zanotti, G. Inorg. Chim.
Acta 1979, 33, 155.
3
3
4
m, 3H); 4.86 (m, J HPt ) 61.2 Hz, Hc); 3.62 (ddd, J HHc ) 7.1 Hz, J HH
(21) Ph3PCCO: 31P NMR (81 MHz, CD2Cl2, 25 °C, H3PO4 ext.) 5.45
(s); 13C NMR (50 MHz, CD2Cl2, 25 °C, TMS ext.) 20.84 (d, 1J CP ) 190.0
3
2
) 2.4 Hz, J HP ) 2.4 Hz, J HPt ) 13.5 Hz, 1H, Hsin trans to PPh3).
31P{1H} NMR (81 MHz, CD2Cl2, 25 °C, H3PO4 ext.): 24.58 (d, J PP
)
Hz, Câ), 145.57 (d, J CP ) 44.1 Hz, CR).
3
2
6.0 Hz, J PPt ) 4070 Hz); 24.31 (d, J PPt ) 101.3 Hz). 13C{1H} NMR
(22) Mann, B.; Taylor, B. F. 13C NMR Data for Organometallic
Compounds; Academic Press: London, 1981; p 208.
1
2
1
(50 MHz, CD2Cl2, 25 °C, TMS ext.): 57.58 (s, J CPt ) 157.4 Hz, Call);
2
1
1
62.83, (d, J CP ) 33.4, J CPt ) 74.5 Hz, Call), 111.05, (s, J CPt ) 37.3
(23) Crystal structure analysis of 2a : C41H35OP2PtBF4, M ) 887.57;
crystal dimensions 0.25 × 0.30 × 0.20 mm; Philips-PW 1100 computer-
controlled four-circle diffractometer; graphite monochromator, 0.710 70
Å MoKR, 298 K; θ-2θ scan method. The lattice constants were
determined from 25 reflections: a ) 10.907(1), b ) 18.785(2), c ) 9.086-
(1) Å; R ) 100.2(1), â ) 92.1(1), γ ) 79.4(1)°; V ) 1800.9(1) Å3; space
group P1h, Z ) 2, Fcalcd ) 1.64 g cm-3; F(000) ) 875.91; µ(Mo KR) )
38.55 cm-1; hkl range -12 < h < 12, -22 < k < 21, 0 < l < 10. Of
2
1
Hz, Cc); 156.73(d, J CP ) 18.9 Hz, CO), 9.62 (d, J CP ) 59.0 Hz, Câ).
(16) 2b: To a THF (40 mL) solution of [Pd(η3-2-Me-C3H4)(Cl)(PPh3)]
(0.460 g, 1.00 mmol) was added a 0.23 M solution of AgBF4 in acetone
(1.05 mmol). AgCl was filtered off, and the solution, cooled at -30 °C,
was treated with 1 (0.302 g, 1.00 mmol). After 1 h of stirring, the
reaction mixture was taken to dryness at low temperature, obtaining
a pale yellow solid that was washed with cold ethyl ether, filtered out,
and dried under vacuum. Yield: 0.414 g (57%). Anal. Calcd for
C42H37OP2PdBF4: C, 62.05, H, 4.60. Found: C, 61.03, H, 4.70. IR
(Nujol, cm-1): νCO 2070 (s). 1H NMR (200 MHz, CD2Cl2, -50 °C, TMS
ext.): 4.40, 3.62, 2.89, 2.82 (4 m, br, 4H); 1.70 (s, Me). 31P{1H} NMR
(81 MHz, CD2Cl2, -50 °C, H3PO4 ext.): 22.56 (s); 20.05 (s).
(17) (a) Mann, B. E.; Shaw, B. L.; Shaw, G. J . Chem. Soc. A 1971,
3536. (b) Bertani, R.; Carturan, G.; Scrivanti, A. Angew. Chem., Int.
Ed. Engl. 1983, 22, 228.
6348 independent reflections 4161 were considered “observed” [Fo
g
3σ(Fo)]; solution and refinement were obtained by standard Patterson
methods and subsequent Fourier recycling (SHELX-76). All non-
hydrogen atoms were refined with anisotropic displacement param-
eters. All hydrogen atoms were positioned geometrically and not
refined. Final values are R (Rw) ) 0.052 (0.062 with w ) 1/[σ2(Fo) + 3
× 10-3Fo2]), 370 parameters, and maximum residual electron density
1.168 e/Å3.
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3252 Organometallics, Vol. 15, No. 15, 1996
Communications
the bond C(40)-C(41) and its shortening up to 1.28 Å.
The bond angle CdCdO (175(1)°) is in agreement with
this suggestion. Therefore the geometry of the ketenyl
grouping can be more reasonably depicted with the
dipolar form A; the coordination to the metal seems
scarcely to change its geometry as compared with that
of the free ylide Ph3PdCdCdO.29
Preliminary assays on stability and reactivity of η1-
ketenyl compounds 2a -e indicate that the Pt(II)- and
Pd(II)-coordinated CCO moiety presents a reactivity
that resembles that of ketenes. Compound 2a is very
stable in the solid and in solution and reacts with Me2-
NH giving the amidic derivative 3 (eq 3) but is com-
F igu r e 1. ORTEP view of the cation [Pt(η3-C3H5){η1-
C(PPh3)(CO)}(PPh3)] (thermal ellipsoids at 30% probability
level) with atom labeling. Dotted bonds refer to the
disordered location of the allylic central carbon atom.
Selected bond lengths (Å) and angles (deg) of relevant
interest are reported: Pt-P(2) 2.278(1), Pt-C(40) 2.120-
(7), Pt-C(37) 2.188(2), Pt-C(38) 2.138(2), Pt-C(38′) 2.256-
(5), Pt-C(39) 2.230(2), P(1)-C(40) 1.75(1), P(1)-C(1) 1.798-
(7), P(1)-C(7) 1.786(9), P(1)-C(13) 1.796(7), C(40)-C(41)
1.280(8), C(41)-O 1.160(8); P(2)-Pt-C(40) 98.9(4), P(2)-
Pt-C(37) 96.8(2), C(40)-Pt-C(39) 95.4(4), C(37)-Pt-C(39)
68.7(2), C(40)-C(41)-O 175(1), Pt-C(40)-C(41) 118(1),
Pt-C(40)-P(1) 124.0(7), P(1)-C(40)-C(41) 118(1).
(3)
in a potential ylide grouping in the same molecule. Yet,
the question arises whether this structure deals with
an ylidic or a mere ketene nature of the complex cation.
The bond length P(1)-C(40) (1.75(1) Å) is almost in
the norm for an ylide and has been shown to indicate a
substantial double-bond character26 arising from the
dipolar contribution of the form Pδ+-Cδ-; thereby the
bond lengths C(40)-C(41), (1.280(8) Å) and C(41)-O
(1.160(8) Å) seem to be influenced as to exhibit a partial
triple-bond character. Actually these values are in the
range of those reported in literature for some η1-ketenyl
complexes8c,25 and other similar compounds27 and have
been tentatively explained in terms of mesomeric effects
involving nonpolar, acylium, and dipolar forms.3a How-
ever, for an ylidic character, in terms of mesomeric
effects, we would expect in the presence of the observed
P-C(40)-C(41) bond angle (118(1)°) a longer distance
C(40)-C(41);27 in contrast, it is here even shorter than
the values so far reported (1.31-1.33 Å).3a,25,28
On the other side, the geometrical parameters in the
coordination sphere of Pt are almost in the norm, thus
we believe that the Pt-C(40) bond electrons do not take
part to any mesomeric state of the cation. In this case
a somewhat measurable shortening of the bond Pt-
C(40) was expected. Rather, the metal center seems to
influence through inductive effects the charge distribu-
tion in the ketenyl grouping in cooperation with the
ylide moiety, so provoking an increased polarization of
pletely unreactive toward alcohols and water. Com-
pound 3 is obtained as a mixture (ca. 1:1) of two
diastereomeric forms, due to the contemporary presence
of the coordinated prochiral allyl group and the asym-
metric carbon atom Pt-CH(PPh3)(CONMe2). Com-
pound 2b is much more reactive than 2a and reacts even
in the solid state with moisture undergoing further
decomposition giving unidentified compound(s) through
elimination of CO2 well detected by IR. Other typical
ketene reactions, i.e. cycloadditions, on 2a ,b and the
reactivity of 2c,d ,e are at the present under study.
The synthesis of compounds 2a -e shows that the use
of Ph3PdCdCdO furnishes a possible easy entry to new
late transition metal ketenyl complexes. The extension
of the reaction to different Pd, Pt, and Rh substrates
offers a new platform for further developments.
Ack n ow led gm en t. This work was supported by the
Ministero dell’Universita` e della Ricerca Scientifica e
Tecnologica (MURST) and by the Consiglio Nazionale
delle Ricerche (CNR).
Su p p or tin g In for m a tion Ava ila ble: Text giving the
synthesis procedure and analytical and spectroscopic data for
3 and listings of final values of refined atomic coordinates and
thermal parameters, calculated atomic coordinates of hydrogen
atoms, anisotropic thermal parameters (Uij), complete bond
lengths and angles, and unit cell and complete crystal struc-
ture determination data for 2a (7 pages). Ordering informa-
tion is given on any current masthead page.
(24) Kreissl, F. R.; Frank, A.; Shubert, U.; Lindner, T. L.; Huttner,
G. Angew. Chem., Int. Ed. Engl. 1976, 15, 632.
(25) Kreissl, F. R.; Reber, G.; Mu¨ller, G. Angew. Chem., Int. Ed. Engl.
1986, 25, 643.
(26) J ohnson, A. W. Ylides and Imines of Phosphorus; Wiley: New
York, 1993; and references therein.
(27) Burlaff, H.; Wilhelm, E.; Bestmann, H. J . Chem. Ber. 1977, 110,
3168.
(28) (a) Casey, C. P.; Fagan, P. J . J . Am. Chem. Soc. 1982, 104, 7360.
(b) Gil, J . M.; Howard, J . A. K.; Navarro, R.; Stone, F. G. A. J . Chem.
Soc., Chem. Commun. 1979, 1168.
OM9602668
(29) Daly, J . J .; Wheatley, P. J . J . Chem. Soc. A 1966, 1703.
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