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Formation of 2H-1 2-Azaphosphole Tungsten Complexes by Trapping Reactions of Nitrilium Phosphane Ylide Complexes.

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[31] This is evident from the fact that the energy increases from 43 to 4.9kJmol-'
for configuration B by inclusion of the BSSE and even results in an endothermic binding energy for the dider. The binding energies for configuration A and
C(D) are -4.8 and -1.0 (MP2), -4.0 and 1.8 (B3LYP) and -4.4 and
-0.6 kJmol-' for CCSD(T).
[32] G. R. Desiraju, Angew. Chem. 1995, 107, 2541-2558;Angew. Chem. Int. Ed.
Engl. 1995, 24, 2328-2335, 0.Navon, J. Bernstein, V. Khodorkovsky, ibid.
1997. 109, 640-642 and 1997,36, 601-603.
[33] V.R. Pedirreddi, D. S. Reddi, B. S.Goud, D. C. Craig, D. Rae, G. R. Desiraju,
.I. Chem. Soc. Perkin Trans. 2, 1992, 2353-2360.
[34] S. C.Nyhurg, C. H. Faerman, Acta Crystallogr. Sect. B 1985,41, 274-279.
[35] D.Kirkin, Acfa Crystallogr. Sect. B 1987, 43, 405-406.
[36] G. Brauer, Handbnch der Praparativen Anorganischen Chemie, Vol. 1, Ferdinand Enke Verlag Stuttgart, 1975, p. 189.
[37] R. Boese, D.Blaser, N. Niederpriim, T. Miebach in Orpmic Crystal Chemistry
(Eds.: J. Garbarcryk, D.W. Jones), Oxford University Press, Oxford, 1991,pp.
109- 128.
[38] R.Boese, M. Nussbaumer, in Correlations, Transformations,andlntrractions in
Organic Crystal Chemistry, In situ Crisfullizution Techniques, vol. 7 (Eds. D. W.
Jones, A. Katrnsiak) Oxford University Press, Oxford, 1994, p. 20.
[39] Crystal system: monoclinic, space group P2,/c, Z = 4, at -188"C, a =
6378(1), b = 4.247(1), c = 6.425(1)& fl =104.55(3)", V=168.5(1)A3,
= 2.141gcm-3, ,u = 1.73mm-'. Diffractometer Nicolet-Siemens R3m/
V, Mo,, radiation, graphite monochromator, 1 = 0.7107A. A total number of
3747 reflections in the 20 interval 2-90" were measured by using the Wyckoff
scan technique (a half sphere of the reciprocal space in the interval 20 = 2- 60",
and two independent octants in the interval 20 = 60-90"). During data collection some misalignment of the single crystal was observed (probably because
of icing of the capillary at the low temperature) that resulted in relatively large
variations of the intensities of the check reflections and high Rintvalue after
averaging the equivalents (R,,, = 0.130). Therefore, only one independent part
ofthe total data set (one octant, 20 = 2-75") with 765 independent observable
(F, > 4.0u(F)) reflections was used in further calculations. The structure was
solved and refined (on F ) in the anisotropic approximation (SHELXTL Plus
programs Version 4.2)to R = 0.0357,Rw = 0.0401,and GOF = 1.73.Further
details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany), on quoting the depository number CSD-406442.
Scheme 1. Propargylic resonance structures of various nitrile ylides I and nitrilium phosphane ylide complexes I1 (R = alkyl, aryl; [MI = metal complex fragment).
phosphane ylidesL6](I, E = PR), nor their q1 complexes (II), nor
corresponding q1 complexes of the above-mentioned nitrogen
ylides are known. Our previous investigations of the thermal
decomposition of a 2H-azaphosphirene tungsten complex in the
presence of trapping reagents such as carbonyl,['] phosphaacetylene,['] or acetylene derivative^,^^' provided evidence
solely for the formation of a terminal phosphanediyl tungsten
complex as a transient intermediate."'] Here we report the synthesis and structural characterization of tungsten complexes of
the novel 2H-1,2-azaphospholes,~' which we explain on the
basis of trapping reactions of transient nitrilium phosphane
ylide tungsten complexes with dimethylacetylenedicarboxylate
(DMAD; 2).
The thermal decomposition of 2H-azaphosphirene tungsten
complexes 1 all2]and 1b,c[I3]in toluene at 75 "C in the presence
of DMAD (2) forms the 1H-phosphirene tungsten complex[915
as the main product, and also the 2H-1,2-azaphosphole tungsten complexes 6 a-c and the corresponding aryl nitriles[l4I
(Schcme 2). The complexes are isolated by low-temperature
Formation of 2H-l,2-Azaphosphole Tungsten
Complexes by Trapping Reactions of
Nitrilium Phosphane Ylide Complexes**
Rainer Streubel,* Hendrik Wilkens,
Annette Ostrowski, Christoph Neumann,
Frank Ruthe, and Peter G. Jones
Dedicated to Professor Gottfried Huttner
on the occasion of his 60th birthday
Nitrile oxides['a1 and nitrile imines['a,21 (I, E = 0 and
E = NR, respectively; Scheme 1) are of great importance in heterocycle syntheses because of their versatility in 1,3-dipolar cycloadditi~ns;[~l
the properties of stable membcrs of these classes
of compounds have been thoroughly investigated. The synthesis
of these 1,3-dipoles is usually based on readily available acyclic
precursors.['", 21 Nitrile sulfides[41(I, E = S) have until now only
been identified by UV/IR spectro~copy[~]
in inert matrices (e.g.
PVC) at low temperature or as reactive intermediates by trapping reaction^.^^] As far as we are aware, neither nitrilium
[*I Dr. R. Streubel, Dipl.-Chem. H. Wilkens, Dip1.-Chem. A. Ostrowski,
C. Neumann, Dipl.-Chem. F. Ruthe, Prof. Dr. P. G. Jones
Institnt fur Anorganische und Analytische Cheinie
der Technischen Universitat
Postfach 3329,D-38023-Braunschweig (Germany)
Fax: lnt. code (531)391-5387
e-mail: streubel(
[**I Chemistry of 2H-azaphosphirene complexes, Part 6.This work was supported
by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen
Industrie. Part 5 : Ref. [lo].
Vrrlagsgesellschuft mbH, 0-69451 Weinheim, 1997
la,3a,6a:Ar = pMeOC,H,
I b,3b,6b Ar = Ph
lc,3c,6c:Ar = pF3CC,H,
Scheme 2 . Postulated reaction course for the formation of the three- and five-membered rings of the complexes 5 and 6a-c, respectively.
chromatography and crystallization. The suggested structures
of the complexes 6a-c are based on solution NMR and IR
spectroscopic and MS data (Table I), and confirmed in the case
of 6 b in the solid-state by X-ray structure analysis.['51
As reaction mechanism we propose a thermal opening of the
three-membered ring to form the ylidic complexes 3a-c, which
then decompose to the terminal phosphanediyl tungsten complex 4 and the respective aryl nitrile, and subsequent ring-form-
0570-0833/97/3613-1492$17.50+ .50/0
Angew. ('hem. Int. Ed. Engl. 1997, 36, No. 13/14
Table 1 Selected NMR [a] and IR spectroscopic and MS data for 6a-c [b]
6 a : I3C{'H} NMR: 6 = 2.7 (d, 'J(P,C) = 2.0 Hz,SiMe,), 3.3 (d, 'J(P,C) = 2.6 Hz,
SiMe,), 19.2 (s, CH), 52.8 (s, OMe), 53.3 (s, OMe), 55.5 (s, C,C,OCH,), 114.3 (s,
o-Ph), 126.9 (d, '4P.C) =17.2Hz, i-Ph), 130.5 (s, m-Ph), 143.1 (d, J(P,C) =
26.5 Hz), 161 5 (d. J(P,C) =1.6 Hz), 162.7 ( s , p-Ph), 162.9 (d, J(P,C) = 2 2 Hz),
165.7 (d. J(P,C)=14.3Hz), 166.2 (d, J(P,C)=11.6Hz), 196.8 (d. 'J(P,C)=
6.6 Hz, cis-CO), 198.4 (d, 'J(P.C) = 22.9 Hz, trans-CO); 'IP NMR: 6 = 101.0 (s,
1J(P,'83W)= 238.4 Hz); IR (KBr, J(C=O) region): G = 2072 m, 1948 vs, 1919 s,
1741 m. 1724 m cr n- l , MS (EI, 70eV, la4W). m j z : 789 [M'].
6b: ',C{'H) NMR: 6 = 2.6 (d, 'J(P,C) = 1.9 Hz, SiMe,), 3.2 (d, 3J(P,C) = 2 4 Hz,
SiMe,). 18.9 (s. CH), 53.0(s. OMe), 53.2 (s, OMe), 128.4(s, o-Ph), 128.8 (s,m-Ph),
131.7 (s,p-Ph), 134.4 (d, 3J(P,C)=16.6Hz, i-Ph). 142.7 (d. J(P,C)=25.9Hz),
162.0(d.J(P.C) =1.4Hz),162.7(d,J(P,C) =13.1 Hz),165.1 (d,J(P,C) =14.2Hz),
167.2 (d. J(P,C) =11.5 Hz), 196 7 (d, 'J(P,C) = 6.5 Hz, cis-CO), 198.0 (d,
'J(P,C) = 23.1 Hz. oms-CO); 31P{'H} NMR: 6 =102.8 (s, IJ(P,'*'W) =
237.9 Hz); IR (KBr.C(C=O) region). i = 2073 s, 1992 m, 1953 vs, 1926 vs, 1914 vs,
1745 S , 1719 s cm - I , MS (EI, 70eV, lE4W):mjz: 759 [M+].
6c: I3C('H} NMR: d = 2.7 (s. SiMe,), 3.2(s, SiMe,). 18.9 (s, CH), 53.0(s,OMe),
53.4 (s. OMe), 123 7 (4.'J(C,F) = 272.6 Hz, CF,), 125.9 (4,'J(C,F) = 3.7 Hz,
m-Ph), 128.8 (s, o-Ph), 133.2 (4. 'J(C,F) = 33.1 Hz, p-Ph), 137.6 (d,
'J(P,C)=17.0Hz,I-Pb), 141.4(d,J(P,C)=25.1 Hz),162.7(d,J(P,C)=13.2Hz),
163.3 (d, J(P,C)=4.1Hz), 164.7 (d, J(P,C)=13.9Hz), 166.0 (d, J(P,C)=
10.7 Hz). 196.5 (dd. 'J(P,C) = 6.5, 1J(C,'83W) =127.2 Hz, cir-CO), 197.6 (d,
'J(P+C) = 23.0 Hz. trans-CO); 'IP{'H} NMR: 6 =104.9 (s, 1J(P,183W)=
237.4 Hz); IR (KBr. i.(C=O) region): J = 2075 s, 1994 m, 1950- 1914 vs (br ), 1741
s, 1725 sc m - l ; MS (EI, 70eV, lS4W); mjz: 827 [M+].
[a] In CDCI, at 25 'C; 13C NMR: 50.3, "P NMR: 81.0 MHz. The deuterated
solvents were used as internal and 85% H,PO, as external standards.
[bl Satisfactory C.H elemental analyses were obtained for 6a-c.
ing reaction of the reactive intermediates 3a-c and 4 with
DMAD ( 2 ) . This is based on the following findings. 1) The
three-membered heterocycles cannot be converted to five-membered heterocycles by warming the complexes in solution in the
presence of the corresponding aryl nitrile (5 + 6a-c), but
neither can a ring contraction by extrusion of aryl nitrile
(6a-c + 5) be observed. 2) The relative amount of 2H-1,2-azaphosphole complex formed depends on the electronic influence
of the para aryl substituents, in a way that can be interpreted in
terms of increased reactivity and/or lifetime of the reactive intermediates 3a-c; similar results have been obtained forpara-substituted aryl nitrile sulfides.[161The complexes 6a-c display
31P resonance signals in the range 6 = 102- 105 and characteristic I3C chemical shifts of the carbon atoms of the five-membered rings in the range 6 = 135- 168;[17,181
the magnitudes
of the 1J(31P.'83W)coupling constants are about 238 Hz (cf.
Table 1).
As also observed for lH-pyrazoles["] or q'-phosphole complexes,[191a notable feature of the molecular structure of complex 6b in the crystal (Figure 1) is the planar five-membered
ring. The bond lengths indicate localized double bonds; the
C-N double bond (129.1(6)pm) is shorter than that in 1Hpyrazoles,[' *I 2H-1,2,3-diazaphospholes,[' or a 1,2,3,4-diazadiphosphole.[201The phosphorus center displays a distorted
tetrahedral coordination; the W-P bond length is 250.45(12) pm.
Further investigations of the formation and reactivity of the
2H-1,2-azaphosphole tungsten complexes 6 a-c are currently in
Figure 1. Molecular structure of complex 6 b in the crystal (ellipsoids represent
50% probability levels; hydrogen atoms omitted for clarity). Selected bond lengths
[pmland angles("]: P-N 171.1(4), N-Cl5 129.1(6).C15-C14 149 7(6),C14-C13
134.3(6), C13-P 184 3(4); N-P-C13 91.8(2), P-Cl3-Cl4 108.2(3), C13-Cl4-Cl5
112.1(4),C14-C15-N 115.1(4), CIS-N-P 112.7(3).
6 a : orange powder, yield: 240mg (12%), m.p. 132'C (decomp); 6b: red powder,
yield: 160mg (9%), m.p. 121 'C (decomp); 6c: red powder, yield: 90mg (5%),
m.p. 113 "C (decomp)
Received: February 14, 1997 [Z10119IE]
German version: Angew. Chem. 1997, 109, 1549-1550
Keywords: coordination modes
tungsten ylides
. phosphorus
[I] a) Review: P. Caramella, P. Griinanger in ref. [lb], chapter 3; b) 1,3-DipoIur
Cyrloaddirion Chemistry (Ed.: A. Padwa), Wiley, New York. 1984.
[2] Review: G. Bertrand, C. Wentrup, Angeu,. Chem. 1994. 106, 549; Angew.
Chem. Int. Ed. Engt. 1994, 33, 527, and references therein.
[3] Reviews: a) R. Huisgen, Angew. Chem. 1963, 75, 604; Angrw. Chem. I n t . Ed.
Engl. 1963, 75, 742; b) in ref. [l b], p. 1 ff.
141 Review: R. M. Paton. Chem. SOC.Rev. 1989, 18, 33.
[5] a) A. Holm, N. Harrit, I. Trabjerg, J. Chem. Soc. Perkin Trans I , 1978, 746;
b) N. Harrit, A. Holm, I. R. Dunkin, M. Poliakoff, J. J. Turner, J. Chem. Soc.
Perkin Trans. 2 1987, 1227.
[6] To denote the zwitterionic form of the triatomic central framework of the
compounds of type I with E = PR, and to draw attention to the relationship
with other nitrogen ylides (the nitrile oxides, sulfides, and ylides), we propose
the term nitrilium phosphane ylides. In recent publications we used the term
phosphanitrile ylide for this reactive intermediate. Although confusion with
(R,PN), introduced by G. Bertrand, does not appear too
evident, we decided in favor of the new term.
[7] R. Streubel, A. Kusenberg, J. Jeske, P. G. Jones, Angew. Chem. 1994, 106,
2564; Angeu,. Chem. Int. Ed. Engl. 1994,33,2427.
[XI R. Streubel, L. Ernst, J. Jeske, P. G. Jones, J. Chem. SOC.Chem. Commun. 1995.
[9] A. Ostrowski, J. Jeske, P. G. Jones, R. Streubel. J Chem. Soc Chem. Commun.
1995, 2507.
[lo] We recently reported the transient formation of phosphacarbonyl ylide complexes: R. Streubel, A. Ostrowski, H. Wilkens, F. Ruthe, J. Jeske, P. G. Jones,
Angew. Chem. 1997,109,409; Angew. Chem. Int. Ed. €ng/. 1997,36, 378.
[ l l ] Review of azaphospholes: a) A Schmidpeter, K. Karaghiosoff in Mulriple
Bonds and Low Coordination Chemistry (Eds.. M. Regitz, 0.J Scherer),
Thieme, Stuttgart, 1990, pp. 258ff.; b) A. Schmidpeter in Comprehensive Hereroc.vclicChemi.~tr);II,Vol.3, (Eds.:A. R. Katritzky, C. W. Rees, E. F. V. Scriven), Pergamon, Oxford, 1996, pp. 709ff.
[12] R. Streubel, J. Jeske, P. G. Jones, R. Herbst-Irmer, AngeM.. Chem. 1994, 106,
Experimental Section
115-117; Angeu,. Chem Inl. Ed. Eitgl. 1994,33,80-82.
6a-c:la(1.62g,2.5mmol),lb(1.54g,2.5mmol),orlc(1.7ig,2.5mmol)was [13] R Streubel, A. Ostrowski, unpublished results.
dissolved in toluene (7.5 mL). After addition of DMAD 2 (0.5 mL, ca. 5 mmol) the
= 2227 (la/2),2229
[14] IR bands of the corresponding reaction solutions: ),V
reaction mixture was stirred for 2 h (6c: 3 h) at 75°C. When the reaction was
(1b/2), 2234 (lc/2)cm-'.
complete (as monitored by "P NMR spectroscopy), the solution wasevaporated to
[15] Crystal structure analysis of complex 6b: C,,H,,NO,PSi,W. M , =759.50;
dryness in vacuo (ca. 0.1 mbar), and the residue subjected to low-temperature
monoclinic, space group P2Jn. a =1050.9(2), b = 2178.5(4). c =
column chromatography on silica ( - 2 0 T , hexane/diethyl ether 97.5/2.5). The
1359.412) pm,
D = 103.46(2)", V = 3.0268(9)nm3; Z = 4, pCvrcd=
eluates were evaporated to dryness in vacuo (ca. 0.1 mbar), and the residues recrys1.667 Mgm-', i. = 0.71073 pm, T = 143 K. A crystal (0.54 x 0.38 x 0.20 mm)
tallized from pentane.
was mounted in inert oil at - 130 'C on a Stoe STADI-4 diffractorneter. IntenAngew. Chem. hi.Ed. Engl. 1997, 36. No. 13/14
Verlagsgesellschaft mbH, 0-69451 Weinheim, 1997
0570-0833/97/3613-14933 17.50+.50/0
sities were registered to 25 = 50'. Of 8639 reflections, 5330 were independent
(R,,, = 0.0406). An absorption correction based on $ scans was applied. The
structure was solved with the heavy atom method and refined against F2
(SHELXL-93). Methyl H atoms were included by using rigid groups, all other
H atoms with a riding model. Final w3R2 = 0.0732 based on F 2 for all data,
conventional R(F) 0.0309, for 360 parameters and 162 restraints; max. A p
955 enm - 3 Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no CCDC-100 177. Copies
of the data can be obtained free of charge on application to The Director,
CCDC, 12 Union Road, Cambridge CB2 lEZ, UK (fax: int. code +(1223)
336-033; e-mail: deposit($
1161 A. Holm, J. J. Christiansen, C. Lohse, J Chem. Soc. Perkrn Puns. 1 1979,
[17] The "C NMR resonance signals of comparable 3-aryl-4,5-di(methyloxycarbony1)isothiazole derivatives also fall in this range; see for example: P. A.
Brownsort, R. M. Paton. J Chem. Soc. Perkin Trans 1 1987, 2339.
1181 Review of 1H-pyrazoles: K. Krischke, Methoden Org. Chem., (Houhen- Weyl),
4th ed. 1952- Voi. E86, 1994, pp. 399 ff.
[19] Review of 1H-phosphole complexes: a) F. Mathey, J. Fischer, H. J. Nelson,
Struct. Bonding (Berlin) 1983,55,153; b) F. Mathey, Chem. Rev. 1988,88,429.
[20] C. Charrier, N. Maigrot, L Ricard, P. le Floch, F Mathey, Angeu. Chem.
1996, 108, 2282; Angew. Chem. Int. Ed. Engl. 1996, 35, 2133.
Palladium-Catalyzed AmidocarbonylationA New, Efficient Synthesis of
N-Acyl Amino Acids**
Industrial interest in racemic N-acyl amino acids has led to a
broad range of applications such as chelating agents, detergents,
and lubrication agents for boring machines.['] In addition,
enantiomerically pure, nonnaturai amino acids are important in
medical chemistry as components in peptidomimetics.[*IAsymmetric synthesis of amino acid derivatives has been studied intensively in recent years,[31but none of the known processes has
yet found industrial application. The development of technically
feasible multicomponent reactions with low-cost starting materials will become even more important in the
An example of a successful, efficient, three-component reaction for
the synthesis of N-acyl-a-amino acids from aldehydes, amides,
and carbon monoxide, amidocarbonylation (W-3-CR), was
first described by H. Wakamatsu in 1971.['I Amidocarbonylation is an economic improvement on the classical synthesis
methods and more environmentally friendly, since low-cost
starting materials can be used and the production of stoichiometric amounts of side products is avoided. For the past 25
years, amidocarbonylation has been catalyzed solely by cobalt
carbonyl complexes, but harsh reaction conditions and insufficiently active catalysts often lead to poor product selectivity,
which has prevented technical exploitation of the reaction.
[*] Prof. Dr. M. Beller, Dip1.-Chem. M. Eckert, Dip].-Chem. F. Vollmiilier
Anorganisch-chemisches Institut der Technischen Universitat Miinchen
Lichtenbergstrasse 4, D-85747 Garching (Germany)
Fax: Int. code +(89)289-13473
e-mail : mbeller@arthur.anorg.chemie
Dr. S. Bogdanovic, Dr. H. Geissler
Hoechst AG, Corporate Research & Technology, Frankfurt am Main (Germany)
This work was supported by the Deutsche Forschungsgemeinschaft (BE19311
1.1: BE1931/1-2). We thank Hoechst AG for the loan of a high-pressure reactor. Palladium-Catalyzed Reactions for the Synthesis of Fine Chemicals,
Part 1
0 VCH Verlag.rgeselischuft mbH, 0.69451
Weinhelm. 1997
LiBr, H+
Scheme 1. Palladium-catalyzed amidocarbonylation; R', R2, R3 = H, aryl, or
alkyl; [Pd] = PdBr, or [Pd(PPh,),Br,], for example.
We investigated the reaction of isovaleraidehyde with acetamide and carbon monoxide in the present of different metal
complexes as part of a project aimed at developing new amidocarbonylation catalyst^.^'^ Palladium(n) halides proved to be
fundamentally capable of catalyzing the reaction in the presence
of two equivalents of triphenylphosphane. Subsequently, comprehensive screening was carried out to determine the characteristic reaction parameters for palladium-catalyzed amidocarbonyiation (Table 1). Surprisingly, the presence of halide ions is
Table 1. Selected palladium-catalyzed amidocarbonylation experiments [a]
Matthias Beller,* Markus Eckert, Frank Vollmuller,
Sandra Bogdanovic, and Holger Geissler
Despite the well-known reasons why only cobalt carbonyl
complexes should be effective,[6]we now present amidocarbonylation reactions which have been successfully catalyzed by palladium and which show significant advantages over the cobalt
system (Scheme 1).
3 IbI
5 [bl
6 [bl
7 icl
8 [bl
9 [bl
[mol %]
[mol %.I
0 25
0 25
0 25
0 25
0 25
0 25
[mol %I
["/.I [d]
[a] Isovaleraldehyde and acetamide (25.0 mL each of 1 M solutions in N-methylpyrrolidone) were treated with carbon monoxide. [b] The catalyst dibromobis(triphenylphosphane)palladium(ii), was prepared in situ; 60 barCO pressure. [c] The
catalyst was palladium(I1) bromide; 10 barCO pressure. [d] Yield of isolated
essential for the reaction (Table 1, no. 2, 4 and 5). The order of
activity (I > Br > C1) correlates qualitatively with the C-X bond
energy. A synergistic effect, doubling the rate of reaction without lowering the selectivity, was observed when a strong acid
(for example H,SO,) was added as a cocatalyst (Table 1, no. 6).
N-methylpyrrolidone (NMP) was found to be a particularly
suitable solvent for the palladium-catalyzed amidocarbonylation reaction. Other aprotic solvents such as N,N'-dimethyiformamide (DMF), N,N-dimethylacetamide (DMAc), and dioxane can also be used. A temperature and pressure study revealed
that no further improvement in the reaction rate was achieved
by increasing the temperature above 130 "C and the pressure
above 60 bar CO.
With the new catalysts, it is now possible to carry out amidocarbonylation under the very mild conditions of 80 "C and
10 barCO (Table 1, no. 7). Both pailadium(I1) (e.g., PdBr,,
PdC1,) and palladium(o) (e.g., [Pd,(dba),] where dba = 1,sdiphenyl-l,4-pentadien-3-one,[Pd(PPh,),] ) compounds could
be used as catalyst precursors. Palladium(I1) bromide was shown
to be particularly effective. This catalyst gave the highest ever
turnover number (TON) of 25 000 (mol product per mol Pd-cat.)
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Angew. Chem. Int. Ed Engl. 199?,36, No. 13/14
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reaction, phosphane, formation, nitrilium, azaphosphol, complexes, tungsten, ylide, trapping
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