Synthesis of 2-(2-pyridyl)phosphaalkenes [Mes*P=C(R)Py] (R = H, SiMe3) and their complexes η1,η1-[Mes*P=C(R)Py]XPdCl (X = Cl, Me, Ac)

Article abstract of DOI:10.1021/om960925g

Bidentate ligands of the type Mes*P=C(R)Py ((E)-2, R = H; (Z)-9, R = SiMe₃; Mes* = supermesityl = 2,4,6-tri-tert-butylphenyl; Py = 2-pyridyl) were synthesized. Ligand (E)-2 was synthesized by reacting Mes*P(Li)SiMe₂(t-Bu) (4) with 2-

Full text of DOI:10.1021/om960925g

1144
Organometallics 1997, 16, 1144-1152
Syn th esis of 2-(2-P yr id yl)p h osp h a a lk en es
[Mes*P dC(R)P y] (R ) H, SiMe3) a n d Th eir Com p lexes
η1,η1-[Mes*P dC(R)P y]XP d Cl (X ) Cl, Me, Ac)†
Marcel van der Sluis,‡ Vincent Beverwijk,‡ Arjan Termaten,‡ Elena Gavrilova,‡
Friedrich Bickelhaupt,*,‡ Huub Kooijman,§ Nora Veldman,§ and
Anthony L. Spek§,|
Scheikundig Laboratorium, Vrije Universiteit, De Boelelaan 1083,
1081HV Amsterdam, The Netherlands, and Bijvoet Center for Biomolecular
Research, Vakgroep Kristal- en Structuurchemie, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Received November 1, 1996X
Bidentate ligands of the type Mes*PdC(R)Py ((E)-2, R ) H; (Z)-9, R ) SiMe3; Mes* )
supermesityl ) 2,4,6-tri-tert-butylphenyl; Py ) 2-pyridyl) were synthesized. Ligand (E)-2
was synthesized by reacting Mes*P(Li)SiMe2(t-Bu) (4) with 2-pyridinecarboxaldehyde.
Ligand (Z)-9 was synthesized via a PdCl2(dppb)-catalyzed coupling reaction between
2-bromopyridine and Mes*PdC(SiMe3)M ((E)-7, M ) ZnCl; (Z)-8, M ) MgBr). Compound
(E)-2 was also characterized by an X-ray crystal structure determination; it has a planar
structure with the (E)-configuration. The complexes η1,η1-[Mes*PdC(R)Py]PdCl2 (11, R )
H; 12, R ) SiMe3) were prepared by the reaction of bis(benzonitrile)palladium dichloride
with (E)-2 and (Z)-9, respectively. The complexes η1,η1-[Mes*PdC(R)Py]MePdCl (13, R )
H; 14, R ) SiMe3) were obtained by a ligand exchange reaction of MePdCl(COD) with (E)-2
and (Z)-9, respectively. Complex 13 was alternatively prepared by reaction of 11 with
methylmagnesium chloride. Complex 14 was unambiguously identified by an X-ray crystal
structure determination. Both 13 and 14 reacted with CO, resulting in the acetyl complexes
η1,η1-[Mes*PdC(R)Py]AcPdCl (16, R ) H; 17, R ) SiMe3).
In tr od u ction
Several groups have recently been engaged in the
synthesis of such ligand systems. Geoffroy et al. have
been active in the field of 2-(2-pyridyl)phosphaalkenes
and di(phosphaalkenyl)benzene ligands.1 Mathey et al.
developed phosphinine-based bidentate ligands by a
Stille-type cross-coupling reaction of 2-bromophosphin-
ines with the appropriate stannanes.2 These investiga-
tions led to bidentate ligands which are analogues of
the widely applied 2,2-bipyridine (bipy).6 Yoshifuji et
al. explored the field of 1,2-diphosphinidenecyclobu-
tenes.3d The palladium dichloride complexes of the 1,2-
diphosphinidenecyclobutenes showed catalytic activity
in a Heck-type coupling reaction between trimethylsil-
ylacetylene and p-bromonitrobenzene.3d
For some time we have been involved in the develop-
ment of methodologies for the synthesis of functionalized
phosphaalkenes from halogen-substituted phosphaal-
kenes, as the ultimate starting material.7 Recently, we
described a Pd(0)-catalyzed cross-coupling reaction of
bromophosphaalkenes [(E/Z)-Mes*PdC(H)Br] with Grig-
nard reagents. This has led to a variety of novel
functionalized phosphaalkenes (E)-Mes*PdC(H)R, where
R is an olefinic, (functionalized) aromatic, or heterocyclic
group.7c The present investigations were initiated with
the purpose of extending this methodology to the
Recent developments in the field of phosphaalkene-
and phosphinine-based ligand systems and their com-
plexes with metals reveal great interest in the possibly
unique coordinative properties of these novel species.1-4
This is motivated by the fact that phosphaalkenes and
phosphinines are the phosphorus analogues of imines
and pyridines, which are widely used in homogeneous
catalysis.5
* To whom correspondence should be addressed: tel (31)(0)20-
4447479; fax (31)(0)20-4447488; e-mail bicklhpt@chem.vu.nl.
† Part of this paper was presented at the XVIIth International
Conference on Organometallic Chemistry, Brisbane, Australia, J uly
7-12, 1996.
‡ Vrije Universiteit.
§ Utrecht University.
| Address correspondence pertaining to crystallographic studies to
this author.
X Abstract published in Advance ACS Abstracts, February 1, 1997.
(1) (a) J ouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett.
1992, 33, 5071. (b) J ouaiti, A.; Geoffroy, M.; Terron, G.; Bernardinelli,
G. J . Chem. Soc., Chem. Commun. 1992, 155. (c) J ouaiti, A.; Geoffroy,
M.; Bernardinelli, G. Tetrahedron Lett. 1993, 34, 3413. (d) J ouaiti, A.;
Geoffroy, M.; Bernardinelli, G. J . Chem. Soc., Dalton Trans. 1994, 1685.
(e) J ouaiti, A.; Geoffroy, M.; Terron, G.; Bernardinelli, G. J . Am. Chem.
Soc. 1995, 117, 2251. (f) J ouaiti, A.; Geoffroy, M.; Bernardinelli, G. J .
Chem. Soc., Chem. Commun. 1996, 437.
(2) (a) Le Floch, P.; Carmichael, D.; Ricard, L.; Mathey, F. J . Am.
Chem. Soc. 1993, 115, 10665. (b) Trauner, H.; Le Floch, P.; Lefour,
M.; Ricard, L.; Mathey, F. Synthesis 1995, 717. (c) Mathey, F.; Le Floch,
P. Chem. Ber. 1996, 129, 236. (d) Le Floch, P.; Mansuy, S.; Ricard, L.;
Mathey, F. Organometallics 1996, 15, 3267.
(5) Zassinovich, G.; Mestroni, G.; Gladiali, S. Chem. Rev. 1992, 92,
1051.
(3) (a) Yoshifuji, M.; Toyota, K.; Inamoto, N. J . Chem. Soc., Chem.
Commun. 1984, 689. (b) Yoshifuji, M.; Toyota, K.; Inamoto, N.
Tetrahedron Lett. 1985, 26, 1727. (c) Yoshifuji, M.; Toyota, K.; Matsuda,
I.; Niitsu, T.; Inamoto, N.; Hirotsu, K.; Higuchi, T. Tetrahedron 1988,
44, 1363. (d) Toyota, K.; Masaki, K.; Abe, T.; Yoshifuji, M. Chem. Lett.
1995, 221.
(6) Seddon, E. A.; Seddon, K. R. In The Chemistry of Ruthenium;
Clark, R. J . H., Ed.; Elsevier: Amsterdam, 1984; pp 430-432.
(7) (a) van der Sluis, M.; Bickelhaupt, F.; Eisfeld, W.; Regitz, M.;
Veldman, N.; Kooijman, H.; Spek, A. L. Chem. Ber. 1995, 128, 465. (b)
van der Sluis, M.; Wit, J . B. M.; Bickelhaupt, F. Organometallics 1996,
15, 174. (c) van der Sluis, M.; Klootwijk, A.; Wit, J . B. M.; Bickelhaupt,
F.; Veldman, N.; Spek, A. L.; J olly, P. W. J . Organomet. Chem. 1997,
in press.
(4) Dillon, K. B.; Goodwin, H. P. J . Organomet. Chem. 1994, 469,
125.
S0276-7333(96)00925-9 CCC: $14.00 © 1997 American Chemical Society

Synthesis of Novel 2-(2-Pyridyl)phosphaalkenes
Organometallics, Vol. 16, No. 6, 1997 1145
Sch em e 1
Sch em e 2
the reaction mixtures by 31P NMR spectroscopy showed
only starting material (E)-3 (δ(31P) ) 322) in all at-
tempts (Scheme 1).
So we prepared (E)-2 by the “classical” approach,
which had been reported earlier by Geoffroy et al.:1 a
stoichiometric amount of 2-pyridinecarboxaldehyde was
reacted with Mes*P(Li)SiMe2(t-Bu) (4) at -65 °C in THF
solution. After the reaction mixture was warmed to
room temperature and worked up, (E)-2 (δ(31P) ) 285;
2J (PH) ) 25.4 Hz) was isolated in 65% yield and 100%
isomeric purity as air stable yellow crystals (Scheme 2);
the conditions reported1a for the preparation of (E)-2
were slightly adjusted, which led to higher yields, see
synthesis of bidentate ligands containing a phosphaal-
kene moiety and their complexes with transition metals.
In this paper we present our attempts to prepare 2-(2-
pyridyl)phosphaalkenes of the type: Mes*PdC(R)Py (R
) H, SiMe3) by a palladium-catalyzed cross-coupling
reaction between a phosphaalkene and a pyridine moi-
ety and their application as bidentate ligands in novel
palladium(II) complexes of the type η1,η1-[Mes*PdC(R)-
Py]XPdCl (R ) H, SiMe3; X ) Cl, Me, Ac). The chelating
properties of the 2-(2-pyridyl)phosphaalkenes in Pd(II)
complexes will be compared with those of their nitrogen
analogues: the well-studied R-PyCa ligands (R-PyCa
) 2-Pyridyl-CdNR).8,9
1
Experimental Section. The H NMR spectrum of (E)-2
shows a characteristic signal of the ortho-proton of the
pyridine ring at δ(1H) ) 8.5; it proved to be important
for monitoring η1-coordination of the nitrogen atom to
palladium (vide infra). The phosphorus nucleus in (E)-2
(δ(31P) ) 285) is strongly deshielded compared to that
in the phenyl analogue (δ(31P) ) 259).3b,c This suggests
a certain degree of conjugation between the electron
withdrawing pyridine ring and the PdC double bond,
whereby the π-electrons of the phosphaalkene are
shifted toward the pyridine ring. Optimal conjugation
requires a planar conformation of (E)-2; this was
experimentally found in a crystal structure determina-
tion, which was reported to show the s-trans conforma-
tion exclusively.1a
We obtained yellow crystals of (E)-2 (from acetoni-
trile), which were subjected to an X-ray crystal structure
determination. The crystal contained two rotational
conformers around the C(1)-C(8) bond in a disordered
fashion; the s-trans:s-cis ratio was fixed at 1:1. The
crystal structure of (E)-2 has been reported earlier by
Geoffroy et al.1a The magnitude and shape of the atomic
displacement ellipsoids as well as the magnitude of the
bond lengths strongly suggest that the pyridyl ring is
also disordered in this earlier crystal structure deter-
mination, although no disorder model was introduced.
The P(1)-C(1) (PdC) bond length is 1.663(3) Å, which
is normal, and the C(1)-C(8) bond length is 1.470(4) Å,
which is relatively short compared to the analogous
bond length in other phosphaalkenes.1d,3c,7a The pres-
ence of two rotational conformers indicates that in the
crystal, both conformations are practically equivalent
which, in view of the minor differences between the
ortho-pyridyl positions (C-H vs N), is not too surprising.
The rotational barrier is expected to be so small that in
solution, (E)-2 will easily coordinate to a metal center
in a bidentate s-cis fashion.
Resu lts a n d Discu ssion
Syn th esis of 2-(2-P yr id yl)p h osp h a a lk en es. Re-
cently, we described the use of a palladium(0)-catalyzed
cross-coupling reaction of bromophosphaalkenes (E/Z)-
Mes*PdC(H)Br with Grignard reagents (RMgBr), fur-
nishing functionalized phosphaalkenes of the type (E)-
Mes*PdC(H)R.7c However, the introduction of a pyridine
functionality, which would furnish the bidentate ligand
(E)-2, failed. Both the Grignard reagent prepared from
2-bromopyridine10 and 2-(trimethylstannyl)pyridine11
did not react with bromophosphaalkene (E)-1 in the
presence of a catalytic amount (5 mol %) of tetrakis-
(triphenylphosphine)palladium(0) [Pd(PPh3)4] (Scheme
1); the 31P NMR spectra of the crude reaction mixture
showed only the presence of starting material (E)-1 in
both cases. Therefore, we investigated the reverse
combination by reacting (E)-trimethylstannylphosphaalk-
ene (E)-3 with 2-bromopyridine in the presence of Pd-
(PPh3)4. Isomerically pure (E)-3 was prepared by the
reaction of (E)-1 with magnesium and trimethylchlo-
rostannane under Barbier conditions; this method had
been applied by Mathey et al. for the preparation of a
2-trimethylstannylphosphinine.2b Presumably, trimeth-
ylchlorostannane reacts with the in situ prepared Grig-
nard reagent of (E)-1 to furnish (E)-3, an oil which was
used without further purification. However, under a
variety of conditions, a Stille coupling between (E)-3 and
2-bromopyridine could not be accomplished; analysis of
The structure of (E)-2 (Figure 1, Table 1, 2) proves it
to be almost planar, with dihedral angles of C(2)-P(1)-
C(1)-C(8) ) 178.5(2)° and P(1)-C(1)-C(8)-N(1) )
-18(2)°. The C(1)-P(1)-C(2) angle is 99.15(14)°, which
is small compared to the analogous angle in other
phosphaalkenes.7a This implicates that the lone pair
on phosphorus has relatively more s-character which
is expected to result in weaker σ-bonding to transition
metals.
(8) (a) Ru¨lke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769. (b)
Ru¨lke, R. E.; Delis, J . G. P.; Groot, A. M.; Elsevier, C. J .; van Leeuwen,
P. W. N. M.; Vrieze, K.; Goubitz, K.; Schenk, H. J . Organomet. Chem.
1996, 508, 109.
(9) Cucciolito, M. E.; De Felice, V.; Panunzi, A.; Vitagliano, A.
Organometallics 1989, 8, 1180.
(10) von Paradies, H. H.; Go¨rbing, M. Angew. Chem. 1969, 81, 293.
(11) Yamamoto, Y.; Yanagi, A. Heterocycles 1981, 16, 1161.

1146 Organometallics, Vol. 16, No. 6, 1997
Ta ble 1. Cr ysta llogr a p h ic Da ta for (E)-2 a n d 14
van der Sluis et al.
complex
(E)-2
14
C28H45NPPdSi
Crystal Data
formula
mol wt
cryst syst
space group
a, Å
C24H34NP
367.51
596.60
monoclinic
P21/c (No. 14)
9.6550(6)
9.5829(5)
25.2514(14)
112.108(5)
2164.6(2)
1.128
monoclinic
P21/c (No. 14)
17.521(3)
8.971(3)
18.7463(19)
98.651(10)
2913.0(11)
1.360
b, Å
c, Å
â, deg
V, Å3
D
Z
calcd, g cm-3
4
4
F(000)
800
1.3
1248
8.4
0.05 × 0.15 × 0.15
µ [Mo KR], cm-1
crystal size, mm
0.25 × 0.50 × 0.50
Data Collection
1.7, 26.48
0.84 + 0.35 tan θ
2.49 + 1.25 tan θ, 4.00
9
θ
min, θmax, deg
1.1, 27.5
∆ω, deg
0.50 + 0.35 tan θ
3.00 + 1.50 tan θ, 4.00
39
Hor., ver. aperture, mm
X-ray exposure time, h
linear instability, %
ref reflns
data set
total data
3
15
02h7h,41h2h,2h2h2
-11:0, 0:12, -28:30
4509
2h23h,2h22h,2h32h
-22:22, -11:11, -24:16
17 502
total unique data
4246 [Rint ) 0.039]
6677 [Rint ) 0.081]
Refinement
no. of refined params
final Ra
250
330
0.0600 [3027 Fo > 4σ(Fo)]
0.1444
0.0514 [4503 Fo > 4σ(Fo)]
0.1090
final wR2b
goodness of fit
1.06
1.01
weighting schemec
(∆/σ)av, (∆/σ)max
[σ2(F2) + (0.0520P)2 + 1.76P]-1
0.000, 0.001
[σ2(F2) + (0.0415P)2 + 0.60P]-1
0.000, 0.002
min. and max. residual density, e Å-3
-0.23, 0.33
-0.92, 0.65 [near Pd]
a
b
2
R ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
c P ) (max(Fo2, 0) + 2Fc2)/3.
Sch em e 3
effects associated with a lower HOMO-LUMO gap are
F igu r e 1. ORTEP27 (30% probability level) drawing of (E)-
2. Only one of the rotational conformers is shown; hydrogen
atoms have been omitted for clarity.
also important.
Although a stable pyridyl-functionalized phosphaal-
kene can be prepared by the classical route, we kept
searching for the synthesis of such a species by a
transition-metal-catalyzed cross-coupling reaction start-
ing from halogen-substituted phosphaalkenes. Re-
cently, we described investigations which led to reactive
and configurationally stable 2-(trimethylsilyl)phos-
phaalkenylmetal halides Mes*PdC(SiMe3)M ((E)-7, M
) ZnCl; (Z)-8, M ) MgBr) Scheme 3.7b These reagents
were obtained by transmetalation of 2-lithio-2-(trimeth-
ylsilyl)phosphaalkenes (E/Z)-6 with zinc dichloride or
magnesium dibromide, respectively. The use of phos-
phaalkenylzinc chloride reagent (E)-7 in transition-
metal-catalyzed coupling reactions would be highly
attractive from a synthetic point of view; it would
facilitate the introduction of sensitive organic function-
alities to the phosphaalkene moiety, such as carbonyl
containing groups. We found an efficient method for
the coupling of 2-bromopyridine with reagents (E)-7 and
Ta ble 2. Selected Bon d Len gth s (Å), Bon d An gles
(d eg), a n d Tor sion An gles (d eg) for (E)-2 (Esd in
P a r en th eses)
Bond Lengths
P1-C1
C1-C8
C8-C9
C9-C10
1.663(3)
1.470(4)
1.33(5)
1.38(5)
C10-C11
C11-C12
C12-N1
N1-C8
1.369(6)
1.358(5)
1.39(5)
1.31(5)
Bond Angles and Torsion Angles
C1-P1-C2
99.15(14)
123.8(2)
118(2)
119(4)
120(2)
C11-C12-N1
120(2)
119(4)
119(2)
178.5(2)
-18(2)
2.5(4)
P1-C1-C8
C12-N1-C8
C1-C8-C9
N1-C8-C1
C8-C9-C10
C9-C10-C11
C10-C11-C12
C2-P1-C1-C8
P1-C1-C8-N1
C2-C3-C4-C5
118.3(3)
As in previous cases,7a the high degree of deshielding
of the phosphorus nucleus cannot be explained by
diamagnetic effects alone; presumably, paramagnetic

Synthesis of Novel 2-(2-Pyridyl)phosphaalkenes
Organometallics, Vol. 16, No. 6, 1997 1147
Sch em e 4
not improve our methodology for the formation of (E)-
2. We attempted to improve the conversion of (Z)-9 by
using other reagents. However, KF‚2H2O in THF did
not react and Bu4NF‚H2O in THF gave decomposition
products (δ(31P) ) 22). Even lithium methoxide, which
had been highly effective in the removal of a silyl group
from the bromo analogue (E)-Mes*PdC(SiMe3)Br,7c did
not show any reactivity toward (Z)-9. These results
clearly reveal that the formation of (E)-2 from (Z)-9 by
a protio-desilylation reaction is not attractive from a
synthetic point of view.
For m a tion a n d Rea ctivity of P a lla d iu m (II) Com -
p lexes. As described in the Introduction, the applica-
tion of phosphaalkenes and phosphinines in bidentate
ligands and their incorporation into new phosphaalkene-
and phosphininemetal complexes attracts quite some
interest, as these species may represent the phosphorus
analogues of imine- and pyridinemetal complexes, which
are widely explored for their use in homogeneous
catalysis. Phosphaalkene-based ligands, such as (E)-2
and (Z)-9, would be of interest for catalysis for several
reasons. The electronic properties of the phosphaal-
kenes are different from those of imines. Calculations
and photoelectron spectroscopic investigations have
shown that in phosphaalkenes, the HOMO is usually
of π-type, while the phosphorus lone pair σ-orbital is
only slightly more stable.14 In imines, however, the
HOMO is the lone pair.14 Additionally, the lone pair of
a dicoordinate phosphorus atom has more s-character
compared to that of comparable imines. Furthermore,
the inherent polarity of the EdC double bond (E ) P or
N) is reversed due to the difference in the electronega-
tivity (x) between the two heteroatoms: contrary to
nitrogen (x(N) ) 3.0), phosphorus (x(P) ) 2.1) is slightly
more electropositive compared to carbon (x(C) ) 2.5).16
These factors lead to weaker σ-coordination properties
of the phosphorus lone pair compared to that of nitro-
gen. On the other hand, the phosphaalkene π*-orbital
(LUMO) is relatively low in energy and enhances the
π*-acceptor properties of these species in organometallic
complexes, which would result in stronger back-bond-
ing.14 Moreover, 31P NMR spectroscopy is a powerful
tool for mechanistic studies on certain catalytic cycles
in which the phosphaalkenes are involved.
(Z)-8. Minato et al. had described the analogous cross-
coupling reaction between R-trimethylsilyl-substituted
vinylmetallic reagents with 2-bromopyridines;13 this
coupling reaction was efficiently catalyzed by PdCl2-
(dppb) (dppb ) 1,4-bis(diphenylphosphino)butane). When
this catalyst (5 mol %) was applied in the cross-coupling
reaction of (E)-7 with 2-bromopyridine in refluxing THF
solution for 6 h, the product (Z)-9 (δ(31P, CDCl3) ) 333)
was isolated in 56% yield (Scheme 3). The reaction was
monitored by 31P NMR spectroscopy of the crude reac-
tion mixture. Besides the formation of (Z)-9, a substan-
tial amount (35%) of the “protonated” product (Z)-
Mes*PdC(H)SiMe3 (δ(31P, crude reaction mixture) )
335; J (PH) ) 18 Hz) was observed. The progress of the
reaction was also monitored by hydrolysis of the zinc
reagent (E)-7, as the phosphavinylidene reagents (E)-7
and (Z)-8 cannot be observed directly by 31P NMR
spectroscopy.7b The reaction was considered to be
finished when the signal of the “hydrolysis product” (δ-
(31P) ) 335) did not increase relative to that of (Z)-9,
after adding water to a sample of the reaction mixture.
Extending these investigations, we discovered the
first example of the direct formation of a Grignard
reagent from the corresponding bromophosphaalkene.
Previously, a methodology for the preparation of phos-
phaalkene Grignard reagents had not been reported,
except for our transmetalation reaction of (E/Z)-6 with
magnesium dibromide, resulting in (Z)-8.7b Now, it
turned out that Grignard reagent (Z)-8 was formed by
stirring a THF solution of (Z)-5 with magnesium metal.
Analysis of the reaction mixture by 31P NMR spectros-
copy after deuterolysis showed the mixture to contain
only the deuterolysis product (Z)-10 (δ(31P, crude reac-
tion mixture) ) 334) and the protonated product in a
ratio of 87:13, corresponding to a 87% yield in Grignard
reagent formation (Scheme 4). The remarkable inver-
sion of configuration during this process is the subject
of ongoing investigations, and the results will be re-
ported in the near future.
Recently, Venanzi et al. reported on the formation and
properties of transition metal (Pt(II), Ir(I)) complexes
of 2-(2′-pyridyl)-4,5-dimethylphosphinine15 and Geoffroy
et al. reported the preparation of the 2-(2-pyridyl)-
phosphaalkene complex [Cu(Mes*PdC(H)-(2-pyridyl))-
(MeCN)2][PF6].1a We investigated the formation of
palladium(II) complexes of (E)-2 and (Z)-9. The pal-
ladium dichloride complexes 11 and 12 were obtained
by reacting bis(benzonitrile)palladium dichloride with
the bidentate ligands (E)-2 and (Z)-9, respectively, in
dichloromethane at room temperature for 10 min
(Scheme 5). The complexes were isolated in 83% and
The Grignard reagent (Z)-8 was used for the palla-
dium(II)-catalyzed coupling reaction with 2-bromopyri-
dine. A mixture of (Z)-8 and 2-bromopyridine was
heated under reflux for 6 h in the presence of PdCl2-
(dppb) (5 mol %) in THF solution, as described above
for the analogous zinc reagent (E)-7. After workup, 53%
of the desired product (Z)-9 was isolated (Scheme 4).
While we were able to prepare ligand (E)-2 by the
classical reaction (vide supra), it was attractive to try
the conversion of (Z)-9 to (E)-2 by exchanging the silyl
group for a hydrogen atom (Scheme 4). The application
of potassium fluoride in wet boiling DMF was described
by Appel et al. in the analogous conversion of the phenyl
derivative (Z)-Mes*PdC(SiMe3)Ph.12 However, their
yield (approximately 50%) was disappointing and would
(12) Appel, R.; Menzel, J .; Knoch, F.; Voltz, P. Z. Anorg, Allg. Chem.
1986, 534, 100.
(13) Minato, A.; Suzuki, K.; Tamao, K.; Kumada, M. Tetrahedron
Lett. 1984, 25, 83.
(14) Gilheany, D. G. In The Chemistry of Organophosphorus Com-
pounds; Hartley, F. R., Ed.; J ohn Wiley and Sons: New York, 1990;
Patai Series, Vol. 1, Chapter 2, p 44 and references cited therein.
(15) (a) Schmid, B.; Venanzi, L. M.; Albinati, A.; Mathey, F. Inorg.
Chem. 1991, 30, 4693. (b) Schmid, B.; Venanzi, L. M.; Gerfin, T.;
Gramlich, V.; Mathey, F. Inorg. Chem. 1992, 31, 5117.
(16) Nyula´szi, L.; Veszpre´mi, T.; Re´ffy, J . J . Phys. Chem. 1993, 97,
4011.

1148 Organometallics, Vol. 16, No. 6, 1997
van der Sluis et al.
Sch em e 5
F igu r e 2. ORTEP27 (30% probability level) drawing of 14.
Hydrogen atoms have been omitted for clarity.
alternative procedure was used. Ligand (E)-2 was
reacted with 1 equiv of (1,5-cyclooctadiene)methylpal-
ladium chloride8 by stirring the reaction mixture in
dichloromethane for 10 min at room temperature. After
evaporation of the solvent and purification of the yellow
product as described above, pure 13 was isolated as a
yellow powder in 90% yield. Analogously, 14 (δ(1H, Pd-
3
Me, CDCl3) ) 1.11, d, J (HP) ) 3.45 Hz) was obtained
from (Z)-9 in 83% yield (Scheme 5).
91% yield, respectively, as yellow-orange powders.
Complexation with palladium dichloride shows some
In principle, the reactions leading to complexes 13 and
14 could furnish two stereoisomers; the methyl group
might be positioned trans or cis toward the phosphorus
center of the bidentate ligand. However, only one of the
two possible products is formed with high selectivity.
The methyl group is expected to be cis to the phosphorus
center of the bidentate ligand because of its charac-
1
characteristic features in the H and 31P NMR spectra
of the ligands, which prove the presence of η1,η1-bonding
of the ligands to the palladium(II) center. In the 1H
NMR spectra, a characteristic deshielding of the pyri-
dine ortho-proton signal8b is observed; for 11 and 12
∆δ(1H) ) 1.36 and 1.56, respectively. The phosphorus
chemical shifts of the complexes show considerable
shielding compared to the free ligands. For 11 (δ(31P)
) 247) and 12 (δ(31P) ) 283), a ∆δ(31P) of -37.6 and
-51.9 ppm is observed, respectively. This shielding is
completely in line with the values reported in the case
of other η1-phosphaalkene-palladium complexes.1,3d
Palladium complexes are of interest because of their
potential application in catalysis, e.g., in carbon mon-
oxide-olefin or carbon monoxide-acetylene copolym-
erization reactions. One of the important requirements
for such a polymerization reaction is the possibility of
a CO insertion reaction into a carbon-palladium bond
of the corresponding complex. Complexes with a meth-
yl-palladium bond can be used as models for investi-
gating the ability of CO insertion.8b,17
3
teristic coupling value of J (HP) ) 3.99 and 3.45 Hz,
respectively, which is analogous to the 3J (HP) coup-
ling constants of this magnitude in (PAN)MePdCl [PAN
) 1-(dimethylamino)-8-(diphenylphosphino)naphtha-
lene] complexes; according to the X-ray structure of this
complex, the phosphorus atom and the methyl group
are cis oriented.18
Str u ctu r a l Asp ects of η1,η1-[Mes*P dC(SiMe3)P y]-
MeP d Cl (14). In order to unambiguously prove the
structure of 14 and to obtain a better insight into the
coordinative properties of ligand (Z)-9 in 14, we deter-
mined the X-ray crystal structure of this novel complex.
The X-ray data were compared with those of [2-(N-(2-
propyl)carbaldimino)-6-(methyl)pyridyl]methylpalladium-
(II) chloride ((i-Pr-6-Me-PyCa)MePdCl (15)),8b which
can be considered as the imine analogue of 14 (Figure
2, Tables 1, 3, and 4).
Single crystals of 14 were obtained by slow concentra-
tion of a chloroform solution of the complex. The crystal
structure shows a square planar arrangement of the
ligands around the palladium center, and (Z)-9 is indeed
coordinated as a bidentate ligand to the MePdCl moiety.
The methyl group bonded to palladium is positioned cis
toward the coordinating phosphorus nucleus, in line
For this reason, model complex 13 was prepared by
reacting the palladium dichloride complex 11 with 1
equiv of methylmagnesium chloride in THF at -65 °C.
The yellow suspension of 11 in THF changed into an
orange solution immediately. At room temperature, the
solvent was evaporated and the residue thoroughly
washed with diethyl ether and pentane to furnish 13
1
as a yellow-orange powder (Scheme 5). In the H NMR
spectrum, a characteristic doublet of the methyl group
at palladium (δ(1H, CDCl3) ) 1.14, d, 3J (HP) ) 3.99 Hz)
appeared. The 31P NMR spectrum showed only one
signal at δ(31P) ) 253, proving the stereoselective
substitution of only one chlorine atom. However, com-
plex 13 was difficult to separate from the magnesium
salts which are formed as byproducts. Therefore, an
3
with our expectation based on the small J (HP) value.
The preference of the methyl group for the position
trans toward the pyridine ring in 14 was also found in
the case of 15.8b This indicates that the phosphaal-
kene displays a stronger trans-influence19 compared
to the pyridine ligand. The C(1)-P(1)-C(2) angle is
(18) Dekker, G. P. C. M.; Buijs, A.; Elsevier, C. J .; Vrieze, K.; van
Leeuwen, P. W. N. M.; Smeets, W. J . J .; Spek, A. L.; Wang, Y. F.; Stam,
C. H. Organometallics 1992, 11, 1937.
(17) Ankersmit, H. A. Thesis, University of Amsterdam, Amsterdam,
The Netherlands, 1996.

Synthesis of Novel 2-(2-Pyridyl)phosphaalkenes
Organometallics, Vol. 16, No. 6, 1997 1149
Ta ble 3. Selected Bon d Len gth s (Å), Bon d An gles
(d eg), a n d Tor sion An gles (d eg) for 14 (Esd in
P a r en th eses)
in 14 compared to that of 15 (Table 4) suggests a
stronger trans-influence, or back-bonding, of the phos-
phaalkene compared to the imine moiety, which must
have its origin in an energetically lower π*-orbital.
Indeed, the calculated lower energy of the π*-orbital
(LUMO) of a phosphaalkene compared to that of an
imine is capable of increasing the back-donation of the
metal dπ-orbital to the phosphaalkene pπ*-orbital.14 As
a consequence, the P(1)-Pd bond is expected to be
relatively short and strong, as experimentally observed
(vide supra).
Bond Lengths
P1-Pd1
N1-Pd1
Pd1-C30
Pd1-C11
C2-P1
2.1744(14)
2.164(4)
2.029(5)
2.3545(14)
1.808(4)
1.431(5)
1.674(4)
1.478(5)
1.395(7)
C9-C10
C10-C11
C11-C12
C12-N1
N1-C8
1.371(8)
1.370(7)
1.380(7)
1.332(6)
1.369(5)
1.911(4)
1.866(5)
1.866(6)
1.856(5)
C2-C3
Si1-C1
P1-C1
Si1-C27
Si1-C28
Si1C29
C1-C8
C8-C9
It should be noted that the Pd-N(1) bond is also
shorter than the corresponding bond in 15. For 14, this
might imply a stronger back-bonding to the pyridine
ring, too. As a result, the Pd-Me bond is lengthened.
Analogous simultaneous shortening of ligand-palladi-
um bonds was also observed when two (i-Pr-6-R-PyCa)-
MePdCl (R ) Me, C(O)H) complexes were com-
pared.8b
CO In ser tion Rea ction s. The relative extent of
back-bonding from the palladium center to the pyridine
ring should influence the CdO stretching frequencies
of the acetyl derivatives derived from 13, 14, and 15 by
CO insertion. Stronger back-bonding from palladium
to the pyridine moiety must decrease the amount of
back-bonding to the trans-acetyl CdO π*-orbital, result-
ing in a stronger CdO double bond and, therefore,
higher infrared absorption frequencies.
Bond Angles and Torsion Angles
Pd1-P1-C1
Pd1-N1-C8
P1-Pd1-N1
P1-Pd1-C30
C30-Pd1-C11
Cl1-Pd1-N1
C2-P1-C1
110.98(15) C11-C12-N1
123.7(4)
119.2(4)
118.2(3)
-0.2(2)
-174(4)
5.8(5)
-121.6(3)
118.9(3)
-1.5(4)
174.6(2)
178.1(3)
86.3(3)
119.3(3)
79.45(10) N1-C8-C1
C12-N1-C8
95.40(15) N1-Pd1-P1-C1
88.75(15) C2-P1-C1-C8
96.85(10) P1-C1-C8-N1
114.26(19) P1-C1-Si1-C27
P1-C1-C8
111.8(3)
122.9(4)
120.7(5)
119.8(5)
117.7(5)
P1-C1-Si1-C28
P1-C1-Si1-C29
C1-P1-Pd1-C30
C8-N1-Pd1-Cl1
C1-P1-C2-C3
C1-C8-C9
C8-C9-C10
C9-C10-C11
C10-C11-C12
Ta ble 4. Com p a r ison of Bon d Len gth s (Å) a n d
Bon d An gles (d eg) for 14 a n d 158b (Esd in
P a r en th eses)
In order to verify these assumptions, we performed
preliminary experiments to test the activity of 13 and
14 toward CO insertion by bubbling CO under atmo-
spheric pressure through a deuterochloroform solution
of the complex in a NMR tube at room temperature. The
progress of the reaction was monitored by 31P NMR
spectroscopy, showing the appearence of a new signal
1
at δ(31P) ) 244 and δ(31P) ) 292, respectively. The H
NMR spectrum showed a characteristic downfield shift
of the methyl-palladium signal to the region of acetyl-
palladium compounds,8b,17,18 indicating the formation of
the CO insertion products 16 and 17 (Scheme 5). For
16 and 17, a singlet was found at δ(1H, CDCl3) ) 2.56
and 2.54, respectively. Although formation of some
palladium black was observed during the formation of
these acetyl complexes, the complexes were stable at
room temperature: a solution of 16 or 17 stored in
CDCl3 in the NMR tube for 1 week showed no change
114.26(19)°, which is large compared to the analogous
angle in [1,2-(diphosphaalkenyl)benzene]PdCl (111.3-
(5)°)1d but relatively small compared to that of (1,2-
diphosphinidenecyclobutene)PdCl2 (116.0(6)°)3d (Figure
2, Table 3).
Comparison of the bond lengths and bond angles of
14 with those of (i-Pr-6-Me-PyCa)MePdCl (15)8b is of
interest (Table 4). The bonds of (Z)-9 to the palladium
nucleus are relatively strong. Compared to 15, the Pd-
N(1) bond is relatively short (∆d ) -0.096(6) Å) and
the Pd-Me and Pd-Cl bonds are relatively long (∆d )
+0.019(10) and +0.048(2) Å, respectively). Comparison
of the length of the P-Pd bond (d ) 2.1744(14) Å) is
not possible, as comparable complexes are not known.
However, in the case of (1,2-diphosphinidenecyclobutene)-
PdCl2,3d longer P-Pd bond lengths of 2.235(4) and
2.242(4) Å were found, which is probably due to the
larger bite angle of this ligand. The bite angle (P-Pd-
N(1)) of (Z)-9 in 14 is 79.45(10)°, which is only slightly
larger (∆ ) +1.0(2)°) than that of 15 (N-Pd-N(1); 78.4-
(2)°, Table 4).8b
1
in the H NMR spectra.
The rate of the CO insertion reaction was not mea-
sured quantitatively, but the formation of 16 was
finished within 1 h, while the formation of 17 was
slower; only 10% conversion was observed after 2 h.
These conversions are relatively slow compared to those
of the comparable (R-PyCa)MePdCl complexes. The
latter usually show 50% conversion to the acetyl deriva-
tives within 4-30 min.8b
The insertion of carbon monoxide was confirmed by
IR spectroscopy (KBr pellets). The insertion of CO in
13 and 14 led to the appearence of a carbonyl absorption
at ν(CO) ) 1711 and 1701 cm-1 for complexes 16 and
17, respectively. These values are relatively large
compared to those for (i-Pr-6-R-PyCa)AcPdCl (18, ν-
(CO) ) 1692-1697 cm-1) and (bipy)AcPdCl (19, ν(CO)
) 1690 cm-1).8b
Although the discussion of the trans-influence exclu-
sively in terms of π-back-bonding is controversial,19 it
does explain our observations. The longer Pd-Cl bond
In the series 19, 18, 16, and 17, changing the ortho-
substituent at pyridine increases the CdO stretching
(19) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.

1150 Organometallics, Vol. 16, No. 6, 1997
van der Sluis et al.
crystals (yield: 2.24 g, 6.08 mmol, 65%); mp 132-134 °C (lit.:
frequency in the order pyridine < imine < phosphaal-
kene. The frequencies of 16 and 17 fall in the range of
those for normal carbonyl compounds (aldehydes, ν(CO)
) 1725-1705 cm-1). The lower absorption frequency
of 19 falls in the characteristic absorption range of the
strongly conjugated amides (ν(CO) ) 1650-1690 cm-1).
These observations agree with an increase in palladium
to trans-pyridine back-bonding in the order: 19 < 18 <
17 < 16. Thus, a direct correlation between the degree
of back-bonding of palladium to the pyridine moiety and
the CO stretching frequency of the trans-acetyl group
seems indicated.
Although the increase of Pddπ-N(Py)pπ* back-bond-
ing might not be the only explanation for the observed
correlation, the correlation between the LUMO energy
of the pyridine, imine, and phosphaalkene moiety and
the CO stretching frequency of the adjacent acetyl group
still holds. Perhaps the observed trend is better de-
scribed by the controversial “cis-influence”19 of the
pyridine, imine, and phosphaalkene moiety: stronger
back-bonding to this ligand results in weaker back-
bonding of palladium to the cis-acetyl group, leading to
stronger CdO bonds. Nevertheless, a more detailed
theoretical analysis will be necessary to fully under-
stand the factors involved.
1a
142-144 °C). 1H NMR (CDCl3): δ 1.27 (s, 9H, p-t-Bu), 1.44
(s, 18H, o-t-Bu), 7.00 (m, 1H, PyH), 7.25 (m, 1H, PyH), 7.36
(d, 2H, 4J (HP) ) 1.2 Hz, ArH), 7.48 (m, 1H, PyH), 8.01 (d, 1H,
2J (HP) ) 25.4 Hz, PdCH), 8.50 (d, 1H, J (HH) ) 3.9 Hz, PyH).
13C{1H}NMR (CDCl3): δ 31.3 (s, p-C(CH3)3), 33.8 (d, 4J (CP) )
7.2 Hz, o-C(CH3)3), 34.8 (s, p-C(CH3)3), 38.1 (s, o-C(CH3)3), 120.9
(d, J (CP) ) 17.7 Hz, Py), 121.7 (s, m-Ar), 121.9 (d, J (CP) )
6.9 Hz, Py), 136.4 (d, J (CP) ) 2.31 Hz, Py), 138.8 (d, 1J (CP) )
53.9 Hz, ipso-Ar), 149.8 (d, 2J (CP) ) 4.8 Hz, o-Ar), 153.9 (s,
1
p-Ar), 157.8 (d, J (CP) ) 13.5 Hz, Py), 173.9 (d, J (CP) ) 34.0
Hz, PdC). 31P NMR (CDCl3): δ 285. MS (70 eV): m/ z (1,
M+), 310 (100, M+ - t-Bu). HRMS: calcd. for C24H34PN,
367.2429; found, 367.2428. Anal. Calcd for C24H34PN: C,
78.43; H, 9.33; P, 8.43. Found: C, 78.15; H, 9.47; P, 8.28.
(E)-(Tr im eth ylsta n n ylm eth ylen e)(2,4,6-tr i-ter t-bu tyl-
p h en yl)p h osp h in e (3). At room temperature, THF (5 mL)
was added to a mixture of (E)-1 (0.18 g, 0.5 mmol), chlorotri-
methylstannane (0.12 g, 0.6 mmol), and magnesium (0.024 g,
1.00 mmol). The reaction mixture was stirred for 1 h. The
solvent was evaporated, and the residue was extracted with
pentane. Evaporation of the pentane furnished (E)-3 as a
yellowish oil, which was used without further purification
(yield: 0.19 g, 0.44 mmol, 87%). 1H NMR (CDCl3): δ 0.29 (s,
9H, SnMe3), 1.38 (s, 9H, p-t-Bu), 1.56 (s, 18H, o-t-Bu), 7.42 (s,
2
2H, ArH), 8.32 (d, 1H, J (HP) ) 26.2 Hz, PdCH). 31P NMR
(CDCl3): δ 323. Spectra were identical with those reported.20
(Z)-((2-P yr idyl)(tr im eth ylsilyl)m eth ylen e)(2,4,6-tr i-ter t-
bu tylp h en yl)p h osp h in e (9). From (E)-7: At room temper-
ature, a solution of (E)-7 (4 mmol) in THF (10 mL) was added
to a suspension of 2-bromopyridine (0.63 g, 4 mmol), bis-
(benzonitrile)palladium dichloride (0.076 g, 0.20 mmol), and
1,4-bis(diphenylphosphino)butane (0.085 g, 0.20 mmol) in THF
(5 mL). The suspension was heated under reflux for 6 h,
furnishing an orange solution. The solvent was evaporated
under reduced pressure, and the residue was dissolved in
dichloromethane. Silica was added, and the dichloromethane
was evaporated. The residue was added on top of a small silica
column. The column was flushed with dichloromethane.
Evaporation of the dichloromethane and crystallization of the
residue from hot acetonitrile furnished yellowish crystals
(yield: 0.98 g, 2.24 mmol, 56%). The spectral data were
identical with those of 9 prepared as described below.
Exp er im en ta l Section
All experiments were performed in oven-dried glassware
and under nitrogen. Solvents were distilled from sodium
benzophenone (THF), lithium aluminum hydride (pentane,
diethyl ether), or calcium chloride (dichloromethane). All solid
starting materials were dried in vacuo. Liquids were distilled
under N2 prior to use. NMR spectra were recorded with a
Bruker AC 200 and Bruker MSL 400 spectrometer (1H, 13C)
or with a Bruker WM 250 spectrometer (31P). Tetramethyl-
silane (1H, 13C) or 85% H3PO4 (31P) was used as an external
standard. Mass spectra were recorded with a Finnigan MAT
90 spectrometer; accurate masses were determined by peak
matching at a mass resolution of approximately 10 000. Infra-
red spectra were measured by using KBr pellets with a Matte-
son Galaxy 6030 FTIR. Elemental analyses were performed
by Microanalytisches Labor Pascher, Remagen, Germany.
Compounds (E)-1,7c (Z)-5,7b,c (E)-7,7b 2-pyridylmagnesium bro-
mide,10 2-(trimethylstannyl)pyridine,11 and MePdCl(COD)8a
were prepared according to literature procedures.
(E)-((2-P yr id yl)m eth ylen e)(2,4,6-tr i-ter t-bu tylp h en yl)-
p h osp h in e (2). This compound was prepared according to
the procedure of Geoffroy et al.,1a but with a slight adjust-
ment: performing the Peterson olefination at -65 °C and
addition of trimethylsilyl chloride at room temperature re-
sulted in higher yields and one stereoisomer only. A solution
of n-butyllithium in hexane (5.86 mL, 1.6 M, 9.36 mmol) was
added to a solution of Mes*PH2 (2.61 g, 9.36 mmol) in THF
(100 mL) at -65 °C, furnishing a yellow/orange precipitate.
Afterward, the reaction mixture was warmed to room tem-
perature, furnishing a dark red solution. After the solution
was stirred for 15 min at ambient temperature, dimethyl(tert-
butyl)silyl chloride (1.41 g, 9.36 mmol) was added all at once.
After the solution was stirred again for 15 min, n-butyllithium
in hexane (5.86 mL, 1.6 M, 9.36 mmol) was added to the
solution at room temperature. After 15 min of stirring at room
temperature, the reaction mixture was cooled to -65 °C and
2-pyridinecarboxaldehyde (1.00 g, 9.36 mmol) was added.
After the reaction mixture was warmed to room temperature,
trimethylsilyl chloride (1.02 g, 9.36 mmol) was added, furnish-
ing a yellow/orange solution. The solvent was evaporated, the
residue was extracted with pentane, and the extract was
filtered. After evaporation of the pentane from the filtrate,
the residue was crystallized from acetonitrile, funishing yellow
From (Z)-8: Compound (Z)-5 (0.88 g, 2 mmol) was mixed
with sublimed magnesium (0.096 g, 4 mmol) and dibromoeth-
ane (0.05 mL, 0.11 g, 0.59 mmol). The exothermic reaction
was started by the slow addition of THF (20 mL). The orange
solution was stirred overnight and was added to a THF (10
mL) solution of 2-bromopyridine (0.32 g, 2.0 mmol), bis-
(benzonitrile)palladium dichloride (5 mol %, 0.038 g, 0.100
mmol), and 1,4-bis(diphenylphosphino)butane (0.043 g, 0.100
mmol). The mixture was heated under reflux for 6 h. The
product was isolated as described above furnishing 9 (yield:
0.48 g, 1.1 mmol, 53%); mp 160-161 °C. 1H NMR (CDCl3): δ
-0.30 (s, 9H, SiMe3), 1.39 (s, 9H, p-t-Bu), 1.64 (s, 18H, o-t-
Bu), 7.17 (m, 1H, PyH), 7.44 (m, 1H, PyH), 7.45 (s, 2H, ArH),
7.70 (m, 1H, PyH), 8.55 (d, 1H, J (HH) ) 3.8 Hz, PyH).
13C{1H}NMR (CDCl3): δ -0.9 (s, Si(CH3)3), 31.2 (s, p-C(CH3)3),
4
33.5 (d, J (CP) ) 7.7 Hz, o-C(CH3)3), 34.9 (s, p-C(CH3)3), 38.2
(s, o-C(CH3)3), 120.5 (s, Py), 121.7 (s, m-Ar), 121.9 (s, Py), 135.7
(s, Py), 138.5 (d, 1J (CP) ) 56.6 Hz, ipso-Ar), 148.6 (s, o-Ar),
150.5 (s, p-Ar), 153.9 (s, Py), 165.5 (d, 1J (CP) ) 31.5 Hz, PdC).
31P NMR (CDCl3): δ 333. MS (70 eV): m/ z (1, M+), 382 (100,
M+ - t-Bu). HRMS: Calcd for C27H42PN28Si, 439.2824; found,
439.2818. Anal. Calcd for C27H42PNSi: C, 73.75; H, 9.63; N,
3.18. Found: C, 71.79; H, 9.76; N, 3.08.
η1,η1-[(E)-((2-P yr id yl)m et h ylen e)(2,4,6-t r i-ter t-b u t yl-
p h en yl)p h osp h in e]p a lla d iu m Dich lor id e (11). A mixture
of (E)-2 (0.37 g, 1.00 mmol) and bis(benzonitrile)palladium
dichloride (0.37 g, 1.00 mmol) was dissolved in dichlo-
(20) Goede, S. J .; Bickelhaupt, F. Chem. Ber. 1991, 124, 2677.

Synthesis of Novel 2-(2-Pyridyl)phosphaalkenes
Organometallics, Vol. 16, No. 6, 1997 1151
romethane (4 mL) at room temperature. The mixture was
stirred for 15 min at ambient temperature. The product was
precipitated by adding pentane (40 mL). The solvent was
removed and the residue dried in vacuo furnishing a micro-
crystalline orange solid, which was crystallized from chloro-
form furnishing orange needles (yield: 0.45 g, 0.83 mmol, 83%);
mp 175-180 °C (dec). 1H NMR (CDCl3): δ 1.33 (s, 9H, p-t-
Bu), 1.70 (d, 18H, 5J (HP) ) 1.75 Hz, o-t-Bu), 7.34 (m, 1H, PyH),
7.35 (d, 1H, J (HP) ) 22.7 Hz, PdCH), 7.56 (d, 2H, J (HP) )
7.56 Hz, ArH), 7.62 (m, 1H, PyH), 7.85 (m, 1H, PyH), 9.86 (d,
1H, J (HH) ) 5.9 Hz, PyH). 13C{1H}NMR (CDCl3): δ 30.9 (s,
p-C(CH3)3), 35.0 (s, o-C(CH3)3), 35.4 (d, 5J (CP) ) 1.0 Hz,
p-C(CH3)3), 39.3 (d, 3J (CP) ) 1.8 Hz, o-C(CH3)3), 117.5 (d,
1J (CP) ) 17.6 Hz, ipso-Ar), 122.8 (d, J (CP) ) 38.5 Hz, Py),
122.9 (s, Py), 124.0 (d, 3J (CP) ) 10.7 Hz, m-Ar), 140.2 (d, J (CP)
) 4.1 Hz, Py), 150.5 (d, 1J (CP) ) 54.3 Hz, PdC), 154.4 (d, J (CP)
) 5.2 Hz, Py), 156.0 (d, 4J (CP) ) 3.3 Hz, p-Ar), 157.3 (d, 2J (CP)
) 3.3 Hz, o-Ar), 159.1 (d, J (CP) ) 6.7 Hz, Py). 31P NMR
(CDCl3): δ 247. Anal. Calcd for C24H34PNPdCl2: C, 52.91;
H, 6.29; Pd, 19.5. Found: C, 49.90; H, 6.08; Pd, 19.5.
138.7 (d, J (CP) ) 3.3 Hz, Py), 151.2 (d, J (CP) ) 4.1 Hz, Py),
4
1
154.2 (d, J (CP) ) 2.7 Hz, p-Ar), 155.8 (d, J (CP) ) 51.7 Hz,
PdC), 156.7 (d, 2J (CP) ) 2.3 Hz, o-Ar), 157.2 (d, J (CP) )
4.0 Hz, Py). 31P NMR (CDCl3): δ 253. Anal. Calcd for
C
25H37ClNPPd: C, 57.26; H, 7.12; Cl, 6.76; Pd, 20.29. Found:
C, 57.51; H, 7.06; Cl, 6.83; Pd, 19.9.
η1,η1-[(Z)-((2-P yr id yl)(tr im eth ylsilyl)m eth ylen e)(2,4,6-
tr i-ter t-bu tylp h en yl)p h osp h in e]m eth ylp a lla d iu m Ch lo-
r id e (14). Dichloromethane (5 mL) was added to a mixture
of 9 (0.21 g, 0.5 mmol) and MePdCl(COD) (0.13 g, 0.5 mmol)
at room temperature. The orange/yellow solution was stirred
for 10 min. The solvent was evaporated under reduced
pressure, and the yellow solid residue was washed twice with
pentane (5 mL). The solid was dried in vacuo furnishing a
yellow-orange, powder which was crystallized from ether
(yield: 0.25 g, 0.42 mmol, 83%); mp 195-198 °C (dec). 1H
NMR (CDCl3): δ 0.00 (s, 9H, SiMe3), 1.11 (d, 3H, 3J (HP) )
3.45 Hz, Me-Pd), 1.40 (s, 9H, p-t-Bu), 1.70 (s, 18H, o-t-Bu),
2
4
4
7.44 (m, 1H, PyH), 7.56 (m, 1H, PyH), 7.64 (d, 2H, J (HP) )
3.56 Hz, ArH), 7.84 (m, 1H, PyH), 9.62 (m, 1H, PyH). 13C-
3
{1H} NMR (CDCl3): δ 0.1 (d, J (CP) ) 3.0 Hz, SiMe3), 3.2 (d,
η1,η1-[(Z)-((2-P yr id yl)(tr im eth ylsilyl)m eth ylen e)(2,4,6-
tr i-ter t-bu tylph en yl)ph osph in e]palladiu m Dich lor ide (12).
A mixture of 9 (0.44 g, 1.00 mmol) and bis(benzonitrile)-
palladium dichloride (0.37 g, 1.00 mmol) was dissolved in
dichloromethane (4 mL) at room temperature. The mixture
was stirred for 15 min at ambient temperature. The product
was precipitated from the solution by adding pentane (40 mL).
The solvent was removed and the residue dried in vacuo
furnishing a microcrystalline yellow solid (yield: 0.56 g, 0.91
mmol, 91%); mp 230-231 °C. 1H NMR (CDCl3): δ -0.00 (s,
9H, SiMe3), 1.37 (s, 9H, p-t-Bu), 1.77 (d, 5J (HP) ) 1.6 Hz, 18H,
o-t-Bu), 7.3 (m, 1H, PyH), 7.61 (d, 4J (HP) ) 4.5 Hz, 2H, ArH),
7.9 (m, 1H, PyH), 10.11 (d, 1J (HH) ) 6.0 Hz, 1H, PyH).
2J (CP) ) 4.6 Hz, Me-Pd), 31.0 (s, p-C(CH3)3), 34.9 (s, o-C-
(CH3)3), 35.3 (s, p-C(CH3)3), 39.8 (d, o-C(CH3)3), 122.2 (d, J (CP)
) 25.1 Hz, Py), 122.7 (d, J (CP) ) 7.3 Hz, Py), 122.9 (d, 1J (CP)
3
) 7.1 Hz, ipso-Ar), 124.9 (d, J (CP) ) 8.7 Hz, m-Ar), 138.1 (d,
J (CP) ) 1.9 Hz, Py), 151.6 (d, J (CP) ) 2.3 Hz, Py), 154.6 (d,
4J (CP) ) 2.5 Hz, p-Ar), 155.6 (d, 2J (CP) ) 2.6 Hz, o-Ar), 160.7
1
(d, J (CP) ) 3.4 Hz, Py), 163.8 (d, J (CP) ) 25.0 Hz, PdC). 31P
NMR (CDCl3): δ 295. Anal. Calcd for C28H45ClNPPdSi: C,
56.37; H, 7.61; Cl, 5.94; Pd, 17.8. Found: C, 56.37; H, 7.60;
Cl, 6.27; Pd, 17.4.
Gen er a l P r oced u r e for th e P r ep a r a tion of 16 a n d 17.
Through a NMR tube containing complex 13 or 14 in CDCl3,
respectively, was bubbled carbon monoxide gas at room
temperature under atmospheric pressure, during which time
the color changed from yellow to orange/red. The formation
of 16 was complete within 1 h. The formation of 17 had
proceeded only halfway after approximately 1 day of reaction.
The insertion of CO was monitored by 31P and 1H NMR
spectroscopies and by IR spectroscopy.
4
13C{1H} NMR (CDCl3): δ 0.55 (d, J (HP) ) 1.4 Hz, Si(CH)3),
30.8 (s, p-C(CH3)3), 35.6 (s, o-C(CH3)3), 35.9 (d, p-C(CH3)3), 40.0
(d, 3J (CP) ) 1.5 Hz, o-C(CH3)3), 118.8 (d, 1J (CP) ) 20.0 Hz,
ipso-Ar), 122.8 (d, J (CP) ) 8.1 Hz, Py), 123.4 (d, J (CP) ) 31.4
3
Hz, Py), 125.0 (d, J (CP) ) 10.6 Hz, m-Ar), 139.6 (d, J (CP) )
4
3.2 Hz, Py), 155.2 (d, J (CP) ) 4.2 Hz, Py), 156.0 (d, J (CP) )
3.1 Hz, p-Ar), 156.2 (d, 2J (CP) ) 3.4 Hz, o-Ar), 160.9 (d, 1J (CP)
) 26.0 Hz, PdC), 163.2 (d, J (CP) ) 3.6 Hz, Py). 31P NMR
(CDCl3): δ 283. Anal. Calcd for C27H42Cl2PPdNSi: C, 52.56;
H, 6.87; N, 2.27; Pd, 17.24. Found: C, 51.22; H, 6.83; N, 2.65;
Pd, 18.1.
η1,η1-[(E)-((2-P yr id yl)m et h ylen e)(2,4,6-t r i-ter t-b u t yl-
p h en yl)p h osp h in e]a cetylp a lla d iu m Ch lor id e (16). 1H
NMR (CDCl3): δ 1.28 (s, 9H, p-t-Bu), 1.59 (s, 18H, o-t-Bu),
2.56 (s, 3H, Ac-Pd) 7.05 (m, 1H, PyH), 7.26 (m, 1H, PyH),
η1,η1-[(E)-((2-P yr id yl)m et h ylen e)(2,4,6-t r i-ter t-b u t yl-
p h en yl)p h osp h in e]m eth ylp a lla d iu m Ch lor id e (13). From
11: At -65 °C, a solution of methylmagnesium chloride (3 M,
0.5 mL, 1.5 mmol) was added to a yellow suspension of 11 (0.82
g, 1.5 mmol) in THF (15 mL). An orange solution was formed
immediately. After the mixture was warmed to room tem-
perature, the solvent was evaporated and the solid residue was
washed thoroughly with ether (20 mL), resulting in an orange/
yellow powder, which was contaminated with magnesium salts
(yield: 0.63 g). The spectral data were identical with those of
13 prepared as described below.
4
7.47 (d, 2H, J (HP) ) 3.19 Hz, ArH), 7.63 (m, 1H, PyH), 7.63
2
(d, 1H, J (HP) ) 23.8 Hz, PdCH), 9.25 (d, 1H, J (HH) ) 4.28
Hz, PyH). 31P NMR (CDCl3): δ 244. IR (KBr): ν(CO) 1711
cm-1
.
η1,η1-[(Z)-((2-P yr id yl)(tr im eth ylsilyl)m eth ylen e)(2,4,6-
tr i-ter t-bu tylp h en yl)p h osp h in e]a cetylp a lla d iu m Ch lo-
r id e (17). 1H NMR (CDCl3): δ 0.09 (s, 9H, SiMe3), 1.32 (s,
5
9H, p-t-Bu), 1.68 (d, 18H, J (HP) ) 1.25 Hz, o-t-Bu), 2.54 (s,
3H, Ac-Pd) 7.39 (m, 1H, PyH), 7.51 (d, 2H, ArH), 7.56 (m,
1H, PyH), 7.75 (m, 1H, PyH), 9.38 (d, 1H, J (HH) ) 5.41 Hz,
PyH). 31P NMR (CDCl3): δ 292. IR (KBr): ν(CO) 1701 cm-1
.
From 2 and MePdCl(COD): Dichloromethane (5 mL) was
added to a mixture of 2 (0.18 g, 0.5 mmol) and MePdCl(COD)
(0.13 g, 0.5 mmol) at room temperature. The orange/yellow
solution was stirred for 10 min. The solvent was evaporated
under reduced pressure, and the yellow solid residue was
washed twice with a mixture of ether and pentane (50/50, 5
mL). Drying the solid in vacuo furnished a yellow powder
(yield: 0.24 g, 0.45 mmol, 90%); mp 195-197 °C (dec). 1H
X-r a y Str u ctu r e Deter m in a tion of (E)-2 a n d 14. Crys-
tals of (E)-2 (yellow) and 14 (orange) suitable for X-ray
diffraction were glued to the tip of a Lindemann-glass capillary
and transferred into the cold nitrogen stream of an Enraf-
Nonius CAD4-Turbo diffractometer on a rotating anode. Ac-
curate unit cell parameters and an orientation matrix were
determined by least-squares fitting of the setting angles of 25
well-centered reflections (SET421), in the range 10.34° < θ <
13.93° and 11.69° < θ < 13.92° for (E)-2 and 14, respectively.
Reduced-cell calculations did not indicate higher lattice sym-
metry.22 Crystal data and details on data collection and
refinement are given in Table 1. Data were collected at 150
K in ω scan mode using graphite-monochromated Mo KR
3
NMR (CDCl3): δ 1.14 (d, 3H, J (HP) ) 3.99 Hz, Me-Pd) 1.33
(s, 9H, p-t-Bu), 1.60 (s, 18H, o-t-Bu), 7.15 (m, 1H, PyH), 7.31
4
(m, 1H, PyH), 7.54 (d, 2H, J (HP) ) 3.44 Hz, ArH), 7.67 (m,
1H, PyH), 7.69 (d, 1H, 2J (HP) ) 21.7 Hz, PdCH), 9.37 (d, 1H,
J (HH) ) 5.09 Hz, PyH). 13C{1H} NMR (CDCl3): δ -0.5 (d,
4
2J (CP) ) 2.6 Hz, Me-Pd), 31.0 (s, p-C(CH3)3), 34.1 (d, J (CP)
) 1.7 Hz, o-C(CH3)3), 35.4 (d, p-C(CH3)3), 39.0 (d, 3J (CP) )
1.4 Hz, o-C(CH3)3), 121.0 (d, J (CP) ) 24.1 Hz, Py), 121.9 (d,
1J (CP) ) 6.7 Hz, ipso-Ar), 123.1 (d, 3J (CP) ) 8.6 Hz, m-Ar),
(21) Boer, J . L. de; Duisenberg, A. J . M. Acta Crystallogr. 1984, A40,
C410.
(22) Spek, A. L.; J . Appl. Crystallogr. 1988, 21, 578.

1152 Organometallics, Vol. 16, No. 6, 1997
van der Sluis et al.
radiation (λ ) 0.710 73 Å). Data were corrected for Lp effects
and for the observed linear instability of the reference reflec-
tions, but not for absorption. The structure of (E)-2 was solved
by automated direct methods (SHELXs 8623). The structure
of 14 was solved by automated Patterson methods and
subsequent differnce Fourier techniques (DIRDIF-9224). Both
compounds were refined on F2′′ by full-matrix least-squares
techniques (SHELXL-9325); no observance criterion was ap-
plied during refinement. Hydrogen atoms were included in
the refinement on calculated positions riding on their carrier
atoms. The methyl groups of both compounds were refined
as rigid groups, allowing for rotation around the C-C, Pd-C,
or Si-C bonds. The pyridine ring of (E)-2 was included in the
refinement in two positions, related by a 180° rotation over
C(1)-C(8). Although all positional parameters of (E)-2 were
freely refined, the anisotropic displacement parameters of the
N,C couples located at approximately the same position were
equated. All non-hydrogen atoms were refined with anisotro-
pic thermal parameters. The hydrogen atoms were refined
with a fixed isotropic thermal parameter related to the value
of the equivalent isotropic displacement parameter of their
carrier atoms by a factor amounting to 1.5 for the methyl
hydrogen atoms and 1.2 for the other hydrogen atoms.
Neutral-atom scattering factors and anomalous dispersion
corrections were taken from the International Tables for
Crystallography.26 Geometrical calculations and illustrations
were performed with PLATON;27 all calculations were per-
formed on a DECstation 5000 cluster.
Ack n ow led gm en t. This work was supported in part
(N.V., A.L.S.) by the Netherlands Foundation of Chemi-
cal Research (SON) with financial aid from the Neth-
erlands Organization for Scientific Research (NWO).
The authors thank Dr. F. J . J . de Kanter for his efforts
in performing the NMR measurements and Dr. B. L.
M. van Baar for the HRMS measurements. Drs. A.
Egberts (ARCBV, representing Cambridge Isotope Labo-
ratories, Inc.) is gratefully acknowledged for a generous
gift of deuterated solvents.
Su p p or t in g In for m a t ion Ava ila b le: Tables of further
details of the structure determination, including atomic coor-
dinates, bond lengths and angles, and thermal parameters for
(E)-2 and 14 (14 pages). Ordering information is given on any
current masthead page.
(23) Sheldrick, G. M. SHELXS86. Program for crystal structure
determination; University of Go¨ttingen: Germany, 1986.
OM960925G
(24) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garc´ıa-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF program system, Technical report of the Crystallography
Laboratory; University of Nijmegen: The Netherlands, 1992.
(25) Sheldrick, G. M. SHELXL-93. Program for crystal structure
refinement; University of Go¨ttingen: Germany, 1993.
(26) International Tables for Crystallography; Wilson, A. J . C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C.
(27) Spek, A. L. Acta Crystallogr. 1990, A46, C34.