Influence of chelating phosphines on the insertion of isocyanides into palladium-methyl bonds in (P-P)Pd(Me)Cl complexes and their further reaction with olefins and isothiocyanates

Article abstract of DOI:10.1021/om020444z

A systematic study of the insertion reactions between (P-P)Pd(Me)Cl (where P-P = dppe, dppp, dppf) and CNR (where R = 2,6-dimethylphenyl, tert-butyl) is presented. The results have demonstrated that the insertion of CNR into the Pd-Me bond is highly dependent on the nature of the chelating phosphine. For the more strained complex formed with dppe, the insertion of isocyanides is slower and multiple insertion is not observed. This is in contrast to (dppp)Pd(Me)Cl, which reacts readily with isocyanides to produce single-, double-, and multiple-inserted products. Results analogous to those of dppp have been observed for the complexes with dppf, although the reactions are more controllable, indicating a less reactive complex. In an attempt to establish some structure-reactivity correlations, structural characterizations of (dppe)Pd{C(Me)=NXyl}Cl (1) and (dppp)Pd{(C=NXyl)(C(Me)=NXyl)}Cl (3) have been carried out. The structural parameters obtained are consistent with the observed reactivity. The reactions between (dppe)Pd{C(Me)=NXyl}Cl and unsaturated (olefins and isothiocyanates) species have also been studied. While norbornadiene (a strained diolefin) inserts into the palladium-iminoacyl bond, an addition is observed when reacting 1 with isothiocyanates.

Full text of DOI:10.1021/om020444z

Organometallics 2002, 21, 4799-4807
4799
In flu en ce of Ch ela tin g P h osp h in es on th e In ser tion of
Isocya n id es in to P a lla d iu m -Meth yl Bon d s in
(P -P )P d (Me)Cl Com p lexes a n d Th eir F u r th er Rea ction
w ith Olefin s a n d Isoth iocya n a tes
Gareth R. Owen, Ramo´n Vilar,* Andrew J . P. White, and David J . Williams
Department of Chemistry, Imperial College of Science, Technology and Medicine,
London SW7 2AY, U.K.
Received J une 3, 2002
A systematic study of the insertion reactions between (P-P)Pd(Me)Cl (where P-P ) dppe,
dppp, dppf) and CNR (where R ) 2,6-dimethylphenyl, tert-butyl) is presented. The results
have demonstrated that the insertion of CNR into the Pd-Me bond is highly dependent on
the nature of the chelating phosphine. For the more strained complex formed with dppe,
the insertion of isocyanides is slower and multiple insertion is not observed. This is in contrast
to (dppp)Pd(Me)Cl, which reacts readily with isocyanides to produce single-, double-, and
multiple-inserted products. Results analogous to those of dppp have been observed for the
complexes with dppf, although the reactions are more controllable, indicating a less reactive
complex. In an attempt to establish some structure-reactivity correlations, structural
characterizations of (dppe)Pd{C(Me)dNXyl}Cl (1) and (dppp)Pd{(CdNXyl)(C(Me)dNXyl)}-
Cl (3) have been carried out. The structural parameters obtained are consistent with the
observed reactivity. The reactions between (dppe)Pd{C(Me)dNXyl}Cl and unsaturated
(olefins and isothiocyanates) species have also been studied. While norbornadiene (a strained
diolefin) inserts into the palladium-iminoacyl bond, an addition is observed when reacting
1 with isothiocyanates.
In tr od u ction
of isocyanides can be easily modified by changing their
substituent group. This feature allows the fine tuning
of their reactivity and also the properties of the products
formed, making isocyanides versatile starting materials
in organometallic chemistry. Moreover, isocyanides can
multiply insert into metal-carbon bonds, leading to the
synthesis of a wider range of products such as hetero-
cyclic and oligomeric compounds.5
More specifically, the insertion of isocyanides occurs
readily into palladium-carbon bonds.6 The products
obtained from such reactions are highly dependent on
the nature of the ligands coordinated to the palladium
center and the properties of the isocyanide’s R group.
Since the 1970s a large number of studies have been
carried out to understand the nature of this organo-
metallic transformation.7 More recently, there has been
increased interest in using the insertion of isocyanides
The insertion of small molecules such as carbon
monoxide, isocyanides, and alkenes into transition-
metal-carbon bonds is an attractive organometallic
reaction, since it leads to the formation of new C-C
bonds.1 Such insertions are found in a wide range of
catalytic transformations, and hence, there has been
widespread interest in their study. In recent years a
large number of these studies have concentrated on the
insertion of carbon monoxide into metal-carbon2 bonds,
since this process plays a crucial role in the copolym-
erization of this molecule with alkenes.3 Another species
that readily inserts into metal-carbon bonds is isocya-
nide (CNR),4 which is generally regarded as a better σ
donor and weaker π acceptor than CO. In contrast to
carbon monoxide, the electronic and steric properties
(1) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987. (b) Tsuji, J . Pal-
ladium Reagents: Innovations in Organic Synthesis; Wiley: Chiches-
ter, U.K., 1995. (c) Yamamoto, A. Organotransition Metal Chemistry;
Wiley-Interscience: New York, 1986.
(2) (a) Wojcicki, A. A. Adv. Organomet. Chem. 1973, 11, 87. (b)
Kulhman, E. J .; Alexander, J . J . Coord. Chem. Rev. 1980, 33, 195. (c)
Becker, T. M.; Alexander, J . J .; Krause Bauer, J . A.; Nauss, J . L.;
Wireko, F. C. Organometallics 1999, 18, 5594.
(3) (a) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663. (b)
Sen, A. Acc. Chem. Res. 1993, 26, 303. (c) Baar, C. R.; J ennings, M.
C.; Puddephatt, R. J . Organometallics 2001, 20, 3459. (d) Carfagna,
C.; Gatti, G.; Martini, D., Pettinari, C. Organometallics 2001, 20, 2175.
(e) Brookhart, M.; Rix, F. C.; DeSimone, J . M.; Barborak, J . C. J . Am.
Chem. Soc. 1992, 114, 5894. (f) Safir, A. L.; Novak, B. M. J . Am. Chem.
Soc. 1998, 120, 11000. (g) Reddy, K. R.; Chen, C.-L.; Lui, Y.-H.; Peng,
S.-M.; Chen, J .-T.; Lui, S.-T. Organometallics 1999, 18, 2574.
(4) (a) Yamamoto, Y.; Yamazaki, H. Coord. Chem. Rev. 1972, 8, 225.
(b) Yamamoto, Y. Coord. Chem. Rev. 1980, 32, 193. (c) Singleton, E.;
Oosthuizen, H. E. Adv. Organomet. Chem. 1983, 22, 209. Some recent
examples are: (d) Becker, T. M.; Alexander, J . J .; Krause Bauer, J .
A.; Nauss, J . L.; Wireko, F. C. Organometallics 1999, 18, 5594. (e)
Crociani, B.; Sala, M.; Polo, A.; Bombieri, G. Organometallics 1986, 5,
1369.
(5) See for example: (a) Tanase, T.; Ohizumi, T.; Kobayashi, K.;
Yamamoto, Y. Organometallics 1996, 15, 3404. (b) Yamamoto, Y.;
Yamazaki, H. Synthesis 1976, 750. (c) Yamamoto, Y.; Yamazaki, H.
Bull. Chem. Soc. J pn. 1981, 54, 787. (d) Onitsuka, K.; Yanai, K.; Takei,
F.; Takashi, J .; Takahashi, S. Organometallics 1994, 13, 3862.
(6) (a) Maitlis, P. N.; Espinet, P.; Russel, M. J . H. In Comprehensive
Organometallic Chemistry I; Wilkinson, G., Stone, F. G. A., Abel, E.
W., Eds.; Pergamon Press: Oxford, U.K., 1982; Vol. 6, p 284. (b) Dixon,
K. R.; Dixon, A. C. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press:
Oxford, U.K., 1995; Vol. 9, p 208.
10.1021/om020444z CCC: $22.00 © 2002 American Chemical Society
Publication on Web 10/02/2002

4800 Organometallics, Vol. 21, No. 22, 2002
Owen et al.
Sch em e 1
into palladium-carbon bonds as one of several steps for
the synthesis of a wider range of organic materials. For
example, Whitby has recently reported the synthesis of
amidines by palladium-catalyzed couplings of amines,
aryl halides, and isocyanides.8 Also of interest is the
multiple insertion of isocyanides into palladium-carbon
bonds, since this can lead to the formation of a wide
range of products such as helical polyisocyanides and
heterocyclic compounds.9
A potentially attractive organometallic transforma-
tion would be the alternating insertion of isocyanides
and alkenes into palladium-metal bonds to produce
polyimines. Although the analogous reaction with car-
bon monoxide and alkenes (to produce polyketones) is
well documented,3 there are very few examples of
insertion reactions of unsaturated hydrocarbons into
palladium-iminoacyl bonds.10 The relative lack of such
alternated insertion reactions might be a consequence
of the difficulties in controlling the multiple insertion
of isocyanides, which prevents the second species from
reacting.
Herein we present a systematic study of the reactions
between (P-P)Pd(Me)Cl (where P-P ) dppe, dppp,
dppf) and CNR (where R ) 2,6-dimethylphenyl, tert-
butyl). Although the reactivity of these palladium-
methyl complexes has been thoroughly studied before,
surprisingly, there has not been a prior systematic study
on their reactions with isocyanides. The reactions
between the iminoacyl products, obtained upon isocya-
nide insertion, and unsaturated species such as olefins
and isothiocyanates has also been studied, and some
preliminary results are presented.
further changes were observed. To force the conversion
of all the starting material to the mono-insertion product
1, the reaction was repeated, adding 2 equiv of CNXyl.
This resulted in the quantitative conversion of (dppe)-
Pd(Me)Cl into 1 after 2 h. The mono-insertion product
1 was isolated as a yellow solid in 83% yield and fully
1
characterized by H and 31P{1H} NMR and IR spectros-
copy, mass spectrometry, elemental analyses, and X-ray
crystallography (vide infra).
To explore the influence of the phosphine’s bite angle
in the isocyanide insertion (which has proven to be very
important in the insertion of other species into metal-
carbon bonds14), analogous reactions were carried out
using (dppp)Pd(Me)Cl and (dppf)Pd(Me)Cl (both of
which have larger P-Pd-P angles). When 1 equiv of
2,6-dimethylphenyl isocyanide was added to (dppp)Pd-
(Me)Cl in THF, a rapid color change from colorless to
yellow was observed. After 1 h the 31P{1H} NMR
spectrum of the reaction mixture showed the presence
of three species, corresponding to starting material
(15%) and two new pairs of doublets (at δ 7.8 (d), -6.6
(d) ppm and δ 16.0 (d), -4.7 (d) ppm). The two new
products were isolated and characterized as the mono-
insertion product (dppp)Pd{C(dNR)Me}Cl (2) (present
in 25% amount in the reaction mixture) and the double-
insertion product (dppp)Pd{C(dNR)C(dNR)Me}Cl (3)
(present in 60% amount in the reaction mixture).
Interestingly, further studies showed that using CH2-
Cl2 as the solvent in this reaction favored the mono-
insertion product 2 (which was isolated in 67% yield)
in favor of 3. To favor the formation of the bis-insertion
product 3, 2 equiv of CNXyl was added to a solution of
(dppp)Pd(Me)Cl in THF (see Scheme 2). In contrast to
the behavior observed for (dppe)Pd(Me)Cl, this reaction
led to the quantitative formation of the bis-insertion
product 3. Both 2 and 3 were fully characterized on the
basis of NMR and IR spectroscopy, FAB(+) mass
spectrometry, and elemental analysis (see Table 1). 3
was also characterized by X-ray crystallography (vide
infra).
Resu lts a n d Discu ssion
In ser tion of 2,6-Dim eth ylp h en yl Isocya n id e in to
P a lla d iu m -Meth yl Bon d s. When 1 equiv of 2,6-
dimethylphenyl isocyanide was added to a solution of
(dppe)Pd(Me)Cl in THF at room temperature, a gradual
color change from colorless to yellow was observed. The
reaction was monitored by 31P{1H} NMR spectroscopy,
which showed, after 1 h, the conversion of approxi-
mately 10% of the starting material (δ 59.3 (d), 30.2 (d)
ppm) to a new product (δ 39.1 (d), 27.3 (d) ppm); this
later proved to be the mono-insertion compound (dppe)-
Pd{C(dNXyl)Me}Cl (1) (see Scheme 1). The reaction
mixture was monitored over a period of 24 h, and no
(7) (a) Yamamoto, Y.; Yamazaki, H. Bull. Chem. Soc. J pn. 1970,
43, 2653. (b) Yamamoto, Y.; Yamazaki, H. Bull. Chem. Soc. J pn. 1970,
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44, 1873. (d) Yamamoto, Y.; Yamazaki, H. Inorg. Chem. 1975, 13, 438.
Some recent examples are: (e) Deis, G. P.; Aubel, P. G.; Vrieze, K.;
Leeuwen, P. W. N. M. Organometallics 1997, 16, 2948. (f) Kim, Y.-J .;
Song, S.-W.; Lee, S.-C.; Lee, S.-W.; Osakada, K.; Yamamoto, T. J .
Chem. Soc., Dalton Trans. 1998, 1775. (g) Crociani, B.; Bandoli, G.;
Clemente, D. A. J . Organomet. Chem. 1980, 184, 269. (h) Crociani, B.;
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Crociani, B.; Granozzi, G. Inorg. Chim. Acta 1987, 132, 197. (j) Crociani,
B.; Nicolini, M.; Richards, R. L. J . Chem. Soc., Dalton Trans. 1978,
1479. (k) Vicente, J .; Abad, J .-A.; Frankland, A. D.; Lo´pez-Serrano, J .;
Ram´ırez de Arellano, M. C.; J ones, P. G. Organometallics 2002, 21,
272.
In the case of (dppf)Pd(Me)Cl, reaction with 1 equiv
of CNXyl led to the formation of (dppf)Pd{(CdNXyl)-
Me}Cl (5) in high yields (as monitored by 31P NMR
(11) Drew, D.; Doyle, J . R. Inorg. Synth. 1972, 13, 52.
(8) Saluste, C. G.; Whitby, R. J .; Furber, M. Angew. Chem., Int. Ed.
2000, 39, 4156.
(9) Takei, F.; Yanai, K.; Onitsuka, K.; Takahashi, S. Chem. Eur. J .
2000, 6, 983
(10) (a) Delies, J . G. P.; Aubel, P. G.; Vrieze, K.; van Leeuwen, P.
W. N. M.; Veldman, N.; Spek, A. L.; van Neer, F. J . R. Organometallics
1997, 16, 2948. (b) Onitsuka, K.; Segawa, M.; Takahashi, S. Organo-
metallics 1998, 17, 4335.
(12) (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)
Ladipo, F. T., Anderson, G. K.; Organometallics 1994, 13, 303.
(13) (a) Appleton, T. G.; Bennett, M. A.; Tomkins, I. B. J . Chem.
Soc., Dalton Trans. 1976, 439. (b) Dekker, G. P. C. M.; Elsevier, C. J .,
Vrieze, K. Organometallics 1992, 11, 1589.
(14) van Leeuwen, P. W. N. M.; Kamer, P. C. J .; Reek, J . N. H.;
Dierkes, P. Chem. Rev. 2000, 100, 2741 and references therein.

Insertion of Isocyanides into Pd-Me Bonds
Organometallics, Vol. 21, No. 22, 2002 4801
demonstrated by 31P NMR studies, which revealed the
presence of free phosphine as the unique product).
Despite this, compound 6 was isolated and characterized
on the basis of NMR and IR spectroscopy, mass spec-
trometry, and elemental analyses.
Sch em e 2
From Table 1 it can be seen that, upon insertion of
CNXyl into the Pd-Me bond, the phosphorus reso-
nances of (P-P)Pd(Me)Cl (P-P ) dppe, dppp, dppf) shift
to lower frequencies. Such shifts are less pronounced
for the phosphorus trans to the R group, which is
consistent with the results obtained previously by van
Leeuwen in analogous carbonylation reactions.15 The
2J (P-P) coupling constant increases on going from (P-
P)Pd(Me)Cl to the corresponding insertion products (see
Table 1), which again follows the same trend observed
previously in the analogous carbonylation reactions. The
1
insertion products were also characterized by H NMR
spectroscopy, which showed, in the case of the mono-
insertion compounds, a measurable H-P coupling be-
tween the protons of the iminoacyl’s methyl and the cis
and trans phosphorus atoms of the phosphine (resulting
in doublets of doublets with 4J (Pa-H) and 4J (Pb-H)
ranging from 3.5 to 5.0 Hz and from 1.0 to 1.5 Hz,
respectively).
The results so far presented suggest that the chelating
phosphines in (P-P)Pd(Me)Cl play a very important
role in determining the nature of the insertion products.
The results indicate that (dppp)Pd(Me)Cl and (dppf)-
Pd(Me)Cl are much more reactive toward insertion of
CNXyl than is (dppe)Pd(Me)Cl. A similar trend has been
previously observed for the insertion of other species
(such as CO) into these palladium-methyl complexes.
Theoretical16 and experimental17 studies have suggested
that the bite angle, relative flexibility, and electronic
properties of the phosphines determine the reactivity
of the complexes toward the insertion of various sub-
strates (e.g. CO and CNR). To obtain a structural insight
into the reactivity differences of the complexes under
study toward isocyanides, it was of interest to obtain
the crystal structures of the mono- and bis-insertion
products 1 and 3. Since in these compounds the R
groups around the phosphorus of dppe and dppp are the
same, the geometrical parameters are likely to play a
more important role than the electronic effectsshence
the interest in getting structural insight into these
specific products.
Crystals of 1 suitable for an X-ray crystallographic
study were grown by vapor diffusion of petroleum ether
(40-60 °C) into a THF solution of the complex. The
geometry at palladium is square planar (Figure 1),
though the metal and its four coordinated atoms are
planar to within only 0.07 Å, the deviation from planar-
ity being a consequence of a ca. 5° twist of the Pd-P(1)-
P(2) plane with respect to that formed by Pd-C(1)-Cl.
The cis angles range between 85.25(4) and 94.19(4)°, the
most acute being associated with the bite of the chelat-
Ta ble 1. Selected NMR Va lu es for Sta r tin g
Ma ter ia ls a n d In ser tion P r od u ctsa
1H NMR (Pd-CH3 or
Pd-C(dNR)n-CH3
31P{1H}
NMR δ
compd
δ [J (Pa-H), J (Pb-H)]
2J (P-P)
(dppe)Pd(Me)Clb
0.64 (dd) [3,8]
0.62 (dd) [4, 8]
0.79 (dd) [4, 8]
1.68 (dd) [1, 5]
1.61 (dd) [ur,d 4]
1.65 (dd) [2, 5]
2.29 (dd) [ur,d 3]
2.25 (s)c
59.6 (d)
32.0 (d)
26.9 (d)
-5.8 (d)
37.8 (d)
8.8 (d)
39.1 (d)
27.3 (d)
7.8 (d)
-6.6 (d)
23.6 (d)
9.1 (d)
40.5 (d)
19.5 (d)
25.1 (d)
6.9 (d)
27
(dppp)Pd(Me)Clb
60
39
37
67
52
46
59
67
47
(dppf)Pd(Me)Clb
1
2
5
7
8
3
6
2.04 (s)
16.0 (d)
-4.7 (d)
28.3 (d)
9.0 (d)
2.03 (s)
a
δ
b
values are given in ppm and J values in Hz. Value taken
d
from ref 15. c Broad peak. ur ) unresolved coupling.
(15) Dekker, G. P. C. M.; Elsevier, C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M. Organometallics 1992, 11, 1598
(16) (a) Berke, H.; Hoffman, R. J . Am. Chem. Soc. 1978, 100, 7224.
(b) Thorn, D. L.; Hoffmann, R. J . Am. Chem. Soc. 1978, 100, 2079. (c)
Koga, N.; Morokuma, K. Chem. Rev. 1991, 91, 823 and references
therein.
(17) (a) Doherty, S.; Eastham, G. R.; Tooze, R. P.; Scanlan, T. H.;
Williams, D.; Elsegood, M. R. J .; Clegg, W. Organometallics 1999, 18,
3558. (b) Dekker, G. P. C. M.; Elsevier, C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M. J . Organomet. Chem. 1992, 430, 357.
spectroscopy). When the reaction was repeated with 2
equiv of CNXyl, the bis-insertion product (dppf)Pd{(Cd
NXyl)(C(Me)dNXyl)}Cl (6) was obtained (see Scheme
2). This complex was found to be unstable both in
solution and in the solid state, leading to the formation
of non-phosphine-containing palladium compounds (as

4802 Organometallics, Vol. 21, No. 22, 2002
Owen et al.
F igu r e 1. Molecular structure of 1. Selected bond lengths
(Å) and angles (deg); Pd-Cl ) 2.3741(12), Pd-P(1) )
2.3738(10), Pd-P(2) ) 2.2336(10), Pd-C(1) ) 2.039(3),
C(1)-N(1) ) 1.251(5); C(1)-Pd-P(2) ) 92.47(10), C(1)-
Pd-P(1) ) 176.09(11), P(2)-Pd-P(1) ) 85.25(4), C(1)-Pd-
Cl ) 88.28(11), P(2)-Pd-Cl ) 176.27(5), P(1)-Pd-Cl )
94.19(4).
F igu r e 2. Molecular structure of 3. The phosphine phenyl
rings have been omitted for clarity. Selected bond lengths
(Å) and angles (deg): Pd-Cl ) 2.379(2), Pd-P(1) ) 2.3811-
(14), Pd-P(2) ) 2.247(2), Pd-C(1) ) 2.058(5), C(1)-N(1)
) 1.271(6), C(2)-N(2) ) 1.284(6); C(1)-Pd-P(2) ) 96.80-
(13), C(1)-Pd-Cl ) 85.88(13), P(2)-Pd-Cl ) 176.80(6),
C(1)-Pd-P(1) ) 174.10(13), P(2)-Pd-P(1) ) 89.10(5), Cl-
Pd-P(1) ) 88.24(5).
ing phosphine; the C(1)-Pd-Cl angle is 88.28(11)° (vide
infra). The five-membered chelate ring has an envelope
conformation with C(23) and C(24) lying +0.17 and
+0.79 Å, respectively, out of the Pd-P(1)-P(2) plane.
The iminoacyl fragment has its 2,6-dimethylphenyl ring
oriented approximately orthogonally (ca. 85°) to the
N(1)-C(1)-C(2) plane, favoring C-H‚‚‚N(pπ) inter-
actions18 between the C(9) and C(10) methyl hydrogen
atoms and N(1); there is a ca. 3° rotation about the Cd
N double bond. There is an intramolecular C-H‚‚‚π
stabilizing interaction (2.81 Å) between one of the C(9)
methyl hydrogen atoms and the C(36)-containing phenyl
ring. There is also an intermolecular C-H‚‚‚π inter-
action (2.73 Å) between the p-C-H of the C(22)-based
phenyl ring in one molecule and the 2,6-dimethylphenyl
ring of a centrosymmetric counterpart; there are no
other intermolecular interactions of note.
The single-crystal structure analysis of 3 confirmed
it to be the desired double-inserted complex shown in
Figure 2. The geometry at palladium is square planar,
the coordination sphere being planar to within 0.02 Å.
The cis angles, however, range between 85.88(13) and
96.80(13)°, the most acute angle being associated with
C(1)-Pd-Cl (contracted by ca. 2.5° compared to that
in 1, vide supra). The Pd-P distances are noticeably
different, with Pd-P(1) being 0.134 Å longer than Pd-
P(2), reflecting the stronger trans influence of the
iminoacyl carbon vis-a`-vis chloride. The two imino
linkages within the bis(iminoacyl) ligand are gauche
with respect to each other, the torsional twists along
the C(3)‚‚‚C(11) backbone being ca. 70, 180, 50, 179, and
77°, respectively. The coordinated bis(iminoacyl) moiety
can be described as having a trans NdCCdN conforma-
tion with anti substituents at both imine nitrogens (i.e.
with the aryl group of the second inserted isocyanide
cis to the palladium center). The geometry adopted by
this moiety in 3 is analogous to the most stable
conformation observed for free R-diimines (suggesting
why, despite the potential steric repulsions, the aryl
group is found cis to the palladium center and not
trans). This is in contrast to the mono-insertion product
1, where the isocyanide inserts to give a product with
the aryl group trans to the palladium center (which
minimizes steric repulsions). Both of these conforma-
tions are in agreement with previously reported data.4e
It is well-known that isocyanides can multiply insert
into metal-carbon bonds9 (in contrast to carbon mon-
oxide). Since the doubly inserted products 3 and 6 had
been obtained in the course of these investigations, it
was of interest to determine what sort of species would
be formed upon reacting (P-P)Pd(Me)Cl with an excess
of isocyanide. Hence, solutions of (P-P)Pd(Me)Cl were
treated with 4 equiv of CNXyl. In the case of (dppe)Pd-
(Me)Cl this reaction led to the formation of the mono-
insertion product 1 only. The reaction was monitored
by 31P NMR spectroscopy over 24 h, and no further
products were formed, indicating the lack of reactivity
of this complex toward multiple insertion. In contrast,
when 4 equiv of CNXyl was added to (dppp)Pd(Me)Cl
and the mixture monitored by 31P{1H} NMR spectros-
copy, the mono- and bis-inserted products 2 and 3 were
not detected. The reaction mixture turned dark orange,
and the 31P{1H} NMR spectrum after 3 h showed only
one singlet at -16.1 ppm, which corresponds to free
dppp. Reduction of the solvent under vacuum led to the
precipitation of a deep red solid, which was formulated
(18) This type of interaction has been observed previously; see: (a)
J agg, P. N.; Kelly, P. F.; Rzepa, H. S.; Williams, D. J .; Woollins, J . D.;
Wylie, W. J . Chem. Soc., Chem. Commun. 1991, 942. (b) Gibson, V.
C.; Newton, C.; Redshaw, C.; Solan, G. A.; White, A. J . P.; Williams,
D. J . Eur. J . Inorg. Chem. 2001, 1895.

Insertion of Isocyanides into Pd-Me Bonds
Organometallics, Vol. 21, No. 22, 2002 4803
{1H} NMR spectrum to two pairs of doublets, indicating
the formation of only two phosphorus-containing com-
pounds (which could be detected during the first 1/2 h
of the reaction). The chemical shifts of such products
(5.4 (d) and -6.8 (d) ppm, J ) 76 Hz; 17.3 (d) and -5.1
(d), J ) 56 Hz) are remarkably similar to those observed
for the mono- and bis-insertion species 2 and 3 (see
Table 1), suggesting the formation of the analogous
complexes with CNtBu. Unfortunately, full character-
ization of these two products was prevented by their
instability both in solution and in the solid state.
Analogous insertion reactions were carried out be-
tween (dppf)Pd(Me)Cl and CNtBu. When 1 equiv of
isocyanide was added to the palladium complex, the
quantitative formation of the mono-insertion product
[(dppf)Pd{C(Me)dNtBu}Cl] (8) was observed. In an
attempt to obtain the corresponding bis-insertion prod-
uct (analogous to 6), (dppf)Pd(Me)Cl was reacted with
2 equiv of CNtBu. The reaction was monitored by 31P-
{1H} NMR, which showed the gradual disappearance
of the starting material and the production of free
phosphine. This suggests that multiple insertion of
CNtBu must be occurring and free-phosphine products
similar to 4 are being formed. No further characteriza-
tion of these products was attempted.
As for the reactions with CNXyl, upon insertion of
CNtBu into (P-P)Pd(Me)Cl a shift of the phosphine
resonances in the 31P{1H} NMR spectra to lower fre-
quencies is observed (see Table 1). Again, such shifts
are more pronounced for the phosphorus cis to the R
group than for the trans.
In ser tion of Nor bor n a d ien e in to P a lla d iu m -
Im in oa cyl bon d s. The systematic study of isocyanide
insertion into (P-P)Pd(Me)Cl provided the required
background to investigate the possibility of further
insertion of alkenes into the palladium-iminoacyl
bonds. While the insertion of olefins into palladium-
acyl bonds is a well-established process, there are very
few reported examples of the analogous insertions into
palladium-iminoacyl bonds (among which are the
papers by Vrieze10a and Takahashi10b). Such organome-
tallic transformations could lead to the copolymerization
of alkenes and isocyanides, yielding polyimines.
The possible insertion of norbornadiene (which due
to its strained nature has proven to undergo insertion
reactions readily20) into the palladium-iminoacyl com-
pound 1 was then investigated. This complex was
chosen, since our previous studies demonstrated it to
be stable and not prone to multiple isocyanide insertion
(which would complicate the study of alkene insertion).
One equivalent of norbornadiene was added to a solu-
tion of (dppe)Pd{C(Me)dNXyl}Cl in THF. The reaction
mixture was monitored by 31P{1H} NMR spectroscopy
for a period of 24 h, and no changes were observed (even
when an excess of norbornadiene was added). Since the
targeted insertion reaction was not observed under
these conditions, 1 equiv of AgBF4 (to remove the
chloride from 1 and produce a vacant site for substrate
coordination) was added to the reaction mixture. Im-
mediately after the addition, a white precipitate was
F igu r e 3. Molecular structure of 4. Selected bond lengths
(Å): Pd-Cl ) 2.4005(13), Pd-N(1) ) 2.085(4), Pd-C(3) )
1.975(5), Pd-C(4) ) 1.924(5).
as the multiple-insertion product (CNXyl)Pd{(CdNXyl)-
(CdNXyl)(C(Me)dNXyl)}Cl (4) (see Scheme 2) on the
basis of IR, 1H NMR, mass spectrometry, and elemental
analysis. The analogous iodide structure has been
reported previously by Yamamoto, who reacted Pd-
(PPh3)2(Me)I with an excess of CNXyl.19 To confirm the
formulation of 4, a single-crystal X-ray analysis was
carried out (see Figure 3). Crystals of this compound
have included dichloromethane solvent, though the
conformation of the complex does not differ significantly
from that of its iodide counterpart reported previously.
Similarly, the addition of 4 equiv of CNXyl to (dppf)-
Pd(Me)Cl leads to the complete displacement of the
chelating phosphine and the consequent formation of
phosphine-free products (as demonstrated by 31P{1H}
NMR spectroscopy). The free-phosphine product formed
is analogous to that obtained with (dppp)Pd(Me)Cl.
In ser tion of ter t-Bu tyl Isocya n id e in to P a lla -
d iu m -Meth yl Bon d s. Once the influence of the phos-
phine had been studied, our attention turned to the
nature of the isocyanide: specifically, the insertion of
the more basic CNtBu isocyanide into the palladium-
carbon bond of (P-P)Pd(Me)Cl (P-P ) dppe, dppp,
dppf). When 1 equiv of CNtBu was added to (dppe)Pd-
(Me)Cl in THF, approximately 50% of the starting
material reacted to yield the mono-insertion product
[(dppe)Pd{C(Me)dNtBu}Cl] (7). Addition of a further 1
equiv of CNtBu to the reaction mixture led to the
complete conversion of (dppe)Pd(Me)Cl to the mono-
insertion product 7. As with CNXyl, no evidence for
further insertion was observed (even after long reaction
times).
In contrast to the relative lack of reactivity of (dppe)-
Pd(Me)Cl toward insertion, when the analogous reaction
between (dppp)Pd(Me)Cl and 1 equiv of CNtBu was
carried out, the formation of a complex mixture was
observed by 31P{1H} NMR spectroscopy (which proved
very difficult to separate and fully characterize). In an
attempt to drive the reaction to a single product, a
further 1 equiv of isocyanide was added. As expected,
the addition of the extra CNR indeed simplified the 31P-
(20) Van Asselt, R.; Gielens, E. C. G.; Ru¨lke, R. E.; Vrieze, K.;
Elsevier, C. J . J . Am. Chem. Soc. 1994, 116, 977.
(21) Kakino, R.; Nagayama, K.; Kayaki, Y.; Shimizu, I.; Yamamoto,
A. Chem. Lett. 1999, 685.
(19) Yamamoto, Y.; Tanase, T.; Yanai, T.; Asano, T.; Kobayashi, K.
J . Organomet. Chem. 1993, 456, 287.

4804 Organometallics, Vol. 21, No. 22, 2002
Owen et al.
Sch em e 3
formed (AgCl) followed by a change in the color of the
reaction mixture (from yellow to colorless). The 31P{1H}
NMR spectrum of this mixture demonstrated the quan-
titative conversion of 1 to a new product after ap-
proximately 15 min (at 34.5 (d), 53.0 (d) ppm). This
product was isolated and characterized on the basis of
analytical and spectroscopic techniques as [(dppe)-
labile Pd-N bond (compared to the Pd-P bond), which,
upon temporary dissociation, allows the substrate to
coordinate to the metal center and subsequently insert
into the Pd-C bond.
Rea ction of Com p lex 1 w ith Isoth iocya n a tes. To
broaden our investigations on the reactivity of pal-
ladium-iminoacyl complexes with unsaturated species,
the reaction between 1 and methyl isothiocyanate was
studied. Our initial aim was to investigate the possibil-
ity of inserting the isothiocyanate into the palladium-
iminoacyl bond, by which a new route for C-N or C-S
bond formation (depending on the insertion process)
would be established. When 1 equiv of MeNdCdS was
reacted with 1 equiv of the iminoacyl complex 1 in the
presence of AgBF4, the immediate formation of a white
precipitate (AgCl) and color change (from yellow to
colorless) were observed. The reaction was monitored
by 31P{1H} NMR spectroscopy, which indicated the
quantitative formation of a new product within the first
10 min of reaction. No further changes were observed
on stirring the mixture for a few hours. The product was
isolated, and its characterization indicated that, instead
of an insertion reaction, the isothiocyanate had under-
gone an addition to the iminoacyl group, yielding
Pd(C7H8C(dNC6H3(CH3)2)CH3][BF4] (9) (see Scheme 3).
The AB pattern in the 31P{1H} NMR spectrum is
consistent with this formulation, as is the presence of
strong stretches at 1612 and 1472 cm-1 in the IR
spectrum, which can be assigned to the CdN and the
1
strained CdC bonds, respectively. The H NMR spec-
trum clearly indicated the presence of each one of the
proton environments with the expected coupling and
integration (see the Experimental Section for detailed
assignments). Particularly indicative for this formula-
tion are the olefinic protons (Hc and Hd) and that bound
to the carbon directly attached to the palladium center,
Ha (which shows a coupling to the phosphorus atoms of
the bis-phosphine). Another important feature of the 1H
NMR that indicates the insertion of norbornadiene is
the disappearance of the H-P coupling between the
iminoacyl’s methyl protons and the phosphine. The
formulation was further confirmed by FAB(+) mass
spectrometric analyses (which showed the presence of
a peak at 742 amu corresponding to the cationic part of
the proposed species) and elemental analyses. Complex
9 is analogous to the complex reported by Vrieze on
inserting norbornadiene into the palladium-iminoacyl
bond of (N-N)Pd{C(Me)dNXyl}Cl (where N-N ) bipy,
phen; X ) Cl, Br, I).10a The insertion reaction reported
for the (N-N)Pd(R)Cl complexes seems to be more facile
than for the compounds here reported (since for the
former chloride removal is not needed for the insertion
reaction to occur). This can be attributed to the more
[(dppe)Pd{C(dCH2)N(Xyl)C(dS)NHMe}][BF4] (10) (see
Scheme 3). To the best of our knowledge, this seems to
be the first example of such a reaction on a palladium
center. Structural characterization of this complex has
not been possible, due to the poor quality of the crystals
obtained. Despite this, NMR and IR spectroscopy to-
gether with FAB(+) mass spectrometry and elemental
analyses provide enough evidence to confirm the pro-
posed formulation of 10 as a result of the addition of
methyl isothiocyanate to the iminoacyl group of 1. The
31P{1H} NMR spectrum of 10 shows the expected AB
pattern due to the two nonequivalent phosphorus atoms.

Insertion of Isocyanides into Pd-Me Bonds
Organometallics, Vol. 21, No. 22, 2002 4805
The 1H NMR spectrum indicates the presence of the
vinylic protons (coupling to the two different phosphorus
environments) as doublets of doublets at 3.9 and 4.3
ppm. The protons corresponding to the methyl of the
former iminoacyl group appear at 3.1 ppm as a doublet
(due to the coupling to the N-H proton). A broad
quartet at 5.9 ppm can be assigned to the proton on the
nitrogen of the former isothiocyanate. The protons
corresponding to the Xyl and dppe groups are integrated
correctly for this formulation (see the Experimental
Section for a complete assignment). The 13C NMR
spectrum is also consistent with the proposed formula-
tion for 10; a doublet of doublets at 176.4 ppm can be
assigned to the CdS carbon, which couples to both the
cis and trans phosphines. The resonances for the two
vinylic carbons appear at 162.8 ppm (for the carbon
directly linked to the palladium) and 110.9 ppm. The
vinylic carbon directly attached to the palladium is
strongly coupled to the trans phosphorus, giving a
reaction with the more reactive unsaturated substrate
MeNdCdS leads to the formation of a product resulting
from addition of the isothiocyanate and the coordinated
iminoacyl. In the future we hope to be able to favor the
insertion (instead of addition) of isothiocyanates into the
palladium-iminoacyl bond.
Exp er im en ta l Section
Ma ter ia ls a n d Ap p a r a tu s. All manipulations were carried
out under an atmosphere of purified and dry nitrogen using
standard Schlenk line techniques unless otherwise stated.
Solvents were dried from the appropriate drying agent, de-
gassed, and stored under nitrogen. All commercially available
solid starting materials were not further purified. All liquid
starting materials were dried over molecular sieves and
1
thoroughly degassed by freeze-pump-thaw prior to use. H,
31P, and 13C NMR spectra were recorded on a J EOL-EX270
spectrometer (270.17, 109.38, and 67.94 MHz, respectively)
with TMS, H2PO4, and TMS, respectively, as internal refer-
ences. IR spectra were recorded on a Research Series FT-IR
instrument using KBr disks in the range 4000-500 cm-1. Mass
spectroscopy and X-ray crystallography were carried out at
Imperial College. Elemental analysis was carried out at the
University of North London. The complexes (COD)PdCl2,11
(COD)PdMeCl,12 and L2PdMeCl (L2 ) dppp, dppe, dppf)13 were
synthesized according to previously reported procedures.
2
doublet with J PC ) 136 Hz. This coupling constant is
larger (though within the same order of magnitude)
than the values previously reported for other (phos-
phine)Pd-C(dCH2) systems.21 The formulation was
further confirmed by FAB(+) mass spectrometry and
elemental analyses.
Syn t h esis of (d p p e)P d {C(Me)dNXyl}Cl (1). 2,6-Di-
methylphenyl isocyanide (0.052 g, 0.40 mmol) was added to a
solution of (dppe)PdMeCl (0.111 g, 0.20 mmol) in THF (30 mL).
The resulting mixture was stirred for 2 h. The product was
isolated by removing the solvent under reduced pressure and
washing the remaining solid with diethyl ether and cold THF.
Yield: 0.12 g; 0.17 mmol; 83%. Anal. Found: C, 62.82; H, 5.29;
N, 2.04. Calcd for C36H36NP2PdCl: C, 62.82; H, 5.36; N, 1.98.
IR (ν (KBr)): 1617, 1583 (NdC). 31P{1H} NMR ((CD3)2CdO):
Con clu sion s
The systematic study of the insertion of CNR (R )
Xyl, Bu) into the palladium-methyl bond of (P-P)Pd-
t
(Me)Cl (P-P ) dppe, dppp, dppf) has been carried out.
The results have demonstrated that the insertion is
highly dependent on the nature of the chelating phos-
phine. For the more strained complex formed with dppe,
the insertion of isocyanides is slower and multiple
insertion is not observed. This is in contrast to the high
reactivity of (dppp)Pd(Me)Cl, which readily reacts with
isocyanides to produce multiply inserted products (even
when only 1 equiv of CNR is present). Similar results
have been observed for the complexes with dppf, al-
though the reactions are more controllable, indicating
a less reactive complex (in comparison to the dppp one).
These results are consistent with the previously ob-
served reactivity trend (dppp ≈ dppf . dppe) in carbo-
nylation reactions. The structural characterization of 1
and 3 has provided a unique structural insight into this
reactivity trend. The P-Pd-P angle in 3 (i.e. P-P )
dppp) is larger than in the dppe complex 1. Conse-
quently, the R-Pd-Cl angle is smaller for dppp than
dppe, which allows closer proximity of the reacting
species. Moreover, dppp with a longer alkyl backbone
provides much more flexibility to the systems which,
presumably, reduces the energy of the transition state
(as occurs with carbonylation reactions). In the case of
dppf, the bite angle is larger than for the other phos-
phines (although in this case the electronic effects due
to the dppf-Cp rings are likely to play important roles
in controlling the reactivity at the palladium center).
The studies presented here have also demonstrated
the possibility of inserting olefins (particularly the
strained norbornadiene) into the palladium-iminoacyl
bond. This could have interesting implications for
potential isocyanide/olefin copolymerization reactions.
Further studies in this area are currently being carried
out. In contrast to the reaction with norbornadiene, the
2
2
δ 39.1 (d, 1P, J PP ) 37 Hz), 27.3 (d, 1P, J PP ) 37 Hz). 1H
4
NMR ((CD3)2CdO): δ 1.68 (dd, 3H, PdC(dNR)CH3, J PH ) 5
4
Hz, J PH ) 1 Hz), 1.75 (s, 6H, (CH3)2C6H3NC), 2.33 (m, 2H,
PCH2CH2P), 2.65 (m, 2H, PCH2CH2P), 6.61 (dd, 1H, 4-H C6H3-
3
3
(CH3)2, J HH ) 8 Hz, J HH ) 7 Hz), 6.74 (2 overlapping d, 2H,
3
3,5-H C6H3(CH3)2, J HH ) 8 Hz), 7.51 (m, 12H, P-Ph(3,4,5)),
8.60 (m, 8H, P-Ph(2,6), 3J HH ≈ 3 Hz). MS (FAB+; m/z (relative
intensity)): 686 (7) [M]+, 650(3) [M - Cl]+, 539(2) [(dppe)-
PdCl]+.
Syn t h esis of (d p p p )P d {C(Me)dNXyl}Cl (2). 2,6-Di-
methylphenyl isocyanide (0.026 g, 0.20 mmol) was added
slowly to a solution of (dppp)Pd(Me)Cl (0.114 g, 0.20 mmol) in
CH2Cl2 (30 mL). The resulting solution was stirred for 1 h. A
mixture of products was obtained (as detected by 31P{1H}
NMR), including starting material and the bis-inserted iso-
cyanide. All volatiles from the reaction mixture were removed
under reduced pressure, and the remaining product was
washed with ether to remove the bis-inserted product. The
resulting solid was dissolved in THF, and a pure sample of 2
was precipitated as a yellow solid upon addition of hexane,
separating it from the remaining starting material. Yield: 0.09
g; 0.13 mmol; 67%. Anal. Found: C, 59.75; H, 5.00; N, 1.71.
Calcd for C37H38NP2PdCl‚0.7CH2Cl2: C, 59.58; H, 5.23; N, 1.84.
IR (ν (KBr)): 1614, 1582 (NdC). 31P{1H} NMR (THF): δ 7.8
3
3
(d, 1P, J PP ) 67 Hz), -6.6 (d, 1P, J PP ) 67 Hz). 1H NMR
4
4
(CDCl3): δ 1.61 (dd, 3H, PdC(dNR)CH3, J PH ) 3.5 Hz, J PH
unresolved), 1.74 (s, 6H, C6H3(CH3)2), 1.82 (m, 4H, PCH2-
CH2CH2P), 2.40 (m, 2H, PCH2CH2CH2P), 6.72 (m, 3H, C6H3-
(CH3)2), 7.35(m, 12H, P-Ph(3,4,5)), 7.78 (m, 8H, P-Ph(2,6)).
MS (FAB+; m/z (relative intensity)): 702 (4) [M+], 664 (7) [M+
- Cl], 518 (11) [Pd(dppp)]+.
Syn th esis of (d p p p )P d {(CdNXyl)(C(Me)dNXyl)}Cl (3).
2,6-Dimethylphenyl isocyanide (0.026 g, 0.20 mmol) was added
to a solution of (dppp)PdMeCl (0.057 g, 0.10 mmol) in THF

4806 Organometallics, Vol. 21, No. 22, 2002
Owen et al.
(30 mL). The resulting mixture was stirred for 20 min. The
solvent was removed under reduced pressure and the remain-
ing solid recrystallized from a diethyl ether/hexane mixture
to yield pure 4 as a yellow crystalline solid. Yield: 0.07 g; 0.08
mmol; 85%. Anal. Found: C, 66.31; H, 5.82; N, 3.28. Calcd for
Hz). 1H NMR (CD2Cl2): δ 1.75 (s, 6H, (CH3)2C6H3), 2.03 (s,
3H, PdC(dNR)CH3), 2.32 (s, 6H, (CH3)2C6H3), 3.09 (br, 2H,
(2′,5′)C5H4PPh2), 4.02 (br, 2H, (3′,4′)C5H4PPh2), 4.43 (br, 4H,
C5H4PPh2), 6.82-7.87 (m, 26H, aromatic H). MS (FAB+; m/z
(relative intensity)): 937 (2) [M - Cl]+, 806 (15) [(dppf)Pd-
(CNR)Me]+, 675 (5) [(dppf)PdMe]+, 660 (6) [Pd(dppf)]+.
Syn th esis of [(d p p e)P d {C(Me)dNtBu }Cl] (7). tert-Butyl
isocyanide (81.4 µL, 0.72 mmol) was added to a solution of
(dppe)PdMeCl (0.20 g, 0.36 mmol) in THF. The resulting
solution was stirred for 2 h. The solvent was removed under
reduced pressure and the remaining solid washed with diethyl
ether and recrystallized from a THF/hexane mixture to yield
pure 7. Yield: 0.17 g; 0.27 mmol; 74%. Anal. Found: C, 58.70;
H, 5.29; N, 2.08. Calcd for C32H36NP2PdCl‚H2O (the added
solvent, which was detected by 1H NMR spectroscopy, could
not be removed even after the sample was left under vacuum
for several days): C, 58.55; H, 5.83; N, 2.13. IR (ν; KBr): 1637,
C
46H47N2P2PdCl: C, 66.43; H, 5.70; N, 3.37. IR (ν (KBr)): 1613,
2
1582 (NdC). 31P{1H} NMR (CDCl3): δ 16.0 (d, 1P, J PP ) 67
2
1
Hz), -4.7 (d, 1P, J PP ) 67 Hz). H NMR (CDCl3): δ 1.81 (br
s, 6H, C6H3(CH3)2), 1.92 (m, 4H, PCH2CH2CH2P), 2.04 (s, 3H,
PdC(dNR)CH3), 2.27 (m, 2H, PCH2CH2CH2P), 2.33 (br s, 6H,
C6H3(CH3)2), 6.77-7.52 (m, 26H, aromatic H). MS (FAB+; m/z
(relative intensity)): 795 (2) [M - Cl]+, 702(3) [M - CNXyl]+,
664 (3) [M - (CNR) - Cl]+, 535 (1) [(dppp)PdMe]+, 518 (4)
[(dppp)Pd]+.
Syn th esis of (NCXyl)P d {(CdNXyl)(CdNXyl)[C(Me)d
NXyl)]Cl (4). 2,6-Dimethylphenyl isocyanide (0.09 g, 0.73
mmol) was added to a solution of (dppp)PdMeCl (0.10 g, 0.18
mmol) in THF (30 mL). The resulting mixture was stirred for
3 h. The resulting red solution was evaporated to dryness, and
the product was extracted with small portions of diethyl ether
(3 × 10 mL). Hexane solvent was then added to the solution,
and the diethyl ether was slowly removed under reduced
pressure to give a red microcrystalline solid. Yield: 0.07 g:
0.10 mmol: 57%. Anal. Found: C, 65.05; H, 5.81; N, 8.21. Calcd
for C37H39N4PdCl: C, 65.20; H, 5.77; N, 8.22. IR (ν): 2194 (Ct
N), 1643, 1590 (NdC). 1H NMR (CDCl3): δ 1.69 (s, 6H,
C6H3(CH3)2, terminally coordinated), 2.08 (s, 6H, C6H3(CH3)2),
2.16 (s, 6H, C6H3(CH3)2), 2.26 (s, 3H, C(dNR)CH3), 2.38 (s, 6H,
C6H3(CH3)2), 6.33 (m, 1H, C6H3(CH3)2), 6.67 (m, 2H, C6H3(CH3)2),
6.83-7.20 (m, 9H, C6H3(CH3)2). MS (FAB+; m/z (relative
intensity)): 680 (3) [M]+, 645 (24) [M - Cl]+, 549 (11) [M -
CNR]+.
2
1587 (NdC). 31P{1H} NMR (THF-d6): δ 40.5 (d, 1P, J PP ) 46
2
1
Hz), 19.5 (d, 1P, J PP ) 46 Hz). H NMR (CD2Cl2): δ 1.04 (s,
9H, (CH3)3NC), 1.50 (m, 2H, PCH2CH2P), 2.29 (dd, PdC(dNR)-
3
3
CH3, 3H, J PH ) 2.5 Hz, J PH unresolved), 2.45 (m, 2H,
PCH2CH2P), 7.30-8.03 (m, P-Ph, 20H). MS (FAB+; m/z
(relative intensity)): 640 (8) [M]+, 602 (8) [M - Cl]+, 539 (2)
[(dppe)PdCl]+, 504 (5) [(dppe)Pd]+.
Syn th esis of [(d p p f)P d {C(Me)dNtBu }Cl] (8). tert-Butyl
isocyanide (12.9 µL, 0.10 mmol) was added to a solution of
(dppf)PdMeCl (0.143 g, 0.20 mmol) in THF (30 mL), and the
reaction mixture was stirred for 5 h. The crude product was
isolated by evaporation of all volatiles. This was washed with
diethyl ether (20 mL) to remove a small quantity of a purple
uncharacterized side product. The crude solid was recrystal-
lized from THF and hexanes, yielding an orange solid. Yield:
0.12 g; 0.15 mmol; 77%. Anal. Found: C, 60.49; H, 4.97; N,
1.73. Calcd for C40H40NP2PdFeCl: C, 60.48; H, 5.07; N, 1.76.
IR (ν; KBr): 1661 (CdN). 31P{1H} NMR (THF-d8): δ 25.1 (d,
Syn t h esis of (d p p f)P d {C(Me)dNXyl}Cl (5). 2,6-Di-
methylphenyl isocyanide (0.013 g, 0.10 mmol) was added to a
solution of (dppf)PdMeCl (0.071 g, 0.10 mmol) in CH2Cl2 (30
mL). The resulting mixture was stirred for 2 h, resulting in
the mono-inserted product and a small amount of bis-inserted
product and starting material (as detected by 31P{1H} NMR).
The solvent was removed under reduced pressure, and the
resulting solid was washed (to remove the bis-inserted product)
with diethyl ether. The crude product was recrystallized from
THF and hexane, yielding 5 as an orange solid. Yield: 0.053
g: 0.06 mmol; 64%. Anal. Found: C, 62.63; H, 4.91; N, 1.61.
Calcd for C44H40NP2PdFeCl: C, 62.70; H, 4.74; N, 1.66. IR (ν;
KBr): 1627, 1583 (NdC). 31P{1H} NMR (CD2Cl2): δ 23.6 (d,
2
2
1
1P, J PP ) 59 Hz), 6.9 (d, 1P, J PP ) 59 Hz). H NMR (THF-
d8): δ 1.26 (s, (CH3)3NC, 9H), 2.25 (s, 3H, PdC(dNR)CH3), 3.42
(br, 2H, (2′,5′)C5H4PPh2), 4.11 (br, 2H, (3′,4′)C5H4PPh2), 4.60,
(m, (3,4)C5H4PPh2 + (2,5)C5H4PPh2), 7.09-8.29 (m, 20H,
P-Ph). MS (FAB+; m/z (relative intensity)): 794 (1) [M]+, 758
(4) [M - Cl]+, 695 (2) [(dppf)PdCl]+, 660 (18) [(dppf)Pd]+.
Syn t h esis of [(d p p e)P d {C7H 8C(dNC6H 3(CH 3)2}CH 3]-
[BF 4] (9). Bicyclo[2.2.1]hepta-2,5-diene (i.e. norbornadiene)
(16.1 µL, 0.15 mmol) was added to a stirred solution of (dppe)-
Pd{C(Me)dNXyl}Cl (0.10 g, 0.15 mmol) in THF (20 mL). To
the resulting reaction mixture was added 1 equiv of AgBF4
(0.03 g, 0.15 mmol) as a solid in one portion. Immediate
formation of AgCl was observed along with a change in the
solution’s color (from yellow to colorless). The reaction mixture
was stirred for 15 min, after which time the precipitated AgCl
was filtered off. The remaining reaction mixture was stirred
for a further 10 min. A white product was obtained by reducing
the reaction mixture’s volume (under vacuum) to ca. 5 mL
followed by addition of hexane (10 mL).
2
2
1P, J PP ) 52 Hz), 9.1 (d, 1P, J PP ) 52 Hz). 1H NMR (CD2-
Cl2): δ 1.65 (dd, 3H, PdC(dNR)CH3, 3J PH ) 5.0 Hz, 3J PH ) 1.5
Hz), 1.71 (s, 6H, (CH3)2C6H3NC), 3.59 (br d, 2H, (2′,5′)C5H4-
PPh2, 3J PH ) 2.0 Hz), 4.16 (br s, 2H, (3′,4′)C5H4PPh2), 4.44 (br
3
s, (3,4)C5H4PPh2), 4.69 (br d, 2H, (2,5)C5H4PPh2, J PH ) 2.0
Hz), 6.69 (m, 1H, (4)-C6H3(CH3)2), 6.77 (m, 2H, (3,5)C6H3-
(CH3)2), 7.24-8.03 (m, 20H, PPh). MS (FAB+; m/z (relative
intensity)): 806 (100) [M - Cl]+, 697 (11) [(dppf)PdCl]+, 660
(58) [Pd(dppf)]+.
Syn th esis of (d p p f)P d {(CdNXyl)(C(Me)dNXyl)}Cl (6).
A solution of 2,6-dimethylphenyl isocyanide (0.088 g, 0.68
mmol) in CH2Cl2 (20 mL) was added slowly to a solution of
(dppf)PdMeCl (0.24 g, 0.34 mmol) in CH2Cl2 (40 mL). The
resulting solution was stirred for 1 h and analyzed by 31P NMR
spectroscopy, which showed the formation of a mixture of
products (corresponding to starting material, 5, and the new
product 6). The solvent was removed under reduced pressure,
and the resulting solid was washed with diethyl ether. The
solution contained 6 together with some free phosphine. The
solution was concentrated under reduced pressure and left to
stand for 1 h, upon which time 6 precipitated as a yellow solid.
Yield: 0.17 g; 0.17 mmol; 51%. Anal. Found: C, 65.82; H, 5.35;
N, 2.35. Calcd for C53H49N2P2PdFeCl‚0.5C4H10O (the added
Yield: 0.09 g; 0.12 mmol; 81%. Anal. Found: C, 57.09; H, 5.01;
N, 1.52. Calcd for C42H44NPdBF4‚CH2Cl2: C, 57.20; H, 5.13;
N, 1.55. IR (ν; KBr): 1612 (CdN), 1472 (CdC), 1100, 1058
1
solvent was detected by H NMR spectroscopy): C, 65.36; H,
2
5.39; N, 2.77. IR (ν; KBr): 1618, 1585 (NdC). 31P{1H} NMR
(BF4). 31P{1H} NMR (CD2Cl2): δ 34.5 (d, 1P, J PP ) 29 Hz),
2
2
2
1
(CD2Cl2): δ 28.3 (d, 1P, J PP ) 47 Hz), 9.0 (d, 1P, J PP ) 47
53.0 (d, 1P, J PP ) 30 Hz). H NMR (CD2Cl2): δ 1.20 (dd, 1H,

Insertion of Isocyanides into Pd-Me Bonds
Organometallics, Vol. 21, No. 22, 2002 4807
Ha, 3J PH ) 9.5 Hz, 3J PH unresolved), 1.75 (s, 3H, C(dNR)CH3),
1.92 (s, 3H, C6H3(CH3)2), 1.96 (s, 3H, C6H3(CH3)2), 2.26 (m, 1H,
Hh), 2.32 (br, 2H, Hf + Hg), 2.80 (dd, 1H, Hb, 3J PH unresolved),
Cr ysta l Da ta for 1: C36H36NP2ClPd, Mr ) 686.5, triclinic,
P1h (No. 2), a ) 11.363(2) Å, b ) 11.787(2) Å, c ) 14.186(4) Å,
R ) 112.85(2)°, â ) 103.79(2)°, γ ) 102.60(1)°, V ) 1594.6(6)
Å3, Z ) 2, Dc ) 1.430 g cm-3, µ(Mo KR) ) 0.79 mm-1, T ) 293
K, clear prisms; 5350 independent measured reflections, F2
refinement, R1 ) 0.036, wR2 ) 0.080, 4384 independent
observed reflections (|Fo| > 4σ(|Fo|), 2θ e 50°), 322 parameters.
CCDC 191378.
3
3
3.19 (s, 1H, He), 5.63 (dd, 1H, Hc, J PH ) 5.0 Hz, J PH ) 2.5
3
3
Hz), 6.08 (dd, 1H, Hd, J PH ) 5.0 Hz, J PH ) 2.5 Hz), 6.43 (d,
3
3
1H, C6H3(CH3)2, J HH ) 7.5 Hz), 6.56 (d, 1H, C6H3(CH3)2, J HH
) 7.5 Hz), 6.67 (τ, 1H, C6H3(CH3)2), 7.04-7.89 (m, 20H, 4 ×
P-Ph). MS (FAB+; m/z (relative intensity)): 742 (24) [M -
BF4]+, 676 (5) [M - BF4 - C5H6]+, 504 (4) [Pd(dppe)]+.
Cr ysta l Da ta for 3: C46H47N2P2ClPd‚C4H8O, Mr ) 903.8,
triclinic, P1h (No. 2), a ) 13.541(4) Å, b ) 13.597(2) Å, c )
13.671(3) Å, R ) 92.46(1)°, â ) 110.99(2)°, γ ) 103.70(2)°, V )
Syn th esis of [(d p p e)P d {C(dCH2)N(Xyl)C(dS)NHMe}]-
[BF 4] (10). Methyl isothiocyanate (0.018 g, 0.24 mmol) was
added to a stirred solution of (dppe)Pd{C(Me)dNXyl}Cl (0.15
g, 0.22 mmol) in CH2Cl2 (25 mL). AgBF4 (0.04 g, 0.22 mmol)
was added in one portion. The AgCl salt immediately precipi-
tated from the yellow solution, and within 5 min the solution
turned clear. The reaction mixture was left for a further 10
min, and then the AgCl was filtered off. The white product
was obtained by the reduction of the solvent to 10 mL and
addition of hexane (15 mL). Yield: 0.13 g; 0.16 mmol; 73%.
Anal. Found: C, 56.27; H, 4.84; N, 3.54. Calcd for C38H39N2P2-
SBF4Pd: C, 56.28; H, 4.85; N, 3.45. IR (ν; KBr): 3448 (N-H),
3055 (alkene C-H), 1560 s (CdC), 1262 m (CdS), 1102, 1058
2260.4(9) Å3, Z ) 2, Dc ) 1.328 g cm-3, µ(Mo KR) ) 0.58 mm-1
,
T ) 293 K, yellow prisms; 7739 independent measured
reflections, F2 refinement, R1 ) 0.050, wR2 ) 0.109, 5778
independent observed reflections (|Fo| > 4σ(|Fo|), 2θ e 50°),
490 parameters. CCDC 191379.
Cr ysta l Da ta for 4: C37H39N4ClPd‚CH2Cl2, Mr ) 766.5,
triclinic, P1h (No. 2), a ) 11.674(1) Å, b ) 12.391(1) Å, c )
14.779(1) Å, R ) 70.45(1)°, â ) 83.80(1)°, γ ) 69.17(1)°, V )
1882.7(2) Å3, Z ) 2, Dc ) 1.352 g cm-3, µ(Cu KR) ) 6.17 mm-1
,
T ) 293 K, orange prisms; 5474 independent measured
reflections, F2 refinement, R1 ) 0.048, wR2 ) 0.120, 4676
independent observed absorption-corrected reflections (|Fo| >
4σ(|Fo|), 2θ e 120°), 416 parameters. CCDC 191380.
2
(BF4). 31P{1H} NMR (CDCl3): δ 46.9 (d, 1P, J PP ) 33 Hz),
2
56.6 (d, 1P, J PP ) 33 Hz). 1H NMR (CDCl3): δ 2.00 (s, 6H,
C6H3(CH3)2), 2.55 (m, 4H, PCH2CH2P), 3.05 (d, 3H, HNCH3,
4
3J HH ) 4.5 Hz), 3.91 (τ, 1H, PdC(dCH2) cis to Pd, J PH ) 6.5
Hz), 4.29 (τ, 1H, PdC(dCH2) trans to Pd, 4J PH ) 16.0 Hz), 5.94
(br q, CH3NH, 3J HH ) 4.5 Hz), 7.10-7-24 (m, 3H, C6H3(CH3)2),
7.40-7.83 (m, 20H, 4 × PC6H5). 13C{1H} NMR (CDCl3): δ 17.6,
Ack n ow led gm en t. We are very grateful to the
EPSRC for financial support (G.R.O.) and J ohnson
Matthey PLC for a loan of palladium.
1
2
25.9 (dd, PCH2CH2P), J PC ) 29 Hz, J PC ) 11 Hz), 30.7 (dd,
1
2
PCH2CH2P, J PC ) 34 Hz, J PC ) 18 Hz), 32.9 (s, N-CH3),
111.0 (br, PdC(dCH2)), 127.3-136.2 (several signals assigned
to the phenyl rings of dppe and Xyl group), 162.8 (dd, PdC(d
Su p p or tin g In for m a tion Ava ila ble: Details about the
X-ray crystal structures, including ORTEP diagrams and
tables of crystal data and structure refinement, atomic coor-
dinates, bond lengths and angles, and anisotropic displacement
parameters for 1, 3, and 4. This material is available free of
charge via the Internet at http://pubs.acs.org.
2
2
CH2), J CPtrans ) 136 Hz, J CPcis unresolved), 176.4 (dd, CdS,
3J PC ) 16 Hz, J PC unresolved). MS (FAB+; m/z (relative
3
intensity)): 723 (31) [M]+, 504 (4) [(dppe)Pd]+.
Cr ysta l Str u ctu r e Deter m in a tion s. Data for all three
compounds were collected on Bruker P4 diffractometers with
graphite-monochromated Mo or Cu KR radiation as indicated
and using ω-scans.
OM020444Z