Chiral phosphinoferrocene carboxamides with amino acid substituents as ligands for Pd-catalysed asymmetric allylic substitutions. Synthesis and structural characterisation of catalytically relevant Pd complexes

Article abstract of DOI:10.1039/c1dt11230a

An extensive series of chiral amino acid amides prepared from 1′-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) or its planar-chiral isomer, 2-(diphenylphosphino)ferrocene-1-carboxylic acid, have been tested as ligands for Pd-catalysed asymmetric allylic substitution reactions. In alkylation of 1,3-diphenylallyl acetate as a model substrate with dimethyl malonate the ligands performed well in terms of both reaction rate and enantioselectivity, achieving up to 98% ee. In contrast, the reactions of the same substrate with other nucleophiles proceeded either slowly and with poor ee's (amination with benzylamine) or not at all (etherification with benzyl alcohol). In order to rationalise the influence of the ligand structure on the reaction course, three model complexes, viz. [(η³-methallyl) PdCl(L-κP)], [(η³-methallyl)Pd(L-κ²O,P)] ClO₄ and [(η³-methallyl)Pd(L-κP) ₂]ClO₄ have been prepared from the achiral amide Ph ₂PfcCONHCH₂CO₂Me (L; fc = ferrocene-1,1′- diyl) and structurally characterised. The coordination study showed that the amido-phosphines readily form 1:1 complexes as O,P-chelates where the amino acid chirality is brought close to the Pd atom. At higher ligand-to-metal ratios, however, simple P-monodentate coordination prevails, minimising the influence of the chiral amino acid pendant. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt11230a

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PAPER
Chiral phosphinoferrocene carboxamides with amino acid substituents as
ligands for Pd-catalysed asymmetric allylic substitutions. Synthesis and
structural characterisation of catalytically relevant Pd complexes†
ˇ
Jirˇ´ı Tauchman, Ivana C´ısarˇova´ and Petr Steˇpnicˇka*
Received 28th June 2011, Accepted 16th August 2011
DOI: 10.1039/c1dt11230a
An extensive series of chiral amino acid amides prepared from 1¢-(diphenylphosphino)ferrocene-1-
carboxylic acid (Hdpf) or its planar-chiral isomer, 2-(diphenylphosphino)ferrocene-1-carboxylic acid,
have been tested as ligands for Pd-catalysed asymmetric allylic substitution reactions. In alkylation of
1,3-diphenylallyl acetate as a model substrate with dimethyl malonate the ligands performed well in
terms of both reaction rate and enantioselectivity, achieving up to 98% ee. In contrast, the reactions of
the same substrate with other nucleophiles proceeded either slowly and with poor ee’s (amination with
benzylamine) or not at all (etherification with benzyl alcohol). In order to rationalise the influence of
3
the ligand structure on the reaction course, three model complexes, viz. [(h -methallyl)PdCl(L-kP)],
3
2
3
[(h -methallyl)Pd(L-k O,P)]ClO4 and [(h -methallyl)Pd(L-kP)2]ClO4 have been prepared from the
achiral amide Ph2PfcCONHCH2CO2Me (L; fc = ferrocene-1,1¢-diyl) and structurally characterised.
The coordination study showed that the amido-phosphines readily form 1 : 1 complexes as O,P-chelates
where the amino acid chirality is brought close to the Pd atom. At higher ligand-to-metal ratios,
however, simple P-monodentate coordination prevails, minimising the influence of the chiral amino
acid pendant.
catalytic properties and easy synthesis led us to extend our studies
Introduction
towards amides prepared from ferrocene phosphinocarboxylic
acids and amino acid esters as a readily available chiral pool.7
Although similar ligands with organic backbones are known,8 this
concept did not yet pervade the chemistry of ferrocene ligands.
This contribution details catalytic results obtained with a
series of chiral phosphinoferrocene carboxamides bearing amino
acid pendants (Scheme 1) in Pd-catalysed asymmetric allylic
substitution reactions. Also reported are the preparation and
Palladium-catalysed asymmetric allylic substitution is a powerful
synthetic tool allowing for stereoselective construction of C–C and
C-heteratom bonds from a range of substrates.1 Functional group
tolerance and wide applicability in the synthesis of various chiral
molecules led to a search for efficient ligands for this reaction,
which meanwhile turned into a benchmark test for chiral donors.
Particularly attractive proved to be donor-unsymmetric bidentate,
potentially chelating ligands which electronically differentiate al-
3
structural characterisation of several (h -allyl)Pd(II) complexes as
models for the plausible reaction intermediates.
3
lylic termini in (h -allyl)palladium intermediates and thus provide
the necessary bias for the reaction to proceed selectively.1,2
During the last few decades, numerous chiral, ferrocene-based
donors of this kind have been developed and tested in allylic
substitutions. As illustrious examples1g–h,3 may serve ferrocene
diphosphines and the related mixed-donor ligands (mostly P,N-
and P,O-donors), 2-ferrocenyl-4,5-dihydrooxazoles (oxazolines)
and diphosphine diamides analogous to Trost’s ligands.1,4
Results
The preparation of amino acid amides 1–4 and 7–10 was reported
elsewhere.7 Two new ligands included in this study, (S)-5 and
(S,S)-6, were obtained in an analogous manner by amide coupling
of 1¢-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) with
amino acid methyl esters formed in situ from the respective
hydrochlorides and triethylamine.
In our previous work, we focused on catalytic utilisation of
phosphinoferrocene carboxamides in Suzuki-Miyaura and Heck
reactions5 and in asymmetric allylic alkylation.6 The favourable
Chiral phosphine-amide ligands 2–10 (Scheme 1) were tested
in palladium-catalysed asymmetric allylic alkylation using the
common model reaction system comprising 1,3-diphenylallyl
acetate (11a) as the allylic substrate and an ‘instant’ nucleophile9
generated from dimethyl malonate and N,O-bis(trimethylsilyl)-
acetamide (BSA; Scheme 2). The pre-catalyst was formed
Department of Inorganic Chemistry, Faculty of Science, Charles University
in Prague, Hlavova 2030, 12840, Prague, Czech Republic. E-mail: stepnic@
natur.cuni.cz
† CCDC reference numbers 823874–823876. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt11230a
11748 | Dalton Trans., 2011, 40, 11748–11757
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Table 1 Summary of catalytic results obtained with ligands (S)-2 and
(Sp)-7 in asymmetric allylic alkylationa
Entry Ligand Solvent
Base/additive Conv./% ee/% [config]f
1
2
3
4
(Sp)-7
(Sp)-7
(Sp)-7
(Sp)-7
(Sp)-7
(Sp)-7
(Sp)-7
(Sp)-7
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
(S)-2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
THF
BSA/none
BSA/LiOAc
BSA/NaOAc 80
BSA/KOAc 54
BSA/RbOAc 47
BSA/CsOAc
BSA/none
BSA/NaOAc 24
BSA/none
BSA/LiOAc
BSA/NaOAc 100
BSA/KOAc 80
BSA/RbOAc 84
BSA/CsOAc
BSA/none
BSA/NaOAc 90
BSA/none
81
79
85 [R]
61 [R]
81 [R]
55 [R]
61 [R]
64 [R]
98 [R]
37 [R]
-85 [S]
-67 [S]
-65 [S]
-50 [S]
-41 [S]
-70 [S]
-40 [S]
-58 [S]
-45 [S]
—
5
6
75
10
7b
8b
9
100
90
10
11
12
13
14
15b
16b
17
18
19
20
21
22
23
24
25
26
27
28c
29c
30d
31d
100
10
56
0
0
dioxane BSA/none
toluene
MeCN
DMF
BSA/none
BSA/none
BSA/none
NaN(SiMe3)2
KN(SiMe3)2
KOt-Bu
—
100
67
49
11
72
5
37
82
0
-77 [S]
-74 [S]
-26 [S]
-20 [S]
-4 [S]
—
Scheme 1 Chiral phosphine-amide ligands tested in this study.
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
K2CO3
K3PO4
0
DBUe
-6 [S]
BSA/none
BSA/NaOAc
BSA/none
—
0
100
—
-78 [S]
-61 [S]
Scheme 2
BSA/NaOAc 100
a Reaction of 11a with 3 equiv. of dimethyl malonate and 3 equiv. of
BSA in the presence of 5 mol.% of Pd catalyst generated in situ from
[Pd(m-Cl)(h-C3H5)]2 and a ligand (Pd : L = 1 : 1) in 3 mL of solvent at
room temperature for 24 h. b Reaction performed at 0 ◦C. c Reaction with
di-tert-butyl malonate. d Reaction with 11b as the substrate. e DBU = 1,8-
diazabicyclo[5.4.0]undec-7-ene. f ee = ([R] - [S])/([R] + [S]).
3
in situ from [Pd(m-Cl)(h -C3H5)]2 and the respective ligand. Initial
catalytic tests were carried out with ligands (Sp)-7 and (S)-2 as the
representatives (Table 1).
The first catalytic tests with the planar-chiral ligand (Sp)-7
(Table 1, entries 1–8) already showed that the reaction proceeds
with reasonable conversions and good ee’s. Subsequent attempts
to improve the reaction outcome by addition of catalytic amounts
of alkali metal acetates (10% with respect to the allylic substrate)
failed, the addition resulting in lower conversions and ee’s. In
contrast, cooling the reaction system containing only BSA to 0
◦C considerably increased the enantioselectivity (ee 98%!), albeit
on account of the reaction rate (10% conversion after 24 h; entry
7). Addition of NaOAc as a base additive slightly improved the
conversion at 0 ◦C but the ee dramatically decreased (entry 8).
A similar reaction with catalyst based on ligand (S)-2 featuring
chirality only in the amino acid side chain was faster, affording
complete conversion within 24 h (entries 9–16 in Table 1). Notably,
however, the catalyst based on (S)-2 produced the alkylation
product with the same degree of asymmetric induction as for (Sp)-
7 but with an inverted ratio of the enantiomers ((S)-12 dominant;
cf . entries 1 and 9). Similarly to (Sp)-7, the addition of alkali
metal acetates to (S)-2/Pd system did not improve the catalytic
performance, resulting in lower ee’s while the conversions either
remained virtually unchanged (Na and Cs) or decreased (Li, K
and Rb). A decrease in the conversion and ee’s was surprisingly
noted also when the reaction temperature was lowered to 0 ◦C
(entries 15 and 16).
the conversion remained high but selectivity decreased (conversion
100% after 24 h, ee = -77% with (S)-2). The use of bases other than
BSA also resulted in lower conversions and markedly decreased the
enantioselectivity. Finally, changing the reaction partners (entries
28–31) had a detrimental effect on the reaction outcome. The
reaction with 11a and di-tert-butyl malonate as a more bulky
nucleophile did not proceed while carbonate 11b and dimethyl
malonate afforded the alkylation product still quantitatively but
with a relatively lower selectivity.
Additional experiments with ligand (S)-2 revealed that the
reaction outcome depends strongly on the ligand-to-metal ratio
(results not tabulated). Whereas the conversions achieved with
(S)-2 remained practically complete in all cases (98–100% after 24
h), the enantioselectivity decreased from ee -85% at L : Pd ratio
1 : 1 to -71% at L : Pd = 1 : 1.2 and -62% at L : Pd = 1 : 1.5 and,
finally, to zero at L : Pd = 2 : 1. A similar but less pronounced trend
was noted also in reactions with ligand (Sp)-7, which afforded the
alkylation product with 81% conversion and 85% ee at L : Pd ratio
1 : 1 and with an 82% conversion and 77% ee at L : Pd ratio 2 : 1.
After surveying the reaction parameters, the whole series of lig-
ands was assessed under optimised conditions (BSA without any
added alkali metal acetate, dichloromethane, room temperature).
The results are summarised in Table 2.
Upon testing different solvents or bases (entries 17–27) it was
found that the reaction becomes slower and less selective in THF
and DMF, and stops entirely in dioxane or toluene. In acetonitrile,
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Table 2 Survey of the ligands in the Pd-catalysed allylic alkylationa
Table 3 Summary of catalytic results obtained in allylic aminationa
Amino acid
Hdpf
(Sp)-Hpfc
Entry
Base
t/h
Conv. (ee)/%
Ligand Conv./% ee/%
Ligand
(Sp)-7
Conv./% ee/%
1
2
3
4
BSA
BSA
none
none
24
48
24
48
62 (0)
96 (0)
20 (12) [R]
29 (13) [R]
Gly
1
—
—
81
55
85 [R]
52 [R]
83 [R]
60 [R]
57 [R]
—
(S)-Ala
(R)-Ala
(S)-Val
(R)-Val
(S)-Leu
(S,S)-Ile
(S)-Phe
(R)-Phe
(S)-2
(R)-2
(S)-3
(R)-3
(S)-5
100
100
23
25
93
-85 [S] (S,Sp)-8
84 [R] (R,Sp)-8b 34
-24 [S] (S,Sp)-9
26 [R] (R,Sp)-9
-65 [S]
-11 [S]
-67 [S] (S,Sp)-10 51
80
12
—
—
a Conditions: 5 mol.% Pd catalyst prepared in situ from [Pd(m-Cl)(h -
C3H5)]2 and (S)-2 (L : Pd = 1 : 1); PhCH2NH2 (3 equiv.), BSA (3 equiv.)
in CH2Cl2 (3 mL), room temperature.
3
—
—
(S,S)-6 53
(S)-4
(R)-4
—
56
92
65 [R]
58 [R]
66 [R] (R,Sp)-10 15
a For conditions, see Table 1, footnote a. Data for compounds (S)-2 and
(Sp)-7 are included from Table 1 for a comparison. b The enantiomeric
ligand (S,Rp)-8 gave 12 with 43% conversion and -85% ee.
In general, the reaction rate (conversion) and stereoselectivity
varied greatly with the ligand structure. Reactions with ligands
derived from achiral Hdpf and (S)-amino acid esters produced
the alkylation product enriched in (S)-12, while the enantiomeric
ligands expectedly favoured the formation of (R)-12. Among
donors obtained from (S)-amino acids, which constitute a more
extensive set, the best conversion and ee were achieved with
(S)-2 as a ligand possessing the smallest substituent in the
amino acid residue. Increasing the steric bulk of the amino
acid substituent significantly decreased the enantioselectivity. For
instance, (S)-5 featuring an amino acid residue branched in g-
position and the ligand obtained from (S)-phenylalanine afforded
the alkylation product with a lower, ca. 65–67% ee. The more
sterically encumbered ligands branched in b-position ((S)-3 and
(S,S)-6) performed even worse (Table 2).
Trends among ligands derived from planar-chiral 2-
(diphenylphosphino)ferrocene-1-carboxylic acid (Hpfc) are less
obvious, probably because of an interplay of the two chirality
elements. Yet again, the best results were obtained with ligand
(Sp)-7 containing the least sterically demanding glycine pendant.
Ligand (S)-2 was chosen for further testing in allylation of
model N- and O-nucleophiles. Amination performed with 11a and
benzylamine in the presence of BSA as a base (Scheme 3, Table
3) afforded only racemic 13 (96% conversion after 2 days with
5% mol.% of Pd catalyst). Similar reactions without any additive
proceeded much slower and with only a poor enantioselectivity
(Table 3). An analogous etherification of 11a with benzyl alcohol
(Scheme 4) in the presence of 5 mol.% of the same Pd-catalyst and
BSA or Cs2CO3 as the base (3 equiv.) did not proceed at all.
Scheme 4
attempts to prepare any well-defined (solid) samples of the most
3
catalytically relevant (h -1,3-diphenylallyl)palladium complexes
with (S)-2 failed.10 Therefore, we turned to similar reactions with
achiral donor 1.11
3
Indeed, the reaction of [(h -Ph2C3H3)PdCl]2 and 1 produced an
orange solid, which showed a signal due to [(h -Ph2C3H3)Pd(1)]+
3
(m/z 784) in ESI mass spectra and contained one dominant and
two very minor species according to H (ref.)12 and 31P NMR
1
analysis. The NMR spectra suggested that the PPh2 group is
coordinated in all cases (dP 14.8 major, 15.5 and 16.0 minor).
3
Considering the high conformational flexibility of (h -Ph2C3H3)Pd
moiety and similarity of the 31P NMR chemical shifts, the minor
components are most probably isomers to the major component
differing in the overall molecular conformation. However, other
3
species resulting by, e.g., self-ionisation ([(h -Ph2C3H3)PdCl(1)] →
3
[(h -Ph2C3H3)Pd(1)]Cl), cannot simply be excluded.
3
When AgClO4 (1 equiv.) was added to in situ formed [(h -
Ph2C3H3)PdCl(1)], the chloride complex was cleanly converted
to a new compound, which showed one broad, low-field shifted
signal in its 31P NMR spectrum (dP 19.5). The 1H NMR spectrum
displayed very broad resonances, suggesting some dynamic equi-
libria. The ESI mass spectrum expectedly showed a peak at m/z
784 ([(h -Ph2C3H3)Pd(1)]+).
Because our subsequent attempts at obtaining crystalline ma-
terials from [(h -Ph2C3H3)PdCl(1)] and [(h -Ph2C3H3)Pd(1)]ClO4
met with no success, we ultimately turned to h -methallyl com-
3
3
3
3
plexes with non-chiral ligand 1 as even simpler (an potentially
better crystallising) compounds (Scheme 5). Thus, the dipalladium
complex 14 reacted smoothly with 1 yielding the bridge-cleavage
product 16 in which the ferrocene ligand coordinates as a P-
monodentate donor. The reactions of 1 with complex 15, which
was obtained from 14 via halogen abstraction with AgClO4,13
proceeded under displacement of the coordinated acetonitrile
ligands to afford complex 17 featuring the amidophosphine as
an O,P-chelate donor or bis-phosphine complex 18 depending on
the Pd/1 molar ratio. According to NMR analysis of the reaction
mixtures, the complexation reactions proceed cleanly, affording
only the products specified.
Scheme 3
Coordination study
In order to gain an insight into the nature of putative reaction
intermediates and structural factors governing the reaction course,
we decided to synthesise and structurally characterise some
Complexes 16 and 17 are highly soluble in common organic
solvents and were therefore isolated by precipitation as yellow air-
stable solids showing a high tendency to hold solvent residua. The
3
model (h -allyl)palladium(II) complexes. Unfortunately, repeated
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Allylic CH2 groups in complex 18 are equivalent, being observed
as a pair of signals in the 1H NMR spectrum and one 13C NMR
resonance which overlaps with the solvent signal (dC ª 76.6).
Owing to the presence of two identical phosphine groups in
1
18, the 13C{ H} NMR signals due to carbons within the Ph2P-
substituted cyclopentadienyl and phenyl rings (except for CHpara
)
and signal of the allylic Cipso carbon are seen as characteristic non-
binomial triplets typical of virtually coupled ABX spin systems
of the type 12C–31P(A)–M–31P(B)–13C(X) (M = metal).14 Similar
features were observed in the spectra of bis-phosphine complexes
with other 1¢-functionalised (diphenylphoshino)ferrocene ligands,
trans-[PdCl2(Ph2PfcX-kP)2] (X = a functional group)15 and trans-
[W(CO)4(Ph2PfcCH CH2-kP)2].16
Crystal structures. Complex 15 (Fig. 1) crystallises in the
monoclinic space group P21/m so that both ions constituting
the structure reside on the crystallographic mirror planes, similar
3
to [Pd(h -C3H5)(MeCN)2]2(B10H10)·C6H6.17 Similarly to other p-
allyl complexes,18 the allyl plane is tilted with respect to the plane
defined by palladium and its ligating nitrogen atoms, {Pd, N, N¢},
at the dihedral angle of 117.4(2)◦. The Pd–Cterminal distance in 15
˚
is by ca. 0.04 A shorter than the Pd–Cmeso bond and the methyl
group in meso position is displaced from the allyl plane {C1, C2,
˚
C1¢} towards the Pd atom by 0.301(3) A. The geometry of the
Pd-NCMe moiety in 15 compares well with that in the mentioned
3
h -C3H5 complex. In the crystal, the ions constituting the structure
of 15 are interconnected via C–H ◊ ◊ ◊ O interactions19 into layers
oriented parallel to the ab plane.
3
Scheme 5 Preparation of (h -methallyl)palladium complexes.
solubility of complex 18 is relatively lower. It is noteworthy that
complex 16 did not appreciably react with BSA, NaN(SiMe)3 or
KOt-Bu (2 equiv.; reactions in CH2Cl2 at room temperature for ca.
20 h). In contrast, addition of NaH and stirring overnight caused
extensive decomposition.
1
Complexes 16–18 exhibit single resonances in their 31P{ H}
NMR spectra, shifted markedly to lower fields versus free 1 due
to P-coordination of the ferrocene ligand (cf. 16: dP = 11.6, 17:
dP = 20.8, 18: dP = 18.2; 1: dP = -16.9). Coordination of the amide
oxygen in 17 is manifested by a shift of the associated 13C NMR
resonance to lower fields (cf . dC(CONH) ca. 170 for 16 and 18,
and ca. 174 for 17) and further in IR spectra, where the amide
I band (largely nC O) moves to lower energies (1652/1655 cm-1
for 16/18 vs. 1596 cm-1 for 17) while the amide II band shifts in
the opposite direction (1538/1536 cm-1 for 16/18 and 1558 cm-1
for 17).6b,7a The response of the terminal ester group, which is not
Fig. 1 PLATON plot of the molecular structure of 15 (30% probability
1
level). Primed atoms are generated by the (x, - y, z) symmetry operation.
2
˚
Selected distances and angles (in A and deg): Pd–N 2.079(1), N–C4
involved in coordination, remains practically unaffected (nC
ª
O
1.131(2), C4–C5 1.454(2), Pd–N–C4 176.8(1), N–C4–C5 179.6(3); Pd–C1
2.103(2), Pd–C2 2.144(2), C1–C2 1.402(2), C2–C3 1.501(4), C1–C2–C1¢
114.7(2); Cl–O 1.429(2)–1.439(2), O–Cl–O 109.03(9)–109.8(1).
1750 cm-1, dC ª 170).
The non-equivalent allylic CH2 groups in 16 and 17 give rise
to two pairs of signals (Hsyn/anti) in the 1H NMR and two separate
1
signals in the 13C{ H} NMR spectra. For both compounds, the
The molecular structures of 16·H2O and 17 are presented in
Fig. 2 and 3. Selected distances and angles are given in Table 4.
The Pd-donor (Cl, O, P, and allyl carbons) distances in 16·H2O
low-field 13C NMR signals show splitting with 31P (dC 78.65 for 16,
83.34 for 17; 2JPC ca. 30 Hz) and can thus be attributed to the CH2
groups located trans to the phosphorus donor atom. The signals
due to CH2 trans to Cl or O appear as singlets at higher fields (dC
64.13 for 16, and 55.44 for 17). It is noteworthy that a larger differ-
ence in the 13C chemical shifts in this case corresponds to a larger
difference in trans-influence of the respective donor groups (DP/Cl
< DP/O) and also in the lengths of the Pd–CH2 bonds (see below).
3
and 17 are unexceptional in view of the data reported for [(h -
methallyl)PdCl(L-kP)] (L = PPh320 or Hdpf21) and the O,P-chelate
3
complexes [(m-O,P:O¢,P¢-L1)Pd2(h -C3H5)2](OTf)2 (L1 = (R,R)-
3
1,2-(2-Ph2PC6H4CONH)C6H10; Trost’s ligand),22 and [Pd(h -1,3-
2
5
Ph2C3H5)(L2-k O,P)] (L2 = [Fe(h -C5H3-1-PPh2-2-CONHCH2Ph)
(h -C5H5)].6b The allyl unit in 16·H2O extends away from the
5
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◦
Table 4 Selected geometric data (in A and ) for 16·H2O and 17a
˚
Parameter
16·H2O (X = Cl)d
17 (X = O1)
Pd–X
Pd–P
Pd–C30
Pd–C31
Pd–C32
X–Pd–P
X–Pd–C30
P–Pd–C32
C30–Pd–C32
C30–C31
C31–C32
C31–C33
C30–C31–C32
C30/C32–C31–C33
C11–O1
2.3730(8)
2.3163(7)
2.198(3)
2.173(3)
2.110(3)
106.09(3)
93.35(9)
93.56(9)
66.7(1)
1.394(4)
1.425(4)
1.485(5)
114.4(3)
122.0(3)/122.4(3)
1.235(3)
1.340(3)
121.6(2)
0.5(4)
2.142(3)
2.313(1)
2.210(5)
2.173(4)
2.087(4)
101.76(8)
94.2(1)
97.4(1)
67.0(2)
1.388(6)
1.428(6)
1.497(6)
114.9(4)
122.3(4)/121.9(4)
1.249(5)
1.326(4)
120.1(3)
3.3(6)
C11–N
O1–C11–N
O1–C11–N–C24
b
j
6.3(3)
21.8(5)
C25–O2
1.198(4)
1.328(4)
124.8(3)
1.647(1)
1.650(1)
3.4(2)
1.190(6)
1.335(5)
124.9(4)
1.645(2)
1.649(2)
5.9(3)
C25–O3
O2–C25–O3
Fe–Cg1
Fig. 2 PLATON plot of the complex molecule (major contributing part)
in 16·H2O. Displacement ellipsoids enclose the 30% probability level.
Fe–Cg2
∠Cp1,Cp2
c
t
85
63
a Definition of the ring planes: Cp1 = C(1–5), Cp2 = C(6–10). Cg1/2 denote
the respective ring centroids. b Dihedral angle subtended by the amide
{C11,O1,N} and Cp2 ring planes. c Torsion angle C1–Cg1–Cg2–C6. d Data
for the major contributing part (see Experimental).
closure of the O,P-chelate ring requires reorientation of the
cyclopentadienyl (Cp) rings and rotation of the amide plane
from an arrangement coplanar with its parent cyclopentadienyl
ring. The amide moieties C(O)NHCH2 in both structures are
practically planar (see the O1–C11–N–C24 torsion angles in
Table 4) but assume mutually opposite orientations. In 16·H2O,
the amide plane is oriented with its N atom to the side of the
phosphorus substituent while in 17 the amide oxygen is closer
to PPh2 due to chelation. Furthermore, the coordination results
in a slight elongation of the C O and shortening of the C–N
˚
amide bonds (uniformly by 0.014 A). Similar changes can be
Fig. 3 PLATON plot of the complex cation the crystal structure of 17.
detected in the structures of the mentioned bis[(allyl)palladium]
complex featuring Trost’s ligand22 and in Pd(II) complexes with
phosphinoferrocene carboxamides.6b,7a
Displacement ellipsoids enclose the 30% probability level.
ferrocene unit and above the amino acid residue whereas in 17 it is
embedded within a donor pocket created by the chelate ligand.23
The allyl planes are tilted with respect to the plane defined by the
Pd and the s-donor atoms (the dihedral angles are 115.5(3)◦ for
16·H2O and 112.1(5)◦ for 17) and the methyl substituent is inclined
towards palladium (the distances of the methyl carbon from the
It also is noteworthy that complex 16 isolated from the reaction
mixture is amorphous and does not crystallise under anhydrous
conditions. The crystallisation commences readily once some
adventitious water is present, affording the stoichiometric solvate
16·H2O. The reason for such behaviour becomes evident upon
inspection of the crystal assembly. The water molecules in 16·H2O
behave as molecular clips, connecting two adjacent molecules of
the complex into a centrosymmetric array via hydrogen bonds
to carbonyl oxygen as a bifurcate H-bond acceptor (Fig. 4). The
amide NH group oriented towards the (allyl)Pd unit forms an
intramolecular hydrogen bond with the Pd-bound chloride. On
the other hand, the solid-state packing of non-solvated 17 is
dominated by hydrogen bonds between NH25 and CH protons
as H-bond donors and perchlorate oxygen atoms as acceptors.
˚
˚
allyl planes are 0.271(5) A for 16·H2O and 0.248(6) A for 17). In
both structures, the Pd–C(allyl) bond lengths gradually decrease
from C30 to C32. A smaller absolute difference in 16·H2O (cf . ca.
˚
˚
0.09 A for 16·H2O and ca. 0.12 A for 17) corresponds with the
nature of donors in trans positions (trans-influence: PR3 > Cl >
O).24 The allylic C–C bond lengths follow a similar though less
pronounced trend.
Change in the mode of coordination such in 16·H2O and
17 obviously alters the geometry of the ferrocene ligand. The
11752 | Dalton Trans., 2011, 40, 11748–11757
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the Hdpf-based ligands, which may result in sterically crowded
intermediates and a diminished preference for a single reaction
intermediate.
Experimental
Materials and methods
All syntheses were performed under an argon atmosphere with
exclusion of the direct daylight. Solvents used in the synthe-
ses and catalytic tests were dried over by appropriate drying
agents and distilled under argon: dichloromethane (K2CO3),
1,4-dioxane, toluene and tetrahydrofuran (sodium metal). An-
hydrous acetonitrile and N,N-dimethylformamide were pur-
chased from Fluka. Methanol was distilled from MeONa.
Benzylamine and benzyl alcohol were distilled under vacuum.
Amino acid methyl ester hydrochlorides [H3NCH(R)CO2Me]Cl
(R = (S)-CH2CHMe2 and (S,S)-CHMeCH2Me) were pre-
pared by reactions of the respective amino acids with thionyl
chloride in dry methanol.28 Hdpf,29 ligand 17a and its chi-
ral analogues (2–4, 7–10),7b rac-1,3-diphenylprop-2-en-1-yl ac-
etate (11a),30 rac-ethyl-(1,3-diphenylprop-2-en-1-yl) carbonate
(11b),31 rac-N-benzyl-(1,3-diphenylprop-2-en-1-yl)amine (13),32
Fig. 4 Hydrogen bonding interactions (dashed lines) in the structure of
16·H2O. For clarity, only relevant hydrogen atoms and pivotal carbons
of the phenyl rings are shown. H-bond parameters are as follow◦s:
˚
O1W–H1W ◊ ◊ ◊ O1, O1W ◊ ◊ ◊ O1 = 2.863(3) A, angle at H1W = 167◦;
˚
O1W–H2W ◊ ◊ ◊ O1, O1W ◊ ◊ ◊ O1 = 2.895(3) A, angle at H2W = 172 ;
◦
˚
N1–H1N ◊ ◊ ◊ Cl, N1 ◊ ◊ ◊ Cl = 3.292(2) A, angle at H1N = 158 .
Discussion and conclusion
Unlike many other chiral phosphinoferrocene ligands obtained by
multi-step procedures, the chiral amides prepared by conjugation
of ferrocene phosphinocarboxylic acids with amino acid esters are
readily accessible in good yields and purity and, above all, are
highly structurally versatile. The results collected indicate that
these amides are efficient ligands for Pd-catalysed asymmetric
allylic alkylation. In the model reaction of dimethyl malonate
with in the presence of BSA, they produce the alkylation product
with up to 98% ee under optimised reaction conditions. On the
other hand, the ligands perform only poorly in the corresponding
amination and etherification reactions.
3
and [Pd(m-Cl)(h -MeC3H4)]2 (14)33 were prepared according to
literature procedures. Other chemicals (Aldrich, Fluka) and sol-
vents used for crystallisations and in chromatography (Lach-Ner)
were used as received.
NMR spectra were recorded with a Varian UNITY Inova 400
spectrometer (1H, 399.95 MHz, 13C, 100.58 MHz; and 31P, 161.90
MHz) at 298 K. Chemical shifts (d (ppm)) are given relative to
internal SiMe4 (1H and 13C) or to external 85% aqueous H3PO4
(31P). IR spectra were obtained with an FT IR Nicolet Magna 760
instrument. High resolution electrospray ionisation mass spectra
(ESI MS) were obtained with an LTQ Orbitrap XL spectrometer
(Thermo Fisher Scientific). Optical rotations were determined
with an automatic polarimeter Autopol III (Rudolph Research) at
room temperature.
The model coordination study expectedly demonstrated that
the phosphine-amide ligands coordinate the soft palladium(II)
ion26 preferentially via their soft P-donor site. At 1 : 1 metal-to-
ligand ratio, however, they form chelates. Although this has not
been proven in situ (i.e., under conditions mimicking exactly the
reaction mixture), the formation of chelated Pd(II) intermediates
appears to be the only plausible explanation for the observed
reaction outcome. Regardless of whether O,P- (neutral ligand)
or P,N-chelates (deprotonated ligand) are formed as catalytically
active intermediates, the chelation brings the chirality inherent in
the amino acid into a vicinity of the catalytic centre. The catalysed
reaction (conversion and ee) is then controlled largely by spatial
properties of the amino acid substituent. Besides, the coordination
of two different donor atoms leads to an electronic differentiation
Safety Note. Caution! Although we have not encountered any
problems it should be noted that perchlorate salts of metal
complexes with organic ligands are potentially explosive and
should be handled only in small quantities and with care.
Syntheses and catalytic tests
3
of allylic termini in (h -allyl)palladium(II) reaction intermediates
(see structural data above), which then react with relatively
different rates with the incoming nucleophile (preferentially at the
site opposite to the donor with a larger trans-influence).1,27
Increasing the Pd-to-ligand ratio to 1 : 2 results in the formation
of bis(phosphine) complexes, where the amino acid chirality is
located rather far from the catalytic centre. This particularly holds
true for ligands obtained from achiral Hdpf, with which only
racemic alkylation product was obtained at the Pd : L ratio of
1 : 2.
The situation becomes more complicated (and less predictable)
upon introduction of planar chirality into the system mostly
because the chirality elements may combine in a matched or a
mismatched manner (cf . the catalytic performance of (S,Sp)- and
(R,Sp)-8). In addition, the donor groups attached in positions 1
and 2 of the ferrocene moiety are closer to each other than in
N-[(1S)-1-methoxycarbonyl-3-methylbutyl] [1¢-(diphenylphos-
phino)ferrocene-1-carboxamide]
((S)-5). Hdpf
(207
mg,
0.50 mmol) and 1-hydroxybenzotriazole (81 mg, 0.60 mmol) were
mixed with dry dichloromethane (10 mL). The suspension was
cooled in an ice bath and treated with 1-(3-dimethylaminopropyl)-
3-ethylcarbodiimide (0.1 mL, 0.6 mmol). The resultant
mixture was stirred at 0 ◦C for 15 min, whereupon the
solids dissolved to give a clear orange-red solution. A mixture
of (S)-[H3NCH(CH2CHMe2)CO2Me]Cl (127 mg, 0.70 mmol),
triethylamine (0.1 mL, 0.8 mmol) and dichloromethane (20 mL)
prepared separately was introduced and the resulting mixture
was stirred at room temperature overnight. Then, it was washed
successively with 10% aqueous citric acid (25 mL), saturated
aqueous NaHCO3 (2¥ 25 mL), and brine (25 mL). The organic
phase was dried (MgSO4), evaporated under vacuum, and the
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orange residue was purified by column chromatography over
silica gel using dichloromethane/methanol (10 : 1, v/v) as the
eluent. A single orange band was collected and evaporated to
afford analytically pure (S)-5 as an orange solid (262 mg, 97%).
Asymmetric allylic alkylation. General procedure. Ligand
(12.5 mmol), [Pd(m-Cl)(h -C3H5)]2 (2.3 mg, 6.3 mmol) and alkali
3
metal acetate (25 mmol; if appropriate) were mixed with dry
dichloromethane (3 mL) and the mixture was stirred at room
temperature for 20 min. Allylic substrate (0.25 mmol; 63.1 mg
of acetate 11a or 70.6 mg of carbonate 11b) was added and, after
stirring for another 5 min, malonate ester (0.75 mmol; 0.09 mL
of dimethyl malonate or 0.17 mL of di-tert-butyl malonate) and
N,O-bis(trimethylsillyl)acetamide (BSA; 0.75 mmol, 0.19 mL)
were introduced successively. The resulting mixture was stirred
for 24 h at reaction temperature (see Table 1), and then diluted
with dichloromethane (3 mL) and washed with saturated aqueous
NH4Cl (2 ¥ 5 mL). The organic layer was separated, dried over
MgSO4, and evaporated under vacuum. Subsequent purification
by column chromatography (silica gel; hexane-ethyl acetate, 3 : 1
v/v) afforded the alkylation product 12 (or its mixture with 11a in
the case of incomplete conversions).
Conversions were determined by 1H NMR spectroscopy. Enan-
tiomeric excesses were established from 1H NMR spectra recorded
in C6D6 in the presence of the chiral lanthanide shift reagent tris(3-
trifluoroacetyl-d-camphorato)europium(III). The configuration of
the major component was assigned on the basis of optical
rotation.34
3
1H NMR NMR (CDCl3): d 0.96 (d, JHH = 6.4 Hz, 3 H,
3
CHMe2), 0.97 (d, JHH = 6.4 Hz, 3 H, CHMe2), 1.59–1.79 (m,
3 H, CH2CHMe2), 3.72 (s, 3 H, OMe), 4.08 (dq, J = 1.2, 3.1 Hz,
1 H, fc), 4.21 (dt, J = 1.3, 2.4 Hz, 1 H, fc), 4.23 (dt, J = 1.2, 2.4
Hz, 1 H, fc), 4.26 (dq, J = 1.2, 3.4 Hz, 1 H, fc), 4.43 (dt, J = 1.3,
2.5 Hz, 1 H, fc), 4.48 (dt, J = 1.2, 2.4 Hz, 1 H, fc), 4.53 (dt, J =
1.3, 2.6 Hz, 1 H, fc), 4.62 (dt, J = 1.3, 2.5 Hz, 1 H, fc), 4.72 (ddd,
3JHH = 5.0, 8.6, 9.1 Hz, 1 H, NHCH), 6.16 (d, 3JHH = 8.3 Hz, 1 H,
1
NH), 7.29–7.40 (m, 10 H, PPh2). 13C{ H} NMR (CDCl3): d 21.82
(CHMe2), 22.95 (CHMe2), 25.00 (CHMe2), 41.53 (CH2), 50.70
(NHCH), 52.25 (OMe), 69.53 (CH fc), 69.65 (d, JPC = 1 Hz, CH
fc), 71.76 (CH fc), 71.82 (d, JPC = 1 Hz, CH fc), 72.91 (d, JPC = 4
Hz, CH fc), 73.15 (d, JPC = 4 Hz, CH fc), 74.13 (d, JPC = 13 Hz, CH
fc), 74.60 (d, JPC = 15 Hz, CH fc), 76.06 (C-CONH fc), 128.29 (2¥
d, 3JPC = 7 Hz, CH PPh2), 128.78 (CH PPh2), 128.84 (CH PPh2),
2
2
133.35 (d, JPC = 9 Hz, CH PPh2), 133.54 (d, JPC = 10 Hz, CH
PPh2), 137.96 (d, 1JPC = 8 Hz, Cipso PPh2), 138.21 (d, 1JPC = 8 Hz,
Cipso PPh2), 169.86 (CONH), 173.69 (CO2Me). The signal due to
1
C-P of fc was not found. 31P{ H} NMR (CDCl3): d -16.9 (s). IR
(Nujol): nNH 3287 m, nCO 1731 vs, amide I 1622 vs, amide II 1539
Asymmetric allylic amination. General procedure. Ligand (S)-
vs; 1435 s, 1301 m, 1251 w, 1181 w, 1163 w, 1096 w, 1027 m, 997 w,
3
2 (6.2 mg, 12.5 mmol) and [Pd(m-Cl)(h -C3H5)]2 (2.3 mg, 6.3 mmol)
837 m, 744 s, 697 s, 497 m, 454 w cm-1. HR MS (ESI+) calc. for
were mixed with dry dichloromethane (3 mL) and the mix-
ture was stirred at room temperature for 20 min. Acetate 11a
(0.25 mmol, 63.1 mg was introduced and, after stirring for
another 5 min, benzylamine (0.75 mmol, 0.08 mL) and N,O-
bis(trimethylsillyl)acetamide (BSA; 0.75 mmol, 0.19 mL) were
added successively. The resulting mixture was stirred for 24 h or
48 h at room temperature, diluted with diethyl ether (5 mL) and
washed with saturated aqueous NH4Cl (2¥ 5 mL). The organic
layer was separated, dried over MgSO4, and concentrated under
vacuum. Subsequent purification by column chromatography
(silica gel; hexane-ethyl acetate, 3 : 1 v/v) afforded the alkylation
product (or its mixture with 11a in the case of incomplete
conversions).
Conversions were determined by 1H NMR spectroscopy. Enan-
tiomeric excesses were established by HPLC analysis using Daicel
Chiralcel OD-H column and hexane/2-propanol 99 : 1 (v/v) as
the eluent; tR((R)-13) = 18.4, tR((S)-13) = 19.8 min at a flow rate
of 0.50 mL min-1. The configuration was assigned on the basis
of optical rotation. Spectroscopic data of the product were in
accordance with the literature.35
◦
C30H33NO3PFe [M + H]+ 542.1547, found 542.1542. [aD]25 C +2 (c
0.5, CHCl3).
N-[(1S,2S)-1-methoxycarbonyl-2-methylbutyl]
[1¢-(diphenyl-
phosphino)ferrocene-1-carboxamide] ((S,S)-6). Amide (S,S)-6
was prepared similarly to (S)-5, starting with Hdpf (207 mg,
0.50 mmol), 1-hydroxybenzotriazole (81 mg, 0.60 mmol), 1-(3-
dimethylaminopropyl)-3-ethylcarbodiimide (0.1 mL, 0.6 mmol),
(S,S)-[H3NCH(CHMeCH2Me)CO2Me]Cl (127 mg, 0.7 mmol)
and triethylamine (0.1 mL, 0.8 mmol). Isolation as described
above afforded (S,S)-6 as an orange oil (255 mg, 94%).
1H NMR NMR (CDCl3): d 0.95 (t, 3JHH = 7.4 Hz, 3 H, CH2Me),
0.96 (d, 3JHH = 6.8 Hz, 3 H, CHMe), 1.25 (m, 1 H, CH2), 1.50 (m,
1H, CH2), 1.96 (m, 1 H, CHMe), 3.72 (s, 3 H, OMe), 4.10 (dq, J =
1.1, 3.0 Hz, 1 H, fc), 4.22 (m, 3 H, fc), 4.42 (dt, J = 1.2, 2.4 Hz, 1 H,
fc), 4.47 (dt, J = 1.2, 2.4 Hz, 1 H, fc), 4.54 (dt, J = 1.5, 2.5 Hz, 1 H,
fc), 4.60 (dt, J = 1.3, 2.4 Hz, 1 H, fc), 4.69 (dd, 3JHH = 5.0, 8.7 Hz, 1
H, NHCH), 6.16 (d, 3JHH = 8.7 Hz, 1 H, NH), 7.28–7.40 (m, 10 H,
1
PPh2). 13C{ H} NMR (CDCl3): d 11.60 (CH2Me), 15.74 (CHMe),
25.36 (CH2), 37.87 (CHMe), 52.08 (OMe), 56.38 (NHCH), 69.30
(CH fc), 69.65 (d, JPC = 1 Hz, CH fc), 71.79 (CH fc), 71.83 (d,
Asymmetric allylic etherification. General procedure. Ligand
3
JPC = 1 Hz, CH fc), 72.93 (d, JPC = 4 Hz, CH fc), 73.09 (d, JPC
=
(S)-2 (6.2 mg, 12.5 mmol) and [Pd(m-Cl)(h -C3H5)]2 (2.3 mg,
4 Hz, CH fc), 74.15 (d, JPC = 13 Hz, CH fc), 74.41 (d, JPC = 15
Hz, CH fc), 76.24 (C-CONH fc), 128.24 (2¥ d, JPC = 7 Hz, CH
6.3 mmol) were mixed with dry dichloromethane (3 mL) and the
mixture was stirred for 20 min. Then, acetate 11a (0.25 mmol,
63.1 mg was added and, after stirring for another 5 min, neat
benzyl alcohol (0.75 mmol, 0.08 mL) and a base (0.75 mmol;
0.19 mL of N,O-bis(trimethylsilyl)acetamide or 244 mg of Cs2CO3)
were added successively. The resulting mixture was stirred at
room temperature for 24 h or 48 h, diluted with diethyl ether
(5 mL) and washed with saturated aqueous NH4Cl (2¥ 5 mL). The
organic layer was separated, dried over MgSO4, and evaporated
under reduced pressure. Purification by column chromatography
(conditions as above) recovered only 11a.
3
2
PPh2), 128.66 (CH PPh2), 128.72 (CH PPh2), 133.35 (d, JPC
=
2
6 Hz, CH PPh2), 133.54 (d, JPC = 7 Hz, CH PPh2), 138.36 (d,
1JPC = 9 Hz, Cipso PPh2), 138.52 (d, 1JPC = 10 Hz, Cipso PPh2), 169.84
(CONH), 172.71 (CO2Me). The signal due to C-P of fc was not
found. 31P{ H} NMR (CDCl3): d -17.0 (s). IR (neat): nNH 3334
1
m, nCO 1743 vs, amide I 1652 vs, amide II 1520 vs; 1435 s, 1299 m,
1201 w, 1179 m, 1163 s, 1094 w, 1027 m, 998 w, 833 m, 746 s, 699
s, 497 s, 451 w cm-1. HR MS (ESI+) calc. for C30H33NO3PFe [M
◦
+ H]+ 542.1547, found 542.1541. [aD]25 -2 (c 0.5, CHCl3).
C
11754 | Dalton Trans., 2011, 40, 11748–11757
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©

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Preparation of palladium(II) complexes
[(g3-C3H4Me)Pd(1-j2O,P)]ClO4 (17). A solution of 1 (43 mg,
0.09 mmol) in chloroform (2 mL) was added to solid
[Pd(MeCN)2(h -C3H4Me)]ClO4 (15; 30 mg, 0.09 mmol). The
resulting mixture was stirred at room temperature for 1 h and then
poured into pentane (30 mL). After standing overnight at -18 ◦C,
the precipitated product was filtered off, washed with pentane and
dried under vacuum. Yield: 63 mg (96%), yellow solid.
[Pd(MeCN)2(g3-C3H4Me)]ClO4 (15). A solution of AgClO4
(415 mg, 2.0 mmol) in acetonitrile (5 mL) was added to a
dichloromethane solution of 14 (394 mg, 1.0 mmol in 10 mL). An
off-white precipitate formed immediately and the yellow colour
due to the starting Pd complex disappeared. The mixture was
stirred for 10 min in the dark and filtered. The colourless filtrate
was evaporated to an oil, which was taken up with acetonitrile
(5 mL). The solution was precipitated with diethyl ether (35 mL),
yielding an oil, which quickly crystallised. The separated product
was filtered off, washed with diethyl ether and dried under vacuum.
Yield: 542 mg (79%), white powdery solid. Note: The product is
quite stable in the air but deposits Pd(0) upon prolonged standing.
It appropriate, it can be purified by dissolving in acetonitrile,
filtration and precipitation with diethyl ether.
3
1H NMR NMR (CDCl3): d 2.18 (s, 3 H, Me allyl), 2.94 (br d,
3JHH = 2.0 Hz, 1 H, CH2 allyl), 3.10 (br q, 3JHH ª 2.6 Hz, 1 H, CH2
allyl), 3.68 (s, 3 H, OMe), 4.06 (d, 2JHH = 9.3 Hz, 1 H, CH2 allyl),
4.08 (br m, 1 H, P–C5H4), 4.16 (d, 3JHH = 6.0 Hz, 2 H, CH2NH),
3
4.29 (br m, 1 H, P–C5H4), 4.39 (br dt, JHH = 1.3, 2.6 Hz, 1 H,
C–C5H4), 4.44 (br dt, 3JHH = 1.3, 2.6 Hz, 1 H, C–C5H4), 4.64 (br
m, 1 H, P–C5H4), 4.71–4.76 (br m, 2 H, CH2 allyl + P–C5H4), 5.16
(br dt, 3JHH = 1.3, 2.6 Hz, 1 H, C–C5H4), 5.32 (br dt, 3JHH = 1.3,
2.6 Hz, 1 H, C–C5H4), 7.41–7.54 (m, 10 H, PPh2), 8.07 (t, 3JHH
=
1H NMR (CDCl3): d 2.16 (s, 3 H, Me allyl), 2.41 (s, 6 H,
5.9 Hz, 1 H, NH). 13C{ H} NMR (CDCl3): d 23.23 (Me allyl),
42.04 (CH2N), 52.16 (OMe), 55.44 (CH2 allyl), 71.56 (d, JPC = 49
Hz, Cipso P–C5H4), 71.73 (CH C–C5H4), 71.96 (CH C–C5H4), 72.71
(CH C–C5H4), 72.96 (CH C–C5H4), 73.85 (d, JPC = 7 Hz, CH P–
C5H4), 74.27 (d, JPC = 7 Hz, CH P–C5H4), 74.35 (Cipso C–C5H4),
75.00 (d, JPC = 10 Hz, CH P–C5H4), 75.76 (d, JPC = 12 Hz, CH
1
1
MeCN), 3.04 and 4.41 (2¥ br s, 2 H, CH2 allyl). 13C{ H} NMR
(CDCl3): d 3.13 (MeCN), 22.81 (Me allyl), 63.04 (CH2 allyl),
121.92 (MeCN), 134.41 (Cipso allyl). IR (Nujol): 2318 m, 2292
m, n3(ClO4) 1098/1082 vs composite, n1(ClO4) 931 w, 961 m, 839
m, n4(ClO4) 624 s cm-1. Anal. calc. for C8H13ClNO4Pd: C 28.01,
H 3.82, N 8.17%. Found: C 28.23, H 3.95, N 8.24%.
2
3
P–C5H4), 83.34 (d, JPC = 27 Hz, CH2 allyl), 129.01 (d, JPC = 10
3
Hz, CHmeta PPh2), 129.07 (d, JPC = 10 Hz, CHmeta PPh2), 131.19
[(g3-C3H4Me)PdCl(1-jP)] (16). A solution of 1 (146 mg,
(d, 4JPC = 2 Hz, CHpara PPh2), 131.29 (d, 4JPC = 2 Hz, CHpara PPh2),
3
0.30 mmol) in chloroform (3 mL) was added to solid [Pd(m-Cl)(h -
132.00 (d, 1JPC = 45 Hz, Cipso PPh2), 132.77 (d, 2JPC = 13 Hz, CHortho
2
2
C3H4Me)]2 (14; 59 mg, 0.15 mmol). The reaction mixture was
stirred at room temperature for 1 h and then poured into pentane
(30 mL). After standing at -18 ◦C overnight, the precipitated
product was filtered off, washed thoroughly with pentane and
dried under vacuum. Yield: 195 mg (95%), yellow solid.
PPh2), 133.01 (d, JPC = 14 Hz, CHortho PPh2), 136.09 (d, JPC = 5
Hz, Cipso allyl), 169.51 (CO2Me), 174.12 (CONH). 31P{ H} NMR
1
(CDCl3): d 20.8 (s). IR (Nujol): nNH 3350 m, nCO 1754 vs, 1652 m,
amide I 1596 vs, amide II 1558 vs, 1436 vs, 1311 m, 1213 s, 1198 s,
1169 s, n3(ClO4) 1097 br vs, n1(ClO4) 930 w, 908 w, 837 m, 750 s, 697
vs, n4(ClO4) 624 vs, 471 vs. cm-1. ESI MS: m/z 646 ([M - ClO4]+;
i.e., the cation). Anal. calc. for C30H31ClFeNO7PPd·0.25C5H12: C
49.27, H 4.53, N 1.82%. Found: C 49.27, H 4.68, N 2.02%. The
amount of solvent was verified by NMR.
1H NMR NMR (CDCl3): d 1.89 (s, 3 H, Me allyl), 2.47 (s, 1
2
H, CH2 allyl), 2.81 (s, 1 H, CH2 allyl), 3.51 (d, JHH = 10 Hz, 1
H, CH2 allyl), 4.29 (m, 1 H, C–C5H4), 3.72 (s, 3 H, OMe), 3.90
(m, 1 H, C–C5H4), 3.94 (dd, 2JHH = 17.5 Hz, 3JHH = 5.8 Hz, 1 H,
CH2NH), 4.21 (dd, 2JHH = 17.5 Hz, 3JHH = 6.4 Hz, 1 H, CH2NH),
[(g3-C3H4Me)Pd(1-jP)2]ClO4 (18) was prepared and isolated
similarly to 17, using 14 (34 mg, 0.10 mmol) and 1 (97 mg,
0.20 mmol). Yield: 119 mg (97%), yellow powder.
2
3
4.29 (m, 1 H, P–C5H4), 4.44 (dd, JHH = 6.8 Hz, JPH = 3.0 Hz,
1 H, CH2 allyl), 4.61 (m, 1 H, P–C5H4), 4.70 (m, 1 H, P–C5H4),
4.81 (m, 1 H, P–C5H4), 5.02 (m, 1 H, C–C5H4), 5.31 (m, 1 H, C–
C5H4), 7.31–7.54 (m, 8 H, PPh2), 7.79–7.86 (m, 2 H, PPh2), 7.92
1H NMR NMR (CDCl3): d 1.84 (s, 3 H, Me allyl), 3.47 (m, 2
3
1
(t, 3JHH = 5.9 Hz, 1 H, NH). 13C{ H} NMR (CDCl3): d 23.12 (Me
H, CH2 allyl), 3.69 (dt, JHH = 1.3, 2.6 Hz, 2 H, C–C5H4), 3.73
3
(s, 8 H, OMe and CH2 allyl), 3.78 (dt, JHH = 1.3, 2.6 Hz, 2 H,
allyl), 41.05 (CH2N), 51.96 (OMe), 64.13 (CH2 allyl), 70.07 (CH
C–C5H4), 70.32 (CH C–C5H4), 71.94 (2C, CH C–C5H4), 73.37 (d,
JPC = 10 Hz, CH P–C5H4), 73.55 (d, JPC = 6 Hz, CH P–C5H4), 74.25
(d, JPC = 46 Hz, Cipso P–C5H4), 74.41 (d, JPC = 9 Hz, CH P–C5H4),
C–C5H4), 4.09–4.13 (m, 6 H, CH2NH and P–C5H4), 4.19 (br s,
3
2 H, P–C5H4), 4.61 (m, 2 H, P–C5H4), 4.63 (dt, JHH = 1.2, 2.6
3
Hz, 2 H, P–C5H4), 4.64 (m, 2 H, C–C5H4), 4.68 (dt, JHH = 1.3,
3
2
2.6 Hz, 2 H, C–C5H4), 7.04 (t, JHH = 5.9 Hz, 2 H, NH), 7.24–
76.90 (Cipso C–C5H4), 78.65 (d, JPC = 32 Hz, CH2 allyl), 128.29
1
7.51 (m, 20 H, PPh2). 13C{ H} NMR (CDCl3): d 23.48 (Me allyl),
(d, 3JPC = 10 Hz, CHmeta PPh2, 4C), 129.77 (d, 4JPC = 1 Hz, CHpara
PPh2), 130.26 (d, 4JPC = 2 Hz, CHpara PPh2), 132.27 (d, 2JPC = 12 Hz,
41.25 (CH2NH), 52.12 (OMe), 69.66 (CH C–C5H4), 69.95 (CH
C–C5H4), 72.13 (CH C–C5H4), 72.36 (CH C–C5H4), 73.69 (t, J¢ =
6 Hz, CH P–C5H4), 73.93 (t, J¢ = 4 Hz, CH P–C5H4), 74.08 (t,
J¢ = 4 Hz, CH P–C5H4), 74.58 (t, J¢ = 7 Hz, CH P–C5H4), ca. 76.6
(CH2 allyl; partly obscured by the solvent signal), 78.25 (t, J¢ =
23 Hz, Cipso P–C5H4), 128.70 (t, J¢ = 5 Hz, CHmeta PPh2), 128.78
(t, J¢ = 5 Hz, CHmeta PPh2), 130.94 (CHpara PPh2), 131.29 (CHpara
PPh2), 131.40 (d, J¢ = 23 Hz, Cipso PPh2), 132.08 (d, J¢ = 23 Hz,
Cipso PPh2), 132.85 (t, J¢ = 6 Hz, CHortho PPh2), 133.20 (t, J¢ = 7
Hz, CH PPh2), 137.70 (t, J¢ = 5 Hz, Cipso allyl), 169.68 (CONH),
170.59 (CO2Me). The resonance due to Cipso of C–C5H4 overlaps
CHortho PPh2), 133.37 (d, 2JPC = 5 Hz, Cipso allyl), 133.69 (d, 2JPC
=
1
12 Hz, CHortho PPh2), 135.06 (d, JPC = 43 Hz, Cipso PPh2), 137.56
1
(d, JPC = 44 Hz, Cipso PPh2), 170.05 (CONH), 170.82 (CO2Me).
A resonance due to one CH of P–C5H4 is obscured by the solvent
1
signal. 31P{ H} NMR (CDCl3): d 11.6 (s). IR (Nujol): nNH 3305
m, nCO 1750 vs, amide I 1652 vs, amide II 1538 vs, 1436 vs, 1304 m,
1211 s, 1196 s, 1178 s, 1098 m, 1172 w, 1030 m, 979 w, 837 m, 750
s, 697 vs, 629 w, 617 w, 519 m, 497 w, 471 w cm-1. ESI MS: m/z
646 ([M - Cl]+). Anal. calc. for C30H31ClFeNO3PPd ·0.15 CH2Cl2:
C 52.10, H 4.54, N 2.02%. Found: C 52.19, H 4.54, N 1.79%. The
amount of solvent was confirmed by NMR.
1
with the signal of solvent. 31P{ H} NMR (CDCl3): d 18.2 (s). IR
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Table 5 Summary of crystallographic parameters, data collection and structure refinement parameters for 15, 16·H2O and 17a
Compound
15
16·H2O
17
Formula
M
C8H13ClN2O4Pd
343.05
C30H33ClFeNO4PPd
700.24
C30H31ClFeNO7PPd
746.23
Crystal system
Space group
Monoclinic
P21/m (no. 14)
7.3756(2)
10.4597(3)
8.3592(2)
95.8421(17)
641.53(3)
2
1.655
0.654–0.750
8315
1543
1505
Monoclinic
P21/c (no. 14)
10.0468(7)
30.550(2)
9.7502(7)
105.252(4)
2887.2(3)
4
1.310
0.603–0.711
28502
6639
5960
Monoclinic
P21/n (no. 14)
14.4397(6)
15.1067(6)
15.0910(7)
112.494(1)
3041.4(2)
4
1.256
0.641–0.746
26854
6962
4760
˚
a/A
˚
b/A
˚
c/A
b (◦)
3
˚
U/A
Z
m(Mo-Ka)/mm-1
Tb
Diffrns collected
Unique diffrns
Obsdc diffrns
Rintd/%
2.78
1.76
1.80, 4.45
0.41, –0.46
823874
2.65
3.22
3.77, 7.47
0.54 –0.46
823875
3.96
3.86
7.69, 10.3
2.02,e –1.15
823876
Rd obsd diffrns/%
R, wRd all data/%
-3
˚
Dr/e A
CCDC entry
ꢀ
ꢀ
2
a Common details: T = 150(2)K. b The range of transmission factors. c Observed diffractions with I > 2s(I). d Rint
=
|Fo - Fo2(mean)|/ Fo2, where
ꢀ
ꢀ
ꢀ
ꢀ
Fo2(mean) is the average intensity of symmetry-equivalent diffractions. R = ꢀFo| - |Fcꢀ/ |Fo|, wR = [ {(wFo - Fc2)2}/ (wFo2)2]1/2
.
e Residual
2
electron density in vicinity of the Pd atom.
(Nujol): nNH 3385 m, nCO 1753 vs, amide I 1655 vs, amide II 1536
vs, 1437 vs, 1303 m, 1211 s, 1196 s, 1177 s, 1164 m, 1101 vs, 1037
m, 1000 w, 839 w, 748 m, 697 s, 624 m, 484 s cm-1. MS (ESI+): m/z
1131 ([(C3H4Me)Pd(1)2]+), 938, 646 ([(C3H4Me)Pd(1)]+). Anal.
calc. for C56H55ClFe2N2O10P2Pd·0.15C5H12: C 54.86, H 4.61, N
2.26%. Found: C 54.87, H 4.90, N 2.00%. The presence of solvent
was verified by NMR.
Acknowledgements
This work was supported by the Grant Agency of Charles
University in Prague (project no. 58009) and by the Ministry
of Education of the Czech Republic (project nos. LC06070 and
MSM0021620857).
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This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 11748–11757 | 11757
©