Organo-palladium(ii) complexes bearing unsymmetrical N,N,N-pincer ligands: Synthesis, structures and oxidatively induced coupling reactions

Article abstract of DOI:10.1039/c5dt00216h

The 2-(2′-aniline)-6-imine-pyridines, 2-(C₆H₄-2′-NH₂)-6-(CMe=NAr)C₅H₃N (Ar = 4-i-PrC₆H₄ (HL1a), 2,6-i-Pr₂C₆H₃ (HL1b)), have been synthesised via sequential Stille cross-coupling, deprotection and condensation steps from 6-tributylstannyl-2-(2-methyl-1,3-dioxolan-2-yl)pyridine and 2-bromonitrobenzene. The palladium(ii) acetate N,N,N-pincer complexes, [{2-(C₆H₄-2′-NH)-6-(CMe=NAr)C₅H₃N}Pd(OAc)] (Ar = 4-i-PrC₆H₄ (1a), 2,6-i-Pr₂C₆H₃ (1b)), can be prepared by reacting HL1 with Pd(OAc)₂ or, in the case of 1a, more conveniently by the template reaction of ketone 2-(C₆H₄-2′-NH₂)-6-(CMe=O)C₅H₃N, Pd(OAc)₂ and 4-isopropylaniline; ready conversion of 1 to their chloride analogues, [{2-(C₆H₄-2′-NH)-6-(CMe=NAr)C₅H₃N}PdCl] (Ar = 4-i-PrC₆H₄ (2a), 2,6-i-Pr₂C₆H₃ (2b)), has been demonstrated. The phenyl-containing complexes, [{2-(C₆H₄-2′-NH)-6-(CMe=NAr)C₅H₃N}PdPh] (Ar = 4-i-PrC₆H₄ (3a), 2,6-i-Pr₂C₆H₃ (3b)), can be obtained by treating HL1 with (PPh₃)₂PdPh(Br) in the presence of NaH or with regard to 3a, by the salt elimination reaction of 2a with phenyllithium. Reaction of 2a with silver tetrafluoroborate or triflate in the presence of acetonitrile allows access to cationic [{2-(C₆H₄-2′-NH)-6-(CMe=N(4-i-PrC₆H₄)C₅H₃N}Pd(NCMe)][X] (X = BF₄ (4), X = O₃SCF₃ (5)), respectively; the pyridine analogue of 5, [{2-(C₆H₄-2′-NH)-6-(CMe=N(4-i-PrC₆H₄)C₅H₃N}Pd(NC₅H₅)][O₃SCF₃] (5′), is also reported. Oxidation of phenyl-containing 3a with one equivalent of 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor) in acetonitrile at low temperature leads to a new palladium species that slowly decomposes to give 4 and biphenyl; biphenyl formation is also observed upon reaction of 3a with XeF₂. However, no such oxidatively induced coupling occurs when using 3b. Single crystal X-ray diffraction studies have been performed on HL1b, 1a, 1b, 2a, 2b, 3a, 3b and 5′.

Full text of DOI:10.1039/c5dt00216h

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Organo-palladium(II) complexes bearing
unsymmetrical N,N,N-pincer ligands: synthesis,
structures and oxidatively induced coupling
reactions†
Cite this: DOI: 10.1039/c5dt00216h
Luka A. Wright,a Eric G. Hope,a Gregory A. Solan,*a Warren B. Crossa,b and
Kuldip Singha
The 2-(2’-aniline)-6-imine-pyridines, 2-(C6H4-2’-NH2)-6-(CMevNAr)C5H3N (Ar = 4-i-PrC6H4 (HL1a),
2,6-i-Pr2C6H3 (HL1b)), have been synthesised via sequential Stille cross-coupling, deprotection and con-
densation steps from 6-tributylstannyl-2-(2-methyl-1,3-dioxolan-2-yl)pyridine and 2-bromonitro-
benzene. The palladium(II) acetate N,N,N-pincer complexes, [{2-(C6H4-2’-NH)-6-(CMevNAr)C5H3N}Pd-
(OAc)] (Ar = 4-i-PrC6H4 (1a), 2,6-i-Pr2C6H3 (1b)), can be prepared by reacting HL1 with Pd(OAc)2 or, in
the case of 1a, more conveniently by the template reaction of ketone 2-(C6H4-2’-NH2)-6-(CMevO)-
C5H3N, Pd(OAc)2 and 4-isopropylaniline; ready conversion of 1 to their chloride analogues, [{2-(C6H4-2’-
NH)-6-(CMevNAr)C5H3N}PdCl] (Ar = 4-i-PrC6H4 (2a), 2,6-i-Pr2C6H3 (2b)), has been demonstrated. The
phenyl-containing complexes, [{2-(C6H4-2’-NH)-6-(CMevNAr)C5H3N}PdPh] (Ar = 4-i-PrC6H4 (3a), 2,6-
i-Pr2C6H3 (3b)), can be obtained by treating HL1 with (PPh3)2PdPh(Br) in the presence of NaH or with
regard to 3a, by the salt elimination reaction of 2a with phenyllithium. Reaction of 2a with silver tetrafluoro-
borate or triflate in the presence of acetonitrile allows access to cationic [{2-(C6H4-2’-NH)-6-(CMev
N(4-i-PrC6H4)C5H3N}Pd(NCMe)][X] (X = BF4 (4), X = O3SCF3 (5)), respectively; the pyridine analogue of 5,
[{2-(C6H4-2’-NH)-6-(CMevN(4-i-PrC6H4)C5H3N}Pd(NC5H5)][O3SCF3] (5’), is also reported. Oxidation of
phenyl-containing 3a with one equivalent of 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo-[2.2.2]octane
bis(tetrafluoroborate) (Selectfluor™) in acetonitrile at low temperature leads to a new palladium species
that slowly decomposes to give 4 and biphenyl; biphenyl formation is also observed upon reaction of 3a
with XeF2. However, no such oxidatively induced coupling occurs when using 3b. Single crystal X-ray
diffraction studies have been performed on HL1b, 1a, 1b, 2a, 2b, 3a, 3b and 5’.
Received 16th January 2015,
Accepted 6th March 2015
DOI: 10.1039/c5dt00216h
www.rsc.org/dalton
developments have been reagents such as Selectfluor™
[1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis-
Introduction
Recent years have seen a surge of interest in oxidatively (tetrafluoroborate)] and xenon difluoride that can oxidise the
induced coupling reactions involving Pd(III) and Pd(IV) inter- metal centre as a two electron oxidant (from Pd(II) to Pd(IV))4,5
mediates due, in part, to their potential to promote transform- or as a one electron oxidant (from Pd(II) to Pd(III))6,7 and more-
ations inaccessible using the conventional low valent Pd(0)/(II) over provide a source of F (e.g., as F+ or F•). In cases where
cycle.1–3 For example, the historically challenging arene–fluor- these types of oxidant deliver a fluorine atom direct to the
ide bond forming reaction has become a reality with both metal centre, selective C–F reductive elimination from the
types of high valent intermediate isolated and/or proposed in high valent organo–metal intermediate can be challenging as
reaction pathways derived from Pd(II) species.3 Central to these alternative (and potentially desirable) degradation pathways
can prove competitive.3d Sanford, for example, has reported
that the Pd(IV) mono-aryl complex, [(4,4-t-Bu2bipy)Pd(Ar)-
aDepartment of Chemistry, University of Leicester, University Road, Leicester LE1
7RH, UK. E-mail: gas8@leicester.ac.uk
(F)2(FHF)] (Ar = 4-FC6H4), only undergoes selective Caryl–F
reductive elimination when heated in the presence of excess
oxidant, otherwise competitive Ar–Ar coupling occurs through
a process described as σ-aryl exchange between metal centres.5
Indeed this type of intermolecular Ar–Ar coupling involving
palladium mono-aryl species has some precedent in Pd(II) and
bSchool of Science and Technology, Nottingham Trent University, Clifton Lane,
Nottingham NG11 8NS, UK
†Electronic supplementary information (ESI) available. CCDC 1043191–1043198.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c5dt00216h
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modest yield (see later for a higher yielding template approach
to L1a). The precursor ketone and the two N,N,N pro-ligands,
HL1a and HL1b, have been characterised using a combination
1
of electrospray mass spectrometry, IR, H NMR and 13C NMR
spectroscopy (see Experimental section).
Compounds, HL1a, and HL1b, both display protonated
molecular ions peaks in their electrospray mass spectra and
downfield shifted signals for the amino protons (range:
δ 5.72–5.79) in their 1H NMR spectra. Characteristic imine
stretching frequencies of ca. 1638 cm−1 are seen in their IR
Fig. 1 N,N,N palladium(II) mono-aryl pincer, 3, and the stoichiometric spectra as are higher wavenumber bands corresponding to the
reactivity to be examined.
N–H stretches. Further confirmation of the composition of
HL1b was achieved in the form of a single crystal X-ray
determination.
A perspective view of HL1b is depicted in Fig. 2; selected
Pd(III) chemistry involving complexes bearing a variety of
bond distances and angles are listed in Table 1. The structure
multidentate ligands.2c,8,9
consists of a central pyridine ring that is substituted at its
Given the apparent variation in coupling events that can
2-position by a phenyl-2′-amine group and at the 6-position by
occur from a high valent organo-Pd species,1–7 we have been
interested in exploring the influence of a supporting multi-
dentate ligand on the oxidatively induced reaction pathway.
Herein, we report the reactivity of a family of N,N,N-pincer
a trans-configured N-arylimine unit [C(7)–N(1) 1.277(3) Å].
The pyridine nitrogen atoms adopt a cis conformation with
respect to the neighbouring aniline nitrogen (tors: N(2)–C(13)–
C(14)–C(15) 8.1°) as a result of a hydrogen-bonding interaction
bearing Pd(II) mono-phenyl complexes of the type, [{2-(C6H4-
between one of the amino hydrogen atoms and the pyridine
2-NH)-6-(CMevNAr)C5H3N}PdPh] (Ar
= aryl (3)), towards
nitrogen [N(3)⋯N(2) 2.675 Å]; a similar arrangement has been
Selectfluor and XeF2 (Fig. 1);10 as an additional point of inter-
est the effects that steric variation (Ar = 4-i-PrC6H4, 2,6-i-
Pr2C6H3) has on the reactivity, will be investigated. Further-
more, we report the full synthetic details for the preparation of
the novel pro-ligands (HL1) and their palladium(II) acetate (1),
chloride (2) and phenyl (3) derivatives.
reported for a related quinolinyl-substituted aniline.11
Palladium(II) complexes of L1
Interaction of HL1b with Pd(OAc)2 at 60 °C in toluene gave on
work-up, [{2-(C6H4-2-NH)-6-(CMevN(2,6-i-Pr2C6H3))C5H3N}Pd-
(OAc)] (1b)), in good yield (Scheme 2). While [{2-(C6H4-2-NH)-
6-(CMevN(4-i-PrC6H4))C5H3N}Pd(OAc)] (1a) could also be
made by this route, it was more conveniently prepared by the
template reaction of ketone 2-(C6H4-2-NH2)-6-(CMevO)C5H3N,
Results and discussion
Preparation of pro-ligand HL1
The 2-(2′-aniline)-6-imine-pyridines, 2-(C6H4-2′-NH2)-6-(CMev Pd(OAc)2 and 4-isopropylaniline. Compounds 1 can be readily
NAr)C5H3N (Ar = 4-i-PrC6H4 (HL1a), 2,6-i-Pr2C6H3 (HL1b)), converted to their chloride analogues, [{2-(C6H4-2-NH)-
have been prepared in reasonable yield via sequential Stille 6-(CMevNAr)C5H3N}PdCl] (Ar = 4-i-PrC6H4 (2a), 2,6-i-Pr2C6H3
coupling, deprotection and condensation reactions from 6-tri- (2b)), by treatment of a dichloromethane solution of 1 with
butylstannyl-2-(2-methyl-1,3-dioxolan-2-yl)pyridine and 2-bromo- aqueous sodium chloride. All four complexes are air stable
nitrobenzene (Scheme 1). For both HL1a and HL1b, the and have been characterised using a combination of FAB mass
condensation step proved sluggish in alcoholic media but pro- spectrometry, IR and NMR (1H and 13C) spectroscopy and
ceeded more effectively by running the reaction in the neat elemental analyses (see Experimental section). In addition,
aniline at high temperature; nevertheless problems encoun- crystals of each complex have been the subject of single crystal
tered in the work-up of HL1a resulted in its isolation in only a X-ray diffraction studies.
Scheme 1 Reagents and conditions: (i) 2-BrC6H4NO2, cat. Pd(OAc)2–PPh3, toluene, 100 °C, microwave; (ii) SnCl2, ethanol; (iii) HCl(aq.); (iv) ArNH2,
225 °C.
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Fig. 2 Molecular structure of HL1b, including a partial atom numbering
scheme. All hydrogen atoms, apart from H3A and H3B, have been
omitted for clarity.
Fig. 3 A segment of the network based on 1a linked by water mole-
cules. A partial atom numbering scheme is included while all hydrogen
atoms, apart from H3 and those belonging to the water molecule, have
been omitted for clarity; dotted lines show the intermolecular hydro-
gen-bonding interactions.
Table 1 Selected bond distances (Å) and angles (°) for HL1b
Bond lengths
C(15)–N(3)
C(7)–N(1)
C(7)–C(8)
1.366(4)
1.277(3)
1.504(4)
C(13)–C(14)
C(7)–C(9)
1.477(4)
1.482(4)
Bond angles
C(8)–C(7)–N(1)
125.3(2)
C(9)–C(7)–N(1)
116.4(3)
Views of acetate-containing 1a and 1b are given in Fig. 3
and 4; selected bond distances and angles are collected for
both structures in Table 2. There are two independent mole-
cules for 1b in the unit cell (A and B) which differ most notice-
ably in the relative inclination of neighbouring pyridyl and
anilido ring planes (vide infra). The structures of 1a and 1b are
similar consisting of a four-coordinate palladium centre
bound by a tridentate monoanionic 2-(2′-anilido)-6-imine-pyri-
dine ligand and a monodentate O-bound acetate, but contrast
in the nature of the hydrogen bonding involving the acetate
ligand. In 1a, a water molecule present within the unit cell
links the palladium-acetate units to form a hydrogen-bonded
network [O(1)acetate⋯O(3)water 2.837, O(3)water⋯O(2A)acetate
2.877 Å], while in 1b the hydrogen bonding is intramolecular
in origin involving the pendant acetate oxygen and the anilido
proton [N(3)⋯O(2)acetate 2.799A, 2.889B Å]. Within the N,N,N-
ligand there are both 5- and 6-membered chelate rings with
the bite angle for the 6-membered ring being more compatible
with the square planar geometrical requirements of the
Fig. 4 Molecular structure of 1b (molecule A) including a partial atom
numbering scheme. All hydrogen atoms, apart from H3 have been
omitted for clarity.
palladium(II) centre [N(3)–Pd(1)–N(2)6-membered: 93.7(2) (1a),
92.2(3)A, 93.6(2)B (1b) vs. N(2)–Pd(1)–N(1)5-membered 82.2(2) (1a),
82.6(3)A, 82.1(2)B° (1b)]. In both cases some twisting of the
anilido unit with respect to the adjacent pyridyl plane is appar-
ent [tors. N(2)–C(13)–C(14)–C(15) 3.6(4) (1a), 4.9(4)A, 9.0(5)B°
(1b)]. For a given complex, the Pd–Nimine bond distance is the
longest of the three metal–ligand interactions involving the
N,N,N-ligand followed by the Pd–Npyridine distance and then
by the Pd–Nanilido distance which is best exemplified for 1a
Scheme 2 Reagents and conditions: (i) Pd(OAc)2, toluene, 60 °C; (ii) NaCl(aq.), CH2Cl2, RT.
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Table 2 Selected bond distances (Å) and angles (°) for 1a and 1b
Table 3 Selected bond distances (Å) and angles (°) for 2a and 2b
1b
2a
1a
Molecule A
Molecule B
Molecule A
Molecule B
2b
Bond lengths
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–O(1)
C(7)–N(1)
C(9)–C(7)
C(15)–N(3)
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(3)
N(1)–Pd(1)–O(1)
N(2)–Pd(1)–N(3)
N(3)–Pd(1)–O(1)
Bond lengths
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–Cl(1)
C(7)–N(1)
C(15)–N(3)
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(3)
N(2)–Pd(1)–N(3)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
N(3)–Pd(1)–Cl(1)
2.014(6)
1.963(5)
1.932(5)
2.036(5)
1.286(8)
1.469(9)
1.347(9)
2.017(8)
1.970(9)
1.920(9)
2.011(8)
1.285(12)
1.468(13)
1.316(12)
2.019(8)
1.977(7)
1.922(8)
2.021(7)
1.300(11)
1.458(13)
1.323(12)
2.022(5)
1.976(5)
1.934(5)
2.2971(18)
1.297(7)
1.335(8)
2.035(6)
1.984(5)
1.931(6)
2.2931(18)
1.298(7)
1.334(8)
2.025(3)
1.987(3)
1.927(3)
2.3123(17)
1.289(5)
1.336(5)
81.6(2)
174.4(2)
93.1(2)
96.66(16)
178.21(17)
88.54(16)
82.2(3)
174.0(2)
92.2(3)
96.56(17)
175.39(15)
89.14(17)
82.01(13)
173.63(13)
91.91(13)
97.63(10)
179.27(9)
88.47(10)
82.2(2)
174.6(3)
93.8(2)
93.7(2)
90.3(2)
82.6(3)
174.3(3)
89.6(3)
92.2(3)
95.6(3)
82.1(2)
174.4(2)
93.8(2)
93.6(2)
90.5(2)
Replacing a chloride for an O-bound acetate has little effect
on the trans Pd–Npyridine distance [1.976(5)A, 1.984(5)B (2a),
1.987(3) (2b) vs. 1.963(5) (1a), 1.970(9)A 1.977(7)B Å (1b)].
Unlike 1b, the anilido NH proton is not involved in any inter-
or intra-molecular contacts of note.
[Pd(1)–N(1)imine 2.014(6) > Pd(1)–N(2)pyridine 1.963(5) > Pd(1)–
N(3)anilido 1.932(5) Å]. The N-aryl groups are inclined towards
orthogonality with regard to the neighbouring CvNimine
vector [tors. C(7)–N(1)–C(1)–C(6) 87.6(4) (1a), 86.4(4)av° (1b)],
with the 2,6-diisopropyl substitution on the N-aryl group in 1b
additionally providing some steric protection to the axial sites
of the palladium centre. The closest crystallographically
characterised comparators to 1 are the phenolate-containing
Complexes 1a, 1b, 2a and 2b, all display molecular ion
peaks in their FAB mass spectra along with fragmentation
peaks corresponding to the loss of an acetate or a chloride,
respectively. In their IR spectra the imine stretching frequen-
cies are shifted between 28 and 35 cm−1 to lower wavenumber
in comparison with the corresponding free HL1, characteristic
of imine-nitrogen coordination.13–15 In 1b and 2b two distinct
counterparts,
[{2-(C6H4-2′-O)-6-(CMevNAr)C5H3N}Pd(OAc)]
(Ar = 4-i-PrC6H4, 2,6-i-Pr2C6H3), which display similar bonding
characteristics.12
A view of chloride-containing 2b is given in Fig. 5; selected
bond distances and angles are collected for both 2a and 2b in
Table 3. The two independent molecules present in the unit
cell for 2a (A and B) differ most noticeably in the inclination of
the N-aryl plane to the adjacent imine unit. The structures of
2a and 2b are similar to those of their acetate precursors (1)
with a tridentate monoanionic 2-(2′-anilido)-6-imine-pyridine
filling three coordination sites of the distorted square planar
geometry but differ with a chloride now filling the fourth site.
1
doublets are seen for the isopropyl methyl groups in their H
NMR spectra consistent with some restricted rotation about
the N-2,6-diisopropylphenyl bond in solution. The acetate
1
methyl groups in 1 can be seen at δ ca. 1.5 in their H NMR
spectra with the MeC(O)O carbon atoms observable at δ
ca. 177.1 in their 13C NMR spectra. The anilido NH proton in 2
is observable at a similar chemical shift (ca. δ 5.8) to that seen
in free HL1, but in acetate-containing 1 there is some variation
with that observed in 1b being more downfield (δ 5.60 (1a),
7.39 (1b)); this is likely to be due to the influence of the intra-
molecular NH⋯Oacetate hydrogen bonding seen in 1b (see
Fig. 4). As with related monodentate acetate complexes, 1a and
1b both show strong bands assignable to the symmetric and
asymmetric ν(COO) vibrations.16
Their phenyl derivatives, [{2-(C6H4-2-NH)-6-(CMevNAr)-
C5H3N}PdPh] (Ar = 4-i-PrC6H4 (3a), 2,6-i-Pr2C6H3 (3b)), could
be readily accessed by treatment of HL1 with NaH followed by
(PPh3)2PdPh(Br) (Scheme 3). Alternatively, 3a can be prepared
by treating chloride 2a with phenyl lithium; a related salt elim-
ination approach to make 3b has not proved possible. In the
case of 2a, chloride abstraction with both silver tetrafluoro-
borate and triflate in acetonitrile proved facile affording
[{2-(C6H4-2′-NH)-6-(CMevN(4-i-PrC6H4)C5H3N}Pd(NCMe)][X]
(X = BF4 (4), X = O3SCF3 (5)) in high yield (Scheme 3). Mono-
phenyl 3a and 3b are air and water stable, whereas 4 and 5
proved hygroscopic on prolonged standing. All four complexes
Fig. 5 Molecular structure of 2b including a partial atom numbering
scheme. All hydrogen atoms, apart from H3, have been omitted for
clarity.
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Scheme 3 Reagents and conditions: (i) xs. NaH, THF, heat; (ii) (PPh3)2PdPh(Br), THF, heat; (iii) LiPh, THF, −78 °C; (iv) AgX (X = BF4, O3SCF3), MeCN,
RT.
have been characterised using a combination of FAB mass
Table 4 Selected bond distances (Å) and angles (°) for 3a and 3b
spectrometry, IR and NMR (1H and 13C) spectroscopy and
3a
3b
elemental analyses (see Experimental section).
The mass spectra of 3a and 3b exhibit molecular ions while
4 and 5 display peaks corresponding to their cationic units. As
with 1 and 2, all four complexes exhibit ν(CvN)imine stretches
at lower wavenumber (typically by 35 cm−1) when compared
with HL1, supporting coordination of L1 to the metal
centre.13–15 The imine methyl resonances are seen between δ
2.2 and 2.5 in their 1H NMR spectra, while signals for the
imine carbon fall between δ 170.5 and 174.8 in their 13C{1H}
NMR spectra. Signals attributable to [BF4]− and [O3SCF3]−
counterions could also be seen in the 19F NMR spectra of 4
and 5. In addition, crystals of 3a, 3b and the pyridine analogue
of 5, [{2-(C6H4-2′-NH)-6-(CMevN(4-i-PrC6H4)C5H3N}Pd(NC5-
H5)][O3SCF3] (5′), have been the subject of single crystal X-ray
diffraction studies.
Bond lengths
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–C(23)
C(7)–N(1)
C(9)–C(7)
C(15)–N(3)
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(3)
N(1)–Pd(1)–C(23)
N(2)–Pd(1)–C(23)
N(3)–Pd(1)–N(2)
2.060(6)
2.066(6)
1.937(6)
2.016(8)
1.302(9)
1.452(10)
1.326(9)
2.041(2)
2.069(2)
1.959(3)
2.013(3)
1.291(4)
1.472(4)
1.348(4)
81.0(3)
172.5(3)
99.2(3)
178.5(3)
91.5(3)
79.88(10)
171.38(10)
99.68(11)
169.73(11)
79.88(10)
As a representative of the mono-phenyl pair of structures, a
view of the molecular structure of 3a is depicted in Fig. 6;
selected bond distances and angles are listed in Table 4 for
both 3a and 3b. As with 1 and 2, 2-(2′-anilido)-6-imine-pyridine
ligand acts a tridentate ligand with the σ-phenyl ligand now
occupying the fourth coordination site to complete a distorted
square planar geometry. The phenyl ligand in both structures
is tilted with respect to the trans-pyridine unit of the N,N,N-
ligand and most noticeably for 3a, presumably as a conse-
quence of the variation in steric hindrance imposed by the
N-aryl groups [tors. C(13)–N(2)–C(23)–C(24) 46.4(4) (3a),
41.4(4)° (3b)]. When compared to 1 and 2, the presence of
a σ-phenyl group in 3 results in an elongation of the trans
Pd–Npyridine distance [Pd–N(2) 2.066(6) (3a), 2.069(2) (3b) vs.
1.963(5) (1a), 1.974(8)av. (1b), 1.980(5)av. (2a), 1.987(3) (2b) Å],
an observation attributable to the strong trans-influence
exhibited by the aryl group. In contrast, the exterior nitrogen-
palladium distances remain similar in length to those seen in
1 and 2. To accommodate the increased Pd–N(2)pyridine distance,
there is increased twisting of the ligand backbone which is
most apparent in 3b [tors. N(2)–C(13)–C(14)–C(15) 25.2(4) and
N(1)–C(7)–C(9)–N(2) 13.7(4)°]. As with chloride-containing 2, the
anilido NH proton shows no notable intra- or inter-molecular
contacts of note.
Unfortunately cationic 4 and 5 were not amenable to
forming crystals suitable for an X-ray determination. To over-
come this practical issue, small amounts of pyridine were
added to a solution of 5 in chloroform and hexane slowly
diffused forming single crystals of [{2-(C6H4-2′-NH)-6-(CMev
N(4-i-PrC6H4)C5H3N}Pd(NC5H5)][O3SCF3] (5′). The molecular
structure of the cationic unit 5′ is depicted in Fig. 7; selected
bond distances and angles are listed in Table 5. As with a
number of the structures reported in this study, two indepen-
dent molecules (A and B) were present in the unit cell which,
in this case, differ most noticeably in the inclination of the
N-aryl groups. The structure of 5′ consists of a palladium(II)
cationic unit charge balanced by a non-coordinating triflate
counteranion. Within the distorted square planar cationic
Fig. 6 Molecular structure of 3a including a partial atom numbering
scheme. All hydrogen atoms, apart from H3, have been omitted for
clarity.
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pincer undergoes a modest interaction with a triflate oxygen
atom [N(3)⋯O(1) 3.096A, 3.175B Å].
Reactivity of 3 towards Selectfluor and XeF2
In the first instance the reactivity of mono-phenyl containing
3a towards Selectfluor was explored. Typically 3a was treated
with excess Selectfluor at 100 °C in a toluene–MeCN mixture;
these higher temperature conditions having been identified as
more conducive to formation of the C–F reductive elimination
product.4c,3c However, biphenyl was the only aryl-containing
organic product identified by GC-MS. Likewise using XeF2 as
the oxidant instead of Selectfluor under the same conditions
gave only biphenyl.
Fig. 7 Molecular structure of cationic unit in 5’, including a partial atom
numbering scheme. All hydrogen atoms, except for H3, have been
omitted for clarity.
To investigate the reaction further and potentially observe
any possible intermediates, a reaction involving an equimolar
ratio of 3a and Selectfluor was undertaken in CD3CN at a
series of lower temperatures and the reaction monitored by
1H and 19F NMR spectroscopy (Scheme 4). After 15 minutes at
room temperature the 19F NMR spectrum revealed full con-
sumption of Selectfluor and a new peak at δ −181 attributable
to the formation of hydrogen fluoride.17 The 1H NMR spec-
trum contained signals consistent with biphenyl, the salt
[{2-(C6H4-2-NH)-6-(CMevN(4-i-PrC6H4)C5H3N}Pd(NCCD3)][BF4]
(4) (vide supra) and 1-(chloromethyl)-1,4-diazabicyclo[2.2.2]-
octan-1-ium tetrafluoroborate, the Selectfluor degradation
product. In addition, there were signals present attributable to
another palladium species that slowly reduced in intensity
over time.
When the reaction was carried out at −40 °C, full consump-
tion of Selectfluor was again evident from the 19F NMR spec-
trum which also contained a peak attributable to HF, albeit
temperature shifted (δ −172). In the 1H NMR spectrum full
conversion of 3a to a single palladium species was observed
with the aromatic/pyridyl region integrating to sixteen protons;
no peaks assignable to biphenyl nor 4 could be identified. As
the reaction mixture was warmed to 0 °C, only sharpening of
the 1H NMR spectrum was observed with peaks that clearly
match those observed for the decomposing palladium species
seen at room temperature (Fig. S9 in ESI†). In the 19F NMR
spectrum a 1 : 8 ratio between the HF signal (δ −174) and the
BF4 peak (δ −152) accounts for all the fluorine introduced
from the Selectfluor (Fig. S10 in ESI†). On warming to room
temperature, decomposition of the palladium intermediate
ensued generating biphenyl and 4; full conversion being
Table 5 Selected bond distances (Å) and angles (°) for 5’
Molecule A
Molecule B
Bond lengths
Pd(1)–N(1)
Pd(1)–N(2)
2.049(12)
1.992(11)
2.034(12)
1.952(11)
1.962(11)
2.105(11)
1.279(16)
1.316(16)
Pd(1)–N(3)
Pd(1)–N(4)
1.937(11)
2.010(11)
C(7)–N(1)
C(15)–N(3)
1.276(16)
1.336(15)
Range S–O (triflate)
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(3)
N(1)–Pd(1)–N(4)
N(2)–Pd(1)–N(3)
N(2)–Pd(1)–N(4)
N(3)–Pd(1)–N(4)
1.424(11)–1.485(10)
82.9(5)
175.3(5)
93.7(5)
92.6(5)
176.6(5)
90.8(5)
82.0(5)
174.9(4)
94.0(5)
93.8(5)
175.7(5)
90.3(4)
unit, the 2-(2′-anilido)-6-imine-pyridine ligand acts a tridentate
ligand and an N-bound pyridine fills the fourth coordination
site. Similar to phenyl-bound 3, the monodentate hetero-
aromatic in 5′ is not co-planar with the trans-pyridine unit of
the tridentate ligand. Instead it adopts a tilted configuration
[C(13)–N(2)–N(4)–C(27) 58.1(5)A, 60.0(5)B°] which is ca. 8°
greater than that for the aryl group in 3b. Inspection of the
trans Pd–N(2)pyridine distance involving the N,N,N-ligand
reveals a bond length [Pd(1)–N(2) 1.992(11)A, 1.952(11)B Å]
comparable with those seen in 1 and 2, but shorter than that
in 3 (vide supra). The NH proton of the anilido unit of the
Scheme 4 Low temperature oxidation of 3a and Ar–Ar coupling on warming.
Dalton Trans.
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observed after 48 hours (Fig. S11 in ESI†). Unfortunately, Technical Support Unit, London Metropolitan University. The
further attempts to fully characterise the high valent palladium reagents 4-isopropylaniline, 2,6-diisopropylaniline, tin(II)
intermediate were unsuccessful.
chloride dihydrate, phenyllithium (1.8 M in n-Bu2O), silver tri-
The 1 : 1 reaction of 2,6-diisopropylphenyl-containing 3b flate, silver tetrafluoroborate, 1-chloromethyl-4-fluoro-1,4-di-
with Selectfluor was also explored at a range of different temp- azoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor™)
eratures. However, despite consumption of 3b, there was no and 2-bromonitrobenzene were purchased from Aldrich
evidence for the formation of biphenyl, fluorobenzene nor Chemical Co. and used without further purification. The com-
could any characterisable palladium species be identified. It is pounds
6-tributylstannyl-2-(2-methyl-1,3-dioxolan-2-yl)pyri-
unclear as to the origin of these differences in reactivity dine19 and [(PPh3)2PdPh(Br)]20 were prepared using literature
between 3a and 3b towards Selectfluor.
procedures. All other chemicals were obtained commercially
and used without further purification.
Synthesis of 2-(2-methyl-1,3-dioxolan-2-yl)-6-(2-nitrophenyl)-
pyridine
Conclusions
A new family of imino-based monoanionic N,N,N pincer A 25 mL microwave vial was loaded with 2-bromonitrobenzene
ligands have been developed that can support neutral palla- (0.536 g, 2.70 mmol), 6-tributylstannyl-2-(2-methyl-1,3-dioxo-
dium(II) acetate (1), chloride (2) and phenyl (3) species; the lan-2-yl)pyridine (1.226 g, 2.70 mmol), Pd(OAc)2 (0.025 g,
tetrafluoroborate (4) and triflate (5) salts are also reported. The 0.11 mmol) and triphenylphosphine (0.058 g, 0.22 mmol) and
oxidatively induced Ph–Ph coupling reactions involving 3a the contents dissolved in bench toluene (13 mL). The system
described in this work highlights the ability of Selectfluor and was then sealed and stirred for 30 s in a microwave before
xenon difluoride to behave as bystanding oxidants.3d Using the heating to 100 °C (with 100 W power and 10 bar pressure
more sterically bulky 3b, neither biphenyl nor fluorobenzene limits) for 1 h. The resulting dark brown reaction mixture was
were produced under similar oxidative conditions. The identity concentrated under reduced pressure to yield a dark brown oil.
of the palladium intermediate that generates biphenyl and cat- This oil was then dry loaded on to a silica column and eluted
ionic 4 remains uncertain but investigations into the precise with a 70 : 30 mixture of petroleum ether (40–60) and ethyl ace-
nature of this species are ongoing.
tate affording 2-(2-methyl-1,3-dioxolan-2-yl)-6-(2-nitrophenyl)-
pyridine as a yellow solid (0.517 g, 67%) along with trace
amounts of the homocoupled by-product 6,6′-bis(2-methyl-1,3-
dioxolan-2-yl)-2,2′-bipyridine. 1H NMR (400 MHz, CDCl3): δ
1.66 (s, 3H, CH3), 3.84 (m, 2H, O–CHH–CHH–O), 4.02 (m, 2H,
Experimental
General
3
4
O–CHH–CHH–O), 2.37 (dd, JHH 7.8, JHH 1.0, 1H, Ar–H),
3
4
All operations, unless otherwise stated, were carried out under 7.42–7.46 (m, 1H, Ar–H), 7.50 (dd, JHH 7.5, JHH 0.9, 1H, Ar–
an inert atmosphere of dry, oxygen-free nitrogen using stan- H), 7.54–7.57 (m, 2H, Ar–H), 7.74 (dd, 3JHH 7.8, 3JHH 7.9, Ar–H),
dard Schlenk and cannular techniques or in a nitrogen purged 7.78 (dd, JHH 8.0, JHH 8.1, 1H, Ar–H). 13C {1H} NMR
glove box. Operations involving a Microwave were performed (100 MHz, CDCl3): δ 24.9 (CH3), 65.0 (CH2), 65.1 (CH2), 108.6
on a CEM Discover Explorer Hybrid instrument. Solvents were (C), 118.7 (CH), 121.7 (CH), 124.4 (CH), 129.1 (CH), 131.1 (CH),
distilled under nitrogen from appropriate drying agents18 or 135.3 (C), 137.5 (CH), 149.8 (C), 154.9 (C), 161.1 (C). IR (cm−1):
were employed directly from a Solvent Purification System 1587 (CvN)pyridine, 1530 (NO2)asymm, 1369 (NO2)symm HRMS
(Innovative Technology, Inc.). The electrospray (ESI) mass (TOFMS, ASAP): calcd for C15H15N2O4 [M + H]+ 287.1032,
spectra were recorded using a micromass Quattra LC mass found 287.1034.
3
3
spectrometer with acetonitrile or methanol as the matrix. FAB
mass spectra (including high resolution) were recorded on a
Synthesis of 1-(6-(2-aminophenyl)pyridine-2-yl)ethanone
Kratos Concept spectrometer with NBA as matrix or on a 2-(2-Methyl-1,3-dioxolan-2-yl)-6-(2-nitrophenyl)pyridine (1.040 g,
Waters Xevo QToF mass spectrometer equipped with an atmos- 3.6 mmol) and SnCl2·2H2O (8.220 g, 36.0 mmol) were
pheric solids analysis probe (ASAP). The infrared spectra were suspended in bench ethanol (34 mL) and sonicated for
recorded in the solid state with Universal ATR sampling acces- 2 h, whereupon a bright yellow slurry was obtained. This slurry
sories on a Perkin Elmer Spectrum One FTIR instrument. was concentrated under reduced pressure and partitioned
NMR spectra were recorded on a Bruker DRX400 spectrometer between 1 M NaOH (100 mL) and CHCl3 (100 mL) until a
at 400.13 (1H), 376.46 (19F) and 100.61 MHz (13C) or a Bruker bright yellow organic phase was observed. The organic phase
Avance III 500 spectrometer at 125 MHz (13C), at ambient was separated and the aqueous phase washed with CHCl3 (3 ×
temperature unless otherwise stated; chemical shifts (ppm) 25 mL). The combined organic phases were washed with water
are referred to the residual protic solvent peaks and coupling (2 × 30 mL) and concentrated to a smaller volume under
constants are expressed in hertz (Hz). Melting points (mp) reduced pressure. Aqueous HCl (150 mL, 16% (v/v)) was added
were measured on a Gallenkamp melting point apparatus to the solution and the resultant biphase stirred for 1 h at
(model MFB-595) in open capillary tubes and were un- ambient temperature. The reaction mixture was neutralised
corrected. Elemental analyses were performed at the Science with K2CO3, the organic phase separated and the aqueous
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3
3
4
phase washed with dichloromethane (2 × 30 mL). The com- 3JHH 8.5, 2H, Ar–H), 7.21 (ddd, JHH 7.3, JHH 8.0, JHH 1.5, 1H,
3
4
3
bined organic extracts were washed with water (1 × 30 mL) and Ar–H), 7.59 (dd, JHH 8.0, JHH 1.5, 1H, Ar–H), 7.78 (dd, JHH
brine (1 × 30 mL) and then filtered through Celite layered with 8.0, 3JHH 0.9, 1H, Py–H), 7.90 (dd, 3JHH 7.9, 3JHH 7.9, 1H, Py–H),
magnesium sulphate. The filtrate was concentrated under 8.26 (dd, JHH 7.8, JHH 0.9, 1H, Py–H). 13C{1H} NMR
reduced pressure to afford 1-(6-(2-aminophenyl)pyridin-2-yl)- (100 MHz, CDCl3): δ 17.5 (MeCvN), 22.9 (CHMe2), 23.2
ethanone as a brown/yellow oil which slowly solidifies (0.68 g, (CHMe2), 28.3 (CHMe2), 117.6, 118.2 (CH), 118.8 (C), 122.2
3
4
1
89%). Mp: 95–98 °C. H NMR (400 MHz, CDCl3): δ 2.73 (s, 3H, (CH), 123.0 (CH), 123.4 (CH), 123.7 (CH), 129.6 (CH), 130.1
MeCvO), 5.77 (br, s, 2H, NH2), 6.82 (m, 2H, Ar–H), 7.22 (ddd, (CH), 135.8 (C), 137.6 (CH), 146.1 (C), 146.3 (C), 154.5 (C),
3
4
3
4
3JHH 7.3, JHH 8.1, JHH 1.6, 1H, Ar–H), 7.56 (dd, JHH 7.8, JHH 158.2 (C), 165.0 (Me–CvN). IR (cm−1): 3451, 3282 (br, NH),
1.5, 1H, Ar–H), 7.85–7.95 (m, 3H, Py–H). 13C{1H} NMR 1642 (CvN)imine
,
1584 (CvN)pyridine
.
ESIMS: m/z 372
(100 MHz, CDCl3): δ 26.1 (Me–CvO), 117.4, 118.0, 119.0 (CH), [(M + H)]+. HRMS (FAB): calcd C25H30N3O [M + H]+ 372.24322,
121.3 (C), 125.7 (CH), 129.6 (CH), 130.5 (CH), 137.9 (CH), 146.5 found 372.24310.
(C), 151.7 (C), 158.7 (C), 199.4 (CvO). IR (cm−1): 3456, 3363
Synthesis of [{2-(C6H4-2-NH)-6-(CMevNAr)}Pd(OAc)] (1)
(NH), 1695 (CvO)ketone, 1585 (CvN)pyridine. ESIMS: m/z 213
[M + H]+. HRMS (FAB): calcd for C13H13N2O [M + H]+
213.10246, found 213.10252.
(a) Ar = 4-i-PrC6H4 (1a). A Schlenk flask equipped with stir
bar was evacuated and backfilled with nitrogen and loaded
with Pd(OAc)2 (0.740 g, 3.3 mmol), 1-(6-(2-aminophenyl)-
pyridin-2-yl)ethanone (0.690 g, 0.81 mmol), 4-isopropylaniline
Synthesis of 2-(C6H4-2-NH2)-6-(CMevNAr)C5H3N (HL1)
(a) Ar = 4-i-PrC6H34 (HL1a). To a round bottomed flask (0.660 g, 4.9 mmol) and toluene (70 mL). The reaction vessel
equipped with stir bar was added 1-(6-(2-aminophenyl)pyridin- was stirred and heated to 80 °C for 3 h. The resultant green/
2-yl)ethanone (0.500 g, 2.4 mmol) and 4-isopropylaniline brown solution was evaporated and the resultant solid dis-
(2.070 g, 15.3 mmol). The reaction vessel was then lowered solved in the minimum volume of chloroform before hexane
into a pre-heated heating mantle set at 225 °C and the mixture was added to precipitate 1a as a green/brown solid (1.45 g,
stirred for 15 min before a catalytic amount of glacial acetic 89%). Crystals suitable for an X-ray determination were grown
acid was introduced. After 15 min at 225 °C the reaction vessel by slow diffusion of hexane into a solution of 1a in CHCl3 at
was allowed to cool to room temperature. The excess aniline room temperature. Mp: >260 °C. 1H NMR (400 MHz, CDCl3):
3
was removed by distillation under reduced pressure, the resul- δ 1.22 (d, JHH 6.9, 6H, CHMe2), 1.53 (s, 3H, –OC(O)Me), 2.33
3
tant dark residue heated to reflux in ethanol (10 ml) and hot (s, 3H, MeCvN), 2.98 (sept, JHH 6.9, 1H, CHMe2), 5.60 (br, s,
filtered. The filtrate was concentrated to half volume and 1H, NH), 6.42 (ddd, 3JHH 6.6, 3JHH 8.5, 4JHH 1.2, 1H, Ar–H), 6.86
3
4
3
3
allowed to cool to room temperature to yield HL1a as a yellow (dd, JHH 8.5, JHH 1.2, 1H, Ar–H), 7.02 (ddd JHH 6.6, JHH 7.9,
solid (0.040 g, 5%). Mp: 113–115 °C. 1H NMR (400 MHz, 4JHH 1.4, 1H, Ar–H), 7.07 (d, JHH 8.4, 2H, Ar–H), 7.23 (d, JHH
3
3
3
3
4
CDCl3): δ 1.28 (d, JHH 7.0, 6H, CHMe2), 2.37 (s, 3H, MeCvN), 8.3, 2H, Ar–H), 7.59 (dd, JHH 7.4, JHH 1.0, 1H, Py–H), 7.89 (d,
2.92 (sept, JHH 7.0, 1H, CHMe2), 5.79 (br, s, 2H, NH2), 3JHH 8.0, 1H, Ar–H), 7.99 (dd, JHH 7.4, JHH 8.8, 1H, Py–H),
3
3
3
6.76–6.84 (m, 4H, Ar–H), 7.20 (ddd, 3JHH 8.1, 3JHH 7.4, 4JHH 1.5, 8.56 (d, JHH 8.8, 1H, Py–H). 13C{1H} NMR (100 MHz, CDCl3):
3
1H, Ar–H), 7.23 (d, 3JHH 8.2, 2H, Ar–H), 7.58 (dd, 3JHH 7.8, 3JHH δ 16.3 (MeCvN), 21.9 (MeCO2), 22.9 (CHMe2), 32.9 (CHMe2),
3
4
1.5, 1H, Ar–H), 7.74 (dd, JHH 8.0, JHH 0.9, 1H, Py–H), 7.86 111.8 (CH), 112.9 (C), 119.7 (CH), 121.5 (CH), 122.0 (CH), 125.4
(dd, 3JHH 7.93, 3JHH 7.9, 1H, Py–H), 8.76 (dd, 3JHH 7.9, JHH 1.0, (CH), 125.6 (CH), 128.3 (CH), 129.1 (CH), 133.5 (CH), 141.7 (C),
4
1H, Py–H). 13C{1H} NMR (100 MHz, CDCl3): δ 16.6 (MeCvN), 146.9 (C), 148.5 (C), 148.8 (C), 152.7 (C), 169.5 (Me–CvN),
24.1 (CHMe2), 33.6 (CHMe2), 117.3, 117.9, 118.8, 119.3 (CH), 177.0 (Me–CO2). IR (cm−1): 1600 (CvN)imine, 1591 (COOasymm
/
122.1 (C), 123.2 (CH), 126.9 (CH), 129.6 (CH), 130.1 (CH), 137.4 CvNpyridine), 1367 (COO)symm FABMS: m/z 493 [M]+, 433
(CH), 144.2 (C), 146.5 (C), 148.8 (C), 155.2 (C), 158.2 (C), 166.5 [M − OAc]+. Anal Calc. for (C24H25N3O2Pd): C, 58.36; H, 5.10;
(MeCvN). IR (cm−1): 1635 (CvN)imine, 1587 (CvN)pyridine
.
N, 8.51. Found: C, 58.26; H, 5.23; N, 8.51%.
(b) Ar = 2,6-i-Pr2C6H3 (1b). A Schlenk flask equipped with
stir bar was evacuated and backfilled with nitrogen and loaded
ESIMS: m/z 330 [(M + H)]+. HRMS (FAB): calcd C22H24N3
[M + H]+ 330.1970, found 330.1968.
(b) Ar = 2,6-i-Pr2C6H3 (HL1b). Employing a similar pro- with Pd(OAc)2 (0.180 g, 0.81 mmol), HL1b (0.300 g,
cedure to that described for HL1a with 1-(6-(2-aminophenyl)- 0.81 mmol) and toluene (30 mL). After stirring at 60 °C over-
pyridin-2-yl)ethanone (0.700 g, 3.3 mmol), 2,6-diisopropyl- night, the green reaction mixture was cooled to room tempera-
aniline (3.800 g, 21.5 mmol) gave following work-up HL1b ture and filtered through Celite and the Celite cake washed
as a yellow solid (0.54 g, 44%). Crystals suitable for an X-ray thoroughly with dichloromethane. The filtrate was concen-
determination were grown by slow cooling of an ethanol trated to ca. 1 mL whereupon hexane (20 mL) was added. The
1
solution containing the compound. Mp: 139–141 °C. H NMR resulting green precipitate was filtered and dried under
3
(400 MHz, CDCl3): δ 1.14 (d, JHH 6.9, 6H, CHMe2), 1.15 (d, reduced pressure forming 1b as a dark green powder (0.38 g,
3
3JHH 7.0, 6H, CHMe2), 2.21 (s, 3H, MeCvN), 2.75 (sept, JHH 88%). Crystals suitable for an X-ray diffraction study could be
3
4
6.9, 2H, CHMe2), 5.72 (br, s, 2H, NH2), 6.80 (dd, JHH 8.2, JHH grown by slow diffusion of hexane into a chloroform solution
3
3
4
1.0, 1H, Ar–H), 6.82 (ddd, JHH 8.2, JHH 8.2, JHH 1.3, 1H, Ar– of the complex at room temperature. Mp: >260 °C. 1H NMR
3
3
3
3
H), 7.08 (dd, JHH 8.7, JHH 6.3, 1H, Ar–H), 7.17 (dd, JHH 6.9, (400 MHz, CDCl3): δ 1.14 (d, JHH 6.8, 6H, CHMe2), 1.39
Dalton Trans.
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3
(d, JHH 6.8, 6H CHMe2), 1.51 (s, 3H, –OC(O)Me), 2.41 (s, 3H, (dd, 3JHH 8.6, 4JHH 1.2, 1H, Ar–H), 7.06 (ddd, 3JHH 8.2, 3JHH 6.5,
MeCvN), 3.14 (sept, 3JHH 6.8, 2H, CHMe2), 6.53 (ddd, 3JHH 8.6, 4JHH 1.4, Ar–H), 7.19 (m, 2H, Ar–H), 7.28 (dd, JHH 8.5, JHH
3
3
4
3
4
3
4
3JHH 6.5, JHH 1.4, 1H, Ar–H), 7.06 (dd, JHH 8.5, JHH 1.2, 1H, 8.5, 1H, Ar–H), 7.77 (dd, JHH 7.3, JHH 1.1, 1H, Py–H), 7.92
3
3
4
3
4
3
3
Ar–H), 7.13 (ddd, JHH 8.5, JHH 6.4, JHH 1.4, 1H, Ar–H), 7.26 (dd, JHH 8.6, JHH 1.5, 1H, Ar–H), 8.06 (dd, JHH 8.8, JHH 8.4,
(m, 2H, Ar–H), 7.36 (dd, JHH 8.7, 3JHH 6.8, 1H, Ar–H), 7.39 (br, 1H, Py–H), 8.63 (d, JHH 8.6, 1H, Py–H). 13C {1H} NMR
3
3
s, 1H, NH), 7.82 (dd 3JHH 7.4, 4JHH 1.0, 1H, Py–H), 8.01 (d, 3JHH (125 MHz, CDCl3): δ 18.0 (Me–CvN), 23.7 (CHMe2), 23.8
3
3
8.6, 1H, Ar–H), 8.10 (dd, JHH 8.8, JHH 7.3, 1H, Py–H), 6.80 (d, (CHMe2), 28.7 (CHMe2), 113.6 (CH), 113.8 (C), 121.3 (CH),
3JHH 8.7, 1H, Py–H). 13C{1H} NMR (100 MHz, CDCl3): δ 17.0 122.1 (CH), 123.6 (CH), 127.2 (CH), 128.1 (CH), 129.1 (CH),
(CHMe2), 22.3 (CHMe2), 22.7 (MeCO2), 22.8 (MeCvN), 27.6 130.8 (CH), 134.1 (CH), 139.7 (C), 141.6 (C), 150.0 (C), 150.3
(CHMe2), 112.0 (CH), 112.6 (C), 120.3 (CH), 121.0 (CH), 122.4 (C), 153.7 (C), 172.1 (Me–CvN). IR (cm−1): 1608 (CvN)imine
,
(CH), 125.7 (CH), 126.7 (CH), 127.7 (CH), 129.2 (CH), 132.5 1577 (CvN)pyridine. FABMS: m/z 511 [M + H]+, 475 [M − Cl]+.
(CH), 139.0 (C), 139.4 (C), 149.0 (C), 149.2 (C), 152.7 (C), 170.1 Anal Calc. for (C25H28ClN3Pd): C, 58.60; H, 5.51; N, 8.20.
(Me–CvN), 177.2 (Me–CO2). IR (cm−1): 1614 (CvN)imine, 1583 Found: C, 58.49; H, 5.35; N, 8.26%.
(COO)asymm/CvNpyridine), 1367 (COO)symm ESIMS: m/z 476
Synthesis of [{2-(C6H4-2-NH)-6-(CMevNAr)}Pd(C6H5)] (3)
[M − OAc]+. TOFMS (ASAP): m/z 536 [M+], 476 [M − OAc]+. Anal
Calc. for (C28H32Cl3N3O2Pd): C, 51.32; H, 4.92; N, 6.41. Found:
C, 50.92; H, 4.18; N, 7.36%.
(a) Ar = 4-i-PrC6H4 (3a). A Schlenk flask equipped with stir
bar was evacuated and backfilled with nitrogen and loaded
with 2a (0.208 g, 0.44 mmol) and THF (20 mL). The reaction
mixture was stirred and cooled to −78 °C for 15 min. A solu-
Synthesis of [{2-(C6H4-2-NH)-6-(CMevNAr)}PdCl] (2)
(a) Ar = 4-i-PrC6H4 (2a). A round bottomed flask equipped tion of PhLi (861 µL, 1.55 mmol, 1.8 M in n-Bu2O) was added
with stir bar and open to the air was loaded with 1a (0.595 g, slowly and the reaction mixture stirred at −78 °C for a further
1.20 mmol), dichloromethane (5 mL) and brine (5 mL). The 2 h. One drop of water was added and the solution slowly
reaction mixture was stirred rapidly for 1 h at room tempera- warmed to room temperature. All volatiles were removed under
ture whereupon both phases were diluted and the aqueous reduced pressure and the resultant green solid re-dissolved in
layer removed via a separating funnel. The organic phase was dichloromethane (20 mL) and washed with water (2 × 20 mL)
washed with water (2 × 20 mL) and concentrated to a smaller and brine (10 mL). Following drying over anhydrous mag-
volume under reduced pressure. The dark green solution was nesium sulphate and filtration, the resulting green solution
filtered through a Celite plug and the plug washed thoroughly was concentrated to a smaller volume (ca. 5 mL) and hexane
with dichloromethane. All volatiles were removed under added to precipitate 3a as a green solid (0.161 g, 71%). Single
reduced pressure affording 2a as a dark brown solid (0.56 g, crystals suitable for an X-ray determination were obtained by
99%). Single crystals suitable an X-ray determination were slow diffusion of hexane into a solution of 3a in chloroform at
1
3
grown by diffusion of hexane into a solution of 2a in chloro- room temperature. H NMR (400 MHz, CDCl3): δ 1.19 (d, JHH
1
3
form at room temperature. Mp: >260 °C. H NMR (400 MHz, 6.9, 6H, CHMe2), 2.46 (s, 3H, MeCvN), 2.80 (sept, JHH 6.9,
CDCl3): δ 1.23 (d, JHH 6.9, 6H, CHMe2), 2.28 (s, 3H, MeCvN), 1H, CHMe2), 5.48 (br, s, 1H, NH), 6.44 (ddd, 3JHH 6.5, JHH 8.0,
3
3
2.89 (sept, JHH 6.9, 1H, CHMe2), 5.59 (br, s, 1H, NH), 6.43 4JHH 1.1, 1H, Ar–H), 6.65 (d, JHH 8.4, 2H, Ar–H), 6.73–6.75 (m,
3
3
(ddd, JHH 6.1, JHH 8.0, JHH 1.20, 1H, Ar–H), 6.81 (dd, JHH 3H, Ar–H), 6.90 (dd, 3JHH 8.6, 4JHH 1.3, 1H, Ar–H), 6.95 (d, 3JHH
3
3
4
3
4
3
3
3
4
8.6, JHH 1.0, 1H, Ar–H), 6.99–7.03 (m, 5H, Ar–H), 7.19 (d, JHH 8.4, 2H, Ar–H), 7.05 (ddd, JHH 6.6, JHH 8.1, JHH 1.4, 1H, Ar–
8.2, 2H, Ar–H), 7.55 (dd, JHH 7.5, JHH 0.9, 1H, Py–H), H), 7.07–7.09 (m, 2H, Ar–H), 7.82 (d, JHH 7.1, 1H, Py–H), 7.98
3
4
3
3
4
3
3
7.73–7.79 (m, 2H, Py–H/Ar–H), 8.30 (d, 3JHH 8.7, 1H, Py–H). 13
C
(dd, JHH 8.5, JHH 1.3, 1H, Ar–H), 8.05 (dd, JHH 7.5, JHH 8.6,
{1H} NMR (125 MHz, CDCl3): δ 17.0 (CH3CvN), 22.9 (CHMe2), 1H, Py–H), 8.58 (d, JHH 8.8, 1H, Py–H). 13C{1H} NMR
32.7 (CHMe2), 112.1 (CH), 112.8 (C), 119.7 (CH), 121.6 (CH), (100 MHz, CDCl3) δ 18.3 (Me–CvN), 24.0 (CHMe2), 33.7
122.3 (CH), 125.1 (CH), 125.5 (CH), 128.2 (CH), 129.5 (CH), (CHMe2), 111.9 (CH), 114.0 (C), 121.3 (CH), 122.2 (CH), 122.6
133.4 (CH), 142.9 (C), 146.6 (C), 148.4 (C), 148.4 (C), 153.1 (C), (CH), 122.9 (CH), 125.9 (CH), 126.0 (CH), 126.1 (CH), 129.9
3
171.0 (Me–CvN). IR (cm−1): 1603 (CvN)imine
,
1576 (CH), 130.0 (CH), 134.2 (CH), 135.9 (CH), 145.1, 146.9, 152.0,
(CvN)pyridine. FABMS: m/z 469 (M)+, 434 (M–Cl)+. Anal Calc. 152.1, 153.1, 158.5 (C), 170.5 (MeCvN). IR (cm−1): 1602
for (For C22H22ClN3Pd): C, 56.18; H, 4.71; N, 8.93. Found: (CvN)imine, 1567 (CvN)pyridine. FABMS: m/z 511 [M]+. Anal
C, 56.11; H, 4.69; N, 9.00%.
Calc. for (C28H27N3Pd·1.5OH2): C, 62.40; H, 5.61; N, 7.80.
(b) Ar = 2,6-i-Pr2C6H3 (2b). Employing a similar procedure Found: C, 62.04; H, 5.33; N, 8.16%.
to that described for 2a using 1b (0.544 g, 1.02 mmol) gave 2b
(b) Ar = 2,6-i-Pr2C6H3 (3b). A Schlenk flask equipped with
as a dark green solid (0.520 g, 99%). Single crystals suitable for stir bar was evacuated and backfilled with nitrogen and loaded
an X-ray diffraction study could be grown by slow diffusion of with HL1b (0.100 g, 0.13 mmol), NaH (0.052 g, 2.20 mmol)
hexane into a chloroform solution of 2b at room temperature. and THF (10 mL). The resulting slurry was stirred and heated
1
3
Mp: >260 °C. H NMR (400 MHz, CDCl3): δ 1.05 (d, JHH 6.9, to reflux for 72 h before being allowed to cool to room temp-
3
6H, CHMe2), 1.35 (d, JHH 6.9, 6H, CHMe2), 2.28 (s, 3H, erature. The reaction mixture was transferred by cannular fil-
MeCvN), 2.99 (sept, JHH 6.9, 2H, CHMe2), 5.91 (br, s, 1H, tration to a second Schlenk flask containing [(PPh3)2PdPh(Br)]
NH), 6.49 (ddd, JHH 8.5, JHH 6.7, JHH 1.3, 1H, Ar–H), 6.92 (0.100 g, 0.13 mmol) and the contents stirred and heated to
3
3
3
4
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reflux for a further 72 h. On cooling to room temperature, the petroleum ether (40–60) into a solution of the salt in aceto-
resulting green solution was concentrated under reduced nitrile–dichloromethane (5 : 95) gave 5 as a microcrystalline
pressure and re-dissolved in chloroform (10 mL) before being powder. Single crystals of pyridine-containing 5′ suitable for
filtered through a Celite plug. All volatiles were removed under X-ray diffraction could be obtained by slow diffusion of hexane
reduced pressure and the resulting residue triturated with into a chloroform solution of 5 that contained a few drops of
hexane (3 × 20 mL) and 3b collected as a green solid (0.067 g, pyridine. Complex 5: Mp: >260 °C. 1H NMR (400 MHz,
93%). Crystals suitable for an X-ray determination were grown CD3CN): δ 1.32 (d, 3JHH 6.9, 6H, CHMe2), 2.51 (s, 3H, MeCvN),
3
by slow diffusion of hexane into a solution of 3b in chloroform 3.05 (sept, JHH 6.9, 1H, CHMe2), 6.14 (br, s, 1H, NH), 6.74
at room temperature. 1H NMR (400 MHz, CDCl3): δ 0.90 (d, (app. t, 3JHH 7.7, 1H, Ar–H), 7.17–7.23 (m, 3H, Ar–H), 7.26–7.29
3
3JHH 6.7, 6H, CHMe2), 0.95 (d, JHH 6.8, 6H, CHMe2), 2.32 (s, (m, 1H, Ar–H), 7.48 (d, 3JHH 8.3, 2H, Ar–H), 8.16 (m, 2H, Ar–H),
3
3
3
3H, MeCvN), 2.94 (sept, 3JHH 6.8, 2H, CHMe2), 6.40 (ddd, 3JHH 8.33 (dd, JHH, 8.0, JHH 8.0, 1H, Py–H), 8.54 (d, JHH 8.5, 1H,
3
4
8.1, JHH 6.6, JHH 1.3, 1H, Ar–H), 6.66–6.73 (m, 3H, Ar–H), Py–H), the coordinated CH3CN ligand was not observed due to
6.84 (dd, JHH 8.4, JHH 1.2, 1H, Ar–H), 6.88–6.93 (m, 2H, Ar– rapid exchange with bulk CD3CN. 13C{1H} NMR (100 MHz,
3
4
3
3
4
H), 6.99 (ddd, JHH 8.3, JHH 6.6, JHH 1.6, 1H, Ar–H), 6.99 (d, CD3CN): δ 17.0 (MeCvN), 22.9 (CHMe2), 33.3 (CHMe2), 115.4
3JHH 7.8, 2H, Ar–H), 7.12 (dd, JHH 7.7, JHH 7.7, 1H, Ar–H), (CH), 119.2 (C), 119.7 (CH), 122.4 (CH), 124.9 (CH), 126.9 (CH),
3
3
3
4
3
4
7.80 (dd, JHH 7.5, JHH 1.0, 1H, PyH), 7.91 (dd, JHH 8.6, JHH 129.7 (CH), 131.0 (CH), 136.7 (CH), 142.8 (C), 146.7 (C), 148.8
3
3
−
1.4, 1H, Ar–H), 8.02 (dd, JHH 8.8, JHH 7.5, 1H, Py–H), 8.55 (d, (C), 149.3 (C), 154.8 (C), 174.7 (MeCvN), CF3SO3 not
3JHH 8.7, 1H, Py–H). 13C{1H} NMR (100 MHz, CDCl3): δ 19.3 observed. 19F{1H} NMR (375 MHz, CD3CN): δ −79 (O3SCF3). IR
(MeCvN), 22.9 (CHMe2), 24.2 (CHMe2), 28.2 (CHMe2), 112.1 (cm−1): 1602 (CvN)imine, 1570 (CvN)pyridine. ESIMS (+ve): m/z
(CH), 114.5 (C), 121.3 (C), 122.5 (CH), 122.8 (CH), 123.5 (CH), 475 [M − O3SCF3]+; ESIMS (−ve): m/z: 149 [O3SCF3]−. Anal Calc.
125.8 (CH), 126.5 (CH), 127.1 (CH), 130.0 (CH), 130.1 (CH), for (C25H25N4O3F3PdS·CH2Cl2): C, 43.99; H, 3.83; N, 7.89.
134.3 (CH), 135.9 (CH), 139.5 (CH), 142.9 (C), 151.5 (C), 152.4 Found: C, 44.13; H, 3.78; N, 7.60%.
(C), 153.2 (C), 155.5 (C), 172.1 (Me–CvN). IR (cm−1): 1605
Reaction of 3a with Selectfluor in NMR tube at reduced
temperatures
(CvN)imine, 1571 (CvN)pyridine. FABMS: m/z 553 [M + H]+.
Synthesis of [{2-(C6H4-2-NH)-6-(CMevN(4-i-PrC6H4)}Pd-
(NCMe)][X] (4 and 5)
(a) −40 to 0 °C. Complex 3a (0.005 g, 0.0098 mmol) and
Selectfluor™ (0.0035 g, 0.0098 mmol) were loaded into a
(a) X = BF4 (4). A Schlenk flask equipped with stir bar was Young’s NMR tube open to the air and then cooled to −100 °C
evacuated and backfilled with nitrogen and loaded with 2a before acetonitrile-d3 was added and the system sealed. The
(0.200 g, 0.426 mmol), AgBF4 (0.083 g, 0.426 mmol) and MeCN NMR tube was inserted into a 400 MHz NMR spectrometer
(20 mL). The reaction mixture was stirred at room temperature pre-cooled to −40 °C and the 19F and 1H NMR spectra were
for 12 h, at which point the suspension was allowed to settle recorded at −40 °C and then at 10 °C intervals up to 0 °C. At
3
and the solution transferred by cannula filtration into another −40 °C, 1H NMR (400 MHz, CD3CN): δ 1.16 (d, JHH 6.8, 6H,
3
Schlenk flask. All volatiles were removed under reduced CHMe2), 2.40 (s, 3H, MeCvN), 2.82 (sept, JHH 6.8, 1H,
pressure to afford 4 as a dark green solid (0.233 g, 97%). Mp: CHMe2), 6.70 (d, 3JHH, 8.5, 2H, Ar–H), 6.72–6.77 (m, 2H, Ar–H),
1
3
>260 °C. H NMR (400 MHz, CD3CN): δ 1.21 (d, JHH 6.9, 3H, 6.84–6.86 (m, 2H, Ar–H), 7.04 (d, 3JHH 8.4, 2H, Ar–H), 7.36–7.43
3
3
CHMe2), 2.27 (s, 3H, CH3CvN), 2.93 (sept, JHH 6.9, 1H, (m, 2H, Ar–H), 7.47–7.55 (m, 2H, Ar–H), 7.86 (dd, JHH 7.7,
CHMe2), 6.60 (dd, JHH 7.5, JHH 7.5, 1H, Ar–H), 6.98 (d, JHH 4JHH 1.9, 1H, Ar–H), 8.17 (m, 1H, Ar–H), 8.40 (m, 2H, Ar–H).
3
3
3
8.4, 1H, Ar–H), 7.04 (d, JHH 7.8, 2H, Ar–H), 7.10 (dd, JHH 7.6, 19F{1H} NMR (375 MHz, CD3CN): δ −152 (BF4), −172 (HF).
3
3
3JHH 7.8, 1H, Ar–H), 7.34 (d, JHH 8.0, 2H, Ar–H), 7.83 (d, JHH At −30 °C, 1H NMR δ no change. 19F{1H} NMR: δ −152
3
3
7.5, 1H, Py–H), 7.89 (d, JHH 8.0, 1H, Ar–H), 8.08 (dd, JHH 8.0, (BF4), −172 (HF). At −20 °C, 1H NMR δ no change. 19F{1H}
3
3
3JHH 8.0, 1H, Py–H), 8.53 (d, JHH 8.6, 1H, Py–H), the co- NMR: δ −152 (BF4), −173 (HF). At −10 °C, 1H NMR δ no
3
ordinated CH3CN ligand was not observed due to rapid change. 19F{1H} NMR: δ −152 (BF4), −173 (HF). At 0 °C:
exchange with bulk CD3CN. 13C{1H} NMR (100 MHz, CD3CN): 1H NMR δ no change. 19F{1H} NMR: δ −152 (8F, BF4), −174
δ 17.0 (CH3CvN), 22.9 (CHMe2), 33.3 (CHMe2), 115.3 (CH), (1F, HF).
117.0 (C), 119.6 (CH), 122.3 (CH), 124.9 (CH), 126.9 (CH), 127.0
(b) 0 °C to room temperature. The reaction mixture pre-
(CH), 129.7 (CH), 131.2 (CH), 136.8 (CH), 142.9 (C), 147.1 (C), pared in (a) was further warmed to room temperature and the
148.8 (C), 149.5 (C), 155.0 (C), 174.8 (CvN). 19F{1H} NMR 1H NMR spectrum recorded periodically. After 48 h, complete
(375 MHz, CD3CN): δ −151 (-BF4). ESIMS (+ve) m/z: 475 conversion to 4 (data as reported for 4 above) and biphenyl
[M − BF4]+; ESIMS (−ve): m/z 87 [BF4]−. Anal Calc. for was observed. 19F{1H} NMR δ −152 (BF4), −181 (HF).
(C24H25N4F4PdB): C, 51.23; H, 4.48; N, 9.96. Found: C, 51.13;
Crystallographic studies
H, 4.40; N, 9.87%.
(b) X = O3SCF3 (5). Employing a similar procedure to that Data for HL1b, 1a, 1b, 2a, 2b, 3a, 3b and 5′ were collected on a
described for 4 using 2a (0.205 g, 0.44 mmol), AgOSO2CF3 Bruker APEX 2000 CCD diffractometer. Details of data collec-
(0.112 g, 0.44 mmol) and MeCN (20 mL) gave 5 as a dark tion, refinement and crystal data are listed in Table 6. The data
green solid (0.259 g, 95%). Crystallisation by slow diffusion of were corrected for Lorentz and polarisation effects and empiri-
Dalton Trans.
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Table 6 Crystallographic and data processing parameters for HL1b, 1a, 1b, 2a, 2b, 3a, 3b and 5’a
Complex
HL1b
1a
1b
2a
Formula
C
25H29N3
C24H25Cl3N3O2Pd·CHCl3·OH2
631.25
0.27 × 0.05 × 0.04
150(2)
C28H32Cl3N3O2Pd
655.32
0.27 × 0.17 × 0.11
150(2)
C22H22ClN3Pd
470.28
0.23 × 0.20 × 0.04
150(2)
M
371.51
0.24 × 0.17 × 0.12
150(2)
Crystal size (mm3)
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Orthorhombic
Pbca
12.906(10)
8.308(6)
39.43(3)
90
90
90
4228(5)
8
1.167
Triclinic
P1
Triclinic
P1
Monoclinic
P2(1)/n
17.674(4)
8.9111(19)
24.267(5)
90
93.133(5)
90
3816.2(14)
8
ˉ
ˉ
6.9770(16)
12.184(3)
15.543(4)
87.923(4)
84.029(5)
84.203(5)
1307.0(5)
2
14.194(4)
15.316(4)
15.711(4)
61.002(5)
77.050(7)
80.162(7)
2903.6(14)
4
α (°)
β (°)
γ (°)
U (Å3)
Z
Dc (Mg m−3
F(000)
)
1.604
640
1.049
1.499
1336
0.945
1.637
1904
1.124
1600
0.069
μ(Mo-Kα)(mm−1
)
Reflections collected
Independent reflections
Rint
28 600
3715
0.2201
0/258
10 332
5074
0.1059
20/319
22 854
11 293
0.1479
0/679
28 912
7469
0.1336
1/493
Restraints/parameters
Final R indices (I > 2σ(I))
R1 = 0.0628
wR2 = 0.1155
R1 = 0.1397
wR2 = 0.1377
0.871
R1 = 0.0683
wR2 = 0.1067
R1 = 0.1235
wR2 = 0.1232
0.861
R1 = 0.0873
wR2 = 0.1788
R1 = 0.1888
wR2 = 0.2173
0.848
R1 = 0.0582
wR2 = 0.0914
R1 = 0.1237
wR2 = 0.1078
0.890
All data
Goodness of fit on F2 (all data)
Complex
2b
3a
3b
5′
Formula
C
26H29Cl4N3Pd
C28H27N3Pd
511.93
0.26 × 0.12 × 0.05
150(2)
C31H33N3Pd
554.00
0.25 × 0.22 × 0.10
150(2)
C28H26F3N4 O3PdS·2CHCl3
900.72
0.46 × 0.14 × 0.04
150(2)
M
631.72
0.36 × 0.31 × 0.04
150(2)
Crystal size (mm3)
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
P2(1)/n
11.410(8)
17.663(13)
12.991(9)
90
94.182(13)
90
2611(3)
4
Monoclinic
P2(1)/c
17.244(11)
11.142(8)
12.238(8)
90
105.925(14)
90
2261(3)
4
Orthorhombic
Pbca
12.118(3)
10.844(3)
40.250(10)
90
90
90
5289(2)
8
1.391
Triclinic
P1
ˉ
14.155(7)
16.226(8)
17.503(8)
89.109(9)
76.364(11)
70.267(10)
3668(3)
α (°)
β (°)
γ (°)
U (Å3)
Z
4
Dc (Mg m−3
F(000)
)
1.607
1280
1.141
1.504
1048
0.842
1.631
1804
1.053
2288
1.391
μ(Mo-Kα)(mm−1
)
Reflections collected
Independent reflections
Rint
Restraints/parameters
Final R indices (I > 2σ(I))
19 939
5116
0.0775
0/312
R1 = 0.0446
wR2 = 0.0904
R1 = 0.0615
wR2 = 0.0955
1.044
17 292
4444
0.2311
0/292
R1 = 0.0732
wR2 = 0.1210
R1 = 0.1615
wR2 = 0.1450
0.867
41 613
5763
0.0699
0/321
R1 = 0.0431
wR2 = 0.0906
R1 = 0.0569
wR2 = 0.0955
1.122
26 756
12 826
0.2649
749/889
R1 = 0.1055
wR2 = 0.2112
R1 = 0.2711
wR2 = 0.2821
0.829
All data
Goodness of fit on F2 (all data)
a Data in common: graphite-monochromated Mo-Kα radiation, λ = 0.71073 Å; R1 = ∑||Fo| − |Fc||/∑|Fo|, wR2 = [∑w(Fo − Fc2)2/∑w(Fo2)2]1/2, w−1
=
2
[σ2(Fo)2 + (aP)2], P = [max(Fo2, 0) + 2(Fc2)]/3, where a is a constant adjusted by the program; goodness of fit = [∑(Fo − Fc2)2/(n − p)]1/2 where n is
the number of reflections and p the number of parameters.
2
cal absorption corrections applied. Structure solution by direct 0.96–1.00 Å) riding on the bonded atom with isotropic displa-
methods and structure refinement based on full-matrix least- cement parameters set to 1.5 Ueq(C) for methyl H atoms and
squares on F2 employed SHELXTL version 6.10.21 Hydrogen 1.2 Ueq(C) for all other H atoms. All non-H atoms were refined
atoms were included in calculated positions (C–H
=
with anisotropic displacement parameters.
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and A. M. Echavarren, J. Am. Chem. Soc., 2006, 128, 5033–
5040.
Acknowledgements
We thank the University of Leicester for financial assistance.
Johnson Matthey PLC are thanked for their generous loan of
palladium salts.
9 H. B. Kratz, M. E. van der Boom, Y. Ben-David and
D. Milstein, Isr. J. Chem., 2001, 41, 163–171.
10 While the N,N,N pincer framework is anticipated to be
inert, the possibility of a Caryl–Nanilide coupling reaction
involving the anilide moiety of the N,N,N ligand represents
an alternative pathway. For Csp3–N coupling via high valent
Pd, see for example: (a) S. R. Whitfield and M. S. Sanford,
J. Am. Chem. Soc., 2007, 129, 15142–15143; (b) A. Iglesias
and K. Muñiz, Helv. Chim. Acta, 2012, 95, 2007–2025;
(c) M. H. Perez-Temprano, J. M. Racowski, J. W. Kampf and
M. S. Sanford, J. Am. Chem. Soc., 2014, 136, 4097–4100;
(d) T.-S. Mai, X. Wang and J.-Q. Yu, J. Am. Chem. Soc., 2009,
131, 10806–10807; (e) P. A. Sibbald and F. E. Michael, Org.
Lett., 2009, 11, 1147–1149; (f) P. A. Sibbald, C. F. Rosewall,
R. D. Swartz and F. E. Michael, J. Am. Chem. Soc., 2009, 131,
15945–15951; (g) A. Iglesias, R. Alvarez, A. R. de Lera and
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