Palladium(II) aryl-amido complexes of diphosphinoazines in unsymmetrical PNP' pincer-type configuration

Article abstract of DOI:10.1016/j.jorganchem.2008.06.024

Square planar palladium(II) aryl-amido complexes of diphosphinoazines in monoanionic unsymmetrical PNP' pincer-type coordination were prepared by reactions of phenyl-, o-tolyl-, or 2,6-dimethylphenyllithium with previously described chloro-amido complexes of diphosphinoazines having isopropyl, cyclohexyl and tert-butyl substituents on phosphorus atoms. The compounds were characterized by NMR showing free rotation around metal-aryl bond in the complexes; the presence of C_ipso-Pd bond was detected by two-dimensional experiments. In addition to that, crystal and molecular structure of one phenyl-amido complex, [Pd(C₆H₅){P(C₆H₁₁)₂CH{double bond, long}C(Bu^t)NN{double bond, long}C(Bu^t)CH₂P(C₆H₁₁)₂}], was determined by X-ray diffraction together with the structure of a chloro-amido complex [PdCl{PBu^t₂CH{double bond, long}C(Bu^t)NN{double bond, long}C(Bu^t)CH₂PBu^t₂}]. In both structures the ligand trans to the amide nitrogen is well surrounded by substituents on phosphorus atoms, the former complex showing significant interactions between two cyclohexyl hydrogen atoms and the π-system of the phenyl ring. The values od Pd-C and Pd-N bond distances in this complex are the same as those in a monodentate analog [Pd(PMe₃)₂(C₆H₅)(NHC₆H₅)] which contrasts with the different values in a similar PNP symmetrical pincer complex reported in the literature.

Full text of DOI:10.1016/j.jorganchem.2008.06.024

Journal of Organometallic Chemistry 693 (2008) 3029–3034
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Palladium(II) aryl-amido complexes of diphosphinoazines in unsymmetrical
PNP’ pincer-type configuration
a
a,
a
a
b
ˇ
*
´
ˇ
Jan Storch , Jan Cermák , Martin Pošta , Jan Sykora , Ivana Císarová
a Institute of Chemical Process Fundamentals AS CR v.v.i., Rozvojová 135, Prague 6, Czech Republic
b Center of Molecular and Crystal Structures, Faculty of Natural Science, Charles University, Hlavova 2030, 128 40 Prague, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 April 2008
Received in revised form 6 June 2008
Accepted 17 June 2008
Available online 25 June 2008
Square planar palladium(II) aryl-amido complexes of diphosphinoazines in monoanionic unsymmetrical
PNP’ pincer-type coordination were prepared by reactions of phenyl-, o-tolyl-, or 2,6-dimethylphenylli-
thium with previously described chloro-amido complexes of diphosphinoazines having isopropyl, cyclo-
hexyl and tert-butyl substituents on phosphorus atoms. The compounds were characterized by NMR
showing free rotation around metal–aryl bond in the complexes; the presence of Cipso–Pd bond was
detected by two-dimensional experiments. In addition to that, crystal and molecular structure of one
phenyl-amido complex, [Pd(C6H5){P(C6H11)2CH@C(But)NN@C(But)CH2P(C6H11)2}], was determined by
X-ray diffraction together with the structure of a chloro-amido complex [PdCl{PBut2CH@C(But)NN@C
(But)CH2PBut2}]. In both structures the ligand trans to the amide nitrogen is well surrounded by substit-
uents on phosphorus atoms, the former complex showing significant interactions between two cyclo-
Keywords:
Diphosphinoazines
Pincer complexes
Aryl-amido complexes
Palladium
hexyl hydrogen atoms and the
p-system of the phenyl ring. The values od Pd–C and Pd–N bond
Polydentate ligands
distances in this complex are the same as those in a monodentate analog [Pd(PMe3)2(C6H5)(NHC6H5)]
which contrasts with the different values in a similar PNP symmetrical pincer complex reported in the
literature.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
We have recently used ligands of diphosphinoazine type in one
of their coordination modes, the monoanionic ene-hydrazone form
More than 30 years since the first report by Shaw [1], transition
metal complexes with pincer ligands continue to attract attention
in modern coordination and organometallic chemistry and also
find applications in new or considerably improved catalytic pro-
cesses [2]. The most frequent combinations of atoms involved in
pincer-type coordination modes are PCP and NCN systems but
other two-electron donors like O, S, Se or C (of N-heterocyclic car-
bene) are now quite commonly found at the ends of pincer arms.
Similarly, the central formally monoanionic carbon atom can be re-
placed by other elements. The important case represents nitrogen
which can form monoanionic amide complexes. Chemistry of PNP
systems has, indeed, seen significant advance in recent years [3].
There are some examples of PCP aryl pincer complexes with amide
ligands [4], the reverse cases, that is PNP amido complexes with
aryl–metal bonds, are also known. The important examples can
be found in the articles of Ozerov on the use of iridium and rho-
dium PNP pincers for activation of aromatic C–H bonds [5] and
Liang on similar platinum complexes [6]. There is also related work
of Harkins and Peters dealing with NNN pincer complexes of plat-
inum [7].
(PNP’), to support transition metals as unsymmetrical tridentate
pincer-like ligands. Palladium(II) chloro-amido complexes [8] and
rhodium(I) carbonyl-amido complexes [9] were prepared, the for-
mer compounds were used as catalysts for the Heck reaction of
bromo and activated chloro arenes [10]. Here we present synthesis
and characterization of new palladium(II) aryl-amido diphosphi-
noazine complexes with varied substitution both on phosphine
donor arms and on the aryl ligand.
2. Experimental
2.1. General
All manipulations were carried out in an inert atmosphere of
nitrogen or argon using standard Schlenk techniques. Hexane
was distilled from Na, THF from sodium benzophenone ketyl.
Starting palladium complexes 1–3 were prepared according to a
literature method [8]. Solutions of phenyllithium (4), 2-methyl-
phenyllithium (5), and 2,6-dimethylphenyllithium (6) were pre-
pared in situ from the corresponding arylbromides (Aldrich, used
as received) and n-butyllithium in hexane (Aldrich) at –78 °C. 1H,
31P{1H}, and 13C{1H}, spectra were measured on a Varian Mercury
300 spectrometer at 299.98, 80.98 and 75.44 MHz, respectively, in
* Corresponding author. Tel.: +420 220390356; fax: +420 220920661.
ˇ
E-mail address: cermak@icpf.cas.cz (J. Cermák).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.06.024

3030
J. Storch et al. / Journal of Organometallic Chemistry 693 (2008) 3029–3034
C6D6 solvent. Chemical shifts are reported in ppm (d) relative to
2.2.3. [Pd{2,6-(CH3)2C6H3}{PPri2CH@C(But)NN@C(But)CH2PPri2}] (9)
Solution of [PdCl{PPri2CH@C(But)NN@C(But)CH2PPri2}] (0.3 g,
0.54 mmol) in hexane (10 ml) was treated with 2,6-dim-
ethylphenyllithium (0.9 ml of 0.64 M solution in hexane:diethyl
ether (5:2), 0.42 mmol). The mixture was stirred 15 h at room tem-
perature. Water (0.1 ml) was added and the solvent evaporated in
vacuum. The residue was extracted with hexane (2 ml), filtered
and evaporated to dryness in vacuum giving 0.24 g (71%) of a red
product.
TMS, referenced to hexamethyldisilane and external H3PO4
(
31P{1H}). A monocrystal of 3 suitable for X-ray analysis was ob-
tained by slow evaporation of solvent at room temperature.
2.2. Synthesis of the palladium complexes
2.2.1. [Pd(C6H5){PPri2CH@C(But)NN@C(But)CH2PPri2}] (7)
Solution of [PdCl{PPri2CH@C(But)NN@C(But)CH2PPri2}] (0.2 g,
0.35 mmol) in hexane (10 ml) was treated with phenyllithium
(0.6 ml of 0.7 M solution in hexane, 0.42 mmol). The mixture
turned orange immediately, it was further stirred 15 h at room
temperature. Water (0.1 ml) was added to destroy the excess of
phenyllithum and the solvent evaporated in vacuum. The resi-
due was extracted with hexane (3 ml), filtered and evaporated
31P–{1H} NMR (C6D6): 38.5, 62.5 [AB, 2J(PP) = 377 Hz]; 1H NMR
(C6D6): 0.97 [6H, dd, 3J(HH) = 6.8 Hz, 3J(PH) = 14.2 Hz, CH3, Pri],
1.00 [6H, dd, 3J(HH) = 7.3 Hz, 3J(PH) = 14.6 Hz, CH3, Pri], 1.16 [6H,
dd, 3J(HH) = 7.2 Hz, 3J(PH) = 11.7 Hz, CH3, Pri], 1.21 [6H, dd,
3J(HH) = 7.4 Hz, 3J(PH) = 14.3 Hz, CH3, Pri], 1.23 [9H, s, CH3, But],
1.58 [9H, s, CH3, But], 2.05 [4H, br m, CH, Pri], 2.07 [2H, dd,
2J(PH) = 10.5 Hz, 4J(PH) = 2.7 Hz, CH2], 2.22 [6H, s, CH3, 2,6-
(CH3)2C6H3], 3.65 [1H, dd, 2J(PH) = 5.0 Hz, 4J(PH) = 1.1 Hz, CH],
6.73–6.90 [3H, m, CH, 2,6-(CH3)2C6H3]; 13C–{1H} NMR (C6D6):
11.64 [d, 1J(CP) = 12.7 Hz, CH2P], 17.88 [d, 2J(PC) = 2.0 Hz,
(CH3)2CH], 18.22 [s, (CH3)2CH], 18.57 [d, 2J(PC) = 4.0 Hz, (CH3)2CH],
18.80 [d, 2J(PC) = 6.0 Hz, (CH3)2CH], 23.21 [dd, 1J(PC) = 16.0 Hz,
3J(PC) = 2.8 Hz, PCH(CH3)2], 23.71 [s, CH3], 24.99 [dd, 1J(PC) =
24.1 Hz, 3J(PC) = 4.2 Hz, PCH(CH3)2], 29.48 [s, (CH3)3C], 31.57 [s,
(CH3)3C], 39.12 [d, 3J(PC) = 12.9 Hz, C(CH3)3], 39.32 [d, 3J(PC) =
2.6 Hz, C(CH3)3], 66.52 [d, 1J(PC) = 45.3 Hz, PCH@], 126.67 [s, Cpara],
128.31 [s, Cmeta], 138.16 [s, Cortho], 141.57 [d, 2J(PC) = 1.7 Hz, Cipso],
149.01 [s, C–N], 187.85 [d, 2J(PC) = 18.1 Hz, C@N].
to dryness in vacuum giving 0.21 g (95%) of
product.
a red-brown
Anal. Calc. for C33H61N2P2Pd (7 ꢀ ½ C6H14): C, 60.58; H, 9.40; N,
4.28. Found: C, 60.55; H, 9.39; N, 4.25%.31P–{1H} NMR (C6D6): 40.9,
62.8 [AB, 2J(PP) = 369 Hz]; 1H NMR (C6D6): 0.81 [6H, dd, 3J(HH) =
7.2 Hz, 3J(PH) = 14.3 Hz, CH3 Pri], 0.90 [6H, dd, 3J(HH) = 6.9 Hz,
3J(PH) = 8.7 Hz, CH3 Pri], 0.95 [6H, dd, 3J(HH) = 7.1 Hz, 3J(PH) =
10.7 Hz, CH3 Pri], 1.09 [6H, dd, 3J(HH) = 7.1 Hz, 3J(PH) = 14.3 Hz,
CH3 Pri], 1.23 [9H, s, CH3 But], 1.60 [9H, s, CH3 But], 1.80 [2H, br
m, CH, Pri], 1.89 [2H, br m, CH, Pri], 2.07 [2H, dd, 2J(PH) = 10.8 Hz,
4J(PH) = 3.0 Hz, CH2], 3.72 [1H, dd, 2J(PH) = 5.3 Hz, 4J(PH) = 2.0 Hz,
CH], 6.92–7.55 [5H, m, CH, Ph]; 13C–{1H} NMR (C6D6): 11.33 [dd,
1J(CP) = 11.7 Hz, 3J(PC) = 1.4 Hz, CH2P], 17.36 [d, 2J(PC) = 1.7 Hz,
(CH3)2CH], 17.77 [s, (CH3)2CH], 18.00 [d, 2J(PC) = 2.6 Hz, (CH3)2CH],
18.05 [d, 2J(PC) = 4.3 Hz, (CH3)2CH], 22.88 [dd, 1J(PC) = 17.6 Hz,
3J(PC) = 2.6 Hz PCH(CH3)2], 23.70 [dd, 1J(PC) = 27.1 Hz, 3J(PC) =
3.5 Hz, PCH(CH3)2], 29.43 [s, (CH3)3C], 31.61 [s, (CH3)3C], 39.26
[d, 3J(PC) = 6.8 Hz, C(CH3)3], 39.43 [d, 3J(PC) = 2.6 Hz, C(CH3)3],
67.55 [d, 1J(PC) = 45.8 Hz, PCH@], 122.20 [s, Cpara], 126.91 [s, Cmeta],
139.33 [t, 5J(CP) = 3.2 Hz, Cortho], 142.80 [s, C–N], 148.14 [dd,
2J(PC) = 12.7 Hz, 2J(PC) = 8.4 Hz, Cipso], 189.32 [d, 2J(PC) = 18.7 Hz,
C@N].
2.2.4. [Pd(C6H5){P(C6H11)2CH@C(But)NN@C(But)CH2P(C6H11)2}] (10)
Solution
of
[PdCl{P(C6H11)2CH@C(But)NN@C(But)CH2P-
(C6H11)2}] (0.2 g, 0.27 mmol) in hexane (10 ml) was treated with
phenyllithium (0.45 ml of 0.7 M solution in hexane, 0.32 mmol).
The mixture turned orange immediately; it was stirred for further
15 h at room temperature. Water (0.1 ml) was added and the sol-
vent evaporated in vacuum. The residue was extracted with hex-
ane (4 ml), filtered and evaporated to dryness in vacuum giving
0.14 g (66%) of a red-brown product. A monocrystal suitable for
X-ray analysis was obtained by slow evaporation of solvent at
room temperature.
2.2.2. [Pd(2-CH3C6H4){PPri2CH@C(But)NN@C(But)CH2PPri2}] (8)
Solution of [PdCl{PPri2CH@C(But)NN@C(But)CH2PPri2}] (0.16 g,
0.29 mmol) in THF (10 ml) was treated with 2-methylphenyllithi-
um (0.55 ml of 0.63 M solution in THF, 0.35 mmol). The mixture
was stirred 15 h at room temperature. Water (0.1 ml) was added
and the solvent evaporated in vacuum. The residue was extracted
with hexane (4 ml), filtered and evaporated to dryness in vacuum
giving 0.18 g (97%) of a dark red product.
Anal. Calc. for C48H84N2P2Pd (10 ꢀ C6H14): C, 67.23; H, 9.87; N,
3.27. Found: C, 60.27; H, 9.90; N, 3.25%. 31P–{1H} NMR (C6D6):
32.4, 51.9 [AB, 2J(PP) = 369 Hz]; 1H NMR (C6D6): 0.78–2.37 [44H,
m, CH2 + CH, C6H11], 1.28 [9H, s, CH3, But], 1.64 [9H, s, CH3, But],
2.16 [2H, dd, 2J(PH) = 10.8 Hz, 4J(PH) = 2.7 Hz, CH2], 3.82 [1H, dd,
2J(PH) = 5.1 Hz, 4J(PH) = 2.1 Hz, CH], 6.94–7.65 [5H, m, CH, Ph];
13C–{1H} NMR (C6D6): 12.80 [d, 1J(CP) = 11.8 Hz, CH2P], 29.54 [s,
(CH3)3C], 31.70 [s, (CH3)3C], 33.01 [dd, 1J(PC) = 17.5 Hz, 3J(PC) =
2.5 Hz, PCH], 33.69 [dd, 1J(PC) = 27.4 Hz, 3J(PC) = 3.5 Hz, PCH],
39.31 [d, 3J(PC) = 13.2 Hz, C(CH3)3], 39.55 [d, 3J(PC) = 2.9 Hz,
C(CH3)3], 68.73 [d, 1J(PC) = 46.1 Hz, PCH@], 122.30 [s, Cpara],
126.89 [s, Cmeta], 139.47 [t, 5J(CP) = 3.0 Hz, Cortho], 143.42 [s, C–N],
149.68 [dd, 2J(PC) = 12.6 Hz, 2J(PC) = 8.2 Hz, Cipso], 188.97 [d,
2J(PC) = 18.7 Hz, C@N].
31P–{1H} NMR (C6D6): 58.1, 79.3 [AB, 2J(PP) = 420 Hz]; 1H NMR
(C6D6): 1.01 [6 H, dd, 3J(HH) = 6.9 Hz, 3J(PH) = 14.4 Hz, CH3, Pri],
1.11 [6H, dd, 3J(HH) = 6.9 Hz, 3J(PH) = 15.0 Hz, CH3, Pri], 1.13 [9 H,
s, CH3, But], 1.25 [6H, dd, 3J(HH) = 7.4 Hz, 3J(PH) = 15.5 Hz, CH3,
Pri], 1.36 [6H, dd, 3J(HH) = 7.2 Hz, 3J(PH) = 16.8 Hz, CH3, Pri], 1.44
[9H, s, CH3, But], 1.90 [2H, dd, 2J(PH) = 10.2 Hz, 4J(PH) = 3.6 Hz,
CH2], 2.16 [4 H, bm, CH, Pri], 2.11 [3H, s, CH3, 2-CH3C6H4], 3.83
[1H, dd, 2J(PH) = 6.3 Hz, 4J(PH) = 2.4 Hz, CH], 6.84 – 7.12 [4H, m,
CH, 2-CH3C6H4]; 13C-{1H} NMR (C6D6): 10.33 [dd, 1J(CP) = 10.8 Hz,
3J(PC) = 2.5 Hz, CH2P], 17.73 [d, 2J(PC) = 2.3 Hz, (CH3)2CH], 18.34
[d, 2J(PC) = 2.3 Hz, (CH3)2CH], 18.60 [d, 2J(PC) = 2.9 Hz, (CH3)2CH],
18.82 [d, 2J(PC) = 4.0 Hz, (CH3)2CH], 19.15 [s, CH3], 23.99 [dd,
2.2.5. [Pd(2-CH3C6H4){P(C6H11)2CH@C(But)NN@C(But)CH2P(C6H11)2}]
(11)
Solution
of
[PdCl{P(C6H11)2CH@C(But)NN@C(But)CH2P-
(C6H11)2}] (0.17 g, 0.23 mmol) in THF (10 ml) was treated with 2-
methylphenyllithium (0.45 ml of 0.63 M solution in THF,
0.28 mmol). The mixture was stirred 15 h at room temperature.
Water (0.1 ml) was added and the solvent evaporated in vacuum.
The residue was extracted with hexane (4 ml), filtered and evapo-
rated to dryness in vacuum giving 0.10 g (56%) of a red product.
31P–{1H} NMR (C6D6): 49.9, 69.0 [AB, 2J(PP) = 420 Hz]; 1H NMR
(C6D6): 0.95–2.35 [44H, m, CH2 + CH, C6H11], 1.20 [9H, s, CH3,
But], 1.51 [9H, s, CH3, But], 2.01 [2H, dd, 2J(PH) = 10.7 Hz, 4J(PH) =
1J(PC) = 17.3 Hz,
3J(PC) = 3.2 Hz,
PCH(CH3)2],
24.92
[dd,
1J(PC) = 27.3 Hz, 3J(PC) = 4.2 Hz, PCH(CH3)2], 29.06 [s, (CH3)3 C],
31.41 [s, (CH3)3C], 39.41 [d, 3J(PC) = 11.5 Hz, C(CH3)3], 39.52 [s,
C(CH3)3], 71.93 [d, 1J(PC) = 45.2 Hz, PCH@], 125.89 [s, CH@],
126.02 [s, CH@], 128.91 [s, CH@], 130.19 [s, CH@], 135.48 [s,
˜C@], 140.77 [s, PdC@], 149.07 [s, C–N], 190.55 [dd,
2J(PC) = 21.5 Hz, 4J(PC) = 1.1 Hz, C@N].

J. Storch et al. / Journal of Organometallic Chemistry 693 (2008) 3029–3034
3031
3.8 Hz, CH2], 2.10 [3H, s, CH3, 2-CH3C6H4], 3.95 [1H, dd,
2J(PH) = 6.2 Hz, 4J(PH) = 2.3 Hz, CH], 6.98–7.09 [4H, m, CH, 2-
CH3C6H4]; 13C-{1H} NMR (C6D6): 11.62 [d, 1J(CP) = 13.3 Hz, CH2P],
19.16 [s, CH3], 29.20 [s, (CH3)3C], 31.57 [s, (CH3)3C], 33.91 [dd,
1J(PC) = 17.2 Hz, 3J(PC) = 3.1 Hz, PCH], 34.39 [dd, 1J(PC) = 27.0 Hz,
3J(PC) = 4.3 Hz, PCH], 39.53 [d, 3J(PC) = 14.6 Hz, C(CH3)3], 39.68 [d,
3J(PC) = 2.0 Hz, C(CH3)3], 73.01 [d, 1J(PC) = 45.2 Hz, PCH@], 125.96
[s, CH@], 126.09 [s, CH@], 128.98 [s, CH@], 130.26 [s, CH@],
135.57 [s, ˜C@], 140.85 [s, PdC@], 149.28 [s, C–N], 190.27 [d,
2J(PC) = 22.1 Hz, C@N].
idue was extracted with hexane (4 ml), filtered and evaporated to
dryness in vacuum giving 0.21 g (95%) of a red product.
31P–{1H} NMR (C6D6): 68.2, 105.5 [AB, 2J(PP) = 416 Hz]; 1H NMR
(C6D6): 1.20 [9H, s, CH3, But], 1.34 [18H, d, 3J(PH) = 12.3 Hz, CH3,
But], 1.41 [18H, d, 3J(PH) = 6.3 Hz, CH3, But], 1.47 [9H,s, CH3, But],
1.99 [2H, dd, 2J(PH) = 9.8 Hz, 4J(PH) = 3.2 Hz, CH2], 2.10 [3H, s,
CH3, 2-CH3C6H4], 4.34 [1H, t, 4J(PH) = 3.6 Hz, CH], 6.97–7.10 [4H,
m, CH, 2-CH3C6H4]; 13C–{1H} NMR (C6D6): 12.76 [dd, 1J(CP) =
6.9 Hz, 3J(PC) = 1.7 Hz, CH2P], 19.14 [s, CH3], 29.68 [dd, 2J(PC) =
4.0 Hz, 4J(PC) = 1.4 Hz, (CH3)3CP], 30.02 [dd, 2J(PC) = 3.2 Hz,
4J(PC) = 1.0 Hz, (CH3)3CP], 30.34 [s, (CH3)3C], 31.14 [s, (CH3)3C],
36.58 [dd, 1J(PC) = 17.0 Hz, 3J(PC) = 5.2 Hz, PC(CH3)3], 36.90 [dd,
1J(PC) = 5.5 Hz, 3J(PC) = 4.3 Hz, PC(CH3)3], 39.36 [dd, 3J(PC) =
14.0 Hz, 5J(PC) = 1.3 Hz, C(CH3)3], 39.64 [d, 3J(PC) = 2.6 Hz,
C(CH3)3], 81.10 [d, 1J(PC) = 43.5 Hz, PCH@], 125.90 [s, CH@],
126.03 [s, CH@], 128.12 [s, CH@], 130.21 [s, CH@], 135.49 [s,
˜C@], 140.77 [s, PdC@], 157.61 [s, C–N], 187.93 [dd, 2J(PC) =
20.2 Hz, 4J(PC) = 1.3 Hz, C@N].
2.2.6. [Pd{2,6-(CH3)2C6H3}{P(C6H11)2CH@C(But)NN@C(But)CH2-
P(C6H11)2}] (12)
Solution
of
[PdCl{P(C6H11)2CH@C(But)NN@C(But)CH2P-
(C6H11)2}] (0.25 g, 0.34 mmol) in hexane (15 ml) was treated with
2,6-dimethylphenyllithium (0.6 ml of 0.64 M solution in hex-
ane:diethyl ether (5:2), 0.38 mmol). The mixture faded a little then
it was stirred 20 h at room temperature. Water (0.1 ml) was added
and the solvent evaporated in vacuum. The residue was extracted
with hexane (4 ml), filtered and evaporated to dryness in vacuum
giving 0.17 g (61%) of a red product.
2.2.9. [Pd{2,6-(CH3)2C6H3}{PBut2CH@C(But)NN@C(But)CH2PBut2}]
(15)
31P–{1H} NMR (C6D6): 48.9, 65.9 [AB, 2J(PP) = 423 Hz]; 1H NMR
(C6D6): 0.95–2.32 [44H, m, CH2 + CH, C6H11], 1.19 [9H, s, CH3,
But], 1.48 [9H, s, CH3, But], 2.00 [2H, dd, 2J(PH) = 10.5 Hz,
4J(PH) = 3.3 Hz, CH2], 2.23 [6H, s, CH3, 2,6-(CH3)2C6H3], 3.91 [1H,
dd, 2J(PH) = 6.5 Hz, 4J(PH) = 2.0 Hz, CH], 6.72 [3H, m, CH, 2,6-
(CH3)2C6H3]; 13C–{1H} NMR (C6D6): 11.56 [d, 1J(CP) = 10.9 Hz,
CH2P], 23.71 [s, CH3], 29.20 [s, (CH3)3C], 31.52 [s, (CH3)3C], 33.38
[dd, 1J(PC) = 16.4 Hz, 3J(PC) = 3.2 Hz, PCH], 33.92 [dd, 1J(PC) =
26.4 Hz, 3J(PC) = 3.9 Hz, PCH], 39.51 [d, 3J(PC) = 15.0 Hz, C(CH3)3],
39.72 [d, 3J(PC) = 2.0 Hz, C(CH3)3], 72.43 [d, 1J(PC) = 45.8 Hz,
PCH@], 126.70 [s, Cpara], 128.31 [s, Cmeta], 138.15 [s, Cortho],
148.88 [s, C–N], 190.49 [d, 2J(PC) = 21.0 Hz, C@N].
Solution of [PdCl{PBut2CH@C(But)NN@C(But)CH2PBut2}] (0.23 g,
0.37 mmol) in hexane (15 ml) was treated with 2,6-dim-
ethylphenyllithium (0.7 ml of 0.64 M solution in hexane:diethyl
ether (5:2), 0.45 mmol). The mixture was stirred 3 h at reflux, then
15 h at room temperature. Water (0.1 ml) was added and the sol-
vent evaporated in vacuum. The residue was extracted with hex-
ane (4 ml), filtered and evaporated to dryness in vacuum giving
0.15 g (58%) of a red product.
31P–{1H} NMR (C6D6): 66.4, 95.7 [AB, 2J(PP) = 416 Hz]; 1H NMR
(C6D6): 1.19 [9H, s, CH3, But], 1.38 [18H, d, 3J(PH) = 12.6 Hz, CH3,
But], 1.40 [18H, d, 3J(PH) = 9.3 Hz, CH3, But], 1.46 [9H,s, CH3, But],
1.96 [2H, dd, 2J(PH) = 9.9 Hz, 4J(PH) = 3.3 Hz,CH2], 2.22 [6H, s,
CH3, 2,6-(CH3)2C6H3], 4.29 [1H, dd, 2J(PH) = 4.2 Hz, 4J(PH) = 3.0 Hz,
CH], 6.72–6.94 [3H, m, CH, 2,6-(CH3)2C6H3]; 13C–{1H} NMR
(C6D6): 11.93 [dd, 1J(PC) = 8.1 Hz, 3J(PC) = 1.8 Hz, CH2P], 23.67 [s,
CH3], 29.49 [dd, 2J(PC) = 4.1 Hz, 4J(PC) = 1.2 Hz, (CH3)3CP], 30.34
[s, (CH3)3C], 31.24 [s, (CH3)3C], 36.22 [dd, 1J(PC) = 17.3 Hz,
3J(PC) = 5.1 Hz, PC(CH3)3], 36.47 [dd, 1J(PC) = 3.9 Hz, 3J(PC) = 1.4 Hz,
PC(CH3)3], 39.45 [dd, 3J(PC) = 13.7 Hz, 5J(PC) = 0.9 Hz, C(CH3)3],
39.84 [d, 3J(PC) = 2.6 Hz, (CH3)3C], 79.45 [d, 1J(PC) = 43.5 Hz,
PCH@], 126.67 [s, Cpara], 128.31 [s, Cmeta], 138.14 [s, Cortho],
154.64 [s, C–N], 188.66 [d, 2J(PC) = 21.0 Hz, C@N].
2.2.7. [Pd(C6H5){PBut2CH@C(But)NN@C(But)CH2PBut2}] (13)
Solution of [PdCl{PBut2CH@C(But)NN@C(But)CH2PBut2}] (0.23 g,
0.37 mmol) in hexane (15 ml) was treated with phenyllithium
(0.65 ml of 0.7 M solution in hexane, 0.46 mmol). The colour of
the mixture faded immediately then slowly turned red-brown, it
was further stirred 20 h at room temperature. Water (0.1 ml) was
added and the solvent evaporated in vacuum. The residue was ex-
tracted with hexane (4 ml), filtered and evaporated to dryness in
vacuum giving 0.15 g (62%) of a red-brown product.
Anal. Calc. for C48H84N2P2Pd: C, 61.20; H, 9.37; N, 4.20. Found:
C, 61.37; H, 9.42; N, 4.23%. 31P-{1H} NMR (C6D6): 56.3, 93.2 [AB,
2J(PP) = 373 Hz]; 1H NMR (C6D6): 1.08 [18H, d, 3J(PH) = 12.3 Hz,
CH3, But], 1.19 [18H, d, 3J(PH) = 13.2 Hz, CH3, But], 1.31 [9H, s,
CH3, But], 1.44 [9H,s, CH3, But], 2.07 [2H, dd, 2J(PH) = 10.2 Hz,
4J(PH) = 2.1 Hz, CH2], 4.35 [1H, t, 4J(PH) = 3.2 Hz, CH], 6.86–7.73
[5H, m, CH, Ph]; 13C–{1H} NMR (C6D6): 14.47 [d, 1J(PC) = 7.2 Hz,
CH2P], 29.49 [d, 2J(PC) = 4.0 Hz, (CH3)3CP], 29.54 [d, 2J(PC) = 3.5 Hz,
(CH3)3CP], 30.91 [s, (CH3)3C], 30.96 [s, (CH3)3C], 35.76 [dd,
1J(PC) = 16.4 Hz, 3J(PC) = 4.9 Hz, PC(CH3)3], 36.20 [dd, 1J(PC) =
6.6 Hz, 3J(PC) = 3.5 Hz, PC(CH3)3], 39.04 [d, 3J(PC) = 3.5 Hz,
(CH3)3C], 39.20 [d, 3J(PC) = 11.2 Hz, (CH3)3C], 79.38 [d, 1J(PC) =
44.4 Hz, PCH@], 122.34 [s, Cpara], 126.22 [s, Cmeta], 142.11 [t,
5J(PC) = 2.9 Hz, Cortho], 147.25 [dd, 2J(PC) = 11.1 Hz, 2J(PC) = 8.7 Hz,
3. Crystallographic data
The diffraction-quality crystals of complexes were grown as
mentioned above. The crystals were selected in mother liquor
and quickly transferred into Fluorolube oil, then mounted on glass
fibres in random orientation and cooled to 150(1) K. Diffraction
data were collected using Nonius Kappa CCD diffractometer
(Enraf-Nonius) at 150(1) K (Cryostream Cooler Oxford Cryosystem)
and analyzed using the HKL program package [11]. The structures
were solved by direct methods and refined by full-matrix least-
squares techniques on F values (SIR92 [12] and CRYSTALS [13]). The
graphical presentation of the structures were done in ORTEP-3 [14]
and ACCELRYS DS Visualizer [15].
C
ipso], 149.70 [s, C–N], 185.25 [d, 2J(PC) = 18.7 Hz, C@N].
[PdCl{P(C6H11)2CH@C(But)NN@C(But)CH2P(C6H11)2}] (3), M =
625.57 g/mol, monoclinic system, space group P21/c, a =
18.2271(3), b = 10.6897(2), c = 16.8968(2) Å, b = 103.347(1)°, Z =
2.2.8. [Pd(2-CH3C6H4){PBut2CH@C(But)NN@C(But)CH2PBut2}] (14)
Solution of [PdCl{PBut2CH@C(But)NN@C(But)CH2PBut2}] (0.20 g,
0.32 mmol) in THF (10 ml) was treated with 2-methylphenyllithi-
um (0.805 ml of 0.63 M solution in THF, 0.50 mmol). The mixture
was stirred 3 h at reflux, then 15 h at room temperature. Water
(0.2 ml) was added and the solvent evaporated in vacuum. The res-
4, V = 3203.29(9) Å3, Dc = 1.30 g mꢁ3 ) = 0.78 mmꢁ1, crys-
, l(MoKa
tal dimensions of 0.2 ꢂ 0.2 ꢂ 0.3 mm. All heavy atoms were refined
anisotropically. All hydrogen atoms were localized from the
expected geometry and were refined isotropically. This model

3032
J. Storch et al. / Journal of Organometallic Chemistry 693 (2008) 3029–3034
converged to the final R = 0.0258 and Rw = 0.0312 using 5836 inde-
pendent reflections (hmax = 27.51°).
In 1H NMR spectra, the proton shifts of CH2P groups were in the
range of 1.90–2.07 ppm whereas protons of @CHP groups reso-
nated between 3.65 and 4.35 ppm. Both signals appeared as dou-
blets of doublets coupled to both phosphorus atoms. The similar
features could be found in 13C NMR spectra. The CH2P carbons ap-
peared in the range of 10.33–12.80 ppm whereas @CHP carbons
were considerably more deshielded (66.52–81.10 ppm) as ex-
pected and as is common with other known complexes with ene-
hydrazone backbone. The signals of carbons next to phosphorus
were doublets, 1J(PC) being always greater for the carbon in a
five-membered ring.
Signals of special importance were resonances of carbons of the
aryl ligands, especially the ipso carbon directly bonded to palla-
dium. With the exception of complexes 12 and 15, its resonance
was found in all the complexes. Comparison of carbon chemical
shifts of complex 9 with those of complexes 12 and 15 strongly
suggested, however, that the latter complexes had structures anal-
ogous to the former one. In all cases there was only one signal for
each couple of ortho and meta carbons as well as for para carbons
documenting a free rotation of aryl ligands around Pd–C bonds at
room temperature. The fast rotation of aryl groups in our com-
plexes contrasts with the work of van Koten et al. who found re-
stricted rotation of o- and m-tolyl (but not phenyl and p-tolyl)
groups in platinum NCN pincer complexes [17]. Whereas dimeth-
ylamino donor groups of the NCN pincers are certainly smaller
than diisopropyl-, dicyclohexyl- or di-tert-butylphosphino groups
of our PNP’ pincers, the ligand framework of the former pincers
is much more rigid. We believe that it is the possibility of compa-
rably easy ring inversion, especially of the six-membered ring, that
[Pd(C6H5){P(C6H11)2CH@C(But)NN@C(But)CH2P(C6H11)2}] ꢀ C6-
ꢀ
H
14 (10 ꢀ C6H14), M = 857.56 g/mol, triclinic system, space group P1,
a = 9.4293(2), b = 14.9696(3), c = 18.4260(5) Å,
b = 104.248(1)°,
1.17 g cmꢁ3
(MoK
a = 93.591(1)°,
c
= 103.5659(1)°, Z = 2, V = 2430.5(1) Å3, Dc =
,
l
a
) = 0.48 mmꢁ1, crystal dimensions of 0.2 ꢂ
0.2 ꢂ 0.3 mm. The independent part is created by one molecule
of the complex and one solvent molecule. All heavy atoms of the
complex were refined anisotropically, the hydrogen atoms were
localized from the expected geometry and were refined isotropi-
cally. The hexane carbon atoms were refined only isotropically
and the positions of hydrogen atoms were calculated from the
geometry and were not refined. This model converged to the final
R = 0.0412 and Rw = 0.0496 using 8811 independent reflections
(hmax = 27.48°).
4. Results and discussion
Reaction of palladium(II) chloro-amido complexes 1–3
with aryllithiums 4–6 led to new aryl-amido complexes 7–15
(Scheme 1) in which diphosphinoazines coordinated as monoan-
ionic unsymmetrical pincer-type ligands with amide nitrogens in
positions trans to the aryl carbon. Yields generally decreased with
the bulkiness of the incoming aryl substituent and with steric con-
gestion created by substituents on both phosphoruses, tert-butyl
complexes being the most resistant to substitution. Nevertheless,
using reflux conditions the tert-butyl complex 14 with 2-methyl-
phenyl ligand could be obtained in 95% isolated yield.
F
H3COOC
But
PPh2
PPri2
PPri2
N
Pd
N
Pd
Cl
N
Pd
CH3
COOCH3
18
N
PPh2
PPri2
PPri2
But
17
16
F
The NMR spectra of all products were in accordance with
structures with ene-hydrazone monoanionic ligand backbone.
Large 2J(PP) coupling constants (369–423 Hz) confirmed trans
arrangement of phosphine donor groups [16]. The ene-hydrazone
coordination mode created two metallarings of inequal size (5-
membered and 6-membered) as was confirmed by the presence
of signals of both methylene and methine protons and carbons.
allows the aryl groups to mesh with substituents on phosphorus
atoms while rotating. The signals of ipso carbons were doublets
of doublets, the signals of ortho carbons were virtual triplets con-
firming thus the coupling to both phosphorus atoms. For example,
the signal of Cipso in complex 7 was found at 148.14 ppm with
2J(CP) 12.7 Hz and 8.4 Hz whereas the signal of Cortho was a virtual
triplet at 139.33 with |3J(PC) + 3J(P0C)| = 3.2 Hz. These values were
But
But
R = Pri, Ar = Ph, 7
PR2
PR2
Pd Cl
R = Pri, Ar =
o-tolyl, 8
ArLi
N
Pd
Ar
PR2
R = Pri, Ar = 2,6-dimethylphenyl, 9
N
R = Cy, Ar = Ph, 10
hexane or THF
N
N
PR2
R = Cy, Ar = o-tolyl,11
R = Cy, Ar = 2,6-dimethylphenyl, 12
R = But, Ar = Ph, 13
R = Pri, 1
R = Cy, 2
R = But, 3
But
But
R = But,A r =
o
-tolyl, 14
R = But, Ar = 2,6-dimethylphenyl, 15
Scheme 1.

J. Storch et al. / Journal of Organometallic Chemistry 693 (2008) 3029–3034
3033
in accordance with data for a known trans-[Pd(PMe3)2(C6H5)
(NHC6H5)] complex where the Cipso signal was
a triplet at
157.2 ppm with 2J(CP) = 12 Hz [18].
In addition to the direct proof from the molecular structure
determination of complex 10 (see below), the evidence for the
presence of Pd–Cipso bond in some other complexes was also pro-
vided by HMBC correlations. Complex 7 showed a four-bond cou-
pling of the ipso carbon with methine protons and also a four-
bond coupling with the methine protons of isopropyl groups, both
in the five membered ring of the compound. In complex 8 this ipso
carbon was coupled across five bonds with the methyl protons of
isopropyl groups in the five membered ring whereas in complex
9 the Cipso showed interaction with methylene protons in the six-
membered ring.
We were able to grow single crystals of the cyclohexyl diph-
osphinoazine complex with phenyl ligand 10. In addition to that,
X-ray structure of one of the starting chloro-amido complexes 3
was determined (Figs. 1 and 2). The crystal structures confirmed
the square-planar coordination sphere of the palladium central
atom and the formation of five- and six-membered rings of the
PNP’ ligand suggested by NMR techniques.
So far only one structure of a palladium complex with a diph-
osphinoazine in monoanionic ene-hydrazone form [16] is reported
in Cambridge Structure Database (CSD version 5.29, January 2008
release). However the Pd(II) coordination sphere in 3 and 10 can
be compared also with other known PNP palladium complexes.
The angle P1–Pd–P8 in complex 3 is 170.75(2)° and Pd–N4 dis-
tance is 2.0648(15) Å which contrasts with the values of
163.54(2)° and 2.0258(19) Å, respectively, found by Ozerov [19]
for a symmetrical pincer complex 16. The smaller values for the lat-
ter complex are likely due to a higher ring strain of the structure
with two condensed five membered rings, the Pd–Cl bond lengths
being essentially equal. Palladium–nitrogen bond was found to be
considerably longer (2.0938(15) Å) in the methyl-amido complex
17 than in complex 16, which is explained by trans influence of
the methyl ligand [20]. The same trend, i.e. lengthening of the Pd–
N4 bond trans to a carbon ligand compared to the Pd–N4 bond trans
to a chlorine, was also observed going from 3 to 10 (2.0648(15) Å vs.
2.123(2) Å) and also in a trans-vinyl complex 18 [16] although there
the effect is smaller (2.087(11) Å) due to a more electron accepting
Fig. 2. ORTEP projection of 10. The solvent molecule was omitted for clarity.
Selected bond distances (Å) and angles (°): Pd–C41 2.033(3), Pd–P1 2.2785(6), Pd–
P8 2.2705(6), Pd–N4 2.123(2), P1–Pd–P8 166.85(3), N4–Pd–C41 175.52(9).
character of the substituted vinyl ligand. An interesting comparison
is offered with the structure determined by Boncella of a square-pla-
nar diphosphine palladium aryl-amido complex containing only
monodentate ligands. The Pd–C as well as Pd–N bond lengths in
the complex [Pd(PMe3)2(C6H5)(NHC6H5)] [21] are within experi-
mental error equal to the values for complex 10 (2.033(3) Å and
2.123(2) Å, respectively). However, while P1–Pd–P8 angle in com-
plex 10 amounts to 166.85(3)°, i.e. phosphine donor atoms are bent
away from the phenyl ligand due to their involvement in the two
metallarings, in complex [Pd(PMe3)2(C6H5) (NHC6H5)] the two trim-
ethylphosphines are actually bent towards the phenyl (and away
from the anilide ligand) the analogous P–Pd–P angle being approx-
imately 185.8°. The explanation offered by authors [21] is steric (less
repulsion from the phenyl than from the anilide ligand).
The five- and six-membered rings in the PNP’ ligand can be de-
scribed as any ring using the ring puckering parameters [22]. Both
structures (3 and 10) adopt the E5 conformation for the five-mem-
bered ring and the B2,5 conformation for the six-membered ring (in
the series of atoms Pd1–N4–C3–C2–P1 and Pd1–N4–N5–C6–C7–
P8, respectively). In the case of 3 the six-membered ring is more
puckered and its conformation reaches the border between B2,5
and 4T2 [22].
Both the tert-butyl and cyclohexyl groups are highly sterically
demanding. Mutual interactions between these groups thus prevail
in the molecular packing of 3 and 10. The tert-butyl hydrogen
atoms in 3 minimize the influence of the chlorine atom on the
molecular assembly. The cyclohexyl groups in 10 do not surround
the phenyl substituent as close as the tert-butyl groups envelop the
chlorine atom in 3. There are CHꢀꢀꢀ
p
p
interactions between two
-system of the phenyl ring.
cyclohexyl hydrogen atoms and the
The adjacent complex molecules (two enantiomers generated by
the center of symmetry) are mutually rotated by 180° making their
phenyl substituents parallel (in the direction of internal diagonal).
No interaction of the phenyl rings is apparent. The complex mole-
cules are arranged stepwise in the X dimension creating thereby a
solvent accessible void in the corners of the lattice cell (532 Å3;
calculated by Squeeze [23]). This void is filled with two hexane
solvent molecules which represent a kind of the third nonpolar
group within this structure (together with the cyclohexyl and
tert-butyl groups).
Fig. 1. ORTEP projection of 3. Selected bond distances (Å) and angles (°): Pd–Cl
2.3302(6), Pd–P1 2.2795(6), Pd–P8 2.3181(6), Pd–N4 2.0648(15), P1–Pd–P8
170.75(2), N4–Pd-Cl 176.20(5).

3034
J. Storch et al. / Journal of Organometallic Chemistry 693 (2008) 3029–3034
[d] M. Albrecht, G. van Koten, Angew. Chem., Int. Ed. 40 (2001) 3750;
5. Conclusions
[e] M. Montag, L. Schwartsburd, R. Cohen, G. Leitus, Y. Ben-David, J.M.L.
Martin, D. Milstein, Angew. Chem., Int. Ed. 46 (2007) 1901;
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[g] H. Salem, Y. Ben-David, L.J.W. Shimon, D. Milstein, Organometallics 25
(2006) 2292.
Trans-aryl-amido palladium complexes were obtained by
reactions of the corresponding easily accessible chloro-amido com-
plexes with aryllithiums using as supporting pincers unsymmetri-
cal PNP’ diphosphinoazines in monoanionic ene-hydrazone form.
The complexes are square-planar with aryl groups rotating freely
in solution at room temperature despite relative bulkiness of the
substituents on phosphorus atoms. The X-ray diffraction analysis
of the phenyl substituted complex with bis(dicyclohexylphos-
phino)azine ligand revealed that the preferred conformation in
the solid state is the one with the phenyl ring perpendicular to
the coordination plane of the complex. This conformation also al-
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and the -system of the phenyl ring.
p
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Acknowledgements
The support of grant agencies (Grant Agency of the Czech
Republic, 203/01/0554, 203/06/0738; Ministry of Education, Youth
and Sports of the Czech Republic, LC06070 and MSM0021620857)
is gratefully acknowledged.
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Appendix A. Supplementary material
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Delft, 1997. For reference, see: Z. Otwinovski, W. Minor, Methods Enzymol.
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G. Polidori, J. Appl. Crystallogr. 27 (1994) 435.
CCDC 684195 and 684196 contain the supplementary crystallo-
graphic data for [PdCl{P(C6H11)2CH@C(But)NN@C(But)CH2P-
(C6H11)2}] (3) and [Pd(C6H5){P(C6H11)2CH@C(But)NN@C(But)CH2P-
(C6H11)2}] ꢀ C6H14 (10 ꢀ C6H14). These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.06.024.
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