Mononuclear and dinuclear palladium and nickel complexes of phosphinimine-based tridentate ligands

Article abstract of DOI:10.1039/c1dt10131e

The tridentate bis-phosphinimine ligands O(1,2-C₆H ₄NPPh₃)₂1, HN(1,2-C₂H ₄NPR₃)₂ (R = Ph 2, iPr 3), MeN(1,2-C ₂H₄NPPh₃)₂4 and HN(1,2-C ₆H₄NPPh₃)₂5 were prepared. Employing these ligands, monometallic Pd and Ni complexes O(1,2-C₆H ₄NPPh₃)₂PdCl₂6, RN(1,2-CH ₂CH₂NPPh₃)₂PdCl][Cl] (R = H 7, Me 8), [HN(1,2-CH₂CH₂NPiPr₃)₂PdCl][Cl] 9, [MeN(1,2-CH₂CH₂NPPh₃)₂PdCl] [PF₆] 10, [HN(1,2-CH₂CH₂NPPh₃) ₂NiCl₂] 11, [HN(1,2-CH₂CH₂NPR ₃)₂NiCl][X] (X = Cl, R = iPr 12, X = PF₆, R = Ph 13, iPr 14), and [HN(1,2-C₆H₄NPPh₃) ₂Ni(MeCN)₂][BF₄]Cl 15 were prepared and characterized. While the ether-bis-phosphinimine ligand 1 acts in a bidentate fashion to Pd, the amine-bis-phosphinimine ligands 2-5 act in a tridentate fashion, yielding monometallic complexes of varying geometries. In contrast, initial reaction of the amine-bis-phosphinimine ligands with base followed by treatment with NiCl₂(DME), afforded the amide-bridged bimetallic complexes N(1,2-CH₂CH₂NPR₃)₂Ni ₂Cl₃ (R = Ph 16, iPr 17) and N(1,2-C₆H ₄NPPh₃)₂Ni₂Cl₃18. The precise nature of a number of these complexes were crystallographically characterized.

Full text of DOI:10.1039/c1dt10131e

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PAPER
Mononuclear and dinuclear palladium and nickel complexes of
phosphinimine-based tridentate ligands†
Renan Cariou, Fatme Dahcheh, Todd W. Graham and Douglas W. Stephan*
Received 22nd January 2011, Accepted 22nd February 2011
DOI: 10.1039/c1dt10131e
The tridentate bis-phosphinimine ligands O(1,2-C6H4N PPh3)2 1, HN(1,2-C2H4N PR3)2 (R = Ph 2,
iPr 3), MeN(1,2-C2H4N PPh3)2 4 and HN(1,2-C6H4N PPh3)2 5 were prepared. Employing these
ligands, monometallic Pd and Ni complexes O(1,2-C6H4N PPh3)2PdCl2 6,
RN(1,2-CH2CH2N PPh3)2PdCl][Cl] (R = H 7, Me 8), [HN(1,2-CH2CH2N PiPr3)2PdCl][Cl] 9,
[MeN(1,2-CH2CH2N PPh3)2PdCl][PF6] 10, [HN(1,2-CH2CH2N PPh3)2NiCl2] 11,
[HN(1,2-CH2CH2N PR3)2NiCl][X] (X = Cl, R = iPr 12, X = PF6, R = Ph 13, iPr 14), and
[HN(1,2-C6H4N PPh3)2Ni(MeCN)2][BF4]Cl 15 were prepared and characterized. While the
ether-bis-phosphinimine ligand 1 acts in a bidentate fashion to Pd, the amine-bis-phosphinimine
ligands 2–5 act in a tridentate fashion, yielding monometallic complexes of varying geometries. In
contrast, initial reaction of the amine-bis-phosphinimine ligands with base followed by treatment with
NiCl2(DME), afforded the amide-bridged bimetallic complexes N(1,2-CH2CH2N PR3)2Ni2Cl3 (R =
Ph 16, iPr 17) and N(1,2-C6H4N PPh3)2Ni2Cl3 18. The precise nature of a number of these complexes
were crystallographically characterized.
ceived very limited attention.16 We have recently communicated
Introduction
the unusual rearrangement reactivity of phosphinimine-arene-
based pincer ligands in Pd complexes (Scheme 1).17 Nonetheless,
these early data demonstrate the predicted pocketing provided
by such ligands. Herein, we explore related ligand systems that
incorporate ether and amine central donors in tridentate bis-
phosphinimine ligands. The variety of Ni and Pd coordination
geometries accessible employing these ligands are demonstrated
and the implications for future chemistry is considered.
Complexes of tridentate or pincer ligands have attracted great
interest as ligand variations affords tunable reactivity. Group 10
metal complexes bearing pincer ligands have found applications
in diverse areas of chemistry such as sensors, switches and
catalysts.1 Although PCP pincer type ligands have attracted the
most interest,2 PNP type ligands, which offer electronic and steric
flexibility, have proven to be able to stabilize highly reactive species,
such as group IV alkylidene, phosphinidene,3 metalhydrides,4,5 and
three coordinate complexes.6,7 In addition, PNP pincer complexes
display interesting reactivity such as oxidative addition of C-
Halogen bonds,8,9 C–H bond activation,5 N2 activation and
homolytic cleavage of H2.7
In targeting new ligand systems that might also find applications
in catalysis, we are developing strategies based on the notion that
steric protection of an active site can be provided by appropriate
ligand design. To this end, we sought to employ phosphinimine
donors in tridentate ligands as the N atoms are basic and
the inclusion of phosphinimine substituents would sterically
shield the adjacent coordination site. While mono- and bidentate
phosphinimide and phosphinimine ligands have been employed
to access a variety of complexes and catalyst precursors,10–12,13–15
tridentate ligands incorporating phosphinimine donors have re-
Scheme 1 Reactions of bis-phosphinimine ligands with Pd complexes.
Experimental Section
Department of Chemistry, University of Toronto, 80 St. George Street,
Toronto, Ontario, Canada, M5S 3H6. E-mail: dstephan@chem.utoronto.ca;
Tel: 416-946-3294
General Remarks
All manipulations were carried out under an atmosphere of dry,
O2-free N2 employing an Innovative Technology glove box and
† CCDC reference numbers 809529–809536. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt10131e
4918 | Dalton Trans., 2011, 40, 4918–4925
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a Schlenk vacuum-line. Solvents were purified with a Grubbs-
type column system manufactured by Innovative Technology
and dispensed into thick-walled Schlenk glass flasks equipped
with Teflon-valve stopcocks (pentane, toluene, CH2Cl2), or were
dried over the appropriate agents and distilled. All solvents were
thoroughly degassed after purification (repeated freeze-pump-
thaw cycles). Deuterated solvents were dried over the appropriate
agents, vacuum-transferred into storage flasks with Teflon stop-
cocks and degassed accordingly (CD2Cl2). Toluene and pentane
in vacuo. 2: Yield: 5.20 g (70%).1H NMR (C6D6): 7.78 (m, 12 H,
3
3
C6H5); 7.01 (M, 18 H, C6H5); 3.68 (dt, JHP = 14.6 Hz, JHH
=
1
5.7 Hz, CH2); 3.28 (t, 3JHH = 5.7 Hz, CH2). 31P{ H} NMR (C6D6):
1
5.9. 13C{ H} NMR (C6D6): 134.0 (Cq), 132.6 (d, CH, JCP = 12 Hz),
130.6 (d, CH, JPC = 4 Hz), 128.8 (d, CH, JCP = 15 Hz), 55.4 (d,
2
3
CH2, JCP = 29 Hz), 45.6 (d, CH2, JCP = 7 Hz). +ESI-MS(m/z):
624 [M+H]+. Anal. Calcd. for C40H39N3P2: C, 77.03; H, 6.30; N,
6.74. Found: C, 76.61; H, 6.90; N, 6.72., 3: Yield: 1.04 g (80%).
1H NMR (C6D6): 3.61 (dt, 4H, HNCH2CH2, 3JHH = 6 Hz, 4JHP
=
were stored over potassium mirrors, while bromobenzene and
12 Hz), 3.08 (t, 4H, HNCH2CH2, 3JHH = 6 Hz), 2.69 (s broad, 1H,
NH), 2.14 (dq, 6H, CHiPr, 3JHH = 7 Hz, 2JHP = Hz), 1.26 (dd, 36H,
1
dichloromethane were stored over 4 A molecular sieves. H, 13C
˚
and 31P NMR spectra were recorded at 25 ◦C on Varian 400 MHz
and Bruker 400 MHz spectrometers. Chemical shifts are given
relative to SiMe4 and referenced to the residue solvent signal (1H,
13C) or relative to an external standard (31P: 85% H3PO4). Chemical
shifts are reported in ppm and coupling constants as scalar values
in Hz. Combustion analyses were performed in house employing
a Perkin–Elmer CHN Analyzer. HN(1,2-C6H4NH2)2 was synthe-
sized according to literature procedure.18 In several cases, repeated
attempts to obtain suitable carbon analysis were unsuccessful.
This is thought to result from the formation of metal-carbides
during combustion. O(1,2-C6H4NH2)2, HN(CH2CH2NH2)2 were
purchased from Aldrich and Me(CH2CH2NH2)2 from TCI. Liq-
CH3 iPr, 3JHH = 7 Hz, 3JHP = 13 Hz). 31P{ H} NMR (C6D6): 27.9.
1
1
13C{ H} NMR (C6D6): 56.6 (d, NHCH2CH2, JCP = 18 Hz), 46.6
(d, HNCH2CH2, JCP = 6 Hz), 24.6 (d, CH iPr, JCP = 57 Hz), 17.4 (d,
CH3 iPr, JCP = 3 Hz). +ESI-MS(m/z): 420 [M+H]+. Anal. Calcd.
for C22H51N3P2: C, 62.97; H, 12.25; N, 10.01. Found: C,62.42; H,
12.06; N, 9.88.
Synthesis of MeN(1,2-CH2CH2N PPh3)2 4
A solution of PPh3Br2 (2.00 g, 6.25 mmol) in 50 mL CH2Cl2 was
added dropwise at 0 ◦C to a solution of MeN(CH2CH2NH2)2
(0.32 g, 3.11 mmol) in 50 mL CH2Cl2 and 15 mL Et3N. The
suspension was stirred and allowed to warm to 25 ◦C and then
was left stirring for one hour. The solvent was removed in vacuo
to afford a white solid. A solution of K[N(SiMe3)2] (1.25 g,
6.25 mmol) in 5 mL THF was added dropwise at -35 ◦C to
a suspension of the white solid in 50 mL THF at -35 ◦C. The
suspension was stirred and allowed to warm to 25 ◦C. The solvent
was removed in vacuo to afford a white solid. The same step
was repeated to afford the product as a white solid. Yield: 1.04
g (80%).1H NMR (C6D6): 7.75 (m, 12 H, C6H5); 7.03 (m, 18H,
C6H5); 3.72 (m, 4H, CH2); 3.07 (t, 4H, 3JHH = 7 Hz CH2), 2.41 (s,
˚
uids were degassed and stored over 4 A molecular sieves.
Synthesis of O(1,2-C6H4N PPh3)2 1
A solution of PPh3Br2 (4.22 g, 9.99 mmol) in 50 mL CH2Cl2 was
added dropwise at 0 ◦C to a solution of O(1,2-C6H4NH2)2 (1.00 g,
4.99 mmol) in 50 mL CH2Cl2 and 15 m◦L Et3N. The suspension
was stirred and allowed to warm to 25 C and was then stirred
for one hour further. The solvent was removed in vacuo to afford
a white solid. The product was extracted into THF and filtered
through Celite to remove the HNEt3Br salt. The solvent was then
removed in vacuo to afford an off-white solid. Yield: 3.42 g (95%).
1
1
3H, N–CH3). 31P{ H} NMR (C6D6): 6.0. 13C{ H} NMR (C6D6):
132.7 (d, CH, JCP = 8.8 Hz), 130.6 (d, CH, JCP = 2.7 Hz), 128.2 (Cq),
127.7 (d, CH, JCP = 24.4 Hz) 64.9 (d, CH2, 2JCP = 21.1 Hz), 44.6 (d,
CH2, 3JCP = 4.9 Hz), 44.0 (N-CH3). Anal. Calcd. for C41H41N3P2
(637.73): C, 77.22; H, 6.48; N, 6.59. Found: C, 77.02; H, 6.22; N,
6.34.
1
1
31P{ H} NMR (CD2Cl2): 2.5. H NMR (CD2Cl2): 7.69–7.65 (m,
12H, o-ArH); 7.46–7.41 (m, 6H, p-ArH); 7.34–7.30 (m, 12H, m-
ArH); 6.68–6.62 (m, 2H, OArH); 6.61–6.59 (m, 2H, OArH); 6.39–
6.34 (m, 2H, OArH); 6.27–6.25 (m, 2H, OArH). 13C { H} NMR
1
(CD2Cl2): 149.9 (d, 1,2-C6H4, JCP = 17 Hz); 141.3 (1,2-C6H4); 132.6
(d, C6H5, JCP = 10 Hz); 131.5 (C6H5); 131.2 (d, C6H5, JCP = 3 Hz);
128.3 (d, C6H5, JCP = 12 Hz); 123.4 (d, 1,2-C6H4, JCP = 14 Hz);
122.3 (1,2-C6H4); 118.4 (1,2-C6H4), 117.1 (1,2-C6H4).
Synthesis of HN(1,2-C6H4N PPh3)2 5
A solution of Ph3PBr2 (2.15 g, 5.10 mmol) in of CH2Cl2 (100 mL)
was added slowly to a solution of HN(1,2-C6H4NH2)2 (0.508
g, 2.55 mmol) in CH2Cl2 (10 mL) and NEt3 (7 mL) at 0 ◦C.
The reaction was stirred 15 min at this temperature and allowed
to warm up to room temperature for 30 min. Volatiles were
evaporated under vacuum and the residue extracted with THF
(150 mL) and filtered through a pad of Celite. Solvents were
evaporated to dryness to afford a green solid. Recrystallisation
from CH2Cl2–Et2O. Yield: 1.62 g (88%). 1H NMR (CD2Cl2): 8.63
Synthesis of HN(1,2-CH2CH2N PR3)2 R = Ph 2, iPr 3
These compounds were prepared in a similar fashion with the
variations noted. Thus only one preparation is detailed. Ph3PBr2
(10.0 g, 23.7 mmol) in ca. 200 mL of CH2Cl2 was added at 0 ◦C to
a solution of HN(CH2CH2NH2)2 (1.27 mL, 11.8 mol) in 60 mL of
1 : 1 CH2Cl2/NEt3. The mixture was stirred at room temperature
for 1 h and then the solvent was removed in vacuo. The residue was
suspended in THF (100 mL) and cooled to 0 ◦C. K[N(SiMe3)2]
(4.71 g, 23.6 mmol) in THF (50 mL) was added, stirred at room
temperature for 30 min and the volatiles removed in vacuo. The
residue was redissolved in THF and the second deprotonation was
repeated in the same way. The solution was filtered through Celite
and the solvent was removed. The residue was triturated with ether
(ca. 100 mL), the resulting solid was collected filtered and dried
(s br, 1H, NH), 7.83 (m, 12H, ArH), 7.44 (dt, 3JHH = 7.4 Hz, 4JHH
=
3
4
1.4 Hz, 8H, ArH), 7.27 (dt, JHH = 7.7 Hz, JHH = 2.9 Hz, 12H,
3
4
ArH), 6.64 (td, 2H, JHH = 7.6 Hz, JHH = 1.5 Hz, C6H4), 6.46
3
4
3
(dt, JHH = 7.7 Hz, JHH = 1.3 Hz, 2H, C6H4), 6.40 (td, JHH
=
7.5 Hz, JHH = 1.5 Hz, 2H, C6H4), 31P{ H} NMR (CD2Cl2): 3.8.
4
1
13C{ H} NMR (CD2Cl2): 140.1 (Cq),138.5 (d, CH, JCP = 21 Hz),
1
133.0 (d, CH, JCP = 10 Hz), 131.9 (d, CH, JCP = 3 Hz), 131.8
(CH), 130.8 (CH), 128.4 (d, CH, JCP = 12 Hz), 120.2 (d, CH, JCP
=
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10 Hz), 118.6 (CH), 117.9 (CH), 113.4 (CH). +ESI-MS(m/z): 720
[M+H]+. Anal. Calcd for C48H39N3P2 (719.79): C, 80.09; H, 5.46;
N, 5.84. Found: C, 79.98; H, 5.89; N, 5.80.
(76%). 1H NMR (400 MHz, CD2Cl2): 8.46 (broad s, 1H, NH); 3.44
(m, 2H, HNCH2CH2); 3.07 (m, 2H, HNCH2CH2); 2.95 (septet,
3
6H, CH(CH3)2, JHH = 7 Hz); 2.63 (m, 4H, HNCH2CH2); 1.46
3
(dd, 18H, CH(CH3)2, JHH = 7 Hz, JHP = 15 Hz); 1.40 (dd, 18H,
3
1
CH(CH3)2, JHH = 7 Hz, JHP = 15 Hz). 31P{ H} NMR (CD2Cl2):
Synthesis of O(1,2-C6H4N PPh3)2PdCl2 6
63.4. 13C NMR (101 MHz, CD2Cl2): 56.6 (d, HNCH2CH2, JCP
=
A solution of Pd(CH3CN)2Cl2 (0.090 g, 0.347 mmol) in 3 mL
CH2Cl2 was added dropwise to a solution of 1 (0.250 g,
0.347 mmol) in 5 mL CH2Cl2. A color change from light orange
to dark orange/red was observed when left stirring for an hour.
The solution was concentrated and product recrystallized upon
addition of Et2O yielding an orange powder. Yield: 0.271 g (87%).
1H NMR (CD2Cl2): 8.19 (br s, 4H, PPh3); 7.96 (m, 2H, 1,2-C6H4);
7.64 (br s, 4H, PPh3); 7.45 (m, 10H, PPh3); 7.19 (m, 6H, PPh3);
11 Hz); 53.8 (d, HNCH2CH2, JCP = 4 Hz); 25.6 (d, CH(CH3)2,
JCP = 2 Hz); 17.7 (d, CH(CH3)2, JCP = 4 Hz); 16.5 (d, CH(CH3)2,
JCP = 54 Hz). Anal. Calcd. for C22H51N3P2PdCl2: C, 44.27; H, 8.61;
N, 7.04. Found: C, 44.04; H, 8.58; N, 7.46.
Synthesis of [MeN(1,2-CH2CH2N PPh3)2PdCl][PF6] 10
NaPF6 (0.025 g, 0.015 mmol) was added to a stirring solution
of 8 (0.100 g, 0.012 mmol) in 10 ml CH2Cl2. The solution was
left stirring for one hour and was then filtered over Celite. The
filtrate was concentrated and the product isolated as a yellow
powder by adding Et2O. Yield: 0.101 g (89%). 1H NMR (400 MHz,
CD2Cl2): 7.76 (m, 12H,C6H5); 7.66 (m, 6H, C6H5); 7.56 (m, 12H,
C6H5); 3.61 (ddd, 2H, MeNCH2CH2, 3JHH = 6 Hz, JHP = 18 Hz);
6.92 (m, 6H, PPh3); 6.50 (t, 4H, 1,2-C6H4), 5.67 (dt, 2H, 1,2-C6H4).
1
31P{ H} NMR (CD2Cl2): 37.1. 13C NMR (CD2Cl2): 150.1 (d, JCP
=
9 Hz); 137.3; 136.4 (d, JCP = 3 Hz); 134.4 (d, JCP = 11 Hz); 132.7;
130.2 (d, JCP = 14 Hz); 128.0; 124.8 (d, JCP = 3 Hz); 123.1 (d, JCP
=
3 Hz); 120.6 (d, JCP = 2 Hz). Anal. Calcd. for C48H38N2P2OPdCl2:
C, 64.19; H, 4.26; N, 3.12. Found: C, 62.19; H, 4.34; N, 3.32.
3
3.29 (dt, 2H, MeNCH2CH2, JHH = 3 Hz, JHP = 12 Hz); 3.04 (s,
3H, MeNCH2CH2); 2.81 (m, 2H, MeNCH2CH2); 2.56 (m, 2H,
Synthesis of [RN(1,2-CH2CH2N PPh3)2PdCl][Cl] (R = H 7, Me
8)
1
1
MeNCH2CH2). 31P{ H} NMR (CD2Cl2): 35.6; -143.4. 19F{ H}
NMR (377 MHz, CD2Cl2): -73.2. 13C NMR (100 MHz, CD2Cl2):
These compounds were prepared in a similar fashion with
the variations noted. A solution of Pd(CH3CN)2Cl2 (0.042 g,
0.160 mmol) in 5 mL CH2Cl2 was added dropwise to a solution
of 2 (0.10 g, 0.160 mmol) in 5 mL CH2Cl2. A color change from
yellow to light orange was observed when left stirring for one hour.
The solution was concentrated and the product recrystallized by
the addition of Et2O yielding a yellow powder. 7: Yield: 0.104 g
(81%). 1H NMR (CD2Cl2): 8.94 (t, 1H, NH, 3JHH = 10 Hz); 7.88–
7.83 (m, 12H, C6H5); 7.63–7.59 (m, 6H, C6H5); 7.54–7.49 (m, 12H,
C6H5); 3.46 (m, 2H, HNCH2CH2); 2.85 (m, 2H, HNCH2CH2);
134.3 (d, Ar–C, JCP = 10 Hz); 133.4 (Ar–C); 129.2 (d, Ar–C, JCP
=
13 Hz); 127.4 (d, Ar–Cq, JCP = 102 Hz); 66.9 (d, MeNCH2CH2,
JCP = 15 Hz); 53.3 (MeNCH2CH2); 45.8 (MeNCH2CH2). Anal.
Calcd. for C41H41N3P2PdClPF6: C, 53.26; H, 4.47; N, 4.54. Found:
C, 53.05; H, 5.06; N, 4.38.
Synthesis of [HN(1,2-CH2CH2N PPh3)2NiCl2] 11, [HN(1,2-
CH2CH2N PiPr3)2NiCl][Cl] 12
These compounds were prepared in a similar fashion, thus only
one preparation is detailed. NiCl2(DME) (0.350 g, 1.592 mmol)
was added to 2 (1.0 g, 1.603 mmol) in THF (5 mL) and the
mixture was stirred overnight. After cooling to -35 ◦C, the yellow
solid was collected by vacuum filtration on a plug of Celite and
was washed with cold THF (2 mL) and then dried in vacuo. The
yellow solid dissolved in CH2Cl2 (ca. 10 mL) and then the purple
solution was filtered through Celite. Ether (ca. 20 mL) was added
dropwise resulting in the precipitation of a lemon yellow solid.
The suspension was cooled to -35 ◦C, and the solid was collected
by vacuum filtration and dried in vacuo. Yield: 0.980 g (82%). 11:
meff = 3.13 BM. Anal. Calcd. for C40H39Cl2N3NiP2: C, 63.78; H,
5.22; N, 5.58. Found: C, 63.98; H, 5.50; N, 6.01. 12: pink solid.
Yield: 85%. meff = 3.08 BM. Anal. Calcd. for C22H51Cl2N3NiP2:
C, 48.11; H, 9.36; N, 7.65. Found: C,45.37; H,8.86; N,7.92. IR
(CH2Cl2) n: 3442 (NH).
1
2.70 (m, 2H, HNCH2CH2); 2.47 (m, 2H, HNCH2CH2). 31P{ H}
NMR (CD2Cl2): 34.0. 13C NMR (CD2Cl2): 133.8 (d, JCP = 10 Hz);
132.2; 128.8 (d, JCP = 10 Hz); 128.2 (d, JCP = 13 Hz); 56.7
(HNCH2CH2); 54.7 (HNCH2CH2). Repeated attempts to obtain
EA were unsuccessful.
1
8: Yield: 0.200 g (78%). H NMR (400 MHz, CD2Cl2): 7.66
(m, 12H,C6H5); 7.63 (m, 6H, C6H5); 7.55 (m, 12H, C6H5);
3
3.64 (dt, 2H, MeNCH2CH2, JHH = 6 Hz, JHP = 18 Hz);
3
3.31 (tt, 2H, MeNCH2CH2, JHH = 3 Hz, JHP = 12 Hz); 3.14
(s, 3H, MeNCH2CH2); 2.81 (m, 2H, MeNCH2CH2), 2.75 (m,
1
2H, MeNCH2CH2). 31P{ H} NMR (CD2Cl2): 35.4. 13C NMR
(100 MHz, CD2Cl2): 134.3 (d, Ar–C, JCP = 15 Hz); 133.0 (Ar–
C); 128.8 (d, Ar–C, JCP = 13 Hz); 127.2 (d, Ar–C, JCP = 102 Hz);
66.7 (d, MeNCH2CH2, JCP = 15 Hz); 53.1 (MeNCH2CH2); 45.6
(MeNCH2CH2). Anal. Calcd. for C41H41N3P2PdCl2: C, 60.42; H,
5.07; N, 5.16. Found: C, 56.30; H, 5.32; N, 5.03.
Synthesis of [HN(1,2-CH2CH2N PR3)2NiCl][PF6] R = Ph 13,
iPr 14
Synthesis of [HN(1,2-CH2CH2N PiPr3)2PdCl][Cl] 9
A suspension of Pd(CH3CN)2Cl2 (0.120 g, 0.462 mmol) in 5 mL
THF was added to a solution of 3 (0.200 g, 0.476 mmol) in
5 mL THF. The resulting mixture was heated at 60 ◦C in a sealed
Schlenk bomb for two hours. The solvent was removed in vacuo
and the product was extracted into CH2Cl2 and the mixture was
then filtered. The filtrate was concentrated and the pale brown
product was obtained by the addition of Et2O. Yield: 0.217 g
These compounds were prepared in a similar fashion, thus only
one preparation is detailed. (0.147 g, 0.875 mmol) of NaPF6 was
added to 11 (0.100 g, 0.133 mmol) of in ca. 2 mL of CH2Cl2. The
mixture was stirred overnight and was then filtered through Celite.
10 mL of ether was added dropwise to precipitate a purple solid
that was triturated for one hour. The solvent was decanted and the
solid was washed with 2 ¥ 5 mL of ether and dried in vacuo. 13:
4920 | Dalton Trans., 2011, 40, 4918–4925
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Yield: 0.077 g (67%). Recrystallization of 13 from CH2Cl2 afforded
purple crystals of 13a; recrystallization of 13 from BrC6H5 afforded
MS (m/z): 881 [M-NiCl2]+. Anal. Calcd. for C48H38Cl3N3Ni2P2: C,
61.17; H, 4.06; N, 4.46. Found: C, 59.49; H, 4.74; N, 4.70.
1
13b. 31P{ H} NMR (CD2Cl2): 40.1, -141.3. meff = 3.23 BM. Anal.
Calcd. for C40H39ClF6N3NiP3: C, 55.68; H, 4.56; N, 4.87. Found:
C, 53.77; H, 4.66; N, 4.90. 14: Yield: 0.054 g (91%). meff = 3.08 BM,
Anal. Calcd. for C22H51ClF6N3NiP3: C, 40.11; H, 7.80; N, 6.38.
Found: C, 41.09; H, 7.57; N, 6.81.
X-ray Data Collection, Reduction, Solution and Refinement
Single crystals were coated in Paratone-N oil in the glove-
box, mounted on a MiTegen Micromount and placed under
an N2 stream. The data were collected on a Bruker Apex II
diffractometer. The data were collected at 150( 2) K for all
crystals. Data reduction was performed using the SAINT software
package and an absorption correction applied using SADABS.
The structures were solved by direct methods using XS and refined
by full-matrix least-squares on F2 using XL as implemented
in the SHELXTL suite of programs.19 All non-hydrogen atoms
were refined anisotropically. Carbon-bound hydrogen atoms were
placed in calculated positions using an appropriate riding model
and coupled isotropic temperature factors (see Table 1 and
supplementary data†). In the case of compounds 7 and 11, disorder
of the halides were modeled by initial refinement of the site
occupancy factors.
Synthesis of [HN(1,2-C6H4N PPh3)2Ni(MeCN)2][BF4]Cl 15
A solution of 5 (0.153 g, 0.21 mmol) in THF (4 mL) was added
to [Ni(MeCN)6][BF4)2] (0.102 g, 0.21 mmol) in THF (2 mL). The
resulting suspension was stirred at room temperature overnight.
Volatiles were evaporated in vacuo and the solid was crystallized
1
from CH2Cl2–Et2O. Yield: 0.210 g (96%), 31P{ H} NMR (CD2Cl2):
37.1. meff = 3.17 BM. Anal. Calcd (%) for C52H44BF4Cl N5NiP2: C,
63.55; H, 4.61; N, 7.13. Found: C, 61.43; H, 4.88; N, 7.27.
Synthesis of N(1,2-CH2CH2N PR3)2Ni2Cl3 R = Ph 16, iPr 17
and HN(1,2-C6H4N PPh3)2Ni2Cl3 18
These compounds were prepared in a similar fashion, thus only
one preparation is detailed. A solution of K[N(SiMe3)2] (0.066 g,
0.33 mmol) in THF (2 mL) was added dropwise to a solution of 2
(0.205 g, 0.33 mmol) in THF (3 mL) at -35 ◦C and was left stirring
for 30 min. The mixture was left stirring at room temperature for
30 min. A suspension of NiCl2(DME) (0.145 g, 0.66 mmol) in THF
(3 mL) was added to the ligand mixture and was stirred overnight
and a color change from yellow to dark purple/blue was oberved.
The solvent was removed in vacuo and solid extracted into CH2Cl2
and filtered. The solvent was then removed in vacuo yielding a
Results and Discussion
Ligand Synthesis
The ligand O(1,2-C6H4N PPh3)2 1 was synthesized in 95% yield
using a modified literature procedure via condensation of prepared
Ph3PBr2 and 2,2¢-oxydianiline in the presence of NEt3.20 Related
amino-bis-phosphinimine ligands are also readily synthesized by
the reaction of the corresponding triamine with two equivalents of
either Ph3PBr2 or iPr3PBr2 in the presence of NEt3 (Scheme 2). In
this fashion the ligands HN(1,2-C2H4N PR3)2 (R = Ph 2, iPr 3),
MeN(1,2-C2H4N PR3)2 4 and HN(1,2-C6H4N PPh3)2 5 were
prepared. While the synthesis of 2, 3 and 4 requires deprotonation
with a comparatively strong base such as tBuOK or K[N(SiMe3)2],
the latter procedure is preferred as deprotonation with tBuOK
yields small amounts of phosphine oxide contamination. In the
1
blue solid. Yield: 0.230 g (83%). 16: 31P{ H} NMR (CD2Cl2): 51.0.
meff = 4.97 BM, Anal. Calcd. for C40H38Cl3N3Ni2P2: C, 56.76; H,
4.53; N, 4.96. Found: C, 54.89; H, 4.90; N, 4.99 17: Yield: 0.073 g
1
(55%).31P{ H} NMR (CD2Cl2): 79.3. meff = 4.63 BM. Anal. Calcd
for C22H50Cl3N3Ni2P2: C, 41.14; H, 7.85; N, 6.54. Found: C, 40.92;
H, 7.42; N, 6.06. 18: Yield: 0.274 g (75%). meff = 5.02 BM. +ESI-
Table 1 Crystallographic data
6
7·2CH2Cl2
9
11
12
13a
13b
18·C6H6
Formula
C50H41Cl2N3- C42H43Cl6N3P2- C22H51Cl2N3- C40H39 Br0.5
-
C22H51Cl2N3- C40H39ClF6N3-
C40H40ClF6N3-
NiP3
C59H50Cl3N3-
Ni2P2
OP2Pd
Pd
P2Pd
Cl1.5N3NiP2
NiP2
NiP3
wt
939.10
Monoclinic
P21/c
970.83
Orthorhombic
Ibca
12.260(4)
20.121(6)
35.895(11)
90.00
90.00
90.00
8855(5)
8
1.456
596.90
Monoclinic
P21/n
8.6503(2)
26.8756(5)
12.0880(3)
90.00
93.1560(10)
90.00
2805.98(11)
4
1.413
0.0381
0.981
21416
4934
775.52
Monoclinic
P21/n
12.0407(13)
22.977(3)
13.4590(14)
90.00
97.437(5)
90.00
3692.3(7)
4
1.395
0.0759
1.295
74014
8424
549.21
Monoclinic
P21/n
8.6286(6)
32.013(2)
10.8902(8)
90.00
99.150(2)
90.00
2969.9(4)
4
1.228
0.0322
0.955
22133
5222
862.81
Orthorhombic
Pmn21
21.7288(9)
7.6413(3)
11.6265(5)
90.00
90.00
90.00
1930.42(14)
2
1.484
0.0391
0.759
54670
7697
247
0.0420
0.1217
1.043
863.82
1086.73
Monoclinic
C2/c
33.823(3)
8.9261(9)
23.968(2)
90.00
133.969(4)
90.00
5207.9(9)
4
1.386
0.0901
0.980
21713
5929
Cryst. syst.
Space grp
Triclinic
¯
P1
˚
˚
˚
a/A
20.2104(7)
24.1180(10)
20.0246(8)
90.00
118.446(2)
90.00
8582.2(6)
8
10.0118(7)
13.1874(10)
16.4704(12)
67.100(4)
89.195(4)
77.437(4)
1949.2(2)
2
b/A
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
d(calc) g cm-1 1.454
1.472
0.0993
0.752
27269
10660
491
0.0732
0.1994
R(int)
0.0783
0.674
139535
15098
1063
0.0353
0.0816
1.011
0.0646
0.887
67942
5096
m/cm-1
Total data
2
>2s(Fo
)
Variables
R (>2s)
Rw
262
271
441
271
317
0.0647
0.1644
1.177
0.0368
0.0862
1.032
0.0436
0.1016
1.008
0.0408
0.0922
1.133
0.0670
0.2239
0.892
GOF
0.971
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Fig. 1 ORTEP drawing of 6, hydrogen atoms are omitted for clarity.
Scheme 2 Synthesis of bis-phosphinimine ligands. i) CH2Cl2, NEt3. ii)
2 ¥ 2 K[N(SiMe3)2], THF.
3.46, 2.85, 2.70, and 2.47 ppm. A single crystal of compound
7 was obtained and the X-ray structure (Fig. 2) shows a distorted
square planar geometry around the palladium centre with the
amine proton at an angle about 94◦ to the plane formed by the
N3-ligand and the metal centre. The bond length Pd–N(2) in 7
case of 1 and 5, NEt3 is sufficiently basic to effect deprotonation
of the phosphiniminium salt. These new ligands 2–5 give rise to
31P resonances at 5.9, 27.9, 6.0 and 3.8 ppm respectively.16
Pd-Complexes
˚
is 2.008(9) A which is slightly shorter than the phosphinimine
Addition of (MeCN)2PdCl2 to a solution of 1 in CH2Cl2 proceeds
cleanly with the formation of a single product 6 which was
˚
nitrogen-Pd bonds of 2.043(1) and 2.046(1) A for Pd–N(1) and
Pd–N(3), respectively. The source of the bromide counter-ion is
likely residual HNEt3Br as purification of the ligand 2 proved
challenging. This was not the case for ligand 3.
1
isolated in 87% yield (Scheme 3). This species exhibited a 31P{ H}
NMR signal at 37.1 ppm inferring a symmetric disposition of
the phosphinimine fragments. X-ray crystallography revealed the
formulation of 6 as O(1,2-C6H4N PPh3)2PdCl2 (Fig. 1) in which
the Pd occupies a square planar coordination sphere with the
phosphinimine nitrogens bound in a cis orientation. The ligand
was bound to the metal centre in a bidentate mode. The non-
˚
bonded Pd–O distance is 4.110(2) A. The bite angle for the
bidentate bis-phosphinimine fragment, that is the N(1)–Pd–N(2)
is 85.8◦.
Fig. 2 ORTEP drawing of the cation of 7, hydrogen atoms and bromide
anion are omitted for clarity.
X-ray crystallographic characterization of compound 9 was also
performed. The geometry about Pd is similar to that seen in 7. The
Pd–N bond distances for the phosphinimine groups are slightly
˚
˚
shorter at 2.054(3) A and 2.066(3) A for Pd–(N1) and Pd–(N3)
respectively, while the central Pd–N distance in 9 was found to
˚
be 2.019(3) A (Fig. 3). An interesting feature of these molecules
Scheme 3 Synthesis of Pd-complexes of bis-phosphinimine ligands, (i)
anion exchange required for 10.
is the generation of the protective pocket about the Cl-site on
Pd generated by the phosphine-substituent of the phosphinimine
fragments.
In contrast, reaction of ligands 2–4 with (MeCN)2PdCl2 in
CH2Cl2 led to the formation of the complexes formulated as
[HN(CH2CH2N PR3)2PdCl][Cl] (R = Ph 7, R = iPr 9) and
[MeN(CH2CH2N PPh3)2PdCl][Cl] 8. These species were spec-
Subsequent reaction of 8 with NaPF6 resulted in anion exchange
and isolation of [MeN(CH2CH2N PPh3)2PdCl][PF6] 10. The
product was isolated in 89% yield and showed two resonances in
1
the 31P{ H} NMR spectrum at 35.6 and -143.4 ppm attributable
1
1
troscopically similar. In the case of 7, the 31P{ H} NMR spectrum
to the cation and anion respectively. In addition the 19F{ H}
showed a resonance at 34.0 ppm and the 1H NMR spectrum
showed the expected resonances for the ethylene backbone at
NMR spectrum showed the typical resonance for the PF6 anion
at -73.2 ppm.
4922 | Dalton Trans., 2011, 40, 4918–4925
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Fig. 3 ORTEP drawing of the cation of 9, hydrogen atoms are omitted
for clarity.
Fig. 4 ORTEP drawing of 11, all hydrogen atoms except the NH are
omitted for clarity, X = disordered Br/Cl.
Ni-Complexes
In contrast, the Ni cation in 12 has a distorted pseudo-
tetrahedral geometry at Ni with N(3)–Ni–N(1) and N(2)–Ni–Cl(1)
angles of 125.45(10)◦ and 142.85(8)◦ (Fig. 5). The phosphinimine-
The formation of 6–10 suggests that the diaryl-ether fragment of
ligand 1 is insufficiently basic to afford chelation in the tridentate
fashion seen with the amine linked analogs. It is for this reason that
the exploration of Ni chemistry focused on these latter ligands.
The reactions of 2 and 3 with NiCl2(DME) in THF afford the
corresponding mononuclear complexes 11 and 12 in good yields
(Scheme 4). Complexes are paramagnetic with magnetic moments
of 3.13 and 3.08 BM for 11 and 12, respectively. The values are
in agreement with the spin only value of 2.82 BM expected for
two unpaired electrons. Single crystals of 11 and 12 were grown
from C6H5Br. X-Ray analysis of yellow crystals of 11 revealed a
five coordinate Ni centre with the ligand adopting a meridional
coordination mode (Fig. 4). The halide ions were shown to be
a disordered mixture of Br and Cl with an approximate X(1)–
Ni–X(2) angle of 155.6◦. As with the Pd complex, 7, the Br is
derived from the difficulties of complete separation of the ligand
from Et3NHBr. The distorted trigonal bypyramid geometry (t =
0.18),21 at Ni results in N(1)–Ni–N(3) angle of 166.4(2)◦. The Ni–
˚
nickel bond lengths, Ni–N(1) and Ni–N(3) are 1.993(2) A and
˚
1.989(2) A, respectively while the Ni–Cl(1) bond length of
˚
˚
2.2547(8) A is about 0.2 A shorter than the Ni–Cl distances in
11. These shorter distances in 12 are consistent with the four
coordinate cationic character of 12. However, it is noteworthy that
˚
˚
the Ni–N(2) bond of 2.069(2) A is lengthened by about 0.06 A
compared to that in 11, most likely a result of the presence of
stronger electron donor NPiPr3 groups in 12.
˚
N(2) bond length is of 2.013(5) A which is significantly shorter
than the nickel-phosphinimine bonds Ni–N(1) and Ni–N(3) of
˚
˚
2.127(5) A and 2.113(5) A, respectively, presumably the impact of
both steric and electronic effects.
Fig. 5 ORTEP drawing of 12, hydrogen atoms are omitted for clarity.
The corresponding PF6 salts of complexes 13 and 14, were
synthesised by salt metathesis using NaPF6 in CH2Cl2 (Scheme
3) and isolated as purple solids. These products 13 and 14 were
paramagnetic with meff of 3.23 and 3.28 BM, respectively. In the
case of 13, two crystal forms were obtained. Purple crystals of 13a
were obtained by recrystallization from CH2Cl2. Single crystals
analysis of 13a reveals a distorted two fold symmetric square
planar geometry at the Ni center (Fig. 6(a)) with the N(2)–
Ni–N(2)¢ and N(1)–Ni–Cl(1) angles of 166.2(1)◦ and 165.5(2)◦,
˚
respectively. The Ni–N(1) is 1.922(2) A, while the Ni–N(2) bond
˚
distance is found to be 1.926(1) A. The latter as well as the Ni–
˚
Cl(1) bond distance of 2.1657(6) A, are slightly shorter than those
in 12. In contrast, recrystallization of the purple solution of 13
in bromobenzene, afforded yellow crystals of 13b (Fig. 6(b)). In
this case, the Ni cation adopts a pseudo-tetrahedral geometry
with Ni–N(1), Ni–N(2), Ni–N(3) and Ni–Cl(1) distances of
˚
˚
˚
˚
1.942(4) A, 2.026(4) A, 1.980(4) A and 2.2781(12) A, respectively.
The observation of these two forms of 13 is consistent with
subtle solvation effects that result in an equilibrium mixture of
Scheme 4 Synthesis of Ni-complexes of bis-phosphinimine ligands.
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Interestingly, treatment of ligands 2, 3 and 5 with K[N(SiMe3)2]
prior to the reaction NiCl2(DME) did not lead to the expected
mononuclear nickel amide complexes. Rather, unusual dinuclear
complexes formulated as N(1,2-CH2CH2N PR3)2Ni2Cl3 R =
Ph 16, iPr 17 and N(1,2-C6H4N PPh3)2Ni2Cl3 18 were formed
(Scheme 5). Even if the ligand to metal ratio was equimolar, the
dinuclear species were obtained in 50% yield as determined by
1H NMR spectroscopy. An additional equivalent of unreacted
protonated ligand (3.HCl) was detected. Subsequent treatment of
this mixture with one equivalent of base and NiCl2(DME) led to
the full conversion to the dinuclear complex. These complexes 16–
18 are paramagnetic, a feature attributable to pseudo-tetrahedral
environments at the Ni centers. Magnetic moments are in the range
4.63–5.02 BM representing a total of four unpaired electrons,
consistent with two unpaired electrons per d8 Ni centre.
Fig. 6 ORTEP drawings of (a) the cation of 13a, (b) 13b; hydrogen atoms
except the NH are omitted for clarity.
presumably diamagnetic and paramagnetic geometries, 13a and
13b as dissolution of either crystalline product results in the
generation of the mixture.
A mononuclear complex 15 bearing ligand 5 was synthesized
from the reaction of 5 with [Ni(MeCN)6][(BF4)2] generated
from NiCl2 (Scheme 3). This species was isolated in 96% yield
and observed to have a magnetic moment of 3.17 BM, con-
sistent with a mononuclear Ni complex of formula [HN(1,2-
C6H4N PPh3)2Ni(MeCN)2][BF4]Cl 15. Attempts to characterize
15 by X-Ray analysis afforded only preliminary data. While the
geometry about the Ni of 15 was confirmed to be five coordinate
trigonal bipyramidal Ni(II) centre, disorder of the anions and
included solvent, preclude a publishable solution. Nonetheless,
the two phosphinimine-fragments of the N3-ligand are bound in
the equatorial plane while the central amine donor of the N3-
ligand is bound in one of the axial positions with two acetonitrile
molecules completing the coordination sphere (Fig. 7). The poor
crystal quality precludes discussion of the metric parameters.
Scheme 5 Syntheses of dinuclear Ni(II) complexes.
The precise nature of the geometries of these dinuclear species
were probed by X-ray analysis. In the case of 18, the data confirmed
the dinuclear formulation with two pseudo-tetrahedral Ni centres
bridged by the ligand and a chlorine atom (Fig. 8). The bridging
nature of the ligand is unusual and unexpected and suggests that
the phosphinimine moiety is labile. To our knowledge only a few
examples of Ni complexes with bridging amides are reported in
the literature.22–26 The nickel-amide bond Ni–N(2) (2.014(2) A)
˚
is slightly longer than nickel-phosphinimine bonds Ni–N(1) of
◦
˚
1.981(5) A. The angle Ni(1)–N(2)–Ni(2) is of 88.21(27) and the
˚
two Ni centers are separated by 2.803 A. The terminal Ni–Cl bond
˚
distance of 2.2029(17) A was found to be significantly shorter than
˚
the bridging Ni–Cl distances of 2.2964(18) A.
Fig. 7 PLUTO drawing of the cation of 15.
4924 | Dalton Trans., 2011, 40, 4918–4925
Fig. 8 ORTEP drawing of 18.
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The contrasting nature of the monometallic and bimetallic
chemistry derived from the tridentate bis-phosphinimine ligands
resulting from treatment with base is an interesting aspect and
presumably results from the propensity of Ni amides to bridge two
metal centers. This provides a facile control over the formation of
mono versus bimetallic complexes.
3 B. C. Bailey, J. C. Huffman, D. J. Mindiola, W. Weng and O. V. Ozerov,
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5 L.-C. Liang, P.-S. Chien and Y.-L. Huang, J. Am. Chem. Soc., 2006,
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16772–16773.
Conclusions
In summary, new types of pincer ligands containing phosphin-
imine fragments have been synthesized and used to complex Pd
and Ni. The Pd chemistry supports the view that amino-bis-
phosphinimines provides convenient access to cationic square
planar complexes, where the phosphinimine-substituents sterically
shelter the metal-bound halide site. In the case of Ni, both
mononuclear and dinuclear complexes are derived from variation
in the ligand precursor. This synthetic chemistry sets the stage
for an investigation of these and related systems in various
applications. The reactivity of the sterically protected pocket of
the mono-metallic systems as well as the cooperative reactivity
of amide bridged bimetallic systems are now the subject of
exploration. These results will be reported in due course.
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The financial support of NSERC of Canada and LANXESS Corp
is gratefully acknowledged. DWS is also grateful for the award of
a Killam Research Fellowship.
Notes and references
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 4918–4925 | 4925
©