Nickel(II) and palladium(II) bis-aminophosphine pincer complexes

Article abstract of DOI:10.1021/om200439q

The aminophosphine ligands CH₂(CH₂NHPtBu ₂)₂ (1), (CH₂NHPtBu₂)₂ (2), and (CH₂NMePtBu₂)₂ (3) were prepared from the corresponding amines and ClPtBu₂. The ligand 1 reacts with PdI₂ to give the pincer complex (κ³P,C,P-CH(CH ₂NHPtBu₂)₂)PdI (4). The analogous reaction of 1 with NiCl₂(dme) gave a the purple product (κ³P,N,P- tBu₂PNH(CH₂)₃NPtBu₂)NiCl (5), which contains a strained three-membered P-N-Ni ring. Subsequent reaction of 5 with B(C₆F₅)₃ resulted in conversion to (κ³P,C,P-CH(CH₂NHPtBu₂)₂)NiCl (6). The related reaction of the aminophosphine ligand 2 with PdI₂ and with NiCl₂(dme) led, in both cases, to the complexes (κ³P,N,P-tBu₂PNH(CH₂) ₂NPtBu₂)MX (MX = PdI (7), NiCl (8)), respectively, whereas the reaction of 3 with PdX₂ gave (κ³P,C,P-tBu ₂PN(Me)CHCH₂N(Me)PtBu₂)PdX (X = I (9), Br (10), Cl (11)). The analogous reaction of 3 with NiCl₂(dme) afforded [(tBu₂PH)(NMe)(CH₂)₂(NMe)(tBu ₂P)NiCl₃], (12), which upon treatment with B(C ₆F₅)₃ afforded the species (κ ³P,C,P-tBu₂PN(Me)CHCH₂N(Me)PtBu ₂)NiCl (13). Crystallographic studies of 4-6, 8, 9, 11, and 12 are reported. The implications of these results are considered.

Full text of DOI:10.1021/om200439q

ARTICLE
pubs.acs.org/Organometallics
Nickel(II) and Palladium(II) Bis-Aminophosphine Pincer Complexes
Erin A. Gwynne and Douglas W. Stephan*
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
S Supporting Information
b
ABSTRACT: The aminophosphine ligands CH2(CH2NHPtBu2)2 (1),
(CH2NHPtBu2)2 (2), and (CH2NMePtBu2)2 (3) were prepared from the
corresponding amines and ClPtBu2. The ligand 1 reacts with PdI2 to give the
pincer complex (k3P,C,P-CH(CH2NHPtBu2)2)PdI (4). The analogous reac-
tion of 1 with NiCl2(dme) gave a the purple product (k3P,N,P-tBu2PNH-
(CH2)3NPtBu2)NiCl (5), which contains a strained three-membered
PꢀNꢀNi ring. Subsequent reaction of 5 with B(C6F5)3 resulted in conversion to (k3P,C,P-CH(CH2NHPtBu2)2)NiCl (6). The
related reaction of the aminophosphine ligand 2 with PdI2 and with NiCl2(dme) led, in both cases, to the complexes (k3P,N,
P-tBu2PNH(CH2)2NPtBu2)MX (MX = PdI (7), NiCl (8)), respectively, whereas the reaction of 3 with PdX2 gave (k3P,C,
P-tBu2PN(Me)CHCH2N(Me)PtBu2)PdX (X = I (9), Br (10), Cl (11)). The analogous reaction of 3 with NiCl2(dme) afforded
[(tBu2PH)(NMe)(CH2)2(NMe)(tBu2P)NiCl3], (12), which upon treatment with B(C6F5)3 afforded the species (k3P,C,
P-tBu2PN(Me)CHCH2N(Me)PtBu2)NiCl (13). Crystallographic studies of 4ꢀ6, 8, 9, 11, and 12 are reported. The implications
of these results are considered.
’ INTRODUCTION
’ EXPERIMENTAL SECTION
All preparations were performed under an atmosphere of dry, O2-free
N2 employing both Schlenk line and inert-atmosphere glovebox tech-
niques. Solvents (CH2Cl2, Et2O, and pentane) were purified employing
a Grubbs type column system manufactured by Innovative Technology.
1H, 13C{1H}, and 31P{1H} NMR spectra were acquired on a Bruker
Avance 400 MHz spectrometer, a Varian Mercury 300 MHz spectro-
Chelating ligands have proven instrumental in the develop-
ment of new catalysts; furthermore trans-chelating “pincer”
ligands have garnered considerable attention over the years.1ꢀ13
The most extensively investigated pincer complexes feature
ligands based on a meta-substituted arene skeleton (PCP).
Variations of the PCP-pincer framework have been shown to
alter the electronic and steric properties of the corresponding
metal complexes, resulting in unique reactivity.14,15
1
meter, or a Varian Mercury 400 MHz spectrometer. H NMR reso-
nances were referenced internally to the residual protonated solvent
resonances, 13C resonances were referenced internally to the deuterated
solvent resonances, and 31P resonances were referenced externally to
Aminophosphine chelating ligands of the form (linker)-
(NR0PR2)2 have also garnered attention, as such ligands are
readily prepared from diamines and chlorophosphines.5,16 While
linked diaminophosphine ligands such as (CH2N(R0)PR2)2
(R0 = H, alkyl; R = alkyl, aryl) have been reported by Wollins,17
Gusev,9 Vogt,16 and others,18ꢀ21 investigations of PCP amino-
phosphine-based pincer ligand complexes have received less
attention.10 We were drawn to these systems, as such ligands
offer adjacent P and N donors, suggesting the possibility of
unique binding modes and thus subsequent reactivity. In this
regard, the only report in which the N atom of an aminopho-
sphine has been shown to participate in binding to a metal was
recently reported by Palacios et al. In this case a bis-aminopho-
sphine ligand was shown to bind to Ru via both P atoms as well as
one of the amino NH groups, affording the Ru cation
[Cp*Ru(k3P,N,P-(iPr2PNH)2C6H10]+.21 In this paper, we de-
scribe the synthesis and characterization of Ni and Pd complexes
of bis-aminophosphine chelating ligands. Interestingly, these
ligands are shown to readily adopt two tridentate binding modes.
Participation of the secondary N adjacent to P affords k3P,N,P
ligands that incorporate three-membered NPM metallacycles.
Alternatively, metalation of the alkyl chain in the ligand backbone
affords k3P,C,P pincer complexes.
13
85% H3PO4. 1Hꢀ C HSQC experiments were carried out using
conventional pulse sequences to aid in the assignment of peaks in
13C{1H} NMR spectroscopy. Coupling constants (J) are reported as
absolute values. All glassware was dried overnight at 120 °C and
evacuated for 1 h prior to use. Combustion analyses were performed
in house employing a Perkin-Elmer 2400 Series II CHNS Analyzer. All
diamines were purchased from Aldrich and degassed prior to use.
tBu2PCl was purchased from Strem Chemical Co. All other chemicals
were purchased from Aldrich Chemical Co. and used without further
purification. THF-d8 was purchased in 1 g ampules and dried over 4 Å
activated molecular sieves prior to use. C6D6 and toluene-d8 were
vacuum-distilled from Na/benzophenone and freezeꢀpumpꢀthaw
degassed (ꢁ3). Hyflo Super Cel (Celite) was purchased from Aldrich
and dried for at least 12 h in a vacuum oven or on a Schlenk line prior to
use. Molecular sieves (4 Å) were purchased from Aldrich and dried at
100 °C under vacuum using a Schlenk line.
Synthesis of CH2(CH2NHPtBu2)2 (1).9. A solution of 1,3-diami-
nopropane (695 mg, 9.38 mmol) and triethylamine (2.0 g, 19.8 mmol)
was stirred in THF (5 mL). To this was added a solution of ClPtBu2
Received: May 24, 2011
Published: July 08, 2011
r
2011 American Chemical Society
4128
dx.doi.org/10.1021/om200439q Organometallics 2011, 30, 4128–4135
|

Organometallics
ARTICLE
2
2
(1.4 equiv, 2.43 g, 13.4 mmol) in THF (15 mL). After the mixture was
stirred overnight, the white salt precipitate was allowed to settle and the
clear supernatant was filtered through Celite. THF and unreacted
diamine were removed under vacuum to give a colorless liquid (2.36
g, 97%). 1H NMR (C6D6): δ 3.00 (m, 4H, CH2), 1.56 (dt, 2JHꢀP = 7 Hz,
(toluene-d8): δ 41.7 (d, JCꢀP = 16 Hz, CH2N), 40.7 (d, JCꢀP = 5,
CCH2C), 38.1 (dd, 1JCꢀP = 10 Hz, 3JCꢀP = 3.5 Hz, C(CH3)3), 34.4 (dd,
1JCꢀP = 6 Hz, 3JCꢀP = 2 Hz, C(CH3)3), 29.0 (dd, 2JCꢀP = 4 Hz, 4JCꢀP
=
2
1.0 Hz), 28.8 (d, JCꢀP = 5 Hz), 27.46 (s). Anal. Calcd for
C19H43ClN2NiP2: C, 50.08; H, 9.51; N, 6.15. Found: C, 49.70; H,
9.87; N, 5.75.
3
3JHꢀH = 7 Hz, 2H, NH), 1.06 (d, JHꢀP = 11 Hz, 36H, C(CH3)3).
31P{1H} NMR (C6D6): δ 78.8. 13C{1H} NMR (C6D6): δ 48.53 (d,
2JCꢀP = 29 Hz, 2C, NCH2CH2), 37.67 (t, 3JCꢀP = 7 Hz, 1C, CCH2C),
Synthesis of (j3P,C,P-CH(CH2NHPtBu2)2)NiCl (6). To a pur-
ple solution of 5 (20 mg, 0.044 mmol) in toluene (2 mL) was added a
colorless solution of B(C6F5)3 (22 mg, 0.044 mmol) in toluene (4 mL).
After 10 min of stirring at room temperature, the solution turned yellow
and a small amount of green oil had formed. The yellow solution was
decanted from the green oil, and toluene was removed under vacuum to
afford a yellow crystalline solid (isolated yield 48%). Yellow crystals
suitable for X-ray diffraction were grown from hexanes. 1H NMR
(C6D6): δ 3.10 (m, 2H, CH2), 3.01 (m, 4H, CH2), 1.45 (d, J = 7 Hz,
1H, NH), 1.44 (d, JPꢀH = 7 Hz, 1H, NH), 1.38 (d, JPꢀH = 6 Hz, 18H,
PC(CH3)3), 1.37 (d, JPꢀH = 6 Hz, 18H, PC(CH3)3). 31P{1H} NMR
(C6D6): δ 119.0. 13C{1H} NMR (C6D6): δ 55.0 (vt, JCꢀP = 10.3 Hz,
2C, CH2NP), 42.3 (vt, JCꢀP = 12 Hz, 1C, HCNi), 39.0 (vt, JCꢀP = 5 Hz,
1
2
34.48 (d, JCꢀP = 22 Hz, 4C, C(CH3)3), 28.98 (d, JCꢀP = 15 Hz,
C(CH3)3). Anal. Calcd for C19H44N2P2: C, 62.95; H, 12.23; N, 7.73.
Found: C, 63.07; H, 12.12; N, 7.43.
Synthesis of (CH2NHPtBu2)2 (2). A solution of ClPtBu2 (2.00 g,
11.1 mmol) in THF (15 mL) was added with stirring to a solution of
ethylenediamine (500 mg, 8.32 mmol) and triethylamine (2.0 g, 19.8
mmol) in THF (5 mL). After the mixture was stirrred overnight, the
white salt precipitate was allowed to settle and the clear supernatant was
filtered through Celite. THF and unreacted diamine were removed
under vacuum, and the resulting oily solid was recrystallized from
1
hexanes at ꢀ40 °C to give a white crystalline solid (3.24 g, 84%). H
2
NMR (C6D6): δ 3.04 (m, 4H, CH2), 1.24 (br d, JPꢀH = 11 Hz, 2H,
2C, C(CH3)3), 38.0 (vt, JCꢀP = 12 Hz, 2C, C(CH3)3), 28.4 (vt, JCꢀP
=
NH), 1.09 (d, 3JPꢀH = 11 Hz, 36H, C(CH3)3). 31P{1H} NMR (C6D6):
3 Hz, 6C, C(CH3)3), 27.9 (vt, JCꢀP = 3 Hz, 6C, C(CH3)3). Anal. Calcd
for C19H43ClN2NiP2: C, 50.08; H, 9.51; N, 6.15. Found: C, 50.10; H,
9.63; N, 6.05.
2
δ 78.3. 13C{1H} NMR (C6D6): δ 53.83 (dd, JCꢀP = 27 Hz, 3JCꢀP
=
=
7 Hz, 2C, CH2), 34.46 (d, 1JCꢀP = 21 Hz, 4C, C(CH3)3), 28.91 (d, 2JCꢀP
15 Hz, C(CH3)3). Anal. Calcd for C18H42N2P2: C, 62.04; H, 12.15; N,
8.04. Found: C, 62.07; H, 12.12; N, 8.13.
Synthesis of (j3P,N,P-tBu2PNH(CH2)2NPtBu2)PdI (7) and
(k3P,N,P-tBu2PNH(CH2)2NPtBu2)NiCl (8). These compounds
were prepared in a similar fashion, and thus only one preparation is
detailed. On addition of an orange suspension of (dme)NiCl2 (60 mg,
0.287 mmol) in THF (6 mL) to a clear solution of 1 (100 mg, 0.287
mmol) in THF (5 mL) with stirring, the reaction mixture turned dark
red. After 15 min, all (dme)NiCl2 had dissolved and the solution was
dark fuchsia. The solution was stirred for 4 h and then filtered through a
plug of Celite to remove a forest green precipitate, affording a bright
fuschia solution. The solvent was removed under vacuum to give the
purple crystalline solid 8 (65 mg, 54%).
Synthesis of (CH2NMePtBu2)2 (3).22. n-BuLi (22.66 mmol,
1.7 M in THF, 13.3 mL) was added dropwise to a solution of N,N0-
dimethylethylenediamine (1.0 g, 11.34 mmol) in THF (20 mL). After
3 h of stirring, a solution of ClPtBu2 (2.40 g, 22.7 mmol) in THF
(15 mL) was added slowly to the lithiated diamine and the mixture was
stirred at room temperature for 6 h. The mixture was filtered to remove
LiCl, and volatiles were removed from the filtrate under vacuum. The
resulting white waxy solid was recrystallized from pentane to give a
colorless crystalline solid (3.46 g, 81%). 1H NMR (C6D6): δ 3.34 (m,
CH2), 2.71 (6H, d, 3JHꢀP = 6 Hz, NCH3), 1.23 (d, 3JHꢀP = 12 Hz, 36H,
C(CH3)3). 31P{1H} NMR (C6D6): δ 108.0, 104.8, 104.0. 13C{1H}
NMR (C6D6): δ 60.7 (d, 2JCꢀP = 41 Hz), 39.1 (br s), 36.1 (d, 1JCꢀP = 28
Hz, PC(CH3)3), 30.1 (d, 2JCꢀP = 17 Hz, PC(CH3)3). Anal. Calcd for
C20H46N2P2: C, 63.80; H, 12.31; N, 7.44. Found: C, 63.78; H, 12.34;
N, 7.41.
Data for 7 are as follows. Yield: 66%. 1H NMR (C6D6): δ 2.71 (m,
3
2H, CH2), 2.63 (m, 2H, CH2), 1.17 (d, JPꢀH = 14 Hz, 18H, PC-
(CH3)3), 1.05 (d, JPꢀH = 16 Hz, 18H, PC(CH3)3). 31P{1H} NMR
3
(C6D6): δ 86.5, 17.7 (d, 2JPꢀP = 372 Hz). 13C{1H} NMR (C6D6): δ
2
2
52.3 (t, JCꢀP = 9 Hz, NCH2), 47.4 (dd, JCꢀP = NCH2), 37.8 (dd,
3JCꢀP = 10 Hz, JCꢀP = 6 Hz, PC(CH3)3), 37.2 (dd, JCꢀP = 10 Hz,
1JCꢀP = 4 Hz, PC(CH3)3), 29.0 (d, 2JCꢀP = 3 Hz, PC(CH3)3), 28.3 (d,
2JCꢀP = 7 Hz, PC(CH3)3). Anal. Calcd for C18H41N2P2PdI: C, 37.22; H,
7.12; N, 4.82. Found: C, 35.86; H, 7.18; N, 5.17.23
1
3
Synthesis of (j3P,C,P-CH(CH2NHPtBu2)2)PdI (4). A solution
of PdI2 (100 mg, 0.278 mmol) in THF (6 mL) was added dropwise with
stirring to a solution of CH2((CH2)2PtBu2)2 (100 mg, 0.277 mmol) in
THF (5 mL). Stirring overnight led to formation of a red solution, which
was filtered through Celite. THF was removed under vacuum to give 98
mg (62%) of a pale red solid. 1H NMR (C6D6): δ 3.37 (m, 1H, HCPd),
2.84 (m, 4H, CH2N), 1.46 (br s, 2H, NH), 1.37 (vt, JHꢀP = 7 Hz,
PC(CH3)3), 1.31 (vt, JHꢀP = 7 Hz, PC(CH3)3). 31P{1H} NMR (C6D6):
δ 130. 13C{1H} NMR (C6D6): δ 61.2 (t, 2JCꢀP = 5 Hz, HCPd), 55.3 (t,
Data for 8 are as follows. Yield: 54%. 1H NMR (C6D6): δ 2.56 (br m,
3
2H, NCH2), 2.18 (br m, 2H, NCH2), 1.45 (d, JPꢀH = 13 Hz, 18H,
PC(CH3)3), 1.28 (d, 3JPꢀH = 15 Hz, 18H, PC(CH3)3). 31P{1H} NMR
(C6D6): δ 98, ꢀ19 (d, 2JPꢀP = 262 Hz). 13C{1H} NMR (C6D6): δ 48.7
(dd, 3JCꢀP = 9 Hz, 2JPꢀC = 4 Hz, NCH2CH2), 43.7 (dd, 3JCꢀP = 16 Hz,
2JCꢀP = 5 Hz, NCH2CH2), 38.0 (dd, JCꢀP = 14 Hz, JCꢀP = 4 Hz,
1
3
1
2JCꢀP = 7 Hz, NCH2), 40.2 (t, JCꢀP = 6 Hz, PC(CH3)3), 37.6 (t,
1
3
1JCꢀP = 12 Hz, PC(CH3)3), 29.1 (t, 2JCꢀP = 3 Hz, PC(CH3)3), 28.5 (t,
2JCꢀP = 3 Hz, PC(CH3)3). Anal. Calcd for C19H43N2P2PdI: C, 38.36; H,
7.29; N, 4.71. Found: C, 37.88; H, 7.17; N, 4.61.
PC(CH3)3), 35.2 (dd, JCꢀP = 6 Hz, JCꢀP = 4 Hz, PC(CH3)3), 29.4
(dd, 2JCꢀP = 6 Hz, 4JCꢀP = 2 Hz, C(CH3)3), 28.7 (dd, 2JCꢀP = 6 Hz,
4JCꢀP = 1 Hz, C(CH3)3). Anal. Calcd for C18H41ClN2NiP2: C, 48.95; H,
9.36; N, 6.34. Found: C, 49.21; H, 9.89; N, 6.49.
Synthesis of (j3P,N,P-tBu2PNH(CH2)3NPtBu2)NiCl (5). A
suspension of NiCl2(dme) (108 mg, 0.554 mmol) in THF (6 mL)
was added with stirring to a solution of 2 (200 mg, 0.552 mmol) in THF
(4 mL) in the presence of triethylamine. The resulting green-brown
solution was stirred overnight to give a purple mixture, which was then
filtered through Celite to give a bright fuchsia solution. Volatiles were
removed under vacuum, and the purple solid was recrystallized from
Synthesis of (j3P,C,P-tBu2PN(Me)CHCH2N(Me)PtBu2)PdX
(X = I (9), Br (10), Cl (11)). These compounds were prepared in a
similar fashion, and thus only one preparation is detailed. A solution of
PdI2 (285 mg, 0.792 mmol) in THF (6 mL) was added dropwise with
stirring to a solution of 3 (300 mg, 0.796 mmol) in THF (6 mL) in the
presence of Et3N. The dark solution was stirred overnight and then
filtered through Celite. Volatiles were removed under vacuum, and the
resulting golden brown solid was extracted into toluene and filtered
again through Celite. Removal of the toluene under vacuum gave a
yellow solid (417 mg, 86% yield).
1
pentane. Yield: 197 mg, 78%. H NMR (toluene-d8): δ 3.05 (m, 2H,
CCH2C), 2.54 (m, 2H, CH2N), 2.09 (m, 2H, CH2N), 1.44 (d, 3JHꢀP
=
3
12 Hz, 18H, PC(CH3)3), 1.37 (d, JHꢀP = 15 Hz, 18H, PC(CH3)3.
31P{1H} NMR (C6D6): δ 106, ꢀ29 (d, 2JPꢀP = 261 Hz). 13C{1H} NMR
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dx.doi.org/10.1021/om200439q |Organometallics 2011, 30, 4128–4135

Organometallics
ARTICLE
Table 1. Crystallographic Parameters
4
5
6
8
9
11
12 2CH2Cl2
3
formula
fw
C19H43N2P2PdI C19H43N2P2NiCl C19H43N2P2NiCl C18H41N2P2NiCl C20H45N2P2PdI C20H45N2P2PdCl C22H51N2P2NiCl7
594.79
455.65
orthorhombic
P212121
11.646 (1)
14.188(1)
15.041(1)
90.00
455.65
monoclinic
P21/n
441.63
monoclinic
P21/m
8.024(1)
14.249(2)
10.444(1)
90.00
608.82
hexagonal
P421m
11.7919(4)
11.7919(4)
9.4299(3)
90.00
517.37
monoclinic
P21/c
712.45
orthorhombic
Pna21
cryst syst
space group
a (Å)
monoclinic
P21/n
15.454(2)
10.741(1)
16.245(2)
90.00
11.8428(8)
14.4447(9)
14.715(1)
90.00
8.7937(3)
11.7012(4)
24.3196(9)
90.00
10.8771(6)
20.2402(12)
15.8448(11)
90.00
b (Å)
c (Å)
R (deg)
β (deg)
γ (deg)
V (Å3)
Z
112.477(4)
90.00
90.00
103.688(4)
90.00
99.858(9)
90.00
90.00
90.332(2)
90.00
90.00
90.00
90.00
90.00
2491.6(6)
4
2485.3(4)
4
2445.7(3)
4
1176.4(3)
2
1311.20(6)
2
2502.37(15)
4
3488.3(4)
4
dcalcd (g cmꢀ3
)
1.586
1.218
1.238
1.247
1.542
1.373
1.357
μ (mmꢀ1
)
2.188
1.022
1.022
1.078
2.015
0.981
1.199
total no. of data 21 720
40 754
0.1284
5706
49 993
0.0872
5626
18 769
0.0622
4858
47 434
0.0612
3212
42 913
0.0356
9802
39 600
0.0452
10343
Rint
0.0288
5716
Fo2 > 3σ(Fo
)
2
no. of params
R1
226
226
226
160
75
271
307
0.0228
0.0591
0.978
0.0482
0.998
0.0529
0.1434
1.025
0.0546
0.1550
1.074
0.0415
0.0980
1.093
0.0381
0.996
0.0554
0.1544
1.048
wR2
GOF
1.005
1.022
Data for 9 are as follows. 1H NMR (C6D6): δ 2.98 (m, 1H,
NC(H)H), 2.84 (m, H, HCPd), 2.74 (m, 1H, NC(H)H), 2.52 (d,
3JHꢀP = 4 Hz, 3H, NCH3), 2.30 (d, 3JHꢀP = 9 Hz, 3H, NCH3), 1.49 (d,
3JHꢀP = 14 Hz, 9H, PC(CH3)3), 1.35 (d, 3JHꢀP = 9 Hz, 9H, PC(CH3)3),
PC(CH3)3). Anal. Calcd for C20H45ClN2P2Pd: C, 46.43; H, 8.77; N,
5.41. Found: C, 46.32; H, 8.69; N, 5.43.
Alternative Synthesis of 11. A solution of PdCl2(MeCN)2 (0.5
equiv) and Pd2(dba)3 (0.25 equiv) in THF (8 mL) was added dropwise
to a clear colorless solution of 3 in THF (5 mL). The mixture was stirred
overnight to produce a dark yellow-green mixture. Removal of an olive
green precipitate via filtration left a golden solution which upon removal
of volatiles afforded 11 as the exclusive product. Yield: 95%.
Synthesis of (tBu2P(H)N(Me)CH2CH2N(Me)PtBu2)NiCl3 (12).
A solution of 3 (100 mg, 0.265 mmol) in THF (4 mL) was added to a
suspension of (dme)NiCl2 in THF (6 mL) and stirred at 25 °C for 4 h to
give a green solution. Filtration of the mixture through Celite and evapora-
tion of the solvent under vacuum afforded a blue-green crystalline solid.
Yield: 95%. The paramagnetic species was determined to be 12 by X-ray
crystallography. 31P NMR (CD2Cl2): 53.3 (1JPꢀH = 508 Hz). Anal. Calcd
for C20H47N2P2NiCl3: C, 44.27; H, 8.73; N, 5.16. Found: C, 44.70; H,
8.35; N, 5.56.
3
3
1.33 (d, JHꢀP = 14 Hz, 9H, PC(CH3)3), 1.31 (d, JHꢀP = 8 Hz, 9H,
PC(CH3)3). 31P{1H} NMR (C6D6): δ 132.6, 15.2 (d, 2JPꢀP = 388 Hz).
2
2
13C{1H} NMR (C6D6): δ 67.4 (dd, JCꢀP = 19 Hz, JCꢀP = 9 Hz,
HCPd), 46.4 (dd, 2JCꢀP = 10 Hz, 3JCꢀP = 7 Hz, H2C), 39.6 (d, 2JCꢀP = 4
2
Hz, CH2N(CH3)P), 38.7 (d, JCꢀP = 7 Hz, CHN(CH3)P), 30.5 (dd,
2JCꢀP = 7, JCꢀP = 1 Hz, PC(CH3)3), 30.3 (dd, 2JCꢀP = 6 Hz, JCꢀP = 1 Hz,
PC(CH3)3), 29.8 (dd, 2JCꢀP = 6 Hz, JCꢀP = 1.3 Hz, PC(CH3)3), 28.7 (d,
2JCꢀP = 5 Hz, PC(CH3)3). Anal. Calcd for C20H45N2P2PdI: C, 39.45; H,
7.45; N, 4.60. Found: C, 38.98; H, 7.09; N, 4.47.
Data for 10 are as follows. Yellow solid. Yield: 26 mg (22%). 1H NMR
(C6D6): δ 2.98 (td, 3JHꢀP = 10 Hz, 3JHꢀP = 2 Hz, 1H, PdCH), 2.76 (m,
1H, CHH), 2.68 (m, 1H, CHH), 2.51 (d, 3JHꢀP = 4 Hz, 3H, NCH3),
3
3
2.30 (d, JHꢀP = 9 Hz, 3H, NCH3), 1.49 (d, JHꢀP = 14 Hz, 9H,
PC(CH3)3), 1.35 (d, 3JHꢀP = 14 Hz, 9H, PC(CH3)3), 1.32 (d, 3JHꢀP
=
Synthesis of (j3-P,C,P-tBu2PN(Me)CHCH2N(Me)PtBu2)NiCl
(13). Addition of B(C6F5)3 to a suspension of 12 in C6D6 immediately
produced a green oil and yellow solution. Decanting the solution to
separate the oil gave a bright yellow solution which was revealed by
NMR spectroscopy to contain exclusively the PCP pincer complex. Slow
addition of hexane afforded 13 in 85% yield. 1H NMR (C6D6): δ 2.49 (d,
3JHꢀP = 4 Hz, 3H, NCH3), 2.33 (m, 1H, HCNi), 2.31 (m, 2H, H2CC),
3
14 Hz, 9H, PC(CH3)3), 1.32 (d, JHꢀP = 14 Hz, 9H, PC(CH3)3).
31P{1H} NMR (C6D6): δ 129.3, 19.0 (d, 2JPꢀP = 397 Hz). Anal. Calcd
for C20H45N2P2PdBr: C, 42.75; H, 8.07; N, 4.99. Found: C, 42.29; H,
8.09; N, 4.87.
Data for 11 are as follows. Pale yellow crystalline solid. Recrystalliza-
tion from dichloromethane and hexanes (1:1) afforded light yellow
crystals suitable for X-ray diffraction (29 mg, 21%). 1H NMR (CD2Cl2):
3.05 (m, 1H, PdCH), 2.97 (m, 1H, PdC(H)CHH), 2.77 (m, 1H,
3
3
2.23 (d, JHꢀP = 9 Hz, 3H, NCH3), 1.56 (d, JHꢀP = 13 Hz, 9H,
PC(CH3)3), 1.46 (d, 3JHꢀP = 14 Hz, 9H, PC(CH3)3), 1.44 (d, 3JHꢀP
=
3
3
PdC(H)CHH), 2.82 (d, JHꢀ3 P = 4 Hz, 3H, NCH3), 2.62 (d, JHꢀP
=
3
13 Hz, 9H, PC(CH3)3), 1.41 (d, JHꢀP = 13 Hz, 9H, PC(CH3)3).
9 Hz, 3H, NCH3), 1.39 (d, JHꢀP = 14 Hz, 9H, PC(CH3)3), 1.33 (d,
31P{1H} NMR (C6D6): δ 120.7, 31.9 (d, JPꢀP = 289 Hz). 13C{1H}
2
3JHꢀP = 14 Hz, 9H, PC(CH3)3), 1.32 (d, JHꢀP = 15 Hz, 9H,
3
NMR (C6D6): δ 58.6 (dd, 2JCꢀP = 19 Hz, 2JCꢀP = 9 Hz, HCNi), 41.1
PC(CH3)3), 1.28 (d, 3JHꢀP = 14 Hz, 9H, PC(CH3)3). 31P{1H} NMR
(C6D6): δ 128.9, 22.9 (d, 2JPꢀP = 403 Hz). 13C{1H} NMR (C6D6): δ
67.3 (dd, 2JCꢀP = 19 Hz, 2JCꢀP = 9 Hz, HCPd), 43.0 (dd, 2JCꢀP = 11 Hz,
2
3
2
(dd, JCꢀP = 10 Hz, JCꢀP = 5 Hz, H2C), 39.1 (d, JCꢀP = 7 Hz,
2
CH2N(CH3)P), 38.2 (d, JCꢀP = 4 Hz, CHN(CH3)P), 28.8 (dd,
2JCꢀP = 8, JCꢀP = 1 Hz, PC(CH3)3), 28.7 (dd, JCꢀP = 6 Hz, JCꢀP
=
2
3JCꢀP = 6 Hz, H2C), 39.9 (d, JCꢀP = 7 Hz, CH2N(CH3)P), 38.6 (d,
2
1 Hz, PC(CH3)3), 28.5 (dd, 2JCꢀP = 6 Hz, JCꢀP = 1 Hz, PC(CH3)3),
2JCꢀP = 4 Hz, CHN(CH3)P), 29.7 (dd, JCꢀP = 8, JCꢀP = 1.2 Hz,
2
2
28.4 (d, JCꢀP = 6 Hz, PC(CH3)3). 11B NMR: δ ꢀ7.2. 19F NMR:
PC(CH3)3), 29.4 (dd, 2JCꢀP = 6 Hz, JCꢀP = 1 Hz, PC(CH3)3), 29.3 (dd,
2JCꢀP = 6 Hz, JCꢀP = 1 Hz, PC(CH3)3), 28.7 (d, JCꢀP = 6 Hz,
δ ꢀ131.66 (d, 3JFꢀF = 17, 6F, o-F), ꢀ163.41 (t, 3JFꢀF = 20 Hz, 3F, p-F),
2
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Scheme 1. Synthesis of Ligands 1ꢀ3
Scheme 2. Synthesis of Ni and Pd Complexes of 1 and 2
ꢀ167.71 (t, 3JFꢀF = 18 Hz, 6F, m-F). Anal. Calcd for C20H45ClN2NiP2:
C, 51.14; H, 9.66; N, 5.96. Found: C, 51.07; H, 9.28; N, 5.83.
DFT Calculations. Preliminary calculations were performed with
Gaussian0324,25 using density functional theory (DFT). The geometries
of compounds 6 and 7 were optimized by starting from the X-ray data
using the B3LYP exchange-correlational functional with the 6-311-G(d,p)
basis set. Optimizations were performed without (symmetry) con-
straints, and the resulting structures were confirmed to be minima on
the potential energy surface by frequency calculations (the number of
imaginary frequencies is zero). Visualization of the computed structures
and molecular orbitals was achieved using the program WebMO.
X-ray Data Collection and Reduction. Crystals were coated in
Paratone-N oil in the glovebox, mounted on a MiTegen Micromount,
and placed under a N2 stream, thus maintaining a dry, O2-free environ-
ment for each crystal. The data for crystals of 10 were collected on a
Nonius Kappa-CCD diffractometer; for crystals of 4, 6, 7, and 8, data
were collected on a Bruker Apex II diffractometer. The data were
collected at 150(2) K for all crystals. The frames were integrated with
the Bruker SAINT software package using a narrow-frame algorithm.
Data were corrected for absorption effects using the empirical multiscan
method (SADABS).
Structure Solution and Refinement. Non-hydrogen atomic
scattering factors were taken from the literature tabulations. The heavy-
atom positions were determined using direct methods employing the
SHELXTL direct methods routine. The remaining non-hydrogen atoms
were located from successive difference Fourier map calculations. The
refinements were carried out by using full-matrix least-squares techni-
ques on F, minimizing the function σ(Fo ꢀ Fc)2, where the weight σ is
Figure 1. Pov-ray depiction of 4: (black) C; (blue-green) N; (orange)
P; (pink) I; (light wood) Pd. Hydrogen atoms, except for NH, are
omitted for clarity.
2
2
defined as 4Fo /2σ(Fo ) and Fo and Fc are the observed and calculated
structure factor amplitudes, respectively. In the final cycles of each
refinement, all non-hydrogen atoms were assigned anisotropic tempera-
ture factors in the absence of disorder or insufficient data. In the latter
cases, atoms were treated isotropically. CꢀH atom positions were
calculated and allowed to ride on the carbon to which they were bonded,
assuming a CꢀH bond length of 0.95 Å. H atom temperature factors
were fixed at 1.10 times the isotropic temperature factor of the C atom to
which they were bonded. The H atom contributions were calculated but
not refined. The locations of the largest peaks in the final difference
Fourier map calculation and the magnitude of the residual electron
densities in each case were of no chemical significance. In the case of
compound 8, disorder of the ligand backbone carbons and one tBu
group was modeled. For 9 and 11 some degree of full-molecule disorder
was evident. The models were refined by employing only the positions of
the Pd and halide atoms, as the remainder of the disordered molecule
could not be located. Additional details are provided in the Supporting
Information. Crystallographic parameters for 4ꢀ6, 8, 9, 11, and 12 are
given in Table 1.
(CH2NMePtBu2)2 (3) were prepared from 1,3-diaminopropane,
N,N0-ethylenediamine, and dimethylethylenediamine, respec-
tively, and each were fully spectroscopically characterized
(Scheme 1). The ligands 1 and 2 gave rise to 31P NMR
resonances at 78.8 and 78.3 ppm and were isolated in 97 and
84% yields, respectively. In the case of the bis-aminophosphine
derived from the secondary diamine, this required deprotonation
with an alkyllithium reagent. In this fashion (CH2NMePtBu2)2
(3) was prepared and isolated as a crystalline solid in 81% yield.
The 31P NMR spectrum reflects the steric demands of the ligand,
as one broad resonance at 50 ppm is observed and, on heating to
50 °C, this signal becomes a sharp singlet. On cooling to ꢀ30 °C,
three sharp signals are observed at 108.0, 104.8, and 104.0 ppm.
These signals are attributed to diastereomers of 3 resulting from
steric inhibition of inversion about the pyramidal nitrogen atoms.
The bis-aminophosphine ligand 1 reacts with PdI2 in THF at
room temperature to give the symmetrical PCP-pincer complex
4, which is characterized by the appearance of a single resonance
in the 31P NMR spectrum at 130 ppm and a pattern of virtual
1
triplets for the tert-butyl groups in the H and 13C{1H} NMR
’ RESULTS AND DISCUSSION
N,N0-substituted diamine-based ligands were prepared using
the appropriate substituent and a minor modification of the
known methodology for such ligands.26ꢀ28 Reaction of the
diamines with 2 equiv of ClPtBu2 afforded the corresponding
bis(aminophosphine) compounds in good yield. In this
fashion CH2(CH2NHPtBu2)2 (1), (CH2NHPtBu2)2 (2), and
spectra. The phosphorus chemical shift of 130 ppm is in
accordance with the more electron-rich environment provided
by the amino groups. These data support the formulation of 4
as the symmetric pincer complex CH(CH2NHPtBu2)2PdI, in
which the central carbon of the chelate is metalated (Scheme 2).
This was confirmed crystallographically (Figure 1). This
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Figure 3. Pov-ray depiction of 6: Hydrogen atoms, except for NH, are
omitted for clarity. C: black, N: blue-green, P: orange: Cl: green, Ni:
burnt orange.
Figure 2. Pov-ray depiction of 5: (black) C; (blue-green) N; (orange) P;
(green) Cl; (burnt orange) N. Hydrogen atoms, except for NH, are
omitted for clarity.
NiꢀPꢀN angle of 58.08(12)°. This dissymmetric binding mode
for an aminophosphine fragment is rare. In a 1993 report a
geometrically related NPCo fragment was reported in the
complex (Ph2PNPPh2NPPh2)2Co,34 while Valerga and co-
workers21 have more recently reported the Ru cation
[Cp*Ru(k3-P,N,P-(iPr2PNH)2C6H10)]+, in which the amine N
adjacent to P coordinates to Ru. This latter species exhibits a
single 31P resonance at 92.3 ppm in solution,21 as the binding of
the NH in the Ru cation appears to be fluxional. In contrast, the N
atom in the present NPNi metallacycle 5 is deprotonated and
thus the nitrogen binding is not fluxional in solution. To our
knowledge this amido-phosphine binding represents an unpre-
cedented form of binding for a PNP pincer ligand.
In an effort to probe the inherent stability of this strained
NPNi metallacycle, we reasoned that interaction with a Lewis
acid could prompt ring opening. To this end, we examined the
subsequent reaction of 5 with B(C6F5)3. This resulted in the
initially purple solution becoming yellow, with separation of a
green oil. Separation of this oil and subsequent recrystallization
ultimately afforded the yellow crystalline product 6 in an isolated
yield of 48% (Scheme 2). In contrast to the case for 5, this species
shows a single 31P{1H} NMR signal at 119.0 ppm and 1H and
13C{1H} NMR resonances consistent with a symmetric ligand
and metalation at the central C of the ligand backbone. X-ray
diffraction confirmed the formulation of 6 as (k3P,C,P-CH-
(CH2NHPtBu2)2)NiCl (Figure 3). The metalation of the central
carbon results in two adjacent five-membered rings, with a NiꢀC
bond length of 1.974(4) Å and NiꢀP bond lengths of 2.1908(10)
and 2.1941(10) Å. In this pseudo-square-planar complex, the
PꢀNiꢀP angle in 6 is 168.09(4)°, while the CꢀNiꢀCl angle is
171.93(17)°. DFT calculations performed at the B3LYP/6311-
G(d,p) level for the optimized structures of 5 and 6 revealed a
small energy difference, with the CꢀH activated complex 6 being
lower in energy than the NꢀH activated complex 5 by ΔG = 9.96
kcal molꢀ1. While this observation suggests that 5 is a kinetic
product, the nature of the conversion to 6 via a boron-mediated
process remains the subject of speculation. It is reasonable to
suggest that a reversible interaction of B with either the NPNi
metallacycle or possibly Ni-bound halide could generate a site of
unsaturation, prompting activation of the alkyl CꢀH bond and
thus proton migration from the central C to N.
geometry is reminiscent of the known species (k3P,C,
P-CH((CH2)2PtBu2)2)PdI.29ꢀ31 Structural data for 4 reveal a
square-planar Pd center with a PdꢀC distance of 2.061(3) Å while
the PdꢀP and PdꢀI distances are 2.3089(6) and 2.3191(6) Å and
2.7227(3) Å, respectively, with a PꢀPdꢀP angle of 164.42(2)°.
The CꢀPdꢀI angle of 173.9(2)° is bent slightly out of the plane
defined by the P2PdI atoms. The PdꢀP distances in 4 are slightly
longer than those reported by Kirchner and co-workers in the
pyridyl bis-aminophosphine cation [(k3P,N,P-(C5H3N)(NHPt-
Bu2)2)PdCl]+ (2.2987(5), 2.2985(5) Å).32 The PꢀN bond lengths
in 4 are ca. 1.67 Å, typical of PꢀN bonds.33
The corresponding reaction of 1 with NiCl2(dme) gave a
reaction mixture from which the purple solid 5 was obtained.
Repetition of the reaction in the presence of NEt3 was found to
enhance the isolated yield of 5 to 78% (Scheme 2). The 31P{1H}
NMR spectrum of 5 showed two resonances at 106 and ꢀ29
ppm, each showing a coupling constant of 261 Hz, while the 1H
NMR data revealed two resonances attributable to the tBu
groups at 1.44 and 1.37 ppm. These data are consistent with a
trans disposition of inequivalent phosphine fragments. The
nature of 5 was unambiguously confirmed as (k3P,N,P-tBu2PNH-
(CH2)3NPtBu2)NiCl by X-ray crystallography (Figure 2). These
data show a four-coordinate nickel center in which the coordina-
tion sphere about Ni is comprised of two P atoms, a Cl atom, and
a N atom. The resulting strained three-membered PꢀNꢀNi ring
results in a significant distortion of the pseudo-square-planar
geometry about Ni and presumably accounts for the dramatic
difference in 31P chemical shift between the two P atoms. The
inequivalence of the P environments is reflected in the NiꢀP
distances of 2.161(1) and 2.222(1) Å, the former being the P in
the three-membered NiPN metallacycle ring. The latter NiꢀP
distance in 5 is only slightly longer than the NiꢀP bond lengths
in the pyridyl bis-aminophosphine cation [(k3-P,N,P-(C5H3N)-
(NHPtBu2)2)NiCl]+ (2.2067(4), 2.2062(4) Å);32 this is perhaps
a reflection of the strained geometry. The corresponding NiꢀN
distance in the ring is 1.891(3) Å. Similarly, the PꢀN bond
lengths differ quite significantly, as the PꢀN bond length within
the NiPN three-membered ring was found to be 1.603(3) Å,
while the other PꢀN bond in the ligand was significantly longer
at 1.679(3) Å. The NiꢀCl distance was found to be 2.1989(11) Å.
The PꢀNiꢀP, NꢀNiꢀCl, and PꢀNiꢀCl angles in 5 were
found to be 145.94(4), 157.11(10), and 111.20(4)°, respectively.
The constraint in the NiPN metallacycle is reflected in the
The related reactions of amino-phosphine ligand 2 with
PdI2 and with NiCl2(dme) led, in both cases, to the comp-
lexes k3-P,N,P-(tBu2PNH(CH2)2NPtBu2)PdI (7) and k3-P,N,
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Figure 4. Pov-ray depiction of 8: (black) C; (blue-green) N; (orange) P;
(green) Cl; (burnt orange) Ni. Hydrogen atoms, except for NH, are
omitted for clarity.
Figure 5. Pov-ray depiction of 9: (black) C; (blue-green) N; (orange) P;
(pink) I; (light wood) Pd. Hydrogen atoms are omitted for clarity.
Scheme 3. Synthesis of Ni and Pd Complexes of 3
Figure 6. Pov-ray depiction of 11: (black) C; (blue-green) N; (orange) P;
(green) Cl; (light wood) Pd. Hydrogen atoms are omitted for clarity.
P-(tBu2PNH(CH2)2NPtBu2)NiCl (8), respectively (Scheme 2).
Both species are characterized by the presence of two coupled
phosphorus species in the 31P NMR spectra. The chemical shifts
of these doublets in the spectrum for 7 were observed at 85
and ꢀ32 ppm (Δ = 117 ppm) with a 2JPꢀP of 262 Hz, while for 8
the chemical shifts were seen at 87 and 18 ppm (Δ = 69 ppm) and
inequivalent phosphorus environments that are oriented trans to
one another. The corresponding H NMR spectrum revealed
1
four distinct tert-butyl environments, giving further support to
the existence of two separate phosphorus environments and also
suggesting that some degree of rigidity exists in the ligand
backbone. These data are consistent with the formulation of 9
as (k3P,C,P-tBu2PN(Me)CHCH2N(Me)PtBu2)PdI, in which
CH activation of the ligand backbone occurs to yield the
asymmetric pincer. This binding mode stands in contrast to that
observed for related group VI and Pd and Pt complexes where
bis-aminophosphine ligands are observed to be simple bidentate
ligands.18 In a similar fashion, the species (k3-P,C,P-tBu2PN-
(Me)CHCH2N(Me)PtBu2)PdX (X = Br (10), Cl (11)) were
prepared. Compounds 9 and 11 were characterized by X-ray
diffraction studies (Figures 5 and 6, respectively). The Pd center
in each adopts a distorted-square-planar geometry defined by the
P atoms, the metalated C atom, and the halide. PdꢀP distances
were determined to be 2.298(1) Å in 9 and 2.2847(8) and
2.3023(8) Å in 11. The PdꢀC bond distances were found to be
2.062(8) Å in 9, while the disorder in 11 generates some
uncertainty in the PdꢀC bond lengths. The PꢀPdꢀP bond
angle is 149.62(6)o in 9 and 149.50(3)o in 11, which deviate
significantly from the typical square-planar angle of 180°. These
1
JPꢀP of 372 Hz. The H NMR spectrum also revealed inequi-
valent t-butyl environments, consistent with some dissymmetry
of the coordination sphere about the metals. The backbone
methylene protons give rise to two multiplets, consistent with
molecular dissymmetry. The solid-state structure of 8 was
determined via X-ray crystallography (Figure 4), confirming
the geometries of these species in which the pseudosquare planar
coordination sphere comprised of three- (NPNi) and six-
(NC2NPNi) membered rings. The NiꢀP bond lengths are
2.1844(8) and 2.1850(8) Å while the NiꢀN distance was found
to be 1.825(2) Å. The PꢀNiꢀP angle of 8 was found to be
141.49(3)° while the NꢀNiꢀP in the NNiP three membered
ring was found to be 45.34(8)°.
To probe the effect of substitution at nitrogen, complexation
of 3 with Pd and Ni was investigated (Scheme 3). When 3 was
treated with PdI2, the new product 9 gave rise to a 31P NMR
spectrum comprised of two doublets at 132.6 and 15.2 ppm with
a large PꢀP coupling of 388 Hz. This is consistent with two
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The results above indicate that in the case of Ni complexes of
the three-carbon chain secondary diamino-phosphine ligand 1,
amido-phosphine metallacycles constituting an unprecedented
form of a PNP-pincer ligand are obtained. This PNP binding
mode isomerizes to the PCP binding mode which is observed
directly in the case of analogous Pd complexes. Shortening the
alkyl chain or alkylation of the N in the ligand resulted in PCP-
type pincer complexes. In addition, the chelating nature of these
ligands dictates the close proximity of the resulting electron-rich
metal center to CꢀH and NꢀH bonds, prompting activation of
one of the NꢀH or CꢀH bonds.
’ CONCLUSIONS
In conclusion, we have described the synthesis of a series of Ni
and Pd complexes of seemingly bidentate bis-aminophosphine
ligands. In all cases the resulting products incorporate tridentate
bound ligands in which the NꢀH or an alkyl CꢀH bond has
been activated, affording either PNP- or PCP-pincer complexes.
The utility of these unusual species in subsequent chemistry is
the subject of current investigations.
Figure 7. Pov-ray depiction of 12: (black) C; (blue-green) N; (orange) P;
C(green) Cl; (burnt orange) Ni. Hydrogen atoms, except for PH, are
omitted for clarity.
distortions result from the constraints associated with the four-
membered ring.
In attempts to prepare Ni analogues of 9ꢀ11, 3 was reacted
with NiCl2(dme), yielding a bright turquoise product. Broad
NMR spectra suggested the formation of a paramagnetic species
and thus a tetrahedral geometry. Despite the poor solubility, a
broad signal was observed in the 31P NMR spectrum at 53.3
ppm (1JPꢀH = 508 Hz) indicative of the presence of a phospho-
nium fragment. Light green crystals were crystallographically
characterized as the zwitterionic nickel phosphonium
complex [(tBu2PH)(NMe)(CH2)2(NMe)(tBu2P)NiCl3], (12)
(Figure 7), in which phosphine acts as a monodentate ligand
binding to a NiCl3 anionic moiety. The source of proton that
gives rise to the counter phosphonium cation is unclear but could
arise from adventitious moisture or residual base-HCl in the
ligand. The geometry at Ni is pseudotetrahedral with a NiꢀP
distance of 2.372(1), NiꢀCl distances of 2.250(1), 2.267(1), and
2.270(1) Å, and PꢀNiꢀCl angles of 112.72(4), 106.50(4), and
111.66(4)°. An intermolecular interaction in the solid state
between Cl and the PH proton is also evident at a distance of
3.053 Å. A similar zwitterionic by-product was observed by
Zargarian and co-workers in their efforts to isolate Ni-pincer
complexes incorporating tBu2P(CH2)5PtBu2.35 In this case,
further protonation gave the salt [(tBu2PH(CH2)2)2CH2]-
[NiCl4].
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files giving crystallo-
b
graphic data for 4ꢀ6, 8. 9, 11, and 12. This material is available
free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: dstephan@chem.utoronto.ca. Tel: 416-946-3294.
’ ACKNOWLEDGMENT
The support of LANXESS Inc., the NSERC of Canada, and
the Ontario Centres of Excellence is gratefully acknowledged.
D.W.S. is grateful for the award of a Canada Research Chair and a
Killam Research Fellowship.
’ REFERENCES
(1) Rietveld, M. H. P.; Grove, D. M.; Van Koten, G. New J. Chem.
1997, 21, 751–771.
(2) Rybtchinski, B.; Milstein, D. Angew. Chem., Int. Ed. 1999,
38, 870–883.
Attempts to abstract HCl with triethylamine, tri-tert-butylpho-
sphine, or Proton Sponge from 12 failed, yielding only intractable
mixtures. However, treatment of 12 with B(C6F5)3 afforded the
species 13, which exhibited the appearance of the characteristic
doublets in the 31P NMR spectrum at 120.7 and 31.9 ppm with a
PꢀP coupling of 289 Hz. This observation is consistent with a
trans arrangement of the P atoms. Subsequent isolation of 13
confirmed removal of the anion, presumably as the acid salt. The
formulation of 13 was spectroscopically confirmed as (k3P,C,P-
tBu2PN(Me)CHCH2N(Me)PtBu2)NiCl and supported by pre-
liminary structural data. However, the poor crystal data and
apparent full molecular disorder precluded the presentation of
these data. The 11B NMR spectrum of the reaction mixture
showed a singlet resonance at ꢀ6.7 ppm, consistent with the
formation of the anion [ClB(C6F5)3]ꢀ.36 Formally, the conver-
sion of 12 to 13 involves both loss of HCl and H[ClB(C6F5)3]
presumably prompted by halide abstraction from Ni, although
the mechanistic details of this reaction have not been elucidated.
(3) Vigalok, A.; Milstein, D. Acc. Chem. Res. 2001, 34, 798–807.
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