Ag(i) and Au(i) complexes of sterically crowded cyclic phosphinimine ligands

Article abstract of DOI:10.1039/c0dt00261e

Cyclic phosphinimines are strong bases with structural similarities to carbene ligands. The cyclic phosphinimines R₂PNCPh ₂(CH₂CH(CO₂Me)) (R = Ph 4, i-Pr 5, Me 6), R₂PNCPh₂(CCOMe)₂ (R = Ph 7, i-Pr 8) and Ph ₂PNCPh₂(CH₂CH(CN)) 9 are readily prepared via cycloaddition of the compounds R₂PNCPh₂ (R = Ph 1, i-Pr 2, Me 3) and olefins or alkynes. In the case of 4 this phosphinimine proved to be moisture sensitive, converting to Ph₂C(NH₂)CH(CO ₂Me)CH₂P(O)Ph₂10 upon hydrolysis. Nonetheless, the Ag(i) and Au(i) complexes [{Ph₂PNCPh₂(CH ₂CH(CO₂Me)}₂Ag][NO₃] 11 (Ph ₂PNCPh₂(CH₂CH(CO₂Me)AuCl 12 and (Ph₂PNCPh₂(C(CO₂Me)₂)AuCl 13 were prepared and characterized. Compounds 1, 2 and 7-13 have been characterized crystallographically.

Full text of DOI:10.1039/c0dt00261e

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PAPER
www.rsc.org/dalton | Dalton Transactions
Ag(I) and Au(I) complexes of sterically crowded cyclic phosphinimine ligands†
Christopher C. Brown, Christoph Glotzbach and Douglas W. Stephan*
Received 5th April 2010, Accepted 5th August 2010
DOI: 10.1039/c0dt00261e
Cyclic phosphinimines are strong bases with structural similarities to carbene ligands. The cyclic
phosphinimines R2PNCPh2(CH2CH(CO2Me)) (R = Ph 4, i-Pr 5, Me 6), R2PNCPh2(CCOMe)2 (R = Ph
7, i-Pr 8) and Ph2PNCPh2(CH2CH(CN)) 9 are readily prepared via cycloaddition of the compounds
R2PNCPh2 (R = Ph 1, i-Pr 2, Me 3) and olefins or alkynes. In the case of 4 this phosphinimine proved to
be moisture sensitive, converting to Ph2C(NH2)CH(CO2Me)CH2P(O)Ph2 10 upon hydrolysis.
Nonetheless, the Ag(I) and Au(I) complexes [{Ph2PNCPh2(CH2CH(CO2Me)}2Ag][NO3] 11
(Ph2PNCPh2(CH2CH(CO2Me)AuCl 12 and (Ph2PNCPh2(C(CO2Me)2)AuCl 13 were prepared and
characterized. Compounds 1, 2 and 7–13 have been characterized crystallographically.
Introduction
The advent of N-heterocyclic carbene (NHCs) ligands (Scheme 1)
has had a dramatic impact on inorganic and organometallic
chemistry.1 These ligands have allowed access to unique coordina-
tion geometries and, in some cases, the generation of remarkably
reactive catalysts.2 The steric and electronic features of NHCs are
unique. For example, the strong sigma bonding nature of carbenes
is well understood to play a role in stabilizing reactive metal species.
In addition, judicious choice of substituents permits the tuning
of the steric and stereochemical environment proximal to the
metal. Variants of these ligands have been described. For example,
Bertrand et al. have described complexes of alkylaminocarbenes
(CAACs) (Scheme 1).3 In addition, carbodiphosphoranes (CDPs),
(Scheme 1) which are formally dianionic at the carbon atom,
have been extensively investigated as ligands in transition metal
chemistry.4 More recently, complexes of cyclic carbodiphospho-
ranes have also been described.5
With these precedents in mind, we sought to explore other
ligand systems that might offer similar features. Phosphinimines
are a class of donors which are known to be strongly basic.6
Nonetheless, these systems are electronically distinct from car-
benes in that the donor N atom formally has a filled p-orbital
orthogonal to the donor pair, whereas in carbenes the orthogonal
p-orbital is vacant. While anionic phosphinimide ligands have
been exploited extensively as ancillary ligands,6–7 phosphinimine
ligand systems have drawn much less attention, although some
recent work has incorporated such donors into chelating ligand
systems.8 The structural similarity of cyclic phosphinimines to
NHCs suggests that such ligands may also combine the features
of a strong donor with the additional flexibility of controlling
the steric environment via alteration of the substituents on C and
P. While cyclic phosphinimines were first prepared some 40 years
ago,9 to our knowledge, the ability of these systems to act as ligands
has not been explored. In this paper, we explore synthetic routes
Scheme 1 Structural similarity and electronic difference among NHCs,
CAACs, CDPs and cyclic phosphinimines.
to a series of saturated and unsaturated cyclic phosphinimines and
probe their viability as ligands for Ag(I) and Au(I) complexes. The
implications for use of these ligands in subsequent chemistry are
considered.
Experimental section
All preparations were performed under an atmosphere of dry, O2-
free N2 employing both Schlenk line techniques and a MBraun
Labmaster inert atmosphere glove box. Solvents (CH2Cl2, Et2O
and pentane) were purified employing a Grubbs’ type column sys-
tem manufactured by Innovative Technology. 1,2-Dichloroethane
was dried over CaH2 and distilled under a nitrogen atmosphere.
˚
Solvents were stored in the glove box over 4 A molecular sieves.
˚
Molecular sieves (4 A) were purchased from Aldrich Chemical
Company and dried at 150 ◦C under vacuum for 48 h prior to use.
All glassware was dried overnight at 120 ◦C and evacuated for 1 h
prior to use. The chlorophosphines were purchased from Strem
Chemicals. All other chemicals were purchased from Aldrich
1
Chemical Co. and used without further purification. 1H, 13C{ H}
1
and 31P{ H} NMR spectroscopy spectra were recorded on Varian
1
1
400 MHz and Bruker 400 MHz spectrometers. H and 13C{ H}
NMR spectra are referenced to SiMe4 using the residual solvent
peak impurity of the given solvent. 31P{ H} NMR spectra were
1
referenced to 85% H3PO4. Chemical shifts are reported in ppm
and coupling constants in Hz. C6D6 and CD2Cl2 were used as the
NMR solvents after being dried over Na/benzophenone (C6D6)
or CaH2 (CD2Cl2), vacuum-transferred into Young bombs and
freeze–pump–thaw degassed (three cycles). Combustion analyses
were performed in-house employing a Perkin Elmer 2400 Series II
CHN Analyzer.
Department of Chemistry, University of Toronto, 80 St. George St. Toronto,
Ontario, Canada M5S 3H6. E-mail: dstephan@chem.utoronto.ca; Tel: +1
416-946-3294
† CCDC reference numbers 772411–772420. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00261e
9626 | Dalton Trans., 2010, 39, 9626–9632
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3
Synthesis of R2PNCPh2 (R = Ph 1, i-Pr 2, Me 3)
CH(CH3)2), 1.38 (dd, 3H, CH(CH3)2, 3JPH = 10.2 Hz, JHH = 7.3
3
3
Hz), 1.34 (dd, 3H, CH(CH3)2, JPH = 10.2 Hz, JHH = 7.3 Hz),
0.98 (dd, 3H, CH(CH3)2, 3JPH = 14.7 Hz, 3JHH = 7.2 Hz), 0.79 (dd,
These compounds were prepared in a similar fashion and thus
only one preparation is detailed. A solution of benzophenone
imine (9.69 g, 53.5 mmol) and Et3N (6.77 mL, 48.6 mmol) in
diethyl ether (400 mL) was cooled to 0 ◦C before adding Ph2PCl
(8.72 mL, 48.6 mmol) dropwise. The reaction mixture turned
yellow and was stirred overnight. The suspension was filtered
and the solvent removed in vacuo. Purification via recrystallization
from acetonitrile afforded 1 as yellow crystals (12.4 g, 34.0 mmol,
3H, CH(CH3)2, JPH = 15.5 Hz, JHH = 7.1 Hz). 31P{ H} NMR
3
3
1
(CD2Cl2): 73.80. 13C{ H} NMR (CD2Cl2): 173.97, 173.91, 152.85,
1
152.82, 149.56, 149.38, 127.94, 127.52, 127.28, 126.57, 125.53,
82.78, 54.58, 54.47, 53.96, 53.69, 53.42, 53.15, 52.88, 50.92, 27.53,
26.99, 26.14, 25.49, 24.41, 24.03, 17.60, 17.58, 17.14, 17.11, 16.41,
16.38, 16.34, 16.31. C,H,N analysis calc. for C23H30NO2P (383.47):
C, 72.04; H, 7.89; N, 3.65. Found: C, 71.83; H, 8.05; N, 3.72. 6:
(642 mg, 1.96 mmol, 85%). Purification via recrystallization from
70%) 1H NMR (CD2Cl2) : 7.35–7.47 (m, 20H, Ph). 13C{ H} NMR
1
2
(CD2Cl2): 175.70 (d, (Ph)2CN, JCP = 13.7 Hz), 142.65 (2JCP
=
1
dichloromethane yields colourless needles. H NMR (CD2Cl2):
13.7 Hz, o-PPh2), 140.56 (d, o-PPh2,1JCP = 7.5 Hz), 132.48 (Ph),
7.48–7.54 (m, 4H, Ph), 7.22–7.26 (m, 2H, Ph), 7.12–7.18 (m, 3H,
Ph), 7.06–7.10 (tt, 1H, Ph), 4.17 (m, 1H, CHCO2CH3), 3.00 (s,
3H, CH3), 2.44 (m, 1H, CH2), 2.02–2.10 (m, 1H, CH2), 1.78
132.27 (Ph), 130.16 (Ph), 129.04 (Ph), 128.62–128.73 (m, Ph).
1
31P{ H} NMR (CD2Cl2) : 36.8. C,H,N analysis calc. for C25H20NP
(365.42): C, 82.17; H, 5.52; N, 3.83. Found: C, 82.02; H, 5.69; N,
2
2
(d, 3H, JPH = 14.0 Hz, P(CH3)2), 1.09 (d, 3H, JPH = 14.0 Hz,
1
3.88. 2: orange crystals (8.52 g, 28.7 mmol, 87.5%), H NMR
(CD2Cl2) : 7.38–7.47 (m, 10H, Ph), 1.89 (m, 2H, CH(CH3)2),
P(CH3)2). 31P{ H} NMR (CD2Cl2): 52.7. 13C{ H} NMR (CD2Cl2):
174.59, 151.56, 149.03, 148.78, 128.18, 128.08, 128.06, 127.50,
127.40, 126.32, 126.28, 82.97, 66.22, 51.45, 31.00, 30.57, 19.20,
18.62, 17.02, 16.28, 15.67. C,H,N analysis calc. for C19H22NO2P
(327.36): C, 69.71; H, 6.77; N, 4.28. Found: C, 71.09; H, 7.05;
N, 4.52.
1
1
3
3
1.09 (dd, 6H, CH(CH3)2, JHH = 7.4 Hz, JPH = 14.8 Hz), 1.00
(dd, 6H, CH(CH3)3, JHH = 7.4 Hz, JPH = 14.8 Hz). 13C{ H}
NMR (CD2Cl2) : 177.27 (d, (Ph)2CN, 2JCP = 13.7 Hz), 141.04 (d,
Ph,1JCP = 7.5 Hz), 129.90 (s, Ph), 129.16 (s, Ph), 129.14 (s, Ph),
128.49 (s, Ph), 27.55 (m, CH(CH3)2), 19.09 (s, CH(CH3)2), 18.90
3
3
1
(s, CH(CH3)2), 18.61 (s, CH(CH3)2), 18.51 (s, CH(CH3)2). 1P{ H}
1
Synthesis of R2PNCPh2(CCO2Me)2 (R = Ph 7, i-Pr 8)
NMR (CD2Cl2): 68.6. C,H,N analysis calc. for C19H24NP (297.38):
C, 76.74; H, 8.13; N, 4.91. Found: C, 76.75; H, 8.10; N, 5.04. X-Ray
quality crystals were grown from cooling a saturated diethyl ether
solution to -35 ◦C. 3: orange oil 1H NMR (C6D6): 7.49–7.51 (m,
4H, Ph), 7.06–7.09 (m, 6H, Ph), 1.07 (d, 6H, CH3, 2JPH = 4.7 Hz)
These compounds were prepared in a similar fashion and thus only
one preparation is detailed. Compound 1 (365 mg, 1.0 mmol) was
dissolved in diethyl ether (5 mL) to which dimethyl acetylenedi-
carboxylate (150 mg, 1.05 mmol) dissolved in diethyl ether (5 mL)
was added dropwise. The reaction turned from light yellow to
light orange with a precipitate forming in 10 min. The reaction
was stirred overnight. The reaction was filtered and washed with
cold pentane (15 mL) to give a pure yellow powder 7 (380 mg,
.75 mmol, 75%). 1H NMR (CD2Cl2): 7.56–7.61 (m, 6H, Ph), 7.42–
7.46 (m, 4H, Ph), 7.29–7.32 (m, 4H, Ph), 7.22–7.25 (m, 6H, Ph),
1P{ H} NMR (C6D6): 27.81 (31P{ H} NMR shows 93% purity).
Attempts to purify were unsuccessful, thus the crude product was
used as prepared in subsequent reactions.
1
1
Synthesis of R2PNCPh2(CH2CH(CO2Me)) (R = Ph 4, i-Pr 5,
Me 6)
3.68 (s, 3H, CH3), 3.59 (s, 3H, CH3). 31P{ H} NMR (CD2Cl2):
1
1
These compounds were prepared in a similar fashion and thus only
one preparation is detailed. 1 (731 mg, 2.0 mmol) was completely
dissolved in diethyl ether (5 mL) before the addition of methyl
acrylate (181 mg, 2.10 mmol). The yellow colour of the solution
faded to a clear solution and a white precipitate formed. The
solution was stirred overnight. The solution was filtered and
washed with cold pentane (15 mL) to afford 4 as a white solid
(772 mg, 1.71 mmol, 85.5%). 1H NMR (CD2Cl2) : 7.02–7.38, 7.46–
7.61, 7.88–7.97 (m, 20H, Ph), 4.25–4.37 (m, 1H, CHCO2CH3),
2.93–3.03 (m, 4H, CH3 and CH2 trans to CO2Me), 2.70–2.85 (m,
49.04. 13C{ H} NMR (CD2Cl2): 176.71, 176.33, 166.57, 166.33,
162.48, 162.36, 146.58, 146.51, 132.60, 132.50, 132.18, 132.16,
128.40, 128.30, 128.16, 127.36, 126.62, 88.08, 52.49, 52.28, 43.92.
C,H,N analysis calc. for C31H26NO4P (507.52): C, 73.36; H, 5.16;
N, 2.76. Found: C, 72.91; H, 5.59; N, 2.71. 8: orange powder
(1.20 g, 2.73 mmol, 75%). Orange crystals (8.52 g, 28.7 mmol,
1
88%), H NMR (CD2Cl2): 7.84–7.87 (m, 2H, Ph), 7.65–7.68 (m,
2H, Ph), 7.27–7.49 (m, 6H, Ph), 4.32 (m, 1H, CHCOOCH3),
3.30 (s, 3H, CH3), 2.66–2.77 (m, 2H, CH(CH3)2), 2.37 (m, 1H,
CH2), 1.83–1.93 (m, 1H, CH2), 1.55–1.63 (m, 6H, CH(CH3)2),
1H, CH2 cis to CO2CH3). 13C{ H} NMR (CD2Cl2) : 173.5 (d,
1.20 (dd, 3H, CH(CH3)2,3JPH = 15.9 Hz, JHH = 7.3 Hz), 1.01
1
3
3
1
J = 6 Hz), 150.95, 148.63, 148.43, 132.26, 132.17, 131.57, 131.55,
131.11, 131.01, 130.74, 130.71, 128.22, 128.10, 128.02, 127.97,
127.91, 127.42, 127.14, 126.80, 125.92, 125.58, 82,89, 50.90, 31.85,
(dd, 3H, CH(CH3)2,3JPH = 16.9 Hz, JHH = 7.2 Hz). 13C{ H}
NMR (CD2Cl2) : 173.95, 152.85, 149.48, 127.94, 127.52, 127.28,
126.57, 125.53, 82.77, 54.54, 50.92, 27.27, 25.79, 24.22, 17.61,
31.40. 31P{ H} NMR (CD2Cl2): 48.61. C,H,N analysis calc. for
17.34, 16.37. 1P{ H} NMR (CD2Cl2): 73.79 C,H,N analysis calc.
1
1
C29H26NO2P (451.51): C, 77.15; H, 5.80; N, 3.10. Found: C, 76.62;
H, 5.89; N, 3.19. X-Ray quality crystals were grown by slow
diffusion of pentane into a saturated dichloromethane solution.
for C25H30NO4P (439.48): C, 68.32; H, 6.88; N, 3.19. Found: C,
68.43; H, 6.66; N, 3.65. X-Ray quality crystals were grown by slow
cooling of a saturated diethyl ether solution.
1
5: (800 mg, 2.02 mmol, 63%) white solid, H NMR (CD2Cl2):
7.62–7.63 (m, 2H, Ph), 7.42–7.45 (m, 2H, Ph), 7.25 (tt, 2H, J =
8 Hz, Ph), 7.12–7.16 (m, 3H, Ph), 7.06 (tt, 1H, J = 7 Hz, Ph),
4.05–4.13 (m, 1H, CHCO2CH3), 3.08 (s, 3H, CH3), 2.45–2.54
(m, 2H, CH2), 2.08–2.18 (m, 1H, CH(CH3)2), 1.63–1.68 (m, 1H,
Synthesis of R2PNCPh2(CH2CH(CN)) 9
Compound 1 (1.096 g, 3.00 mmol) was dissolved in diethyl ether
(10 mL) to which acrylonitrile (160 mg, 3.03 mmol) dissolved
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1
in diethyl ether (5 mL) was added in addition. The reaction
turned from light yellow to colourless with a white precipitate
upon stirring for 12 h. The reaction volume was reduced by half
in vauco, filtered, and washed with cold pentane (20 mL) to give a
white powder (961 mg, 2.20 mmol, 77%). %). 1H NMR (CD2Cl2):
7.75–7.91 (m, 4H, Ph), 7.11–7.68 (m, 16H, Ph), 4.34 (m, 1H,
CH), 3.03 (m, 2H, CH2). 31P{ H} NMR (CD2Cl2) 46.0. 13C{ H}
NMR (CD2Cl2): 149.00, 148.95, 148.74, 148.56, 132.82, 132.71,
132.22, 131.88, 131.78, 131.63, 130.59, 129.25, 129.12, 129.01,
128.89, 128.42, 128.29, 127.84, 127.11, 127.03, 126.85, 121.32,
81.56, 42.40, 42.27, 33.86, 33.42.
89%. H NMR (CD2Cl2): 7.70–7.75 (m, 6H, Ph), 7.56–7.60 (m,
4H, Ph), 7.32–7.44 (m, 10H, Ph), 3.70 (s, 3H, OCH3), 3.58 (s, 3H,
OCH3). 31P{ H} NMR (CD2Cl2): 51.28. 13C{ H} NMR (CD2Cl2):
164.6, 161.35, 143.2, 134.89, 134.01, 133.90, 129.82, 129.78,
129.29, 129.02, 128.64, 86.38, 68.1, 28.1, 20.1. C,H,N analysis calc.
for C29H26AuNO2P (683.92): C, 50.93; H, 3.83; N, 2.05. Found: C,
50.52; H, 3.85; N, 2.31. X-Ray quality crystals were grown by slow
diffusion of pentane into a saturated dichloromethane solution.
1
1
1
1
1
13: Yield: 324 mg, 0.44 mmol, 82%. H NMR (CD2Cl2):8.03–
8.09 (m, 2H, Ph), 7.48–7.77 (m, 10H, Ph), 7.35–7.41 (m, 2H, Ph),
7.26–7.30 (m, 6H, Ph), 4.32 (m, 1H, CHCO2CH3), 3.30 (m, 1H,
CH2 trans to CO2CH3), 3.17 (s, 3H, CH3), 2.97–3.05 (m, 1H,
CH2 cis to CO2CH3). 31P{ H} NMR (CD2Cl2): 49.89. 13C{ H}
NMR (CD2Cl2) :171.84 (d, COOCH3), 146.5, 146.7, 144.58,
144.47, 133.69, 132.96, 132.86, 131.82, 131.72, 129.0, 128.95,
128.83, 128.28, 128.05, 128.01, 127.57, 127.51, 127.41, 80.00,
51.9, 29.5 (d, CH2). C,H,N analysis calc. for C31H26AuClNO4P
(739.94): C, 50.32; H, 3.54; N, 1.89. Found: C, 50.82; H, 3.93;
N, 1.92.
1
1
Synthesis of Ph2C(NH2)CH(CO2Me)CH2P(O)Ph2 10
Compound 4 (45 mg, 0.1 mmol) was dissolved in dichloromethane
(5 mL) and exposed to air for 5 min. The initially clear solution
immediately formed a fine white precipitate. After 5 min. the
reaction was complete, the volume reduced to 1 mL and filtered.
Washing the solid with cold dichloromethane (2 mL) yields a pure
white solid. 1H NMR (CDCl3): 7.62–7.74 (m, 4H, Ph), 7.41–7.51
(m, 8H, Ph), 7.28 (t, 4H, Ph), 7.13–7.20 (m, 3H, Ph), 7.06 (m, 1H,
Ph), 4.10 (m, 1H, CH2), 2.82–2.90 (m, 1H, CHCO2CH3), 2.80 (s,
3H, CHCO2CH3), 2.48 (m, 1H, CH2), 1.70–2.30 (br, 2H, NH2).
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 environment 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. For crystals of 5, data were processed
with the DENZO-SMN package. For crystals of 4, 6, 7, and
8, 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).
1
1
31P{ H} NMR (CDCl3): 29.9. 13C{ H} NMR (CDCl3): 174.63 (s,
CO2CH3), 146.00, 144.78, 133.97, 132.98, 132.15, 132.12, 132.03,
132.00, 131.53 (d, J = 10 Hz), 130.90 (d, J = 10 Hz), 128.97,
128.92, 128.85, 128.65, 128.53, 128.03, 128.20, 126.95, 126.68,
126.34, 63.90 (d, J = 13 Hz, C(Ph)2(NH2)), 51.47 (s, CO2CH3),
46.66 (CHCO2CH3), 29.44 (d, J = 70 Hz, CH2P(O)Ph2). C,H,N
analysis calc. for C29H28NO3P (469.51): C, 74.19; H, 6.01; N, 2.98.
Found: C, 73.32; H, 6.62; N, 2.97.
Synthesis of [{Ph2PNCPh2(CH2CH(CO2Me)}2Ag][NO3] 11
Compound
4 (226 mg, 0.50 mmol.) was dissolved in
dichloromethane (5 mL) and added to a slurry of silver nitrate
(85 mg, 0.50 mmol, 1 eq.) in dichloromethane (3 mL). The solution
was stirred for 24 h in the dark. The solution colour slowly changed
from colourless to a light yellow. The solution was filtered through
Celite and the solvent removed in vacuo to yield an off-white solid.
Structure solution and refinement
Non-hydrogen atomic scattering factors were taken from the
literature tabulations.10 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 techniques
on F, minimizing the function w (Fo - Fc),2 where the weight
w is defined as 4Fo2/2s(Fo2) 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 temperature factors in the absence of disorder
or insufficient data. In the latter cases, atoms were treated
isotropically. C–H atom positions were calculated and allowed
to ride on the carbon to which they were bonded, assuming a C–H
1
(227 mg, 73%) H NMR (CD2Cl2):6.73–7.70 (br. m, 40H, Ph),
4.23–4.34 (br. m, 2H, CH), 3.31–3.41 (m, 2H, CH2), 3.08 (s, 6H,
1
CH3), 2.93–3.04 (m, 2H, CH2). 31P{ H} NMR (CD2Cl2): 52.83 (d,
1
2JAg–P = 18 Hz), 52.58 (d, 2JAg–P = 18 Hz) 13C{ H} NMR (CD2Cl2):
172.18 (d, C O, J = 6 Hz), 148.30, 145.41, 133.60, 132.3–132.8
(m, Ph), 129.21, 129.08, 128.9, 128.8, 128.4, 127.9, 127.6, 127.17,
126.75, 80.74 (d, CHCOOCH3, J = 8 Hz), 65.7, 51.84 (s, CH3),
30.10. C,H,N analysis calc. for C23H30NO2P (383.47): C, 72.04; H,
7.89; N, 3.65. Found: C, 71.83; H, 8.05; N, 3.72.
Synthesis of (Ph2PNCPh2(CH2CH(CO2Me)AuCl 12 and
(Ph2PNCPh2(C(CO2Me)2)AuCl 13
˚
bond length of 0.95 A. H-atom temperature factors were fixed at
These compounds were prepared in a similar fashion and thus only
one preparation is detailed. (Me2S)AuCl (215 mg, 0.74 mmol) was
dissolved in 1,2-dichloroethane (5 mL) before a 1,2-dichloroethane
(5 mL) solution of 4 (345 mg, 0.75 mmol) was added dropwise.
The reaction was stirred for 20 min. at which time the solvent
was removed in vacuo. The resulting white solid was washed with
pentane (10 mL) to give a white solid. Yield: 450 mg, 0.65 mmol,
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 as well as the magnitude of the residual
electron densities in each case were of no chemical significance.
Additional details are provided in Table 1 and the Supporting
Information.†
9628 | Dalton Trans., 2010, 39, 9626–9632
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Results and discussion
Ligand synthesis
A convenient synthesis of cyclic phosphinimines was established
by Schmidpeter et al.9 in the 1970s. While these researchers
examined the cycloaddition chemistry of these systems, the utility
of such compounds in metal complex chemistry has not been
explored. Thus, we began with the synthesis of a series of
ligands using the Schmidpeter methodology. To this end, the
compounds R2PNCPh2 (R = Ph 1, i-Pr 2, Me 3) were prepared
via the reaction of benzophenone-imine with the corresponding
chlorophosphine in the presence of base as per literature precedent
(Scheme 2). The NMR data was consistent with the formulations
and crystallographic data was obtained for 1 and 2 which
confirmed the formulations (Fig. 1). The metric parameters within
the two molecules were unexceptional with P–N bond distances of
˚
1.7203(14) and 1.7419(17) A, respectively, and N C bond lengths
˚
of 1.282(2)) A.
Scheme 2 Synthesis of compounds 1–10.
Cycloaddition of 1–3 to methyl acrylate affords the phospha-
imines R2PNCPh2(CH2CH(CO2Me)) (R = Ph 4, i-Pr 5, Me 6)
in 86, 63 and 85% yields, respectively. The NMR data were as
1
expected with 31P{ H} chemical shifts of 48.6, 73.8 and 52.7 ppm,
respectively. The crystal structure of 4 (Fig. 2) confirmed the
formation of a puckered five-membered PNC3 ring. The ester
substituent adopts an axial position with respect to the ring,
presumably minimizing steric conflict with the phenyl substituents
on the adjacent carbon. The P–N and P–C bond distances within
˚
˚
the ring are found to be 1.573(3) A and 1.823(3) A, respectively;
while the N–C distance and the C–C distance within the ring were
˚
˚
1.471(4) A and 1.536(4) A, respectively. The corresponding P–N–C
angle in 4 was found to be 109.0(2)◦.
Attempts to effect similar cyclizations with more electron-rich
alkynes such as PhCCPh, tBuCCH, Me3SiCCH, PhCCH were
unsuccessful However, the corresponding reactions of 1 and 2
with dimethyl acetylenedicarboxylate affords the related cyclized
products R2PNCPh2(CCOMe)2 (R = Ph 7, i-Pr 8) in approximately
80% yields.
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Fig. 3 POV-ray depiction of 7, hydrogen atoms are omitted for clarity.
Fig. 1 POV-ray depictions (a): 1, (b): one of the two molecules in the
asymmetric unit of 2, hydrogen atoms are omitted for clarity.
Fig. 4 POV-ray depiction of 8, hydrogen atoms are omitted for clarity.
Reaction of 1 with acrylonitrile results in the isolation of the
white solid in 77% yield. This product 9 was formulated as
Ph2PNCPh2(CH2CH(CN)). The spectroscopic data are similar to
1
the cyclic phosphinimines described above, with a 31P{ H} NMR
resonance at 46.0 ppm. The infrared spectrum was also consistent
with the presence of the nitrile fragment exhibiting a C N stretch
at 2240 cm-1.
Once again, crystallographic data confirmed the formulation
unambiguously (Fig. 5). Similar to 4, the ring conformation
Fig. 2 POV-ray depiction of 4, hydrogen atoms are omitted for clarity.
These five-membered phosphinimine species retain a C
double bond in the ring and are essentially planar. The H and
C
1
1
1
13C{ H} NMR data were as expected while the 31P{ H} chemical
shifts of 7 and 8 were 49.0 ppm and 73.8 ppm, respectively. Whereas
compound 7 has been previously reported, X-ray crystallographic
data for 7 confirmed the cyclic nature and revealed P–N, P–C,
˚
˚
N–C and C C bond lengths of 1.5749(15) A, 1.7998(17) A,
˚
˚
1.457(2) A and 1.331(2) A in the heterocyclic ring (Fig. 3). The
C–N–P angle was found to be 111.98(11)◦. The increase in the
C–N–P angle in comparison to that in 4 is consistent with the
rigidity resulting from the planarity of the five-membered ring. In
a similar fashion, the crystallography study of 8 (Fig. 4) revealed
a planar structure where P–N and N C bond distances were
found to be 1.5801(13) A and 1.4618(19) A, respectively, while
the corresponding C–N–P angle was 112.21(9)◦. These structural
perturbations are consistent with the presence of a more electron-
rich P centre in 8.
˚
˚
Fig. 5 POV-ray depiction of 9, hydrogen atoms are omitted for clarity.
9630 | Dalton Trans., 2010, 39, 9626–9632
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is puckered with the nitrile substituent adopting an axial
position. The P–N and N–C bond distances were found to be
˚
˚
1.5892(13) A and 1.4802(19) A, respectively, while the C–N–P
angle was determined to be 107.81(9)◦. The comparatively long
P–N and N–C bonds, together with the small angle at N are
consistent with the electron-withdrawing nature of the nitrile
substituent.
These phosphinimines proved to be moisture sensitive. In the
case of 4, exposure to H2O resulted in the hydrolytic ring opening
of the phosphinimine. This results in the cleavage of the P–N
bond and formation of the corresponding amine-phosphine-oxide
species Ph2C(NH2)CH(CO2Me)CH2P(O)Ph2 10. This species is
isolated as a white solid, The 1H NMR spectrum reveals a
resonance at 1.70–2.30 attributable to the NH2 fragment, while the
1
31P{ H} NMR spectrum shows a resonance at 29.9 ppm, typical
of phosphine oxides. The formulation of this hydrolysis product
was confirmed crystallographically (Fig. 6). The structure reveals
the open chain nature of this species with a P–O bond distance of
˚
1.490(3) A.
Fig. 7 POV-ray depiction of the cation of 11, hydrogen atoms are omitted
for clarity.
Fig. 6 POV-ray depiction of 10,hydrogen atoms are omitted for clarity.
Complexation
In examining the potential of these cyclic phosphinimines as
ligands, the reactions of 4 with Ag(NO3) was first performed.
Employing a 1 : 1 ligand : silver stoichiometry, crystals of a new
species were isolated in 73% yield. While the NMR data was
consistent with the complexation of the ligand, the nature of
the product 11 was only unambiguously confirmed via X-ray
diffraction methods. These experiments revealed the formulation
of 11 to be [{Ph2PNCPh2(CH2CH(CO2Me)}2Ag] [(NO3)2Ag]
(Fig. 7, Scheme 3). The anion is a linear Ag ion, in which two
nitrate groups bind via one oxygen atom to the Ag centre with
Scheme 3 Synthesis of compounds 11–13.
In reactions conducted in a similar fashion, the cyclic phos-
phinimines 4 and 7 were reacted with (Me2S)AuCl. This resulted
in the isolation of Ph2PNCPh2(CH2CH(CO2Me)AuCl 12 and
(Ph2PNCPh2(C(CO2Me)2)AuCl 13, respectively, in yields of 89 and
82%. While coordination to Au was inferred by the observation of a
complexation shift of the NMR resonances, X-ray crystallography
was employed to confirm the formulations (Fig. 8, 9, Scheme 3). In
both cases these molecules were linear Au(I) complexes in which
the N of the cyclic phosphinimine was coordinated to a AuCl
fragment. The Au–N distances in 12 and 13 were determined to be
˚
a Ag–O distance of 2.223(3) A. The cation of this salt is a
two-coordinate pseudo-linear Ag ion coordinated to the N of
two phosphinimine ligands. The Ag–N distance was determined
˚
to be 2.0675(17) A, while the linearity of the N–Ag–N vector
˚
was crystallographically imposed. This distance is similar to the
distances reported for a series of Ag-carbene complexes of the
2.0253(13) and 2.010(7) A, with corresponding Au–Cl distance◦s
˚
of 2.2612(4) and 2.257(2) A, and N–Au–Cl angles of 177.07(4)
form LAgCl where the Ag–C distances range from 2.094(6) to
and 179.7(2)◦, respectively.
11
˚
2.060(19) A. The geometry of the cation of 11 is similar to
The Au–N distances in 12 and 13 are slightly longer than those
observed for Au–C bond lengths in related NHC-carbene-AuCl
that seen in the bis-carbene complex [(C6H4(NEt)2C)2Ag][AgBr2]12
complexes,13 which range from 1.965(5) A to 2.018(3) A, and
slight shorter than those seen in the CAAC complex cations of
˚
˚
although the Ag–N distance in 11 is slightly shorter than that
˚
reported for this carbene species (2.073(26) A).
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allows for ready derivatization of the substitution on P and on
the backbone of the ring. In addition, we have shown that these
species act as strong sigma donor ligands for Ag(I) and Au(I), while
providing a highly sterically encumbered donor environment. The
utility of these attributes in subsequent chemistry and catalysis are
under study and will be reported in due course.
Acknowledgements
The support of NSERC of Canada is gratefully acknowledged.
D.W.S. is grateful for the award of a Canada Research Chair and
a Killam Research Fellowship.
Notes and references
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Fig. 8 POV-ray depiction of 12, hydrogen atoms are omitted for clarity.
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Fig. 9 POV-ray depictions of 13, hydrogen atoms are omitted for clarity.
+
the form [L2Au] (2.0321(11) 2.033(4) A).3b Consequently the Au–
˚
Cl distances in 12 and 13 are slightly shorter as the Au–Cl in the
˚
related carbene complexes range from 2.2698(11) to 2.3061(11) A.
While the structural features of these cyclic phosphinimine
ligands are reminiscent of that of carbene ligands the data
presented herein is consistent with the anticipated strong donor
ability of these ligands. The metric data suggest that these ligands
exhibit similar sigma donor abilities to N-heterocyclic carbenes,
however the geminal substitution at the P and C adjacent to
N generates a donor environment that is even more sterically
encumbered than that in bulky N-heterocyclic carbenes.
11 P. d. Fre’mont, N. M. Scott, E. D. Stevens, T. Ramnial, O. C. Lightbody,
C. L. B. Macdonald, J. A. C. Clyburne, C. D. Abernethy and S. P. Nolan,
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Conclusions
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13 P. d. Fre’mont, N. M. Scott, E. D. Stevens and S. P. Nolan,
Organometallics, 2005, 24, 2411.
In conclusion, in this initial study in this area, we have described
the facile syntheses of a number of cyclic phosphinimines, which
9632 | Dalton Trans., 2010, 39, 9626–9632
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The Royal Society of Chemistry 2010
©