Organometallics
ARTICLE
Further reaction results in a formal β-cyano elimination in 2,
leading to 3 and benzene. One additional C-H activation of
benzonitrile follows, giving 4 with the aryl-cyano substituent
occupying one of all three possible positions (ortho, meta, and
para). The majority of the reaction follows the pathway 2 f 3 f
4 as the formation of 2 is kinetically favored and 4 is the
thermodynamic product. A series of reactions to evaluate the
pathway of 2 f 4 showed the production of benzyne to be a
possible pathway, and a pathway via a Pt(IV)-dihydride inter-
mediate was ruled out by deuterium labeling studies. Although the
benzynetrappingexperiments proved unsuccessful, the formation
of benzene and deuterated benzene species (from (dippe)PtD2)
is consistent with the β-cyano elimination and hydrogenation of
benzyne as the proposed mechanistic pathway for this system.
Preparation of (dippe)Pt(CN)(C6H4CN), 4. A solution of 1
(0.010 g, 0.013 mmol) in 1 mL of benzonitrile was heated to 140 °C for
7 days under a N2 atmosphere. The solvent was removed under vacuum,
leaving a yellow-brown, oily solid. The solid was recrystallized via slow
evaporation in a mixture of hexanes, benzene, ether, and THF, produ-
1
cing 0.0064 g (64% yield) of a white, crystalline solid. H NMR (400
MHz, THF-d8): δ 0.47-1.4 (m, 72 H, CH-Me2), 1.62-2.12 (m, 24 H,
PCH2CH2P and CH-Me2), 6.94 (m, 1 H, aryl PhCN), 7.09-7.16 (m,
3 H, aryl PhCN), 7.23 (d, 1 H, aryl PhCN), 7.30 (s, 1 H, aryl PhCN),
7.37, (m, 1 H, aryl PhCN), 7.45 (m, 1 H, aryl PhCN), 7.60 (t, 1 H, aryl
PhCN), 7.68 (d, 2H, aryl PhCN), 7.75 (m, 1 H, aryl PhCN). 31P{1H}
NMR (400 MHz, THF-d8): δ 73.6 (3 singlets, with Pt satellites, 1JPt-P
=
1
1600 Hz), 63.5 (3 singlets, with Pt satellites, JPt-P = 2705 Hz). IR
(NaCl): νCN = 2279 cm-1, νCN = 2269 cm-1. An elemental analysis was
obtained of the mixture of o-, m-, and p-isomers of 4. Anal. Calcd
for C22H36N2P2Pt: C 45.12, H 6.20, N 4.78. Found: C 45.32,
H 6.73, N 2.30.
’ EXPERIMENTAL SECTION
Preparation of (dippe)Pt(Ph)Cl, 5a. A solution of (dippe)PtCl2
(0.10 g, 0.189 mmol) in CH2Cl2 was treated with 0.10 mL of
phenylmagnesium chloride (1.94 M, 0.189 mmol) at 25 °C under a
N2 atmosphere and allowed to stir for 10 min. The solvent was removed
under vacuum, giving a white solid, which was then dissolved in benzene
and filtered through a Celite plug. The filtrate was dried under vacuum,
giving 0.073 g (61% yield) of a white solid. 1H NMR (400 MHz, C6D6):
δ 0.94-0.98 (dd, 6 H, CH-Me2), 1.10-1.16 (dd, 6 H, CH-Me2), 1.20-
1.25 (dd, 6 H, CH-Me2), 1.36-1.42 (dd, 6 H, CH-Me2),1.6 (m, 4 H,
PCH2CH2P), 1.9 (m, 4 H, CH-Me2), 6.67 (t, 1 H, J = 7.6 Hz,
aryl PhCN), 6.86 (d, 2 H, J = 7.6 Hz, aryl PhCN), 7.17 (d, 2 H, J =
7.6 Hz, aryl PhCN). 31P{1H} NMR (400 MHz, C6D6): δ 70.2 (s, with Pt
General Considerations. All manipulations were performed
under a nitrogen atmosphere, either on a high-vacuum line using
modified Schlenk techniques or in a Vacuum Atmospheres Corporation
glovebox. Tetrahydrofuran, benzene, and toluene were distilled from
dark purple solutions of sodium/benzophenone ketyl. [(dippe)PtH]2
was synthesized according to the previously reported procedure.8
Titration of phenylmagnesium chloride was performed following a
literature procedure.15 Benzonitrile and deuterium gas were purchased
from Aldrich Chemical Co. All other chemicals, filter aids, and chroma-
tographic materials were used as received. NMR data (1H and 31P{1H})
were recorded on Bruker Avance 400 and 500 instruments. Chemical
shifts are given in δ and referenced to residual solvent resonances (1H,
2H) or external H3PO4 (31P). IR data were recorded on a Shimadzu
FTIR-8400 S IR spectrophotometer. GC-MS data were analyzed on a
Shimadzu GCMS-QP2010 gas chromatograph mass spectrometer.
1
1
satellites, JPt-P = 1701 Hz), 60.7 (s, with Pt satellites, JPt-P
=
3941 Hz).
Preparation of (dippe)Pt(Ph)(CN), 5. A solution of (dippe)Pt-
(Ph)Cl (0.053 g, 0.093 mmol) in 10 mL of THF was treated with excess
AgCN (0.05 g, 0.37 mmol) and stirred at 25 °C for 24 h. The reac-
tion was filtered through a Celite plug, giving a pink solution, which was
dried under vacuum, giving 0.05 g (93% yield) of a pink solid. 1H NMR
(400 MHz, THF-d8): δ 0.8-0.9 (dd, 6 H, CH-Me2), 1.14-1.23 (dd,
12 H, CH-Me2), 1.33-1.39 (dd, 6 H, CH-Me2), 1.8-1.9 (m, 4 H,
PCH2CH2P), 2.3-2.4 (m, 4 H, CH-Me2), 6.68 (t, 1H, J = 7.6 Hz, aryl),
6.86 (t, 2H, J = 7.6 Hz, aryl), 7.18 (d, 2 H, J = 7.6 Hz, JPt-H = 70 Hz, aryl).
All reactions were run in J-Young tubes under a nitrogen atmosphere
or in a bomb apparatus under a H2/D2 atmosphere. Heating of the
samples was performed in a temperature-controlled oil bath. DANGER:
Pressures in sample tubes exceed 1 atm upon heating. Appropriate safety
precautions should be observed.
Preparation of (dippe)Pt(H)(2-C6H4CN), 2. A solution of 1
(0.010 g, 0.013 mmol) in 1 mL of benzonitrile was heated to 140 °C
under a N2 atmosphere for 1 h. After 1 h, the solvent was removed under
vacuum, leaving an orange-brown, oily solid. The solid was dissolved in
THF and crystallized via THF/hexanes vapor diffusion, producing 0.007 g
(70% yield) of a white, crystalline solid. 1H NMR (500 MHz, C6D6): δ
-0.29 (dd, 1 H, JP-H = 16.5, 185 Hz, JPt-H = 1159 Hz), 0.63-1.37 (m,
24 H, CH-Me2), 1.80 (t, 4 H, PCH2CH2P), 1.93 (q, 4 H, CH-Me2), 6.72
(d, 1 H, J = 3.5 Hz, aryl), 6.93 (t, 1H, J = 3.5 Hz, aryl), 7.51 (d, 1 H, J = 3.5
Hz, aryl), 7.65 (t, 1 H, J = 3.5 Hz, aryl). 31P{1H} NMR (500 MHz,
C6D6): δ 83.8 (s, with Pt satellites, 1JPt-P = 1936 Hz), 70.4 (s, with Pt
satellites, 1JPt-P = 1746 Hz). Anal. Calcd for C21H37NP2Pt: C 45.00, H
31P{1H} NMR (500 MHz, THF-d8): δ 73.8 (s, with Pt satellites, 1JPt-P
=
1
1586 Hz), 62.6 (s, with Pt satellites, JPt-P = 2744 Hz). IR (C6D6):
νCN = 2278 cm-1
.
Preparation of [(dippe)PtD]2, 1-d2. A solution of 1 (0.010 g,
0.013 mmol) was dissolved in THF and placed in a bomb apparatus. The
bomb was pressurized to ∼40 psi (∼2.7 atm) with D2 and allowed to sit
at 25 °C for 24 h. The sample was dried under vacuum and redissolved in
1
C6D6. H NMR (400 MHz, C6D6): no resonances observed in the
hydride region. 31P{1H} NMR (400 MHz, C6D6): δ 88.8 (1:1:1 t, JP-D
=
27 Hz, with platinum satellites, JPt-P = 1809 Hz). 2H NMR (400 MHz,
PhCN): δ -2.17 and -1.72 (br d, 2 D, JP-D = 10 Hz). The reactions of
this material with benzonitrile are described in the text.
6.65, N 2.50. Found: C 45.32, H 6.73, N 2.30. IR (NaCl): νCN
=
2280 cm-1
.
Preparation of (dippe)Pt(H)(CN), 3. A solution of 1 (0.010 g,
0.013 mmol) in 1 mL of benzonitrile was heated to 120 °C for 96 h under
a N2 atmosphere. The solvent was removed under vacuum, leaving a
yellow, oily solid. The solid was dissolved in THF and crystallized via
THF/hexanes diffusion, producing 0.004 g (40% yield) of a white,
crystalline solid. 1H NMR (500 MHz, toluene-d8): δ -1.26 (dd, 1 H,
’ ASSOCIATED CONTENT
S
Supporting Information. NMR spectra described in the
b
text, a summary of the crystallographic data, intramolecular bond
distances and angles, and positional and thermal parameters for 2, 3,
ortho-4, meta/para-4, 5a, and 5. CIF files have been deposited with
the Cambridge Crystallographic Data Centre, as CCDC 752157-
752163. A copy of this information may be obtained free of charge
from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK, via fax: (int. code) þ44 1223 336 033, e-mail: deposit@ccdc.
1
JP-H = 16, 185 Hz, JPt-H = 1008 Hz), 0.53-1.45 (m, 32 H, dippe).
31P{1H} (500 MHz, toluene-d8): δ 81.8 (s, with Pt satellites, 1JPt-P
2677 Hz), 77.2 (s, with Pt satellites, 1JPt-P = 1669 Hz). IR (NaCl): νCN
=
=
2274 cm-1. An elemental analysis was not obtained, as a pure sample of 3
could not be isolated.
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dx.doi.org/10.1021/om101069j |Organometallics 2011, 30, 1523–1529