Synthesis, structure, and reactions of 1-fert-butyl-2-diphenylphosphino- imidazole

Article abstract of DOI:10.1021/ic101122n

Metalation reactions were studied of a sterically demanding imidazole derivative, namely, 1-ferf-butylimidazole (1),with different metalation reagents and subsequent reaction with diphenylchlorophosphane. The reaction product, 1-ferf-butyl-2-diphenylphosphino-imidazole (2), was subjected to oxidation and complexation reactions to yield the corresponding products Ph ₂(Imi)P-E (E = O (3),S (4),Se (5),W(CO)₅ (8)) and in the case of borane-THF the N-BH₃ coordination product 10 was obtained. The analytical data of the new compounds are discussed, including X-ray diffraction studies of 3-5.

Full text of DOI:10.1021/ic101122n

Inorg. Chem. 2011, 50, 793–799 793
DOI: 10.1021/ic101122n
Synthesis, Structure, and Reactions of 1-tert-Butyl-2-diphenylphosphino-imidazole
€
€
Susanne Sauerbrey, Paresh Kumar Majhi, Jorg Daniels, Gregor Schnakenburg, Gerhard Markus Brandle,
Katharina Scherer, and Rainer Streubel*
€
Institut fu€r Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universitat Bonn, Gerhard-Domagk-Strasse
1, D-53121 Bonn, Germany
Received June 3, 2010
Metalation reactions were studied of a sterically demanding imidazole derivative, namely, 1-tert-butylimidazole (1), with
different metalation reagents and subsequent reaction with diphenylchlorophosphane. The reaction product, 1-tert-butyl-2-
diphenylphosphino-imidazole (2), was subjected to oxidation and complexation reactions to yield the corresponding
products Ph2(Imi)P-E (E=O(3), S(4), Se(5), W(CO)5 (8)) and in the case of borane-THF the N-BH3 coordination product
10 was obtained. The analytical data of the new compounds are discussed, including X-ray diffraction studies of 3-5.
Introduction
type reactions,12 C-H bond activation reactions,13 hydration
of alkynes,8,10,14-17 or as enzyme model.18 They have also been
used to synthesize different types of mono- and bimetallic
complexes.19,20 Most of the C4 substituted compounds have
been synthesized via cyclization reactions, and only one was
obtained by reaction of a Grignard compound with an
imidazole derivative.21-24 Although the differences between
deprotonation and halogen-metal exchange reactions have
long been studied,25-29 the influence of the size of the N1
Phosphorus-containing imidazole derivatives have attracted
increasing interest over the years.1 For example, N1 substituted
derivatives,2 which are of particular interest as many natural
products and analogues of natural products, for example,
nucleotides,3 are among them and can be easily obtained by
reacting an N-H imidazole derivative with a diorganochloro-
phosphane in the presence of triethylamine as base.4 The C2
position can also be selectively addressed via metalation
reactions as N1 substituted imidazole derivatives were
known to react with, for example, organolithium com-
pounds to give 1,2-disubstituted compounds.5 The C2
substituted products have found application as ligands
in catalysis, like ethylene oligomerization,6 alkene isomeriza-
tions,7-10 aryl aminations,11 Suzuki and Buchwald-Hartwig
(12) Harkal, S.; Rataboul, F.; Zapf, A.; Fuhrmann, C.; Riermeier, T.;
Monsees, A.; Beller, M. Adv. Synth. Catal. 2004, 346, 1742–1748.
(13) Tejel, C.; Bravi, R.; Ciriano, M. A.; Oro, L. A.; Bordonaba, M.;
Graiff, C.; Tiripicchio, A.; Burini, A. Organometallics 2000, 19, 3115–3119.
(14) Grotjahn, D. B.; Incarvito, C. D.; Rheingold, A. L. Angew. Chem.
2001, 113, 4002–4005. Grotjahn, D. B.; Incarvito, C. D.; Rheingold, A. L.
Angew. Chem., Int. Ed. 2001, 40, 3884–3887.
(15) Grotjahn, D. B. Chem.;Eur. J. 2005, 11, 7146–7153.
(16) Grotjahn, D. B.; Miranda-Soto, V.; Kragulj, E. J.; Lev, D. A.;
Erdogan, G.; Zeng, X.; Cooksy, A. L. J. Am. Chem. Soc. 2008, 130, 20–21.
(17) Grotjahn, D. B.; Kragulj, E. J.; Zeinalipour-Yazdi, C. D.; Miranda-
Soto, V.; Lev, D. A.; Cooksy, A. L. J. Am. Chem. Soc. 2008, 130, 10860–
10861.
(18) Slebocka-Tilk, H.; Cocho, J. L.; Frachman, Z.; Brown, R. S. J. Am.
Chem. Soc. 1984, 106, 2421–2431.
(19) Burini, A.; Pietroni, B. R.; Galassi, R.; Valle, G.; Calogero, S. Inorg.
Chim. Acta 1995, 229, 299–305.
(20) Tejel, C.; Ciriano, M. A.; Bravi, R.; Oro, L. A.; Graiff, C.; Galassi,
R.; Burini, A. Inorg. Chim. Acta 2003, 347, 129–136.
(21) Kanazawa, C.; Kamijo, S.; Yamamoto, Y. J. Am. Chem. Soc. 2006,
128, 10662–10663.
*To whom correspondence should be addressed. Phone: 0049-228-735345.
Fax: 0049-228-739616. E-mail: r.streubel@uni-bonn.de.
(1) A literature search yielded more than 500 N1 substituted, more than
100 N1-organyl, C2 substituted, less than 20 N1-organyl, C4 substituted but
not a single N1-organyl, C5 substituted imidazole derivative with a phos-
phanyl- or phosphoryl-substituent.
(2) According to the Hantzsch and Widman nomenclature system, the
imidazole ring is numbered starting from the nitrogen atom bearing the
substitutent with the higher priority in such a way that the two nitrogen
atoms receive the smallest possible numbers; 1 and 3.
(3) Kowalska, J.; Lewdorowicz, M.; Zuberek, J.; Grudzien-Nogalska, E.;
Bojarsaka, E.; Stepinski, J.; Rhoads, R. E.; Darzynkiewicz, E.; Davis, R. E.;
Jemielity, J. RNA 2008, 14, 1119–1131.
(4) Reddy, M. V. N.; Ravi, A. V. R; Reddy, C. S.; Raju, C. N. S. Afr. J.
Chem. 2008, 61, 43–46.
(5) Iddon, B.; Ngochindo, R. I. Heterocycles 1994, 38, 2487–2568.
(6) Spencer, L. P.; Altwer, R.; Wie, P.; Gelmini, L.; Gauld, J.; Stephan,
D. W. Organometallics 2003, 22, 3841–3854.
(7) Grotjahn, D. B.; Larsen, C. R.; Gustafson, J. L.; Nair, R.; Sharma, A.
J. Am. Chem. Soc. 2007, 129, 9592–9593.
(8) Grotjahn, D. B. Dalton Trans. 2008, 6497–6508.
(9) Erdogan, G.; Grotjahn, D. B. J. Am. Chem. Soc. 2009, 131, 10354.
(10) Grotjahn, D. B. Pure Appl. Chem. 2010, 82, 635–647.
(11) Singer, R. A.; Tom, N. J.; Frost, H. N.; Simon, W. M. Tetrahedron
Lett. 2004, 45, 4715–4718.
(22) Huang, W.; Yuan, C. Synthesis 1996, 511–513.
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Chem. 1978, 7, 421–436.
(24) Berens, U. PCT Int. Appl. WO 200331456/A2, 2003.
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(26) Iddon, B.; Lim, B. L. J. Chem. Soc., Perkin Trans. I 1983, 279–283
and 735-739.
(27) Iddon, B.; Khan, N. Tetrahedron Lett. 1986, 27, 1635–1638.
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r
2011 American Chemical Society
Published on Web 01/04/2011
pubs.acs.org/IC

794 Inorganic Chemistry, Vol. 50, No. 3, 2011
Sauerbrey et al.
substituent had not been the subject of intensive studies. Most
of the known C2 or C4 substituted imidazole derivatives
contain small or sterically non-demanding N1 substituents such
as acetyl,30 benzyl,19,23,31 bis(ethoxy)methyl,30 methyl,6,32,33
ethyl,32 n-octyl,22 or phenyl21,34 Just a few examples with
trityl,11 mesityl,12 or differently substituted aromatic groups22,35
were reported. Most often, diphenylchlorophosphane was
used12,31,32,34,35 as it is commercially available and often yields
relatively stable derivatives, but also derivatives with other
phosphanyl groups having substituents such as tert-butyl,12,33
cyclohexyl,11,12 isopropyl,11 chloro,19 and di(alkylamino)22,32
were reported.
addition and then cooled to room temperature. After removal of
the water by rotatory evaporator, the crude product was purified
via vacuum distillation (bp. 53 °C/0.9 mbar) and obtained as a very
pale yellow liquid, yield 70%. Analysis:38 1H NMR (300.1 MHz,
CDCl3, 25 °C): δ = 7.00 (s br, 1H, C2-H), 6.45 (s br, 1H, C5-H),
6.41 (s br, 1H, C4-H), 0.90 (s, 9H, C4H9); 13C{1H}-NMR (75.0
MHz, CDCl3, RT): δ = 134.0 (s, C2), 128.7 (s, C5), 116.2 (s, C4),
54.4 (s, tert-butyl-C), 30.3 (s, tert-butyl-CH3); MS (EI, 70 eV): m/z
124 (Mþ, 92%), 68 (Mþ - C4H9, 76%), 57 (C4H9þ, 42%).
Preparation of 1-tert-Butyl-2-diphenylphosphino-imidazole (2). A
100 mL portion of THF and 1-tert-butylimidazole (1) (1.35 mL, 10
mmol) were placed in a 250 mL Schlenk flask equipped with a
septum stopper. The flask was cooled to -80 °C, and tert-butyl-
lithium (7 mL, 1.5 M solution in pentane, 10.5 mmol) was slowly
added (reaction mixture turned yellow). After 30 min stirring
at -80 °C, diphenylchlorophosphane (1.85 mL, 10.3 mmol) was
added (and the reaction mixture darkened a little bit). The reaction
mixture was slowly warmed up until ambient temperature, the
solvent was then removed in vacuo, and the light yellow residue was
taken up in dichloromethane. It was filtered through a G3 frit
equipped with a layer of Celite to remove the precipitated lithium
chloride. The filtrate was concentrated in vacuo (8 ꢀ 10-3 mbar),
and the crude product was purified by recrystallization from 20 mL
of hot toluene. Colorless crystals were obtained, yield 2.00 g (65%),
mp 124 °C. Analysis: 1H NMR (300.1 MHz, THF-d8, 25 °C): δ =
7.58-7.26 (m, 11H, C5-H and C6H5), 7.09 (d, 3JH,H = 1.1 Hz, 1H,
C4-H), 1.80 (s, 9H, C4H9); 13C{1H} NMR (75.0 MHz, THF-d8,
25 °C): δ = 144.5 (d, 1JP,C = 8.7 Hz, C2), 138.0 (d, 1JP,C = 5.5 Hz,
Here, we present metalation of 1-tert-butylimidazole (1)
and subsequent reaction with diphenylchlorophosphane as
well as further studies on the reactivity of the 1-tert-butyl-2-
diphenylphosphino-imidazole (2).
Experimental Section
General Considerations. All reactions except the synthesis of
1-tert-butylimidazole (1) and the oxidation reactions were car-
ried out under an argon atmosphere, using common Schlenk
techniques and dry solvents. Diethyl ether, petrol ether, and
tetrahydrofuran (THF) were dried over sodium wire, dichloro-
methane over calcium hydride, and further purified by sub-
sequent distillation. Diphenylchlorophosphane was distilled
prior to use and stored under argon. The [W(CO)5(thf)] complex
was synthesized by irradiating W(CO)6 in THF with a 150 W
low-pressure mercury lamp (TQ150, Heraeus Noblelight, Hanau,
Germany).36 All other chemicals were used as received. All NMR
spectra were recorded on a Bruker AX-300 spectrometer, with a
2
ipso-phenyl), 134.3 (d, JP,C = 21.0 Hz, ortho-phenyl), 129.3 (d,
3þ4
J
P,C
= 2.3 Hz, C5), 128.6 (s, para-phenyl), 128.1 (d, 3JP,C = 7.3
=
Hz, meta-phenyl), 120.0 (d, 3þ4JP,C = 1.9 Hz, C4), 57.0 (d, 3JP,C
1.3 Hz, tert-butyl-C), 31.4 (d, 4JP,C = 12.0 Hz, tert-butyl-CH3); 31
P
NMR (121.5 Hz, THF-d8, 25 °C): -23.6 (quin, 3JP,H = 7.6 Hz);
MS (EI, 70 eV): m/z 308 (Mþ, 64%), 251 (Mþ - C4H9, 100%), 183
(P(C6H5)2þ, 40%); IR (KBr): ν~ = 2983 (m, ν(CH), 1477 (m,
ν(CN)), 1434 (s, ν(P-C6H5)), 1246 (vs, δ(CH-C4H9)), 754 þ 748
(vs, δ(CH-C6H5)), 697.3 (vs, δ(ring-C6H5)); UV/vis (CH2Cl2):
λmax = 205 nm; EA: calcd C 74.01, H 6.86, N 9.08, found C
73.73, H 6.88, N 8.89; Rf-value (1:1 diethyl ether/petrol ether):
0.683.
1
1
frequency of 300.1 MHz for H. The H and 13C spectra were
referenced to the residual protons and the 13C signals of the
deuterated solvents, the 11B to BF3*OEt2 and 31P to 85% H3PO4
as external standard, respectively. Melting points were deter-
€
mined in one-sided melted off capillaries using a Buchi Type S
apparatus; they are uncorrected. Elemental analyses were carried
out on a Vario Type EL gas chromatograph. Mass spectrometric
data were collected on a Kratos MS 50 spectrometer using
EI, 70 eV. The Infrared spectra were recorded on a Nicolet 380
FT-IR spectrometer using KBr plates. The UV/vis spectra were
recorded in solution on a Shimadzu UV-1650 PC spectrometer.
The X-ray analyses were performed on a Nonius Kappa CCD
type diffractometer.
Preparation of 1-tert-Butylimidazole (1)37. In a 100 mL three-
necked flask connected to two dropping funnels and a condenser
was placed 50 mL of distilled water. One dropping funnel
contained a mixture of 40% aqueous glyoxal (11.5 mL, 0.1 mol)
and 40% aqueous formaldehyde (8.1 mL, 0.1 mol), the other
tert-butylamine (10.6 mL, 0.1 mol) and 25% aqueous ammonia
(6.8 mL, 0.1 mol). The water was heated until boiling, and then
both solutions were added simultaneously. The reaction mixture
turned brown and was stirred for 30 min at 100 °C after complete
Preparation of 1-tert-Butyl-2-diphenylphosphoryl-imidazole
(3). Twenty milliliters of CH2Cl2 and 1-tert-butyl-2-diphenyl-
phosphino-imidazole (2) (617 mg, 2 mmol) were placed in a
50 mL round-bottom flask. To it, meta-chloroperoxybenzoic
acid (345 mg, 2 mmol) was added, and the reaction mixture was
stirred for 30 min at ambient temperature. The solvent was
removed in vacuo (8 ꢀ 10-3 mbar), and the colorless residue
was purified via column chromatography at ambient temperature,
using aluminum oxide (90 active neutrale) as stationary phase and
petrol ether/diethyl ether-mixture as eluents. A colorless solid was
1
obtained, yield 467 mg (72%), mp 145 °C. Analysis: H NMR
(300.1 MHz, CDCl3, 25 °C): δ = 7.77-7.43 (m, 10H, C6H5-H),
7.28 (pt, 3þ4JH,H = 1.2 Hz, 1H, C5-H), 7.19 (pt, 3þ4JH,H = 1.2 Hz,
1H, C4-H), 1.76 (s, 9H, C4H9); 13C{1H}-NMR (75.0 MHz, CDCl3,
1
1
25 °C): δ = 139.4 (d, JP,C = 147.7 Hz, C2), 133.0 (d, JP,C
=
113.2 Hz, ipso-phenyl), 130.9 (d, JP,C = 9.7 Hz, ortho-phenyl),
2
130.6 (d, 4JP,C = 2.9 Hz, para-phenyl), 127.5 (d, 3þ4JP,C = 18.1 Hz,
(30) Saxon, E.; Armstrong, J. I.; Bertozzi, C. R. Org. Lett. 2000, 2, 2141–
2143.
(31) Komarov, I. V.; Strizhak, A. V.; Kornilov, M. Y.; Kostyuk, A. N.;
Tolmachev, A. A. Synth. Commun. 1998, 28, 2355–2370.
(32) Tolmachev, A. A.; Yurchenko, A. A.; Merculov, A. S.; Semenova,
M. G.; Zarudnitskii, E. V.; Ivanov, V. V.; Pinchuk, A. M. Heteroat. Chem.
1999, 10, 585–597.
(33) Grotjahn, D. B.; Gong, Y.; Zakharov, L.; Golen, J. A.; Rheingold,
A. L. J. Am. Chem. Soc. 2006, 128, 438–453.
(34) Cingolani, E. A.; Martini, D.; Pettinari, C.; Skeldon, B. W.; White,
A. H. Inorg. Chim. Acta 2006, 359, 2183–2193.
C5), 127.3 (d, 3JP,C = 12.6 Hz, meta-phenyl), 120.8 (d, 3þ4JP,C
=
3.2 Hz, C4), 57.5 (s, tert-butyl-C), 30.3 (s, tert-butyl-CH3);
31P NMR (121.5 Hz, CDCl3, 25 °C): 21.7 (quin, 3JP,H = 12.1 Hz);
MS (EI, 70 eV): m/z 324 (Mþ, 64%), 268 (Mþ - C4H9, 100%), 191
(Mþ - C4H9 - C6H5, 65%);): exact mass calcd 324.1389 found
324.1391; IR (KBr): ν~ = 3049 (w, ν(CH)), 2983 (m, ν(CH)), 1476
(m, ν(CN)), 1440 (vs, ν(P-C6H5)), 1254 (vs, ν(PO)); UV/vis
(CH2Cl2): λmax = 209 nm; EA: calcd C 70.36, H 6.53, N 8.64,
found C 69.01, H 6.37, N 8.65.
(35) Hanaoka, H.; Yamamoto, M.; Goto, F.; Jpn. Kokai Tokkyo Koho
JP 2008247745/A, 2008.
(36) Almaraz, E.; Foley, W. S.; Denny, J. A.; Reibenspies, J. H.; Golden,
M. L.; Darensbourg, M. Y. Inorg. Chem. 2009, 48, 5288–5295.
(37) Graf, F.; Hupfer, L.; U. S. Patent 4,450,277, 1984.
(38) Chadwick, D. J.; Ngochindo, R. I. J. Chem Soc., Perkin Trans. I
1984, 481–486.

Article
Preparation of 1-tert-Butyl-2-diphenylthiophosphoryl-imida-
Inorganic Chemistry, Vol. 50, No. 3, 2011 795
tert-butyl-CH3); 31P NMR (121.5 Hz, DMSO-d6, 25 °C): -35.0
(quin br, 3JP,H = 7.7 Hz); MS (ESI): exact mass calcd 323.1672
found 323.1674 (as C20H24N2Pþ); IR (KBr): ν~ = 2978 (w,
ν(CH)), 1434 (s, ν(P-C6H5)), 746 þ 700 (vs, δ(C6H5)); UV/vis
(CH2Cl2): λmax = 231 nm.
zole (4) and 1-tert-Butyl-2-diphenylselenophosphoryl-imidazole
(5). Ten milliliters of toluene, 1-tert-butyl-2-diphenylphosphi-
no-imidazole (2) (927 mg, 3 mmol), and elemental sulfur or
selenium (96/237 mg, 3 mmol) were placed in a 50 mL round-
bottom flask equipped with a condenser. The reaction mixture
was heated for 3 h at 110 °C and then slowly cooled to ambient
temperature. The product was precipitated from the reaction
mixture in the form of colorless crystals. The crystals were
washed with n-pentane and dried in vacuo (8 ꢀ 10-3 mbar).
Yield: (4) 951 mg (93%), (5) 1057 mg (91%), mp (4) 174 °C, (5)
204 °C. Analysis: (4) 1H NMR (300.1 MHz, CDCl3, 25 °C): δ =
7.66-7.34 (m, 10H, C6H5-H), 7.27 (pt, 3þ4JH,H = 1.4 Hz, 1H,
Reaction of 1-tert-Butyl-2-diphenylphosphino-imidazole (2)
with [W(CO)5(thf)] Complex. To a freshly prepared THF solu-
tion of [W(CO)5(thf)]36 complex (1 mmol), prepared by irradiat-
ing W(CO)6 in THF with a 150 W low-pressure mercury lamp
for 30 min at 10 °C, was added a solution of 1-tert-butyl-
2-diphenylphosphino-imidazole (2) (309 mg, 1 mmol) in 10 mL
of THF at ambient temperature in a Schlenk flask. The reaction
mixture was stirred at ambient temperature, and the reaction
was monitored with 31P NMR. Observed products: 8: 21.3
(1JW,P = 254.3 Hz) and 9: 14.4 (1JW,P = 193.3 Hz). Analysis:
(8) 1H NMR (300.1 MHz, C6D6, 25 °C): δ = 7.49-7.42 (m, 4H,
ortho-C6H5), 7.18 (d, 3JH,H = 1.3 Hz, 1H, C5-H), 6.94-6.88 (m,
6H, meta/para-C6H5), 6.78 (d, 3JH,H = 1.3 Hz, 1H, C4-H), 0.67
(s, 9H, C4H9); 13C{1H}-NMR (75.0 MHz, C6D6, 25 °C): δ =
200.0 (d, 1JW,C = 24.6 Hz, trans-CO), 197.3 (d, 1JW,C = 7.1 Hz,
cis-CO), 139.3 (d, 1JP,C = 66.6 Hz, C2), 135.6 (d, 1JP,C = 40.1
Hz, ipso-phenyl), 130.7 (d, 2JP,C = 11.6 Hz, ortho-phenyl), 129.9
3þ4
C5-H), 7.05 (pt,
J
= 1.4 Hz, 1H, C4-H), 1.72 (s, 9H,
H,H
C4H9); 13C{1H}-NMR (75.0 MHz, CDCl3, 25 °C): δ = 138.9 (d,
1JP,C = 129.0 Hz, C2), 133.3 (d, 1JP,C = 94.0 Hz, ipso-phenyl),
131.1 (d, 2JP,C = 10.6 Hz, ortho-phenyl), 130.3 (d, 4JP,C = 3.0
3þ4
Hz, para-phenyl), 127.5 (d,
J
= 18.0 Hz, C5), 127.2 (d,
P,C
3JP,C = 13.0 Hz, meta-phenyl), 122.4 (d, 3þ4JP,C = 2.5 Hz, C4),
58.3 (s, tert-butyl-C), 30.6 (s, tert-butyl-CH3); 31P NMR (121.5
Hz, CDCl3, 25 °C): 39.5 (quin, 3JP,H = 13.3 Hz); MS (EI, 70 eV):
m/z 340 (Mþ, 50%), 307 (Mþ-S, 5%), 284 (Mþ - C4H9,
100%);): exact mass calcd 340.1160 found 340.1163; IR (KBr):
ν~ = 3103 (w, ν(CH)), 2971 (m, ν(CH)), 1436 (vs, ν(P-C6H5)),
650 (vs, ν-(PS)); UV/vis (CH2Cl2): λmax = 209 nm; EA: calcd C
67.04, H 6.22, N 8.23, found C 65.54, H 6.21, N 8.06.
3þ4
4
(d,
J
= 1.9 Hz, C5), 128.7 (d, JP,C = 1.9 Hz, para-
P,C
phenyl), 129.3 (d, 3JP,C = 9.7 Hz, meta-phenyl), 123.9 (s br, C4),
57.1 (d, 3JP,C = 1.3 Hz, tert-butyl-C), 30.2 (s, tert-butyl-CH3);
31P NMR (121.5 Hz, C6D6, 25 °C): 21.3 (1JW,P = 254.3 Hz); MS
(EI, 70 eV): m/z 604 (Mþ - CO, 20%), 548 (Mþ - 3CO, 76%),
(5) 1H NMR (300.1 MHz, CDCl3, 25 °C): δ = 7.77-7.15 (m,
12H, C4/C5-H and C6H5), 1.72 (s, 9H, C4H9); 13C{1H}-NMR
(75.0 MHz, CDCl3, 25 °C): δ = 137.2 (d, 1JP,C = 119.0 Hz, C2),
132.2 (d, 1JP,C = 84.7 Hz, ipso-phenyl), 131.7 (d, 2JP,C = 11.0
Hz, ortho-phenyl), 130.4 (d, 4JP,C = 3.2 Hz, para-phenyl), 127.7
520 (Mþ - 4CO, 50%), 492 (Mþ - 5CO, 92%), 308 (Mþ
-
W(CO)5, 50%), 251 (Mþ - W(CO)5 - C4H9, 100%), 183
(W, 40%), Rf-value (1: 1 diethyl ether/petrol ether): 0.242.
(9) mp 95 °C, 1H NMR (300.1 MHz, CD3CN, -30 °C): δ =
7.69-7.55 (m, 10H, C6H5), 7.45 (pt, 3JH,H = 1.2 Hz, 1H, C5-H),
3þ4
3
(d,
J
P,C
= 17.5 Hz, C5), 127.2 (d, JP,C = 13.3 Hz, meta-
phenyl), 122.8 (d, 3þ4JP,C = 2.3 Hz, C4), 58.5 (s, tert-butyl-C),
30.8 (s, tert-butyl-CH3); 31P NMR (121.5 Hz, CDCl3, 25 °C):
30.6 1JSe,P = 740.0 Hz (quin, 3JP,H = 7.6 Hz); MS (EI, 70 eV):
m/z 388 (Mþ, 57%), 332 (Mþ - C4H9, 52%), 308 (Mþ - Se,
44%);): exact mass calcd 384.0631 found 388.0608; IR (KBr):
ν~ = 3102 (w, ν(CH)), 2970 (w, ν(CH)), 1477 (m, ν(CN)), 1436
(vs, ν(P-C6H5)), 754 þ 686 (vs, δ(C6H5)); UV/vis (CH2Cl2):
λmax = 210 nm; EA: calcd C 58.92, H 5.46, N 7.23, found C
58.82, H 5.41, N 7.03.
7.30 (pt, JH,H = 1.2 Hz, 1H, C4-H), 1.19 (s, 9H, C4H9);
3
13C{1H}-NMR (75.0 MHz, CD3CN, -30 °C): δ = 216.2 (ssat
,
1JW,C = 184.5 Hz, COax), 208.5 (ssat, 1JW,C = 167.5 Hz, COeq),
200.9 (ssat, 1JW,C = 132.6 Hz, COeq), 148.5 (d, 1JP,C = 28.9 Hz,
C2), 133.2 (d, 1JP,C = 20.9 Hz, ipso-phenyl), 132.5 (d, 1JP,C
=
13.9 Hz, ortho-phenyl), 132.1 (d, 4JP,C = 2.0 Hz, para-phenyl),
129.8 (d, 3JP,C = 9.9 Hz, meta-phenyl), 125.8 (s, C5), 121.3 (s br,
C4), 61.9 (s, tert-butyl-C), 30.1 (s, tert-butyl-CH3); 31P NMR
(121.5 Hz, CD3CN, -30 °C): 10.6 (1JW,P = 187.6 Hz); MS (EI,
70 eV): m/z 604 (Mþ, 9%), 548 (Mþ - 2CO, 37%), 520 (Mþ
-
Preparation of 1-tert-Butyl-2-diphenylphosphino-3-methyl-
imidazolium Iodide (7). A 100 mL portion of THF and 1-tert-
butyl-3-methyl-imidazolium iodide (6) (3.87 g, 14.8 mmol),
prepared from the reaction of 1-tert-butylimidazole (1) with
iodomethane in boiling methanol,39 were placed in a 250 mL
Schlenk flask equipped with a septum stopper. The flask was
cooled to -80 °C, and tert-butyllithium (22.2 mL, 1.5 M
solution in pentane, 14.8 mmol) was slowly added (reaction
mixture turned deep yellow). After 45 min stirring at -80 °C,
diphenylchlorophosphane (2.66 mL, 14.8 mmol) was added
(reaction mixture turned blood-red). The reaction mixture was
slowly warmed up until room temperature. The solvent was
removed in vacuo (8 ꢀ 10-3 mbar), and the obtained dark-red
slurry was taken up in 20 mL of distilled water to remove the
formed lithium chloride; the red color disappeared. The solid
was washed multiple times with water and then n-pentane. The
hygroscopic solid was dried in vacuo (8 ꢀ 10-3 mbar), yield 5.91
g (89%), mp 190 °C. Analysis: 1H NMR (300.1 MHz, DMSO-
d6, 25 °C): δ = 7.57-7.30 (m, 12H, C4/C5-H and C6H5), 3.75 (s,
3H, N-CH3), 1.62 (s, 9H, C4H9); 13C{1H}-NMR (75.0 MHz,
DMSO-d6, 25 °C): δ = 139.0 (s br, C2), 131.9 (d, 1JP,C = 5.2 Hz,
ipso-phenyl), 133.1 (d, 2JP,C = 20.5 Hz, ortho-phenyl), 130.1 (s,
para-phenyl), 129.3 (d, 3JP,C = 7.5 Hz, meta-phenyl), 128.4 (d,
3CO, 40%), 492 (Mþ - 4CO, 76%), 308 (Mþ - W(CO)4, 46%),
251 (Mþ - W(CO)5 - C4H9, 100%), 183 (W, 48%); IR (KBr):
ν~ = 2007 (s, ν(CO)), 1917(s, ν(CO)), 1875 (s, ν(CO)), 1811 (s,
ν(CO)), 1438 (s, ν(P-C6H5)); UV/vis (CH2Cl2): λmax = 232 nm.
Preparation of 1-tert-Butyl-2-diphenylphosphino-3-borane-
imidazole (10). Twenty milliliters of THF and 1-tert-butyl-2-
diphenylphosphino-imidazole (2) (617 mg, 2 mmol) were placed
in a 50 mL Schlenk flask. Borane THF complex (2 mL, 2 mmol,
1 M solution in THF) was added, and the reaction mixture was
stirred for 3 h at ambient temperature. The solvent was removed
in vacuo (8 ꢀ 10-3 mbar), and the colorless residue was washed
multiple times with n-pentane. After drying in vacuo (8 ꢀ 10-3
mbar), a colorless solid was obtained, yield 580 mg (90%), mp
1
130 °C. Analysis: H NMR (300.1 MHz, CDCl3, 25 °C): δ =
7.57-7.21 (m, 12H, C4/C5-H and C6H5), 1.89 (s br, 9H, C4H9),
1.66 (s br, 3H, BH3); 11B{1H}-NMR (96.3 MHz, CDCl3, 25 °C):
δ = -20.6; 13C{1H}-NMR (75.0 MHz, CDCl3, 25 °C): δ =
141.3 (d, 1JP,C = 40.1 Hz, C2), 133.4 (d, 1JP,C = 21.3 Hz, ipso-
2
phenyl), 132.4 (d, JP,C = 20.7 Hz, ortho-phenyl), 131.7 (d,
= 5.2 Hz, C5), 130.0 (s, para-phenyl), 127.7 (d, 3JP,C
3þ4
J
P,C
=
3þ4
29.1 Hz, meta-phenyl), 120.0 (d,
J
P,C
= 3.2 Hz, C4), 59.5 (s,
4
tert-butyl-C), 30.6 (d, JP,C = 13.6 Hz, tert-butyl-CH3); 31P
NMR (121.5 Hz, CDCl3, 25 °C): -19.5 (s br); MS (ESI): exact
mass calcd 345.1664 found 345.1669 (as C19H24BN2PNaþ); IR
(KBr): ν~ = 3048 (w, ν(CH)), 2981 (m, ν(CH)), 2413 (ν(BH) E),
2363 (ν(BH) A0), 1435 (vs, ν(P-C6H5)), 756 þ 692 (s, δ(C6H5));
UV/vis (CH2Cl2): λmax = 210 nm.
3þ4
3þ4
J
P,C
J
= 6.5 Hz, C5), 125.8 (d,
= 4.5 Hz, C4), 60.0
P,C
(s, tert-butyl-C), 34.9 (d, 3JP,C = 10.0 Hz, N-CH3), 28.9 (s br,
(39) Yoshida, Y.; Baba, O.; Larriba, C.; Saito, G. J. Phys. Chem. B 2007,
111, 12204–12210.

796 Inorganic Chemistry, Vol. 50, No. 3, 2011
Sauerbrey et al.
Table 1. Selected NMR Data (Chemical Shifts and Coupling Constants) and Melting Points of Compounds 2, 3-5
data
31P
2
3
4
5
-23.6, 3JP,H = 7.6 Hz
1.80, s, 9H, C4H9
21.7, 3JP,H = 12.1 Hz
1.76 s, 9H, C4H9
39.5, 3JP,H = 13.3 Hz
1.72 s, 9H, C4H9
30.6, 3JP,H = 12.7 Hz, 1JSe,P = 740.0 Hz
1H
1.72 s, 9H, C4H9
13C{1H} 144.5, 1JP,C = 8.7 Hz, C2
129.3, 3þ4JP,C = 2.3 Hz, C5
120.0, 3þ4JP,C = 1.9 Hz, C4
139.4, 1JP,C = 147.7 Hz, C2 138.9, 1JP,C = 129.0 Hz, C2 137.2, 1JP,C = 119.0 Hz, C2
127.5, 3þ4JP,C = 18.1 Hz, C5 127.5, 3þ4JP,C = 18.0 Hz, C5 127.7, 3þ4JP,C = 17.5 Hz, C5
120.8, 3þ4JP,C = 3.2 Hz, C4 122.4, 3þ4JP,C = 2.5 Hz, C4 122.8, 3þ4JP,C = 2.3 Hz, C4
31.4, 4JP,C = 12.0 Hz, t-Bu-CH3 30.3, t-Bu-CH3
30.6, t-Bu-CH3
174 °C
30.8, t-Bu-CH3
204 °C
m.p.
124 °C
145 °C
Scheme 1. Synthesis of 1-tert-Butyl-2-diphenylphosphino-imidazole 2
Scheme 2. Oxidation Reactions of (2) Using m-CPBA or Elemental
Chalcogens (S8 and Se)
Reaction of 1-tert-Butyl-2-diphenylphosphino-imidazole (2)
with cis-[Pt(PhCN)2Cl2] Complex. Ten milliliters of CH2Cl2
and 1-tert-butyl-2-diphenylphosphino-imidazole (2) (308 mg,
1 mmol) were placed in a Schlenk flask and cis-[Pt(PhCN)2Cl2]
complex (472 mg, 1 mmol) was added, and the reaction mixture
was heated at 40 °C for 3 h. The reaction was monitored using
31P NMR. Observed products: 11: -25.4 (1JPt,P = 3756.2 Hz),
12: 10.9 (1JPt,P = 3898.6 Hz). Unfortunately, none of them
could be crystallized or purified by column chromatography.
Analysis: (11) 1H NMR (300.1 MHz, CD2Cl2, 25 °C): δ =
7.30-7.23 (m, 10H, C6H5), 7.05 (d, 3JH,H = 1.13 Hz, 1H, C5-H),
It is interesting to note that all 2-diphenylphosphino
substituted imidazole derivatives described in the literature
so far have a 31P{1H} NMR resonance at around -30.0 ppm,
unaffected by the nature of the N1 substituent,6,30-32,34,35 but
in the case of 2 the phosphorus resonance was shifted to lower
field (-23.6 ppm) (see Table 1); the signal showed a quintet
3
6.66 (d, JH,H = 1.13 Hz, 1H, C4-H), 1.73 (s, 9H, C4H9); MS
(ESI) data: exact mass calcd 538.0779 found 538.0818 (as
C19H21ClN2PPtþ); (12): exact mass calcd 846.2221 found
846.2222 (as C38H42ClN4P2Ptþ).
3
in the proton-coupled spectrum due to a J(P,H) coupling
(7.6 Hz) to the ortho-phenyl protons. In the 13C NMR
spectrum all carbons except the para-phenyl carbon atoms
exhibited couplings to the phosphorus atom. Whereas the
coupling constants to the phenyl and the imidazole carbon
atoms were in the expected range, the coupling to the carbon
atoms of the tert-butyl methyl group was surprisingly large
(12.0 Hz). Attempts to grow crystals suited for X-ray struc-
ture analysis always resulted in twinned crystals, and the
structure of which could not be solved. Therefore, and to
study the reactivity of 2, various oxidation and complexation
reactions were performed as described in Scheme 2.
Results and Discussion
1-tert-butylimidazole (1) was subjected to metalation reac-
tions using different bases and subsequent reaction with diphe-
nylchlorophosphane; all reactions were monitored by 31P NMR
spectroscopy. The metalation reagents used were methyllithium,
n-butyllithium, tert-butyllitium, lithium diisopropylamide, so-
dium bis(trimethylsilyl)amide, potassium tert-butoxide, and the
combination of potassium tert-butoxide and tert-butyllithium
(Lochmann-Schlosser superbase).40 In most of the reactions of 1
the steric demand of the tert-butyl group caused kinetic pro-
blems, which led to the preferred formation of the following
products, identified by their 31P NMR shift (values given in
brackets): tetraphenyldiphosphane (14.6 ppm),41,42 or diphenyl-
methylphosphane (-26.3 ppm).43 The formation of these
products point to the reaction of unreacted metalation reagent
with diphenylchlorophosphane. The 2-diphenylphosphino sub-
stituted imidazole derivative 2 was formed selectively with tert-
butyllithium as base and diphenylchlorophosphane, and was
isolated by crystallization (Scheme 1).
The reactions of compound 2 with meta-chloroperbenzoic
acid, elemental sulfur and selenium were quantitative ac-
cording to 31P NMR spectroscopy (see Scheme 2); the lower
isolated yield of the phosphane oxide 3 was caused by the
necessity to perform column chromatography to remove
meta-chlorobenzoic acid. Elemental tellurium did not react
with 2 under the same conditions. The products 4 and 5
crystallized out of the reaction mixtures and thus could easily
be obtained in pure form; selected analytical data of com-
pounds 2, 3-5 are shown in Table 1. As expected for PV
derivatives the 31P NMR signal of 3-5 was shifted to lower
field compared to phosphane 2, whereby the greatest shift
was observed for the phosphane sulfide 4. The same tenden-
cies were observed before in the series of imidazole phos-
(40) Ishikawa, T. Superbases in Organic Synthesis; John Wiley and Sons:
West Sussex, 2009.
(41) Schmidpeter, A. Phosphorus, Sulfur Silicon Relat. Elem. 1985, 22,
323–325.
(42) Hunter, D.; Michie, J. K.; Miller, J. A.; Stewart, W. Phosphorus,
Sulfur Silicon Relat. Elem. 1981, 10, 267–270.
(43) Moedritzer, K.; Maier, L.; Groenweghe, L. C. D. J. Chem. Eng. Data
1962, 7, 308–310.
1
phane pnictogens.32 In the H NMR spectra the resonance
signals for the aromatic protons were downfield shifted,
whereas the signal for the tert-butyl methyl groups was
upfield shifted. In the 13C NMR spectra the magnitude of

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 797
the 1J(P,C), 3J(P,C), and 4J(P,C) couplings to the aromatic
carbons increased and the 2J(P,C) coupling decreased, with
respect to 2. No coupling to the tert-butyl carbon atoms was
A priori compound 2 possesses two basic centers, the N3
nitrogen and the phosphorus, which might offer options to
tune the reactivity via selective alkylation. To investigate this,
the N-methylated product 7 was synthesized using 1-tert-
butylimidazole (1), which was reacted with iodomethane in
methanol to give the imidazolium salt 6.39 After metalation
using tert-butyllithium and reaction with diphenylchloro-
phosphane, in analogy to the aforementioned reaction (see
Scheme 3), the product 7 was obtained and purified by
concentrating the reaction mixture in vacuo and removal of
the byproduct; selected data are given in Table 2.
First test reactions on the alkylation of 2 using iodo-
methane in toluene showed the selective formation of only
one product, having a 31P NMR resonance at 18.8 ppm,47
clearly indicating that the reaction exclusively occurred at the
phosphorus atom. In agreement with the steric demand of the
1
observed. As usual, the magnitude of the J(P,C) coupling
was strongly influenced by the electronegativity of the pnic-
togens. Interestingly, the coupling to the C5-carbon of the
imidazole ring was much larger than the coupling to the
imidazole C4 carbon (18 Hz vs 2-3 Hz); in the (non-oxidized)
2, both couplings were in the same range.
X-ray single-crystal structure analysis was performed for
all three compounds 3-5; crystals were obtainedfrom diethyl
ether solutions. All three compounds crystallized isostructur-
al in the triclinic crystal system, space group P1; for selected
crystal data see Figure 1. Further information is provided in
the Supporting Information section. Despite that the struc-
tures of 3-5 are the first reported of a diphenylphosphino
substituted imidazole derivative, structural parameters shall
not be discussed further as bond lengths and angles are in the
common range for PV chalcogenide derivatives.44-46
Scheme 4. Reactions of 2 with [W(CO)5(thf)] and the Borane THF
Complex
Figure 1. Molecular structure of 5 For details of the measurement see
the Supporting Information section. Selected bond lengths [pm]: C1-N1
1.3837(19), C1-N2 1.3258(19), C2-C3 1.359(2), C4-N1 1.505(2), P-C1
1.8229(14), P-C8 1.8146(15), P-C14 1.8180(15), P-Se 2.1151(4).
Scheme 3. Synthesis of 1-tert-Butyl-2-diphenylphosphino-3-methyl-
imidazolium Iodide (7)
Table 2. Selected NMR Data (Chemical Shifts and Coupling Constants) and Melting Points of Compounds 7, 8, and 10
analyt. data
7
8
21.3, 1JW,P = 254.3 Hz
0.67 s, 9H, C4H9
10
31P
1H
-35.0, 3JP,H = 7.7 Hz
3.75, s, 3H, N-CH3
1.62, s, 9H, C4H9
-19.5
1.89 s, 9H, C4H9
1.66, s br, 3 H, BH3
13C{1H}
200.0, 1JW,C = 24.6 Hz, trans-CO
197.3, 1JW,C = 24.6 Hz, cis-CO
139.3, 1JP,C = 66.6 Hz, C2
129.9, 3þ4JP,C = 1.9 Hz, C5
123.9, C4
139.0, C2
141.3, 1JP,C = 40.1 Hz, C2
131.7, 3þ4JP,C = 5.2 Hz, C5
120.0, 3þ4JP,C = 3.2 Hz, C4
128.4, 3þ4JP,C = 6.5 Hz, C5
125.8, 3þ4JP,C = 4.5 Hz, C4
34.9, 4JP,C = 10.0 Hz, N-CH3
28.9, t-Bu-CH3
30.2, t-Bu-CH3
30.6, 4JP,C = 13.6 Hz, t-Bu-CH3
130 °C
m.p.
190 °C

798 Inorganic Chemistry, Vol. 50, No. 3, 2011
Sauerbrey et al.
Scheme 5. Reaction of 2 with cis-[Pt(PhCN)2Cl2] Complex
tert-butyl group in 2 the reaction was very slow, even at 110 °C
and was not completed after 8 weeks (maximum conversion
50%); unfortunately, the product could not be isolated.
Aside fromoxidation and alkylation reactions, thepossible
use of 2 as a ligand in coordination chemistry was tested, and,
therefore, the reaction of 2 with [W(CO)5(thf)],36 the borane-
THF complex and cis-[Pt(PhCN)2Cl2]48 was investigated (see
Schemes 4 and 5). When 2 was reacted with [W(CO)5(thf)] at
ambient temperature and the reaction stopped after a max-
imum time of 15 h, the light-yellow complex 8 was formed
exclusively, showing a 31P NMR resonance at 21.3 ppm with
a 1J(W,P) coupling of 254.3 Hz (for more data see Table 2).
Surprisingly, the complex 8 was not stable in solution, and
attempts to purify it via column chromatography failed.
Complex 8 decomposed into the starting materials and the
brown-yellow product 9 having a resonance at 14.4 ppm with
a 1J(W,P) coupling of 193.3 Hz. Heating a THF solution of 8
also resulted in the formation of complex 9. The analytical
data of the formed complexes is in good agreement with those
reported by Yoshifuji et al. on 2-pyridylphosphine tungsten
complexes49 or Coles et al. on 1-aza-3-phospha-tungstacy-
clobut-1-enes.50 Yoshifuji et al. did also observe an upfield
shift combined with a decrease in the tungsten-phosphorus
coupling constant when going from the pentacarbonyl to the
tetracarbonyl chelate complex.
In addition, 9 shows four CO absorption bands in the IR
spectrum, and three signals for the carbonyl groups in the 13C
NMR spectrum, typical for tungsten tetracarbonyl com-
plexes. To the best of our knowlegde, compound 9 is only
the fourth reported tetracarbonyl P,N-chelate tungsten com-
plex, and just three tungsten complexes of diphenylpho-
sphino substituted imidazole derivatives are literature
known: one with κP-coordination (31P NMR: δ = 17) and
two with κN-coordination (31P NMR: δ = -31 and -35).51
Reacting 2 with the borane-THF complex yielded selectively
product 10, which was isolated by removing the solvent in
vacuo and subsequent washing with n-pentane. Interestingly,
the coordination of BH3 exclusively occurred at the nitrogen
atom (31P NMR: δ = -19.5); a P,B-coupling could not be
determined (for more data see Table 2). The N-borane group
was easily identified in the 1H NMR spectra (1.66 ppm, s br),
and the constitution was also established by mass spectro-
metric measurements (exact mass for C19H24BN2PNaþ,
found: 345.1669, calcd 345.1664). Complex 10 is a colorless
solid melting at 130 °C. To the best of our knowledge, no
examples of borane complexes, neither P- nor N-coordi-
nated, of phosphorus substituted imidazole derivatives are
known so far.
The formation of complex 9 increased our interest in
the cis-chelating properties of 2. Therefore, we studied the
reaction of 2 with cis-[Pt(PhCN)2Cl2] complex in dichlo-
romethane, which yielded the two products 11 and 12
(ratio 3:1) having 31P NMR resonances at -25.4 and 10.9
ppm, respectively, and 1J(Pt,P) coupling constants of
3756.2 and 3898.6 Hz. Unfortunately, both compounds
could not be separated via column chromatography or
crystallization. Nevertheless, it can be safely assumed
that a mixture of the cis-chelate 11 and complex 12 having
two P-ligands was formed as we obtained further evi-
dence from electrospray ionization (ESI) mass spec-
trometry, which showed molecular ion peaks with a mass-
charge ratio of 538.0818 for 11 (C19H21ClN2PPtþ, calcd:
538.0779) and a mass-charge ratio of 846.2222 for 12
(C38H42ClN4P2Ptþ, calcd: 846.2221).
Comparison of 11 and 12 with literature-known platinum
complexesrevealed that thecomplex [bis{2-{bis(1,1-dimethy-
lethyl)phosphino-κP}-1-methyl-1H-imidazole}platinum(0)]52
is characterized by a 31P resonance at 55.7 ppm and a 1J(Pt,P)
coupling constant of 4247.1 Hz, whereas the platinum(II)
hydride complex having one bis(1,1-dimethylethyl)phosphi-
no-κP ligand (coordinated via the phosphorus center) and the
second ligand forming a four-membered chelate (via phos-
phorus and nitrogen coordination) has different NMR data
(31P NMR: δ = 52.6, 1J(Pt,P) = 2940.3 Hz; δ = 39.4, 1J(Pt,
P) = 2341.2 Hz, 2J(P,P) = 327.8 Hz).36 Because the first
example has a Pt0 center, the 31P NMR data are not straight-
forwardly comparable, but it is known that, in general,
(52) Grotjahn, D. B.; Gong, Y.; diPasquale, A. G.; Zakharov, L. N.;
Rheingold, A. L. Organometallics 2006, 25, 5693–5695.
(53) Four membered chelate complexes involving C2-phosphorus substi-
tuted imidazole derivatives are known for ruthenium54,55 and palladium.56-58
(54) Caballero, A.; Jalon, F. A.; Manzano, B. R.; Espino, G.; Perez-
Manrique, M.; Mucientes, A.; Poblete, F. J.; Maestro, M. Organometallics
2004, 23, 5694–5706.
(44) Al-Farhan, K. A. J. Crystallogr. Spectrosc. Res. 1992, 22, 687–689.
(45) Codding, P. W.; Kerr, K. A. Acta Crystallogr. 1978, B34, 3785–3787.
(46) Codding, P. W.; Kerr, K. A. Acta Crystallogr. 1979, B35, 1261–1263.
(47) For comparison of the 31P NMR data of methyldiorganylphospho-
nium salts see: Choi, P. C.; Morris, J. H.; J. Chem. Soc., Dalton Trans. 1984,
2119-2125 or Yamamoto, Y.; Kanda, Z.; Bull. Chem. Soc. Jpn. 1980, 53,
3436-3438.
(48) Braunstein, P.; Bender, R.; Jud, J. Inorg. Synth. 1989, 26, 341–350.
(49) Nishide, K.; Ito, S.; Yoshifuji, M. J. Organomet. Chem. 2003, 682,
79–84.
(55) Espino, G.; Jalon, F. A.; Maestro, M.; Manzano, B. R.; Perez-
Manrique, M.; Bacigalupe, A. C. Eur. J. Inorg. Chem. 2004, 12, 2542–2552.
(56) Grotjahn, D. B.; Gong, Y.; Zakharov, L.; Golen, J. A.; Rheingold,
A. L. J. Am. Chem. Soc. 2006, 128, 438–453.
(57) Torborg, C.; Huang, J.; Schulz, T.; Schaeffner, B.; Zapf, A.;
Spannenberg, A.; Boerner, A.; Beller, M. Chem.;Eur. J. 2009, 15, 1329–
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Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 799
formation of a chelate complex leads to a decrease of the
imidazole derivative 10 (instead of the anticipated P-coordina-
tion). First studies on the ligating properties of 2 toward
transition metals reveals that the formation of four-membered
chelate κP- and κN-complexes tungsten and platinum com-
plexes is preferred over end-on coordination, which might be
preferred because of steric repulsion between the N-tert-butyl
group and the C2-bound phosphanyl substituent.
1J(Pt,P) coupling constant magnitude.52
Conclusions
Metalation of 1-tert-butylimidazole (1) was successfully
accomplished with tert-butyllithium, and the subsequent reac-
tion with diphenylchlorophosphane yielded the C2 substituted
product 2, whereas other bases predominantly yielded side-
reaction products. The reactivity of 2 toward oxidation,
alkylation, and complexation reactions was studied. Oxidation
occurred selectively to yield the corresponding PV-E products
(E = O, S, Se) 3-5, as firmly established by their X-ray crystal
structures; derivatives 3-5 represent the first examples within
the series of P-substituted imidazole derivatives. The influence
of the sterical demanding tert-butyl group became apparent in
the reaction of 2 with the borane-THF complex, which led to
the first example of an N-coordinated phosphorus-containing
€
Acknowledgment. Financial support by the Universitat
Bonn, the DAAD PPP USA, and the COST action
cm0802 “PhoSciNet” is gratefully acknowledged.
Supporting Information Available: Refinement details of the
X-ray crystal structure analysis of 3-5. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
The data is also deposited in the Cambridge Crystallographic
Data Centre (CCDC), deposition numbers 778496, 778497, and
778498.