Palladium(II) 3-iminophosphine complexes as intermolecular hydroamination catalysts for the formation of imines and enamines

Article abstract of DOI:10.1021/om701106q

Palladium(II) 3-iminophosphine derivatives were screened as intermolecular hydroamination catalysts, with (3-iminophosphine)(allyl)palladium triflate determined to be the most active for the hydroamination of 1,3-cyclohexadiene and phenylacetylene. The im

Full text of DOI:10.1021/om701106q

Organometallics 2008, 27, 1259–1266
1259
Palladium(II) 3-Iminophosphine Complexes as Intermolecular
Hydroamination Catalysts for the Formation of Imines and
Enamines
Andrew R. Shaffer and Joseph A. R. Schmidt*
Department of Chemistry, The UniVersity of Toledo, 2801 W. Bancroft St. MS 602,
Toledo, Ohio 43606-3390
ReceiVed NoVember 2, 2007
Palladium(II) 3-iminophosphine derivatives were screened as intermolecular hydroamination catalysts,
with (3-iminophosphine)(allyl)palladium triflate determined to be the most active for the hydroamination
of 1,3-cyclohexadiene and phenylacetylene. The iminophosphine ligands were synthesized by a three-
step process and coordinated in an η2 and η1 manner to palladium(II) chloride and (allyl)palladium(II)
chloride, respectively.
arenes,9,16–20 and alkynes5,6,21–28 but few examples involving
cyclic dienes29–33 as substrates.
Introduction
Imines and enamines are very useful compounds because they
function as reagents for the introduction of nitrogen-containing
moieties into a synthetic sequence. Specifically, imines are
commonly employed in carbon-carbon bond formation, as seen
in Mannich reactions and aza Diels–Alder cycloadditions.34
Additionally, they are readily reduced to the corresponding
secondary amines.34 Ketimines are commonly targeted as
hydroamination products because alternative synthetic pathways
often involve the need for elevated temperatures, an acid catalyst
and/or a water scavenger, imposing functional group limitations,
and/or a lack of regio- and stereochemical control. Second,
enamines are other important synthetic targets due to the
subsequent reactivity of their double bonds, often employed as
The wide use of amines and their derivatives across many
fields of chemistry has led to considerable interest concerning
the synthesis of C-N bonds. One of the most attractive routes
for C-N bond formation is through the hydroamination of
unsaturated carbon-carbon double and triple bonds by primary
or secondary amines, due in part to its 100% atom efficiency.
The formation of C-N bonds via hydroamination can occur
through intramolecular or intermolecular processes,1–4 although
the latter are generally preferred due to the large array of
commercially available, low-cost substrates. Typically, inter-
molecular hydroamination is harder to achieve due to the higher
entropic demands and slower reaction kinetics, thus requiring
a more active and selective catalyst than intramolecular hy-
droamination. The products generated by intermolecular hy-
droamination include secondary and tertiary amines, diamines,
imines, and enamines. There are several reports of the inter-
molecular hydroamination of alkenes,5–9 dienes,9–15 vinyl
(16) Horrillo-Martinez, P.; Hultzsch, K. C.; Gil, A.; Branchadell, V. Eur.
J. Org. Chem. 2007, 3311–3325.
(17) Kaspar, L. T.; Fingerhut, B.; Ackermann, L. Angew. Chem., Int.
Ed. 2005, 44, 5972–5974.
(18) Qian, H.; Widenhoefer, R. A. Org. Lett. 2005, 7, 2635–2638.
(19) Utsunomiya, M.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125,
14286–14287.
(20) Utsunomiya, M.; Hartwig, J. F. J. Am. Chem. Soc. 2004, 126, 2702–
2703.
* To whom correspondence should be addressed. E-mail:
Joseph.Schmidt@utoledo.edu.
(21) Pohlki, F.; Doye, S. Chem. Soc. ReV. 2003, 32, 104–114.
(22) Klein, D. P.; Ellern, A.; Angelici, R. J. Organometallics 2004, 23,
5662–5670.
(1) Anderson, L. L.; Arnold, J.; Bergman, R. G. Org. Lett. 2004, 6,
2519–2522.
(2) Bytschkov, I.; Doye, S. Eur. J. Org. Chem. 2003, 935–946.
(3) Shimada, T.; Bajracharya, G. B.; Yamamoto, Y. Eur. J. Org. Chem.
2004, 59–62.
(23) Brunet, J. J.; Chu, N. C.; Diallo, O.; Vincendeau, S. J. Mol. Catal.
A: Chem. 2005, 240, 245–248.
(24) Castro, I. G.; Tillack, A.; Hartung, C. G.; Beller, M. Tetrahedron
Lett. 2003, 44, 3217–3221.
(4) Aillaud, I.; Collin, J.; Hannedouche, J.; Schulz, E. Dalton Trans.
2007, 5105–5118.
(25) Shanbhag, G. V.; Kumbar, S. M.; Joseph, T.; Halligudi, S. B.
Tetrahedron Lett. 2006, 47, 141–143.
(5) Beller, M.; Seayad, J.; Tillack, A.; Jiao, H. Angew. Chem., Int. Ed.
2004, 43, 3368–3398.
(26) Tillack, A.; Jiao, H. J.; Castro, I. G.; Hartung, C. G.; Beller, M.
Chem. Eur. J. 2004, 10, 2409–2420.
(6) Muller, T. E.; Beller, M. Chem. ReV. 1998, 98, 675–703.
(7) Brunet, J. J.; Cadena, M.; Chu, N. C.; Diallo, O.; Jacob, K.; Mothes,
E. Organometallics 2004, 23, 1264–1268.
(27) Yi, C. S.; Yun, S. Y. J. Am. Chem. Soc. 2005, 127, 17000–17006.
(28) Zhang, Y. H.; Donahue, J. P.; Li, C. J. Org. Lett. 2007, 9, 627–
630.
(8) Hultzsch, K. C. AdV. Synth. Catal. 2005, 347, 367–391.
(9) Ryu, J. S.; Li, G. Y.; Marks, T. J. J. Am. Chem. Soc. 2003, 125,
12584–12605.
(29) Guin, J.; Muck-Lichtenfeld, C.; Grimme, S.; Studer, A. J. Am.
Chem. Soc. 2007, 129, 4498–4503.
(10) Bar, G. L. J.; Lloyd-Jones, G. C.; Booker-Milburn, K. I. J. Am.
Chem. Soc. 2005, 127, 7308–7309.
(30) Hartwig, J. F.; Pawlas, J.; Nakao, Y.; Kawatsura, M. J. Am. Chem.
Soc. 2002, 124, 3669–3679.
(11) Brouwer, C.; He, C. Angew. Chem., Int. Ed. 2006, 45, 1744–1747.
(12) Tobisch, S. Chem. Eur. J. 2005, 11, 6372–6385.
(13) Li, Y.; Marks, T. J. Organometallics 1996, 15, 3770–3772.
(14) Qin, H. B.; Yamagiwa, N.; Matsunaga, S.; Shibasaki, M. J. Am.
Chem. Soc. 2006, 128, 1611–1614.
(31) Hartwig, J. F.; Johns, A. M.; Utsunomiya, M.; Incarvito, C. D.
J. Am. Chem. Soc. 2006, 128, 1828–1839.
(32) Minami, T.; Okamoto, H.; Ikeda, S.; Tanaka, R.; Ozawa, F.;
Yoshifuji, M. Angew. Chem., Int. Ed. 2001, 40, 4501–4503.
(33) Johns, A. M.; Tye, J. W.; Hartwig, J. F. J. Am. Chem. Soc. 2006,
128, 16010–16011.
(15) Johns, A. M.; Liu, Z.; Hartwig, J. F. Angew. Chem., Int. Ed. 2007,
46, 7259–7261.
(34) Kobayashi, S.; Ishitani, H. Chem. ReV. 1999, 99, 1069–1094.
10.1021/om701106q CCC: $40.75
2008 American Chemical Society
Publication on Web 02/27/2008

1260 Organometallics, Vol. 27, No. 6, 2008
Shaffer and Schmidt
substrates for addition or redox reactions.35,36 Currently, enamine
synthesis involves allylic amination36 or Buchwald-Hartwig
coupling.37,38 Only a few studies have shown the catalytic
addition of amines to cyclic dienes,29–32 and thus a more
thorough investigation of catalysts for this reaction is necessary
in order to develop an efficient route to enamines that has
substrate tolerance without compromising catalytic activity.
3-Iminophosphine ligands containing an o-phenylene back-
bone have been investigated previously, and their palladium
complexes serve as catalysts for the polymerization of ethyl-
ene,39 Stille reactions,40,41 Heck coupling,42,43 and other bond-
forming reactions.44–46 The new type of 3-iminophosphine
framework employed herein has been constructed around an
alicyclic (cyclopentenyl) backbone and contains features similar
to those of two prominent ligand classes: ꢀ-diketiminates and
phosphinooxazolines. ꢀ-Diketiminates, when used as ancillary
ligands in late-transition-metal catalysis, employ steric bulk to
help shield reactive metal centers and provide stability for
reactive intermediates.47 Phosphinooxazolines use an asym-
metric and rigid backbone to facilitate several catalytic pro-
cesses, such as asymmetric allylic substitution,30 Heck cou-
pling,34 and hydrogenation.36,48,49 Phosphinooxazolines help
stabilize reactive intermediates and reactive metal centers
through a combination of steric protection and strong σ-donation
from the phosphorus donor atom. There has been only minimal
investigation of the effect of ligand rigidity on hydroamination
catalysis using bidentate ligands containing at least one phos-
phorus donor atom.31 Our research efforts have focused on a
new variety of 3-iminophosphine ligand with an alicyclic
(cyclopentenyl) backbone, employing soft phosphorus and hard
imine nitrogen donor atoms. It was postulated that these ligands
would have many of the favorable characteristics generally
associated with ꢀ-diketiminate and phosphinooxazoline ligands.
Herein, we report the palladium-catalyzed intermolecular hy-
droamination of the terminal alkyne phenylacetylene, as well
as the cyclic diene 1,3-cyclohexadiene, with a variety of amines
using ancillary 3-iminophosphine ligands (Scheme 1).
Scheme 1. Hydroamination of 1,3-Cyclohexadiene (A) and
Phenylacetylene (B)
Scheme 2. Synthesis of the 3-Iminophosphine Liganda
a
Legend: (i) POCl3, DMF, 0 °C, 40 min; (ii) ice, NaHCO3; (iii)
H2NtBu, Et2O, 0 °C, 14 h; (iv) Ph2PM (M ) Li, Na), toluene, 0 °C,
14 h.
Table 1. 31P NMR Shifts, 1H Coupling Constants, and 13C Coupling
Constants
4
1
compd
31P NMR shift (δ)a JP-H (Hz)b JP-C (Hz)c
3IP (3)
(3IP)PdCl2 (4)
(3IP)Pd(allyl)Cl (5)
[(3IP)Pd(allyl)][OTf] (6)
-24.7
21.5
7.6
2.0
3.0
n/ad
3.0
25.6
44.1
32.6
34.2
16.9
a Relative to 5% H3PO4 in D2O. b Coupling of phosphorus to aldi-
mine proton. c Coupling of phosphorus to adjacent cyclopentyl carbon.
d Broad singlet observed.
Vilsmeier–Haack reagent was combined with cyclopentanone
to generate a ꢀ-chlorovinyl aldehyde (1) after basic workup.
Application of a Vilsmeier–Haack reagent results in the conver-
sion of the enol tautomer of ketones to ꢀ-chloroaldehydes by
formylation of the R-carbon in tandem with chlorination of the
Results and Discussion
The 3-iminophosphine (3IP) ligand (3) was synthesized in
52% yield through a three-step synthesis (Scheme 2). First, a
1
hydroxyl group.50,51 In the H NMR spectrum of 2-chlorocy-
clopentenecarboxaldehyde (1), the aldehyde proton appears as
a singlet at 10.00 ppm, whereas the protons from the cyclo-
pentenyl ring appear as two sets of overlapping triplets of
doublets at 2.81 and 2.58 ppm as well as a pentet at 2.01 ppm.
The subsequent Schiff-base condensation of 1 with tert-
butylamine yields the corresponding imine (2). The aldimine
proton shifts upfield significantly to 8.24 ppm, while the
cyclopentenyl protons show little change, appearing as overlap-
ping triplets of doublets at 2.70 and 2.63 ppm and a pentet at
1.96 ppm. The cyclopentenyl imine, once isolated, is thermally
unstable, decomposing in 8 h at 22 °C or 96 h at -25 °C.
Synthesis of the 3IP ligand (3) is completed when 2 undergoes
a Michael addition with either sodium or lithium diphenylphos-
phide, followed by chloride elimination. The imine proton of 3
is shifted slightly to 8.72 ppm and now exhibits phosphorus-
proton coupling: 4JP-H ) 2.0 Hz (Table 1). The cyclopentenyl
ring protons undergo minimal changes and are observed as broad
triplets of doublets at 2.83 and 2.36 ppm and a pentet at 1.85
ppm. The 31P NMR spectrum reveals a single resonance at
-24.7 ppm. X-ray-quality crystals of 3 were produced by
(35) Davies, S. G.; Long, M. J. C.; Smith, A. D. Chem. Commun. 2005,
4536–4538.
(36) Johannsen, M.; Jorgensen, K. A. Chem. ReV. 1998, 98, 1689–1708.
(37) Hartwig, J. F. Acc. Chem. Res. 1998, 31, 852–860.
(38) Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc. Chem. Res. 1998,
31, 805–818.
(39) Doherty, M. D.; Trudeau, S.; White, P. S.; Morken, J. P.; Brookhart,
M. Organometallics 2007, 26, 1261–1269.
(40) Koprowski, M.; Sebastian, R. M.; Maraval, V.; Zablocka, M.;
Cadierno, V.; Donnadieu, B.; Igau, A.; Caminade, A. M.; Majoral, J. P.
Organometallics 2002, 21, 4680–4687.
(41) Scrivanti, A.; Matteoli, U.; Beghetto, V.; Antonaroli, S.; Crociani,
B. Tetrahedron 2002, 58, 6881–6886.
(42) Schultz, T.; Schmees, N.; Pfaltz, A. Appl. Organomet. Chem. 2004,
18, 595–601.
(43) Scrivanti, A.; Bertoldini, M.; Matteoli, U.; Beghetto, V.; Antonaroli,
S.; Marini, A.; Crociani, B. J. Mol. Catal. A: Chem. 2005, 235, 12–16.
(44) Scrivanti, A.; Beghetto, V.; Matteoli, U.; Antonaroli, S.; Marini,
A.; Crociani, B. Tetrahedron 2005, 61, 9752–9758.
(45) Scrivanti, A.; Matteoli, U.; Beghetto, V.; Antonaroli, S.; Scarpelli,
R.; Crociani, B. J. Mol. Catal. A: Chem. 2001, 170, 51–56.
(46) Shirakawa, E.; Hoshida, H.; Takaya, H. Tetrahedron Lett. 1997,
38, 3759–3762.
(47) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
103, 283–315.
(48) Lightfoot, A.; Schnider, P.; Pfaltz, A. Angew. Chem., Int. Ed. 1998,
37, 2897–2899.
(50) Benson, W.; Pohland, A. E. J. Org. Chem. 1965, 30, 1126–1129.
(51) Vashkevich, E. V.; Potkin, V. I.; Kozlov, N. G.; Skakovskii, E. D.
Russ. J. Org. Chem. 2003, 39, 1587–1592.
(49) Loiseleur, O.; Hayashi, M.; Keenan, M.; Schmees, N.; Pfaltz, A.
J. Organomet. Chem. 1999, 576, 16–22.

Palladium(II) 3-Iminophosphine Complexes
Organometallics, Vol. 27, No. 6, 2008 1261
Figure 1. ORTEP diagram (50% thermal ellipsoids) of 3IP (3).
Hydrogen atoms are omitted for clarity. Bond lengths (in Å):
C1-C2 ) 1.460(6), C2-C3 ) 1.354(8), C3-P1 ) 1.817(7). Bond
angles (in deg): C1-N1-C7 ) 119.5(5), C2-C1-N1 ) 120.6(1),
C3-C2-C1 ) 125.5(3), P1-C3-C2 ) 122.7(2).
Figure 2. ORTEP diagram (50% thermal ellipsoids) of (3IP)PdCl2
(4). Hydrogen atoms and disordered methylene chloride molecules
are omitted for clarity. Bond lengths (in Å): Pd1-N1 ) 2.065(4),
Pd1-P1 ) 2.22(1), C1-N1 ) 1.285(6), C2-C1 ) 1.463(6),
C3-C2 ) 1.351(6), P1-C3 ) 1.804(4). Bond angles (in deg):
P1-Pd1-N1 ) 85.3(7), P1-Pd1-Cl1 ) 93.4(6), P1-Pd1-Cl2
) 166.7(7), Cl1-Pd1-Cl2 ) 90.9(7), N1-Pd1-Cl1 ) 176.0(7),
N1-Pd1-Cl2 ) 90.9(9), Pd1-P1-C3 ) 100.2(2), C3-C2-C1
) 124.1(9), C2-C1-N1 ) 123.6(2), C1-N1-Pd1 ) 123.1(2),
C1-N1-C7 ) 116.6(5).
Scheme 3. Metal Complexationa
a
Legend: (i) PdCl2, MeCN, 14 h; (ii) 0.5 [(allyl)PdCl]2, CH2Cl2,
14 h; (iii) AgOTf, Et2O, 4 h.
layering diethyl ether with pentane at -25 °C, and the crystal
structure confirms the connectivity in this species (Figure 1).
The carbon-carbon single- and double-bond distances and
angles as well as the phosphorus-carbon and imine bond
distances and angles are similar to those observed in related
compounds.52,53
The complex (3IP)PdCl2 (4) was synthesized by treating
anhydrous PdCl2 with 3 in acetonitrile at ambient temperature
and isolated as a yellow solid in 90% yield (Scheme 3). There
is a significant shift in the 31P NMR resonance to 21.5 ppm, 46
ppm downfield compared to the free ligand (Table 1). The imine
doublet also has a larger coupling constant, 4JP-H ) 3.0 Hz, in
comparison to the value for the free ligand, and shifts to 7.48
ppm, indicative of coordination of the imine nitrogen to the
palladium center. X-ray-quality crystals of 4 were grown from
methylene chloride layered with diethyl ether at 22 °C, and the
resulting crystal structure (Figure 2) shows that palladium adopts
a square-planar configuration with a ligand bite angle of 85.7°
(P-Pd-N). The related complex (3IP)Pd(allyl)Cl (5) was
synthesized in a manner similar to that for 4, except for the use
of methylene chloride as solvent, and was isolated as an orange-
yellow solid in 74% yield (Scheme 3). Once again, the 31P NMR
resonance from compound 5 is significantly shifted upon ligand
coordination, appearing at δ 7.6smore than 32 ppm downfield
from the free ligand resonance (Table 1). X-ray-quality crystals
of 5 were obtained from a saturated solution of diethyl ether at
Figure 3. ORTEP diagram (50% thermal ellipsoids) of (3IP)Pd(al-
lyl)Cl (5). Hydrogen atoms are omitted for clarity. Bond lengths
(in Å): Pd1-Cl1 ) 2.378(5), Pd1-P1 ) 2.308(8), Pd1-C23 )
2.202(3), Pd1-C25 ) 2.101(4), C1-N1 ) 1.269(7), C2-C1 )
1.460(4), C3-C2 ) 1.346(6), P1-C3 ) 1.81(1). Bond angles (in
deg): P1-Pd1-Cl1 ) 101.7(2), C23-Pd1-C25 ) 67.7(3),
P1-Pd1-C23 ) 163.4(3), P1-Pd1-C25 ) 95.9(3), C3-P1-Pd1
) 117.2(7), C3-C2-C1 ) 127.5(6), C2-C1-N1 ) 119.7(5),
C1-N1-C7 ) 120.4(4).
-25 °C, and the crystal structure indicates a monodentate
coordination of the 3IP ligand through the phosphorus to
palladium, as well as the presence of a chloride ligand (Figure
3). Treatment of 5 with silver triflate in diethyl ether results in
loss of silver chloride and concomitant formation of the ionic
species [(3IP)Pd(allyl)][OTf] (6) in 90% yield (Scheme 3).
Pronounced shifts in the imine proton resonance to 7.94 ppm
and the 31P NMR signal to 16.9 ppm indicate bidentate ligand
coordination (Table 1). Layering of a tetrahydrofuran solution
of 6 with pentane yielded crystals suitable for X-ray structure
determination. The resulting solid-state structure reveals an ionic
species, in which square-planar palladium is coordinated by an
η2-3IP and an η2-allyl ligand with an outer-sphere triflate anion
(52) Lai, R. Y.; Surekha, K.; Hayashi, A.; Ozawa, F.; Liu, Y. H.; Peng,
S. M.; Liu, S. T. Organometallics 2007, 26, 1062–1068.
(53) Garcia-Yebra, C.; Janssen, J. P.; Rominger, F.; Helmchen, G.
Organometallics 2004, 23, 5449–5470.

1262 Organometallics, Vol. 27, No. 6, 2008
Shaffer and Schmidt
Table 2. Hydroamination of 1,3-Cyclohexadiene using 3–6a
entry
amine
catalyst
yield (%)b
1
2
3
4
5
6
morpholine
morpholine
morpholine
morpholine
piperidine
3IP (3)
(3IP)PdCl2 (4)
(3IP)Pd(allyl)Cl (5)
[(3IP)Pd(allyl)][OTf] (6)
[(3IP)Pd(allyl)][OTf] (6)
[(3IP)Pd(allyl)][OTf] (6)
0
0
4
52
31
9
benzylamine
a Reaction conditions: 3.6 mmol of 1,3-cyclohexadiene, 0.60 mmol of
amine, 0.030 mmol of catalyst, 50 °C, CH2Cl2, 22 h. b Determined by
average of two GC runs.
Table 3. Effect of 1,3-Cyclohexadiene to Morpholine Ratio and
Solvent Effectsa
entry
diene:amine
solvent
yield (%)b
1
2
3
4
5
6
7
8
9
10
1:1
2:1
4:1
6:1
8:1
10:1
4:1
4:1
4:1
4:1
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
THF
dioxane
toluene
chloroform
25
35
41
52
58
62
2
2
1
30
Figure 4. ORTEP diagram (50% thermal ellipsoids) of [(3IP)P-
d(allyl)][OTf] (6). Triflate anion and hydrogen atoms are omitted
for clarity. Bond lengths (in Å): Pd1-P1 ) 2.267(5), Pd1-N1 )
2.141(3), Pd1-C23 ) 2.238(5), Pd1-C25 ) 2.102(4), P1-C3 )
1.81(1), C3-C2 ) 1.342(3), C2-C1 ) 1.465(4), C1-N1 )
1.284(1). Bond angles (in deg): P1-Pd1-N1 ) 92.9(5), C23-Pd1-
C25 ) 67.0(6), C23-Pd1-N1 ) 104.6(7), C25-Pd1-N1 )
171.6(2), C23-Pd1-P1 ) 157.7(8), C25-Pd1-P1 ) 95.3(4),
Pd1-P1-C3 ) 105.6(9), P1-C3-C2 ) 123.4(2), C3-C2-C1
) 129.8(2), C2-C1-N1 ) 127.8(9), C1-N1-Pd1 ) 123.5(8).
a Reaction conditions: 0.030 mmol of 6 (5 mol %), 50 °C, 22 h.
b Determined by average of two GC runs.
display almost no catalytic activity, while compound 6 does
catalyze the hydroamination. Entries 4–6 show that compound
6 readily converts morpholine and piperidine into the corre-
sponding 1,4-hydroamination products, while the activity is
much lower for benzylamine. The relative activities are less than
those observed previously using related diphosphine com-
plexes.30,31 However, it should be noted that a catalytic amount
of triflic acid was used in the previously reported cases, while
we have not investigated its effect on our catalysts. Extending
the reaction time to 72 h results in significant increases in
conversion to product, although it does not result in successful
hydroamination using other amines such as aniline, cyclohexy-
lamine, and diethylamine.
The effects of the 1,3-cyclohexadiene to morpholine ratio and
the reaction solvent on catalytic hydroamination using com-
pound 6 are represented in Table 3. Entries 1–6 demonstrate a
direct correspondence between the ratio of diene to amine and
the percent conversion with the catalytic rate increasing as a
result of higher substrate (diene) concentration. We have
observed that a byproduct of this catalysis is benzene, the
dehydrogenation product of 1,3-cyclohexadiene. To the best of
our knowledge, we are the first to report this phenomenon in
the hydroamination of 1,3-cyclohexadiene. Entries 7–10 show
the effect of different solvents on this catalysis. The Lewis bases
tetrahydrofuran and dioxane most likely function as competitive
inhibitors, due to their ability to coordinate to the palladium
center, leading to substantially less conversion to the product.
The very low solubility of compound 6 leads to its virtual
inactivity in toluene. The use of chloroform provides moderate
conversion to the 1,4-hydroamination product at 50 °C, although
with somewhat slower rates than those observed in methylene
chloride. Increasing the reaction temperature when using
chloroform, tetrahydrofuran, or dioxane as solvent improves
product yields, but with lower conversion when compared to
that observed in methylene chloride at 50 °C.
present (Figure 4). The ligand bite angle in 6 is 92.9°
(P-Pd-N), nearly 7° larger than that observed in compound
4. This can be attributed to a substantial decrease in the steric
demands of the other ligands, as the angle between the terminal
allylic carbons is 67.0° (C23-Pd-C25) compared to 91.0° in
the dichloride complex (Cl1-Pd-Cl2).
Analysis of the NMR spectroscopic data from this series of
compounds (3–6) reveals excellent correlation between the
chemical shifts of the imine and phosphorus resonances and
the ligand coordination mode (Table 1). Compounds 4 and 6,
with η2 coordination of the ligand, show substantial shifts in
the imine 1H resonance (∼1 ppm) and the 31P resonance (>40
ppm downfield) compared to the related signals in the free ligand
(3). In contrast, only the phosphorus resonance for 5 is shifted
significantly (32 ppm downfield), correlating with the observed
η1 coordination of the phosphorus donor atom in the solid-state
structure. Additionally, by comparison of 4 with 6, it is clear
that the allyl group is a better σ-donor ligand than chloride
because of the lengthening of both the Pd-P (0.05 Å longer
than in 4) and Pd-N (0.13 Å longer than in 4) bond distances.
This is further evident in 5, where the Pd-P bond is even longer
(0.09 Å longer than in 4 and 0.04 Å longer than in 6), due to
both the trans effect of the allyl group and the lack of
coordinative constraints imposed by chelation.
Compounds 3–6 were screened for activity as hydroamination
catalysts using the following procedure. A solution of 3.6 mmol
of 1,3-cyclohexadiene, 0.60 mmol of the selected amine, and
1.0 mL of methylene chloride was added to a reaction vial
equipped with a magnetic stir bar that had been preloaded with
0.030 mmol of the catalyst under nitrogen. After the mixture
was heated to 50 °C for 22 h, 100 µL of dodecane was added
to the reaction vial as an internal standard and product
1
distribution was determined via gas chromatography. H and
13C NMR spectra were obtained after column chromatography.
The hydroamination of 1,3-cyclohexadiene with primary and
secondary amines using catalysts 3–6 (Scheme 1A) is sum-
marized in Table 2. Entries 1–4 show that compounds 3–5
The effects of the amount of solvent used for the hydroami-
nation of 1,3-cyclohexadiene with morpholine are illustrated in
terms of amine concentration in Figure 5. The data clearly
indicate that increasing the molar concentration increases the

Palladium(II) 3-Iminophosphine Complexes
Organometallics, Vol. 27, No. 6, 2008 1263
(primary/secondary amines), the hydroamination using catalyst
6 is fastest with the amines having the highest pKb values (lowest
basicity).55
Conclusions
3-Iminophosphine ligands (3) and their palladium(II) chloride
(4), (allyl)palladium(II) chloride (5), and (allyl)palladium(II)
triflate (6) complexes have been successfully synthesized,
isolated, and characterized. The triflate complex (6) shows
moderate catalytic activity for the intermolecular hydroamination
of 1,3-cyclohexadiene and phenylacetylene. Currently, we are
investigating additional substrates, including internal alkynes,
dienes, alkenes, and amine-alkene tethered compounds. Also,
we are in the process of synthesizing alternative palladium(II)
complexes that do not contain an allyl functionality, as well as
the related palladium(0) derivatives. Finally, we are exploring
the electronic effects of the 3-iminophosphine ligand on the rate
and product distribution of hydroamination.
Figure 5. Effect of concentration on the hydroamination of 1,3-
cyclohexadiene with morpholine in the presence of 6. Reaction
conditions: 6:1:0.05 ratio of 1,3-cyclohexadiene to morpholine to
6. The percent yield was determined by the average of two GC
runs.
Table 4. Hydroamination of Phenylacetylenea
Experimental Section
General Considerations. Compounds 1 and 2 were synthesized
under the ambient atmosphere. All other reactions were performed
with standard Schlenk and drybox techniques. n-Butyllithium (1.6
M in hexanes), palladium(II) chloride, (allyl)palladium(II) chloride
dimer, diphenylchlorophosphine, and silver triflate were purchased
from Strem and used without further purification. CDCl3 was
purchased from Cambridge Isotope Laboratories and vacuum-
transferred from CaH2. Pentane, toluene, tetrahydrofuran, and
methylene chloride were purified by passage through a column of
activated 4 Å molecular sieves and degassed with nitrogen prior to
use. Diethyl ether was purified by passage through a column of
activated alumina and degassed with nitrogen prior to use. Aceto-
nitrile was purified by vacuum transfer from CaH2. 1,4-Dioxane
was refluxed over sodium and distilled under nitrogen. Cyclopen-
tanone, POCl3, tert-butylamine, sodium, phenylacetylene, 1,3-
cyclohexadiene, aniline, piperidine, benzylamine, morpholine,
cyclohexylamine, and p-toluidine were purchased from Acros. All
amines used for hydroamination were dried by vacuum transfer or
distillation from CaH2, unless otherwise noted. Morpholine was
purified by distillation from sodium. 1,3-Cyclohexadiene was
vacuum-transferred from NaBH4. Phenylacetylene was purified by
passage through a column of alumina and further vacuum-
transferred from CaH2. 1H NMR data was obtained on a 600 MHz
Inova NMR spectrometer at ambient temperature. 13C, 31P, and
19F NMR data were obtained on a 400 MHz Varian NMR
spectrometer at ambient temperature at 100.580, 161.910, and
a Reaction conditions: 6.0 mmol of phenylacetylene, 0.60 mmol of
amine, 0.030 mmol of 6, 70 °C, THF, 22 h. b Reference 55. c Deter-
mined by average of two GC runs.
overall conversion. At these higher substrate concentrations, our
catalytic hydroamination of 1,3-cyclohexadiene with morpholine
is quite comparable to that in previous reports, although our
system does not require the necessity of an acid cocatalyst.29–31
The hydroamination of phenylacetylene, to form enamines
and imines, is also an important transformation (Scheme 1B).
As such, we have employed our catalyst system for the
hydroamination of phenylacetylene employing a number of
amines (Table 4). This reaction proved to be quite versatile,
with successful catalysis using both primary and secondary
amines. The primary amines (entries 1–4) tautomerize to the
Markovnikov imine, while the secondary amines (entries 5 and
6) yield the Markovnikov enamine. The observed catalytic
activity is similar to other catalysts.52,54 A large excess of
phenylacetylene (10 equiv) was necessary for the catalysis due
to the competing cyclotrimerization of phenylacetylene to form
1,2,4- and 1,3,5-triphenylbenzene. Finally, within each group
1
376.288 MHz, respectively. H NMR shifts are given relative to
CHCl3 (7.26 ppm), and 13C NMR shifts are given relative to CDCl3
(77.3 ppm). Phosphorus and fluorine NMR spectra were externally
referenced to 0.00 ppm with 5% H3PO4 in D2O and CFCl3,
respectively. IR samples were prepared as Nujol mulls and taken
between KBr plates on a Perkin-Elmer XTL FTIR spectrophotom-
eter. Melting points were observed on a Mel-Temp apparatus in
sealed capillary tubes and are uncorrected. Gas chromatography
was performed on a Varian CP-3800 gas chromatograph equipped
with an FID detector. Elemental analyses were determined by Desert
Analytics, Tucson, AZ. X-ray structure determinations were
performed at the Ohio Crystallographic Consortium housed at The
University of Toledo. Sodium diphenylphosphide was prepared
(55) CRC Handbook of Chemistry and Physics; CRC Press: Ann Arbor,
MI, 1991.
(54) Lee, A. V.; Schafer, L. L. Organometallics 2006, 25, 5249–5254.

1264 Organometallics, Vol. 27, No. 6, 2008
Shaffer and Schmidt
according to the literature procedure.56 Diphenylphosphine was
prepared according to a literature procedure for diisopropylphos-
phine.57
vacuum and cooled to -25 °C, resulting in the formation of yellow-
orange crystals in two crops (2.313 g combined, 70.00%).
Method B. Freshly prepared 2 (1.829 g, 9.852 mmol) diluted
with 10 mL of tetrahydrofuran was cooled in an ice bath and added
to a previously prepared slurry of sodium diphenylphosphide (2.666
g, 12.81 mmol), 20 mL of tetrahydrofuran, and 90 mL of
1,4-dioxane. The reaction was stirred at room temperature for 3 h.
A workup identical with that in method A resulted in the formation
of yellow-orange crystals in two crops (2.034 g combined, 61.55%):
2-Chlorocyclopentenecarboxaldehyde (1). The procedure used
was a slight modification of that reported by Benson and Pohland.50
POCl3 (18.315 g, 119.30 mmol) was added to a flask containing
dimethylformamide (10.896 g, 149.10 mmol) in an ice bath and
the mixture stirred for 7 min. The ice bath was replaced with an
ambient-temperature water bath and stirred for an additional 8 min.
The mixture was cooled to 0 °C, and cyclopentanone (6.249 g,
74.54 mmol) was added and stirred for 15 min. The ice bath was
replaced with an ambient-temperature water bath and the mixture
stirred for an additional 15 min. The yellowish red solution was
poured into an Erlenmeyer flask containing ice (150 g). The solution
was made basic using sodium bicarbonate. After extraction with
diethyl ether (3 × 100 mL), the combined organic extracts were
washed with 100 mL of saturated sodium bicarbonate solution, 100
mL of brine, and 100 mL of water. The organic layer was dried
over magnesium sulfate for 5 min and filtered, and the solvent was
evaporated, yielding a yellow liquid (7.397 g, 76.00%): bp 61 °C
4
mp 105–107 °C; 1H NMR δ 8.72 (d, JP-H ) 2.0 Hz, 1H),
7.40–7.31 (m, 10H), 2.83 (m, 2H), 2.36 (m, 2H), 1.85 (pent, 3JH-H
) 7.6 Hz, 2H), 1.19 (s, 9H); 13C{1H} NMR δ 152.8 (d, 20.2 Hz),
136.8 (d, 8.6 Hz), 134.6 (d, 25.6 Hz), 133.4 (d, 19.0 Hz), 129.1 (d,
37.2 Hz), 128.7 (d, 3.7 Hz), 128.6, 57.8, 37.5 (d, 3.7 Hz), 34.4 (d,
5.7 Hz), 30.0, 22.8 (d, 2.1 Hz); 31P{1H} NMR δ -24.7; IR 2719
(w), 2667 (w), 1887 (w), 1825 (w), 1773 (w), 1731 (w), 1700 (m),
1654 (m), 1618 (s), 1576 (m), 1560 (s), 1540 (m), 1431 (s), 1358
(s), 1306 (w), 1275 (w), 1208 (m), 1083 (m), 1026 (w), 995 (w),
964 (w), 891 (m), 824 (m), 787 (m), 746 (s), 694 (s) cm-1. Anal.
Calcd for C22H26NP: C, 78.78; H, 7.81; N, 4.19. Found: C, 78.83;
H, 7.95; N, 4.12.
(12 mm); 1H NMR (600 MHz) δ 10.00 (s, 1H), 2.82 (td, 3JH-H
)
)
2
3
2
7.8 Hz, JH-H ) 2.0 Hz, 1H), 2.81 (td, JH-H ) 7.8 Hz, JH-H
(2-Diphenylphosphinocyclopentene-1-(tert-butyl)imine)palla-
dium(II) Dichloride (4). 3 (3.271 g, 9.752 mmol) was dissolved
in 5 mL of methylene chloride and 30 mL of acetonitrile and added
to a slurry of palladium(II) chloride (1.729 g, 9.752 mmol) in 30
mL of acetonitrile. The mixture was stirred for 12 h at room
temperature. Volatile materials were removed in vacuo. The yellow-
red solid was triturated twice with 5 mL of pentane, washed with
diethyl ether (3 × 10 mL), and extracted into methylene chloride
(3 × 20 mL). The solution was concentrated to 40 mL, and pentane
(40 mL) was added to precipitate the product. This process was
repeated two times to maximize yield (4.512 g, 90.23%): mp 190
°C dec; 1H NMR (600 MHz) δ 7.58–7.53 (m, 6H), 7.48 (d, 4JP-H
) 3.0 Hz, 1H), 7.47–7.45 (m, 4H), 2.92–2.89 (m, 2H), 2.48–2.42
2.4 Hz, 1H), 2.59 (td, 3JH-H ) 7.8 Hz, 2JH-H ) 2.4 Hz, 1H), 2.58
3
2
(td, JH-H ) 7.8 Hz, JH-H ) 2.0 Hz, 1H), 2.01 (pent, 7.8 Hz,
2H); 13C{1H} NMR δ 187.8, 151.3, 137.3, 40.2, 28.6, 20.4; IR
2947 (s), 2719 (m), 1742 (m), 1674 (s), 1618 (s), 1430 (m), 1384
(m), 1332 (s), 1280 (w), 1244 (m), 1202 (w), 1093 (s), 943 (m)
cm-1
.
2-Chlorocyclopentene-1-(tert-butyl)imine (2). 1 (7.397 g, 56.61
mmol) was dissolved in diethyl ether (20 mL) and cooled to 0 °C
for 5 min. tert-Butylamine (4.558 g, 62.32 mmol) diluted with
diethyl ether (10 mL) was added, and the mixture was stirred for
14 h and gradually warmed to room temperature. Magnesium sulfate
was added to the round-bottom flask, the mixture filtered, and the
solvent evaporated, yielding an orange-red liquid (10.247 g, 97.48%)
that shows evidence of decomposition at room temperature after
8 h and at -25 °C after 96 h: bp 102–105 °C; 1H NMR (600 MHz)
3
(m, 2H), 2.14 (pent, JH-H ) 7.8 Hz, 2H), 1.45 (s, 9H); 13C{1H}
NMR δ 159.9, 156.0 (d, 16.1 Hz), 135.6 (d, 44.1 Hz), 133.4 (d,
11.2 Hz), 132.2 (d, 5.8 Hz), 128.9 (d, 12.0 Hz), 125.0 (d, 57.8
Hz), 67.2, 36.5 (d, 2.0 Hz), 36.3 (d, 11.6 Hz), 31.8, 23.1 (d, 7.1
Hz); 31P{1H} NMR δ 21.5; IR 2252 (w), 1872 (w), 1830 (w), 1794
(w), 1773 (w), 1737 (w), 1700 (m), 1680 (w), 1649 (m), 1618 (w),
1576 (w), 1560 (m), 1534 (w), 1493 (w), 1436 (s), 1389 (m), 1316
(w), 1187 (m), 1166 (m), 1099 (s), 1052 (m), 995 (w), 876 (m),
756 (m), 699 (m) cm-1. Anal. Calcd for C22H26Cl2NPPd · 2CH2Cl2:
C, 42.23; H, 4.43; N, 2.05. Found: C, 41.69; H, 4.22; N, 2.00.
3
2
δ 8.24 (s, 1H), 2.70 (td, JH-H ) 7.8 Hz, JH-H ) 2.4 Hz, 1H),
2.70 (td, 3JH-H ) 7.8 Hz, 2JH-H ) 2.0 Hz, 1H), 2.64 (td, 3JH-H
)
)
2
3
2
7.8 Hz, JH-H ) 2.4 Hz, 1H), 2.63 (td, JH-H ) 7.8 Hz, JH-H
2.0 Hz, 1H), 1.96 (pent, 7.8 Hz, 2H), 1.22 (s, 9H); 13C{1H} NMR
δ 150.3, 137.8, 135.9, 57.6 39.3, 30.5, 29.7, 20.6; IR 2968 (s),
1628 (s), 1472 (w), 1363 (m), 1254 (w), 1213 (m), 1099 (m), 1026
(w), 948 (m) cm-1
.
Lithium Diphenylphosphide. A flask charged with diphe-
nylphosphine (18.6 g, 17.4 mL, 0.100 mol) and pentane (300 mL)
under nitrogen was cooled to 0 °C for 15 min. n-Butyllithium (1.6
M in hexanes, 75.0 mL, 0.12 mol) was added dropwise via an
addition funnel. The addition funnel was rinsed with an additional
40 mL of pentane. The reaction was stirred overnight, gradually
warming to ambient temperature, and then placed into a refrigerator
overnight to maximize precipitation. The supernatant solution was
filtered off, leaving behind a yellow semicrystalline solid (16.907
g, 88%) which was used without further characterization.
2-Diphenylphosphinocyclopentene-1-(tert-butyl)imine (3). Meth-
od A. Freshly prepared 2 (1.829 g, 9.852 mmol) was diluted with
10 mL of toluene and cooled to 0 °C. The solution was added to
a slurry of lithium diphenylphosphide (1.893 g, 9.852 mmol) in 10
mL of toluene at 0 °C. The reaction was stirred at 0 °C for 1 h and
at room temperature for 2 h. Volatiles were removed in vacuo. The
resulting orange-yellow residue was triturated with pentane twice
(5 mL each), and extraction with diethyl ether (100 mL) yielded
an orange-red solution. The solution was concentrated under
(2-Diphenylphosphinocyclopentene-1-(tert-butyl)imine)(all-
yl)palladium(II) Chloride (5). 3 (647 mg, 1.93 mmol) was
dissolved in 10 mL of methylene chloride and the mixture added
to [(allyl)PdCl]2 (372 mg, 0.965 mmol) in 10 mL of methylene
chloride. The reaction mixture was stirred for 14 h. Volatile
materials were removed in vacuo, and the residual solid was
triturated with 5 mL of pentane twice. The yellow-orange solid
was dissolved in 20 mL of diethyl ether and cooled to -25 °C
overnight to yield yellow crystals (737 mg, 73.7%): mp 134 °C
dec; 1H NMR δ 8.66 (br s, 1H), 7.73–7.69 (m, 4H), 7.44–7.39 (m,
6H), 5.56 (pent, 3JH-H ) 4.2 Hz, 1H), 4.71 (m, 1H), 3.69 (m, 1H),
2.99 (m, 2H), 2.95–2.92 (br t, 3JH-H ) 7.8 Hz, 2H), 2.43–2.40 (m,
2H), 1.89 (pent, 3JH-H ) 7.8 Hz, 2H), 1.05 (s, 9H); 13C{1H} NMR
δ 153.5 (d, 2.3 Hz), 152.5 (d, 10.7 Hz), 137.8 (d, 32.6 Hz), 134.0
(d, 12.8 Hz), 132.0 (d, 10.7 Hz), 130.6, 128.8 (d, 2.6 Hz), 118.1
(d, 1.2 Hz), 79.5 (d, 1.0 Hz), 61.2, 58.1, 39.6 (d, 1.2 Hz), 35.1 (d,
2.5 Hz), 29.9, 22.6 (d, 1.8 Hz); 31P{1H} NMR δ 7.6; IR 1773 (w),
1747 (w), 1726 (w), 1700 (m), 1680 (w), 1648 (m), 1617 (w), 1576
(w), 1555 (m), 1539 (m), 1519 (w), 1488 (s), 1337 (w), 1306 (w),
1259 (w), 1207 (w), 1181 (w), 1156 (w), 1099 (s), 1041 (s), 969
(w), 860 (m), 829 (m), 767 (w), 741 (m), 694 (s) cm-1. Anal. Calcd
for C25H31ClNPPd: C, 57.93; H, 6.03; N, 2.70. Found: C, 57.88;
H, 6.30, N, 2.72.
(56) King, R. B.; Bakos, J.; Hoff, C. D.; Marko, L. J. Org. Chem. 1979,
44, 1729–1731.
(57) Keming, Z.; Achord, P. D.; Zhang, X.; Krogh-Jespersen, K.;
Goldman, A. S. J. Am. Chem. Soc. 2004, 126, 13044–13053.

Palladium(II) 3-Iminophosphine Complexes
Organometallics, Vol. 27, No. 6, 2008 1265
Table 5. Crystal Data and Collection Parameters
4
3
5
6
formula
fw
space group
temp (K)
C22H26NP
335.41
P1 (No. 2)
C22H26Cl2NPPd · 1.5CH2Cl2
C25H31ClNPPd
518.35
P21/c (No. 14)
140
C26H31F3NO3PPdS
631.99
P21/c (No. 14)
140
640.15
j
P21/n (No. 14)
140
140
a (Å)
b (Å)
c (Å)
9.672(2)
12.669(1)
15.035(1)
14.120(1)
90.000
94.963(2)
90.000
2679.5(5)
4
1.271
9.9685(6)
13.7786(9)
17.649(1)
90.000
97.424(1)
90.000
2403.9(3)
4
1.432
11.2833(5)
8.8106(4)
26.981(1)
90.000
99.783(1)
90.000
2643.3(2)
4
1.588
10.398(2)
10.748(2)
114.074(3)
91.190(3)
102.036(3)
958.5(3)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
2
calcd density (g/cm3)
diffractometer
radiation
1.162
Siemens SMART
Mo KR (λ ) 0.710 69 Å)
graphite
CCD area detector
ω, 0.3°
10.0
monochromator
detector
scan type, width
scan speed (s/frame)
no. of rflns measd
2θ range (deg)
cryst dimens (mm)
no. of rflns measd
no. of unique rflns
no. of observns
no. of params
R, Rw, Rall
GOF
20.0
hemisphere
4.5–57.1
10.0
hemisphere
4.6–56.6
20.0
hemisphere
4.9–56.3
hemisphere
4.6–56.7
0.80 × 0.15 × 0.10
0.30 × 0.24 × 0.06
0.40 × 0.40 × 0.24
0.30 × 0.08 × 0.06
6057
30 524
25 085
29 066
3022
3022
217
6817
6817
301
5981
5981
262
6557
6557
325
0.0431, 0.1181, 0.0504
1.036
0.0434, 0.1196, 0.0539
0.836
0.0269, 0.0682, 0.0311
1.062
0.0286, 0.0670, 0.0348
1.043
(2-Diphenylphosphinocyclopentene-1-(tert-butyl)imine)(all-
yl)palladium(II) Triflate (6). 5 (669 mg, 1.27 mmol) was dissolved
in 10 mL of methylene chloride and added to a slurry of silver
triflate (325 mg, 1.27 mmol) in 10 mL of methylene chloride and
the mixture stirred in the absence of light for 2 h. Solvent was
removed in vacuo, and the grayish red solid was triturated with 5
mL of pentane twice. The residue was extracted with tetrahydro-
furan (3 × 15 mL), leaving behind a gray solid after filtration.
Solvent was removed in vacuo, and the product was triturated with
5 mL of pentane twice to yield an orange-red solid (720 mg, 89.7%):
tetrahydrofuran were added to 6 (0.030 mmol) in a Teflon-capped
4 mL scintillation vial in a drybox. After the mixture was heated
to 70 °C for 22 h, 100 µL of dodecane was added to the reaction
vial as an internal standard and product yield was determined via
gas chromatography. Hydroamination products were readily isolated
by column chromatography (silica gel) and removal of solvent via
rotary evaporation. 1H and 13C NMR were obtained and compared
to literature values.59–61 Gas chromatography standards (entries 1–4,
Table 4) were synthesized by a general procedure outlined by
Bäckvall.62
Crystallography. A summary of crystal data and collection
parameters for the crystal structures of 3–6 is provided in Table 5.
Detailed descriptions of the data collection, as well as data solution,
are provided below. ORTEP diagrams were generated with the
ORTEP-363 software package. For each sample, a suitable crystal
was mounted on a pulled glass fiber using Paratone-N hydrocarbon
oil. The crystal was transferred to a Siemens SMART64 diffracto-
meter with a CCD area detector, centered in the X-ray beam, and
cooled to 140 K using a nitrogen-flow low-temperature apparatus
that had been previously calibrated by a thermocouple placed at
the same position as the crystal. An arbitrary hemisphere of data
was collected using 0.3° ω scans, and the data were integrated by
the program SAINT.65 The final unit cell parameters were
determined by a least-squares refinement of the reflections with I
> 10σ(I). Data analysis using Siemens XPREP66 and the successful
solution and refinement of the structure determined the space group.
Empirical absorption corrections were applied using the program
mp 155 °C dec; 1H NMR δ 7.94 (d, 4JP-H ) 3.0 Hz, 1H), 7.53–7.50
3
(m, 6H), 7.42–7.37 (m, 4H), 5.76–5.69 (m, 1H), 5.00 (t, JH-H
)
3
3
6.6 Hz, 1H), 3.99 (dd, JP-H ) 14.4 Hz, JH-H ) 9.6 Hz, 1H),
3
3
3.25 (d, JH-H ) 4.8 Hz, 1H), 2.98 (dm, JP-H ) 37.2 Hz, 2H),
3
2.63 (dm, JP-H ) 12.0 Hz, 2H), 2.49–2.46 (m, 1H), 2.08–2.04
(m, 2H), 1.31 (s, 9H); 13C{1H} NMR58 δ 159.7 (d, 7.9 Hz), 154.9
(d, 17.3 Hz), 134.3 (d, 34.2 Hz), 133.0 (d, 13.6 Hz), 131.8 (d, 61.5
Hz), 129.6 (d, 17.3 Hz), 129.5, 120.4 (d, 6.6 Hz), 83.7 (d, 30.5
Hz), 64.3, 55.8 (d, 4.1 Hz), 38.0 (d, 11.6 Hz), 36.6, 29.7, 22.5 (d,
6.2 Hz); 31P{1H} NMR δ 16.9; 19F{1H} NMR δ -78.5; IR 1794
(w), 1768 (w), 1737 (w), 1716 (w), 1700 (w), 1685 (m), 1654 (m),
1618 (w), 1576 (w), 1560 (m), 1540 (m), 1519 (w), 1493 (m), 1265
(s), 1218 (m), 1187 (w), 1150 (s), 1099 (m), 1031 (s), 876 (w),
824 (w), 803 (w), 751 (w), 704 (w), 637 (w) cm-1. Anal. Calcd
for C26H31F3NO3PPdS: C, 49.41; H, 4.94; N, 2.22. Found: C, 49.56;
H, 4.99; N, 2.29.
General Procedure for Hydroamination of Cyclohexadiene. 1,3-
Cyclohexadiene (3.6 mmol), amine (0.60 mmol), and 1.0 mL of
methylene chloride were added to 6 (0.030 mmol) in a Teflon-
capped 4 mL scintillation vial in a drybox. After the mixture was
heated to 50 °C for 22 h, 100 µL of dodecane was added to the
reaction vial as an internal standard and the product yield was
determined via gas chromatography. Hydroamination products were
readily isolated by column chromatography (silica gel) and removal
of solvent via rotary evaporation. 1H and 13C NMR were obtained
and compared to literature values.30
(59) Verkade, J. G.; Reddy, C.; Reddy, V.; Urgaonkar, S. Org. Lett.
2005, 7, 4427–4430.
(60) Lin, M.; Watson, W. H.; Kashyap, R. P.; le Noble, W. J. J. Org.
Chem. 1990, 55, 3597–3602.
(61) Knettle, B. W.; Flowers, R. A. I. Org. Lett. 2001, 3, 2321–2324.
(62) Samec, J. S. M.; Backvall, J. E. Chem. Eur. J. 2002, 8, 2955–
2961.
(63) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(64) SMART: Area-Detector Software Package, v5.625; Bruker AXS,
Inc., Madison, WI, 1997–2001.
General Procedure for Hydroamination of Phenylacetylene. Phe-
nylacetylene (6.0 mmol), amine (0.60 mmol), and 1.0 mL of
(65) SAINT: SAX Area-Detector Integration Program, v6.22; Bruker
AXS, Inc., Madison, WI, 1997–2001.
(66) XPREP: Reciprocal Space Exploration Program, v6.12; Bruker
AXS, Inc., Madison, WI, 2001.
(58) The CF3 carbon of the triflate anion was not detected.

1266 Organometallics, Vol. 27, No. 6, 2008
Shaffer and Schmidt
SADABS.67 Equivalent reflections were averaged, and the structure
was solved by direct methods using the SHELXTL68 software
package. Unless otherwise noted, all non-hydrogen atoms were
refined anisotropically, and hydrogen atoms were included as fixed
atoms but not refined.
Compound 3. X-ray-quality crystals were grown from a layered
solution of diethyl ether and pentane which was cooled to -25 °C.
The final cycle of full-matrix least-squares refinement was based
on 3022 observed reflections and 217 variable parameters and
converged yielding final residuals: R ) 0.0431, Rall ) 0.0504, and
GOF ) 1.036.
Compound 5. X-ray-quality crystals were grown from a
saturated solution of diethyl ether at -25 °C. The final cycle of
full-matrix least-squares refinement was based on 5981 observed
reflections and 262 variable parameters and converged yielding final
residuals: R ) 0.0269, Rall ) 0.0311, and GOF ) 1.062.
Compound 6. X-ray-quality crystals were grown from a layered
solution of tetrahydrofuran and pentane at ambient temperature.
The final cycle of full-matrix least-squares refinement was based
on 6557 observed reflections and 325 variable parameters and
converged yielding final residuals: R ) 0.0286, Rall ) 0.0348, and
GOF ) 1.043.
Compound 4. X-ray-quality crystals were grown from a layered
solution of methylene chloride and diethyl ether at room temper-
ature. One and a half molecules of disordered methylene chloride
existed in the asymmetric unit and were refined isotropically.
Hydrogen atoms were included for all ordered atoms. The final
cycle of full-matrix least-squares refinement was based on 6817
observed reflections and 301 variable parameters and converged
yielding final residuals: R ) 0.0434, Rall ) 0.0539, and GOF )
0.836.
Acknowledgment. We gratefully acknowledge the Uni-
versity of Toledo for generous start-up funding, as well as a
University of Toledo Summer Research Fellowship (J.A.R.S.).
Additionally, we thank Dr. Kristin Kirschbaum for X-ray
crystallographic assistance.
Supporting Information Available: CIF files providing ad-
ditional crystallographic data, including bond lengths and angles,
for compounds 3–6. This material is available free of charge via
the Internet at http://pubs.acs.org.
(67) SADABS: Bruker/Siemens Area Detector Absorption Program,
v2.03; Bruker AXS, Inc.:, Madison, WI, 2001.
(68) SHELXTL-97: Structure Solution Program, v6.10; Bruker AXS,
Inc., Madison, WI, 2000.
OM701106Q