Bicyclic N-heterocyclic carbene (NHC) ligand precursors and their palladium complexes

Article abstract of DOI:10.1080/00958972.2016.1185780

Eight bicyclic amidinium precursors (3), prepared from R,S-tmcp (R,S-tmcp: (1R,3S)-diamino-1,2,2-trimethylcyclopentane) were described. Only five of the precursors (3a–e) could be converted to palladium complexes, (PdX₂(6,7-NHC)PEPPSI) (4) by t

Full text of DOI:10.1080/00958972.2016.1185780

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Bicyclic N-heterocyclic carbene (NHC) ligand
precursors and their palladium complexes
Rukiye Gümüşada, M. Emin Günay, Namık Özdemir & Bekir Çetinkaya
To cite this article: Rukiye Gümüşada, M. Emin Günay, Namık Özdemir & Bekir Çetinkaya
(2016): Bicyclic N-heterocyclic carbene (NHC) ligand precursors and their palladium complexes,
Journal of Coordination Chemistry, DOI: 10.1080/00958972.2016.1185780
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1185780
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Download by: [University of Nebraska, Lincoln]
Date: 26 May 2016, At: 05:02

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2016.1185780
Bicyclic N-heterocyclic carbene (NHC) ligand precursors and their
palladium complexes
a
b
c
d
RUKİYE GÜMÜŞADA , M. EMİN GÜNAY* , NAMIK ÖZDEMİR and BEKİR ÇETİNKAYA
a
Department of Chemistry, Adnan Menderes University, 09100 Aydın, Turkey
Faculty of Arts and Science, Department of Chemistry, 09100, Aydın-Turkey
Department of Physics, Ondokuz Mayıs University, 55139 Samsun, Turkey
Department of Chemistry, Ege University, 35100 Izmir, Turkey
b
c
d
Eight bicyclic amidinium precursors (3), prepared from R,S-tmcp (R,S-tmcp: (1R,3S)-diamino-
,2,2-trimethylcyclopentane) were described. Only five of the precursors (3a-e) could be
1
converted to palladium complexes, (PdX (6,7-NHC)PEPPSI) (4) by treatment with PdCl ,
2
2
K
2
CO
3
and pyridine (additional KBr was used for (PdBr
2
(6,7-NHC)PEPPSI)). The salts and
complexes were fully characterized by spectroscopic methods and X-ray crystallography.
Keywords: Chiral bicyclic N-heterocyclic carbine; Expanded ring N-heterocyclic carbine;
PEPPSI-type palladium complex; Camphoric acid; X-ray diffraction
1
. Introduction
N-heterocyclic carbenes (NHCs) are attractive ligands in coordination chemistry and catalysis
due to their readily tunable steric and electronic nature [1-10]. Ring-expanded N-heterocyclic
carbenes have become popular, as it has been established that they possess quite different
properties in comparison to the more traditional five-membered derivatives [11-17]. Interest has
also extended to the behavior of bicyclic NHCs, which contain two expanded rings, and
*Corresponding author. Email: megunay@adu.edu.tr
1

therefore, unlike the expanded ring NHCs, where the ring is rigid, will not twist in conformation
to enable coordination. These chiral ligand systems were first introduced by Wilhelm [18],
Cavell [11], and Newman [19, 20], furthermore a series of bicyclic N-heterocyclic carbenes with
coordination to silver [19], rhodium [19, 20], iridium [19, 20], nickel [19, 20], and copper [21]
have been reported.
The ring expanded NHC complexes indicate the N-C-N angle in the NHC frame is an
important factor for efficiency. However, the deprotonation step in preparation of ring expanded
NHC complexes proved to be more challenging than expected and this property has been
attributed to the relatively low acidity of the NCHN proton in the expanded ring NHC salts [22].
Chiral bicyclic PEPPSI-type palladium-NHC complexes have not been described (where
PEPPSI stands for Pyridine-Enhanced Precatalyst Preparation Stabilization and Initiation).
Therefore, this work focuses on coordination of chiral bicyclic NHCs to Pd(II). The complexes
obtained have been characterized by elemental analysis, NMR spectroscopy, and 4a, 4b, 4d and
4
e by X-ray crystallography.
2
2
. Experimental
.1. General procedure
Air sensitive experiments were carried out using standard Schlenk techniques under an
atmosphere of argon. R,S-tmcp [23] and 3f [18] were synthesized according to literature
methods. Glassware was dried overnight at 120 °C and flame dried prior to use. Solvents were
dried prior to use. All chemicals were obtained from commercial sources and used as received.
1
13
H and C NMR measurements were performed using a Varian AS 400 spectrometer operating
1
at 400 and 100 MHz, respectively. Chemical shifts were reported in ppm relative to TMS for H
1
3
and C NMR spectra. Melting points were measured in open capillary tubes with a Stuart SMP
0 melting point apparatus. Elemental analyses were performed by ODTU Microlab (Ankara,
3
Turkey). Optical rotations were measured using a 1 dm path length (c is given as g/100 mL) on
an ADP-410 (Bellingham-Stanley) polarimeter in the reported solvent.
2
.2. Synthesis of 1
(1R,3S)-1,2,2-trimethylcyclopentane-1,3-diamine (1.0 g, 7.0 mmol) was dissolved in 10.0 mL
DCM and Et O·HCl was added slowly until forming a white solid. The reaction mixture was
2
2

filtered. The precipitate was washed with Et O and dried. The product (1.25 g, 8.8 mmol) and
2
triethyl orthoformate (10.0 mL) were refluxed for 24 h. Then, the reaction mixture was cooled;
2
added Et O for precipitation of yield. The product was filtered and dried. The white solid product
was recrystallized from DCM/Et O.
2
2
6
Yield: 1000 mg (92.0%) Mp > 250 °C. [α]
D
3
= +50 (c = 0.06, CHCl ). Anal. Calcd. for
-
C H ClN (188.69 g mol ): C, 57.30; H, 9.08; N, 14.85. Found: C, 56.55; H, 8.93; N, 14.74.
9
17
2
1
H NMR (400 MHz, CDCl ): δ (ppm) 7.81 (s, 1H, NCHN); 3.37 (d, J = 4.3 Hz, 1H,
3
NC(CH
2
)(CH
2
)CHN); 2.41-2.34 (m, 1H, NC(CHH)(CH
2
)CHN); 2.12-2.05 (m, 2H,
NC(CH )(CH )CHN); 2.03-1.93 (m, 1H, NC(CHH)(CH )CHN) 1.28 (s, 3H, NCCH ); 1.06 (s,
2
2
2
3
1
3
3
H, C(CH
3
)(CH
3
)); 0.98 (s, 3H, C(CH
3
)(CH
3
)]. C NMR (100 MHz, CDCl
3
): δ (ppm) 150.8
(
NCHN); 65.3 (NCCH ); 61.4 (NC(CH )(CH )CHN); 42.5 (C(CH )(CH )); 38.9
3
2
2
3
3
(
NC(CH )(CH )CHN); 20.8 (NCCH ); 16.9 (C(CH )(CH )); 16.3 (C(CH )(CH )).
2
2
3
3
3
3
3
2
.3. General procedure for 3a-c
,8,8-Trimethyl-2,4-diazabicyclo[3.2.1]oct-2-ium chloride (2, 2.6 mmol) was placed in a
5
Schlenk flask and potassium carbonate (5.2 mmol), benzyl bromides (5.2 mmol), and acetonitrile
10.0 mL) were added. The reaction mixture was heated to 90 °C for 4 days. The mixture was
(
then cooled slowly to room temperature, the acetonitrile was removed on a rotary evaporator, the
remaining solid was dissolved in DCM (25.0 mL), filtered to remove the impurity, and solvent
was removed in vacuum. The product was recrystallized from DCM/Et
2
O.
2
7
3
a: Yield: 713 mg (61%) Mp: 218-219 °C. [α] = +183.3 (c = 0.06, CHCl ). Anal.
D
3
-
Calcd. for C H ClN (396.99 g mol ): C, 75.63; H, 8.38; N, 7.06. Found: C, 75.35; H, 8.02; N,
2
5
33
2
1
7
.53. H NMR (400 MHz, CDCl
3
): δ (ppm) 10.03 (s, 1H, NCHN); 7.31 (d, J = 8.2 Hz, 2H, C
6
H -
4
p-(CH )); 7.24 (d, J = 8.2 Hz, 2H, C H -p-(CH )); 7.10 (d, J = 5.8 Hz, 2H, C H -p-(CH )); 7.08
3
6
4
3
6
4
3
(d, J = 8.2 Hz, 2H, C
6
H
4
-p-(CH
3
)); 4.92 (dd, J = 18.4 Hz, J = 14.9 Hz, 2H, NCH
2
C
6
H
4
3
-p-(CH ));
4
.62 (dd, J = 21.5 Hz, J = 14.9 Hz, 2H, NCH C H -p-(CH )); 3.07 (d, J = 4.7 Hz, 1H,
2
6
4
3
NC(CH )(CH )CHN); 2.27 (s, 3H, C H -p-(CH )); 2.25 (s, 3H, C H -p-(CH )); 2.21-2.14 (m,
2
2
6
4
3
6
4
3
1
H, NC(CHH)(CH
2
2
)CHN); 2.02-1.95 (m, 1H, NC(CHH)(CH )CHN); 1.92-1.85 (m, 1H,
NC(CH )(CHH)CHN); 1.71-1.63 (m, 1H, NC(CH )(CHH)CHN); 1.15 (s, 3H, NCCH ); 0.88 (s,
2
2
3
1
3
3
H, C(CH
3
)(CH
3
)); 0.72 (s, 3H, C(CH
3
)(CH
3
)). C NMR (100 MHz, CDCl
3
): δ (ppm) 138.7
(
NCHN); 138.1 (C H -p-(CH )); 132.3 (C H -p-(CH )); 130.0 (C H -p-(CH )); 129.5 (C H -p-
6
4
3
6
4
3
6
4
3
6
4
3

(
CH )); 129.3 (C H -p-(CH )); 127.9 (C H -p-(CH )); 70.7 (NCH C H (CH )); 65.2 (NCH
3
6
4
3
6
4
3
2
6
4
3
2
C H (CH )); 56.4 (NC(CH )(CH )CHN); 53.3 (NC(CH )(CH )CHN); 40.6
6
4
3
2
2
2
2
(
NC(CH
2
)(CH
2
)CHN); 39.6 (NC(CH
2
)(CH
2
)CHN); 31.3 (C(CH
3
)(CH
3
)); 21.3 (C
6
H
4
3
-p-(CH ));
2
1.1 (C H -p-(CH )); 21.0 (NCCH ); 16.9 (C(CH )(CH )); 14.6 (C(CH )(CH )).
6
4
3
3
3
3
3
3
2
7
3
b: Yield: 780 mg (56%) Mp > 250 °C. [α]
D
3
= +40.0 (c = 0.05, CHCl ). Anal. Calcd.
-
for C H ClN (481.15 g mol ): C, 77.38; H, 9.43; N, 5.82. Found: C, 77.95; H, 9.72; N, 6.01.
3
1
45
2
1
H NMR (400 MHz, CDCl ): δ (ppm) 10.04 (s, 1H, NCHN); 7.37 (d, J = 2.7 Hz, 4H, C H -p-
3
6
4
C(CH
3
)
3
); 7.33 (d, J = 3.5 Hz, 4H, C
6
H
4
-p-C(CH )
3 3
); 5.01-4.93 (m, 2H, NCH
2
C
6
H
4
3 3
-p-C(CH ) );
4
.68 (dd, J = 29.0 Hz, J = 14.9 Hz, 2H, NCH C H -p-C(CH ) ); 3.09 (d, J = 5.1 Hz, 1H,
2
6
4
3 3
NC(CH
2
)(CH
2
)CHN); 2.32-2.24 (m, 1H, NC(CHH)(CH
2
)CHN); 2.12-2.04 (m, 1H,
NC(CHH)(CH )CHN); 1.94-1.86 (m, 1H, NC(CH )(CHH)CHN); 1.74-1.67 (m, 1H,
2
2
NC(CH )(CHH)CHN); 1.27 (s, 9H, C H -p-C(CH ) ); 1.26 (s, 9H, C H -p-C(CH ) ); 1.20 (s,
2
6
4
3 3
6
4
3 3
1
3
3
H, NCCH
3
); 0.94 (s, 3H, C(CH
3
)(CH
3
)); 0.79 (s, 3H, C(CH
3
)(CH
3
)). C NMR (100 MHz,
CDCl ): δ (ppm) 154.5 (NCHN); 152.0 (C H -p-C(CH ) ); 151.5 (C H -p-C(CH ) ); 132.3
3
6
4
3 3
6
4
3 3
(C
6
H
4
-p-C(CH
3
)
3
); 130.1 (C
6
H
4
-p-C(CH
3
)
3
); 129.1 (C
6
H
4
-p-C(CH
3
)
3
); 127.7 (C
6
H
4
3 3
-p-C(CH ) );
1
25.9 (C H -p-C(CH ) ); 70.7 (NCH C H -p-C(CH ) ); 65.5 (NCH C H -p-C(CH ) ); 56.6
6
4
3 3
2
6
4
3 3
2
6
4
3 3
(
NC(CH )(CH )CHN); 53.4 (NC(CH )(CH )CHN); 40.8 (NC(CH )(CH )CHN); 39.7
2
2
2
2
2
2
(
NC(CH
2
)(CH
2
)CHN); 34.6 (C(CH
3
)(CH
3
)); 31.4 (C
6
H
4
-p-C(CH
3
)
3
); 31.2 (C
6
H
4
3 3
-p-C(CH ) );
2
1.5 (NCCH ); 17.1 (C(CH )(CH )); 14.8 (C(CH )(CH )).
3
3
3
3
3
2
7
3
c: Yield: 980 mg (74%) Mp: 211-212 °C. [α]
D
3
= +80.0 (c = 0.05, CHCl ). Anal. Calcd.
-
for C H ClN (453.10 g mol ): C, 76.87; H, 9.12; N, 6.18. Found: C, 76.38; H, 8.98; N, 6.02.
2
9
41
2
1
H NMR (400 MHz, CDCl ): δ (ppm) 10.02 (s, 1H, NCHN); 7.37 (d, J = 7.8 Hz, 2H, C H -p-
3
6
4
CH(CH
3
)
2
); 7.31 (d, J = 8.2 Hz, 2H, C
6
H
4
-p-CH(CH
3
)
2
); 7.19 (d, J = 7.4, Hz 2H, C
6
H
4
-p-
CH(CH ) ); 7.19 (t, J = 7.4, Hz, 4H, C H -p-CH(CH ) ); 4.97 (dd, J = 17.8 Hz, J = 14.7 Hz, 2H,
3
2
6
4
3 2
NCH
2
C
6
H
4
-p-CH(CH
3
)
2
); 4.67 (dd, J = 29.7 Hz, J = 14.9 Hz, 2H, NCH
2
C
H
6 4
3 2
-p-CH(CH ) ); 3.09
(
d, J = 4.7 Hz, 1H, NC(CHH)(CH )CHN); 2.89-2.84 (m, 2H, C H -p-CH(CH ) ); 2.30-2.22 (m,
2
6
4
3 2
1
H, NC(CHH)(CH )CHN); 2.10-2.03 (m, 1H, NC(CH )(CHH)CHN); 1.95-1.86 (m, 1H,
2
2
NC(CH
2
)(CHH)CHN); 1.74-1.66 (m, 1H, NC(CH
2
)(CH
2
)CHN); 1.21 (s, 3H, C
6
H
4
3 2
-p-CH(CH ) );
1
3
.20 (s, 6H, C H -p-CH(CH ) ); 1.19 (s, 3H, C H -p-CH(CH ) ); 1.18 (s, 3H, NCCH ); 0.93 (s,
6
4
3 2
6
4
3 2
3
1
3
H, C(CH
3
)(CH
3
)); 0.78 (s, 3H, C(CH
3
)(CH
3
)). C NMR (100 MHz, CDCl
3
): δ (ppm) 154.5
(
NCHN); 149.8 (C H -p-CH(CH ) ); 149.2 (C H -p-CH(CH ) ); 132.7 (C H -p-CH(CH ) );
6
4
3 2
6
4
3 2
6
4
3 2
4

1
30.5 (C H -p-CH(CH ) ); 129.4 (C H -p-CH(CH ) ); 128.0 (C H -p-CH(CH ) ); 127.0 (C H -
6
4
3 2
6
4
3 2
6
4
3 2
6
4
p-CH(CH ) ); 70.7 (NCH C H -p-CH(CH ) ); 65.4 (NCH C H -p-CH(CH ) ); 56.7
3
2
2
6
4
3 2
2
6
4
3 2
(
NC(CH
2
)(CH
2
)CHN); 53.5 (NC(CH
2
)(CH
2
)CHN); 40.8 (NC(CH
2
)(CH
2
)CHN); 39.7
(
NC(CH )(CH )CHN); 33.8 (C(CH )(CH )); 33.7 (C H -p-CH(CH ) ); 31.4 (C H -p-CH(CH ) );
2
2
3
3
6
4
3 2
6
4
3 2
2
3.8 (C
6
H
4
-p-CH(CH
3
)
2
); 21.5 (NCCH
3
); 17.1 (C(CH
3
)(CH
3
)); 14.8 (C(CH
3
3
)(CH )).
2
.4. General procedure for 3d,e
Derivatives of benzaldehyde (6.0 mmol) and 1,2,2-trimethylcyclopentane-1,3-diamine
(1, 3.0 mmol) were refluxed in degassed EtOH (15.0 mL) for 2 h under argon. After cooling, the
solution was concentrated to small volume in vacuo giving a white solid. This was filtered under
argon, washed sparingly with cold EtOH and dried under vacuum. To a solution of diimine
(
3.0 mmol) in MeOH was added portionwise NaBH (8.1 mmol). The mixture was stirred
4
overnight at RT and then hydrolyzed by careful addition of conc. HCl (1.0 mL). The methanol
was removed under reduced pressure and the residue dissolved in water (50.0 mL). The aqueous
solution was made basic by the addition of 6 M NaOH solution and extracted into Et
2
O
(
3×20.0 mL). After drying over MgSO and removal of volatiles, the product was obtained.
4
Synthesized product (3.0 mmol) and NH BF (3.0 mmol) were heated in triethyl orthoformate
4
4
(5.0 mL) at 100 °C under argon for 2 h. After cooling, the white precipitate was filtered and
recrystallized from DCM/Et O.
2
2
7
3
d: Yield: 352 mg (52%) Mp: 155-156 °C. [α]
D
= +166.7 (c = 0.06, CHCl
3
). Anal.
-
Calcd. for C H ClN O (428.99 g mol ): C, 69.99; H, 7.75; N, 6.53. Found: C, 69.67; H, 7.29;
2
5
33
2
2
1
N, 6.79. H NMR (400 MHz, CDCl ): δ (ppm) 8.28 (s, 1H, NCHN); 7.28 (d, J = 8.6 Hz, 2H,
3
C
6
H
4
-p-(OCH
3
)); 7.24 (d, J = 9.0 Hz, 2H, C
6
H
4
-p-(OCH
3
)); 6.86 (d, J = 2.0 Hz, 2H, C
6
4
H -p-
(
OCH )); 6.84 (d, J = 2.0 Hz, 2H, C H -p-(OCH )); 4.68-4.63 (m, 2H, NCH C H -p-(OCH ));
3
6
4
3
2
6
4
3
4
.54-4.44 (m, 2H, NCH
2
C
6
H
4
-p-(OCH
3
)); 3.77 (s, 3H, C
6
H
4
-p-(OCH
3
)); 3.76 (s, 3H, C
6
H
4
-p-
(
OCH )); 3.11 (d, J = 5.1 Hz, 1H, NC(CH )(CH )CHN); 2.31-2.24 (m, 1H,
3
2
2
NC(CHH)(CH )CHN); 2.13-2.06 (m, 1H, NC(CHH)(CH )CHN); 1.96-1.87 (m, 1H,
2
2
NC(CH
2
)(CHH)CHN); 1.75-1.67 (m, 1H, NC(CH
2
)(CHH)CHN); 1.20 (s, 3H, NCCH
3
); 0.93 (s,
1
3
3
H, C(CH )(CH )); 0.77 (s, 3H, C(CH )(CH )). C NMR (100 MHz, CDCl ): δ (ppm) 160.0
3
3
3
3
3
(NCHN); 159.6 (C
6
H
4
-p-(OCH
3
)); 153.6 (C
6
H
4
-p-(OCH
3
)); 131.0 (C
6
H
4
3
-p-(OCH )); 129.5
(
C H -p-(OCH )); 127.0 (C H -p-(OCH )); 124.9 (C H -p-(OCH )); 114.5 (C H -p-(OCH ));
6
4
3
6
4
3
6
4
3
6
4
3
5

1
14.4 (C H -p-(OCH )); 71.0 (NCH C H -p-(OCH )); 65.3 (NCH C H (OCH )); 56.9
6
4
3
2
6
4
3
2
6
4
3
(
(
(
NC(CH )(CH )CHN); 55.2 (C H -p-(OCH )); 53.7 (NC(CH )(CH )CHN); 40.6
2
2
6
4
3
2
2
NC(CH
2
)(CH
2
)CHN); 39.8 (NC(CH
2
)(CH
2
)CHN); 31.3 (C(CH
3
)(CH
3
)); 21.4 (NCCH
3
); 16.9
C(CH )(CH )); 14.7 (C(CH )(CH )).
3
3
3
3
2
D
7
3
e: Yield: 972 mg (60%) Mp: 162-163 °C. [α]
3
= +220.0 (c = 0.06, CHCl ). Anal.
-
Calcd. for C H ClN O (457.04 g mol ): C, 70.95; H, 8.16; N, 6.13. Found: C, 70.57; H, 8.48;
2
7
37
2
2
1
N, 6.42. H NMR (400 MHz, CDCl ): δ (ppm) 8.27 (s, 1H, NCHN); 7.26 (d, J = 8.6 Hz, 2H,
3
C
6
H
4
-p-(OCH
2
CH
3
)); 7.21 (d, J = 8.6 Hz, 2H, C
6
H
4
-p-(OCH
2
CH
3
)); 6.84 (d, J = 1.2 Hz, 2H,
C H -p-(OCH CH )); 6.82 (d, J = 1.6 Hz, 2H, C H -p-(OCH CH )); 4.65-4.61 (m, 2H,
6
4
2
3
6
4
2
3
NCH
2
C
6
H
4
-p-(OCH
2
CH
3
)); 4.52-4.42 (m, 2H, NCH
2
C
6
H
4
2 3
-p-(OCH CH )); 4.00-3.93 (m, 4H,
C H -p-(OCH CH )); 3.11 (d, J = 4.7 Hz, 1H, NC(CH )(CH )CHN); 2.27-2.20 (m, 1H,
6
4
2
3
2
2
NC(CHH)(CH )CHN); 2.08-2.01 (m, 1H, NC(CHH)(CH )CHN); 1.95-1.87 (m, 1H,
2
2
NC(CH
2
)(CHH)CHN); 1.73-1.65 (m, 1H, NC(CH
2
)(CHH)CHN); 1.37 (m, 6H, C
6
H
4
-p-
(
1
OCH CH )); 1.19 (s, 3H, NCCH ); 0.91 (s, 3H, C(CH )(CH )); 0.75 (s, 3H, C(CH )(CH )).
2
3
3
3
3
3
3
3
C NMR (100 MHz, CDCl
3
): δ (ppm) 159.4 (NCHN); 159.0 (C
6
H
4
2 3
-p-(OCH CH )); 153.4
(
C H -p-(OCH CH )); 130.9 (C H -p-(OCH CH )); 129.4(C H -p-(OCH CH )); 126.8 (C H -p-
6
4
2
3
6
4
2
3
6
4
2
3
6
4
(
OCH CH )); 124.7 (C H -p-(OCH CH )); 114.9 (C H -p-(OCH CH )); 114.8 (C H -p-
2
3
6
4
2
3
6
4
2
3
6
4
(
OCH
2
CH
3
)); 71.0 (NCH
2
C
6
H
4
(OCH
2
CH
3
)); 65.2 (NCH
2
C
6
H
4
2 3
(OCH CH )); 63.4
(
NC(CH )(CH )CHN); 56.8 (C H (OCH CH )); 53.6 (NC(CH )(CH )CHN);
2
2
6
4
2
3
2
2
5
3.7(NC(CH
2
)(CH
2
)CHN); 40.5 (NC(CH
2
)(CH
2
)CHN); 39.7 (C
6
H
4
-p-(OCH
2
3
CH )); 31.3
(
C(CH )(CH )); 21.3 (NCCH ); 16.8 (C(CH )(CH )); 14.7 (C(CH )(CH )).
3
3
3
3
3
3
3
2
.5. General procedure for 3f-h
Derivatives of benzyl chloride (4.0 mmol) in dry acetonitrile (15 mL) were added to the stirred
solution of diamine (R,S-tmcp, 2.0 mmol) and triethylamine (4.0 mmol, 2 eq.) at RT. The
resulting mixture was heated at reflux for 20 h. Triethylamine hydrochloride was filtered off and
the solvent was removed under vacuum. Excess derivatives of benzyl chloride separated from the
2 2
product by FCC on silica gel with CH Cl as eluent and the product was eluted with 10%
EtOAc/CH Cl . Evaporation of the solvent gave the product. Product (1.0 mmol), triethyl
2
2
orthoformate (1.2 mmol) and ammonium tetrafluoroborate (1.0 mmol) were heated in dry
6

toluene (5.0 mL) for 5 h at 100 °C in a Schlenk flask. The product was filtered and then washed
twice with Et O to give a solid. The product was recrystallized from DCM/Et O.
2
2
2
8
3
g: Yield: 260 mg (48%) Mp: 199-200 °C. [α]
D
3
= +33.1 (c = 0.05, CHCl ). Anal.
-
Calcd. for C H ClN (481.15 g mol ): C, 77.38; H, 9.43; N, 5.82. Found: C, 77.75; H, 9.62; N,
3
1
45
2
1
6
.13. H NMR (400 MHz, CDCl
3
): δ (ppm) 6.82 (d, J = 6.5 Hz, 2H, C
6
3 4
H(CH ) ); 5.76 (s, 1H,
NCHN); 4.59-4.46 (m, 2H, NCH C H(CH ) ); 4.44-4.27 (m, 2H, NCH C H(CH ) ); 3.78 (d, J =
2
6
3 4
2
6
3 4
4
.7 Hz, 1H, NC(CH )(CH )CHN); 2.58-2.49 (m, 1H, NC(CHH)(CH )CHN); 2.47-2.35 (m, 1H,
2
2
2
NC(CHH)(CH
2
)CHN); 2.31-2.25 (m, 1H, NC(CH
2
)(CHH)CHN); 2.23-2.12 (m, 1H,
NC(CH )(CHH)CHN); 2.07 (s, 6H, C H(CH ) -m-CH ); 2.06 (s, 6H, C H(CH ) -m-CH ); 1.86
2
6
3 4
3
6
3 4
3
(
s, 12H, C
6
H(CH
3
)
4
-o-CH
3
); 1.54 (s, 3H, NCCH
3
); 1.26 (s, 3H, C(CH
3
3
)(CH )); 1.14 (s, 3H,
13
C(CH )(CH )). C NMR (100 MHz, CDCl ): δ (ppm) 147.3 (NCHN); 134.9 (C H(CH ) ); 134.5
3
3
3
6
3 4
(
(
(
(
(
C H(CH ) ); 133.2 (C H(CH ) ); 133.0 (C H(CH ) ); 126.5 (C H(CH ) ); 71.5
6
3 4
6
3 4
6
3 4
6
3 4
NCH
2
C
6
H(CH
3
)
4
); 67.9 (NCH
2
C
6
H(CH
3
)
4
); 51.6 (NC(CH
2
)(CH
2
)CHN); 47.0
NC(CH )(CH )CHN); 41.0 (C(CH )(CH )); 39.6 (C(CH )(CH )CH); 32.0
2
2
3
3
2
2
NC(CH
2
)(CH
2
)CHN); 21.3 (NCCH
3
); 20.3 (C
6
H(CH
3
)
4
-m-CH
3
); 16.9(C
6
H(CH
3
)
4
-o-CH
3
); 14.9
C(CH )(CH )); 14.0 (C(CH )(CH )).
3
3
3
3
2
8
3
h: Yield: 280 mg (44%) Mp: 222-223 °C. [α]D = +83.8 (c = 0.05, CHCl ). Anal.
3
-
Calcd. for C33
H
49ClN
2
(509.20 g mol ): C, 77.84; H, 9.70; N, 5.50. Found: C, 77.96; H, 9.93; N,
1
5
.71. H NMR (400 MHz, CDCl ): δ (ppm) 5.93 (s, 1H, NCHN); 4.52-4.27 (m, 4H,
3
NCH
2
C
6
(CH
3
)
5
); 3.78 (d, J = 4.7 Hz, 1H, NC(CH
2
)(CH
2
)CHN); 2.59-2.20 (m, 4H,
NC(CH )(CH )CHN); 2.15 (s, 6H, C (CH ) -p-CH ); 2.02 (s, 12H, C (CH ) -m-CH ); 1.89 (s,
2
2
6
3 5
3
6
3 5
3
1
2H, C (CH ) -o-CH ); 1.53 (s, 3H, NCCH ); 1.26 (s, 3H, C(CH )(CH )); 1.16 (s, 3H,
6
3 5
3
3
3
3
13
C(CH
3
)(CH
3
)). C NMR (100 MHz, CDCl
3
): δ (ppm) 147.5 (NCHN); 136.5 (C
6
3 5
(CH ) ); 133.5
(
C (CH ) ); 133.4 (C (CH ) ); 132.7 (C (CH ) ); 123.6 (C (CH ) ); 71.9 (NCH C (CH ) ); 67.9
6
3 5
6
3 5
6
3 5
6
3 5
2
6
3 5
(
NCH
2
C
6
(CH
3
)
5
); 52.1 (NC(CH
2
)(CH
2
)CHN); 47.6 (NC(CH
2
)(CH
2
3 3
)CHN); 41.0 (C(CH )(CH ));
3
9.6 (NC(CH )(CH )CHN); 32.0 (NC(CH )(CH )CHN); 25.0 (NCCH ); 21.4 (C (CH ) -p-CH );
2
2
2
2
3
6
3 5
3
1
6.8 (C (CH ) -m-CH ); 16.7 (C (CH ) -o-CH ); 16.0 (C(CH )(CH )); 14.0 (C(CH )(CH )).
6
3 5
3
6
3 5
3
3
3
3
3
2
.6. General procedure for 4a-e
2 2 3
A mixture of amidinium salt (3a-e, 1.0 mmol), PdCl (1.1 mmol), K CO (5.0 mmol) and excess
KBr (only necessary to synthesize 4a-c) was heated in pyridine (5.0 mL) at 110 °C for 18 h
7

(
unless excess KBr is added to the reaction media a mixture of dibromo, dichloro and bromo-
chloro complexes were obtained [24]). The pyridine was then removed in vacuum. The residue
was washed with saturated aqueous CuSO solution and extracted in DCM (2×20.0 mL). The
4
organic layer was separated and dried over anhydrous MgSO and filtered. The filtrate was
4
concentrated under vacuum and then pumped dried to give the crude product as a yellow solid.
The products were recrystallized from THF/hexane.
2
7
4
a: Yield: 140 mg (27%) Mp: 240-241 °C. [α] = +120.0 (c = 0.05, CHCl ). Anal.
D
3
-
2 3
Calcd. for C30H37Br N Pd (705.86 g mol ): C, 51.05; H, 5.28; N, 5.95. Found: C, 52.00; H, 5.64;
1
N, 5.83. H NMR (400 MHz, CDCl ): δ (ppm) 8.86 (d, J = 6.3 Hz, 2H, C H N); 7.69-7.61 (m,
3
5
5
3
6
4
2
H, C
5
H
5
N); 7.22-7.16 (m, 8H, C
6
H
4
-p-(CH
3
)); 6.71 (d, J = 14.5 Hz, 1H, NCHHC
6
H
4
-p-(CH
3
));
.41 (d, J = 16.4 Hz, 1H, NCHHC H -p-(CH )); 5.56 (d, J = 16.4 Hz, 1H, NCHHC H -p-(CH ));
.98 (d, J = 14.9 Hz, 1H, NCHHC H -p-(CH )); 2.91 (d, J = 4.7 Hz, 1H, NC(CH )(CH )CHN);
.57-2.51 (m, 1H, NC(CHH)(CH
6
4
3
6
4
3
6
4
3
2
2
2
)CHN); 2.37 (s, 3H, C
6
H
4
-p-(CH
3
)); 2.34 (s, 3H, C
6
H
4
-p-
(
CH )); 2.24-2.17 (m, 1H, NC(CHH)(CH )CHN); 1.86-1.75 (m, 1H, NC(CH )(CHH)CHN);
3
2
2
1
.68-1.61 (m, 1H, NC(CH
2
)(CHH)CHN); 1.15 (s, 3H, NCCH
3
); 1.00 (s, 3H, C(CH
3 3
)(CH )); 0.78
1
3
(s, 3H, C(CH )(CH )). C NMR (100 MHz, CDCl ): δ (ppm) 175.4 (Pd-C
); 152.5 (C H N);
3
3
3
carbene
5
5
1
37.7 (C H -p-(CH )); 137.5 (C H -p-(CH )); 136.5 (C H N); 136.1 (C H -p-(CH )); 132.7
6
4
3
6
4
3
5
5
6
4
3
(
(
(
(
(
C
6
H
4
-p-(CH
3
)); 129.8 (C
6
H
4
-p-(CH
3
)); 129.2 (C
6
H
4
-p-(CH
3
)); 129.0 (C
6
H
4
-p-(CH
3
)); 127.7
C H -p-(CH )); 124.3 (C H N); 72.1 (NCH C H -p-(CH )); 65.3 (NCH C H -p-(CH )); 60.8
NC(CH
NC(CH )(CH )CHN); 30.3 (C(CH )(CH )); 22.2 (C H -p-(CH )); 21.3 (C H -p-(CH )); 21.2
NCCH ); 18.2 (C(CH )(CH )); 17.2 (C(CH )(CH )).
6
4
3
5
5
2
6
4
3
2
6
4
3
2
)(CH
2
)CHN); 58.8 (NC(CH
2
)(CH
2
)CHN); 41.8 (NC(CH
2 2
)(CH )CHN); 38.6
2
2
3
3
6
4
3
6
4
3
3
3
3
3
3
2
7
4
b: Yield: 226 mg (41%) Mp: 265-266 °C (decomposition). [α]
D
= +80.0 (c = 0.05,
-
CHCl ). Anal. Calcd. for C H Br N Pd (790.02 g mol ): C, 54.73; H, 6.25; N, 5.32. Found: C,
3
36 49
2
3
1
5
7
4.23; H, 6.42; N, 5.15. H NMR (400 MHz, CDCl
3
): δ (ppm) 8.88 (d, J = 5.1 Hz, 2H, C
5
H N);
5
.73-7.64 (m, 3H, C H N); 7.42-7.37 (m, 4H, C H -p-C(CH ) ); 7.22-7.18 (m, 4H, C H -p-
5
5
6
4
3 3
6
4
C(CH ) ); 6.71 (d, J = 14.5 Hz, 1H, NCHHC H -p-C(CH ) ); 6.35 (d, J = 16.8 Hz, 1H,
3
3
6
4
3 3
NCHHC
6
H
4
-p-C(CH
3
)
3
); 5.63 (d, J = 16.4 Hz, 1H, NCHHC
6
H
4
-p-C(CH ); 5.02 (d, J = 14.5
3
)
3
Hz, 1H, NCHHC H -p-C(CH ) ); 2.94 (d, J = 4.7 Hz, 1H, NC(CH )(CH )CHN); 2.57-2.50 (m,
6
4
3 3
2
2
1
H, NC(CHH)(CH
2
2
)CHN); 2.26-2.17 (m, 1H, NC(CHH)(CH )CHN); 1.85-1.75 (m, 1H,
NC(CH )(CHH)CHN); 1.68-1.60 (m, 1H, NC(CH )(CHH)CHN); 1.34 (s, 9H, C H -p-C(CH ) );
2
2
6
4
3 3
8

1
.32 (s, 9H, C H -p-C(CH ) ); 1.18 (s, 3H, NCCH ); 1.01 (s, 3H, C(CH )(CH )); 0.79 (s, 3H,
6
4
3 3
3
3
3
1
3
C(CH )(CH )). C NMR (100 MHz, CDCl ): δ (ppm) 175.2 (Pd-C
); 152.6 (C H -p-
3
3
3
carbene
6
4
C(CH
3
)
3
); 150.9 (C
6
H
4
-p-C(CH
3
)
3
); 149.8 (C
5
H
5
N); 137.4 (C
5
H
5
N); 136.0 (C
6
H
4
3 3
-p-C(CH ) );
1
32.7 (C H -p-C(CH ) ); 129.4 (C H -p-C(CH ) ); 127.6 (C H -p-C(CH ) ); 125.4 (C H -p-
6
4
3 3
6
4
3 3
6
4
3 3
6
4
C(CH
3
)
3
); 125.2 (C
6
H
4
-p-C(CH
3
)
3
); 124.3 (C
5
H
5
N); 72.1 (NCH
2
C
6
H
4
-p-C(CH
3
)
3
); 65.4
(
NCH C H -p-C(CH ) ); 60.8 (NC(CH )(CH )CHN); 58.9 (NC(CH )(CH )CHN); 41.8
2
6
4
3 3
2
2
2
2
(
NC(CH )(CH )CHN); 38.9 (NC(CH )(CH )CHN); 34.6 (C H -p-C(CH ) ); 34.5 (C H -p-
2
2
2
2
6
4
3 3
6
4
C(CH
3
)
3
); 31.4 (C
6
H
4
-p-C(CH
3
)
3
); 31.3 (C
6
H
4
-p-C(CH
3
)
3
); 30.3 (C(CH
3
)(CH
3
)); 22.3 (NCCH
3
);
1
8.2 (C(CH )(CH )); 17.3 (C(CH )(CH )).
3
3
3
3
2
7
4
c: Yield: 248 mg (45%) Mp: 208-209 °C (decomposition). [α]
D
= +120.0 (c = 0.05,
-
CHCl ). Anal. Calcd. for C H Br N Pd (761.97 g mol ): C, 53.59; H, 5.95; N, 5.51. Found: C,
3
34 45
2
3
1
5
8
3.45; H, 6.20; N, 5.36. H NMR (400 MHz, CDCl ): δ (ppm) 8.88 (dd, 2H, C H N); 7.71 (d, J =
3
5
5
.2 Hz, 3H, C
5
H
5
N); 7.65 (d, J = 7.8 Hz, 2H, C
6
H
4
-p-CH(CH
3
)
2
); 7.26-7.19 (m, 6H, C
6
4
H -p-
CH(CH ) ); 6.72 (d, J = 14.5 Hz, 1H, NCHHC H -p-CH(CH ) ); 6.37 (d, J = 16.4 Hz, 1H,
3
2
6
4
3 2
NCHHC
6
H
4
-p-CH(CH
3
2
) ); 5.61 (d, J = 16.4 Hz, 1H, NCHHC
6
H
4
-p-CH(CH
3
)
2
); 5.01 (d, J = 14.5
Hz, 1H, NCHHC H -p-CH(CH ) ); 2.93 (d, J = 4.7 Hz, 1H, NC(CH )(CH )CHN); 2.90-2.87 (m,
6
4
3 2
2
2
2
H, C H -p-CH(CH ) ); 2.61-2.51 (m, 1H, NC(CHH)(CH )CHN); 2.25-2.19 (m, 1H,
6
4
3 2
2
NC(CHH)(CH
2
)CHN); 1.84-1.76 (m, 1H, NC(CH
2
)(CHH)CHN); 1.67-1.60 (m, 1H,
NC(CH )(CHH)CHN); 1.27 (d, J = 3.9 Hz, 6H, C H -p-CH(CH ) ); 1.25 (d, J = 3.9 Hz, 6H,
2
6
4
3 2
C
6
H
4
-p-CH(CH
3
)
3
2
); 1.17 (s, 3H, NCCH
3
); 1.00 (s, 3H, C(CH
3
)(CH
3
)); 0.79 (s, 3H,
1
C(CH )(CH )). C NMR (100 MHz, CDCl ): δ (ppm) 175.3 (Pd-C
); 152.6 (C H N); 148.6
3
3
3
carbene
5
5
(
C H -p-CH(CH ) ); 147.5 (C H -p-CH(CH ) ); 137.4 (C H N); 136.4 (C H -p-CH(CH ) );
6
4
3 2
6
4
3 2
5
5
6
4
3 2
1
33.1 (C
6
H
4
-p-CH(CH
3
2
) ); 129.8 (C
6
H
4
-p-CH(CH
3
)
2
); 127.8 (C
6
H
4
-p-CH(CH
3
)
2
6 4
); 126.6 (C H -
p-CH(CH ) ); 126.3 (C H -p-CH(CH ) ); 124.2 (C H N); 72.1 (NCH C H -p-CH(CH ) ); 65.4
3
2
6
4
3 2
5
5
2
6
4
3 2
(
NCH
2
C
6
H
4
-p-CH(CH
3
)
2
); 60.8 (NC(CH
2
)(CH
2
)CHN); 58.9 (NC(CH
2
)(CH
2
)CHN); 41.8
(
NC(CH )(CH )CHN); 38.9 (NC(CH )(CH )CHN); 33.8 (C H -p-CH(CH ) ); 33.7 (C H -p-
2
2
2
2
6
4
3 2
6
4
CH(CH ) ); 30.3 (C(CH )(CH )); 24.0 (C H -p-CH(CH ) ); 23.9 (C H -p-CH(CH ) ); 22.3
3
2
3
3
6
4
3 2
6
4
3 2
(
NCCH
3
); 18.2 (C(CH
3
)(CH
3
)); 17.3 (C(CH
3
3
)(CH )).
2
7
4
d: Yield: 193 mg (46%) Mp: 203-204 °C. [α] = +140 (c = 0.05, CHCl ). Anal. Calcd.
D
3
-
for C30
H37Cl
2
N
3
O
2
Pd (648.96 g mol ): C, 55.52; H, 5.75; N, 6.48. Found: C, 55.85; H, 6.68; N,
1
5
.96. H NMR (400 MHz, CDCl ): δ (ppm) 8.87-8.85 (m, 2H, C H N); 7.71 (d, J = 8.6 Hz, 2H,
3
5
5
9

C H N); 7.66 (d, J = 8.6 Hz, 1H, C H N); 7.24-7.21 (m, 4H, C H -p-OCH ); 6.90 (dd, J = 8.8
5
5
5
5
6
4
3
Hz, J = 2.2 Hz, 4H, C H -p-(OCH )); 6.57 (d, J = 14.9 Hz, 1H, NCHHC H -p-(OCH )); 6.06-
6
4
3
6
4
3
5
.96 (m, 2H, NCH
2
C
6
H
4
-p-(OCH
3
)); 5.20 (d, J = 14.5 Hz, 1H, NCHHC
6
H
4
3
-p-(OCH )); 3.81 (s,
3
H, C H -p-(OCH )); 3.79 (s, 3H, C H -p-(OCH )); 2.90 (d, J = 4.7 Hz, 1H,
6
4
3
6
4
3
NC(CH
2
)(CH
2
)CHN); 2.42-2.35 (m, 1H, NC(CHH)(CH
2
)CHN); 2.10-2.03 (m, 1H,
NC(CHH)(CH )CHN); 1.80-1.72 (m, 1H, NC(CH )(CHH)CHN); 1.62-1.55 (m, 1H,
2
2
NC(CH )(CHH)CHN); 1.06 (s, 3H, NCCH ); 1.05 (s, 3H, C(CH )(CH )); 0.78 (s, 3H,
2
3
3
3
13
C(CH
3
)(CH
3
)). C NMR (100 MHz, CDCl
3
): δ (ppm) 174.7 (Pd-Ccarbene); 159.4 (C
6
H
4
-p-
(
OCH )); 158.7 (C H -p-(OCH )); 151.2 (C H N); 137.6 (C H N); 131.2 (C H -p-(OCH ));
3
6
4
3
5
5
5
5
6
4
3
1
31.1 (C
6
H
4
-p-(OCH
3
)); 129.1 (C
6
H
4
-p-(OCH
3
)); 127.9 (C
5
H
5
N); 124.3 (C
6
H
4
-p-(OCH
3
)); 113.9
(
(
(
(
C H -p-(OCH )); 113.7 (C H -p-(OCH )); 71.7 (NCH C H -p-(OCH )); 65.3 (NCH C H -p-
6
4
3
6
4
3
2
6
4
3
2
6
4
OCH )); 60.0 (NC(CH )(CH )CHN); 57.7 (NC(CH )(CH )CHN); 55.2 (C H -p-(OCH )); 41.4
3
2
2
2
2
6
4
3
NC(CH
2
)(CH
2
)CHN); 39.1 (NC(CH
2
)(CH
2
)CHN); 30.6 (C(CH
3
)(CH
3
3
)); 22.2 (NCCH ); 17.8
C(CH )(CH )); 16.7 (C(CH )(CH )).
3
3
3
3
2
D
7
4
e: Yield: 163 mg (47%) Mp: 203-204 °C. [α]
3
= +26.0 (c = 0.04, CHCl ). Anal. Calcd.
-
for C H Cl N O Pd (677.01 g mol ): C, 56.77; H, 6.10; N, 6.21. Found: C, 56.53; H, 6.34; N,
3
2
41
2
3
2
1
5
.81. H NMR (400 MHz, CDCl ): δ (ppm) 8.85 (dd, J = 6.7 Hz, J = 1.6 Hz, 1H, C H N); 7.69
3
5
5
(d, J = 9.0 Hz, 2H, C
5
H
5
N); 7.63 (d, J = 8.6 Hz, 1H, C
5
H
5
N); 7.24-7.20 (m, 4H, C
6
H
4
-p-
(
OCH CH )); 6.88 (dd, J = 8.6 Hz, J = 2.4 Hz, 4H, C H -p-(OCH CH )); 6.56 (d, J= 14.5 Hz,
2
3
6
4
2
3
1
1
1
H, NCHHC
6
H
4
-p-(OCH
2
CH
3
)); 6.00 (s, 2H, NCH
2
C
6
H
4
-p-(OCH
2
CH
3
)); 5.18 (d, J= 14.5 Hz,
H, NCHHC H -p-(OCH CH )); 4.05-3.98 (m, 4H, C H -p-(OCH CH )); 2.89 (d, J= 4.7 Hz,
6
4
2
3
6
4
2
3
H, NC(CH )(CH )CHN); 2.41-2.34 (m, 1H, NC(CHH)(CH )CHN); 2.09-2.02 (m, 1H,
2
2
2
NC(CHH)(CH
2
)CHN); 1.79-1.70 (m, 1H, NC(CH
2
)(CHH)CHN); 1.61-1.53 (m, 1H,
NC(CH )(CHH)CHN); 1.39 (q, J = 6.8 Hz, 6H, C H -p-(OCH CH )); 1.04 (s, 3H, NCCH ); 1.03
2
6
4
2
3
3
1
3
(
(
(
(
(
(
(
s, 3H, C(CH
3
)(CH
3
)); 0.76 (s, 3H, C(CH
3
)(CH
3
)). C NMR (100 MHz, CDCl
3
): δ (ppm) 174.5
Pd-Ccarbene); 158.7 (C H -p-(OCH CH )); 158.0 (C H -p-(OCH CH )); 153.3 (C H -p-
6
4
2
3
6
4
2
3
6
4
OCH CH )); 151.1 (C H N); 137.6 (C H N); 131.1 (C H -p-(OCH CH )); 130.9 (C H -p-
2
3
5
5
5
5
6
4
2
3
6
4
OCH
2
CH
3
)); 129.1 (C
H
6 4
-p-(OCH
2
CH
3
)); 127.6 (C
6
H
4
-p-(OCH
2
CH
3
)); 124.9 (C
6
H
4
-p-
OCH CH )); 124.2 (C H N); 114.3 (C H -p-(OCH CH )); 114.2 (C H -p-(OCH CH )); 71.7
2
3
5
5
6
4
2
3
6
4
2
3
NCH
2
C
6
H
4
-p-(OCH
2
CH
3
)); 65.2 (NCH
2
C
6
H
4
-p-(OCH
2
CH
3
)); 63.3 (C
6
H
4
-p-(OCH
2
3
CH )); 63.2
C H -p-(OCH CH )); 60.0 (NC(CH )(CH )CHN); 57.7 (NC(CH )(CH )CHN); 41.3
6
4
2
3
2
2
2
2
10

(
NC(CH )(CH )CHN); 39.0 (NC(CH )(CH )CHN); 30.6 (C(CH )(CH )); 22.1 (NCCH ); 17.8
2
2
2
2
3
3
3
(
C(CH )(CH )); 16.7 (C(CH )(CH )); 14.8 (C H -p-(OCH CH )); 14.7 (C H -p-(OCH CH )).
3
3
3
3
6
4
2
3
6
4
2
3
3
3
. Results and discussion
.1. Synthesis of the chiral bicyclic amidinium precursors (3a-h)
A limited number of chiral (NHC)Pd(II) complexes have been reported [25]. For us the use of
readily available camphoric acid derivative R,S-tmcp was appealing [11, 18]. Camphoric acid
was converted to R,S-tmcp ((1R,3S)-diamino-1,2,2-trimethylcyclopentane) [23] as described via
a Schmidt reaction using concentrated sulfuric acid and sodium azide [18, 26, 27]. For synthesis
of amidinium precursors, two different routes (A and B) were employed as shown in scheme 1.
Route (A) involves the initial ring closure and subsequent introduction of the exo N-substituents,
whereas route (B) [18, 19] involves the initial modification of the diamine through alkylation of
the nitrogen prior to ring closure, as shown in scheme 1.
11

Reagent and conditions: (i) Et
2
O.HCl; (ii) HC(OEt)
3
, reflux; (iii) K
2 3
CO , R-X
(
3a-c), CH CN, 80 °C, 4 days; (iv) a) EtOH, RCHO (3d,e), reflux, b) NaBH ,
3
4
MeOH, RT; (v) NEt , R-X (3f-h), CH CN, 80 °C, 24 h; (vi) NH BF , HC(OEt) ,
3
3
4
4
3
reflux; (vii) K
2
CO
3
2 5 5
, PdCl , C H N, KBr (for 4a-c), 110 °C, 18 h.
Scheme 1. Synthesis of bicyclic NHC precursors and their PEPPSI-type (NHC)Pd(II) complexes.
First, diamine derivative was converted to diamine hydrochloride by ether hydrochloride. This is
followed by ring closure with triethyl orthoformate to form 1 (Route A). The ring closure was
1
3
1
successful as shown by appearance of the NCHN peak in both the C NMR and H NMR at
50.8 ppm and 7.81 ppm, respectively. Single crystals of 1 were obtained from vapor diffusion
1
of DCM and diethyl ether. The alkyl derivatives were synthesized by deprotonation of the
nitrogens using potassium carbonate, followed by reaction with benzyl bromides to form 3a-c. In
Route (B) the alkylation reaction was performed either by treating the diamine with an aromatic
aldehyde followed by reduction of the imine or directly with an arylmethylene bromide. The
diamine obtained was converted to the amidinium precursors as a white solid by cyclization with
4 4
triethyl orthoformate in the presence of NH BF (3d-h).
1
13
Compounds 3a-h were characterized by H NMR and C NMR spectroscopy. In the
1
H NMR spectra of the salts the characteristic NCHN proton shifts were 5.93-10.04 ppm and in
12

1
3
-
C NMR the NCHN shifts were 138.7-160.0 ppm. The NCHN of 3f-h, having BF , moved
4
upfield to 5.89, 5.76 and 5.93 ppm, respectively. In 3f-h a restricted rotation was observed by the
1
H NMR signal of the NCHN. It is likely that the large upfield shifts of the protons of 3f-h are
due to proximity to the middle of the arene rings next to C9 (figure 1) methyl group of the
camphor skeleton [18].
3
.2. Synthesis of the chiral PEPPSI-type bicyclic 6,7-NHC palladium complexes (4a-e)
All attempts to react 4a with the standard palladium precursors Pd(OAc) and PdCl in PhMe in
the presence of conventional bases did not lead to the target complexes. We therefore decided to
react the amidinium salts with PdCl /K CO in pyridine as a base and supporting ligand and
2
2
2
2
3
obtained the expected complexes as yellow solids. This procedure is suitable for deprotonation
and coordination of acidic ring-expanded NHC precursors [28]. Attempts to coordinate the
bulkier NHC precursors (3f-h) to palladium were unsuccessful; after heating PdCl
2
2 3
/3f/K CO
and KBr in pyridine for several days, only unreacted material was recovered.
Incorporation of the chiral bicyclic NHC to 4a-e was evident from the NMR spectra
showing the conspicuous absence of the NCHN resonance of the reacting NHC precursors while
1
3
1
a new Pd-Ccarbene resonance appeared at 174.2-175.4 ppm in C{ H}NMR spectra.
These chemical shifts of 4 are similar to that observed for ring-expanded (Pd(NHC)(3-
ClPy)Cl ) [24] but are at lower field (by ∼4 ppm for six-membered and/or 14 ppm for seven-
2
membered rings compared to related expanded ring NHC complexes) [13]. In order to confirm
the proposed structures of the complexes unequivocally, 4a, 4b, 4d and 4e have been further
characterized by single crystal X-ray diffraction.
3
.3. Crystal structure determination of 1, 4a, 4b, 4d and 4e
The perspective ORTEP-3 [29] views of the compounds are depicted in figures 1 and 2, while
the key bond lengths and angles are given in table S1. All the compounds are chiral and
crystallize in noncentrosymmetric space groups, except 4a, which is racemic and crystallizes in
ꢀ
the centrosymmetric space group P1 [30, 31].
1
crystallizes as a salt in which the charge of the NHC cation is balanced by a chloride.
The C—N bond lengths compared to amidinium carbon are almost equal (1.290(3) and
.302(3) Å) with the C—N—C angle of 121.64(17)°. These geometric parameters are
1
13

comparable with those reported for similar compounds [19, 20, 32]. In the crystal structure, the
NHC cation is connected to the anion by a N1—H1···Cl1 hydrogen bond with D—H, H···A,
D···A and D—H···A values being 0.83(4) Å, 2.31(4) Å, 3.127(2) Å and 168(4)°, respectively.
In 4a, 4b, 4d and 4e, Pd(II) has a trans-square-planar coordination geometry from one
carbene C of NHC ligand, one pyridine N and two halides (Br or Cl). The Pd—Br, Pd—Cl, Pd—
N and Pd—C bond lengths are from 2.367(4) to 2.4094(14) Å, 2.301(6) to 2.331(6) Å, 2.086(12)
to 2.16(2) Å and 1.909(15) to 2.00(2) Å, respectively. From cis angles, which vary from 85.0(6)
to 93.8(5)°, and the trans angles, which vary from 172.72(15) to 178.73(6)° (table S1), the
coordination around the Pd(II) is distorted. When the C—N bond lengths in the complexes are
compared with those in 1, coordination elongates the N1—C1 and N2—C1 bonds. The C—N—
C angles contract except for that in 4e. In the coordination plane, the r.m.s. deviation through
these five atoms is 0.0274 Å, 0.0376 Å (0.0197 Å), 0.0169 Å (0.0360 Å) and 0.0113 Å, while the
coordination plane makes dihedral angles of 51.32(5)°, 27.60(9)° (15.39(11)°), 47.89(5)°
(48.22(5)°) and 43.98(7)° with the pyridine ring for 4a, 4b, 4d and 4e, respectively. In 4b and
4
d, there are two molecules in the asymmetric unit. For the sake of clarity, only one of the two
molecules is shown in figure 2. In the foregoing discussion, parameters belonging to the second
molecule are quoted in square brackets.
3
.4. X-ray crystallography
Intensity data of the compounds were collected on a STOE IPDS II diffractometer at room
temperature (296 K) using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) by
applying the ω-scan method. Data collection and cell refinements were carried out using
X-AREA [33]. Data reduction was applied using X-RED32 [33]. The structures were solved by
direct methods using SHELXS-2013 [34] and refined with full-matrix least-squares calculations
2
on F using SHELXL-2014 [34] implemented in the WinGX [29] program suite. All carbon
bound hydrogens were placed geometrically and treated using a riding model, fixing the bond
lengths at 0.93, 0.98, 0.97 and 0.96 Å for aromatic CH, methine CH, CH and CH , respectively.
2
3
The nitrogen bound hydrogens in 1 were located in a difference Fourier map and refined
isotropically. The displacement parameters of the carbon bound hydrogens were fixed at Uiso(H)
=
1.2U (1.5U for methyl) of their parent atoms. C3, C4, C6, C7 and C8 of bicyclic NHC ring
eq
eq
in 4a and tert-butyl groups in 4b show positional disorder, so geometric and atomic displacement
14

parameter (ADP) restraints were applied to the disordered atoms to stop distortion. The details of
the data collection and structure solution are collected in table S2.
4
. Conclusion
A series of cyclic amidinium precursors (3a-h) derived from camphoric acid have been
synthesized in good yields. The amidinium precursors (3a-e) having relatively acidic NCHN
protons (δ > 7 ppm) were converted to the corresponding PEPPSI-type Pd-NHC complexes
[
(6,7-NHC)PdX (pyridine)] via reaction of PdCl , K CO in boiling pyridine in the presence of
2
2
2
3
KBr. To the best of our knowledge, they represent the only structurally characterized chiral
bicyclic PEPPSI-type Pd-NHC complexes. The change of the N-substituents on the precursors
has a pronounced influence on the complex formation; Ar rings with o-substituents are resistant
to complexation.
Supplementary material
CCDC 1041983, 1041984, 1041985, 1041986 and 1041987 contain the supplementary
crystallographic data for 1, 4a, 4b, 4d and 4e, respectively. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336-
0
33; or E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
This work was financially supported by the “The Scientific and Technological Research Council
of Turkey” [TUBITAK, Grant Number: 110T765] and “Scientific Research Project Unit (BAP)
of Adnan Menderes University” [Grant Number: FEF-11019]. We acknowledge the Faculty of
Arts and Sciences, Ondokuz Mayıs University, Turkey, for the use of the STOE IPDS II
diffractometer (purchased under Grant Number F-279 of the University Research Fund).
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17

Figure 1. A view of 1 showing the atom-numbering scheme. Thermal ellipsoids are drawn at
0% probability and hydrogens are shown as small spheres of arbitrary radii.
3
18

4
b
4a
4d
4
e
Figure 2. A view of 4a, 4b, 4d and 4e showing the atom-numbering scheme. Thermal ellipsoids
are drawn at the 30% probability level. Hydrogens are omitted for clarity and only the major
parts of disordered fragment are drawn for 4a and 4b.
19

Graphical abstract
20