1,3-Bis(α-aminoisopropyl)benzene, meta-C6H4(CMe2NH2)2: An N,N-bridging and N,C,N-cyclometalating ligand

Article abstract of DOI:10.1016/j.ica.2007.08.027

Saponification of the bis(carbamic acid ester) 1,3-C₆H₄(CMe₂NHCO₂Me)₂ (1), made by the addition of methanol to commercial 1,3-C₆H₄(CMe₂NCO)₂, yielded the me

Full text of DOI:10.1016/j.ica.2007.08.027

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Inorganica Chimica Acta 361 (2008) 1311–1318
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1
,3-Bis(a-aminoisopropyl)benzene, meta-C H (CMe NH ) : An
6
4
2
2 2
N,N-bridging and N,C,N-cyclometalating ligand
*
Lutz Dahlenburg , Harald Treffert, Frank W. Heinemann
Institut f u¨ r Anorganische Chemie der Universit a¨ t Erlangen-N u¨ rnberg, Egerlandstrasse 1, D-91058 Erlangen, Germany
Received 13 August 2007; accepted 18 August 2007
Available online 31 August 2007
Abstract
Saponification of the bis(carbamic acid ester) 1,3-C
6
H
4
(CMe
2 2 2
NHCO Me) (1), made by the addition of methanol to commercial 1,3-
4
C
C
6
H
4
(CMe
12)RhCl}
2
NCO)
{l-1,3-C
2
, yielded the meta-phenylene-based bis(tertiary carbinamine) 1,3-C
6
H
4
(CMe
12)Rh(l-Cl)}
2
NH
2
)
2
(2). Dinuclear [{(g -1,5-
4
8
H
2
H
6 4
(CMe
2
NH
2
)
2
}] (3) resulted from the action of 2 on [{(g -1,5-C
8
H
2
] in toluene. Combination
of 2 with PdCl or K [PdCl ] gave the dipalladium macrocycle trans,trans-[{l-1,3-C H (CMe NH ) } (PdCl ) ] (4) along with cyclo-
2
2
4
6
4
2
2 2
2
2 2
1
0
metalated [{2,6-C
6
H
3
(CMe
-jN,jC , jN }Pd(PEt
2
NH
2
)
2
-jN,jC ,jN }PdCl] (5). Substitution of PEt
3
for the labile chlorido ligand of 5 afforded [{2,6-
)]Cl (6). The crystal structures of the following compounds were determined: bis(carbamic acid
1
0
C
6
H
3
(CMe
2
NH
2
)
2
3
ester) 1, ligand 2 as its bis(trifluoroacetate) salt [1,3-C H (CMe NH ) ](O CCF ) , 2 Æ (HAc ) , complexes 3 and 6, as well as 1,3-
6
4
2
3 2
2
3 2
f 2
C
ꢀ
6
H
4
(CMe
2007 Elsevier B.V. All rights reserved.
2 2
OH) (the diol analogue of 2).
Keywords: 1,3-Bis(a-aminoisopropyl)benzene; Rhodium complex; Palladium complexes; X-ray structure analysis
1
. Introduction
1,3-bis(a-aminoisopropyl)benzene, 1,3-C H (CMe NH ) ,
6 4 2 2 2
where the meta-phenylene backbone was introduced to pro-
mote cyclometalation producing metal complexes similar
to the wide range of organometallic products derived from
van Koten’s ‘‘pincer’’ ligand 1,3-C H (CH NMe ) [6].
It is well known that coordinatively unsaturated amido
derivatives of the platinum metals can make good catalysts
for the heterolytic activation of the dihydrogen molecule
but tend to decompose through b-hydride elimination to
generate imine products [1–4]. However, they can be iso-
lated when there are no hydrogen atoms adjacent to the
amide function, such as in the 16e ruthenium and iridium
complexes [RuH(PPh ) (HNCMe CMe NH )] [2] and
6
4
2
2 2
Prior to this contribution, 2-phenyl-6-(a-aminoisopro-
pyl)pyridine, 2-C H C H NCMe NH -6, which coordi-
6
5
5
3
2
2
nates through its two nitrogen donors and one
deprotonated ortho carbon atom of the phenyl ring, was
introduced into organometallic chemistry by Song and
Morris as the only other example of a cyclometalating tri-
dentate amine ligand having no hydrogen atoms on the a-
3
2
2
2
2
4
[
(g -1,5-C H )Ir(HNCMe CH PPh )] [4] described by
8 12 2 2 2
Morris et al. and ourselves.
With the aim of expanding the family of elimination-
resistant a-peralkylated nitrogen donors we recently
designed the novel N \ N \ N tridentate ligand 2,6-bis-
carbon atom of the NH group [7].
2
2. Experimental
(
a-aminoisopropyl)pyridine, 2,6-C H N(CMe NH ) [5].
5 3 2 2 2
In this paper, we report on its N \ C(H) \ N analogue
2.1. General remarks
*
All manipulations were performed under nitrogen using
standard Schlenk techniques. Solvents were distilled from
the appropriate drying agents prior to use. – IR: Mattson
Corresponding author. Tel.: +49 9131 8527353; fax: +49 9131
8
527387.
E-mail address: dahlenburg@chemie.uni-erlangen.de (L. Dahlenburg).
0
020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.08.027

1312
L. Dahlenburg et al. / Inorganica Chimica Acta 361 (2008) 1311–1318
Infinity 60 AR. – NMR: Bruker DPX 300 (300.1 MHz for
lected by filtration, washed with n-pentane, and dried in the
1
13
31
1
H, 75.5 MHz for C, and 121.5 MHz for P) with SiMe4
as internal or H PO as external standards (downfield posi-
vacuum of an oil pump. – H NMR (CDCl , ꢁ50 ꢁC):
3
d = 1.51, 1.63 (both m, 4H each, CH ), 1.76 (s, 12H,
3
4
2
tive; ‘‘m’’: deceptively simple multiplet) at ambient temper-
ature, unless stated otherwise. – Mass spectra: Micromass
ZabSpec (FAB mode with 3-nitrobenzylalcohol as
CH ), 2.12, 2.24 (both m, 4H each, CH ), 3.40, 3.54, 4.42
3
2
(all ‘‘s’’ (br), 4H each, diene CH and NH ), 7.41 (‘‘s’’,
2
+
3H, H-4,5,6), 7.91 (s, 1H, H-2). Anal. Calc. for
matrix). – Dimethyl isophthalate, 1,3-bis(1-isocyanato-1-
methylethyl)benzene, and triethylphosphine were used as
purchased from Aldrich. The diol 1,3-C H (CMe OH)
2
C H Cl N Rh (685.37): C, 49.07; H, 6.47; N, 4.09.
Found: C, 49.14; H, 6.48; N, 4.31%.
2
8
44
2
2
2
6
4
2
(
which is also commercially available), resulted from treat-
2.3.2. trans,trans-[{l-1,3-C H (CMe NH ) } (PdCl ) ]
6
4
2
2 2 2
0
2 2
1
ment of 1,3-C H (CO Me) with slightly more than
(4) and [{2,6-C H (CMe NH ) -jN,jC ,jN }PdCl] (5)
6
4
2
2
6
3
2
2 2
4
equiv. of MeMgI in diethyl ether. The platinum metal
Equimolar mixtures of 2 (510 mg, 2.65 mmol) with PdCl2
compounds RhCl Æ xH O (x @ 3), PdCl and K [PdCl ]
(469 mg, 2.65 mmol) and K [PdCl ] (864 mg, 2.65 mmol),
3
2
2
2
4
2
4
were products of Pressure Chemical Co. (Pittsburgh) and
respectively, were heated in acetonitrile (50 mL) at reflux
temperature for 16 h. Complex 4 separated from solution
as a sparingly soluble pale yellow precipitate which was fil-
tered off, washed with 3 · 5 mL of acetonitrile and dried
4
Strem Chemicals, Inc. (Bischheim); [{(g -1,5-C H )Rh(l-
8
12
Cl)} ] [8,9] was prepared as reported in the literature.
2
1
2
.2. 1,3-Bis(a-aminoisopropyl)benzene
.2.1. 1,3-C H (CMe NHCO Me)] (1)
under vacuum; yield 705 mg (72%). – H NMR (DMSO-
d ): d = 1.79 (s, 24H, CH ), 3.99 (br, 8H, NH ), 7.30 (m,
6
3
2
1
3
1
2
6H, H-4,5,6), 7.72 (s, 2H, H-2). C{ H} NMR (DMSO-
6
4
2
2
A solution of 10 mL (ꢀ43 mmol) of 1,3-bis(1-isocya-
d ): d = 31.26 (CH ), 57.31 (Ctert), 123.42 (C-5), 123.72
6
3
nato-1-methylethyl)benzene in 30 mL of methanol was stir-
red for 3 days at ambient conditions. Concentration of the
mixture under vacuum resulted in the deposition of the
product as a colorless precipitate which was filtered off,
(C-4,6), 128.33 (C-2), 147.10 (C-1,3). IR (CsCl):
3
5,37
ꢁ1
m(Pd–
Cl) = 318, 313(sh) cm . FAB-MS: m/z = {703
+
(100%), 705 (99%), 702 (79%), 701 (76%)} [M ꢁ Cl] ,
{631 (100%), 633 (84%), 629 (82%), 630 (78%)} [M ꢁ Cl ꢁ 2
+
washed with pentane, and dried under vacuum; yield
HCl] . Anal. Calc. for C H Cl N Pd (739.25): C, 38.99;
2
4
40
4
4
2
1
1
2.44 g (93%). H NMR (CDCl ): d = 1.59 (s, 12H,
H, 5.45; N, 7.58. Found: C, 39.40; H, 5.59; N, 7.51%.
Evaporation of the mother liquor followed by re-disso-
lution of the residue in methanol, filtration and renewed
removal of the volatiles furnished 245 mg (27%) of the
cyclometalated product 5 as orange yellow microcrystals
which pertinaciously retained residual solvent and, hence,
3
CCH ), 3.51 (s, 6H, OCH ), 5.0 (br, 2H, NH), 7.22 (m,
3
3
1
3
1
3
H, H-4,5,6), 7.36 (s, 1H, H-2). C{ H} NMR (CDCl ):
3
d = 29.67 (CCH ), 51.99 (C ), 55.74 (OCH ), 121.64 (C-
3
tert
3
4
(
,6), 123.62 (C-5), 128.74 (C-2), 147.48 (C-1,3), 155.58
C@O). Anal. Calc. for C H N O (308.37): C, 62.30;
1
6
24
2
4
1
H, 7.85; N, 9.09. Found: C, 62.88; H, 7.86; N, 8.92%.
did not give satisfactory analyses. – H NMR (DMSO-
d ): d = 1.37 (s, 12H, CH ), 4.71 (br, 4H, NH ), 6.46 (d,
6
3
2
3
1
2
.2.2. 1,3-C H (CMe NH ) (2)
2
J(H,H) = 7.53 Hz, 2H, H-3,5), 6.75 (t, 1H, H-4).
6
4
2 2
3
1
A solution of 10.79 g (35.0 mmol) of 1 in 100 mL of n-
C{ H} NMR (DMSO-d ): d = 29.49 (CH ), 65.63 (Ctert),
6 3
butanol containing 12.0 g of added potassium hydroxide
was heated under reflux for 24 h. Vacuum evaporation of
the solvent left an oily residue which was dissolved in
116.90, 118.76, 121.82, 155.13 (C-1). Anal. Calc. for
C H ClN Pd (333.17): C, 43.26; H, 5.75; N, 8.41. Found:
1
2
19
2
C, 40.24; H, 5.41; N, 7.46%.
5
0 mL of water. Extraction into THF (3 · 50 mL), fol-
1
0
lowed by drying over Na SO and removal of all volatile
2.3.3. [{2,6-C H (CMe NH ) -jN,jC ,jN }Pd(PEt )]Cl
2
4
6
3
2
2 2
3
material afforded 5.80 g (86%) of the product as a colorless
to bright yellow oil. IR (KBr): 3353, 3277, 3099, 3062,
(6)
A solution of 60 mg (0.18 mmol) of cyclometalated com-
plex 5 in 4 mL of MeOH/THF (1:1) was treated with
ꢁ
1 1
3
020, 2964, 2928, 2868, 1601, 799 cm . H NMR (CDCl3):
d = 1.41 (s, 12H, CH ), 1.63 (br, 4H, NH ), 7.22, 7.35, 7.72
0.25 mL (20 mg, 0.17 mmol) of PEt , which caused the
3
2
3
1
3
1
(
(
(
all m, 4 phenylene H). C{ H} NMR (CDCl ): d = 31.83
mixture to change color from orange to bright yellow. After
stirring for 30 min at room temperature all volatile mate-
rial was evaporated in vacuo to leave a pale yellow solid
3
CH ), 51.45 (Ctert), 119.74 (C-4,6), 121.49 (C-5), 126.83
3
C-2), 149.06 (C-1,3).
3
1
1
shown by P{ H} NMR to be a 3:1 mixture of 6 (see below)
and trans-[PdCl (PEt ) ]: d(CDCl ) = 19.05; Ref. [10]:
2
2
.3. Metal complexes
2
3 2
3
d(CH Cl ) = 17.8. Recrystallization from dichloromethane
2
2
4
.3.1. [{(g -1,5-C H )RhCl} {l-1,3-C H (CMe NH ) }] (3)
afforded almost colorless single crystals of the cyclometalat-
ed complex as an addition compound containing two mole-
8
12
2
6
4
2
2 2
A quantity of 120 mg (0.62 mmol) of ligand 2 dissolved
1
in 1 mL of toluene was added dropwise to a stirred solution
cules of lattice solvent per formula unit, 6 Æ 2CH Cl . – H
2
3
2
4
3
of 149 mg (0.28 mmol) of [{(g -1,5-C H )Rh(l-Cl)} ] in
NMR (CDCl ): d = 1.12 (dt, J(H,H) = 7.95, J(P,H) =
8
12
2
3
1
0 mL of the same solvent to precipitate 160 mg (83%) of
15.90 Hz, 9H, phosphine CH ), 1.63 (s, 12H, amine CH ),
3
3
2
the product as bright yellow microcrystals which were col-
1.86 (dq, J(P,H) = 15.45 Hz, 6H, PCH ), 4.42 (br, 4H,
2

L. Dahlenburg et al. / Inorganica Chimica Acta 361 (2008) 1311–1318
1313
3
6
NH ), 6.61 (dd, J(H,H) = 7.53 Hz, J(P,H) = 2.64 Hz, 1H,
4854 reflections collected (0 6 h 6 +13, 0 6 k 6 +12,
ꢁ25 6 l 6 +25), 4604 unique (R = 0.0371); wR =
2
3
1
1
H-4), 6.96 (t, 2H, H-3,5). P{ H} NMR (CDCl ): d = 8.67
3
int
2
(
s).
0.0942 for all data and 307 parameters, R = 0.0499 for
1
2
967 intensities I > 2r(I). – 6 Æ 2CH Cl (0.22 · 0.21 ·
2
2
2
.4. X-ray structure determinations
0.17 mm): C H N PPd, Cl, 2(CH Cl ) (621.14): mono-
18 34 2 2 2
clinic, P2 , a = 13.3080(14), b = 13.0846(7), c =
1
˚
3
˚
ꢁ1
Single crystals of 1,3-C H (CMe OH) and bis(carbamic
17.1308(11) A, b = 108.616(7)ꢁ, V = 2826.9(6) A , Z = 4,
6
4
2
2
ꢁ3
acid methyl ester) 1 were grown from THF/n-pentane.
Ligand 2 was structurally characterized as its bis(trifluoro-
acetate) [1,3-C H (CMe NH ) ](O CCF ) , 2 Æ (HAcf)2,
D
calc
= 1.459 g cm , l (Mo Ka) = 1.196 mm ; 2.95ꢁ 6
H 6 28.70ꢁ, 56486 reflections collected (ꢁ17 6 h 6 +17,
ꢁ17 6 k 6 +17, ꢁ23 6 l 6 +23), 14384 unique (R
=
int
6
4
2
3 2
2
3 2
crystals of which were obtained from ethanol/trifluoroace-
0.0334); wR = 0.0515 for all data and 524 parameters,
2
tic acid. Compounds 3 and 6 Æ 2CH Cl were crystallized
R = 0.0236 for 12971 intensities I > 2r(I); the specimen
1
2
2
from dichloromethane. Diffraction measurements were
investigated showed twinning by inversion with a ratio of
the twin domains close to unity: absolute structural param-
eter x = 0.51(2) [17].
made at +20(2) (1, 2 Æ (HAc ) , 3) and ꢁ90(2) ꢁC [1,3-
f 2
C H (CMe OH) ] on an Enraf–Nonius CAD-4 MACH 3
6
4
2
2
diffractometer and, for 6 Æ 2CH Cl , at ꢁ173(2) ꢁC on a
2
2
Bruker–Nonius Kappa CCD instrument using Mo Ka
3. Results and discussion
˚
radiation (k = 0.71073 A); data either uncorrected for
absorption [1,3-C H (CMe OH) , 1, 2 Æ (HAc ) ] or cor-
3.1. Ditertiary carbinamine ligand 2
6
4
2
2
f 2
rected for absorption using appropriate semi-empirical
[
[
11] (6 Æ 2CH Cl : T = 0.749, Tmax = 0.820) or refined
12] (3: Tmin = 0.522, Tmax = 0.850) methods. The struc-
Traditionally, tertiary carbinamines (compounds in
which the amino group is bonded to a tertiary carbon
atom) have been prepared by the Ritter reaction of tertiary
alcohols. The method employs the alcohol together with a
cyanide salt or an organic nitrile, typically MeCN, under
2
2
min
tures were solved by direct methods and subsequently
refined by full-matrix least-squares procedures on F with
2
allowance for anisotropic thermal motion of all non-hydro-
gen atoms employing both the SHELXTL NT 6.12 [13] and
the WINGX [14a] packages with some of the relevant pro-
grams (SIR-97 [15], SHELXL-97 [16], ORTEP-3 [14b]) imple-
mented therein. – 1,3-C H (CMe OH) (0.45 · 0.20 ·
strongly acidic conditions to form – by addition of the ini-
+
tially generated carbenium ions R C to the nitrile func-
3
0
+
0
tion – aminium intermediates [R CNCR ] (R = H, Me).
3
These are subsequently reacted with aqueous alkali to give
6
4
2
2
0
0
5
.13 mm): C H O (194.26); monoclinic, P2 /c, a =
acid amides R CNHC(O)R , from which the ‘‘Ritter
1
2
18
2
1
3
˚
.7178(9), b = 20.907(2), c = 9.030(1) A, b = 93.23(1)ꢁ,
amines’’ R CNH are set free by alkaline hydrolysis
3
2
3
ꢁ3
˚
V = 1077.7(2) A , Z = 4, D = 1.197 g cm , l (Mo
[18,19]. However, this protocol failed with 1,3-
C H (CMe OH) which is commericially available as a
calc
ꢁ
1
Ka) = 0.080 mm ; 1.95ꢁ 6 H 6 25.27ꢁ, 2151 reflections
collected (0 6 h 6 +6, 0 6 k 6 +25, ꢁ10 6 l 6 +10), 1951
unique (R = 0.0377); wR = 0.1739 for all data and 127
6
4
2
2
cheap industrial by-product formed in one of the technical
resorcinol processes. Attempted conversion of this diol to
1,3-C H (CMe NH ) with NaN in acidic solution and
int
2
parameters, R = 0.0626 for 1098 intensities I > 2r(I). – 1
1
6
4
2
2 2
3
(
0.40 · 0.32 · 0.27 mm): C H N O (308.37); monoclinic,
reduction of the resulting diazide to the diamine as
described for the preparation of cumylamine from a-cumyl
alcohol [20] likewise remained unsuccessful.
1
6
24
2
4
˚
P2 /n, a = 10.204(1), b = 12.196(2), c = 13.934(3) A,
1
3
˚
b = 100.40(1)ꢁ, V = 1705.6(5) A , Z = 4, Dcalc = 1.201
ꢁ
3
ꢁ1
g cm , l (Mo Ka) = 0.086 mm ; 2.24ꢁ 6 H 6 30.36ꢁ,
In the literature, the synthesis of tertiary carbinamines
has also been achieved by the Ciganek reaction of nitriles,
which involves the double addition to the RC „ N triple
bond of organocerium reagents, generated in situ from
anhydrous cerium trichloride and alkyllithium reagents
[21–23]. In fact, the para and meta isomers of dicyanoben-
zene were briefly reported to produce 1,4-C H (CMe NH )
2 2
5
0
341 reflections collected (ꢁ14 6 h 6 +14, 0 6 k 6 +17,
6 l 6 +19), 5153 unique (R = 0.0185); wR = 0.1512
int
2
for all data and 202 parameters, R = 0.0517 for 3396
intensities I > 2r(I). – 2 Æ (HAc ) (0.35 · 0.25 · 0.23 mm):
C H N , 2(C F O ) (420.36); monoclinic, P2 /c, a =
1
f 2
1
2
22
2
2
3
2
1
˚
1
0.363(2), b = 17.0298(9), c = 11.538(2) A, b = 102.93(1)ꢁ,
6
4
2
3
ꢁ3
˚
V = 1984.6(5) A , Z = 4, D = 1.407 g cm , l (Mo
and 1,3-C H (CMe NH ) , i.e., compound 2, if reacted with
6 4 2 2 2
calc
ꢁ
1
Ka) = 0.136 mm ; 2.02ꢁ 6 H 6 25.37ꢁ, 3832 reflections
the CeCl /MeLi reagent [22]. As previously communicated,
3
collected (ꢁ12 6 h 6 +12, 0 6 k 6 +20, 0 6 l 6 +13),
we ourselves used the Ciganek protocol as a method of syn-
thesis for the pyridine-based N \ N \ N ligand 2,6-
C H N(CMe NH ) from 2,6-pyridinedicarbonitrile but
3
641 unique (R = 0.0275); wR = 0.1308 for all data
int 2
and 335 parameters, R = 0.0503 for 2036 intensities
I > 2r(I); CF
threefold rotational disorder of the CF3 groups. – 3
(
1
5
3
2
2 2
ꢁ
3
CO2 anions with two- and, respectively,
observed that its successful preparation critically depended
on the strict keeping to very narrow reaction parameters
[5]. In view of these limitations a more straightforward
(and less cost-intensive) method of synthesis was sought
for 1,3-C H (CMe NH ) (2). 1,3-Bis(1-isocyanato-1-meth-
0.35 · 0.08 · 0.06 mm): C H Cl N Rh (685.37); mono-
2
8
44
2
2
2
clinic, P2 /n, a = 11.594(3), b = 10.978(4), c = 22.521(4)
1
3
˚
˚
A, b = 90.96(2)ꢁ, V = 2866(1) A , Z = 4, D = 1.588
calc
6
4
2
2 2
ꢁ
3
ꢁ1
g cm , l (Mo Ka) = 1.357 mm ; 1.81ꢁ 6 H 6 24.18ꢁ,
ylethyl)benzene – a low-cost technical intermediate made by

1314
L. Dahlenburg et al. / Inorganica Chimica Acta 361 (2008) 1311–1318
C8
C7
C1
C9
2
MeOH
C13
O3
O
NH
HN
O
OCN
NCO
C15
C2
C12
C3
N1
MeO
(1)
OMe
C10
C16
N2
O4
O1
C14
O2
4
KOH / n-BuOH (refl.)
2 K2CO3, − 2 MeOH
C6
C4
C5
C11
−
H2N
NH2
(
2)
Fig. 2. Perspective view of 1,3-C
6
H
4
(CMe
2
NHCO
2
2
Me) (1); selected bond
˚
lengths (A) and angles (ꢁ): N1–C7, 1.477(2); N2–C12, 1.485(2); C1–C7,
.542(2), C3–C12, 1.534(2). N1–C7–C1, 111.6(1); N2–C12–C3, 110.4(1).
Scheme 1.
1
˚
Hydrogen bonds (A and ꢁ): N1(H)ꢂ ꢂ ꢂO3#1, 3.076(2) and 171.7(2);
N2(H)ꢂ ꢂ ꢂO1#2, 3.059(2) and 121.4(2) (symmetry transformations used
to generate equivalent atoms: #1 ꢁx + 1, ꢁy, ꢁz; #2 ꢁx + 1/2, y ꢁ 1/2,
the addition of isocyanic acid to 1,3-diisopropenylbenzene –
turned out to be particularly suitable for this purpose: stir-
ring with methanol at ambient conditions cleanly afforded
the bis(carbamic acid ester) 1,3-C H (CMe NHCO Me)
2
ꢁ
z + 1/2). Dihedral angles [ꢁ]: l.s.q. plane C1–C6 vs. plane N1ꢂ ꢂ ꢂC7ꢂ ꢂ ꢂC1,
1
7.5; l.s.q. plane C1–C6 vs. plane N2ꢂ ꢂ ꢂC12ꢂ ꢂ ꢂC3, 39.4.
6
4
2
2
(
(
1) which then was saponified in strongly alkaline medium
KOH/refluxing n-butanol) to produce high yields (>85%)
groups oriented to the same side of the phenylene backbone
ꢁ
as a result of hydrogen-bonding to the two F CCO2 coun-
3
of 2 (Scheme 1).
terions (Fig. 3). The OH functions of 1,3-C H (CMe OH)
2
6
4
2
Compound 2 was fully characterized by an X-ray struc-
ture analysis of the bis(trifluoroacetate) salt [1,3-
C H (CMe NH ) ](O CCF ) , 2 Æ (HAc ) . For the sake of
comparison, crystal structure determinations were also car-
ried out for its direct precursor 1 and the diol 1,3-
C H (CMe OH) representing the amide and OH analogues
likewise participate in multiple intermolecular hydrogen
bonds as do the NHCO Me residues of 1. Bond lengths
2
6
4
2
3 2
2
3 2
f 2
and angles within the a-CMe X groups of the three com-
2
pounds do not warrant further discussion since they are
close to those measured for some related molecules, such
as diol 1,4-C H (CMe OH) [24], the triol 1,3,5-
6
4
2
2
6
4
2
2
of 2. In the solid state, molecules of 1,3-C H (CMe OH)
2
exhibit approximate C symmetry with the hydroxyl groups
6
4
2
C H (CMe OH) [25], the 1,1,3,3-tetramethylisoindolinium
6
3
2
3
2
þ
cation 1; 2-C
tive C H CMe NHC(O)CH(Br)Bu-t [27].
6
H
4
ðCMe
2
Þ NH [26], and the amido deriva-
on opposite sides of the aromatic systems and only slightly
different dihedral angles between the ring l.s.q. plane and
the two planes defined by the meta- and a-carbon as well
as the oxygen atoms (Fig. 1). Molecules of bis(carbamic acid
ester) 1 deviate more severely from axial symmetry as shown
by the disparity of the two dihedral angles given in the leg-
2
2
6
5
2
C8
C11
+
+
þ
end to Fig. 2. Diammonium dication 2
has its NH3
C10
C9
C2
C3
N2
C7
O1
C12
C1
N1
C6 C5
C4
C4
C5
F1a
O3
F2
F4b F5a
C15
F1
C3
O4
C16
F2a
F4
C14
F5
C13
F3a
F4a
C9
C12
C11
F5b
C6
C7
C2
F3
O2
C10
O2
F6b
F6a
C1
F6
C8
Fig. 3. Perspective view of [1,3-C
with rotationally disordered CF
6
H
4
(CMe
2
NH
3
)
2
2 3 2 f 2
](O CCF ) , 2 Æ (HAc ) ,
groups in the anions; selected bond
lengths (A) and angles (ꢁ): N1–C7, 1.515(3); N2–C10, 1.520(3); C1–C7,
.537(4); C3–C10, 1.529(4). N1–C7–C1, 108.6(2); N2–C10–C3, 108.3(2).
O1
3
˚
1
˚
Fig. 1. Perspective view of 1,3-C
6
H
4
(CMe
2
OH)
2
; selected bond lengths
A˚ ) and angles (ꢁ): O1–C7, 1.445(4); O2–C10, 1.442(3); C2–C7, 1.535(4),
Hydrogen bonds (A and ꢁ): N1(H)ꢂ ꢂ ꢂO1, 2.856(3) and 174.9(2);
N2(H)ꢂ ꢂ ꢂO3, 2.815(3) and 164.3(2); N1(H)ꢂ ꢂ ꢂO2#1, 2.862(3) and
168.7(3); N1(H)ꢂ ꢂ ꢂO4#2, 2.839(3) and 174.4(2); N2(H)ꢂ ꢂ ꢂO1#3, 2.892(3)
and 156.9(3); N2(H)ꢂ ꢂ ꢂO3#3, 2.836(3) and 168.2(2) (symmetry transfor-
mations used to generate equivalent atoms: #1 x, ꢁy + 1/2, z ꢁ 1/2; #2
x + 1, y, z; #3 ꢁx, ꢁy, ꢁz + 1). Dihedral angles (ꢁ): l.s.q. plane C1–C6 vs.
plane N1ꢂ ꢂ ꢂC7ꢂ ꢂ ꢂC1, 45.6; l.s.q. plane C1–C6 vs. plane N2ꢂ ꢂ ꢂC10ꢂ ꢂ ꢂC3,
68.6.
(
C6–C10, 1.530(4). O1–C7–C2, 107.9(2); O2–C10–C6, 108.4(2). Hydrogen
˚
bonds (A and ꢁ): O1(H)ꢂ ꢂ ꢂO2#1, 2.892(3) and 164.0(3); O2(H)ꢂ ꢂ ꢂO1#2,
2
.892(3) and 166.3(2) (symmetry transformations used to generate
equivalent atoms: #1 x + 1, ꢁy + 1/2, z + 1/2; #2 x ꢁ 1, ꢁy + 1/2,
z ꢁ 1/2). Dihedral angles (ꢁ): l.s.q. plane C1–C6 vs. plane O1ꢂ ꢂ ꢂC7ꢂ ꢂ ꢂC2,
3
6.9; l.s.q. plane C1–C6 vs. plane O2ꢂ ꢂ ꢂC10ꢂ ꢂ ꢂC6, 36.4.

L. Dahlenburg et al. / Inorganica Chimica Acta 361 (2008) 1311–1318
1315
3
.2. Metal complexes
C11
C13
C24
Cl1
C10
C9
C12
C23
1
,3-Disubstituted aromatic hydrocarbons with two
meta-positioned alkylated or arylated nitrogen, phospho-
rus, sulfur, or selenium donors CH D (D = NR [6], PR
C6
N1
C20
C25
C26
Rh1
C22
C21
2
2
2
C27
C28
C5
C7
C8
C4
[
28], SR [29], or SeR [30]) are well known for their propen-
C19
C1
sity to form ‘‘pincer’’ complexes [{C H (CH D) -
o,o }ML ] by chelation-assisted orthometalation at C-2 if
C2
C3
6
3
2
2
C14
Rh2
0
C18
n
N2
C15
Cl2
treated with suitable precursors of the platinum metals.
Thus, the cyclometalation through activation of aryl-C–H
bonds adjacent to tertiary benzylamine (or 2-pyridyl) func-
tionalities has been established as one of the most simple
and widely applicable methods for the construction of met-
alacycles – in particular, palladacycles [31]. However, this
orthometalation (specifically, orthopalladation) reaction
will normally not occur with primary benzylamines except
that the amine, the metal precursor and the reaction condi-
tions (solvent and temperature) meet very narrow require-
ments [31–33].
C17
C16
4
Fig. 4. Perspective view of the complex molecule [{(g -1,5-
8 2 6 4 2 2 2
C H12)RhCl} {l-1,3-C H (CMe NH ) }], 3 (hydrogen atoms are omitted
˚
for clarity); selected bond lengths (A) and angles (ꢁ): Rh1–N1, 2.186(5);
Rh1–Cl1, 2.386(2); Rh2–N2, 2.165(6); Rh2–Cl2, 2.382(2). N1–Rh1–Cl1,
4.1(1); N2–Rh2–Cl2, 83.8(1); Rh1–N1–C9, 126.4(4); Rh2–N2–C15,
8
129.9(4).
III
those previously measured for the Rh complex mer-
[RhCl {2,6-C H N(CMe NH ) }] bearing 2,6-bis(a-
aminoisopropyl)pyridine chelate ligand: 2.165 and
When 1,3-C H (CMe NH ) (2) was reacted with
a
6
4
2
2 2
3
5
3
2
2 2
RhCl Æ xH O in ethanol under the conditions described
3
2
0
˚
˚
for the preparation of [RhCl {C H (CH NMe ) -o,o }-
2.185 A versus 1.948 and 2.075 A [5]. The near axial-sym-
metric geometry of the molecule observed in the solid state
is stabilized by intermolecular NHꢂ ꢂ ꢂCl hydrogen bonds:
2
6
3
2
2 2
(
OH )] [34], a red–brown precipitate was formed that con-
2
1
tained non-metalated 2 ( H NMR) but could not be worked
up to give any unequivocally identifiable product. We
assume that this material is similar to the one postulated
to be composed of the initial coordination complexes
between 1,3-C H (CH NMe ) and hydrated RhCl , i.e.,
˚
d(NHꢂ ꢂ ꢂCl), 3.446(6) A; N–Hꢂ ꢂ ꢂCl, 158.4(2)ꢁ.
1
The H NMR spectra of 3 are significantly temperature-
dependent: at ꢁ50 ꢁC in CDCl , the NH and @CH signals
3
2
appear as slightly broadened singlets at d = 3.40, 3.54, and
4.42 with relative intensities corresponding to 4H each; the
16 methylene protons give rise to four unresolved multiplets
6
4
2
2 2
3
has an N \ C(H) \ N ligand bonded in a bidentate fashion
to a single metal center and/or bears one rhodium atom
on each nitrogen donor of a bridging diamine [34]. With
of equal intensity located at d = 1.51, 1.63, 2.12, and 2.24
and the four CH groups show equivalence of their H
I
1
Rh as the central metal, such a 1,3-bis(a-aminoisopro-
3
4
pyl)benzene-linked dinuclear complex, [{(g -1,5-C H )-
nuclei causing a singlet resonance at d = 1.76. At 25 ꢁC,
the signals of the amine and olefinic protons merge into a
very broad resonance centered at d = 4.25, the methyl and
methylene protons appearing as two broadened peaks at
d = 1.66 and 2.35. The low-temperature spectrum is consis-
tent with the presence in solution of 3 as N,N-bridged mol-
ecules with conformations resembling the one found in the
solid state. The broad overlapping resonances observed at
higher temperature point to exchange processes between
8
12
RhCl} {l-1,3-C H (CMe NH ) }] (3), was isolated from
2
6
4
2
2 2
4
the reaction of 2 with [{(g -1,5-C H )Rh(l-Cl)} ] in
8
12
2
toluene (Scheme 2). As far as we are aware, there are only
two well-defined previous examples possessing a non-cyclo-
metalated 1,3-C H (CR D) linkage with two terminally
6
4
2
2
‘
‘dangling’’ complex fragments, viz. [(MeReO ) {l-1,3-
3 2
C H (CH NMe ) }] [35] and [{[2,6-C H N(CH NMe ) ]R-
6
4
2
2 2
5
3
2
2 2
uCl } {l-1,3-C H (CH PPh ) }] [36].
2
2
6
4
2
2 2
4
In the crystal structure of 3, the CMe NH donors are
differently coordinated ‘‘(g -1,5-C H )Rh’’ forms present
2
2
8
12
positioned on opposite sides of the aromatic ring in such
in temperature-dependent equilibria which, however, could
4
a way that the molecule displays approximate C symmetry
not be resolved. Such species could include [(g -1,5-
2
+
4
ꢁ
2
along the C13ꢂ ꢂ ꢂC19 axis (Fig. 4). Not unexpectedly, the
C H )Rh(N \ N)] and [{(g -1,5-C H )RhCl ] ions as
8
12
8
12
bonds between nitrogen and rhodium are much longer than
were previously proposed in order to account for the
solution behavior of several related [{(g -1,5-C H )-
4
8
12
RhCl} (l-N \ N)] complexes bridged by aliphatic diamines
2
2
[
37], j -bonded tris- and bis(pyrazolyl)amines [38], or
1
,3-C6H4(CMe2NH2)2
Cl
Cl
Rh
Rh
a-diimines [39,40].
Heating equimolar mixtures of 2 with PdCl2 or
K [PdCl ] in acetonitrile gave the sparingly soluble bis(dia-
2
4
Cl
Rh
mine)-bridged dipalladium complex trans,trans-[{l-1,3-
C H (CMe NH ) } (PdCl ) ] (4), precipitating directly
NH2
6
4
2
2 2 2
2 2
NH2
Cl
Rh
from solution, together with cyclometalated [{2,6-
(3)
1
0
C H (CMe NH ) -jN,jC ,jN }PdCl] (5), which was iso-
6
3
2
2 2
Scheme 2.
lated from the mother liquor (Scheme 3).

1316
L. Dahlenburg et al. / Inorganica Chimica Acta 361 (2008) 1311–1318
between 5 and triethylphosphine, which produces [{2,6-
1
0
C H (CMe NH ) -jN,jC ,jN }Pd(PEt )]Cl (6) together
PdCl2 or K2[PdCl4]
6
3
2
2 2
3
with some N \ C \ N-free trans-[PdCl (PEt ) ] within 30
2
3 2
H2N
NH2
min at room temperature (Scheme 3). Prior to this work,
1
0
Cl
[{2,6-C H (CH NMe ) -jN,jC ,jN }Pd(PPh )]BF , obtained
6 3 2 2 2 3 4
H2
N
ꢁ
by substituting PPh for the weakly bound BF ligand of
3
4
N
Pd
Cl
H2
1
0
[{2,6-C H (CH NMe ) -jN,jC ,jN }Pd(FBF )], was briefly
6
3
2
2 2
3
Cl
described as the only other example of an N \ C \ N pincer
complex of Pd(II) containing an additional phosphine
ligand [45a]. Closely related compounds that have been
studied in some more detail, include the P \ C \ P-coordi-
+
H2N
Pd
Cl
NH2
H2
N
N
Pd
Cl
H2
(
4)
(5)
1
0
+
−
Cl
nated cation [{2,6-C H (CH PPh ) -jP,jC ,jP }Pd(PEt )]
6 3 2 2 2 3
PEt3
[46] as well as the Pt(II)-centered N \ C \ N chelates [{2,6-
0
1 +
C H (CH NMe ) -jN,jC ,jN }Pt(PR )] , where PR = PPh
3
6
3
2
2 2
3
3
H2N
Pd
NH2
[
45a–c] or PHPh [45d].
Pincer complex 6 was characterized both spectroscopi-
2
PEt3
(
6)
cally and by an X-ray structure analysis of its solvate
6
3
1
1
Scheme 3.
Æ 2CH Cl . The cation exhibits a P{ H} singlet reso-
2 2
nance at d = 8.67 (downfield of free PEt at d @ ꢁ29). An
3
1
unusual H NMR feature worth mentioning is the observa-
The bimetallic structure of 4 containing a 16-membered
tion of long-range spin–spin coupling over six bonds
between the phosphorus nucleus and the para proton of
the aromatic ring, which appears as a doublet of doublets
with J(H,H) = 7.53 and J(P,H) = 2.64 Hz [47]. The
asymmetric unit of the triclinic unit cell of the dichloro-
methane-solvated complex contains two crystallographi-
macrocycle with two trans-PdCl2 building blocks was
inferred from the results of FAB mass spectrometry and
far-infrared spectroscopy: The mass spectrum showed the
3
6
+
+
dipalladium cations [C H Cl Pd ] and [C H ClPd ]
2
4
40
3
2
24 38
2
with correct isotopic distributions of their traces as the most
abundant fragments in the m/z range covering the molecu-
lar ion and dimetallic fragments derived therefrom, and in
the infrared the complex displayed but one Pd–Cl stretching
C29
C32
C31
C36
N4
ꢁ
1
35
ꢁ1
C30
C33
C28
at 318 cm
[m(Pd– Cl)] with a shoulder at 313 cm
3
7
C34
[
m(Pd– Cl)], as expected for the two trans-Pd(NH R) Cl
2
2
2
C23
P2
building blocks [41]. Although band-broadening due to
the presence of six stable palladium isotopes (102, 104,
C22
C21
Pd2
C24
3
5
C3
C8
C35
1
05, 106, 108, and 110) could blur the m(Pd– Cl)/
C2
3
7
N3
m(Pd– Cl) splitting of the M–Cl vibration of the com-
pound, conditions are favorable for observing (and assign-
ing) the isotopically split Pd–Cl stretching vibration of 4
because of the lessened influence of the high atomic weight
of the metal on the reduced mass of the system [42]. Dipal-
ladium complexes having crystallographically established
macrocyclic trans,trans-[(l-N \ N) (PdCl ) ] structure
C19
C25
C1
C4
C5
C20
C9
C7
N1
C26
C27
C12
C14
C6
Pd1
P1
C10
C11
Cl1
N2
C13
2
2 2
C15
C16
C17
motifs similar to the one derived for 4 from spectroscopic
Cl2
data were recently obtained by combining [PdCl (NCPh) ]
C18
2
2
0
with meta-phenylene-based N,N -bis(pyridin-3-yl)-1,3-ben-
Fig. 5. Perspective view of the two crystallographically independent
zenedicarboxamide ligands such as 1,3-C H (CON-
1
0
6
4
hydrogen-bonded
ion-pairs
Cl (carbon-bonded hydrogen atoms omitted for
[{2,6-C H (CMe NH ) -jN,jC ,jN }-
6 3 2 2 2
HC H N-3) and the like [43].
5
4
2
Pd(PEt )]Cl of 6 Æ 2CH
3
2
2
˚
The presence of a direct metal-to-aryl linkage in [{2,6-
clarity); selected bond lengths (A) and angles (ꢁ): Pd1–P1, 2.3591(7); Pd1–
N1, 2.080(2); Pd1–N2, 2.085(2); Pd1–C6, 1.956(2); Pd2–P2, 2.3652(6);
Pd2–N3, 2.094(2); Pd2–N4, 2.090(2); Pd2–C24, 1.955(2). P1–Pd1–N1,
1
0
C H (CMe NH ) -jN,jC ,jN }PdCl] (5) was evidenced
6
3
2
2 2
1
13
1
from both the H and C{ H} NMR spectra, where the
remaining three meta and para phenylene protons H-3,5
and H-4 appear as separate doublet and triplet signals
9
1
1
8.48(6); P1–Pd1–N2, 101.55(6); P1–Pd1–C6, 177.02(7); N1–Pd1–N2,
59.74(8); N1–Pd1–C6, 79.82(9); N2–Pd1–C6, 80.29(9); P2–Pd2–N3,
01.45(6); P2–Pd2–N4, 99.52(6); P2–Pd2–C24, 176.35(7); N3–Pd2–N4,
1
3
(
d = 6.46 and 6.75) and the C resonance of the metal-
159.01(8); N3–Pd2–C24, 79.53(9); N4–Pd2–C24, 79.48(9). Hydrogen
˚
bonds (A and ꢁ): N1(H)ꢂ ꢂ ꢂCl1, 3.272(2) and 152.72(1); N2(H)ꢂ ꢂ ꢂCl2,
bound ipso atom C-1 displays the significant downfield
shift (d = 155.13 versus d = 126.83 for the free ligand)
known to be diagnostic of carbon coordination to a transi-
tion metal [44]. The chlorido ligand opposite to the Pd–C
bond is substitutionally labile as shown by the reaction
3
.690(2) and 146.78(1); N3(H)ꢂ ꢂ ꢂCl2, 3.510(2) and 148.26(1);
N2(H)ꢂ ꢂ ꢂCl1#1, 3.414(2) and 159.18(1); N3(H)ꢂ ꢂ ꢂCl2#2, 3.389(2) and
1
70.92(1); N4(H)ꢂ ꢂ ꢂCl2#3, 3.341(2) and 151.71(1) (symmetry transforma-
tions used to generate equivalent atoms: #1 ꢁx, y + 1/2, ꢁz + 1; #2 ꢁx,
y ꢁ 1/2, ꢁz + 1; #3 x, y, z + 1).

L. Dahlenburg et al. / Inorganica Chimica Acta 361 (2008) 1311–1318
1317
cally independent ion-pairs linked by multiple hydrogen-
bonding (Fig. 5). The structures of the cations are based
on four-coordinate Pd(II) centers in slightly distorted
square-planar environments where the palladium and
phosphorus atoms deviate from the planes defined by the
donor atoms of the terdentate N \ C \ N ligand by 0.01
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit
@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.ica.2007.08.027.
˚
and 0.28 in molecule 1 as well as by 0.06 and 0.17 A in mol-
References
ecule 2. The Pd–NH2 bond lengths fall in the range
˚
2
.080(2)–2.094(2) A and thus are only marginally shorter
[1] M.D. Fryzuk, C.D. Montgomery, Coord. Chem. Rev. 95 (1989) 1,
˚
than the Pd–NMe distances of 2.108(2) and 2.109(9) A
2
and refs. cited therein.
previously measured for the cation of [{2,6-C H -
[2] (a) K. Abdur-Rashid, A.J. Lough, R.H. Morris, Organometallics 19
(2000) 2655;
6
3
1
0
(
CH NMe ) -jN,jC ,jN }Pd(OH )]BF [45e]. In the latter
2
2 2
2
4
(
(
(
b) K. Abdur-Rashid, A.J. Lough, R.H. Morris, Organometallics 20
2001) 1047;
c) K. Abdur-Rashid, M. Faatz, A.J. Lough, R.H. Morris, J. Am.
complex the length of the Pd–C
bond trans to Pd–OH2
ipso
˚
amounts to 1.909(2) A. Because of the substantially higher
trans-bond weakening influence of a phosphine than that
of an aqua ligand the corresponding Pd–aryl bonds in cat-
Chem. Soc. 123 (2001) 7473;
(d) K. Abdur-Rashid, S.E. Clapham, A. Hadzovic, J.N. Harvey, A.J.
Lough, R.H. Morris, J. Am. Chem. Soc. 124 (2002) 15104.
[3] J.F. Hartwig, J. Am. Chem. Soc. 118 (1996) 7010, and refs. cited
therein.
+
˚
ions 6 are elongated to 1.955(2) and 1.956(2) (A). The
˚
Pd–PEt distances of 2.3591(7) and 2.3652(6) A compare
3
˚
favorably with that of 2.358(2) A found for the two crystal-
[4] (a) L. Dahlenburg, R. G o¨ tz, Inorg. Chem. Commun. 6 (2003) 443;
lographically identical Pd–P bonds of [{2,6-C H -
6
3
(b) L. Dahlenburg, R. Gotz, Eur. J. Inorg. Chem. (2004) 888.
¨
1
0
(
CH PPh ) -jP,jC ,jP }Pd(PEt )]BF [46].
[5] L. Dahlenburg, H. Treffert, J. Dannh a¨ user, F.W. Heinemann, Inorg.
Chim. Acta 360 (2007) 1474.
2
2 2
3
4
[
6] For representative examples of organometallic compounds showing
4
. Concluding remarks
The ditertiary carbinamine 1,3-C H (CMe NH ) has
0
the cyclometalated [{C
6
H
3
(CH
2
NMe
2
)
2
-o,o }ML
n
] ‘‘pincer’’ motif,
see, e.g., the following overviews: (a) G. van Koten, Pure Appl. Chem.
61 (1989) 1681;
6
4
2
2 2
been prepared by a straightforward two-step synthesis
based on commercial 1,3-C H (CMe NCO) as an inex-
(b) P. Steenwinkel, R.A. Gossage, G. van Koten, Chem. Eur. J. 4
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6
4
2
2
(
(
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pensive starting material. A first study of its coordination
behavior towards platinum metal ions has shown that the
3
750.
4
diamine can form bimetallic complexes such as [{(g -1,5-
[
7] D. Song, R.H. Morris, Organometallics 23 (2004) 4406.
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8
12
2
6
4
2
2 2
[
{l-1,3-C H (CMe NH ) } (PdCl ) ] with one or two
6 4 2 2 2 2 2 2
[
[
N,N-bridges but can also produce N \ C \ N-chelated
metalaheterocycles as examplified by [{2,6-C H (CMe -
6
3
2
1
0
NH ) -jN,jC ,jN }PdCl] and [{2,6-C H (CMe NH ) -
jN,jC ,jN }Pd(PEt )]Cl. Further work aiming at the
2
2
6
3
2
2 2
1
0
3
extension of the cyclometalation chemistry displayed by
the 1,3-C H (CMe NH ) ligand and the synthesis of sta-
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6
4
2
2 2
ꢁ
ꢁ
ble amido derivatives with H N \ C \ NH ‘‘pincer’’
2
[
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[
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Acknowledgements
[
[
Support of this work by the Deutsche Forschungsgeme-
inschaft (Bonn, SFB 583) and the Fonds der Chemischen
Industrie (Frankfurt/Main) is gratefully acknowledged.
We are also indebted to Mrs. S. Hoffmann and Mr. P. Bak-
atselos for their skilful assistance.
(
b) J.J. Ritter, J. Kalish, Org. Synth. 44 (1964) 44.
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(
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(
[
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[
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6
4
2
2
f 2
2
2
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[
[
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