Synthesis and coordination compounds of a bis(imino)acenaphthene (BIAN)-supported N-heterocyclic carbene

Article abstract of DOI:10.1039/c0dt00278j

The bis(imino)acenaphthene-supported N-heterocyclic carbene IPr(BIAN) has been prepared by deprotonation of the precursor imidazolium chloride. Treatment of IPr(BIAN) imidazolium chloride with Ag₂O afforded the silver complex [IPr(BIAN)]AgCl which can be converted into the corresponding gold complex [IPr(BIAN)]AuCl by reaction with (tht)AuCl (tht = tetrahydrothiophene). The iridium complex [IPr(BIAN)]Ir(COD)Cl was prepared by reaction of the imidazolium chloride with KO^tBu and [Ir(COD)Cl]₂ and subsequently converted to the carbonyl complex [IPr(BIAN)]Ir(CO)₂Cl by exposure to an atmosphere of CO. All new compounds were characterized by single-crystal X-ray diffraction, multinuclear NMR, MS and HRMS data.

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and coordination compounds of a bis(imino)acenaphthene
(BIAN)-supported N-heterocyclic carbene†‡
Kalyan V. Vasudevan,a Rachel R. Butorac,a Colin D. Abernethyb and Alan H. Cowley*a
Received 9th April 2010, Accepted 25th May 2010
First published as an Advance Article on the web 13th July 2010
DOI: 10.1039/c0dt00278j
The bis(imino)acenaphthene-supported N-heterocyclic carbene IPr(BIAN) has been prepared by
deprotonation of the precursor imidazolium chloride. Treatment of IPr(BIAN) imidazolium chloride
with Ag2O afforded the silver complex [IPr(BIAN)]AgCl which can be converted into the
corresponding gold complex [IPr(BIAN)]AuCl by reaction with (tht)AuCl (tht = tetrahydrothiophene).
The iridium complex [IPr(BIAN)]Ir(COD)Cl was prepared by reaction of the imidazolium chloride
with KOtBu and [Ir(COD)Cl]2 and subsequently converted to the carbonyl complex
[IPr(BIAN)]Ir(CO)2Cl by exposure to an atmosphere of CO. All new compounds were characterized by
single-crystal X-ray diffraction, multinuclear NMR, MS and HRMS data.
Introduction
In comparison with phosphines, N-heterocyclic carbenes are not
particularly amenable to ligand tuning by changing the steric and
electronic characteristics of the substituents. One way to extend
the scope of NHC ligand tuning is by means of architectural
change. In this context, there is a steadily growing interest
in the annulation of NHCs with a variety of carbocyclic and
heterocyclic rings.1,2 Such ring fusions have been shown to have a
significant impact on the stabilities of and bonding in the resulting
annulated species. Representative examples of 4,5-fused rings
include benzene,1a pyridine,1b naphthalene,1c phenanthrene,1c,d
a novel benzene-supported bis(carbene),1e and a redox-active
naphthoquinone derivative.1f (Fig. 1)
Results and discussion
Syntheses of 1–7
Ligands of the bis(imino)acenaphthene (BIAN) class seemed
like promising candidates for fusion to NHCs, not only because
of their structural rigidity, but also on account of their redox
behavior.3 The annulation proposed herein would result in an
Arduengo-type4 NHC (A). Such a carbene would also represent an
interesting contrast with the saturated Wanzlick-type5 (B) BIAN
carbene which has been described recently.6 Thus, A is anticipated
to possess a planar skeleton while B has been shown to be bent
along the saturated C–C bond. A further differentiating feature
is that, in principle, the carbenic carbon of A is in conjugative
contact with the naphthalene moiety. Examples of Group 14
homologues of A are confined to the germylenes (dipp-BIAN)Ge,
(dtb-BIAN)Ge and (bph-BIAN)Ge (dipp = 2,6-i-Pr2C6H3; dtb =
2,5-t-Bu2C6H3; bph = 2-PhC6H4.7
The BIAN imidazolium chloride 1 (Scheme 1) was prepared by
heating a mixture of dipp-BIAN and methoxy(methyl) chloride in
a thick-walled glass tube. Recrystallization of the resulting yellow
powder from a dichloromethane–toluene mixture afforded a crop
of single crystals of 1 suitable for X-ray analysis. The yield of
analytically pure 1 prior to recrystallization was 86%. In some
instances,8 difficulties or failures have been reported in attempted
deprotonations of annulated imidazolium salts to form the corre-
sponding NHCs. However, in the present case, the deprotonation
of 1 with KOtBu in THF solution proceeded smoothly to produce
the corresponding yellow carbene, IPr(BIAN) 2 in moderate (71%)
yield. X-ray quality crystals of 2 were grown from a 1 : 1 toluene–
THF solution. Interestingly, when the deprotonation of 1 was
carried out in THF solution and worked up in toluene, a red,
ring-opened product 3 was also produced in low yield (19%).
Compound 3 is believed to be formed by hydrolysis of 2 since
yellow solutions of the latter slowly develop a red coloration
upon standing. Ring-opened products have also been reported
to be formed in 80–85% yields when the corresponding saturated
imidazolium salts were treated with a variety of deprotonation
agents in THF solution.6 Our results further emphasize the
finding that the deprotonation of annulated imidazolium salts
to the corresponding carbenes is highly sensitive to the reaction
conditions.6,8
aDepartment of Chemistry and Biochemistry, University of Texas at Austin,
1 University Station, A5300, Austin, TX 78712, USA. E-mail: cowley@
mail.utexas.edu; Tel: +1 512 471-7484
bDepartment of Chemistry, Sarah Lawrence College, 1 Mead Way,
Bronxville, NY, 10708, USA
† Dedicated to Professor David W. H. Rankin on the occasion of his
retirement.
‡ CCDC reference numbers for compounds 1–7 are 771968–771974.
For crystallographic data in CIF or other electronic format see DOI:
10.1039/c0dt00278j
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Fig. 1 Representative examples of N-heterocyclic carbenes annulated at the 4 and 5 positions.
Scheme 1 Synthesis of IPr(BIAN) and metal complexes (i) MeOCH2Cl, 100 ◦C, 16 h; (ii) KOtBu, THF, 25 ◦C, 12 h; (iii) Ag2O, CH2Cl2–THF, 25 ◦C,
16 h; (iv) (tht)AuCl, CH2Cl2, 25 ◦C, 12 h; (v) KOtBu, [Ir(COD)Cl]2, tol, 25 ◦C, 2 h; (vi) CO(atm), CH2Cl2, 25 ◦C, 1 h.
The reaction of imidazolium chloride 1 with Ag2O in CH2Cl2–
THF solution at ambient temperature afforded an excellent
(92%) yield of the anticipated IPr(BIAN) silver chloride com-
plex 4. Yellow crystals of 4 appropriate for single-crystal
X-ray analysis were grown from a saturated solution of 4 in 3 : 1
dichloromethane–hexane. In turn, treatment of 4 with (tht)AuCl
afforded the corresponding AuCl complex 5. X-ray quality crystals
of 5 were grown from a saturated THF–hexanes solution. The
Ir(COD)Cl complex of IPr(BIAN) (6) was produced by treatment
of imidazolium chloride 1 with KOtBu and [Ir(COD)Cl]2 in
7402 | Dalton Trans., 2010, 39, 7401–7408
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Table 1 Selected crystal data, data collection and refinement parameters for compounds 1, 2, 4–7
1
2
4
5
6
7
Formula
C53H61Cl5N2
903.29
Monoclinic
C37H40N2
512.71
Monoclinic
C37H40AgClN2
656.03
Triclinic
¯
P1
12.027(2)
15.592(3)
18.241(4)
83.15(3)
83.04(3)
82.24(3)
4
C45H56AuClN2O2
889.33
Monoclinic
C45H52ClIrN2
848.60
Monoclinic
C39H40ClIrN2O2
796.38
Orthorhombic
Formula weight
Crystal system
Space group
P21/c
Cc
P21/c
P21/c
Pnma
˚
a/A
12.958(3)
17.012(3)
21.450(4)
90.0
98.35(3)
90.0
9.823(5)
14.604(5)
21.114(5)
90.0
101.882(5)
90.0
15.007(3)
17.331(4)
17.298(4)
90.0
115.01(3)
90.0
19.933(4)
12.719(3)
15.990(3)
90.0
112.63(3)
90.0
12.468(3)
18.494(4)
14.718(3)
90.0
90.0
90.0
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
Z
4
4
4
4
4
Dc/g cm-3
F(000)
1.283
1912
1.149
1104
1.302
1360
1.449
1808
1.506
1720
1.559
1592
Crystal size/nm
H range/◦
Collected reflections
Independent reflns
Rint
0.13 ¥ 0.12 ¥ 0.05
1.53–27.49
19190
10713
0.0859
0.0774
0.1764
0.33 ¥ 0.20 ¥ 0.12
3.42–27.48
13027
3398
0.0367
0.0707
0.1819
0.10 ¥ 0.07 ¥ 0.06
1.72–27.46
21840
15211
0.0268
0.0463
0.0849
0.43 ¥ 0.46 ¥ 0.16
3.00–26.00
43245
8003
0.0286
0.0248
0.0592
0.14 ¥ 0.08 ¥ 0.05
1.95–25.00
11443
6582
0.0593
0.0395
0.0594
0.29 ¥ 0.27 ¥ 0.11
2.20–26.25
6370
3529
0.0693
0.0436
0.0751
R1 [I > 2s(I)]
wR2 (all data)
◦
˚
Table 2 Selected bond distances (A) and angles ( ) for compounds 1, 2, 4–7
1
2
4
5
6
7
˚
Bond distances/A
C(1)–N(1)
C(1)–N(2)
C(2)–C(3)
1.345(4)
1.336(4)
1.354(4)
1.378(4)
1.374(4)
1.379(5)
1.377(5)
1.373(5)
1.387(5)
1.389(5)
1.363(4) [1.372(4)]
1.376(3) [1.370(4)]
1.349(4) [1.365(4)]
1.377(3) [1.384(4)]
1.383(3) [1.378(3)]
1.362(3)
1.356(3)
1.358(4)
1.374(4)
1.379(3)
1.392(6)
1.382(7)
1.359(7)
1.389(7)
1.388(7)
1.371(6)
1.371(6) [C(1)–N(1)i]
1.348(11) [C(2)–C(2)i]
1.388(7)
C(2)–N(1)
C(3)–N(2)
1.388(7) [C(2)i–N(1)i]
Bond angles/◦
N(1)–C(1)–N(2)
N(1)–C(2)–C(3)
C(2)–C(3)–N(2)
C(1)–N(1)–C(2)
C(1)–N(2)–C(3)
109.4(3)
107.4(3)
107.9(3)
107.6(2)
107.7(2)
103.0(3)
106.8(3)
106.0(3)
111.9(3)
112.3(3)
105.5(2) [105.1(2)]
107.4(2) [107.2(2)]
107.7(2) [107.0(3)]
110.2(2) [110.1(3)]
109.3(2) [110.6(2)]
105.7(2)
107.3(2)
106.9(2)
110.0(2)
110.1(2)
104.9(5)
108.2(5)
107.1(5)
109.4(5)
110.5(4)
105.7(6) [N(1)–C(1)–N(1)i]
107.5(3) [N(1)–C(2)–C(2)i]
107.5(3) [C(2)–C(2)i–N(1)i]
109.6(5)
109.6(5) [C(1)–N(1)i–C(2)i]
toluene solution. Orange-red 6 was isolated in 78% yield and
a small crop of single crystals suitable for X-ray analysis was
grown from a saturated hexanes solution. Finally, the yellow
IPr(BIAN)[Ir(CO)2Cl] complex 7 was produced by exposure of
a dichloromethane solution of 6 to an atmosphere of CO for 1 h.
A few crystals of X-ray quality were produced from a saturated
solution of 7 in hexanes.
˚
The average C(1)–N(1,2) bond length of 1.341(4) A for the
˚
imidazolium cation 1 is 0.037 A shorter than that observed in
the case of the corresponding carbene 2 (Fig. 2) for which this
distance is 1.378(5) A. As discussed elsewhere, bond shortening
of this magnitude is attributable to the loss of p-delocalization
across the N(1)–C(1)–N(2) moiety of the imidazolium salt and is
also consistent with carbene formation. A similar trend is evident
in the corresponding non-annulated imidazolium chloride and
6
˚
IPr for which the pertinent average bond lengths are 1.339(5) and
Characterization of 1–7
9
˚
1.366(3) A, respectively.
Compounds 1, 2, and 4–7 were characterized on the basis
Structural comparisons between our Arduengo-type NHC (A)
and the related, saturated Wanzlick-type NHC (B)6 are also of
interest. The major architectural difference between these two
annulated carbenes relates to the fact that carbon atoms C(2)
and C(3) adopt trigonal planar and tetrahedral geometries in A
and B, respectively. Accordingly, the C(2)–C(3) separation in B
of 1H and 13C NMR, MS, HRMS, and single-crystal X-ray
1
diffraction. The H, 13C, MS and HRMS data are presented in
the Experimental section. Compound 3 was characterized solely
by X-ray crystallography.
˚
(1.558(2) A) corresponds to that of a single bond while A, with a
X-ray crystallographic studies
˚
bond distance of 1.373(5) A, clearly possesses some double bond
Compounds 1–7 were structurally authenticated on the basis
of single-crystal X-ray diffraction studies. A summary of data
collection details appears in Table 1 and a selection of pertinent
metrical parameters is presented in Table 2. Further details are
available as electronic supplementary information (ESI).1
character—albeit less than that in the precursor imidazolium salt
9
˚
(1) or IPr where these distances are 1.354(4) and 1.336(3) A,
respectively. Further comparison of the structure of 2 with that of
IPr9 is also instructive since it reveals the other structural changes
that take place upon annulation. In terms of bond distances, the
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As pointed out earlier, the red, crystalline compound 3 appar-
ently originates from hydrolysis of carbene 2. Complete details
of the X-ray analysis of 3 are provided in the ESI‡. A database
search revealed that there is no structure that is exactly analogous
to that of 3. A noteworthy feature of the structure (Fig. 3) is the
˚
C(2)–C(3) distance of 1.383(2) A which corresponds to that of a
=
somewhat long C C bond. Although C(2)–N(1) and C(3)–N(2)
˚
are both single bonds, the latter is ~0.05 A shorter than the former.
Moreover, the N(1)–C(1) distance is shorter than the N(1)–C(2)
separation which is suggestive of a modicum of delocalization
across the O(1)–C(1)–N(1) fragment.
The IPr(BIAN)AgCl complex 4 crystallizes with two indepen-
dent molecules in the asymmetric unit. However, the metrical
parameters for both molecules are very similar hence only one
molecule is displayed in Fig. 4. The C–Ag and Ag–Cl bond
distances and the C–Ag–Cl bond angles (averaged over the crys-
˚
˚
tallographically independent molecules) of 2.067(3) A, 2.314(1) A
and 175.84(9)◦, respectively, are very similar to those reported
˚
for the non-annulated complex (IPr)AgCl, namely 2.056(6) A,
◦
10
˚
2.316(17) A and 175.2(2) , respectively. The coordination of
IPr(BIAN) 2 to AgCl prompts some significant changes in the
metrical parameters of the NHC ring. Thus, the C–C distance of
˚
1.357(4) A (averaged over the two crystallographically indepen-
dent molecules) is somewhat shorter than that for the unligated
˚
IPr(BIAN) carbene (1.373(5) A). Other noteworthy changes that
accompany the coordination of the AgCl unit are widening of the
N–C–N angle by 2.3◦ and narrowing of the average C(carbene)–
N–C bond angles by ~2.1◦ and widening of the N–C–C bond
angles by ~1◦.
The metrical parameters for the NHC ring of the IPr(BIAN)–
AuCl complex (5) (Fig. 4) are almost identical with those of the
corresponding AgCl complex 4. Moreover, these bond lengths
and angles are very similar to those reported for non-annulated
(IPr)AuCl.11
Fig. 2 ORTEP diagrams of 1 (top) and 2 (bottom) with 35% probability
thermal ellipsoids. Hydrogen atoms except H1 of 1 are omitted for clarity.
The structures of the Ir(COD)Cl (6) and Ir(CO)2Cl (7) com-
plexes of the IPr(BIAN) carbene 2 are displayed in Fig. 5. The
˚
Ir–C(1) bond distance for 6 of 2.040(6) A is similar to the value
reported for the corresponding Wanzlick-type BIAN carbene
6
˚
(2.070(3) A). Furthermore, both values fall within the range of
˚
1.99–2.091 A reported in the literature for other (NHC)Ir(COD)Cl
1f
˚
complexes. Likewise, the Ir–C(1) bond distance of 2.089(7) A for
7 is also encompassed by the range of literature values of 2.065–
12
˚
2.122 A cited for this parameter. Additionally, the cis and trans
˚
Ir-carbonyl distances of 1.850(10) and 1.849(9) A, respectively are
close to the literature values of 1.827(4)–1.888(4) and 1.877(4)–
˚
1.900(5) A, respectively. Overall, the geometries, bond distances
and bond angles for the Ir(COD)Cl and Ir(CO)2Cl moieties
are very similar to those reported for the corresponding IPr
complexes.12 Similarly, the metrical parameters for the NHC rings
of 6 and 7 differ from those of the corresponding IPr complexes
in only a minor way.
Fig. 3 ORTEP diagram of 3 with 35% probability thermal ellipsoids.
Hydrogen atoms except H1 and H2n are omitted for clarity.
Assessment of the donor character of 2
˚
major changes comprise an average decrease of 0.041 A in C(2,3)–
Over the years, several methods have been proposed for deter-
mination of the electronic characteristics of the carbenic ligands
in metal complexes. While no attempt has been made here to
review the merits of the various approaches, we opted to use the
recently proposed method of Nolan et al.12,13 to estimate the donor
˚
N(1,2) and an average increase of 0.012 A in C(1)–N(1,2). From
the standpoint of bond angles, the major change is an increase in
the N(1)–C(1)–N(2) bond angle from 101.5(2)◦ to 103.0(3)◦ and a
decrease of ~1◦ in the average C–N–C angle.
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Fig. 4 ORTEP diagrams of 4 (left) and 5 (right) with 35% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
Fig. 5 ORTEP diagrams of 6 (left) and 7 (right) with 35% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
character of the IPr(BIAN) carbene 2. The method is based on
the magnitude of the average CO stretching frequency nav for each
particular [(NHC)Ir(CO)2Cl] complex. The Tolman Electronic
Parameter (TEP) is derived from the equation TEP = 0.847 ¥ nav
+ 336 cm-1.12,13 In the case of 7 the trans CO stretching frequencies
appear at 2053.95 and 2061.54 cm-1, while the cis CO stretching
frequencies appear at 1966.40 and 1973.90 cm-1 (doublets due to
Fermi resonance). These values are close to the ranges of 2055–
2072 and 1971–1989 cm-1 reported for other (NHC)Ir(CO)2Cl
complexes.11 The computed TEP value of 2042 cm-1 for 2 suggests
that it is a relatively strong donor. Unfortunately, despite several
attempts, it was not possible to record the 13C chemical shift for
the carbenic carbon of 2 due to low solubility and relaxation
effects.
Summary and conclusions
The first example of an “Arduengo-type” bis(imino)acenaphthene
(BIAN)-supported N-heterocyclic carbene, IPr(BIAN), has been
prepared and structurally authenticated. The AgCl, AuCl,
Ir(COD)Cl and Ir(CO)2Cl complexes of IPr(BIAN) have also
been synthesized, each of which was characterized on the basis
of single-crystal X-ray diffraction, multinuclear NMR, MS and
HRMS data. The magnitudes of the cis and trans infrared carbonyl
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stretching frequencies for IPr(BIAN)Ir(CO)2Cl and the TEP value
suggest that the carbenic carbon of IPr(BIAN) is a relatively strong
donor.
Preparations
IPr(BIAN) imidazolium chloride (1). IPr(BIAN) (1.00 g,
0.002 mol) and methoxy(methyl)chloride (3.22 g, 0.040 mol) were
added to an argon-flushed thick-walled reaction vessel. The vessel
was sealed and the reaction mixture was stirred at 100 ◦C for
16 h, during which time the mixture changed from a murky brown
suspension to a clear red solution. Cooling of the reaction mixture
to ambient temperature and the subsequent addition of 10 mL of
diethyl ether resulted in the formation of a yellow precipitate. The
resulting solid was filtered off and washed with 50 mL of diethyl
ether and dried in vacuo to afford 1 as an analytically pure yellow
powder (0.92 g, 83.9%). Crystals of 1 suitable for X-ray diffraction
experiments were obtained from a saturated solution of 1 in a
3 : 1 dichloromethane–toluene solvent mixture following 3 days of
storage at -40 ◦C.
Experimental
General procedures
All manipulations and reactions were performed under a dry,
oxygen-free, catalyst scrubbed argon atmosphere using a com-
bination of standard Schlenk techniques or in an M-Braun or
Vacuum Atmospheres drybox. All glassware was oven-dried and
vacuum- and argon flow-degassed before use. All reagents were
obtained commercially and used without further purification. The
starting materials dipp-BIAN14 and (tht)AuCl15 were synthesized
according to published procedures. Toluene, THF, hexanes and
diethyl ether were dried over Na and freshly distilled prior to use.
The dichloromethane was dried over CaH2 and freshly distilled
prior to use.
MS (CI+, CH4): m/z 513 [M + H]+ (–Cl); HRMS (CI+, CH4):
calcd for C37H41N2 m/z 513.3270; found, 513.3262; 1H NMR
(CD2Cl2): d 1.20 (d, 12H, CH3), 1.41 (d, 12H, CH3), 2.75 (sept,
4H, –CH), 7.18–7.29 (d of d, 4H, Ar–H), 7.48 (d, 2H, Naph-
H), 7.60 (t, 2H, Ar–H), 7.68 (t, 2H, Naph-H), 8.02 (d, 2H,
Naph-H), 12.23 (s, 1H, C–H); 1H NMR (CD2Cl2): d 1.45 (d,
12H, CH3), 1.59 (d, 12H, CH3), 2.97 (sept, 4H, –CH), 7.55 (d,
2H, Naph-H), 7.80 (d, 4H, Ar–H), 7.92 (t, 2H, Ar–H), 8.03 (t,
2H, Naph-H), 8.35 (d, 2H, Naph-H), 11.32 (s, 1H, C–H); 13C
NMR (CD2Cl2): d 23.51, 24.84, 29.75, 123.37, 123.46, 125.46,
128.74, 129.43, 130.40, 130.87, 132.68, 138.08, 142.51, 145.44,
206.83 (C–H); mp (decomp): 286–290 ◦C.
Physical measurements
Low-resolution CI mass spectra were obtained on a Thermo
Scientific TSQ Quantum GC mass spectrometer and high-
resolution CI mass spectra were recorded on a magnetic sector
Waters Autospec Ultima instrument. MS analysis of compound
2 was performed on a sample that had been sealed in a glass
1
capillary under an argon atmosphere. 1H and 13C{ H} NMR
spectra were recorded at 295 K in the indicated solvent on a
Varian Unity 300 (1H, 300 MHz; 13C, 75 MHz) or a Varian
AS400 spectrometer (1H, 400 MHz; 13C, 100 MHz) immediately
following sample preparation and, in the cases of 2 and 3,
removal of the sample from the drybox. Deuterated solvents
IPr(BIAN) (2). Chilled THF (20 mL) was added to a 100 mL
Schlenk flask containing 1 (0.10 g, 0.182 mmol) and K(tBuO)
(0.028 g, 0.273 mmol). The reaction mixture was stirred at ambient
temperature for 12 h, after which the solvent was removed under
reduced pressure. The crude solid was digested in toluene, filtered
and the solvent was stripped from the filtrate thereby leaving
a mixture of red-orange and yellow solids. The crude material
was washed with cold hexanes to remove the red-orange product.
The remaining yellow solid was dried under vacuum to afford
a moderate yield of analytically pure 2 (0.066 g, 70.8%). A single
crystal of 2 was grown from a saturated 1 : 1 toluene–THF solution
of 2 that had been stored at -40 ◦C for 3 days.
˚
were obtained from Cambridge Isotopes and stored over 4 A
molecular sieves prior to use. 1H and 13C{ H} chemical shift
1
values are reported in parts per million (ppm) relative to SiMe4
(d 0.00), using solvent resonances as internal standards. The FTIR
spectrum of 7 was obtained on a Perkin–Elmer Spectrum BX
system.
X-ray crystallography
MS (CI+, CH4): m/z 513 [M + H]+ (+ H); HRMS (CI+, CH4):
calcd for C37H40N2 m/z 513.3270; found, 513.3283; 1H NMR
(C6D6): d 1.13 (d, 12H, CH3), 1.36 (d, 12H, CH3), 3.38 (sept,
4H, –CH), 6.91 (d, 2H, Ar–H), 6.94 (d, 2H, Naph-H), 7.24 (d,
2H, Naph-H), 7.29 (t, 2H, Ar–H), 7.31 (d, 2H, Ar–H), 3.38 (t, 2H,
Naph-H); 13C NMR (C7D8): d 23.35, 24.70, 29.05, 119.89, 123.97,
124.74, 127.01, 127.23, 129.35, 130.35, 131.76, 140.30, 146.34; mp:
299–302 ◦C.
For compounds 1 and 4–7, a crystal of suitable quality was
removed from a vial, covered with mineral oil and mounted on
a nylon thread loop. In the cases of compounds 2 and 3, the
selected crystal was removed from a vial that had been stored
in a drybox, then covered immediately with mineral oil and
mounted on a nylon thread loop. The X-ray diffraction data were
collected on either a Nonius Kappa CCD diffractometer with an
Oxford Cryostream low-temperature device at 153 K or a Rigaku
AFC-12 with Saturn 724+ CCD diffractometer with a Rigaku
XStream low temperature device at 100 K. Both instruments
were equipped with a graphite-monochromated Mo-Ka radiation
IPr(BIAN)[AgCl] (4). A 1 : 1 dichloromethane–THF solution
(30 mL) was added to a 50 mL round bottom flask that had
been covered with aluminium foil, then charged with 1 (0.10 g,
0.182 mmol) and Ag2O (0.20 g, 0.863 mmol). The reaction mixture
was stirred for 16 h at ambient temperature, following which it was
filtered and the solvent stripped from the filtrate under reduced
pressure to afford 4 as an analytically pure yellow solid (0.110 g,
92.1%). X-ray quality crystals of 4 were grown by storage of a
saturated solution of 4 in dichloromethane–hexanes at -40 ◦C for
5 days in the dark.
˚
source (l = 0.71073 A). Corrections were applied for Lorentz
and polarization effects. All structures were solved by direct
methods and refined by full-matrix least-squares cycles on F2 using
the Siemens SHELXTL PLUS 5.0 (PC) software package16 and
PLATON.17 All non-hydrogen atoms were refined anisotropically,
and hydrogen atoms were placed in fixed, calculated positions
using a riding model.
7406 | Dalton Trans., 2010, 39, 7401–7408
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MS (CI+, CH4): m/z 656 [M + H]+; HRMS (CI+, CH4): calcd for
C37H40N2AgCl m/z 654.1931; found, 654.1922; 1H NMR (CDCl3):
d 1.09 (d, 12H, CH3), 1.30 (d, 12H, CH3), 2.80 (sept, 4H, –
CH), 7.00 (d, 2H, Naph-H), 7.38 (d of d, 4H, Ar–H), 7.43 (t,
2H, Naph-H), 7.58 (t, 2H, Ar–H), 7.80 (d, 2H, Naph-H); 13C
NMR (CDCl3): d 23.81, 24.78, 28.85, 121.11, 124.63, 125.10,
127.82, 128.49, 129.86, 130.82, 130.96, 133.22, 139.26, 145.54; mp
(decomp): 305–310 ◦C.
88.8%). Crystals of 7 suitable for X-ray diffraction study were
grown from a saturated hexanes solution that had been stored at
-40 ◦C for 3 days.
MS (CI+, CH4): m/z 761 [M + H]+; HRMS (CI+, CH4): calcd for
C39H40N2IrO2 m/z 761.2719; found, 761.2724; 1H NMR (CDCl3):
d 0.98 (d, 5H, CH3), 1.16 (d, 7H, CH3), 1.42 (d, 12H, CH3), 2.74
(sept, 3H, –CH), 3.17 (sept, 1H, –CH), 6.84 (d, 1H, Naph-H),
7.29 (d, 1H, Naph-H), 7.40 (t, 1H, Ar–H), 7.45–7.55 (d of d, 4H,
Ar–H), 7.63 (t, 2H, Naph-H), 7.68–7.79 (m, 2H, Naph-H, Ar–H),
8.06 (d, 1H, Naph-H); 13C NMR (CDCl3): d 23.52, 24.06, 24.16,
25.63, 29.01, 29.43, 122.13, 123.02, 123.17, 124.59, 125.09, 125.80,
127.43, 128.34, 129.06, 129.66, 130.12, 130.65, 130.83, 132.37,
133.46, 137.69, 138.25, 140.35, 140.92, 144.95, 146.16, 167.57
(CO), 168.80 (CO), 215.10 (C–Ir); IR (KBr pellet) (nmax/cm-1:
2061.54 and 2053.95 (CO, trans), 1973.90 and 1966.40 (CO, cis);
mp (decomp): 217–220 ◦C.
IPr(BIAN)[AuCl] (5). Dichloromethane (30 mL) was added to
a 50 mL aluminium foil-wrapped round bottom flask containing
4 (0.051 g, 0.079 mmol) and (tht)AuCl (0.025 g, 0.078 mmol).
The reaction mixture was stirred for 12 h at ambient temperature,
after which the solvent was removed under reduced pressure. The
crude product was digested in toluene, filtered and the solvent
stripped under reduced pressure to afford analytically pure 5 as
a bright yellow solid (0.0511 g, 86.8%). A suitable crystal for X-
ray diffraction analysis was grown from a saturated THF–hexanes
solution of 5 stored at -40 ◦C for 5 days.
Isolation of N-(2,6-diisopropyl)-N-[(2,6-diisopropyl-phenyla-
mino)acenaphthylen-l-yl]-formamide (3). As noted in the Results
and discussion section, yellow toluene solutions of the IPr(BIAN)
carbene 2 gradually assume a red coloration when stored under an
argon atmosphere for ~12 h in a sealed reaction vessel at ambient
temperature. In a typical procedure, filtration of the reaction
mixture, followed by solvent stripping under reduced pressure,
afforded a mixture of red-orange and yellow solids. The crude
reaction mixture was then stirred with 20 mL of hexanes for 10 min,
after which the red hexanes solution was cannulated into a Schlenk
flask, leaving the yellow IPr(BIAN) carbene 2 as an analytically
pure solid. The extracted red hexanes solution was filtered and the
solvent was removed under reduced pressure to afford 3. Large
red crystals of 3 suitable for X-ray diffraction study were grown by
slow evaporation of a saturated benzene solution. The yield was
19.0%.
MS (CI+, CH4): m/z 745 [M + H]+; HRMS (CI+, CH4): calcd
for C37H40N2AuCl m/z 744.2546; found, 744.2548; 1H NMR
(CD2Cl2): d 1.12 (d, 12H, CH3), 1.38 (d, 12H, CH3), 2.83 (sept,
4H, –CH), 7.04 (d of d, 2H, Naph-H), 7.46 (t, 2H, Naph-H),
7.47 (d, 4H, Ar–H), 7.68 (t, 2H, Ar–H), 7.85 (d of d, 2H, Naph-
H);13C NMR (CD2Cl2): d 23.91, 24.59, 29.35, 121.70, 125.00,
125.62, 128.26, 128.96, 130.56, 131.33, 133.12, 138.41, 146.11; mp
(decomp): 337–340 ◦C.
IPr(BIAN)[Ir(COD)Cl] (6). Toluene (40 mL) was added to a
50 mL Schlenk flask that contained 1 (0.10 g, 0.182 mmol), KOtBu
(0.028 g, 0.273 mmol) and [Ir(COD)Cl]2 (0.61 g, 0.0091 mmol).
The resulting yellow suspension was stirred for 2 h, during which
time the solution assumed a clear red color. The reaction mixture
was filtered and the volatiles were removed under reduced pressure
thereby leaving an orange-red solid residue. The crude product was
washed with cold pentane (10 mL) leaving 0.121 g of analytically
pure 6 (78.4% yield). Single crystals of 6 were grown from a
saturated hexanes solution that had been stored at -40 ◦C for
5 days. The resulting orange plates were suitable for single-crystal
X-ray diffraction experiments.
MS (CI+, CH4): m/z 848 [M + H]+; HRMS (CI+, CH4): calcd for
C45H52N2ClIr m/z 846.3440; found, 848.3447; 1H NMR (CDCl3):
d 0.96 (b, 12H, CH3), 1.10 (d, 4H, COD), 1.35 (d, 12H, CH3), 1.42
(d, 4H, COD), 1.66 (sept, 2H, –CH), 1.94 (b, 1H, –CH), 3.26 (sept,
1H, –CH), 3.12 (m, 2H, COD), 4.29 (m, 2H, COD), 6.80 (d, 2H,
Naph-H), 7.29 (d, 2H, Naph-H), 7.40 (m, 3H, Ar–H), 7.45 (d, 1H,
Ar–H), 7.51–7.66 (m, 4H, Ar–H, Naph-H); 13C NMR (C6D6): d
23.73, 23.92, 24.54, 25.93, 28.71, 28.95, 29.45, 33.57, 50.76, 83.59,
121.58, 122.92, 123.26, 124.39, 124.99, 126.62, 127.13, 127.56,
128.25, 128.28, 129.01, 129.42, 129.59, 130.05, 130.39, 132.24,
134.75, 140.35, 144.97, 191.03 (C–Ir); mp (decomp): 255–260 ◦C.
Acknowledgements
The authors are grateful to the Robert A. Welch Foundation
for financial support of this work (Grant F-0003) as well as the
National Science Foundation (Grant 0741973). The authors also
gratefully acknowledge Vincent M. Lynch for help with the X-ray
crystallography. Gratitude is also expressed to Todd W. Hudnall,
Brent C. Norris and Daphne H. Sung for technical assistance.
References
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Dalton Trans., 2010, 39, 7401–7408 | 7407
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7408 | Dalton Trans., 2010, 39, 7401–7408
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The Royal Society of Chemistry 2010
©