Reactivity of [Cp*Rh(η6-C6H3NH2-2,6-i-Pr2)](OTf)2 toward phosphines and alkynes

Article abstract of DOI:10.1016/j.jorganchem.2006.06.016

The cationic aniline complex [Cp^*Rh(η⁶-2,6-(Me₂CH)₂C₆H₃NH₂)](OTf)₂ (1) was prepared from either [Cp^*Rh(η²-NO₃)(η¹-OTf)] or [Cp^*Rh(OH₂)₃](OTf)₂ and 2,6-diisopropylaniline. Complex 1 underwent substitution with phosphines or phosphites, indicating the labile character of the η⁶-aniline ligand. Complex 1 mediated cycloaddition reactions of several alkynes in refluxing ethanol: the [2 + 2] dimerization for Ph{single bond}C{triple bond, long}C{single bond}Ph and the [2 + 2 + 1] trimerization for Ph{single bond}C{triple bond, long}C{single bond}H and CH₃C₆H₄{single bond}C{triple bond, long}C{single bond}H. The unexpected cyclobutadiene complex [Cp^*Rh(η⁴-C₄(C(O)CH₃)₂H(SiMe₃))] was obtained from complex 1 and Me₃Si{single bond}C{triple bond, long}C{single bond}C{triple bond, long}C{single bond}SiMe₃ and structurally characterized by X-ray diffraction.

Full text of DOI:10.1016/j.jorganchem.2006.06.016

Journal of Organometallic Chemistry 691 (2006) 4100–4108
www.elsevier.com/locate/jorganchem
Reactivity of [Cp*Rh(g6-C6H3NH2-2,6-i-Pr2)](OTf)2 toward
phosphines and alkynes
*
Mi S. Lim, Ji Young Baeg, Soon W. Lee
Department of Chemistry (BK21), Institute of Basic Science, Sungkyunkwan University, Natural Science Campus, Suwon 440-746, Republic of Korea
Received 23 March 2006; received in revised form 4 June 2006; accepted 13 June 2006
Available online 21 June 2006
Abstract
The cationic aniline complex [Cp*Rh(g6-2,6-(Me2CH)2C6H3NH2)](OTf)2 (1) was prepared from either [Cp*Rh(g2-NO3)(g1-OTf)] or
[Cp*Rh(OH2)3](OTf)2 and 2,6-diisopropylaniline. Complex 1 underwent substitution with phosphines or phosphites, indicating the labile
character of the g6-aniline ligand. Complex 1 mediated cycloaddition reactions of several alkynes in refluxing ethanol: the [2 + 2] dimer-
ization for PhAC„CAPh and the [2 + 2 + 1] trimerization for PhAC„CAH and CH3C6H4AC„CAH. The unexpected cyclobutadiene
complex [Cp*Rh(g4-C4(C(O)CH3)2H(SiMe3))] was obtained from complex 1 and Me3SiAC„CAC„CASiMe3 and structurally charac-
terized by X-ray diffraction.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Rhodium aniline complex; Phosphine; Alkynes; [2 + 2 + 1] Cycloaddition
1. Introduction
[Cp*Rh(g6-C6H3NH2-2,6-i-Pr2)](OTf)2 (1),
a
cationic
mixed-sandwich Rh complexes, with mild nucleophiles
such as phosphines and phosphites, we obtained the corre-
sponding substitution products [Cp*Rh(PR3)3](OTf)2 (2a–
e), instead of nucleophilic addition products. This indicates
the labile character of the arene ligand in complex 1, and
therefore we decided to compare its reactivity toward alky-
nes with that found for [Cp*Rh(g2-NO3)(OTf)], whose
reactivity was proposed to come from the labile ligands
(NOꢀ3 and OTfꢀ). Herein, we report the reactivity of com-
plex 1 toward phosphines (PMe3, PEt3, PPh3), phosphites
(P(OMe)3, P(OEt)3), an internal alkyne (PhAC„CAPh),
terminal alkynes (HAC„CAPh and HAC„CAC6H4-
Various transition-metal complexes mediate the
[2 + 2 + 2] cyclotrimerization of alkynes [1–10]. By con-
trast, there have been only a limited number of reports
on the formal [2 + 2 + 1] cyclotrimerization of alkynes to
give five-membered rings [11–22]. Very recently, we
reported the reactivity of [Cp*Rh(g2-NO3)(OTf)] toward
terminal aryl alkynes (HAC„CAPh and HAC„
CAC6H4CH3) in alcohol (EtOH and n-BuOH) [11]. These
reactions produced five-membered cycloadducts, substi-
tuted Cp ligands, by the [2 + 2 + 1] cyclotrimerization of
those aryl alkynes.
Cationic mixed-sandwich complexes such as [Cp*Rh(g6-
arene)]2+ have been attracted because of their oxidizing
properties [23–26]. In particular, the aryl ligand in those
complexes is typically electrophilic and subject to nucleo-
philic addition and substitution reactions [27–29], primarily
because the cationic metal strongly withdraws electron
density from two cyclic ligands. When we treated
CH3), and
a
diyne ((Me3SiAC„CAC„CASiMe3)),
together with some crystal structures of products.
2. Experimental
All reactions were performed under argon. The starting
complex [Cp*Rh(g6-C6H3NH2-2,6-i-Pr2)](OTf)2 (1) was
prepared from either [Cp*Rh(g2-NO3)(g1-OTf)] [30] or
[Cp*Rh(OH2)3](OTf)2 [31]. 1H, 13C{1H}, and 31P{1H}
NMR spectra were recorded with a Bruker AMX
*
Corresponding author. Tel.: +82 31 290 7066; fax: +82 31 290 7075.
E-mail address: swlee@chem.skku.ac.kr (S.W. Lee).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.016

M.S. Lim et al. / Journal of Organometallic Chemistry 691 (2006) 4100–4108
4101
500 MHz spectrometer at CCRF (Cooperative Center for
Research Facilities) in the Sungkyunkwan University. IR
spectra were recorded with a Nicolet Avatar 320 FTIR
spectrophotometer. Elemental analyses were performed
by the Korea Basic Science Institute.
tone. After 4 h stirring at room temperature, the solvent
was removed under vacuum. The residue was washed with
diethyl ether (20 ml · 2), and then dried under vacuum to
give an orange solid of [Cp*Rh(PMe3)3](OTf)2 (2a, 36 mg,
0.047 mmol, 66%). This product was recrystallized from
acetone–hexane.
1H NMR (acetone-d6): d 2.20 (s, 15H, Cp*), 1.98 (m,
27H, PMe3). 13C{1H} NMR (acetone-d6): d 109.8 (m,
C5(CH3)5), 18.8 (m, P(CH3)3), 10.9 (s, C5(CH3)5).
31P{1H} NMR (acetone-d6): d 0.52 (d, JRh–P = 122.2 Hz).
IR (KBr): 2925, 1631, 1430, 1271, 1147, 1032, 945,
636 cmꢀ1. M.p.: 246–248 ꢁC (decomp). Anal. Calc. for
C21H42O6F6P3S2Rh: C, 32.99; H, 5.54; S, 8.39. Found: C,
32.99; H, 5.64; S, 8.47%.
Complex 2b was prepared similarly to complex 2a.
Yield: 45%. 1H NMR (acetone-d6): d 2.45 (m, 18H,
P(CH2CH3)3), 2.17 (s, 15H, Cp*), 1.76 (m, 27H,
P(CH2CH3)3). 13C{1H} NMR (acetone-d6): d 103.5 (m,
C5(CH3)5), 18.9 (m, P(CH2CH3)3), 12.3 (m, P(CH2CH3)3),
10.6 (s, C5(CH3)5). 31P{1H} NMR (acetone-d6): d 40.5 (d,
JRh–P = 134.2 Hz). IR (KBr): 2973, 2049, 1635, 1462,
1420, 1384, 1268, 1154, 1031, 760, 721, 636 cmꢀ1. Anal.
Calc. for C30H60O6F6P3S2Rh: C, 40.45; H, 6.79; S, 7.20.
Found: C, 40.56; H, 6.32; S, 6.41%.
Complex 2c was similarly prepared, but the solution
was refluxed to enhance the yield and to complete the
reaction. Yield: 57%. 1H NMR (CDCl3): d 7.24–7.86
(m, 45H, PPh3), 1.19 (q, 15H, JH–P = 3.5 Hz, Cp*).
13C{1H} NMR (CDCl3): d 125.1–143.3 (m, PPh3), 104.5
(m, C5(CH3)5), 10.2 (s, C5(CH3)5). 31P{1H} NMR
(CDCl3): d 48.5 (d, JRh–P = 146.7 Hz). IR (KBr): 3057,
2965, 2924, 1659, 1636, 1588, 148, 1437, 1381, 1267,
1224, 1154, 1118, 1092, 1030, 747, 723, 696, 638, 541,
520 cmꢀ1. M.p.: 114–116 ꢁC (decomp). Anal. Calc. for
C66H60O6F6P3S2Rh: C, 59.91; H, 4.57; S, 4.85. Found:
C, 58.93; H, 4.31; S, 4.56%.
2.1. Preparation of [Cp*Rh(g6-2,6-(Me2CH)2C6H3NH2)]-
(OTf)2 (1)
2.1.1. Method 1: preparation from [Cp*Rh(g2-NO3)-
(g1-OTf)]
At room temperature, 2,6-diisopropylaniline (0.124 ml,
0.66 mmol) was added to an orange solution of
[Cp*Rh(g2-NO3)(g1-OTf)] (0.100 g, 0.22 mmol) in THF
(30 ml). The mixture was stirred for 3 h. The solvent was
removed under vacuum to give a yellow powder, which
was washed with diethyl ether (3 · 10 ml) and then dried
under vacuum. This product was recrystallized from ace-
tone–hexane to give complex 1 (84 mg, 0.115 mmol, 53%).
1H NMR (acetone-d6): d 7.30 (d, 2H, J = 6.5 Hz, H(9) in
Ph), 7.28 (br, 2H, NH2), 6.98 (t, 1H, J = 6.5 Hz, H(10) in
Ph), 3.36 (m, 2H, CHMe2), 2.23 (s, 15H, Cp*), 1.50 (d,
6H, J = 6.5 Hz, CH(CH3)2), 1.36 (d, 6H, J = 7.0 Hz,
CH(CH3)2). 13C{1H} NMR (acetone-d6): d 132.5 (s, C(7)
in Ph), 112.7 (d, JRh–C = 4.5 Hz, C(8) in Ph), 108.8 (d,
JRh–C = 7.8 Hz,C5Me5), 100.4 (d, JRh–C = 5.0 Hz, C(9) in
Ph), 94.9 (d, JRh–C = 6.7 Hz, C(10) in Ph), 26.8 (s,
CHMe2), 20.2 (s, CH(CH3)2), 19.3 (s, CH(CH3)2), 9.42 (s,
C5(CH3)5). IR (KBr): 3346 (N–H), 3227 (N–H), 3097,
2978, 1659, 1537, 1470, 1377, 1275, 1156, 1073, 1032,
636 cmꢀ1. M.p.: 269–271 ꢁC (decomp). Anal. Calc. for
C24H34F6NO6RhS2: C, 40.40; H, 4.80; N, 1.96; S, 8.99.
Found: C, 40.56; H, 4.95; N, 1.93; S, 8.52%.
(OTf)2
Complex 2d was prepared similarly to 2a. Yield: 49%.
1H NMR (acetone-d6): d 4.16 (m, OMe), 1.93 (q, JH–P
=
Rh
2.5 Hz, C5Me5). 13C{1H} NMR (acetone-d6): d 111.5 (m,
C5Me5), 57.1 (m, OMe), 9.42 (s, C5(CH3)5). 31P{1H}
NMR (acetone-d6): d 119.5 (d, JRh–P = 195.3 Hz). IR
(KBr): 2978, 2931, 1659, 1447, 1275, 1154, 1030, 805,
638 cmꢀ1. M.p.: 194–196 ꢁC (decomp). Anal. Calc. for
C21H42O15F6P3S2Rh: C, 27.76; H, 4.66; S, 7.06. Found:
C, 27.74; H, 4.65; S, 7.25%.
7
10
NH2
8
13
9
11
12
2.1.2. Method 2: preparation from [Cp*Rh(OH2)3](OTf)2
At room temperature, 2,6-diisopropylaniline (0.50 ml,
2.60 mmol) was added to [Cp*Rh(OH2)3](OTf)2 (0.508 g,
0.86 mmol) in THF (30 ml). The mixture was stirred for
3 h. The product was recrystallized from acetone–hexane
to give complex 1 (557 mg, 0.781 mmol, 91%).
Complex 2e was also prepared similarly to 2a. Yield:
51%. 1H NMR (acetone-d6):
d
4.50 (m, 18H,
P(OCH2CH3)3), 2.09 (s, 15H, C5Me5), 1.50 (t, 27H,
JH–P = 7 Hz, P(OCH2CH3)3). 13C{1H} NMR (acetone-
d6): d 110.6 (m, C5(CH3)5), 67.0 (m, P(OCH2CH3)3), 15.5
(m, P(OCH2CH3)3), 9.42 (s, C5(CH3)5); 31P{1H} NMR
(acetone-d6): d 114.4 (d, JP–Rh = 219.8 Hz). IR (KBr):
2986, 1661, 1473, 1389, 1274, 1151, 1030, 963, 784, 636,
569 cmꢀ1. M.p.: 170–172 ꢁC (decomp). Anal. Calc. for
C30H60O15F6P3S2Rh: C, 34.82; H, 5.84; S, 6.20. Found:
C, 35.63; H, 5.41; S, 6.69%.
2.2. Preparation of [Cp*Rh(PR3)3](OTf)2 (R = Me (2a),
R = Et (2b), R = Ph (2c); R = OMe (2d), R = OEt (2e))
Trimethylphosphine (0.25 ml, 0.25 mmol) was added to
a yellow solution of 1 (51 mg, 0.071 mmol) in 30 ml of ace-

4102
M.S. Lim et al. / Journal of Organometallic Chemistry 691 (2006) 4100–4108
2.3. Preparation of [Cp*Rh(g4-C4Ph4)] (3)
77.64 (s, CH(p-tolyl)OEt), 64.91 (s, OCH2CH3), 21.61 (s,
C6H4CH3), 21.57 (s, C6H4CH3), 21.39 (s, C6H4CH3),
15.23 (s, OCH2CH3), 9.50 (s, C5(CH3)5). IR (KBr):
3081, 2974, 1637, 1473, 1386, 1264, 1156, 1031, 826,
769, 638 cmꢀ1. Mp: 188–190 ꢁC (decomp). Anal. Calc. for
C40H44F3O4SRh: C, 61.54; H, 5.68; S, 4.11. Found: C,
61.65; H, 5.49; S, 4.03% [11].
A solution of 1 (52 mg, 0.073 mmol) and diphenylacety-
lene (55 mg, 0.31 mmol) in ethanol (40 ml) was refluxed for
20 h. After cooling at room temperature, the solution was
filtered, and the resulting yellow precipitates were washed
with ethanol (10 ml · 2) and diethyl either (10 ml · 2),
and then dried under vacuum. This product was recrystal-
lized from CH2Cl2–hexane. The resulting complex was
identified by comparing its NMR spectra, melting point,
and X-ray diffraction data with the literature data [33].
2.5. Preparation of [Cp*Rh(g4-C4(C(O)CH3)2H-
(SiMe3))] (5)
1
Yield: 69%, 30 mg, 0.050 mmol. H NMR (CDCl3): d
After a deep purple solution of 1 (53 mg, 0.074 mmol)
and 1,4-bis(trimethylsilyl)-1,3-butadiyne (15 mg, 0.077
mmol) in EtOH (40 ml) was refluxed with stirring for
30 h, the solvent was removed under vacuum. The residue
was washed with hexane (20 ml · 3), and then dried under
vacuum to give a red-orange solid of 5. This product was
crystallized from CH2Cl2–hexane.
1.54 (s, 15H, C5(CH3)5), 7.26–7.12 (m, 20H, C6H5).
13C{1H} NMR (CDCl3): d 9.34 (s, C5(CH3)5), 93.9 (d,
JRh–C = 6.7 Hz, C5(CH3)5). IR (KBr): 3058, 2965, 1635,
1597, 1498, 1065, 1025, 779, 743, 699, 559 cmꢀ1. M.p.:
273–275 ꢁC (decomp).
2.4. Preparation of [Cp*Rh(g5-C5H2Ar2–CH(Ar)OEt)-
(OTf) (Ar = Ph (4a), p-tolyl (4b))
Yield: 42%, 14 mg, 0.031 mmol. H NMR (CDCl3): d
1
4.90 (d, 1H, JRh–H = 1.0 Hz, (g4-C4)H), 1.90 (s, 15H,
C5(CH3)5), 1.85 (s, 6H, C(O)CH3), 0.23 (s, 9H, Si(CH3)3).
13C{1H} NMR (CDCl3): d 195.4 (s, C(O)CH3), 116.5 (s,
CSiMe3), 95.6 (d, JRh–C = 7.3 Hz, C5(CH3)5), 79.8 (d,
A solution of 1 (49 mg, 0.069 mmol) and phenylacety-
lene (0.030 ml, 0.27 mmol) in ethanol (40 ml) was refluxed
for 15 h, and then the solvent was removed under vacuum.
The residue was washed with diethyl either (10 ml · 2) and
hexane (10 ml · 2), and then dried under vacuum to give an
orange solid of 4a. This product was recrystallized from
CH2Cl2–hexane.
JRh–C = 10.1 Hz, CC(O)CH3), 72.0 (d, 1H, JRh–C
=
11.1 Hz, (g4-C3C)H), 25.2 (s, C(O)CH3), 10.4 (s,
Table 1
X-ray data collection and structure refinement for 1 Æ H2O, 2e, and 5
1 Æ H2O
24H36F6
NO7RhS2
731.57
2e
5
1
Yield: 79%, 40 mg, 0.054 mmol. H NMR (CDCl3): d
4
Formula
C
C30H60F6O15
P3RhS2
1034.72
C21H31O2
RhSi
446.46
7.24–7.71 (m, 15H, Ph), 6.29 (d, JH–H = 1.5 Hz, 1H, Cp),
6.08 (d, 4JH–H = 1.5 Hz, 1H, Cp), 5.47 (s, 1H, CH(Ph)OEt),
3.37 (dq, 2JH–H = 3.0 Hz, 3JH–H = 7.0 Hz, 2H, OCH2CH3),
Fw
Temperature (K)
Crystal system
Space group
293(2)
Orthorhombic
Cmc21
19.851(2)
9.870(1)
15.775(1)
293(2)
Monoclinic
P21/c
12.186(2)
20.690(2)
18.774(5)
293(2)
Triclinic
2
3
1.67 (s, 15H, C5(CH3)5), 1.11 (dt, JH–H = 3.0 Hz, JH–H
=
7.0 Hz, 3H, OCH2CH3). 13C{1H} NMR (CDCl3): d 126.45–
ꢀ
P1
˚
1
a (A)
9.152(1)
9.178(1)
14.650(2)
72.649(9)
73.985(9)
72.238(8)
1095.2(2)
2
1.354
0.845
464
0.7849
0.9413
4069
139.32 (m, Ph), 106.98 (d, JRh–C = 7.3 Hz, C5(CH3)5),
˚
b (A)
1
1
106.26 (d, JRh–C = 6.0 Hz, Cp CPh), 103.15 (d, JRh–C
=
˚
c (A)
1
6.7 Hz, Cp CPh), 101.43 (d, JRh–C = 7.8 Hz, Cp CC),
a (ꢁ)
b (ꢁ)
c (ꢁ)
1
1
84.91 (d, JRh–C = 7.3 Hz, Cp CH), 84.40 (d, JRh–C
=
96.90(2)
7.3 Hz, Cp CH), 77.82 (s, CH(Ph)OEt), 65.10 (s,
OCH2CH3), 15.23 (s, OCH2CH3), 9.46 (s, C5(CH3)5). IR
(KBr): 3083, 2972, 1667, 1629, 1454, 1385, 1263, 1160,
1030, 769, 699, 638 cmꢀ1. M.p.: 126–128 ꢁC (decomp).
Anal. Calc. for C37H38F3O4SRh: C, 60.16; H, 5.19; S,
4.34. Found: C, 59.89; H, 5.07; S, 4.21% [11].
3
˚
V (A )
3090.8(4)
4
1.572
0.765
1496
0.8052
0.9345
9456
4699(2)
4
1.463
0.635
2144
0.5716
0.8695
8588
Z
Dcal (g cmꢀ3
)
l (mmꢀ1
F(000)
Tmin
)
Tmax
No. of reflns
measured
Complex 4b was prepared similarly to complex 4a.
Yield: 59%. 1H NMR (CDCl3): d 7.13–7.59 (m, 15H,
4
C6H4CH3), 6.12 (d, JH–H = 1.5 Hz, 1H, Cp), 6.01 (d,
No. of reflns unique
No. of reflns
with I > 2r(I)
No. of params
refined
3611
3414
8184
4405
3809
3690
4JH–H = 1.5 Hz, 1H, Cp), 5.38 (s, 1H, CH(p-tolyl)OEt),
3.33 (dq, 2JH–H = 3.0 Hz, 3JH–H = 7.0 Hz, 2H, OCH2CH3),
2.44 (s, 3H, C6H4CH3), 2.37 (s, 3H, C6H4CH3), 2.32
(s, 3H, C6H4CH3), 1.65 (s, 15H, C5(CH3)5), 1.09
217
440
235
ꢀ3
˚
Max in Dq (e Aꢀ3
)
)
0.604
1.037
0.224
2
3
(dt, JH–H = 3.0 Hz, JH–H = 7.0 Hz, 3H, OCH2CH3).
˚
Min in Dq (e A
ꢀ0.318
ꢀ1.024
ꢀ0.255
13C{1H} NMR (CDCl3): d 124.56–140.71 (m, C6H4CH3),
GOF on F2
1.075
1.029
1.066
a
106.33 (d, 1JRh–C = 7.3 Hz, C5(CH3)5), 106.09 (d, 1JRh–C
=
R1
wR2
0.0329
0.0874
0.0995
0.2600
0.0207
0.0550
b
1
6.2 Hz, Cp CPh), 103.45 (d, JRh–C = 6.7 Hz, Cp CPh),
101.21 (d, JRh–C = 7.8 Hz, Cp CC), 84.32 (d, JRh–C
7.3 Hz, Cp CH), 83.95 (d, JRh–C = 6.7 Hz, Cp CH),
P
1
1
a
R1 = iFoj ꢀ jFciRjFoj.
=
P
P
2
2 1=2
b
wR2 ¼ ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁ
.
1

M.S. Lim et al. / Journal of Organometallic Chemistry 691 (2006) 4100–4108
4103
C5(CH3)5), 0.46 (s, Si(CH3)3). IR (KBr): 2957, 2910, 1659,
1461, 1381, 1213, 842, 455 cmꢀ1. M.p.: 184–186 ꢁC
(decomp). Anal. Calc. for C21H31O2SiRh: C, 56.49; H,
7.00. Found: C, 55.44; H, 6.88%.
the first method, the commercially available [Cp*Rh(l-
Cl)Cl]2 is converted to [Cp*Rh(NO3)(OTf)] [30] by the
two-step addition of AgNO3 and AgOTf, which is subse-
quently treated with 2,6-diisopropylaniline to give complex
1 in 53% yield. The second method starts from [Cp*Rh(O-
H2)3](OTf)2 [31], which can be prepared from [Cp*Rh(l-
Cl)Cl]2 in high yield just in a single step. The reaction
involving [Cp*Rh(OH2)3](OTf)2 produced complex 1 in
91% yield. A series of dicationic Cp*Rh–arene and
Cp*Rh–aniline complexes [Cp*Rh(X)]Y2 (X = aniline or
arene; Y = BF4 or PF6), which closely resemble complex
1, have been reported [31,32].
2.6. X-ray crystal structure determination
X-ray data were collected with either a Bruker CCD
SMART diffractometer (complex 1 Æ H2O) or a Siemens
P4 diffractometer (complexes 2e and 5) equipped with a
Mo X-ray tube. Intensity data were empirically corrected
for absorption with w-scan data, except complex 1 Æ H2O
for which absorption corrections were made with SADABS.
All calculations were carried out with the use of SHELXTL
programs [34]. All the structures were solved by direct meth-
ods. Unless otherwise stated, all non-hydrogen atoms were
refined anisotropically. All hydrogen atoms were generated
in ideal positions and refined in a riding mode (see Table 1).
A dark brown crystal of 1 Æ H2O, shaped as a block of
approximate dimensions 0.33 · 0.18 · 0.10 mm, was used
for crystal- and intensity-data collection. Unit-cell parame-
ters and systematic absences indicated three possible space
groups: Cmc21, Cmcm, and Ama2. The structure analysis
converged only in Cmc21. An orange crystal of 2e (block,
0.26 · 0.24 · 0.20 mm) was used. The atoms in highly disor-
dered triflate counterions in 2e were refined isotropically. A
yellow crystal of 5 (block, 0.54 · 0.49 · 0.44 mm) was used.
The hydrogen (H16) atom attached to the cyclobutadiene
ring was located and refined isotropically. Selected bond
lengths and angles are shown in Table 2.
Complex 1 is stable both in solution and in the solid
state, and has been fully characterized by NMR (1H and
13C{1H}), IR, elemental analysis, and X-ray diffraction.
The N–H bonds in the aniline ligand appear at 3346 and
1
3227 cmꢀ1 in the IR spectrum. The H NMR of complex
1 displays two doublets at d 1.50 and 1.36 ppm, which cor-
respond to two distinct methyl protons. This observation is
due to the presence of the diastereotopic methyl protons in
the isopropyl group that is bonded to the C8 (Fig. 1) on the
aniline ring. This carbon can be thought of as bonding to
four different groups (C7, C9, C11, and Rh), and therefore
as a pseudo-chiral center. The diastereotopic nature of the
germinal dimethyl groups is also reflected in the 13C{1H}
NMR spectrum, which displays a pair of singlets at 19.3
and 20.2 ppm.
The structure of the cationic part of complex 1 with the
atom-numbering scheme is shown in Fig. 1, which shows a
molecular mirror plane passing through C4, C1, Rh1, C10,
C7, and N1 atoms. The coordination sphere of Rh can be
described as pseudo-octahedral if the coordination num-
bers of both rings (Cp* and aniline) are taken to be three.
The g5-Cp* and g6-aniline rings are essentially parallel to
3. Results and discussion
3.1. Preparation of [Cp*Rh(g6-2,6-(Me2CH)2C6H3NH2)]-
(OTf)2 (1)
ꢂ
each other with a dihedral angle of 0.4(3)ꢁ. The Rh–CCp
(CCp is the centroid of the Cp* ring) and Rh–CCp (CCp
ꢂ
0
0
As mentioned in Section 2, the cationic Cp*Rh–aniline
complex 1 could be prepared in two ways (Scheme 1). In
is the centroid of the aniline ring) distances are 1.796 and
˚
ꢂ
0
1.793 A, respectively, and the CCp –Rh–CCp angle is 177ꢁ.
Table 2
˚
Selected bond lengths (A) and bond angles (ꢁ)
Complex 1 Æ H2O
Rh1–C3
Rh1–C10
Rh1–C7
2.159(3)
2.220(4)
2.395(3)
Rh1–C1
Rh1–C9
2.173(5)
2.245(3)
Rh1–C2
Rh1–C8
2.177(3)
2.323(3)
Complex 2e
Rh1–P2
P2–Rh1–P3
2.273(3)
90.6(1)
Rh1–P3
P2–Rh1–P1
2.278(3)
94.6(1)
Rh1–P1
P3–Rh1–P1
2.285(3)
91.9(1)
Complex 5
Rh1–C16
Rh1–C14
C14–C15
O2–C17
2.100(2)
2.132(2)
1.475(3)
1.207(3)
Rh1–C13
C13–C16
C15–C16
C11–C12
2.121(2)
1.449(3)
1.447(3)
1.499(3)
Rh1–C15
C13–C14
O1–C12
2.127(2)
1.475(3)
1.207(3)
1.508(3)
C17–C18
C16–C13–C12
C13–C14–C15
O1–C12–C13
O2–C17–C15
133.0(2)
87.6(2)
122.1(2)
122.1(2)
C16–C13–C14
C16–C15–C14
O1–C12–C11
O2–C17–C18
91.3(2)
91.4(2)
121.5(2)
121.7(2)
C12–C13–C14
C15–C16–C13
C13–C12–C11
C15–C17–C18
135.7(2)
89.7(2)
116.4(2)
116.2(2)

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M.S. Lim et al. / Journal of Organometallic Chemistry 691 (2006) 4100–4108
Rh
O
N O
OTf
(OTf)2
Cl
Cl
Rh Rh
Cl
O
Rh
Cl
(OTf)2
NH2
Rh
H O
2
1
OH
2
H O
2
Scheme 1.
(OTf)2
HCl/THF
(OTf)
Cl
Cl Rh
Cl
Rh
Rh
NH2
1
ð1Þ
3.2. Reactivity of 1 toward phosphines and phosphites
Treatment of 1 with 3 equiv. of PR3 (R = Me, Et, Ph,
OMe, OEt) in refluxing acetone gave [Cp*Rh(PR3)3](OTf)2
(2a–e) in 54–66% yields (Eq. (2)). At room temperature,
these reactions proceed in much lower yields. In particular,
the room-temperature reaction with triphenylphosphine
does not occur at all. This observation suggests that triphe-
nylphosphine may experience steric hindrance on
approaching the rhodium metal center of complex 1, which
may be explained on the basis of cone angles of phosphines
(PMe3: 118ꢁ; PEt3: 132ꢁ; PPh3: 145ꢁ).
Fig. 1. ORTEP drawing of the cationic part of complex 1 Æ H2O, showing
the atom-labeling scheme and 50% probability thermal ellipsoids.
(OTf)
2
(OTf )
2
2a: R = Me
2b: R = Et
2c: R = Ph
2d: R = OMe
2e: R = OEt
Rh
PR
3
Rh
Acetone/Reflux
NH
PR
2
We examined whether complex 1 would return to its
starting complex [Cp*Rh(l-Cl)Cl]2 on addition of HCl.
Interestingly, treating complex 1 with HCl (1.0 M solution
in diethyl ether) in THF gave [Cp*Rh(l-Cl)3RhCp*](OTf),
a dinuclear complex triply bridged by three l-Cl ligands
(Eq. (1)). This product has been identified by comparing
its spectral data (NMR and IR spectra), melting point,
and X-ray crystal structure with those for the genuine
complex in the literature [33]. This reaction gives the same
product (92% isolation yield), regardless of the stoichiom-
etric mole ratios between complex 1 and HCl (1:1, 1:2,
1:3), although the lower-ratio reaction leaves some unre-
acted complex 1. These results indicate that the aniline
ligand in complex 1 is labile enough to be replaced by
the weak nucleophilic Clꢀ ion. Closely related complexes
[Cp*Rh(l-Cl)3RhCp*](BPh4), [Cp*Rh(l-Cl)3RhCp*](PF6),
and [Cp*Rh(l-I)3RhCp*](BF4) have been reported
[35–37].
3
PR
3
PR
3
1
ð2Þ
Complexes 2a–e were characterized by 1H, 13C{1H}, and
31P{1H} NMR, IR, and elemental analysis. In particular,
complex 2e was structurally characterized by X-ray
diffraction. Whereas complexes 2b and 2c are somewhat
air-sensitive, the other complexes are air-stable. The IR
spectra of these complexes display characteristic peaks
for the common OTfꢀ counterion at 1267–1275 (S@O),
1030–1033 (S–O), 1147–1154 (C–F), and 636–638 cmꢀ1
(S–O). Complexes containing the counterion PFꢀ6 ,
[Cp*Rh(P(OMe)3)3](PF6)2 and [Cp*Rh(P(OEt)3)3](PF6)2,
which are quite close to complexes 2d and 2e, were
previously prepared from the acetone solvate complex
[Cp*Rh(acetone)3](PF6)2 and the corresponding phosph-
ites, and characterized by H and 13C{1H} NMR [38].
1

M.S. Lim et al. / Journal of Organometallic Chemistry 691 (2006) 4100–4108
4105
The structure of the cationic part of complex 2e is shown
in Fig. 2. It has a three-legged piano-stool structure with
three triethyl phosphite ligands being regarded as three
legs. The Rh–P bond lengths range from 2.273(3) to
2.285(3) A. The P–Rh–P bond angles are in the range of
90.6(1)–94.6(1)ꢁ with an average of 92.4ꢁ.
ligand. Refluxing an ethanol solution containing complex
1 and diphenylacetylene produced the Rh–cyclobutadiene
complex [Cp*Rh(g4-C4Ph4)] (3) in 69% yield (Scheme 2).
Complex 3 was identified by comparing its NMR, IR, and
X-ray diffraction data with those for the genuine complex
in the literature, which was originally prepared from
[Cp*Rh(g2-NO3)(g1-OTf)] and diphenylacetylene [33]. This
observation also indicates the labile character of the aniline
ligand in complex 1. Unfortunately, reactions involving
other alkynes, terminal or internal, such as
CH3(CH2)3AC„CAH, Me3SiAC„CAH, Me3SiAC„C
ASiMe3, CH3OCH2AC„CAH, PhAC„CAC„CAPh,
EtAC„CAEt, and PhAC„CAMe, gave only intractable
mixtures, from which the products could not be isolated.
We recently observed a rather unusual cyclotrimeriza-
tion of some terminal aryl alkynes HAC„CAAr (Ar = Ph
or p-tolyl) in acetone mediated by [Cp*Rh(g2-NO3)(OTf)]
to give (g4-cyclobutadiene)rhodium complexes [Cp*Rh-
(g4-C4HAr2AC„CAr)] (Eq. (3)) [33]. For a comparative
study, we treated complex 1 with the same terminal alky-
nes, but did not observe any sign of reactivity even in
refluxing acetone. It should be mentioned that Carmona’s
group was the first to report this type of cyclotrimerization
of aryl alkynes with [Cp*Rh(L-alaninate)Cl] [39].
˚
3.3. Reactivity of 1 with alkynes
The reactivity of complex 1 toward alkynes depends on
the nature of the alkyne and the solvent used.
Complex 1 mediated the [2 + 2] cycloaddition of diphe-
nylacetylene to generate
a tetraphenylcyclobutadiene
acetone
+
3
H
Ar
Rh
O
Rh
- OTf-
O
OTf
ð3Þ
Ar
H
-
- NO3
N
Ar
O
Ar
-tolyl
Ar = Ph,
p
Considering the lack of reactivity of complex 1 toward
the terminal aryl alkynes in acetone, we decided to change
the solvent from acetone to ethanol with an attempt to
Fig. 2. ORTEP drawing of the cationic part of complex 2e.
Ph
Ph
Rh
3
EtOH / Reflux
Ph
Ph
Ph
Ph
(OTf )
(OTf )
2
H
Ar
Rh
Rh
H
H
EtOH / Reflux
Ar
OEt
Ar
NH
2
Ar
4a: Ar = Ph
4b: Ar = p-tolyl
1
H
TMS
TMS
O
Rh
H
O
EtOH / Reflux
5
TMS
Scheme 2.

4106
M.S. Lim et al. / Journal of Organometallic Chemistry 691 (2006) 4100–4108
bring about different reactions. Consistent with our expec-
tation, complex 1 did exhibit reactivity in ethanol. Reflux-
ing a mixture of complex 1 and these alkynes (HC„CPh
and HC„CC6H4CH3) in ethanol produced the cationic
rhodonocene-like complexes, [Cp*Rh(g5-C5H2Ar2–CH
(Ar)(OEt))]+(OTf)ꢀ (Ar = Ph (4a), p-tolyl (4b)) (Scheme
2). The same reactivity was very recently observed in the
reactions of [Cp*Rh(g2-NO3)(OTf)] with terminal aryl
alkynes (HC„CPh and HC„CC6H4CH3) in alcohol
(EtOH and n-BuOH) [11]. It is worth noting that
[Cp*Rh(g2-NO3)(OTf)] reacted with the terminal alkynes
at room temperature, but complex 1 reacted under reflux
conditions. These results indicate the lower reactivity of
complex 1 compared to [Cp*Rh(g2-NO3)(OTf)] and sug-
gest that the active species in reactions of both complexes
probably be the cationic [Cp*Rh]+ moiety. In this contest,
the difference in reactivity between these complexes is
believed to arise basically from the difference in lability
between the acting ligands (arene versus NOꢀ3 and triflate).
This type of reactivity also appears to occur in other reflux-
ing alcohol solvents such as methanol and isopropanol,
although we failed to characterize products. Room-temper-
ature reactions, however, do not proceed in all cases.
Although the present results do not give any detailed
information about how rhodocenium cations have been
formed, we do believe that our reaction proceeds according
to the mechanism proposed for the reaction involving
[Cp*Rh(g2-NO3)(OTf)], as shown in Scheme 3 [11]. The
first step involves the formation of the rhodium–vinylidene
species A by proton transfer of an aryl alkyne and the bind-
ing of an alkoxide with the liberation of HOTf. Two aryl
alkynes then sequentially insert to give the metallacyclo-
hexadiene intermediate B, which undergoes reductive elim-
ination to give the fulvene-type species C. Finally, the
coordinated ethoxide attacks the exocyclic carbon of the
intermediate C to give the ultimate product. On the [2 +
2 + 1] cyclotrimerization of alkynes, two mechanisms have
been proposed so far: a metallacyclopentadiene route and a
metallacyclohexadiene route [13–22]. The mechanism
involving the metallacyclohexadiene intermediate seems
to be appropriate to our case.
Complex 1 mediated an unexpected transformation of
bis(trimethylsilyl)butadiene (Me3Si–C„C–C„C–SiMe3).
Refluxing an ethanol solution containing complex 1 and
bis(trimethylsilyl)butadiene for 30 h gave [Cp*Rh(g4-C4-
(C(O)CH3)2H(SiMe3))] (5) in 42% yield (Scheme 2).
However, no reaction occurred in ethanol at room temper-
ature. Furthermore, we did not see any sign of reactivity in
acetone and THF regardless of various reaction conditions.
The chemical formula of complex 5 indicates several facts.
(1) The Rh metal was formally reduced from +3 to +1
during the reaction. (2) One dyne appears to be involved
in the cyclization with the release of one trimethylsilyl
group. (3) The solvent ethanol was oxidized and bound
(OTf)2
OTf
H
Ar
EtOH
H
Rh
Rh
NH2
RO
Ar
1
OTf
OTf
H
H
Ar
alkyne
Rh
Rh
Ar
RO
Ar
H
C
RO
C
insertion
A
Ar
H
alkyne
insertion
H
Ar
OTf
OTf
OTf
H
reductive
elimination
Rh
Rh
Rh
Ar
EtO
H
EtO
Ar
Ar
Ar
H
alkoxide
transfer
H
OEt
Ar
H
H
Ar
H
Ar
B
Ar
C
H
H
4a, 4b
Ar
Scheme 3.

M.S. Lim et al. / Journal of Organometallic Chemistry 691 (2006) 4100–4108
4107
unusual complex [Cp*Rh(g4-C4(C(O)CH3)2H(SiMe3))],
which appears to have been formed through a complex ser-
ies of reactions. Other reactivity studies are currently in
progress.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Center: 602168 (1), 602169 (2e), and 602170 (5). Copies
of this information may be obtained free of charge from:
The director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK, fax: +44 1223 336 033, email: deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk.
Acknowledgement
This work was supported by the 63 Research Fund of
Sungkyunkwan University (2004–2005).
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