Syntheses and crystal structures of mononuclear rhodium hydrido complexes from the reactions of [RH(H)2(PPH3)2(ETOH)2] C1O4 with various nitrogen ligands

Article abstract of DOI:10.1016/S0277-5387(02)01028-8

Reactions of the Rh hydrido complex [Rh(H)₂(PPh₃)₂(EtOH)₂] ClO₄ (1) with nitrogen ligands such as 2-(4-thiazolyl)benzimidazole (tbz), pyridazine (pdz), imidazole (im) and pyrimidine (pmd) in CH₂Cl₂ afforded various mononuclear Rh hydrido complexes, [Rh(H)₂(PPh₃)₂(tbz)]ClO₄ (2), [Rh(H)₂(PPh₃)2(pdz)₂]ClO₄ ·2CH₂Cl₂ (3), [Rh(H)Cl(PPh₃)₂(pdz)₂]ClO₄ ·CH₂Cl₂ (4), [Rh(H)₂(PPh₃)₂(im)₂] ClO₄·2CH₂Cl₂ (5), [Rh(H)Cl(PPh₃)₂(im)₂]ClO₄ ·CH₂Cl₂ (6), [Rh(H)₂(PPh₃)₂(pmd)₂] ClO₄·CH₂Cl₂ (7) and the Rh non-hydrido complex [RhCl₂(pmd)₄]ClO₄ (8). The Rh complexes 2, 3, 5 and 6 were crystallographically characterized. The formation process was monitored by ¹H NMR and UV-Vis spectra. In all the Rh hydrido complexes, the Rh atom is coordinated by two PPh₃ ligands in trans-positions and two nitrogen ligands in the cis-positions. The remaining sites are occupied by one or two hydride atoms to form a saturated 18-electron framework in a slightly distorted octahedral geometry. For complex 2 an appreciable inter-molecular π interaction is observed between planes of tbz and PPh₃ ligands, while an intra-molecular hydrogen bonding interaction between C-H and Cl atoms is found in complex 6.

Full text of DOI:10.1016/S0277-5387(02)01028-8

Polyhedron 21 (2002) 1613ꢀ1620
/
www.elsevier.com/locate/poly
Syntheses and crystal structures of mononuclear rhodium hydrido
complexes from the reactions of [Rh(H)2(PPh3)2(EtOH)2]ClO4 with
various nitrogen ligands
Xiao-Yan Yu a, Masahiko Maekawa b,*, Tomonori Morita b, Ho-Chol Chang a,
Susumu Kitagawa a,*, Guo-Xin Jin c
a Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University,
Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
b Research Institute for Science and Technology, Kinki University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
c State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Science,
Changchun 130022, People’s Republic of China
Received 13 December 2001; accepted 11 February 2002
Abstract
Reactions of the Rh hydrido complex [Rh(H)2(PPh3)2(EtOH)2]ClO4 (1) with nitrogen ligands such as 2-(4-thiazolyl)benzimidazole
(tbz), pyridazine (pdz), imidazole (im) and pyrimidine (pmd) in CH2Cl2 afforded various mononuclear Rh hydrido complexes,
[Rh(H)2(PPh3)2(tbz)]ClO4
[Rh(H)2(PPh3)2(im)2]ClO4×
Rh non-hydrido complex [RhCl2(pmd)4]ClO4 (8). The Rh complexes 2, 3, 5 and 6 were crystallographically characterized. The
formation process was monitored by 1H NMR and UVꢀ
Vis spectra. In all the Rh hydrido complexes, the Rh atom is coordinated
(2),
[Rh(H)2(PPh3)2(pdz)2]ClO4×
/
2CH2Cl2
(3),
[Rh(H)Cl(PPh3)2(pdz)2]ClO4×
/
CH2Cl2
(4),
/
2CH2Cl2 (5), [Rh(H)Cl(PPh3)2(im)2]ClO4×
/
CH2Cl2 (6), [Rh(H)2(PPh3)2(pmd)2]ClO4×
/
CH2Cl2 (7) and the
/
by two PPh3 ligands in trans-positions and two nitrogen ligands in the cis-positions. The remaining sites are occupied by one or two
hydride atoms to form a saturated 18-electron framework in a slightly distorted octahedral geometry. For complex 2 an appreciable
inter-molecular p interaction is observed between planes of tbz and PPh3 ligands, while an intra-molecular hydrogen bonding
interaction between CÃ/H and Cl atoms is found in complex 6. # 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Mononuclear complexes; Rhodium complexes; Hydrido complexes; Nitrogen ligands; Crystal structures
1. Introduction
produce a superior property. However, there are rela-
tively few investigations of mononuclear Rh hydrido
complexes including chloride and nitrogen ligands as
analogous ones to Wilkinson’s complex [4]. Although
Rh non-hydrido complexes with nitrogen ligands have
Considerable interest and many investigations have
been so far devoted to mononuclear Rh hydrido
complexes with tertiary phosphine ligands as highly
effective catalysts for the hydrogenation and hydrofor-
mylation of olefins [1], which are for instance represen-
tative of Wilkinson’s complex RhCl(PPh3)3 [2]. Rh
complexes with nitrogen heterocyclic ligands have been
also known in relation to their catalytic activities [3],
and their hydrido complexes are particularly expected to
been well investigated [5ꢀ7], crystallographic studies of
/
Rh hydrido complexes with nitrogen ligands have been
limited.
We have so far examined the reactions of the Rh
hydrido complex [Rh(H)2(PPh3)2(EtOH)2]ClO4 (1) with
nitrogen bridging ligands such as pyrazine (pyz) and
4,4?-bipyridine derivatives in various organic solvents
[7]. It has been illustrated that these reaction processes
are greatly related to the solvents and the structural
feature of the nitrogen bridging ligands. Complex 1
formed the dinuclear Rh complex [Rh2(PPh3)2{(h6-
* Corresponding authors. Fax: ꢁ
/
81-6-6730-5896 (M.M.); fax: ꢁ81-
/
75-753-4979 (S.K.)
E-mail addresses: maekawa@rist.kindai.ac.jp (M. Maekawa),
kitagawa@sbchem.kyoto-u.ac.jp (S. Kitagawa).
C6H5)Ph2P}]2](ClO4)2×/6CH2Cl2 in CH2Cl2, with the
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 0 2 8 - 8

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X.-Y. Yu et al. / Polyhedron 21 (2002) 1613ꢀ1620
/
reductive elimination of hydrogen. The reaction of
complex 1 with pyrazine (pyz) in CH2Cl2 afforded the
spectrometer. Trimethylsilane was used as an internal
reference.
triangular Rh3 complex [Rh3(PPh3)6(pyz)3](ClO4)3×
CH2Cl2, in contrast to the formation of the dinuclear
Rh hydrido complex [Rh2(H)4(PPh3)4(Me2CO)2(pyz)]-
/
2.2. Preparation of Rh complexes with nitrogen ligands
(ClO4)2×
/
EtOH in Me2CO. The reaction of complex 1
2.2.1. [Rh(H)2(PPh3)2(tbz)]ClO4 (2)
with 4,4’-trimethylenedipyridine (tmdp), having a long
spacer, in CH2Cl2 provided the dinuclear Rh non-
hydrido complex [Rh2(PPh3)4(tmdp)2](ClO4)2. In this
study, as further investigations, the reactions of complex
1 with nitrogen ligands such as 2-(4-thiazolyl)benzimi-
dazole (tbz), pyridazine (pdz), imidazole (im) and
pyrimidine (pmd) in CH2Cl2 were examined according
to Scheme 1. Several mononuclear Rh complexes were
isolated and their structures were crystallographically
characterized.
A 5 ml CH2Cl2 solution of [Rh(H)2(PPh3)2(E-
tOH)2]ClO4 (1) (41.1 mg, 0.05 mmol) was added to the
tbz ligand (10.1 mg, 0.05 mmol) in CH2Cl2 (5 ml). After
stirring for 30 min, the reaction solution was filtered.
The yellow filtrates were introduced into 5 mm diameter
glass tubes and were layered with hexane as the diffusion
solvent. The glass tubes were sealed and allowed to
stand at r.t. for 2 days. Light yellow crystals of complex
2 were collected. Yield: 43.7 mg (94%). IR (KBr pellet,
cmꢂ1): 2081 (RhÃ
NMR (CD2Cl2, 23 8C, ppm): d 11.98 (NÃ
benzimidazole), 8.19 (2-H of thiazolyl), 8.08 (4-H of
benzimidazole), 7.00ꢀ7.59 (Ph of PPh3), 6.03 (5-H of
benzimidazole), ꢂ H) and ꢂ H).
/
H), 1435, 1095, 696 and 519. 1H
/
H of
/
2. Experimental
/
15.60 (RhÃ
/
/
16.30 (RhÃ
/
Anal. Calc. for C46H39P2N3SRhO4Cl: C, 59.40; H, 4.23;
N, 4.52. Found: C, 59.26; H, 3.97; N, 4.33%.
2.1. General procedures
All operations were carried out using standard
Schlenk techniques under N2 atmosphere. All the
organic solvents were distilled by general methods
2.2.2. [Rh(H)2(PPh3)2(pdz)2]ClO4×
/
2CH2Cl2 (3) and
[Rh(H)Cl(PPh3)2(pdz)2]ClO4×CH2Cl2 (4)
/
Complex 3 was prepared in the same manner as for
complex 2, using the pdz ligand (8.0 mg, 0.10 mmol).
Light yellow crystals of complex 3 were obtained 2 days
later at the middle part of the glass tubes. Yield: 43.4 mg
before use. RhCl3×/3H2O, 2-(4-thiazolyl)benzimidazole,
pyridazine, imidazole and pyrimidine were commercially
purchased from Steam and Aldrich and used without
further purifications. [Rh(H)2(PPh3)2(EtOH)2]ClO4 (1)
was synthesized according to the literature [8]. IR
(82%). IR (KBr pellet, cmꢂ1): 2046 (RhÃ
/H), 1435, 1093,
1
697 and 521. H NMR (CD2Cl2, 23 8C, ppm): d 9.16
(3,6-H of prd), 8.57 (5-H of prd), 8.21 (4-H of prd),
spectra were recorded on a Perkinꢀ/Elmer System 2000
FT IR spectrometer as a KBr pellet. UVꢀ/Vis spectra
7.20ꢀ
/
7.48 (Ph of PPh3), and ꢂ
/
16.89 (RhÃ
/H). Anal.
were recorded on a HITACHI U-3500/U-4000 spectro-
meter. 1H NMR spectra were measured at room
temperature (r.t.) on a JEOL JNM-A 500 FT NMR
Calc. for C46H44P2N4RhO4Cl5: C, 52.17; H, 4.19; N,
5.29. Found: C, 51.68; H, 4.11; N, 5.33%.
The reaction solution was allowed to stand for a
further 2 weeks and colorless crystals of complex 4 were
collected at the upper part of the glass tubes. Yield: 4.0
mg (8%). IR (KBr pellet, cmꢂ1): 2174 (RhÃ
/
H), 1435,
1093, 696 and 523. Anal. Calc. for C45H41P2N4RhO4Cl4:
C, 53.59; H, 4.10; N, 5.56. Found: C, 53.32; H, 4.03; N,
5.86%.
2.2.3. [Rh(H)2(PPh3)2(im)2]ClO4×
/
2CH2Cl2 (5) and
[Rh(H)Cl(PPh3)2(im)2]ClO4×CH2Cl2 (6)
/
Complex 5 was prepared in the same manner as for
complex 3, using the im ligand (6.7 mg, 0.10 mmol). The
reaction solution was allowed to stand at r.t. for 2 days
and light yellow crystals of complex 5 were obtained at
the middle part of the glass tubes. Yield: 38.1 mg (74%).
IR (KBr pellet, cmꢂ1): 2051 (RhÃ
/
H), 1435, 1095, 695
and 520. H NMR (CD2Cl2, 23 8C, ppm): d 10.09 (NÃ
H of im), 7.21ꢀ7.61 (Ph of PPh3), 6.71 (2-H of im), 6.57
(4-H of im), 6.31 (5-H of im) and ꢂ16.85 (RhÃH). Anal.
1
/
/
/
/
Calc. for C44H44P2N4RhO4Cl5: C, 51.06; H, 4.28; N,
Scheme 1.
5.41. Found: C, 51.44; H, 4.42; N, 5.57%.

X.-Y. Yu et al. / Polyhedron 21 (2002) 1613ꢀ
/1620
1615
The reaction solution was allowed to stand at r.t. for
another 2 weeks and colorless crystals of complex 6 were
collected at the upper part of the glass tubes. Yield: 1.0
3. Results and discussion
3.1. Crystal structures
mg (2%). IR (KBr pellet, cmꢂ1): 2133 (RhÃ
/H), 1434,
1094, 696 and 523. Anal. Calc. for C43H41P2N4RhO4Cl4:
C, 52.46; H, 4.20; N, 5.69. Found: C, 52.51; H, 4.11; N,
5.53%.
3.1.1. [Rh(H)2(PPh3)2(tbz)]ClO4 (2)
In the reaction of complex 1 with the nitrogen ligand,
the tbz ligand acted as a bidentate chelate ligand and led
to the typical mononuclear Rh hydrido complex 2. Since
no crystallographic structures of Rh complexes contain-
ing the tbz ligand have been reported, complex 2 is the
first example of a Rh hydrido complex with the tbz
ligand. Fig. 1 shows the cation moiety of complex 2
together with the atomic labelling scheme. The Rh atom
is coordinated by two P atoms, two N atoms and two
hydride atoms in a distorted octahedral environment.
The two PPh3 ligands are nearly in trans-positions with
2.2.4. [Rh(H)2(PPh3)2(pmd)4]ClO4×
/
CH2Cl2 (7) and
[RhCl2(pmd)4]ClO4 (8)
Complex 7 was prepared in the same manner as for
complex 3, using the pmd ligand (8.0 mg, 0.10 mmol).
Complex 7 was obtained as white precipitates. Yield:
36.0 mg (74%). IR (KBr pellet, cmꢂ1): 2060 (RhÃ
/
H),
1584, 1435, 1094, 696 and 520. 1H NMR (CD2Cl2,
a P(1)Ã
/
RhÃP(2) angle of 167.06(8)8. The Rh coordina-
/
23 8C, ppm): d 9.17 (2-H of pmd), 8.73 (6-H of pmd),
tion plane defined by two N atoms of the tbz ligand and
two hydride atoms are coplanar with the mean deviation
8.28 (4-H of pmd), 7.26ꢀ/7.38 (Ph of PPh3), 7.01 (5-H of
pmd) and
C45H42P2N4RhO4Cl3: C, 55.49; H, 4.35; N, 5.75. Found:
ꢂ
/
17.30 (RhÃ/H). Anal. Calc. for
˚
of 0.0365 A. Two heterocyclic rings of the tbz ligand are
˚
nearly coplanar with a mean deviation of 0.0707 A. The
H distances of 2.299,
C, 55.92; H, 4.20; N, 5.58%.
average RhÃ
/
P, RhÃ
/
N and RhÃ
/
Yellow crystals of complex 8 were collected 4 days
later at the lower part of the glass tubes. Yield: 3.5 mg
(12%). IR (KBr pellet, cmꢂ1): 1595, 1411, 1122, 706 and
625. Anal. Calc. for C16H16N8RhO4Cl3: C, 32.37; H,
2.72; N, 18.88. Found: C, 32.68; H, 2.61; N, 18.69%.
˚
2.197 and 1.58 A are similar to those of other analogous
˚
hydrido complexes [14]. The Hꢀ ꢀ ꢀH distance of 2.08 A is
characteristic of hydrido complexes [15]. The N(1)Ã
/
RhÃ
/
N(2) angle of 76.1(2)8 is within the range of values of
other Rh complexes with bidentate nitrogen ligands [16].
Selected bond distances and bond angles are listed in
Table 2.
2.3. X-ray crystallography
3.1.2. [Rh(H)2(PPh3)2(pdz)2]ClO4×
/
2CH2Cl2 (3)
For each complex, a suitable crystal was sealed into
the glass capillary (0.7 mm, GLAS) and mounted on the
crystal goniometer. The intensity data of all the single
crystals were collected on the Rigaku/Mercury CCD
The structure of the cation moiety of complex 3 is
presented in Fig. 2. The Rh atom is coordinated by two
PPh3 ligands, two pdz ligands and two hydride atoms to
afford a mononuclear Rh complex in a slightly distorted
octahedral geometry. In each pdz ligands, one of the two
N atoms is bonded to the Rh atom. The two pdz ligands,
in cis-positions, are inclined against the N2RhH2
coordination plane at an angle of 31.2(2)8. On the other
hand, two PPh3 ligands in trans-positions are bent
system using graphite monochromated Mo Ka radiation
˚
0.710691 A). The structures of complexes 2, 5 and 6
(lꢃ
/
were solved by the direct method (SIR-92 for 2 and 5;
SIR-97 for 6) [9], and expanded using Fourier techniques
[10]. The structure of complex 3 was solved by the
heavy-atom Patterson method [11] and expanded using
Fourier techniques [10]. The hydride hydrogen atoms
were located and refined isotropically. All other hydro-
gen atoms were included but not refined. The non-
hydrogen atoms were refined anisotropically. The final
cycle of full-matrix least-squares refinement was based
toward the two hydrides with a P(1)Ã
/
RhÃ
/
P(1?) angle
of 163.89(5)8. The RhÃ
/
P, RhÃ
/
N and RhÃH distances of
/
˚
2.3033(9), 2.181(3) and 1.44(4) A are similar to those of
other Rh hydrido complexes [14]. The Hꢀ ꢀ ꢀH distance of
˚
2.03 A is within the range of values found in other
hydrido complexes [15]. Selected bond distances and
angles are listed in Table 3.
on 5251, 4348, 4418 and 6594 observed reflections (I ꢀ
/
3s(I)) for complexes 2, 3, 5 and 6, respectively. The
unweighted and weighted agreement factors of
Metal complexes with the pdz ligand as a heterocyclic
ligand have been relatively limited, in comparison with
those with the pyrazine ligand [17]. Although recently
there have been several crystallographic reports on
complexes with pdz ligands [18], Rh complexes with
the pyz ligand are few. The crystal structure of complex
3 is remarkable as a Rh hydrido complex with the pdz
ligand.
2
2 2
Fc ) /
Rꢃ
/
ajjFojꢂ
/
jFcjj/ajFoj
and
Rwꢃ
/
[a w(Fo ꢂ
/
2 2 1/2
a w(Fo ) ] were used. The atomic scattering factors
and anomalous dispersion terms were taken from ref.
[12]. All calculations were performed using the TEXSAN
crystallographic software package [13]. The detailed
crystal data of all complexes are summarized in Table 1.

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X.-Y. Yu et al. / Polyhedron 21 (2002) 1613ꢀ1620
/
Table 1
Crystal data and measurement conditions for 2, 3, 5 and 6
Complexes
2
3
5
6
Formula
M
RhP2N3ClO4C46H39
930.20
S
RhP2N4Cl5O4C46H44
1059.00
RhP2N4Cl5O4C44H44
1034.97
RhP2N4Cl4O4C43H41
984.49
Crystal system
Space group
monoclinic
P21/c
orthorhombic
P212121
15.362(6)
orthorhombic
P212121
15.020(2)
Monoclinic
P21/n
˚
a (A)
13.2040(9)
13.7074(9)
23.268(1)
99.3724(8)
4155.0(5)
1.487
22.608(1)
14.2621(5)
13.7827(5)
104.3593(7)
4305.3(3)
1.519
˚
b (A)
15.404(1)
10.048(2)
15.3277(3)
10.1368(2)
˚
c (A)
b (8)
3
˚
V (A )
2377(1)
1.479
1080
2333.8(4)
1.473
1056
Dcalc (g cmꢂ3
F(000)
)
1904
2008
Z
4
6.50
2
7.53
2
7.65
4
7.65
m (Mo Ka) (cmꢂ1
Number of reflections
)
24430 (total)
9159 (unique)
5251 [I ꢀ3.00s(I)]
0.078
14955 (total)
2854 (unique)
4348 [I ꢀ3.00s(I)]
0.042
14544 (total)
2783 (unique)
4418 [I ꢀ3.00s(I)]
0.044
27180 (total)
9470 (unique)
6594 [I ꢀ3.00s(I)]
0.054
Number of observations
R
Rw
0.081
0.055
0.062
0.068
Fig. 1. The crystal structure of the cation moiety of complex 2. Only
Rh(1), N(1), N(2), N(3), S(1), P(1), P(2), C(11), C(17), C(23), C(29),
C(35), C(41), H(1) and H(2) in the coordination sphere are labelled.
Fig. 2. The crystal structure of the cation moiety of complex 3. Only
Rh(1), N(1), N(1?), N(2), N(2?), P(1), P(1?), C(5), C(11), C(17), C(5?),
C(11?), C(17?), H(1) and H(1?) in the coordination sphere are labelled.
Table 2
˚
Selected bond lengths (A) and bond angles (8) of 2
Table 3
Bond lengths
˚
Selected bond lengths (A) and bond angles (8) of 3
Rh(1)ÃP(1)
Rh(1)ÃN(1)
Rh(1)ÃH(1)
2.317(2)
2.192(7)
1.59(6)
Rh(1)ÃP(2)
Rh(1)ÃN(2)
Rh(1)ÃH(2)
2.282(2)
2.203(6)
1.57(8)
Bond lengths
Rh(1)ÃP(1)
Rh(1)ÃH(1)
2.3033(9) Rh(1)ÃN(1)
1.44(4)
2.181(3)
Bond angles
P(1)ÃRh(1)ÃP(2)
P(1)ÃRh(1)ÃN(2)
P(2)ÃRh(1)ÃN(2)
Rh(1)ÃP(1)ÃC(11)
Rh(1)ÃP(1)ÃC(23)
Rh(1)ÃP(2)ÃC(35)
H(1)ÃRh(1)ÃH(2)
167.06(8) P(1)ÃRh(1)ÃN(1)
93.5(2)
96.8(2)
76.1(2)
Bond angles
a
92.9(2)
97.1(2)
P(2)ÃRh(1)ÃN(1)
N(1)ÃRh(1)ÃN(2)
Rh(1)ÃP(1)ÃC(17)
Rh(1)ÃP(2)ÃC(29)
Rh(1)ÃP(2)ÃC(41)
P(1)ÃRh(1)ÃP(1?)
P(1)ÃRh(1)ÃN(1?)
163.89(5) P(1)ÃRh(1)ÃN(1)
92.3(1) P(1) aÃRh(1)ÃN(1)
98.8(1) N(1)ÃRh(1)ÃN(1?)
112.0(2) Rh(1)ÃP(1)ÃC(11)
117.0(1) H(1)ÃRh(1)ÃH(1?)
98.8(1)
92.3(1)
92.7(2)
115.7(2)
89.0(3)
a
P(1)1ÃRh(1)ÃN(1?)
Rh(1)ÃP(1)ÃC(5)
Rh(1)ÃP(1)ÃC(17)
a
a
a
112.2(3)
113.6(3)
114.3(3)
82.0(3)
117.4(3)
111.9(2)
118.0(3)
a
Symmetry codes ꢂXꢂ1, ꢂYꢂ1, Z.

X.-Y. Yu et al. / Polyhedron 21 (2002) 1613ꢀ
/1620
1617
of Rh hydrido complexes with the im ligand. To the best
of our knowledge, this is the first crystal structure of a
Rh hydrido complex with the im ligand.
3.1.4. [Rh(H)Cl(PPh3)2(im)2]ClO4×
/
CH2Cl2 (6)
After light-yellow single crystals of complex 5 were
obtained according to Scheme 1, colorless single crystals
of complex 6 were collected from the same reaction
solution 2 weeks later. The structure of the cation
moiety of complex 6 is revealed in Fig. 4. The
coordination sphere around the Rh atom consists of
two PPh3 ligands, two im ligands, one Cl atom and one
hydride atom, providing a distorted octahedral geome-
try. It is interesting that the two im ligands are located in
the trans-positions and are separated by the Cl atom
and the hydride atom. This structural feature is greatly
Fig. 3. The crystal structure of the cation moiety of complex 5. Only
Rh(1), N(1), N(1?), N(2), N(2?), P(1), P(1?), C(4), C(10), C(16), C(4?),
C(10?), C(16?), H(1) and H(1?) in the coordination sphere are labelled.
different from that in complex 5. The P(1)Ã
/
RhÃ/P(2)
angle of 177.26(4)8 is much larger than those of
163.89(5)8 and 163.13(5)8 in complexes 3 and 5, respec-
tively. Therefore the PPh3 ligands in the trans-positions
3.1.3. [Rh(H)2(PPh3)2(im)2]ClO4×
/
2CH2Cl2 (5)
The structure of the cation moiety of complex 5 is
shown in Fig. 3. The structure of complex 5 essentially
resembles that of complex 3. The Rh atom is coordi-
nated by two PPh3 ligands, two im ligands and two
hydride atoms in a distorted octahedral geometry. The
two im ligands in cis-positions are slightly inclined
against the N2RhH2 coordination plane at an angle of
27.7(2)8, which is smaller than that (31.2(2)8) of complex
3. The two PPh3 ligands are in trans-positions and the
are almost linearly located. The average RhÃ
/
P distance
of 2.362 A is longer than those of normal Rh and Ir
hydrido complexes [4,7]. The average RhÃN distances of
2.056 A are shorter than those of 2.181(3) and 2.189(3)
˚
/
˚
˚
A in complexes 3 and 5, respectively. The RhÃ
/
Cl
˚
distance of 2.498(1) A is longer than those found in
other hydrido complexes [4] owing to the trans influence
of the nitrogen ligands. Selected bond distances and
angles are listed in Table 5.
P(1)Ã
/
RhÃP(1?) angle of 163.13(5)8 is similar to that
/
(163.89(5)8) of complex 3. The Rhà H
distances of 2.2955(9), 2.189(3) and 1.50(4) A are close
/
P, RhÃ
/
N and RhÃ
/
˚
3.2. Reactions of [Rh(H)2(PPh3)2(EtOH)2]ClO4 with
nitrogen ligands in CH2Cl2
to those of other Rh hydrido complexes [14]. The Hꢀ ꢀ ꢀH
˚
distance of 2.07 A is in the range of those found in other
hydrido complexes [15]. Selected bond distances and
angles are listed in Table 4.
Our survey of Rh complexes with the im ligand and its
derivatives described the tetranuclear complex [Rh(2-
According to Scheme 1, the reactions of the Rh
hydrido complex 1 with nitrogen ligands were attempted
and their reaction processes were monitored by 1H
NMR and UVꢀVis spectra. The addition of the tbz
/
Meim)(CO)2]4 (2-Meimꢃ
dinuclear complex [NBu4][Rh2(cod)2(dcbi)]×
(dcbiꢃ4,5-dicarboxyimida-zole) [19b], the mononuclear
complexes [RhCl2(N-Meim)4]Cl×2H2O (MeimꢃN-
/
2-methylimidazole) [19a], the
/
2iPrOH
/
/
/
methyl-imidazole) [19c] and [imH][trans-RhCl4(im)2]
[19d]. However, there are no reports of X-ray structures
Table 4
˚
Selected bond lengths (A) and bond angles (8) of 5
Bond lengths
Rh(1)ÃP(1)
Rh(1)ÃH(1)
2.2955(9) Rh(1)ÃN(1)
1.50(4)
2.189(3)
Bond angles
a
P(1)ÃRh(1)ÃP(1?)
P(1)ÃRh(1)ÃN(1?)
163.13(5) P(1)ÃRh(1)ÃN(1)
96.6(1)
94.9(1)
93.3(2)
116.5(1)
87.0(3)
a
a
94.9(1) P(1) ÃRh(1)ÃN(1)
P(1)1ÃRh(1)ÃN(1?)
Rh(1)ÃP(1)ÃC(4)
Rh(1)ÃP(1)ÃC(16)
96.6(1) N(1)ÃRh(1)ÃN(1?)
112.6(1) Rh(1)ÃP(1)ÃC(10)
117.1(1) H(1)ÃRh(1)ÃH(1?)
a
a
a
Fig. 4. The crystal structure of the cation moiety of complex 6. Only
Rh(1), Cl(1), N(1), N(2), N(3), N(4), P(1), P(2), C(7), C(13), C(19),
C(31), C(25), C(37) and H(1) in the coordination sphere are labelled.
a
Symmetry codes: ꢂXꢁ2, ꢂY, Z.

1618
X.-Y. Yu et al. / Polyhedron 21 (2002) 1613ꢀ1620
/
Table 5
studies, it was concluded that the reaction of complex
1 with nitrogen ligands such as tbz, pdz, im and pmd
ligands provided mononuclear Rh hydrido complexes
without the reductive elimination of hydrogen. We
previously demonstrated that the reactions of complex
1 with nitrogen bridging ligands such as pyrazine and
4,4?-bipyridine derivatives in CH2Cl2 could afford di-
and trinuclear Rh non-hydrido complexes[7] with the
reductive elimination of hydrogen. The results in this
study are greatly different from those previously found.
Although the detailed reason is not obvious at the
present, it is probably considered that nitrogen ligands
such as tbz, pdz and im ligands are structurally difficult
to bridge Rh centers owing to the steric repulsion
against the phenyl group of the PPh3 ligand and should
lead to mononuclear Rh hydrido complexes with nitro-
gen ligands, without the reductive elimination of hydro-
gen.
˚
Selected bond lengths (A) and bond angles (8) of 6
Bond lengths
Rh(1)ÃCl(1)
Rh(1)ÃP(2)
Rh(1)ÃN(3)
2.498(1)
2.364(1)
2.051(4)
Rh(1)ÃP(1)
Rh(1)ÃN(1)
Rh(1)ÃH(1)
2.360(1)
2.061(4)
1.47(6)
Bond angles
Cl(1)ÃRh(1)ÃP(1)
Cl(1)ÃRh(1)ÃN(1)
P(1)ÃRh(1)ÃP(2)
P(1)ÃRh(1)ÃN(3)
P(2)ÃRh(1)ÃN(3)
Rh(1)ÃP(1)ÃC(13)
Rh(1)ÃP(2)ÃC(25)
Rh(1)ÃP(2)ÃC(37)
N(3)ÃRh(1)ÃH(1)
90.94(4) Cl(1)ÃRh(1)ÃP(2)
93.5(1)
Cl(1)ÃRh(1)ÃN(3)
177.26(4) P(1)ÃRh(1)ÃN(1)
91.46(4)
92.2(1)
91.6(1)
88.8(1)
P(2)ÃRh(1)ÃN(1)
Rh(1)ÃP(1)ÃC(7)
Rh(1)ÃP(1)ÃC(19)
Rh(1)ÃP(2)ÃC(31)
N(1)ÃRh(1)ÃH(1)
89.6(1)
89.8(1)
114.5(2)
116.4(2)
112.4(1)
87.0(2)
114.5(2)
115.2(2)
117.9(2)
86.0(2)
ligand to complex 1 in CD2Cl2 initially showed two new
1
quintet H NMR signals of hydride species at ꢂ
and ꢂ16.30 ppm at r.t., together with the quintet H
NMR signal of an hydride species at ꢂ22.16 ppm,
which should be attributed to hydrides of complex 1.
After about 1 h, the 1H NMR signal of complex 1
completely disappeared and the two new 1H NMR
signals only remained. These facts indicate that Rh
hydrido complex 2 with the tbz ligand was formed in
CH2Cl2 solution. Similarly, on the reaction of complex 1
/
15.60
As mentioned in the Section 2, when the reaction
solution of the Rh hydrido complex 1 with pdz, im and
pmd ligands was allowed to stand for more than 2
weeks, Rh complexes 4, 6 and 8 [20] with a coordinated
Cl atom were collected in the same glass tubes,
respectively. The reaction solution of complex 1 with
the tbz ligand did not provide the corresponding Rh
complex with a coordinated Cl atom since the tbz ligand
played a role as a bidentate chelate ligand. In this study,
1
/
/
1
1
with pdz, im and pmd ligands, the H NMR signals of
the monitoring of their formation process by H NMR
the hydride species could be observed at ꢂ
16.85 and ꢂ17.30 ppm for complexes 3, 5 and 7,
respectively. On the other hand, as shown in the time-
course UVꢀVis spectra (Fig. 5), complex 1 dissolved in
/16.89,
and UVꢀVis spectra over 2 weeks has not been carried
/
ꢂ
/
/
out and the structure of 6 could only be crystallogra-
phically characterized. At the present, although their
formation mechanisms are not obvious in detail, it is
considered that the Cl atom is probably derived from
the CH2Cl2 solvent since it has been known that
[RhCl(PPh3)2]2 was produced by the reaction of
[Rh2(H)2(PPh3)4(Me4Si2O)2] with CH2Cl2 as the solvent
[21].
/
CH2Cl2 at 23 8C displayed the color change from
yellow to the dark brown solution of [Rh2(PPh3)2{(h6-
C6H5)Ph2P}]2]2ꢁ (lmax
[7]. The further addition of tbz ligand to the CH2Cl2
ꢃ
/
410 nm (oꢃ
3056 cmꢂ1 Mꢂ1))
/
solution exhibited the color change from dark-brown to
420 nm (oꢃ
2235 cmꢂ1 Mꢂ1))
a yellow solution (lmax
ꢃ
/
/
and the formation of complex 2 was completed after
about 50 min. On the basis of these structural studies in
solution and the above-mentioned crystallographic
3.3. Consideration on crystallographic study
The four crystallographic studies revealed the signifi-
cant structural differences among their bond distances
and bond angles of complexes 2, 3, 5 and 6. In complex
6 with the Cl atom, the average RhÃ
/
N distance of 2.056
˚
˚
˚
A is shorter than those (2 (2.197(7) A), 3 (2.181(3) A)
˚
and 5 (2.189(3) A)) of the other Rh complexes without
the Cl atom. In contrast, the average RhÃP distance of
complex 6 (2.362 A) is slightly longer than those of 2
/
˚
˚
˚
˚
(2.299 A), 3 (2.3033 A) and 5 (2.2955 A). The PÃ
/
RhÃ/P
angle of 6 (177.26(4)8) is rather larger than those of 2
(167.06(8)8), 3 (163.89(5)8), 5 (163.13(5)8) and other Rh
hydrido complexes [4,7]. These changes should probably
be caused by the repulsion between the bulky Cl atom
Fig. 5. The time-course UVꢀ
the dissolving of complex 1: 10 (1) and ]
of the tbz ligand to complex 1: 20 (3), 30 (4), 40 (5) and ]
[c]ꢃ1.7ꢄ
10ꢂ4 M.
/
Vis spectra in CH2Cl2 at 23 8C. After
50 (2) min. After the addition
50 (6) min.
/
and the trans-nitrogen ligands. The RhÃ
/
Cl distance of
˚
2.499(1) A in complex 6 is also longer than those of
/
/
/

X.-Y. Yu et al. / Polyhedron 21 (2002) 1613ꢀ
/1620
1619
other Rh hydrido complexes [4] owing to the trans
influence of the nitrogen ligands.
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/C hydrogen bonds in
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This work was partially supported by Grants-in-Aids
from the Ministry of Education, Science, Culture,
Sports and Technology in Japan and research funds
from Kinki University. Miss. X.-Y. Yu is also grateful
to the Ministry of Education, Science, Culture, Sports
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[20] The crystal data could be only collected in complex 8: complex 8,
formula C16H16N8RhO4Cl3, M 593.62, crystal system tetragonal,
space group P4/n, aꢃ
/
10.592(2), bꢃ
1074.6(3) A , Dcalc
1.834 g cmꢂ3, Zꢃ
12.08 cmꢂ1 and number of total reflections 6412.
/
10.592(2) and cꢃ
/
9.5780(6)
3
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