Rhodium, iridium and gold complexes of the short-bite ligand 1-benzyl-2-imidazolyldiphenylphosphine

Article abstract of DOI:10.1016/S0020-1693(02)01447-0

Reactions of [{M(μ-Cl)(cod)}₂] (M=Rh, Ir) with 1-benzyl-2-imidazolyldiphenylphosphine gave the mononuclear P-bonded compounds [MCl(cod)(Ph₂PBzIm)]. They react with [M(cod)(acetone)_x]BF₄ to give the cationic [{M(cod)}₂(μ-Cl)(μ-Ph₂PBzIm)]⁺ complexes, while they react with silver salts to give the homometallic dinuclear complexes HT-[{M(μ-Ph₂PBzIm)(cod)}₂](BF₄) ₂ (M=Rh, Ir) containing two mutually cis bridging ligands in a HT disposition. Addition of [AuCl(tht)] to [MCl(cod)(Ph₂PBzIm)] gave the heterometallic complexes [MCl(cod)(μ-Ph₂PBzIm)AuCl] with the gold atom coordinated to the P-end. While the Ir-Au compound remained as such in solution, the Rh-Au complex was found to be in equilibrium with [AuCl(Ph₂PBzIm)] and [{Rh(μ-Cl)(cod)}₂]. Reaction of trans-[RhCl(CO)(Ph₂PBzIm)₂] with [{Rh(μ-Cl)(CO)₂}₂] gave the 'A-frame' complex [{RhCl}₂(μ-CO)(μ-Ph₂PBzIm)₂] while the reaction with [PdCl₂(NCMe)₂] resulted in the formation of three isomers of the metal-metal bonded compound [(CO)Cl₂Rh(μ-Ph₂PBzIm)₂PdCl].

Full text of DOI:10.1016/S0020-1693(02)01447-0

Inorganica Chimica Acta 347 (2003) 129ꢂ136
/
www.elsevier.com/locate/ica
Rhodium, iridium and gold complexes of the short-bite ligand 1-
benzyl-2-imidazolyldiphenylphosphine
Cristina Tejel a, Miguel A. Ciriano a,*, Rita Bravi a, Luis A. Oro a,*, Claudia Graiff b,
Rossana Galassi c, Alfredo Burini c
a Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n, Universidad de Zaragoza-C.S.I.C., E-50009 Zaragoza, Spain
b Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Centro di Studio per la Strutturistica Diffrattometrica del CNR,
Universita` di Parma, Parco Area delle Scienze 17A, I-43100 Parma, Italy
c Dipartimento di Scienze Chimiche, Universita` degli Studi di Camerino, I-62032 Camerino, Italy
Received 13 May 2002; accepted 16 August 2002
Dedicated in honor of Professor R. Uso´n
Abstract
Reactions of [{M(m-Cl)(cod)}2] (Mꢀ
/
Rh, Ir) with 1-benzyl-2-imidazolyldiphenylphosphine gave the mononuclear P-bonded
compounds [MCl(cod)(Ph2PBzIm)]. They react with [M(cod)(acetone)x ]BF4 to give the cationic [{M(cod)}2(m-Cl)(m-Ph2PBzIm)]ꢁ
complexes, while they react with silver salts to give the homometallic dinuclear complexes HT-[{M(m-Ph2PBzIm)(cod)}2](BF4)2
(Mꢀ
gave the heterometallic complexes [MCl(cod)(m-Ph2PBzIm)AuCl] with the gold atom coordinated to the P-end. While the Irꢂ
compound remained as such in solution, the RhꢂAu complex was found to be in equilibrium with [AuCl(Ph2PBzIm)] and [{Rh(m-
Cl)(cod)}2]. Reaction of trans-[RhCl(CO)(Ph2PBzIm)2] with [{Rh(m-Cl)(CO)2}2] gave the ‘A-frame’ complex [{RhCl}2(m-CO)(m-
Ph2PBzIm)2] while the reaction with [PdCl2(NCMe)2] resulted in the formation of three isomers of the metalꢂmetal bonded
/
Rh, Ir) containing two mutually cis bridging ligands in a HT disposition. Addition of [AuCl(tht)] to [MCl(cod)(Ph2PBzIm)]
/
Au
/
/
compound [(CO)Cl2Rh(m-Ph2PBzIm)2PdCl].
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: P,N ligands; Homo- and hetero-bimetallic complexes; Ligand transfer reactions
1. Introduction
insertion of small molecules into metalꢂ/metal bonds
[28ꢂ31]. In addition, some complexes with this ligand
were found to be active catalyst precursors for hydro-
formylation reactions [8,32]. In contrast, the related
/
Bifunctional N,P ligands such as 2-pyridyldiphenyl-
phosphine (Ph2PPy) have been the focus of much
interest in building homo- and hetero-dinuclear com-
ligand
(Ph2PBzIm) has been much less studied [33,34]. We
have recently reported [35] an unusual reversible Cꢂ
1-benzyl-2-imidazolyldiphenylphosphine
plexes for which a rich chemistry has been developed [1ꢂ
/
12]. Most of the reported dinuclear complexes with this
ligand have been found to show ‘A-frame’ structures
with the metal atoms in close proximity, due to the
short-bite and small flexibility of the Ph2PPy bridges.
This particular combination has allowed the transfer of
/H
activation process involving the Ir(I)/Ir(III) complex
ligands from one metal to the other [13ꢂ
/
19], the
formation of metalꢂmetal bonds, [20ꢂ27] and the
/
/
* Corresponding authors. Tel.: ꢁ
761-187.
E-mail address: oro@posta.unizar.es (L.A. Oro).
/
34-976-761-143; fax: ꢁ34-976-
/
Scheme 1. (i) 1/2[{Ir(m-Cl)(cod)}2], (ii) Ph2PbzIm.
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01447-0

130
C. Tejel et al. / Inorganica Chimica Acta 347 (2003) 129ꢂ136
/
[IrCl(cod){m-PPh(C6H4)BzIm}IrHCl(cod)] with a brid-
ging ortho-metallated phenyl ring (Scheme 1), while our
attempts to reproduce this reaction with related iridium
Ph2PPy complexes were unsuccessful.
From these results we suspected that the incorpora-
tion of the N-end into a five-membered (imidazol) or a
in dichloromethane (10 ml). The resulting orange
solution was concentrated to ca. 1 ml and diethyl ether
(15 ml) was added to complete the crystallization of a
yellow microcrystalline solid. The solution was de-
canted, and the solid was washed with diethyl ether
(2ꢃ
Calc. for C30H31N2ClPRh: C, 61.18; H, 5.31; N, 4.76.
Found: C, 60.82; H, 4.79; N, 4.56%. 1H NMR (ꢄ
30 8C,
CDCl3): dꢀ
7.66 (dd, 9.4 and 7.6 Hz, 4H, HoPh2P), 7.38
(m, 12H, Phꢁ
H4Im), 6.96 (s, 1H, H5Im), 6.61 (s, 2H,
CH2), 5.54 (br s, 2H) and 3.20 (br s, 2H) (HCÄ cod),
2.24 (m, 4H) and 1.93 (m, 4H) (CH2 cod). 31P{1H}
NMR (ꢄ30 8C, CDCl3): dꢀ13.7 (d, J(PꢂRh)ꢀ148
Hz). MS (FABꢁ): 553 (80%, MꢄClꢁ). Mol. weight
Calc. for C30H31N2ClPRh: 589. Found: 549. LM (5ꢃ
10ꢄ4 M in acetone)ꢀ0.56 S molꢄ1 cmꢄ1
/5 ml) and vacuum-dried. Yield 250 mg (91%). Anal.
six-membered ring (pyridine) in short-bite (Nꢂ
/
CꢂP)
/
bidentate ligands was not innocent. In fact, distinct
structural and dynamic behaviour has been reported for
identical complexes containing imidazol-2-tiolate and
/
/
/
pyridine-2-tiolate (Nꢂ
/
Cꢂ/S) ligands [36]. This prompted
/
us to explore the chemistry of rhodium, iridium and gold
complexes with the Ph2PBzIm ligand and we report here
our results on this topic.
/
/
/
/
/
/
/
.
2. Experimental
2.2.2. [{Rh(cod)}2(m-Cl)(m-Ph2PBzIm)]BF4 (2)
2.1. General considerations
A solution of [{Rh(m-Cl)(cod)}2] (39.5 mg, 0.08
mmol) in acetone (10 ml) was reacted with AgBF4
(33.1 mg, 0.17 mmol) in the darkness for 30 min. The
resulting yellow solution containing [Rh(cod)(ace-
tone)x]BF4 was filtered through kieselguhr (to eliminate
the solid AgCl) and solid [RhCl(cod)(Ph2PBzIm)] (100.0
mg, 0.17 mmol) was added to the filtrate. The resulting
orange solution was stirred for 30 min, concentrated to
ca. 2 ml and carefully layered with diethyl ether (15 ml)
to give orange crystals. The solution was decanted, and
the crystals were washed with diethyl ether and vacuum-
dried. Yield 123.0 mg (87%). Anal. Calc. for
C38H43N2BF4ClPRh2: C, 51.47; H, 4.89; N, 3.16.
Found: C, 51.27; H, 4.77; N, 3.02%. 1H NMR
All the reactions were carried out under argon using
standard Schlenk techniques. Those with silver salts
were protected from lighting with black photographic
paper. The complexes [{M(m-Cl)(cod)}2] [37,38], [{Rh(m-
Cl)(CO)2}2] [39], [PdCl2(NCMe)2] [40], [AuCl(Ph2PB-
zIm)] [33] and 1-benzyl-2-imidazolyldiphenylphosphine
[33] were prepared according to literature methods.
Solvents were dried and distilled under argon before
use by standard methods. Carbon, hydrogen and nitro-
gen analyses were performed with a PerkinꢂElmer 2400
/
microanalyzer. IR spectra were recorded with a Nicolet
550 spectrophotometer. Mass spectra were recorded
with a VG Autospec double-focusing mass spectrometer
operating in the FABꢁ mode. Ions were produced with
the standard Csꢁ gun at ca. 30 kV, 3-nitrobenzyl
alcohol (NBA) was used as matrix. Molecular weights
were determined with a Knauer osmometer using
chloroform solutions. 1H and 31P{1H} NMR spectra
were recorded on a Bruker ARX 300 and on a Varian
UNITY 300 spectrometers operating at 300.13 and
(ꢄ
/
50 8C, HDA): dꢀ7.91 (m, 2H), 7.79 (m, 2H), 7.74
/
(m, 3H) and 7.67 (m, 3H) (Ph2P); 7.85 (br s, 1H) and
7.43 (d, 1.2 Hz, 1H) (H4,5 Im); 7.16 (t, 7.3 Hz, 1H), 7.05
(t, 7.3 Hz, 2H) and 6.27 (d, 7.3 Hz, 2H) (Ph ꢂ
(dA, 1H) and 4.66 (dB, J(AꢂB)ꢀ15.3 Hz, 1H) (Phꢂ
CH2); 5.54 (m, 1H), 4.99 (m, 1H), 4.83 (m, 1H), 4.75
(m, 1H), 4.39 (m, 2H), 4.27 (m, 1H) and 3.53 (m, 1H) (Ä
CH cod); 3.22 (m, 1H), 2.99 (m, 2H), 2.30 (m, 9H) and
1.83 (m, 4H) (CH2 cod). 31P{1H} NMR (ꢄ
50 8C,
HDA): dꢀ15.6 (d, J(PꢂRh)ꢀ
143 Hz). MS (FABꢁ):
799 (25%, Mꢁ), 553 (100%, Rh(cod)(Ph2PBzIm)ꢁ). LM
(4.8ꢃ
10ꢄ4 M in acetone)ꢀ101.3 S molꢄ1 cmꢄ1
/CH2); 4.88
/
/
/
/
1
299.95 MHz for H, respectively. Chemical shifts are
/
reported in parts per million and referenced to SiMe4
using the residual signal of the deuterated solvent as
reference and 85% phosphoric acid, respectively. The
phase sensitive NOESY experiments were carried out on
the Bruker spectrometer using the pulse program
NOESYST with 512 FID’s and a mixing time of 100
/
/
/
/
/
.
2.2.3. HT-[{Rh(m-Ph2PBzIm)(cod)}2](BF4)2 (4)
Solid Ph2PBzIm (140.4 mg, 0.41 mmol) was added to
an acetone solution of [Rh(cod)(acetone)x]BF4 (0.41
mmol) (prepared as described for 2) to give an orange
solution almost immediately. After stirring for 30 min,
the solution was concentrated to ca. 2 ml and carefully
layered with diethyl ether (15 ml). The orange micro-
crystals deposited in three days were washed with
diethyl ether and vacuum-dried. Yield 217.7 mg (85%).
Anal. Calc. for C60H62N4B2F8P2Rh2: C, 56.28; H, 4.88;
ms. Conductivities were measured in 2ꢂ
/
3ꢃ
10ꢄ4 M in
acetone solutions using a Philips PW 9501/01 conducti-
meter.
/
2.2. Preparation of the complexes
2.2.1. [RhCl(cod)(Ph2PBzIm)] (1)
Solid Ph2PBzIm (161.9 mg, 0.47 mmol) was added to
a solution of [{Rh(m-Cl)(cod)}2] (115.8 mg, 0.23 mmol)
1
N, 4.37. Found: C, 55.96; H, 5.06; N, 4.25%. H NMR

C. Tejel et al. / Inorganica Chimica Acta 347 (2003) 129ꢂ
/
136
131
1
(ꢄ
trum: dꢀ
(2H) and 6.60 (m, 2H) (Phaꢂ
(m, 6H) (Phbꢂ
P); 6.96 (d, 1.4 Hz, 2H) and 6.76 (br s,
2H) (H4,5 Im); 7.15 (t, 7.2 Hz, 2H), 7.06 (t, 7.2 Hz, 4H)
and 6.29 (d, 7.2 Hz, 4H) (Ph ꢂCH2); 4.89 (dA, 2H) and
4.43 (dB, J(AꢂB)ꢀ15.0 Hz, 2H) (PhꢂCH2); 5.91 (m,
2H), 5.36 (m, 2H), 4.36 (m, 2H) and 4.14 (m, 2H) (ÄCH
/
50 8C, HDA) assigned from the H,1H-COSY spec-
8.70 (m, 2H), 7.97 (m, 2H), 7.88 (m, 2H), 7.68
P); 768 (m, 4H) and 7.54
Au(Ph2PBzIm)ꢁ).
C30H31N2Cl2PAuIr: 911. Found: 942.
Mol.
weight
Calc.
for
/
/
/
2.2.6. [RhCl(cod)(m-Ph2PBzIm)AuCl] (7)
Compound 7 was prepared as described for 6 starting
from [{Rh(m-Cl)(cod)}2] (34.5 mg, 0.07 mmol) and
[AuCl(Ph2PBzIm)] (80.5 mg, 0.14 mmol) to give yellow
needles of 7. Yield 80.5 mg (70%). Anal. Calc. for
/
/
/
/
/
cod); 3.26 (m, 2H), 3.12 (m, 2H), 2.76 (m, 4H), 2.44 (m,
4H) and 2.20 (m, 4H) (CH2 cod). 31P{1H} NMR
C30H31N2Cl2PAuRh×
/
CH2Cl2: C, 41.08; H, 3.67; N,
3.09. Found: C, 41.47; H, 3.49; N, 3.14%.
(ꢄ
(FABꢁ): 1193 (7%, Mꢁ
Rh(cod)(Ph2PBzIm)ꢁ). LM (2.6ꢃ
tone)ꢀ
205 S molꢄ1 cmꢄ1
/
50 8C, HDA): dꢀ
/
10.6 (d, J(Pꢂ
BF4ꢁ), 553 (100%,
10ꢄ4 M in ace-
/
Rh)ꢀ
/
146 Hz). MS
/
2.2.7. trans-[RhCl(CO)(Ph2PBzIm)2] (8)
/
To a solution of Ph2PBzIm (356.1 mg, 1.04 mmol) in
acetone (4 ml), solid [{Rh(m-Cl)(CO)2}2] (101.0 mg, 0.26
mmol) was added. The pale-yellow solid precipitated for
1 h was separated by filtration, washed with acetone
/
.
2.2.4. HT-[{Ir(m-Ph2PBzIm)(cod)}2](BF4)2 (5)
Compound 5 was prepared as described for 4 starting
from [{Ir(m-Cl)(cod)}2] (100.7 mg, 0.15 mmol), AgBF4
(58.4 mg, 0.30 mmol) and Ph2PBzIm (102.7 mg, 0.30
mmol) to rendered dark-blue needles corresponding to
5. Yield 197.2 mg (90%). Anal. Calc. for
C60H62N4B2F8P2Ir2: C, 49.39; H, 4.28; N, 3.84. Found:
(2ꢃ5 ml) and vacuum-dried. Yield 378.1 mg (83%).
/
Anal. Calc. for C45H38N4ClOP2Rh: C, 63.50; H, 4.50;
N, 6.58. Found: C, 63.43; H, 4.09; N, 6.36%. IR
(CH2Cl2, cmꢄ1) n(CO): 1982 (s). 1H NMR (25 8C,
CDCl3): dꢀ
7.1 (m, 20H, HmꢁpPh2Pꢁ
(d, 6.6 Hz, 4H, HoPh ꢂCH2), 6.86 (s, 2H, H5Im), 5.70 (s,
4H, Phꢂ 15.0
CH2). 31P{1H} NMR (25 8C, CDCl3): dꢀ
(d, J(PꢂRh)ꢀ125 Hz).
/
7.71 (dd, 12.6, 6.9 Hz, 8H, HoPh2P), 7.4ꢂ
/
/
HmꢁpPh ꢂ
/
CH2ꢁ
H4Im), 6.90
/
C, 49.21; H, 4.16; N, 3.79%. 1H NMR (ꢄ
/
50 8C, HDA)
assigned from the H,1H-COSY spectrum: dꢀ
8.56 (m,
2H), 7.92 (m, 2H), 7.71 (2H), 7.58 (2H) and 6.76 (m, 2H)
/
1
/
/
/
/
/
(Phaꢂ
/
P); 7.71 (m, 4H) and 7.58 (m, 6H) (Phbꢂ
P); 7.08
/
(d, 1.6 Hz, 2H) and 6.68 (br s, 2H) (H4,5 Im); 7.16 (t, 7.4
Hz, 2H), 7.07 (t, 7.4 Hz, 4H) and 6.31 (d, 7.4 Hz, 4H)
2.2.8. [{RhCl}2(m-CO)(m-Ph2PBzIm)2] (9)
The addition of solid [{Rh(m-Cl)(CO)2}2] (13.7 mg,
0.035 mmol) to a solution of trans-[RhCl(CO)(Ph2PB-
zIm)2] (8) (60.0 mg, 0.070 mmol) in dichloromethane
causes the immediate precipitation of a purple solid. The
resulting suspension was stirred overnight to give an
orange solution that was concentrated and carefully
(Ph ꢂ
Hz, 2H) (Phꢂ
2H) and 3.79 (m, 2H) (Ä
6H), 2.35 (m, 2H), 2.20 (m, 2H), and 1.95 (m, 4H) (CH2
cod). 31P{1H} NMR (ꢄ
50 8C, HDA): dꢀ0.85 (s). MS
(FABꢁ): 643 (100%, Ir(cod)(Ph2PBzIm)ꢁ). LM (2.6ꢃ
10ꢄ4 M in acetone)ꢀ211 S molꢄ1 cmꢄ1
/
CH2); 4.97 (dA, 2H) and 4.49 (dB, J(Aꢂ
CH2); 5.53 (m, 2H), 5.03 (m, 2H), 3.99 (m,
CH cod); 3.05 (m, 2H), 2.76 (m,
/
B)ꢀ
/
15.1
/
/
/
/
/
layered with diethyl ether to give brownꢂorange micro-
/
/
.
crystals. The solution was decanted, and the solid was
washed with diethyl ether and vacuum-dried. Yield 55.0
mg (75%). Anal. Calc. for C45H38N4Cl2OP2Rh2: C,
54.62; H, 3.87; N, 5.66. Found: C, 54.32; H, 3.72; N,
2.2.5. [IrCl(cod)(m-Ph2PBzIm)AuCl] (6)
Solid [{Ir(m-Cl)(cod)}2] (47.0 mg, 0.07 mmol) was
reacted with a solution of [AuCl(Ph2PBzIm)] (80.5 mg,
0.14 mmol) in dichloromethane (5 ml) for 30 min. The
resulting orange solution was concentrated to ca. 2 ml
and carefully layered with hexane to rendered orange
needles overnight. The crystals were washed with hexane
and vacuum-dried. Yield 102.0 mg (80%). Anal. Calc.
5.48%. IR (CH2Cl2, cmꢄ1) n(CO): 1778 (s). H NMR
1
(25 8C, CDCl3): dꢀ
8.07 (m, 4H, HoPhaP), 7.82 (m, 4H,
/
HoPhbP), 7.39 (m, 12H, Hm,pPh2P); 7.95 (d, 1.5 Hz, 2H)
and 6.72 (d, 1.5 Hz, 2H) (H4,5 Im); 7.09 (m, 6H) and 6.24
(d, 8.4 Hz, 4H) (Ph ꢂ
J(AꢂB)ꢀ15.0 Hz, 2H) (Phꢂ
(25 8C, CDCl3): dꢀ34.5 (AA? part from an AA?XX?
spin system).
/
CH2); 4.64 (dA, 2H) and 4.54 (dB,
/
/
/
CH2). 31P{1H} NMR
for C30H31N2Cl2PAuIr×
2.81. Found: C, 37.07; H, 3.21; N, 2.78%. H NMR
(25 8C, CDCl3): dꢀ7.73 (m, 2H), 7.60 (m, 2H), 7.58
(m, 3H), 7.36 (3H) (Ph2ꢂP); 7.70 (br s, 1H) and 6.96 (br
s, 1H) (H4,5 Im); 7.18 (m, 3H) and 6.58 (d, 6.9 Hz, 2H)
(Ph ꢂCH2); 4.47 (dA, 1H) and 4.52 (dB, J(AꢂB)ꢀ14.8
Hz, 1H) (PhꢂCH2); 4.91 (m, 1H), 4.80 (m, 1H), 3.22 (m,
1H) and 2.98 (m, 1H) (ÄCH cod); 2.61 (m, 1H), 2.41 (m,
2H), 2.09 (m, 1H), 2.01 (m, 1H), 1.59 (m, 1H) and 1.14
(m, 2H) (CH2 cod). 31P{1H} NMR (25 8C, CDCl3): dꢀ
16.3 (s). MS (FABꢁ): 910 (5%, Mꢁ), 875 (20%,
Mꢄ
Clꢁ), 642 (100%, Ir(cod)(Ph2PBzIm)ꢁ), 539 (90%,
/CH2Cl2: C, 37.40; H, 3.34; N,
/
1
/
/
2.2.9. [(CO)Cl2Rh(m-Ph2PBzIm)2PdCl] (10)
To a suspension of trans-[RhCl(CO)(Ph2PBzIm)2] (8)
(100 mg, 0.117 mmol) in dichloromethane (8 ml), solid
[PdCl2(NCMe)2] (45 mg, 0.117 mmol) was added to give
an orange solution almost inmediately. The solution was
concentrated to ca. 2 ml and carefully layered with 10 ml
of diethyl ether to give an orange microcrystalline solid.
The solid was separated by filtration, washed with
diethyl ether and vacuum-dried. Yield 102.6 mg (87%).
/
/
/
/
/
/
/

132
C. Tejel et al. / Inorganica Chimica Acta 347 (2003) 129ꢂ136
/
Anal. Calc. for C45H38N4Cl3OP2RhPd: C, 52.55; H,
3.72; N, 5.45. Found: C, 52.38; H, 3.48; N, 5.53%. IR
(CH2Cl2, cmꢄ1) n(CO): 2027 (s). 31P{1H} NMR (25 8C,
produces the chemical exchange of the olefinic protons,
and a further dissociation of the N-end of the strained
four-membered chelate ring regenerates the square-
planar complex.
The addition of the solvated species [Rh(cod)(aceto-
ne)x]BF4 to [RhCl(cod)(Ph2PBzIm)] (1) gave the catio-
CDCl3): HHꢂ
Rh)ꢀ96 Hz), HHꢂ
HT isomer (48.5%): dꢀ
4J(Pꢂ 10 Hz), 7.30 (d, 4J(Pꢂ
P)ꢀ
(FABꢁ): 993 (76%, Mꢁꢄ
Cl). Mol. weight Calc. for
/
(Rhꢂ
/
P) isomer (48.5%): dꢀ
(PdꢂP) isomer (3%): dꢀ
12.34 (dd, J(PꢂRh)ꢀ
P)ꢀ10 Hz). MS
/
6.68 (J(Pꢂ
7.57 (s),
113 Hz,
/
/
/
/
/
/
/
/
/
/
/
/
nic
dinuclear
complex
[{Rh(cod)}2(m-Cl)(m-
/
Ph2PBzIm)]BF4 (2), analogous to the iridium counter-
part [35]. The analytical data of 2 agreed with the
proposed formulation. The coordination of the P atom
to one of the rhodium atoms was evidenced by a doublet
C45H38N4Cl3OP2RhPd: 1028. Found: 1024.
(J(Pꢂ
/
Rh)ꢀ
/
143 Hz) in the 31P{1H} NMR spectrum.
3. Results and discussion
Moreover, the 1H NMR spectrum of 2 at ꢄ
/
50 8C
corresponded to a non-symmetric dinuclear complex. It
was substantiated by the detection of eight signals for
the olefinic cod protons, an AB spin system for the
diastereotopic CH2 protons, and two multiplets for the
ortho protons of the inequivalent phenyl groups bonded
to phosphorus. On raising the temperature the AB
system becomes a singlet (at d 4.75 ppm), the four
ortho protons of the phenyl groups become equivalent
and the olefinic cod protons gave four broad reso-
nances. As shown in Scheme 3, an easy inversion of the
six membered metallacycle ‘Rh(PCN)(Cl)Rh’ accounts
for this fluxional behaviour, which is similar to that
observed for the analogous iridium complex
[{Ir(cod)}2(m-Cl)(m-Ph2PBzIm)]BF4.
3.1. Diolefin complexes
The addition of Ph2PBzIm to the dinuclear complex
[{Rh(m-Cl)(cod)}2] gave quantitatively [RhCl(cod)-
(Ph2PBzIm)] (1), which was characterized by analytical
and spectroscopic methods. Complex 1 was found to be
mononuclear and non-electrolyte, as deduced from the
molecular weight and conductivity measurements (see
Section 2). The coordination of the Ph2PBzIm ligand
through the P atom was clearly indicated by the 31P{1H}
NMR spectrum, which showed a doublet due to the
coupling with the Rh nucleus (J(Pꢂ
/
Rh)ꢀ148 Hz). The
/
compound was found to be fluxional. Thus, the broad
1
bands due to the olefinic cod protons in the H NMR
spectrum at room temperature became two sharp signals
Attempts to prepare heterobimetallic compounds by
reacting [RhCl(cod)(Ph2PBzIm)] (1) with [Ir(cod)(aceto-
ne)x]BF4 or, alternatively, by reacting [IrCl(cod)(Ph2PB-
zIm)] (3) with [Rh(cod)(acetone)x]BF4 leaded to
mixtures of complexes. Among others, the homodi-
below ꢄ30 8C, while the CH2 protons of the Ph2PBzIm
/
ligand remained as a singlet in this range of temperature.
On heating, the olefinic resonances coalesced ca. 60 8C
and emerged as a single signal over 90 8C. The fluxional
process produces the equivalence of the olefin trans to
the phosphorous atom with the olefin trans to the
chloride ligand. A plausible explanation for the ob-
served chemical exchange involves the participation of a
pentacoordinated species, which is accessible through
the coordination of the N-end of the Ph2PBzIm ligand
to the rhodium (Scheme 2). A Berry’s pseudo-rotation
nuclear
complex
2
and
[{Ir(cod)}2(m-Cl)(m-
Ph2PBzIm)]BF4 were identified by 1H and 31P{1H}
NMR in these mixtures.
Both mononuclear complexes [MCl(cod)(Ph2PBzIm)]
(Mꢀ
to give the dinuclear compounds HT-[{M(m-
Ph2PBzIm)(cod)}2](BF4)2 (MꢀRh (4), Ir (5)) on re-
/Rh (1), Ir (3)) reacted in a similar way with AgBF4
/
moval the chloride ligand. They can be also prepared by
the direct reaction of the solvated species [M(cod)(ace-
tone)x]BF4 with Ph2PBzIm in acetone in a 1:1 molar
ratio. Complexes 4 and 5, isolated as orange (Rh) and
Scheme 2.
Scheme 3.

C. Tejel et al. / Inorganica Chimica Acta 347 (2003) 129ꢂ
/
136
133
dark-blue (Ir) microcrystalline solids in good yields,
were found to be 1:2 electrolytes in acetone, according
to the proposed formulation. Both dinuclear com-
pounds were found to be a single species in solution,
although the disymmetric character of the bridging
ligands could produce two diastereoisomers, namely
the head-to-head (HH, Cs symmetry) and the head-to-
tail (HT, C2 symmetry).
mention that the related complex [RhCl(cod)(Ph2PPy)]
reacts with silver salts to give the P,N-chelated mono-
nuclear complex [Rh(cod)(Ph2Ppy)]X [17], while 4 and 5
are dinuclear. This difference can be attributed to the
influence of the geometrical constrains of the six-
membered ring in Ph2PPy versus the five-membered
heterocycle in Ph2PBzIm on the coordinative interaction
of the N atom, observed also with heterocyclic 2-thiolate
ligands.
The 1H,1H-COSY spectra show that these compounds
possess two mutually cis bridging ligands in a HT
configuration. Thus, the observation of twelve reso-
nances for the cod protons along with the presence of
four cross peaks for each methylenic proton of the cod
ligands excluded the presence of the HH isomers, since
the molecules lack a mirror plane [41]. In addition,
crystals of complex 5 were separated and were used for
the crystal structure determination.1 The poor quality of
the crystals, however, prevented accurate structural
results, even if allowed to confirm the mutually cis
disposition in a head-to-tail (HT) configuration of the
bridging ligands and to determine the rather long IrÁ Á ÁIr
On the other hand, the results of the reactions of the
mononuclear rhodium (1) and iridium (3) compounds
with neutral complexes were found to depend on the
metal. Thus, we have reported [35] that the reaction of
[{Ir(m-Cl)(cod)}2] with 3 (in a 1:2 molar ratio) gives the
Ir(I)/Ir(III)
m}IrHCl(cod)] with a bridging ortho-metallated phenyl
ring, resulting from a CꢂH bond activation process
complex
[IrCl(cod){m-PPh(C6H4)BzI-
/
(Scheme 1). Neither a similar C-H activation reaction
nor even the coordination of the N-end to the
‘RhCl(cod)’ fragment was observed upon addition of
the neutral [{Rh(m-Cl)(cod)}2] to 1 under identical
conditions. Moreover, the imidazolyl nitrogen in the
complexes [MCl(cod)(Ph2PBzIm)] (1, 3) was found to be
unable to split the bridges in [{Rh(m-Cl)(cod)}2], while a
similar reaction with the BzIm ligand gave the mono-
nuclear complex [RhCl(cod)(BzIm)] quantitatively [42].
Furthermore, the addition of [{Ir(m-Cl)(cod)}2] to 1 (in a
1:2 molar ratio) produced a ligand exchange reaction to
give the iridiumphosphine complex [IrCl(cod)(Ph2PB-
zIm)] (3) and [{Rh(m-Cl)(cod)}2], which indicates a
higher affinity of the iridium versus the rhodium center
for the phosphorous atom.
˚
separation (3.41(1) A). A view of the structure of the
cation of 5 is shown in Fig. 1. Therefore, the deep blue
colour of complex 5 is probably due to a metal to ligand
charge-transfer band, since a metalꢂmetal interaction
/
can be excluded. It is noteworthy the relative cis
disposition of the bridging ligands, while most of the
dinuclear complexes with the related Ph2PPy ligand
displayed a trans disposition. It is also interesting to
1
Crystal data for 5: empirical formula, C60H62Ir2N4P2(BF4)2; Fw,
1455.06; crystal system, hexagonal; space group, P63. Unit cell
To obtain more information about the formation of
heterometallic complexes and the ligand redistribution
processes, the reactions of complexes 1 and 3 with
˚
˚
dimensions: aꢀ
/
23.883(5) A, cꢀ
/
17.788(3) A, gꢀ
/
/
120 8, Vꢀ
/
8787(3)
3
˚
A , Zꢀ
/
6, Dx : 1.650 Mg mꢄ3, mꢀ
4.660 mmꢄ1, F(000)ꢀ
/4272.
[AuCl(tht)] (thtꢀtetrahydrothiophene) were also tested.
/
The product from the reaction of the iridium complex 3
with the gold compound was the heterobimetallic
complex [IrCl(cod)(m-Ph2PBzIm)AuCl] (6), which was
isolated as a orange microcrystalline solid. This complex
was found to be a single and non-symmetric species in
solution; the most relevant features of the 1H NMR
spectrum at room temperature were four signals for the
olefinic cod protons and an AB spin system for the
protons of the CH2 group. The coordination of the N-
end of the Ph2PBzIm ligand to the iridium atom was
unequivocally established though the NOESY spectrum
(Fig. 2). Thus, one strong cross peak between one
imidazolyl proton (H4, Scheme 4) and one olefinic
proton of the cod ligand indicates the close proximity
of these groups. Therefore, the iridium atom was found
to be coordinated to the N-end while the gold atom was
coordinated to the P-end. Since iridium was bonded to
the P-end in the starting material [IrCl(cod)(Ph2PBzIm)]
(3) and ends up bonded to the N-end, a linkage
isomerization occurs. As expected, complex 6 was also
Fig. 1. View of the structure of the cation of 5.

134
C. Tejel et al. / Inorganica Chimica Acta 347 (2003) 129ꢂ136
/
Again, a linkage isomerization occurs in this reaction
since the gold atom ends up bonded to the P-end of the
ligand. In addition, the heterodinuclear Rhꢂ
plex splits into the goldꢂphosphine complex and
[{Rh(m-Cl)(cod)}2], which compared with the properties
of the corresponding heterodinuclear IrꢂAu complex
/
Au com-
/
/
suggests a tighter binding of the N-end to iridium than
to rhodium. The availability of an easy way to a linkage
isomerization and the dissociation of Rhꢂ
account for the redistribution reactions observed in the
attempts to isolate heterodinuclear RhꢂIr complexes.
/N bond
/
According with the observed preference of gold for
the P-end of the Ph2PBzIm ligand, the complexes 6 and
7
can be also obtained from the reactions of
[AuCl(Ph2PBzIm)] with [{M(m-Cl)(cod)}2] (MꢀRh,
/
Ir), respectively. The environment of the iridium atom
in complex 6 is similar to the postulated intermediate in
the C-H activation leading to [IrCl(cod){m-
PPh(C6H4)BzIm}IrHCl(cod)]. Therefore, a solution of
complex 6 in d8-toluene was warmed at 100 8C for 1 h in
Fig. 2. Selected region of the NOESY spectrum of the complex
[IrCl(cod)(m-Ph2PBzIm)AuCl] (6).
the NMR cavity looking for a CꢂH activation reaction,
/
but only decomposition products were observed.
3.2. Carbonyl complexes
A potential precursor for homo- and hetero-dinuclear
complexes is the mononuclear complex trans-
[RhCl(CO)(Ph2PBzIm)2] (8), which was easily prepared
by adding [{Rh(m-Cl)(CO)2}2] to
a solution of
Ph2PBzIm in acetone. The yellow solid isolated from
the reaction was fully characterized by analytical and
spectroscopic methods. Complex 8 was reacted with 0.5
molar equiv. of [{Rh(m-Cl)(CO)2}2] to give an insoluble
purple solid showing two strong n(CO) absorptions at
1998 and 1987 cmꢄ1. This solid dissolves slowly in
dichloromethane to give [{RhCl}2(m-CO)(m-Ph2-
PBzIm)2] (9) under evolution of carbon monoxide
(Scheme 5). Complex 9 can be also isolated from the
reaction of 8 with 0.5 molar equiv. of [{Rh(m-
Cl)(C2H4)2}2] as a brownꢂ
was characterized as the carbonyl bridged HTꢂ
/
orange solid. Complex 9
Scheme 4.
/isomer
depicted in Scheme 5. Thus, the bridging carbonyl group
obtained from the reaction of P-coordinated complex
[AuCl((Ph2PBzIm)] with [{Ir(m-Cl)(cod)}2] in a 2:1
molar ratio (Scheme 4).
The rhodium counterpart
1 was reacted with
[AuCl(tht)] to give [RhCl(cod)(m-Ph2PBzIm)AuCl] (7),
which was isolated as yellow needles analyzing for 7.
1
However, the H NMR spectrum of a solution of this
material in CDCl3 showed 7 to be in equilibrium with
[AuCl(Ph2PBzIm)] and [{Rh(m-Cl)(cod)}2]. In addition,
the 31P{1H} NMR of this solution showed a new singlet
at d 17.8 ppm corresponding to 7, which indicates the
coordination of the gold to the P-end in 7, along with
the singlet at d 10.7 ppm from [AuCl(Ph2PBzIm)].
Scheme 5. (i) 1/2[{Rh(m-Cl)(CO)2}2], (ii) 1/2[{Rh(m-Cl)(C2H4)2}2].

C. Tejel et al. / Inorganica Chimica Acta 347 (2003) 129ꢂ
/
136
135
gave a strong n(CO) band at 1778 cmꢄ1 while the two
magnetically inequivalent phosphorus nuclei gave a AA?
part of a AA?XX? spin system in the 31P{1H} NMR
spectrum. Notice that the phosphorus nuclei would be
magnetically equivalent in the HH isomer. The forma-
tion of HT isomers from mononuclear complexes with
redox internal oxidation is similar to the previously
described in the reactions of trans-[MCl(CO)(Ph2PPy)2]
(MꢀRh, Ir) with [PdCl2(L)2] [8,14]. However, while the
/
HH isomer and the HT isomer were the single products
isolated from the reactions with the Ph2PPy compounds
of iridium and rhodium, respectively, in this case both
isomers are formed.
two Pꢂ
/
Rh bonds required the rearrangement of the
Reaction of complex 8 with 1 molar equiv. of
[AuCl(tht)] gave [AuCl(Ph2PBzIm)] and the dinuclear
carbonyl-bridged rhodium complex 9. Again, the reac-
metalꢂligand bonds, an isomerization process pre-
/
viously observed with Ph2PPy complexes [8,16]. As
shown in Scheme 5, the insoluble purple solid with
two terminal carbonyl groups corresponds to the for-
mula [{RhCl(m-Ph2PBzIm)(CO)}2].
Complex 8 was reacted with 1 molar equiv. of
[PdCl2(NCMe)2] to give an orange solid of formula
[(CO)Cl2Rh(m-Ph2PBzIm)2PdCl] (10), which showed a
n(CO) band at 2027 cmꢄ1. Analysis of the 31P{1H}
NMR spectrum of this solid evidenced the presence of
the three isomers shown in Fig. 3. The expected product
tion was directed by the formation of an AuꢂP bond,
/
and the remaining ‘RhCl(CO)(Ph2PBzIm)’ fragment
dimerizes instead of being coordinated to the N-end of
the gold compound.
4. Concluding remarks
The coordination of the Ph2PBzIm ligand to Rh, Ir
and Au in mononuclear complexes was shown to occur
preferentially though the P-end versus the N-end.
Moreover, a preference for a bridging coordination
mode over the P,N-chelating mode has been observed
if the coordination of both donor atoms to a metal
center is possible. Thus, homodinuclear complexes of
rhodium, iridium, and gold have been isolated. How-
ever, the reactions aimed to prepare herodinuclear
complexes of these metals were found to be controlled
from this reaction, the HHꢂ
acterized by a doublet at dꢀ
Nevertheless, this isomer constituted only the 48.5% per
mol of the mixture while the HT isomer was found to be
also in a 48.5% molar ratio. The proposed coordination
of one P-end to the rhodium atom and the other P-end
/
(Rhꢂ
/
P) isomer, was char-
Rh)ꢀ96 Hz).
/
6.68 (J(Pꢂ
/
/
to the palladium in this HTꢂ
with the two resonances found at dꢀ
Rh)ꢀ P)ꢀ
113 Hz, 4J(Pꢂ 10 Hz) and 7.30 (d, 4J(Pꢂ
P)ꢀ10 Hz). The minor compound (in a 3% molar
ratio) was characterized as the HHꢂ(PdꢂP) isomer, with
both P-ends of the bridging ligands bonded to the
palladium atom, by a singlet at dꢀ7.57. From this
/
(Rhꢂ
/
P) isomer is consistent
/
12.34 (dd, J(Pꢂ
/
/
/
/
/
/
by the affinity of the metals (Auꢀ
/
Irꢀ
/
RhꢀPd) for the
/
/
/
P-end of the ligand and, accordingly, ligand transference
reactions and rearrangements of the bridging ligands
were commonly observed.
/
mixture, the HT isomer can be separated by fractional
crystallization, which indicates that the three isomers are
formed during the course of the reaction, but they are
not in a chemical equilibrium in solution.
Acknowledgements
Most probably, the reaction starts with the coordina-
tion of the Pd atom to the free N-end of the ligands in
complex 8, which is followed by a redox internal
The generous financial support from DGES (Project
PB 98-641) and from the Universita` di Camerino for a
fellowship (to R.B.) is also gratefully acknowledged.
oxidation to give the metalꢂ
The oxidation of the rhodium atom is substantiated by
the small PꢂRh coupling constants of the isomers and
/metal bonded compounds.
/
the increase of the n(CO) frequency relative to the
starting material. Most probably the linkage isomeriza-
tion of the bridging ligands framework occurs pre-
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