IrPd, IrHg, IrCu, and IrTl binuclear complexes bridged by the short-bite ligand 2-(diphenylphosphino)pyridine. Catalytic effect in the hydroformylation of styrene due to the monodentate P-bonded 2-(diphenylphosphino)pyridine ligands of trans-[Ir(CO)(Ph2PPy)2Cl]

Article abstract of DOI:10.1021/om970145n

The complex trans-[Ir(CO)Cl(Ph₂PPy)₂] (1; Ph₂PPy = 2-(diphenylphosphino)pyridine) was obtained in good yield from the reaction of [Ir(p-toluidine)(CO)₂Cl] with Ph₂PPy. It has a square-planar geometry, as does the analogous Vaska complex, with two monodentate Ph₂PPy ligands P-bonded to the iridium(I) center. Compound 1 exhibits a reactivity reminiscent of Vaska's complex; in fact, it adds SO₂, halogens, HCl, and CH₃I. The addition of HCl to 1 initially occurs at the pyridine nitrogen atoms of the pendant Ph₂PPy and subsequently at the iridium(I) center, affording [Ir(CO)H(Cl)₂(Ph₂PPyH)₂][Cl]₂ (6). The addition of a benzene solution of[Pd(PhCN)₂Cl₂] to a solution of 1 in the same solvent yielded, nearly quantitatively, the Ir^IIPd^I complex [IrPd(CO)Cl₃(μ-Ph₂PPy)₂] (8). The reaction of 1 with HgCl₂, in benzene, in a 1:1 molar ratio afforded the binuclear complex [Ir(CO)Cl₂(μ-Ph₂PPy)₂HgCl] (9). Using a 1:2 molar ratio the product [Ir(CO)Cl₂(HgCl₂)(μ-Ph₂PPy) ₂HgCl]·2CH₂Cl₂ (10) was obtained. Compounds 8 and 10 were also characterized by a single-crystal X-ray diffraction analysis. The reaction of 1 with [Cu(NCCH₃)₄]BF₄ afforded, almost quantitatively, the ionic compound [Ir(CO)Cl(μ-Ph₂PPy)₂Cu]BF₄ (11) as an orange solid. The compound [Ir(CO)Cl(μ-Ph₂PPy)₂Tl]-PF₆ (12) obtained from the reaction of 1 with TlPF₆, shows the Ir-Tl bonding and is luminescent in frozen CH₂Cl₂ solution at 77 K with a lifetime of 5 ns (±10%). As opposed to analogous compounds, in the bimetallic complexes 8-12 the bridging Ph₂PPy ligands assume a head-to-head structure. The aim of the work was to obtain some insight into the beneficial effect of catalytic precursors containing the pendant Ph₂PPy ligand in the hydroformylation catalytic cycle. Using complex 1 as a precatalyst in the hydroformylation of styrene, at 80°C and under 80 atm of CO/H₂ (1:1) pressure, the rate of the catalytic process increases significantly with respect to that observed with Vaska's complex, making clear a favorable effect of the pendant Ph₂PPy ligand. However, the chemoselectivity of the process was low. A scheme of the catalytic cycle is proposed. The new aspects of the catalytic cycle are: (i) the protonation under equilibrium conditions of one of the two pyridine nitrogen atoms of the pendant Ph₂PPy ligands in the reductive elimination of HCl from the dihydride-iridium(III) species formed by oxidative addition of H₂ to 1 and (ii) protonolysis, by the proton coordinated to the pyridine nitrogen atom, of the acyl or σ-alkyl groups present in the intermediates formed in the reaction pathway. Unexpectedly, 11 and 12 exhibit catalytic activity comparable with that of 1. This occurs because under the experimental conditions used the Cu-N or Tl-N bonds are broken, giving 1.

Full text of DOI:10.1021/om970145n

338
Organometallics 1998, 17, 338-347
Ir P d , Ir Hg, Ir Cu , a n d Ir Tl Bin u clea r Com p lexes Br id ged
by th e Sh or t-Bite Liga n d
2-(Dip h en ylp h osp h in o)p yr id in e. Ca ta lytic Effect in th e
Hyd r ofor m yla tion of Styr en e Du e to th e Mon od en ta te
P -Bon d ed 2-(Dip h en ylp h osp h in o)p yr id in e Liga n d s of
tr a n s-[Ir (CO)(P h 2P P y)2Cl]
Giancarlo Francio`, Rosario Scopelliti, Carmela Grazia Arena, Giuseppe Bruno,
Dario Drommi, and Felice Faraone*
Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica dell’Universita`,
Salita Sperone 31, Villaggio S. Agata, I-98166 Messina, Italy
Received February 25, 1997
The complex trans-[Ir(CO)Cl(Ph2PPy)2] (1; Ph2PPy ) 2-(diphenylphosphino)pyridine) was
obtained in good yield from the reaction of [Ir(p-toluidine)(CO)2Cl] with Ph2PPy. It has a
square-planar geometry, as does the analogous Vaska complex, with two monodentate Ph2PPy
ligands P-bonded to the iridium(I) center. Compound 1 exhibits a reactivity reminiscent of
Vaska’s complex; in fact, it adds SO2, halogens, HCl, and CH3I. The addition of HCl to 1
initially occurs at the pyridine nitrogen atoms of the pendant Ph2PPy and subsequently at
the iridium(I) center, affording [Ir(CO)H(Cl)2(Ph2PPyH)2][Cl]2 (6). The addition of a benzene
solution of [Pd(PhCN)2Cl2] to a solution of 1 in the same solvent yielded, nearly quantitatively,
the IrIIPdI complex [IrPd(CO)Cl3(µ-Ph2PPy)2] (8). The reaction of 1 with HgCl2, in benzene,
in a 1:1 molar ratio afforded the binuclear complex [Ir(CO)Cl2(µ-Ph2PPy)2HgCl] (9). Using
a 1:2 molar ratio the product [Ir(CO)Cl2(HgCl2)(µ-Ph2PPy)2HgCl]‚2CH2Cl2 (10) was obtained.
Compounds 8 and 10 were also characterized by a single-crystal X-ray diffraction analysis.
The reaction of 1 with [Cu(NCCH3)4]BF4 afforded, almost quantitatively, the ionic compound
[Ir(CO)Cl(µ-Ph2PPy)2Cu]BF4 (11) as an orange solid. The compound [Ir(CO)Cl(µ-Ph2PPy)2Tl]-
PF6 (12) obtained from the reaction of 1 with TlPF6, shows the Ir-Tl bonding and is
luminescent in frozen CH2Cl2 solution at 77 K with a lifetime of 5 ns ((10%). As opposed
to analogous compounds, in the bimetallic complexes 8-12 the bridging Ph2PPy ligands
assume a head-to-head structure. The aim of the work was to obtain some insight into the
beneficial effect of catalytic precursors containing the pendant Ph2PPy ligand in the
hydroformylation catalytic cycle. Using complex 1 as a precatalyst in the hydroformylation
of styrene, at 80 °C and under 80 atm of CO/H2 (1:1) pressure, the rate of the catalytic
process increases significantly with respect to that observed with Vaska’s complex, making
clear a favorable effect of the pendant Ph2PPy ligand. However, the chemoselectivity of the
process was low. A scheme of the catalytic cycle is proposed. The new aspects of the catalytic
cycle are: (i) the protonation under equilibrium conditions of one of the two pyridine nitrogen
atoms of the pendant Ph2PPy ligands in the reductive elimination of HCl from the dihydride-
iridium(III) species formed by oxidative addition of H2 to 1 and (ii) protonolysis, by the proton
coordinated to the pyridine nitrogen atom, of the acyl or σ-alkyl groups present in the
intermediates formed in the reaction pathway. Unexpectedly, 11 and 12 exhibit catalytic
activity comparable with that of 1. This occurs because under the experimental conditions
used the Cu-N or Tl-N bonds are broken, giving 1.
In tr od u ction
catalyst, giving rise to mixed mononuclear rhodium(I)
complexes. These species, namely [RhH(CO)(PPh3)2(Ph2-
PPy)] and [RhH(CO)(PPh3)(Ph2PPy)2], contain the
Ph2PPy as a monodentate P-bonded ligand and show a
structure similar to that of [RhH(CO)(PPh3)3]. The
results demonstrate that the addition of Ph2PPy to
Wilkinson’s catalyst exerted a beneficial effect on the
rhodium-catalyzed hydroformylation of styrene as an
improvement in the rate of the low-pressure catalytic
reaction was observed. This favorable effect of Ph2PPy
Recently1 some of us studied the catalytic hydro-
formylation system obtained in situ by addition of
2-(diphenylphosphino)pyridine (Ph2PPy) to [RhH(CO)-
(PPh3)3], at variable ligand-to-metal ratios. At first it
was shown by 31P{1H} NMR that in solution Ph2PPy
easily displaces 1 or 2 mol of PPh3 from Wilkinson’s
(1) Gladiali, S.; Pinna, L.; Arena, C. G.; Rotondo, E.; Faraone, F. J .
Mol. Catal. 1991, 66, 183.
S0276-7333(97)00145-3 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/07/1998

IrPd, IrHg, IrCu, and IrTl Binuclear Complexes
Organometallics, Vol. 17, No. 3, 1998 339
eter. Absorption spectra in the UV and visible regions were
performed with a Kontron Uvikon 860 spectrophotometer.
Luminescence spectra were recorded with a Perkin-Elmer LS-
5B spectrofluorimeter equipped with a red-sensitive Hamamat-
su R928 phototube, and luminescence lifetimes were measured
with an Edinburgh FL 900 single-photon-counting spectrom-
eter. For the low-temperature measurements, a homemade
finger Dewar was employed. 1H and 31P{1H} NMR spectra
were recorded on a Bruker AMX R300. 1H NMR spectra were
referenced to internal tetramethylsilane and 31P{1H} spectra
to external 85% H3PO4; positive chemical shifts are for all
nuclei to higher frequency. Gas chromatographic analyses
were run on a Carlo Erba HRGC 5160 Mega Series apparatus
(split/splitless injector, MEGA OV1 25 m column, film thick-
ness 2 µm, carrier gas He, FID detector). Elemental analyses
were performed by Redox s.n.c., Cologno Monzese, Milano,
Italy.
was considered to be due to the presence of basic
nitrogen in the pendant pyridine.
Subsequently, new catalytic systems, formed by the
combination of a ligand containing the 2-(diphenylphos-
phino)pyridine moiety with a palladium(II) species and
an acid of weakly coordinating anions, have been
developed for the carbonylation of alkynes.2 Such
catalytic systems have been applied in the selective
production of methyl methacrylate by methoxycar-
bonylation of propyne and in the synthesis of Naproxen
precursors.3 The catalytic activity was considered to be
due to the presence of monodentate P-bonded Ph2PPy,
which can be protonated and acts as an effective “proton
messenger”.
Here we report on the results obtained in the hydro-
formylation of styrene using as precatalyst the complex
trans-[Ir(CO)(Ph2PPy)2Cl] (1) structurally analogous to
Vaska’s complex. The choice of 1 as catalyst precursor
has been effected because, in the tertiary phosphine
complexes trans-[Ir(CO)(PR3)2Cl], the iridium(I) center
is so basic that substrate activation affords very stable
iridium(III) species which are not able to promote the
catalytic cycle.4 Thus, the catalytic activity observed
using 1 as catalyst precursor can be due to the presence
of the uncoordinated nitrogen atom in the pendant
Ph2PPy ligands.
Syn th eses. tr a n s-[Ir (CO)(P h 2P P y)2Cl] (1). A benzene
solution (30 mL) of Ph2PPy (0.404 g, 1.535 mmol) was added
to a stirred solution of [Ir(CO)2(p-toluidine)Cl] (0.300 g, 0.767
mmol) in the same solvent (50 mL). During the addition, the
mixture turned yellow. After 1 h, the solvent was removed at
reduced pressure and the yellow solid was washed with
petroleum ether (bp 40-60 °C) and dried in vacuo. Yield: 95%
(0.570 mg, 0.729 mmol). Anal. Calcd for C35H28ClP2N2OIr:
C, 53.74; H, 3.61; N, 3.58; Cl, 4.53. Found: C, 53.80; H, 3.66;
N,3.52; Cl, 4.50. IR (CsI, Nujol): ν(CO) 1952 cm-1 1H NMR
.
(CDCl3): δ 8.77 (d, 6-H Py). 31P{1H} NMR (CDCl3): δ 24.46
(s).
In addition, owing to the lack of reports5 on the
chemistry of iridium(I) species containing the bifunc-
tional ligand Ph2PPy, we synthesized Ir-Cu, Ir-Tl, Ir-
Hg, and Ir-Pd bimetallic species containing bridged
Ph2PPy ligands. The solid-state structures of [Ir(CO)-
Cl2(HgCl2)(µ-Ph2PPy)2HgCl] and [Ir(CO)Cl2(µ-Ph2-
PPy)2PdCl] were determined by X-ray diffraction and
are reported herein. The cationic species [Ir(CO)Cl(µ-
Ph2PPy)2Cu]BF4 (11) and [Ir(CO)Cl(µ-Ph2PPy)2Tl]PF6
(12) were also employed as catalytic precursors in the
hydroformylation of styrene. These catalytic bimetallic
systems were chosen in an attempt to afford insight into
the action of the cocatalyst, generally a metal salt, in
some catalytic cycles. For example,6 a patent reported
that 1-butene can be produced from ethylene with 90%
selectivity, using as the catalytic system Pd(OAc)2,
Ph2PPy, and cupric trifluoromethanesulfonate, in di-
glyme.
Rea ction of 1 w ith SO2. Sulfur dioxide was slowly
bubbled through a benzene solution (10 mL) of 1 (0.110 g, 0.141
mmol) for about 5 min. During this time the solution color
turned from yellow to pale green. Then hexane (30 mL) was
added to give a pale green solid. This was separated by
filtration and washed with diethyl ether and dried in vacuo.
The pure product [Ir(CO)(Ph2PPy)2(SO2)Cl] (2) was obtained
in 95% yield (0.113 g, 0.134 mmol). Anal. Calcd for
C35H28ClP2N2O3SIr: C, 49.67; H, 3.33; N, 3.31; Cl, 4.19; S, 3.79.
Found: C, 49.72; H, 3.31; N, 3.01; Cl, 3.99; S, 3.25. IR (CsI,
Nujol): ν(CO) 2023 cm-1, ν(SO) 1143, 1055 cm-1
.
1H NMR
(CDCl3): δ 8.77 (d, 6-H Py). 31P{1H} NMR (CDCl3): δ 14.69
(s).
[Ir (CO)(P h 2P P y)2(Br )2Cl] (3). To a dichloromethane solu-
tion (20 mL) of 1 (0.090 g, 0.115 mmol) was added a solution
of bromine in the same solvent dropwise until the IR spectrum
indicated the disappearance of the ν(CO) band of the starting
material. After 1/2 h, the volume of the mixture was reduced
to ca. 10 mL. By addition of hexane (30 mL) an orange
precipitate was obtained. This was filtered, washed with
diethyl ether, and dried in vacuo to give 3 in 75% yield (0.081
g, 0.086 mmol). Anal. Calcd for C35H28Br2ClP2N2OIr: C,
44.62; H, 3.00; N, 2.97; Cl, 3.76; Br, 16.96. Found: C, 44.72;
H, 3.11; N, 3.01; Cl, 3.99; Br, 17.15. IR (CsI, Nujol): ν(CO)
Exp er im en ta l Section
Established methods were used to prepare the compounds
[Ir(CO)2(p-toluidine)Cl],7 [Cu(NCMe)4]BF4,8 [Pd(PhCN)2Cl2],9
and Ph2PPy.5 All other reagents were purchased and used as
supplied.
Solvents were dried by standard procedures. All experi-
ments were performed under an atmosphere of purified
nitrogen. IR spectra were obtained as Nujol mulls on KBr or
CsI plates using a Perkin-Elmer FTIR 1720 spectrophotom-
2040 cm-1
.
1H NMR (CDCl3): δ 8.81 (d, 6-H Py, 2H). 31P{1H}
NMR (CDCl3): δ 18.10 (s).
[Ir (CO)(P h 2P P y)2Cl(I)2] (4). This compound was obtained
similarly to 3, as a brown-orange solid in 70% yield, by adding
I2 to a CH2Cl2 solution of 1. Anal. Calcd for C35H28I2ClP2N2-
OIr: C, 40.58; H, 2.72; N, 2.70; Cl, 3.42; I, 24.50. Found: C,
40.53; H, 2.68; N, 2.65; Cl, 3.38; I, 24.75. IR (CsI, Nujol):
ν(CO) 2042 cm-1
.
1H NMR (CDCl3): δ 8.78 (d, 6-H Py).
(2) Drent, E.; Arnoldy, P.; Budzelaar, P. H. M. J . Organomet. Chem.
1993, 455, 247; 1994, 475, 57.
31P{1H} NMR (CDCl3): δ 17.80 (s).
(3) Scrivanti, A.; Matteoli, U. Tetrahedron Lett. 1995, 9015.
(4) (a) Crabtree, R. H. The Organometallic Chemistry of the Transi-
tion Metals; Wiley: New York, 1988; p 192. (b) Henrici-Olive´, G.; Olive´,
S. Coordination and Catalysis; Verlag Chemie: Weinheim, Germany,
1976; pp 162, 236. (c) Halpern, J . Acc. Chem. Res. 1970, 3, 386.
(5) Newkome, G. R. Chem. Rev. 1993, 93, 2067.
(6) Drent, E. Eur. Pat. Appl. EP 307,026, 1989.
(7) Kablunde, V. Inorg. Synth. 1974, 15, 82.
(8) Kubas, G. J . Inorg. Synth. 1979, 19, 90.
(9) Doyle, J .; Slade, P. E.; J onassen, H. B. Inorg. Synth. 1960, 6,
218.
[Ir (CO)(P h 2P P y)2(H)2Cl] (5). Hydrogen was slowly bubbled
through a dichloromethane solution (20 mL) of 1 (0.080 g,
0.102 mmol) for about 2 h. During this time, the yellow color
disappeared. Then the solvent was removed, under an atmo-
sphere of hydrogen, and the white solid 5 obtained was washed
with diethyl ether. Yield: 95% (0.76 g, 0.97 mmol). Anal.
Calcd for C35H30ClP2N2OIr: C, 53.70; H, 3.86; N, 3.57; Cl, 4.52.
Found: C, 53.82; H, 3.96; N, 3.52; Cl, 4.44. IR (CsI, Nujol):
ν(CO) 1984, ν(MH) 2194, 2104 cm-1 1H NMR (CDCl3): δ 8.77
.

340 Organometallics, Vol. 17, No. 3, 1998
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Deter m in a tion Su m m a r y for 8 a n d 10
Francio` et al.
8
10
formula
Mr
temp (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
35H28Cl3IrN2OP2Pd‚H2O
C35H28Cl5Hg2IrN2OP2‚2CH2Cl2
975.48
293(2)
orthorombic
P212121
10.361(2)
15.894(2)
21.711(5)
90
90
90
3575(1)
4
1495.02
293(2)
triclinic
P1h
10.094(2)
12.773(3)
20.198(4)
72.22(2)
78.16(2)
69.67(2)
2310.9(8)
2
Z
F(000)
Dcalcd (g cm-3
λ(Mo KR) (Å)
1888
1.812
0.710 73
4.569
1392
2.149
0.710 73
10.121
1.5-27
)
µ (Mo KR) mm-1
θ range (deg)
1.5-27.5
0 e h e 14, 0 e k e 21, 0 e l e 29
4749
4603
index ranges
0 e h e 13, -17 e k e 17, -26 e l e 26
no. of rflns collected
no. of unique rflns
no. of refined params
GOF on F2
10 891
10 134
488
0.843
0.0795
0.2912
415
0.931
0.0412
0.1037
R1 (on F, I > 2σ(I))
wR2 (on F2, all data)
(d, 6-H Py), -7.54 (td, IrH, 1H, J PH 17.7 Hz, J HH 4.8 Hz),
-18.68 (td, IrH, 1H, J PH 14.3 Hz, J HH 4.8 Hz). 31P{1H} NMR
(CDCl3): δ 11.85 (s).
ν(CO) 2026 cm-1 1H NMR (CDCl3): δ 9.27 (d, 6-H Py).
.
31P{1H} NMR (CDCl3): δ 16.83 (s).
[Ir (CO)(Cl)2(HgCl2)(µ-P h 2P P y)2HgCl]‚2CH2Cl2 (10). To
a stirred solution (25 mL) of 1 (0.110 g, 0.141 mmol) in benzene
(25 mL) was added solid HgCl2 (0.076 g, 0.282 mmol). After 3
h, the volume of the solution was reduced to ca. 5 mL in vacuo;
by addition of hexane (30 mL) a white solid was formed. This
was separated by filtration, recrystallized from CH2Cl2/hexane,
and dried. Yield: 80% (0.190 g, 0.113 mmol). Anal. Calcd
for C37H32Cl9P2N2OIrHg2: C, 26.34; H, 1.91; N, 1.66; Cl, 18.91.
Found: C, 26.38; H, 1.98; N, 1.72; Cl, 18.99. IR (CsI, Nujol):
[Ir (CO)(H)(P h 2P P yH)2(Cl)2][Cl]2 (6). To a dichloromethane
solution (30 mL) of 1 (0.150 g, 0.192 mmol) was added a 1 M
aqueous solution of HCl (0.576 mL). After 1 h, the resultant
pale yellow solution was reduced to ca. 10 mL. By addition of
diethyl ether (40 mL) a pale yellow precipitate was obtained.
This was filtered, washed with diethyl ether, and dried in
vacuo to give 6 in 80% yield (0.137 g, 0.153 mmol). Anal. Calcd
for C35H31Cl4P2N2OIr: C, 47.15; H, 3.50; N, 3.14; Cl, 15.90.
Found: C, 47.20; H, 3.55; N, 3.08; Cl, 15.65. IR (CsI, Nujol):
ν(CO) 2026 cm-1
.
1H NMR (CDCl3): δ 9.27 (d, 6-H Py).
ν(CO) 2040 cm-1
.
1H NMR (CDCl3): δ 8.75 (d, 6-H Py), -15.49
31P{1H} NMR (CDCl3): δ 16.83 (s).
(t, IrH, 1H, J PH 11.88 Hz). 31P{1H} NMR (CDCl3): δ 0.76 (s).
[Ir (CO)(Cl)(µ-P h 2P P y)2Cu ][BF 4] (11). To a stirred solu-
tion (25 mL) of 1 (0.110 g, 0.141 mmol) in benzene (25 mL)
was added solid [Cu(CH3CN)4][BF4] (0.044 g, 0.141 mmol).
After 3 h, the orange solution was vacuum-reduced to ca. 5
mL. An orange solid was obtained by addition of hexane (30
mL). This was separated by filtration, washed with diethyl
ether, and dried. Yield: 85% (0.112 g, 0.120 mmol). Anal.
Calcd for C35H28ClP2N2OIrCuBF4: C, 45.08; H, 3.03; N, 3.00;
Cl, 3.80. Found: C, 44.81; H, 3.55; N,3.20; Cl, 3.60. IR (CsI,
[Ir (CO)(CH3)ClI(P h 2P P y)2] (7). A solution of 1 (0.087 g,
0.111 mmol) dissolved in iodomethane (1.5 mL) was stirred
for 10 min. Then the excess of CH3I was evaporated under
reduced pressure to give 7 as a yellow solid. It was washed
with diethyl ether (40 mL) and dried. Yield: 90% (0.092 g,
0.100 mmol). Anal. Calcd for C36H31ClP2N2IOIr: C, 46.79;
H, 3.38; N, 3.03; Cl, 3.84. Found: C, 46.85; H, 3.45; N, 3.12;
Cl, 3.70. IR (CsI, Nujol): ν(CO) 2045 cm-1
.
1H NMR
(CDCl3): δ 8.77 (d, 6-H Py), 0.90 (t, CH3, 3H, J PH 5.4 Hz).
Nujol): ν(CO) 1983 cm-1, ν(BF4) 1090 cm-1
.
1H NMR
31P{1H} NMR (CDCl3): δ 17.20 (s).
(CDCl3): δ 9.39 (d, 6-H Py). 31P{1H} NMR (CDCl3): δ 27.44
(s).
[Ir (CO)(Cl)2(µ-P h 2P P y)2P d Cl] (8). To a benzene solution
(20 mL) of 1 (0.104 g, 0.133 mmol) was added [Pd(PhCN)2-
(Cl)2] (0.051 g, 0.133 mmol) in the same solvent. During the
addition the solution turned red-orange. After 2 h, the solvent
was removed by vacuum evaporator and the orange solid was
recrystallized from CH2Cl2-hexane (1:3) to give the product.
[Ir (CO)(Cl)(µ-P h 2P P y)2Tl][P F 6] (12). This compound was
obtained similarly to 11, as a red solid, by starting from 1
(0.110 g, 0.141 mmol) and TlPF6 (0.493 g, 0.141 mmol).
Yield: 95% (0.151 g, 0.134 mmol). Anal. Calcd for
35H28ClP3N2F6OIrTl: C, 37.15; H, 2.49; N, 2.48; Cl, 3.13.
Found: C, 38.02; H, 2.80; N, 2.62; Cl, 3.03. IR (CsI, Nujol):
C
Yield: 85% (0.108 g, 0.113 mmol). Anal. Calcd for C35H28
-
Cl3P2N2OIrPd: C, 43.81; H, 2.94; N, 2.91; Cl, 11.08. Found:
ν(CO) 1994 cm-1, ν(PF6) 998 cm-1 1H NMR (CDCl3) δ 9.15
.
C, 43.35; H, 3.07; N, 3.00; Cl, 10.60. IR (CsI, Nujol): ν(CO)
(d, 6-H Py). 31P{1H} NMR (CDCl3): δ 23.20 (s).
2016 cm-1 1H NMR (CDCl3): δ 9.31 (d, 6-H Py). 31P{1H} NMR
.
X-r a y Da ta Collection a n d Str u ctu r e Refin em en t of
[Ir (CO)(Cl)2(µ-P h 2P P y)2P dCl] (8) an d [Ir (CO)(Cl)2(HgCl2)-
(µ-P h 2P P y)2HgCl]‚2CH2Cl2 (10). Suitable crystals of the
complexes 8 and 10 have been obtained by slow evaporation
of CH2Cl2-hexane solutions. X-ray measurements were made
on a Siemens R3m/V four-circle diffractometer. Data were
collected at room temperature. A summary of the crystal-
lographic data and the structure refinements is listed in Table
1. No correction for absorption was applied for Ir-Hg because
of rapid decay of the crystal under X-ray exposure (about 40%),
and this prevented the accuracy of data, as can be seen in
(CDCl3): δ -12.80 (s).
[Ir (CO)(Cl)2(µ-P h 2P P y)2HgCl] (9). To a stirred solution
(25 mL) of 1 (0.100 g, 0.128 mmol) in benzene (25 mL) was
added solid HgCl2 (0.035 g, 0.128 mmol). After 3 h, the volume
of the solution was reduced to ca. 5 mL in vacuo. A white
solid was formed by addition of hexane (30 mL). This was
separated by filtration, recrystallized from CH2Cl2/hexane, and
dried. Yield 80% (0.108 g, 0.102 mmol). Anal. Calcd for
C
35H28Cl3P2N2OIrHg: C, 39.89; H, 2.68; N, 2.66; Cl, 10.09.
Found: C, 39.80; H, 2.63; N, 2.72; Cl, 10.25. IR (CsI, Nujol):

IrPd, IrHg, IrCu, and IrTl Binuclear Complexes
Organometallics, Vol. 17, No. 3, 1998 341
Sch em e 1a
a
Legend: P-N ) 2-(diphenylphosphino)pyridine; (a) SO2 gas, benzene; (b) Br2 or I2, CH2Cl2; (c) H2, CH2Cl2; (d) HCl solution,
CH2Cl2; (e) CH3I, neat; (f) [Pd(PhCN)2Cl2], 1:1 molar ratio, benzene; (g) HgCl2, 1:1 molar ratio, benzene; (h) HgCl2, 1:2 molar
ratio, benzene; (i) [Cu(CH3CN)4]BF4, 1:1 molar ratio, benzene; TlPF6, 1:1 molar ratio, benzene.
Table 1. Absorption correction for Ir-Pd: minimum and
maximum transmissions are 0.746 and 0.792, respectively.
Resu lts
The reactions described are summarized in Scheme
Structures were solved by Patterson and Fourier methods.10
The refinements were carried out by full-matrix least-squares
on F2 with anisotropic thermal parameters for all non-
hydrogen atoms. Hydrogens were placed at their geometrically
calculated positions and refined “riding” on the corresponding
carbon atoms, with a fixed and unique isotropic displacement
parameter (Uiso ) 0.08 Å2 for Ir-Hg and 0.07 Å2 for Ir-Pd).
The Flack11 absolute structure parameter (0.01(1)) confirms
for Ir-Hg its correctness. All calculations were performed on
a Micro-VAX 3400 and on a DEC Alpha 3000/400 using the
SHELXTL 5.010 program library. All other data (fractional,
etc.) are included in the Supporting Information.
1.
Syn t h esis a n d R ea ct ion s of tr a n s-[Ir (CO)-
(P h 2P P y)2Cl] (1). The reaction of [Ir(p-toluidine)(CO)2-
Cl] with Ph2PPy in a 2:1 ligand to metal ratio, in
benzene at room temperature, gave in good yield the
new complex trans-[Ir(CO)(Ph2PPy)2Cl] (1), which was
isolated as a yellow solid soluble in benzene (although
nonconducting), chlorinated solvents, and acetone. In
solution 1 is not air-stable due to easy uptake of oxygen
to give the corresponding adduct. Spectroscopic data
support a square-planar geometry for 1 with the two
bifunctional ligands Ph2PPy acting as monodentate
P-bonded ligands. In accordance, the IR spectrum of a
Nujol mull shows ν(CO) at 1952 cm-1 and the 31P{1H}
NMR spectrum in CDCl3 solution shows a singlet at δ
24.46 ppm. Significantly, the 1H NMR spectrum, in
CDCl3 solution, shows a distinct resonance at δ 8.77
ppm for the 6-hydrogen of the pyridine ring, as usual
when the Ph2PPy acts as a monodentate P-bonded
ligand.12 This resonance is further shifted to higher
frequency when the Ph2PPy acts as a bifunctional
Ca ta lytic Ru n s. All catalytic runs were performed in a
100 mL Berghoff stainless-steel autoclave equipped with gas
and liquid inlets, a heating device, and magnetic stirring. The
reactions were carried out in a Teflon vessel fitted to the
internal wall of the autoclave, thus preventing undesirable
effects due to the metal of the reactor. The autoclave was
closed and degassed through three vacuum-nitrogen cycles.
A solution of the starting complex and of the olefin (in a typical
experiment 5 mmol of substrate and 0.01 mmol of complex),
in benzene (10 mL), was introduced under nitrogen, and gases
(H2/CO 1:1) were admitted up to the desired pressure. At the
end of each catalytic run, the autoclave was cooled in a cold
water bath and slowly vented. A sample of the homogeneous
reaction mixture was then analyzed by gas chromatography.
1
ligand. Both 31P{1H} and H NMR spectra are temper-
(12) (a) Arena, C. G.; Rotondo, E.; Faraone, F.; Lanfranchi, M.;
Tiripicchio, A. Organometallics 1991, 10, 3877. (b) Arena, C. G.; Bruno,
G.; De Munno, G.; Rotondo, E.; Drommi, D.; Faraone, F. Inorg. Chem.
1993, 32, 1601. (c) Arena, C. G.; Drommi, D.; Faraone, F.; Lanfranchi,
M.; Nicolo`, F.; Tiripicchio, A. Organometallics 1996, 15, 3170. (d)
Drommi, D.; Arena, C. G.; Nicolo`, F.; Bruno, G.; Faraone, F. J .
Organomet. Chem. 1995, 485, 115.
(10) Siemens Energy and Automation Inc., Analytical Instrumenta-
tion, Madison, WI, 1996.
(11) Bernardinelli, G.; Flack, H. D. Acta Crystallogr. 1985, A41,
500-511.

342 Organometallics, Vol. 17, No. 3, 1998
Francio` et al.
ature-independent, indicating the lack of a fluxional
process with formation of five-coordinated species by
coordination of the pyridine nitrogen atom of Ph2PPy
ligand to the metal center on the NMR time scale.
Compound 1 exhibits a reactivity similar to that of
trans-[Ir(CO)(PPh3)2Cl];13,14 in fact, it adds SO2, halo-
gens, hydrogen, hydrogen chloride, and methyl iodide
(Scheme 1), giving compounds analogous to those ob-
tained by starting from 1 (see Experimental Section).
Complex 1 exhibits as basic centers either the irid-
ium(I) or both nitrogen pyridine atoms. Following the
configuration. The iridium center assumes an octa-
hedral geometry owing to the coordination of CO and
of two chloride ligands and the formation of the Ir-Hg
bond.
The reaction of 1 with HgCl2, in benzene, in a 1:2
molar ratio afforded the reaction product [Ir(CO)(Cl)2-
(HgCl2)(µ-Ph2PPy)2HgCl] (10). It was structurally simi-
lar to 9 and contained one HgCl2 molecule interacting
with the chloride bonded to iridium and trans to the Ir-
Hg bond (Figure 2). The spectroscopic IR and NMR
data of 10 are almost identical with those of 9; however,
the full characterization of 10 was obtained by an X-ray
crystal structure analysis.
1
reaction course by conductivity measurements and H
NMR spectra in CDCl3 solution, we established that the
addition of HCl to 1 initially occurs to nitrogen atoms
to give the cationic species [Ir(CO)(Ph2PPyH)2Cl][Cl]2
and, subsequently, to the iridium(I) center, affording the
oxidative-addition product [Ir(CO)H(Ph2PPyH)2Cl2][Cl]2
(6). IR, as Nujol mull, and 1H and 31P{1H} NMR, in
CDCl3 solution, support for 6 a structure with the
hydride trans to a chloride ligand and the phosphorus
atoms trans to one another.
With the aim of accessing binuclear complexes in
which two metal atoms are surrounded by the binucle-
ating ligands Ph2PPy, we examined the reactions of 1
with palladium(II), HgCl2, [Cu(NCCH3)4]+, and TlPF6
substrates.
The reaction of 1 with [Cu(NCCH3)4]BF4 and TlPF6
in benzene in a 1:1 molar ratio afforded, almost quan-
titatively, orange and red compounds, respectively.
Both are conducting in methanol solution ((1-5) × 10-4
M) as 1:1 electrolytes. Analytical and spectroscopic data
support their formulation as the ionic compounds
[Ir(CO)Cl(µ-Ph2PPy)2Cu]BF4 (11) and [Ir(CO)Cl(µ-Ph2-
PPy)2Tl]PF6 (12). Compounds 11 and 12 are soluble in
chlorinated solvents, acetone, methanol, and, to a minor
extent, benzene to give air-sensitive solutions. The
31P{1H} NMR spectra of 11 and 12 in CDCl3 solution
show singlets at δ 27.44 and δ 23.20 ppm, respectively,
and support a structure with head-to-head bridging
1
Ph2PPy ligands.12 As expected, in the H NMR spectra
The IrII-PdI species [IrPd(CO)Cl3(µ-Ph2PPy)2] (8)
was obtained, nearly quantitatively, by adding a ben-
zene solution of [Pd(PhCN)2Cl2] to a solution of 1 in the
same solvent (molar ratio 1:1). Compound 8 was
characterized by analytical, IR, and NMR spectroscopic
data and by a single-crystal X-ray diffraction study. The
in CDCl3 solution, the 6-hydrogen of the pyridine ring
is shifted to higher frequency (δ 9.39 and 9.15 ppm,
respectively) with respect to 1.12
A comparison of the electronic absorption spectrum
of 1 with that of 12 shows evidence of the Ir-Tl bonding
(Figure 1). The spectrum of 1 (trace A) is typical of
Vaska-like complexes. The changes observed on going
from trace A (1) to trace B (12) reflect the existence of
the Ir-Tl bonding. Following the suggestion of Balch
IR spectrum as a Nujol mull shows ν(CO) at 2016 cm-1
,
indicating the occurrence of an oxidative-addition proc-
1
ess at the iridium(I) center. In the H NMR spectrum
in CDCl3 solution, the resonances of the 6-hydrogen
atoms of the pyridine rings are shifted to higher
frequency, as is usually observed when the pyridine
nitrogen atom is coordinated.12 The 31P{1H} NMR
spectrum in CDCl3 solution shows a single resonance
at δ -12.80 ppm, indicating a head-to-head configura-
tion of the Ph2PPy bridging ligands.
et al.15 absorption of 12 at 380 nm (ꢀ ) 6600 M-1 cm-1
)
is assigned to the Ir-Tl chromophore with the weak
feature at 470 nm (ꢀ ) 420 M-1 cm-1) taken as its
forbidden counterpart. Complex 12 is luminescent in
a frozen dichloromethane solution at 77 K. The emis-
sion spectrum (excitation in the 350-450 nm range)
shows a intense band peaking at 580 nm (trace C). The
luminescence lifetime is 5 ns ((10%). The solution of
12 does not show luminescence at 25 °C.
The reaction of 1 with HgCl2, in a 1:1 molar ratio in
benzene, afforded as final product the binuclear complex
[Ir(CO)Cl(µ-Ph2PPy)2HgCl] (9) as a white solid. Com-
pound 9 is not conducting in benzene solution; it was
characterized by elemental analysis and spectroscopic
IR and NMR data. All attempts to obtain crystals of 9
suitable for an X-ray diffraction analysis failed. The IR
spectrum (ν(CO) 2026 cm-1, Nujol mull) indicates that
the reaction occurred with oxidative addition to the
iridium(I) center. The 31P{1H} NMR spectrum in CDCl3
solution shows a single resonance at δ 16.83 ppm, while,
A compound which can be related to 11 was recently
obtained16 in our laboratory by reacting trans-
[Rh(CO)(Ph2PPyOMe)2Cl] with [Cu(NCCH3)4]BF4. The
product, characterized by the X-ray crystal structure as
[Rh2Cu(CO)2(Ph2PPyOMe)2(µ-Cl)2]BF4, shows the Cu
atom almost linearly coordinated to pyridine nitrogen
atoms of Ph2PPy ligands of two rhodium(I) centers.
Cr ysta l a n d Molecu la r Str u ctu r e of [Ir (CO)(Cl)2-
(µ-P h 2P P y)2P d Cl] (8). A view of the molecular struc-
ture of 8 with the corresponding atom-labeling scheme
is shown in Figure 2; water molecules of crystallization
are omitted for clarity. Selected bond distances and
angles are given in Table 2. The Ir-Pd distance
(2.6135(10) Å) is consistent with the presence of a single
1
significantly, the H NMR exhibits a shift of 0.5 ppm (δ
9.27 ppm) in the resonances due to the H-6 atoms of
the pyridine rings with respect to 1. IR and NMR data
support for 9 a structure with the Ph2PPy ligands
bridging the Ir and Hg metals in a head-to-head
(13) (a) Vaska, L. Acc. Chem. Res. 1968, 1, 335. (b) Collman, J . P.;
Roper, W. R. Adv. Organomet. Chem. 1968, 7, 54. (c) Deeming, A. J .
In Reaction Mechanisms in Inorganic Chemistry; Emeleus, H. J ., Ed.;
Inorg. Chem. Ser. 9; Butterworths: Oxford, U.K., 1972; Chapter 4. (d)
Vaska, L.; Di Luzio, J . W. J . Am. Chem. Soc. 1962, 84, 680.
(14) (a) Kubas, G. J . Inorg. Chem. 1979, 18, 182. (b) La Placa, S. J .;
Ibers, J . A. Inorg. Chem. 1966, 5, 405.
(15) (a) Balch, A. L.; Neve, F.; Olmstead, M. M. J . Am. Chem. Soc.
1991, 113, 2995. (b) Balch, A. L.; Neve, F.; Olmstead, M. M. Inorg.
Chem. 1991, 30, 3395. (c) Brady, R.; Flynn, B. R.; Goeffroy, G. L.; Gray,
H. B.; Peone, J ., J r.; Vaska, L. Inorg. Chem. 1976, 15, 1485.
(16) Arena, C. G.; Faraone, F.; Lanfranchi, M.; Rotondo, E.; Tirip-
icchio, A. Inorg. Chem. 1992, 31, 4797.

IrPd, IrHg, IrCu, and IrTl Binuclear Complexes
Organometallics, Vol. 17, No. 3, 1998 343
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) of 8
Ir-C(1)
2.01(2)
2.334(3)
2.508(3)
0.94(2)
2.04(1)
1.81(1)
1.87(2)
1.82(1)
Ir-P(1)
2.334(3)
2.391(3)
2.614(1)
2.034(9)
2.389(4)
1.82(1)
Ir-P(2)
Ir-Cl(1)
Ir-Pd
Ir-Cl(2)
C(1)-O(1)
Pd-N(1)
P(1)-C(7)
P(1)-C(13)
P(2)-C(24)
Pd-N(2)
Pd-Cl(3)
P(1)-C(6)
P(2)-C(30)
P(2)-C(23)
1.80(1)
1.84(1)
C(1)-Ir-P(1)
P(1)-Ir-P(2)
P(1)-Ir-Cl(1)
C(1)-Ir-Cl(2)
P(2)-Ir-Cl(2)
C(1)-Ir-Pd
92.4(4)
157.2(1)
86.9(1)
91.1(4)
97.3(1)
89.8(4)
78.53(8)
175.71(9)
178.7(4)
91.4(3)
90.9(3)
C(1)-Ir-P(2)
C(1)-Ir-Cl(1)
P(2)-Ir-Cl(1)
P(1)-Ir-Cl(2)
Cl(1)-Ir-Cl(2)
P(1)-Ir-Pd
91.3(4)
176.5(4)
90.8(1)
105.2(1)
85.8(1)
78.97(8)
93.44(9)
172(2)
P(2)-Ir-Pd
Cl(1)-Ir-Pd
O(1)-C(1)-Ir
N(2)-Pd-Cl(3)
N(2)-Pd-Ir
Cl(2)-Ir-Pd
N(2)-Pd-N(1)
N(1)-Pd-Cl(3)
N(1)-Pd-Ir
89.0(3)
88.8(3)
176.2(1)
Cl(3)-Pd-Ir
phenylphosphine) (Ir-Pd ) 2.694(2) Å):17 and is
comparable with the value of 2.594(1) Å reported for the
complex RhPd(µ-Ph2PPy)2(CO)Cl3,18 analogous to 8,
where nevertheless the bridging ligands are arranged
head-to-tail.
The coordination around the iridium atom is octa-
hedral, albeit strongly distorted. The P(2)-Ir-P(1)
bond angle of 157.18(11)° has a significant deviation
from linearity. This deviation is due to the head-to-head
coordination of the Ph2PPy bridging ligands. In 16
bimetallic compounds containing Ph2PPy ligands coor-
dinated head-to-tail, the P-M-N bond angles range
from 169.39° (refcod ) KUNTOK) to 179.48° (DUSGIH)
(Cambridge Structural Database).19 As expected, the
nonbonded P‚‚‚N separations (P(1)‚‚‚N(1) ) 2.66(1) Å
and P(2)‚‚‚N(2) ) 2.69(2) Å) are longer than the metal-
metal separation. Torsion angles P(1)-Ir-Pd-N(1) and
P(2)-Ir-Pd-N(2) are -40.0(3) and -45.1(3)°, respec-
tively, indicating a great strain in the Ph2PPy ligand.
The equatorial bond angles around the iridium atom
F igu r e 1. Electronic absorption spectra of (A) [Ir(CO)(Ph2-
PPy)2Cl] (1) and (B) [Ir(CO)(Cl)(µ-Ph2PPy)2Tl][PF6] (12) in
dichloromethane solution at 25 °C. Emission spectrum
(excitation in the 350-450 nm range) of (C) [Ir(CO)(Cl)(µ-
Ph2PPy)2Tl][PF6] (12) in a frozen dichloromethane solution
at 77 K.
are C(1)-Ir-Cl(2)
) 91.1(4)°, Cl(1)-Ir-Cl(2) )
85.75(12)°, C(1)-Ir-Pd ) 89.8(4)°, and Cl(1)-Ir-Pd )
93.44(9)°, and their sum is 360.0(7)°. The palladium
atom is in a nearly square-planar configuration; the
least-square-planes calculated for the four binding
atoms (Ir, N(1), N(2), and Cl(3)) shows no deviation
greater than 0.09(1) Å; the Pd atom is 0.060(1) Å out
from this plane. The palladium coordination plane
makes an interplanar angle of 43.6(1)° with the equato-
rial iridium coodination plane.
Most of the bond lengths fall within the ranges
usually found. However, the unusual Ir-Cl(2) and Pd-
Cl(3) lengths can be attributed to the high trans
influence of the metal-metal (Ir-Pd) bond.
Molecular packing is mainly determined by normal
van der Waals interactions and weak hydrogen bonds,
involving chlorine atoms and a water molecule of
crystallization.
Cr ysta l a n d Molecu la r Str u ctu r e of [Ir (CO)(Cl)2-
(HgCl2)(µ-P h 2P P y)2HgCl] (10). The crystals of 10 are
F igu r e 2. ORTEP view of the structure of 8 with the
atomic numbering scheme.
(17) Balch, A. L.; Catalano, V. J . Inorg. Chem. 1992, 31, 2569-2575.
(18) Farr, P. P.; Olmstead, M. M.; Balch, A. L. Inorg. Chem. 1983,
22, 1229.
(19) Allen, F. H.; Davies, J . E.; Galloy, J . J .; J ohnson, O.; Kennard,
O.; Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J . M.; Watson,
D. G. J . Chem. Inf. Comput. Sci. 1991, 31, 187.
intermetallic bond. This distance is shorter than the
corresponding one reported for the only X-ray-charac-
terized IrPd heterobimetallic complex [PdIr(CO)Cl(µ-
dpmp)2][PF6]2 (dpmp ) bis((diphenylphosphino)methyl)-

344 Organometallics, Vol. 17, No. 3, 1998
Francio` et al.
diphenylphosphinomethane) and [Ir(COD)(EpTT)2-
HgCl]220 (EpTT ) C2H5N3-p-CH3C6H4) and longer than
the value reported for the complex [IrCl2(CO)(PPh3)2-
(HgX)]21 (X ) Cl, Br) (Ir-Hg(Cl) ) 2.570(1) Å, Ir-
Hg(Br) ) 2.578(2) Å). The metal-metal bond distance
is shorter than the nonbonded P‚‚‚N separations
(P(1)‚‚‚N(1) ) 2.721 Å and P(2)‚‚‚N(2) ) 2.703 Å); the
latter is in the range found for other Ph2PPy-bridged
complexes.12b Bond distances and angles for the coor-
dinated Ph2PPy are nearly alike, as are the P-M-M-N
torsion angles P(1)-Ir-Hg-N(1) ) 32.2(4)° and P(2)-
Ir-Hg-N(2) ) -28.9(4)°.
Compound 10 contains three metal centers with
different coordination environments. The coordination
of the iridium atom can be described as a strongly
distorted octahedron. The Ir-P(1) and Ir-P(2) bond
distances of 2.353(4) and 2.365(4) Å, respectively, are
in the range observed for other iridium-phosphine
complexes,17 while the P(2)-Ir-P(1) bond angle of
166.4(2)° deviates significantly from linearity. The Ir-
Cl bond distances are different (Ir-Cl(2) ) 2.395(5) Å,
Ir-Cl(3) ) 2.501(5) Å); the longest one is trans to the
metal-metal bond.
The atoms coordinated to iridium in the equatorial
plane are planar, and the iridium is 0.028(7) Å out of
the calculated least-squares plane; the corresponding
bond angles range from 88.6(6)° (C(35)-Ir-Cl(3)) to
91.1(2)° (Cl(2)-Ir-Cl(3)), and their sum is 359.9(3)°.
The mercury bonded to the iridium atom shows a very
distorted tetrahedral coordination; it is bonded to a
chlorine atom (Hg(1)-Cl(1) ) 2.394(5) Å) and to two
nitrogen atoms (mean Hg(1)-N ) 2.565 Å); the Hg-N
values are comparable to the value of 2.595(6) Å found
in [FeHg(µ-Ph2PPy)2(CO)3(SCN)2].22 The small N(1)-
Hg(1)-Ir (89.3(3)°) and N(2)-Hg(1)-Ir (90.1(4)°) bond
angles are both induced by the bridging Ph2PPy ligands.
The N(1)-Hg(1)-N(2) and Ir-Hg(1)-Cl(1) angles are
110.3(5) and 172.7(2)°, respectively; the last value is
indicative of severe distortion in the molecule.
F igu r e 3. ORTEP view of the structure of 10 with the
atomic numbering scheme.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 10
Hg(1)-Cl(1)
Hg(1)-N(1)
Ir-C(35)
2.394(5)
2.58(2)
1.73(3)
2.365(4)
2.501(4)
2.897(4)
2.288(6)
1.83(2)
1.81(2)
1.83(2)
Hg(1)-N(2)
Hg(1)-Ir
2.55(2)
2.604(1)
2.353(4)
2.395(5)
1.22(3)
2.276(6)
1.81(2)
1.84(2)
1.82(2)
Ir-P(1)
Ir-P(2)
Ir-Cl(2)
C(35)-O
Hg(2)-Cl(4)
P(1)-C(6)
P(1)-C(1)
P(2)-C(29)
Ir-Cl(3)
Cl(3)-Hg(2)
Hg(2)-Cl(5)
P(1)-C(12)
P(2)-C(23)
P(2)-C(18)
A peculiar aspect of the molecular structure of 10 is
the presence of a further HgCl2 molecule; the Hg(2)-
Cl(4) and Hg(2)-Cl(5) bond distances of 2.276(6) and
2.288(6) Å, respectively, are in good agreement with the
corresponding values found for HgCl2.23 The Cl(4)-Hg-
Cl(5) bond angle of 171.4(2)° deviates from linearity,
owing to the interaction of Hg(2) with Cl(3) bonded to
the iridium atom (Hg(2)-Cl(3) ) 2.897(4) Å), so that
Hg(2) becomes pseudo-three-coordinate.
The Hg(2) atom has a nonbonding interaction with
Cl(1) of a different molecule of 10 (Hg(2)-Cl(1) ) 3.561
Å) at x, y - 1, z and with chlorine atoms of the two
dichloromethane solvent of crystallization molecules.
Molecular packing is mainly determined by normal van
der Waals interactions and very weak hydrogen bonds
involving the chlorine atoms.
Cl(1)-Hg(1)-N(2)
N(2)-Hg(1)-N(1)
N(2)-Hg(1)-Ir
C(35)-Ir-P(1)
P(1)-Ir-P(2)
94.5(4) Cl(1)-Hg(1)-N(1)
110.3(5) Cl(1)-Hg(1)-Ir
90.1(4) N(1)-Hg(1)-Ir
96.0(6) C(35)-Ir-P(2)
166.4(2) C(35)-Ir-Cl(2)
85.8(2) P(2)-Ir-Cl(2)
88.6(6) P(1)-Ir-Cl(3)
93.8(2) Cl(2)-Ir-Cl(3)
89.5(6) P(1)-Ir-Hg(1)
85.0(1) Cl(2)-Ir-Hg(1)
177.8(1) O-C(35)-Ir
94.5(4)
172.7(2)
89.3(3)
92.4(6)
178.2(6)
85.8(2)
97.0(2)
91.1(2)
84.4(1)
90.7(1)
177(2)
P(1)-Ir-Cl(2)
C(35)-Ir-Cl(3)
P(2)-Ir-Cl(3)
C(35)-Ir-Hg(1)
P(2)-Ir-Hg(1)
Cl(3)-Ir-Hg(1)
Ir-Cl(3)-Hg(2)
Cl(4)-Hg(2)-Cl(3)
132.2(2) Cl(4)-Hg(2)-Cl(5) 171.4(2)
96.6(2) Cl(5)-Hg(2)-Cl(3) 91.9(2)
formed by cocrystallization of the binuclear complex and
two CH2Cl2 molecules of solvation. A view of the
molecular structure of 10 with the labeling scheme for
the non-hydrogen atoms is shown in Figure 3. Selected
bond distances and angles are given in Table 3. Two
Ph2PPy groups are bonded head-to-head to the metal
centers, both phosphorus atoms being coordinated to
iridium. The iridium-mercury bond length of 2.604(1)
Å is indicative of a single covalent metal-metal bond;
this arises from donation of one electron pair from
iridium to mercury. The Ir-Hg bond length is compa-
rable with the value of 2.618 Å found for the complexes
Ca ta lysis. Hydroformylation of styrene has been
carried out at temperatures of 60 and 80 °C under 60
(20) (a) Van Vliet, P. I.; Kokkes, M.; Van Koten, G.; Vrieze, K. J .
Organomet. Chem. 1980, 187, 413-426. (b) Balch, A. L.; Catalano, V.
J . Inorg. Chem. 1992, 31, 2730-2734.
(21) Brotherton, P. D.; Raston, C. L.; White, A. H.; Wild, S. B. J .
Chem. Soc., Dalton Trans. 1976, 1799.
(22) Zhang, Z. Z.; Xi, H. P.; Zhao, W. J .; J iang, K. Y.; Wang, R. J .;
Wang, H. G.; Wu, Y. J . Organomet. Chem. 1993, 454, 221-228.
(23) Subramanian, V.; Seff, K. Acta Crystallogr. 1980, B36, 2132-
2135.
[Cl2Hg(µ-Cl)2HgIr(CO)Cl(dpm)(µ-dpm)AuCl] (dpm
)

IrPd, IrHg, IrCu, and IrTl Binuclear Complexes
Organometallics, Vol. 17, No. 3, 1998 345
Ta ble 4. Hyd r ofor m yla tion of Styr en ea
aldehyded
entry no.
catalyst
P (atm) T (°C) conversn (%)b hydrc branched linear
B/Le
TOFf
1
2
3
4
5
6
7
8
9
trans-[Ir(PPh3)2(CO)Cl]
trans-[Ir(PPh3)2(CO)Cl]
80
60
60
80
80
60
80
80
80
60
80
60
80
80
80
80
60
80
80
80
60
80
80
80
6.5
1.5
2.6
45.8
9.8
56.2
42.3
51.1
31.8
64.5
53.5
70.3
7.8
33.4
34.6
37.8
43.2
46.1
41.7
35.0
8.2
83.0
66.2
65.0
56.9
53.8
40.1
52.3
58.7
85.2
41.2
53.1
40.2
9.2
0.4
0.4
5.3
3.0
3.8
6.0
6.3
6.6
7.0
6.7
3.9
90/10
99/1
99/1
92/8
95/5
91/9
90/10 1322
90/10 1597
93/7
203
47
81
1431
306
1756
trans-[Ir(PPh3)2(CO)Cl] + Py (1:1)
trans-[Ir(Ph2PPy)2(CO)Cl] (1)
trans-[Ir(Ph2PPy)2(CO)Cl] (1)
trans-[Ir(Ph2PPy)2(CO)Cl] (1)
trans-[Ir(Ph2PPy)2(CO)Cl] + Ph2PPy (1:3)
[IrCu(µ-Ph2PPy)2(CO)Cl][BF4]
[IrCu(µ-Ph2PPy)2(CO)Cl][BF4]
[IrCu(µ-Ph2PPy)2(CO)Cl][BF4]
[IrCu(µ-Ph2PPy)2(CO)Cl][PF6]
[IrCu(µ-Ph2PPy)2(CO)Cl][PF6]
994
10
11
12
51.8
40.2
55.9
85/15 2016
89/11 1672
91/9
2197
a
b
Reaction conditions: solvent benzene (10 mL); CO/H2 ) 1; catalyst:styrene ) 1:500. Determined by GC analysis. c Ethylbenzene.
Branched aldehyde 2-phenylpropionaldehyde, linear aldehyde 3-phenylpropionaldehyde. e B/L ) branched/linear. f TOF ) [(mol of product)/
(mol of cat.)(reaction time)] × 100.
d
and 80 atm of CO and H2 (1:1), with relevant results
being obtained using 1, 11, and 12 as catalytic precur-
sors (Table 4). After a typical reaction time of 16 h, the
crude reaction mixture was analyzed and the ratio
between 2-phenylpropanal, 3-phenylpropanal, ethylben-
zene, and unreacted styrene was determined by gas
chromatographic analysis and NMR spectroscopy. At
first the hydroformylation of styrene was carried out at
80 °C and under 80 atm of CO and H2 (1:1) using as
precatalyst trans-[Ir(CO)(PPh3)2Cl] (entry 1). As ex-
pected, the catalytic activity observed was very low, with
a styrene conversion of 6.5%. The regioselectivity in the
branched aldehyde 2-phenylpropanal was in the ratio
90:10, while the ethylbenzene formed was 7.7%. Sig-
nificantly, the addition of an excess of free pyridine to
the catalytic system based on Vaska’s complex does not
change significantly the yield of the styrene conversion
(entry 3). Operating at 80 °C and under 60 atm lowered
the styrene conversion to 1.5%. Comparison of these
results with those obtained, under the same experimen-
tal conditions, using 1 as catalytic precursor (entry 4)
demonstrates that the presence of the pendant pyridine
significantly increases the rate of the catalytic process.
At 80 °C and under 80 atm of CO and H2 (1:1) pressure,
the styrene conversion increases to 37.6% using 1 as
catalytic precursor. Also the regioselectivity increases
to a 2-phenylpropanal to 3-phenylpropanal ratio of 92:
8. The chemoselectivity of the process was low, the
hydrogenated product ethylbenzene being 37.8%. When
the reaction pressure is reduced to 60 atm (entry 6), the
conversion increases while the regioselectivity remains
unchanged. In the rhodium-catalyzed hydroformylation
of styrene, by reduction of the CO/H2 pressure, the
conversion decreases because the σ-acyl derivative is
formed in minor yield. This occurs also in the hydro-
formylation with 1. In fact, the comparison of entries
4 and 6 makes evident that when the pressure is
reduced to 60 atm, the yield of aldehydes decreases
although the amount of styrene conversion increases.
It is noteworthy that the activity of the catalytic system
becomes negligible under 80 atm as the temperature is
lowered to 60 °C (entry 5). The addition of free Ph2PPy,
in the molar ratio 1:3, to the catalytic system based on
1 does not change significantly the yield of the styrene
conversion (entry 7), indicating that dissociation of
Ph2PPy from 1, under equilibrium conditions, does not
occur during the catalytic cycle.
Using complexes 8-10 as catalytic precursors at 80
°C and 80 atm of CO/H2 pressure, we did not observe
significant conversion of styrene. Surprisingly, com-
plexes 11 and 12 exhibit catalytic activity with results
comparable to those for 1 (entries 8-12) under the same
experimental conditions. Analogous to the situation
observed with 1, reducing the reaction pressure to 60
atm (entries 11 and 12), gives an increase in styrene
conversion, although the aldehydes were formed to a
minor extent.
Discu ssion
There are in the literature various homo- and hetero-
binuclear complexes in which d8 metal atoms are
surrounded by two binucleating Ph2PPy ligand mol-
ecules. Surprisingly, to our knowledge,5 there are no
complexes of iridium reported. We prepared the bi-
metallic complexes 8-12 (Scheme 1) using a bridge-
assisted method.24
An important aspect of the reactions of 1 with
[Pd(PhCN)2Cl2] and HgCl2 is the change in the formal
oxidation states of metal centers in the products 8-10
with respect to reagents. Very likely, the first step of
the reaction of 1 with [Pd(PhCN)2Cl2] is nucleophilic
attack of the Ph2PPy nitrogen atoms of 1 on the
palladium(II) center to give an intermediate IrI-PdII
species, namely [(CO)ClIr(µ-Ph2PPy)2PdCl2]. The oxi-
dative addition of a Pd-Cl bond across the iridium(I)
center leads to the binuclear complex 8. The capability
of the bridging short-bite Ph2PPy ligand to promote
intramolecular redox processes was discussed in previ-
ous papers.12a,18,25-27 Differently, the reaction between
the basic iridium(I) center of 1 and the Lewis acid HgCl2
very likely occurs through initial formation of
[Ir(CO)Cl2(Ph2PPy)2HgCl]. This gives 9 by subsequent
coordination of the pyridine nitrogen atoms to an un-
saturated mercury center, in an intramolecular process.
The first step of the reaction was verified13 in the
reaction of Vaska’s complex with HgCl2.
(24) Roberts, D. A.; Geoffroy, G. In Comprehensive Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Perga-
mon: Oxford, U.K., 1982; Chapter 40.
(25) Farr, P. P.; Olmstead, M. M.; Balch, A. L. J . Am. Chem. Soc.
1980, 102, 6654.
(26) Lo Schiavo, S.; Rotondo, E.; Bruno, G.; Faraone, F. Organo-
metallics 1991, 10, 1613.
(27) Farr, P. P.; Olmstead, M. M.; Wood, F. E.; Balch, A. L. J . Am.
Chem. Soc. 1983, 105, 792.

346 Organometallics, Vol. 17, No. 3, 1998
Francio` et al.
Sch em e 2a
a
P-N ) 2-(diphenylphosphino)pyridine.
The formation of 11 and 12 very likely occurs by
nucleophilic attack of the pendant pyridine nitrogen
atoms of 1 on the CuI and TlI metal center.
by NMR spectroscopy of the reaction mixture, described
herein, of 1 with H2 because the equilibrium between
the dihydride and the cationic species results in a
complete shift toward the iridium(III) species. In the
catalytic cycle the cationic four-coordinate iridium(I)
[Ir(CO)(H)(Ph2PPyH)(Ph2PPy)]+ intermediate or the
corresponding dicarbonyl five-coordinate species can
react with the styrene, affording the five-coordinate
species [Ir(CO)(H)(styrene)(Ph2PPyH)(Ph2PPy)]+; this,
in turn, inserts the coordinated olefin into the Ir-H
bond to give the corresponding σ-alkyl derivative; the
resulting vacant coordination site can be occupied by
carbon monoxide. Subsequently, the migratory inser-
tion of CO into the Ir-C σ-bond will give the iridium-
acyl species (branched or linear). The final step,
resulting in the aldehydes 3-phenylpropanal and 2-phen-
ylpropanal, involves protonolysis, by the N-protonated
P-monodentate ligands Ph2PPyH+, of the iridium(I)-
acyl species and coordination of chloride to the metal
center to give 1. The protonolysis of the acyl group does
not occur under equilibrium conditions and indicates
that protonation of the pyridine nitrogen atom in the
pendant Ph2PPy was not stoichiometric. In accordance,
the addition of free pyridine to Vaska’s complex (entry
3) does not significantly increase the styrene conversion
under the catalytic conditions.
As for rhodium-catalyzed hydroformylation,29,30 the
regioselectivity of the process is determined in the step
that converts [Ir(CO)(H)(styrene)(Ph2PPyH)(Ph2PPy)]+
into a branched or linear four-coordinate σ-alkyl inter-
mediate. The Ph2PPyH+ group, as the short-bite bi-
functional ligand Ph2PPy, is rigid. In the intermediate
[Ir(CO)2(acyl)(Ph2PPyH)(Ph2PPy)]+ the Ir-P bond places
the protonated pyridine nitrogen atom in close proximity
to the Ir-C bond. Under these conditions the proton-
olysis of the coordinated acyl group is very easily
achieved. Such an effect can be called the “symphoria
The formation of the head-to-head isomer as the only
reaction product in the synthesis of bimetallic complexes
8-12 assumes particular relevance when we consider
that in the analogous compounds of electron-rich metals,
such as Rh, Pd, and Pt, the bridged Ph2PPy ligands
assume preferentially a head-to-tail configuration.25-28
The formation of 8 as the only product in the reaction
of 1 with [Pd(PhCN)2Cl2] indicates that the head-to-
head isomer of 8 is thermodynamically more stable than
the head-to-tail one.
Because the formation of the head-to-tail isomer
starting from a bis-Ph2PPy P-bonded species involves
the breaking of one metal-phosphorus bond, the strength
of the Ir-P bond is a factor determining the structure
of the isomers. The formation of the head-to-head
isomers starting from 1 is in line with the strength of
the metal-phosphorus bond, which is for the third-row
transition metals more than that of the second row.
The results of this study clearly show that the
coordination of Ph2PPy ligands to an iridium(I) center
causes a pronounced effect on the catalytic activity of
the precatalyst 1 in the hydroformylation of styrene. In
fact, as expected, under the same experimental condi-
tions of 1, Vaska’s complex displays negligible catalytic
activity. These results indicate that the drastic change
in the activity of the two catalytic systems can only be
due to the presence of basic uncoordinated pyridine
nitrogen atoms in the pendant Ph2PPy ligands of 1.
Scheme 2 represents the fundamental steps of the
proposed catalytic cycle. Very likely the protonation,
under equilibrium conditions, of the uncoordinated
nitrogen atom assists the reductive elimination of HCl
from the iridium(III) species [Ir(CO)(H)2(Ph2PPy)2Cl],
formed in the first step of the process by addition of H2
to 1. The cationic four-coordinate iridium(I) intermedi-
ate [Ir(CO)(H)(Ph2PPyH)(Ph2PPy)]Cl was not detected
(29) (a) Casey, C. P.; Whiteker, G. T.; Melville, M. G.; Petrovich, L.
M.; Gavney, J . A., J r.; Powell, D. R. J . Am. Chem. Soc. 1992, 114, 5535.
(b) Gladiali, S.; Bayon, J . C.; Claver, C. Tetrahedron: Asymmetry 1995,
6, 1453.
(30) Brown, J . M.; Kent, A. G. J . Chem. Soc., Perkin Trans. 1987,
2, 1597.
(28) (a) Maisonnat, A.; Farr, J . P.; Balch, A. L. Inorg. Chim. Acta
1981, 53, L217. (b) Farr, J . P., Wood, F. E.; Balch, A. L. Inorg. Chem.
1983, 22, 3387.

IrPd, IrHg, IrCu, and IrTl Binuclear Complexes
Organometallics, Vol. 17, No. 3, 1998 347
effect”,31 as the acyl group and the proton of Ph2PPyH+
are in the right position to interact.
We proved that, under the catalytic experimental
conditions, the Cu-N and Tl-N bonds are broken to
give 1. The occurrence of Cu-N and Tl-N bond
ruptures in 11 and 12 is supported by the fact that, in
benzene solution at 60 °C and under 60 atm of CO/H2
(1:1), these complexes afford as major product, together
with an uncharacterized compound, the five-coordinated
species [Ir(CO)2H(Ph2PPyH)(Ph2PPy)]+ as yellow solid.
Spectroscopic IR and NMR data indicate for this com-
pound a structure with the hydride and CO in axial
positions. The compound shows in the IR spectrum two
ν(CO) bands at 2053 and 2085 cm-1. It exhibits in the
31P{1H} NMR (CDCl3 solution) a singlet at δ 9.30 ppm
and, in the hydride region of the 1H NMR (CDCl3)
spectrum, a triplet at δ -10.34 (2J HP 15.6 Hz). These
data support the proposed structure if we consider that
the protonation of the pyridine nitrogen atom of pendant
Ph2PPy does not modify the phosphorus chemical shift
A noteworthy aspect of the hydroformylation of sty-
rene using 1 as catalyst precursor is the low chemo-
selectivity of the process, with yields of the hydrogen-
ated product ethylbenzene ranging between 38 and 46%.
In the catalytic cycle ethylbenzene can be formed
through protonolysis of the linear or branched σ-alkyl
derivative intermediates by means of the P-monoden-
tate ligand Ph2PPyH+. This step can be operative
because the Ir-P bond is efficient enough to hold the
proton in proximity of the Ir-C(alkyl) bond before CO
insertion to give the corresponding acyl derivative. The
ratio of ethylbenzene to aldehydes is dependent on the
relative rate of the CO insertion and protonolysis steps.
In principle, protonolysis by PPh2PyH+ can occur either
on the Ir-acyl or on the Ir-alkyl bonds. Thus, the
protonolysis steps determine the chemoselectivity and
the overall reaction rate of the catalytic cycle.
2
and the J HP value of the ligand.
In Scheme 2 the dissociation under equilibrium
conditions of one Ph2PPy ligand from 1 or from the
dihydride species was not considered. However, these
steps are considered to occur in the hydroformylation
of olefins by Wilkinson’s catalyst. We observed (entry
7) that the presence of free Ph2PPy does not modify the
conversion of styrene.
Surprisingly, using complexes 11 and 12 as precursor
catalysts, we observed catalytic activity which compares
very well to that of 1.
Ack n ow led gm en t. Financial support from MURST
and the Italian CNR is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables SI-SIX,
giving fractional atomic coordinates and U values for the non-
hydrogen atoms, hydrogen atom coordinates, anisotropic ther-
mal parameters, and complete bond lengths and bond angles
for compounds 8 and 10 and a crystal-packing diagram for 10
(18 pages). Ordering information is given on any current
masthead page.
(31) Morrison, R. T.; Boyd, R. N. Organic Chemistry; Prentice-Hall:
Englewood Cliffs, NJ , 1992; Chapter 29.
OM970145N