Synthesis, characterization and reactivity of tribenzylphosphine rhodium and iridium complexes

Article abstract of DOI:10.1016/j.jorganchem.2005.11.008

New rhodium and iridium complexes, with the formula [MCl(PBz ₃)(cod)] [M = Rh (1), Ir (2)] and [M(PBz₃) ₂(cod)]PF₆ [M = Rh (3), Ir (4)] (cod = 1,5-cyclooctadiene), stabilized by the tribenzylphosphine ligand (PBz ₃) were synthesized and characterized by elemental analysis and spectroscopic methods. The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. The addition of pyridine to a methanol solution of 1or 2, followed by metathetical reaction with NH₄PF ₆, gave the corresponding derivatives [M(py)(PBz₃)(cod)] PF₆ [M = Rh (5), Ir (6)]. At room temperature in CHCl₃ solution, 4 converted spontaneously to the ortho-metallated complex [IrH(PBz₃)(cod){η²-P,C-(C₆H ₄CH₂)PBz₂}]PF₆ (7) as a mixture of cis/trans isomers via intramolecular C-H activation of a benzylic phenyl ring. The reaction of 3 or 4 with hydrogen in coordinating solvents gave the dihydrido bis(solvento) derivative [M(H)₂(S)₂(PBz₃) ₂]PF₆ (M = Rh, Ir; S = acetone, acetonitrile, THF), that transformed into the corresponding dicarbonyls [M(H)₂(CO) ₂(PBz₃)₂]PF₆ by treatment with CO. Analogous cis-dihydrido complexes [M(H)₂(THF)₂(py) (PBz₃)₂]PF₆ (M = Rh, Ir) were observed by reaction of the py derivatives 5 and 6 with H₂.

Full text of DOI:10.1016/j.jorganchem.2005.11.008

Journal of Organometallic Chemistry 691 (2006) 1039–1050
www.elsevier.com/locate/jorganchem
Synthesis, characterization and reactivity of
tribenzylphosphine rhodium and iridium complexes
b,
a
Vanessa R. Landaeta a,b, Maurizio Peruzzini , Veronica Herrera ,
*
´
b,
a,c,
*
*
´
Claudio Bianchini , Roberto A. Sanchez-Delgado
,
d
b
´
Andres E. Goeta , Fabrizio Zanobini
a
Instituto Venezolano de Investigaciones Cientı´ficas (IVIC), Centro de Quı´mica, Apartado 21827, Caracas, 1020-A, Venezuela
Istituto di Chimica dei Composti Organometallici (ICCOM – CNR), Area Ricerca CNR Firenze, Via Madonna del Piano 10,
50019 Sesto Fiorentino (FI), Italy
b
c
Chemistry Department, Brooklyn College of The City University of New York Brooklyn, NY 11210, USA
d
University of Durham, Department of Chemistry, Science Site, South Road, Durham DH1 3LE, UK
Received 30 July 2005; received in revised form 23 October 2005; accepted 7 November 2005
Available online 19 December 2005
Abstract
New rhodium and iridium complexes, with the formula [MCl(PBz3)(cod)] [M = Rh (1), Ir (2)] and [M(PBz3)2(cod)]PF6 [M = Rh (3),
Ir (4)] (cod = 1,5-cyclooctadiene), stabilized by the tribenzylphosphine ligand (PBz3) were synthesized and characterized by elemental
analysis and spectroscopic methods. The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. The addi-
tion of pyridine to a methanol solution of 1or 2, followed by metathetical reaction with NH4PF6, gave the corresponding derivatives
[M(py)(PBz3)(cod)]PF6 [M = Rh (5), Ir (6)]. At room temperature in CHCl3 solution, 4 converted spontaneously to the ortho-metallated
complex [IrH(PBz3)(cod){g2-P,C-(C6H4CH2)PBz2}]PF6 (7) as a mixture of cis/trans isomers via intramolecular C–H activation of a ben-
zylic phenyl ring. The reaction of 3 or 4 with hydrogen in coordinating solvents gave the dihydrido bis(solvento) derivative
[M(H)2(S)2(PBz3)2]PF6 (M = Rh, Ir; S = acetone, acetonitrile, THF), that transformed into the corresponding dicarbonyls
[M(H)2(CO)2(PBz3)2]PF6 by treatment with CO. Analogous cis-dihydrido complexes [M(H)2(THF)2(py)(PBz3)2]PF6 (M = Rh, Ir) were
observed by reaction of the py derivatives 5 and 6 with H2.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Rhodium; Iridium; Tribenzylphosphine; C–H bond activation; X-ray crystallography; Ortho-metallation
1. Introduction
cursors modified with tertiary phosphines, among which
triphenylphosphine (PPh3) plays a major role. Surprisingly,
tribenzylphosphine (PBz3) has received very little attention,
which contrasts with the great potential stemming from its
excellent nucleophilicity and peculiar steric properties. In a
sense, PBz3 lies midway between PPh3 and PCy3: it is more
sterically demanding and a stronger Lewis base than the
former [2–5] and less sterically demanding and less basic
than the latter [6]. In this respect, studying whether PBz3
complexes are efficient catalysts is of importance because,
at variance with PPh3 complexes, PCy3 derivatives show
low activity and are not currently used in metal catalyzed
hydrogenation and hydroformylation.
Excellent coordinating ability and easy-to-tune steric
properties make tertiary phosphines the ligands of largest
use in organometallic chemistry and homogeneous cataly-
sis, especially in conjunction with late transition metals
[1]. A variety of catalytic processes, in particular hydroge-
nation and hydroformylation reactions, involve metal pre-
*
Corresponding authors. Tel.: +39 055 5225289; fax: +39 055 5225203.
E-mail addresses: maurizio.peruzzini@iccom.cnr.it, mperuzzini@
iccom.cnr.it (M. Peruzzini), Claudio.bianchini@iccom.cnr.it (C. Bianchi-
ni), Rsdelgado@brooklyn.cuny.edu (R.A. Sanchez-Delgado).
´
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.11.008

1040
V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
PBz3 metal complexes have been reported with silver
150.5 Hz, typical for Rh(I) complexes, in the spectrum
of 1 [30]. The CH and CH2 groups of the COD ligand
are magnetically inequivalent: four signals in the 1H
NMR spectrum are originated by four CH protons and
two signals by the two methylenic protons. Four sepa-
rated carbon resonances, due to the two pairs of CH
and CH2 carbons, are present in the 13C{1H} NMR
spectrum. 2D-COSY and HMQC NMR spectra were
helpful to unambiguously assign the network of proton
and carbon resonances for these complexes as well as
for all the new complexes described in this paper. Details
of the spectral data and assignments are provided in
Section 4.
[7,8], osmium [9], palladium [2,10–14], platinum [2,11],
nickel [11,15–17], copper [18–20], rhenium [21], and ruthe-
nium [3,22–24], while catalytic applications of PBz3 metal
complexes are limited to the sole example of hydroformy-
lation of allylbenzene by rhodium catalysts [25,26].
Remarkably, only one rhodium compound containing
PBz3, namely RhCl(CO)(PBz3)2 [4,27,28], has been
described and no iridium derivative is known. This lack
of data is surprising indeed as rhodium and iridium con-
stitute the essential ingredients of most catalytic processes
in homogeneous phase as well as of fundamental studies
of organometallic reactions. Aimed at filling this gap,
we decided to carry out a systematic study of the coordi-
nation ability of PBz3 towards rhodium and iridium and
to investigate both the organometallic chemistry and the
application in homogeneous catalysis of the resultant
complexes.
In this paper, we describe the synthesis and character-
ization of some rhodium and iridium complexes, starting
from the parent compounds [MCl(PBz3)(cod)] [M = Rh
(1), Ir (2)] and [M(PBz3)2(cod)]PF6 [M = Rh (3), Ir (4)]
(cod = 1,5-cyclooctadiene). These precursors have proved
amenable to investigating elementary organometallic
reactions such as the activation of CO, H2 and C–H
bonds. In a concomitant paper, a study of the ability of
the Rh and Ir complexes [M(PBz3)2(cod)]PF6 [M = Rh,
Ir] and [M(py)(PBz3)(cod)]PF6 [M = Rh, Ir; py = pyri-
dine] to catalyze the hydrogenation of imines, will be
reported [29].
Suitable crystals of 1 and 2 grown from dilute dichlo-
romethane/ethanol solutions were subjected to X-ray dif-
fraction analysis. An ORTEP drawing showing the
molecular structure of the iridium derivative is given in
Fig. 1. A summary of crystal data and a selection of
bond distances and angles are collected in Tables 1 and
2. Both complexes crystallized in the same space group
(monoclinic, P21/n) and are characterized by a strongly
distorted square planar geometry due to the presence
˚
of the bulky PBz3 ligand. M–P [2.292(1) A for 1 and
˚
˚
2.303(2) A for 2] and M–Cl bond distances [2.377(1) A
˚
for 1 and 2.365(2) A for 2] are within the range expected
for this kind of complexes [31]. A comparison of the
metrical data of 1 with that of trans-RhCl(CO)(PBz3)2
˚
˚
(dRh–Cl = 2.3654(15) A;
dRh–P(ave) = 2.3164(15) A)
[4]
shows a complete matching of the Rh–Cl separations,
but somewhat different Rh–P distances, likely reflecting
the different trans influence exerted by the phosphorus
atoms and the carbon atoms of COD.
2. Results and discussion
2.1. Synthesis and characterization of MCl(cod)(PBz3)
(M = Ir, Rh)
The binuclear precursors [MCl(cod)]2 (M = Rh, Ir)
react smoothly in dichloromethane with two equivalents
of PBz3 to give bright yellow crystals of the neutral
complexes MCl(PBz3)(cod) [M = Rh (1), Ir (2)] in high
yield (>90%) (Scheme 1). Compounds 1 and 2 are air-
stable in the solid state and are soluble in polar organic
solvents.
The 31P{1H} NMR resonance of PBz3 is a singlet in
the spectrum of 2 and a doublet, with a JPRh value of
Cl
Cl
M
M
M
+ 2 PBz3
P
Cl
Fig. 1. ORTEP drawing of the complex IrCl(cod)(PBz3) (2), with 50%
probability displacement ellipsoids. The labeling scheme is the same for
both complexes (M = Rh (1) and Ir (2)) and the displacement ellipsoids
are very similar, slightly smaller for 1 due to the lower temperature of the
experiment. Hydrogen atoms have been omitted for clarity.
M = Rh (1); Ir (2)
Scheme 1.

V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
1041
Table 1
Summary of crystal data for RhCl(cod)(PBz3) (1) and IrCl(cod)(PBz3) (2)
2.2. Reactivity of the neutral complexes MCl(PBz3)(cod)
(M = Rh, Ir)
Compound
1
2
Removal of the chloride ligand from 1 or 2 can be read-
ily achieved either by reaction with silver salts or by
straightforward ligand substitution using an excess of a
strong r-donor such as pyridine (py) in the presence of
NH4PF6. Thus, the reaction of silver triflate with 1 or 2,
dissolved in acetone at room temperature, followed by
addition of one equivalent of PBz3, led to the formation
of cationic derivatives that were isolated as PFꢀ6 salts,
[M(PBz3)2(cod)]PF6 [M = Rh (3); Ir (4)] (Scheme 2).
Complexes 3 and 4 contain two cis-PBz3 ligands. PPh3
rhodium compounds with similar structure, [M(PPh3)2-
(cod)]PF6 [M = Rh, Ir] have been reported by Haines
and Singleton [33] and Osborn et al. [34], yet no bis-PCy3
rhodium derivative has ever been reported in the literature.
A series of comparable complexes with substituted triphe-
nylphosphines [P(p-RC6H4)3, R = Cl, F, CH3, CH3O] were
also synthesized by Oro and co-workers [35].
Formula
RhC29H33PCl
550.986
0.72 · 0.50 · 0.40
Monoclinic
P21/n
10.626(3)
13.208(3)
18.795(5)
102.709(8)
2573.2(12)
4
IrC29H33PCl
640.17
0.575 · 0.25 · 0.20
Monoclinic
P21/n
10.676(1)
13.159(5)
18.862(2)
101.95(1)
2592.4(11)
4
Molecular weight
Cryst size (mm)
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
dcalc (Mg/m3)
Absorption
coefficient (mmꢀ1
F(000)
1.422
0.844
1.640
5.330
)
1136
1264
h Range (ꢁ)
Index ranges
1.90–28.29
ꢀ14 6 h 6 14,
ꢀ17 6 k 6 17,
ꢀ24 6 l 6 25
28161
1.90–24.99
ꢀ12 6 h 6 12,
0 6 k 6 15,
0 6 l 6 22
4696
Total number
of data
Number of unique
data [I P 2r(I)] (Rint
Goodness-of-fit
on F2, S
R1 [I P 2r(I)]
wR2 (all)
The 31P{1H} NMR spectra of 3 and 4 contain, in addi-
tion to the high-field septuplet of PFꢀ6 , a single resonance
for the two phosphine ligands (4, singlet at d ꢀ6.40 ppm;
3, doublet at d 2.75ppm, JRhP = 143.5 Hz). The equiva-
6384/4974 (0.0221)
1.044
4552/2979 (0.0264)
1.076
)
1
0.0307
0.0843
0.409 and ꢀ0.368
0.0294
0.0737
0.576 and ꢀ0.501
lence of the two PBz3 ligands makes the H NMR spectra
simpler than those of 1 or 2 as the CH and CH2 protons of
COD now appear as single signals.
Largest difference in
peak and hole (e/A )
3
˚
Complexes 1 and 2 reacted with an excess of pyridine
and NH4PF6 in methanol to yield the cationic mixed phos-
phine-pyridine complexes [M(py)(PBz3)(cod)]PF6 [M = Rh
Several rhodium(I) and iridium(I) complexes with steri-
cally demanding phosphines (PCy3, PMePh2, PPri3) or
phosphites (P(OMe)Ph2) share the primary structure of 1
and 2 [31,32].
Table 2
+
˚
Selected bond distances (A) and angles (ꢁ) for RhCl(cod)(PBz3) (1) and
IrCl(cod)(PBz3) (2)
AgOTf
Cl
1
2
P
PBz3
M
Distances
Rh–C(43)
Rh–C(44)
Rh–C(47)
Rh–C(40)
Rh–P(1)
M
2.106(3)
2.107(3)
2.192(3)
2.212(3)
2.292(1)
2.377(1)
Ir–C(43)
Ir–C(44)
Ir–C(47)
Ir–C(40)
Ir–P(1)
2.097(7)
2.106(7)
2.179(6)
2.182(6)
2.303(2)
2.365(2)
P
Me2CO
NH4PF6
P
M = Rh (1); Ir (2)
Rh–Cl(1)
Ir–Cl(1)
M = Rh (3); Ir (4)
Angles
py
P(1)–Rh–Cl(1)
C(43)–Rh–C(44)
C(43)–Rh–C(47)
C(44)–Rh–C(47)
C(43)–Rh–C(40)
C(44)–Rh–C(40)
C(47)–Rh–C(40)
C(43)–Rh–P(1)
C(44)–Rh–P(1)
C(47)–Rh–P(1)
C(40)–Rh–P(1)
C(43)–Rh–Cl(1)
C(44)–Rh–Cl(1)
C(47)–Rh–Cl(1)
C(40)–Rh–Cl(1)
86.75(3)
38.56(13)
94.61(14)
81.72(12)
81.53(12)
92.06(12)
36.00(13)
95.69(9)
P(1)–Ir–Cl(1)
C(43)–Ir–C(44)
C(43)–Ir–C(47)
C(44)–Ir–C(47)
C(43)–Ir–C(40)
C(44)–Ir–C(40)
C(47)–Ir–C(40)
C(43)–Ir–P(1)
C(44)–Ir–P(1)
C(47)–Ir–P(1)
C(40)–Ir–P(1)
C(43)–Ir–Cl(1)
C(44)–Ir–Cl(1)
C(47)–Ir–Cl(1)
C(40)–Ir–Cl(1)
87.55(6)
38.6(3)
95.4(3)
81.7(3)
81.2(3)
91.6(3)
37.2(3)
95.9(2)
95.5(2)
157.9(2)
164.4(2)
160.0(3)
160.7(3)
88.3(2)
90.2(2)
NH4PF6
MeOH
+
N
P
M
95.10(8)
158.94(11)
164.62(9)
160.91(11)
160.23(11)
89.49(10)
91.10(8)
M = Rh (5); Ir (6)
Scheme 2.

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V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
(5), Ir (6)] whose structure is quite similar to that of Crab-
treeÕs catalyst, [Ir(py)(PCy3)(cod)]PF6 (Scheme 2) [32].
[23]; in no case, however, the process occurred spontane-
ously at room temperature as observed for 4, but harsh
reaction conditions were required for o-metallation.
Monitoring the stability of 4 in CDCl3 by NMR spec-
troscopy at room temperature showed the bis-PBz3 com-
plex to convert to cis-P,P-7 and to another complex,
later identified as trans-(P,P)-[IrH(PBz3)(cod){g2-P,C-
(C6H4CH2)PBz2}]PF6 (trans-P,P-7), which was initially
the major product. In particular, 4 disappeared completely
after 30 min, to form a ca. 1:1 mixture of the two products,
and trans-P,P-7 completely converted into cis-P,P-7 in ca.
8 h at room temperature.
2.3. Ortho-metallation of [Ir(cod)(PBz3)2]PF6
On standing in CHCl3 for three days under nitrogen, 4
transformed into off-white crystals of a new product that
was later identified as the ortho-metallated complex cis-
(P,P)-[IrH(PBz3)(cod){g2-P,C-(C6H4CH2)PBz2}]PF6 (cis-
P,P-7).
The solution structure of cis-P,P-7 was unequivocally
established by 1D and 2D NMR spectroscopy. The
31P{1H} NMR spectrum consists of two doublets due to
the inequivalent PBz3 ligands (d ꢀ2.86 and ꢀ9.97) which
are mutually cis as shown by the small magnitude of the
homonuclear coupling constant (JPP = 18.5 Hz). The 1H
NMR spectrum contains an eight-line multiplet (ddd) in
the hydride region due to coupling of the Ir–H hydride
The identity of trans-P,P-7 as a kinetic, geometric iso-
mer of cis-P,P-7 (Scheme 3) was readily established on
the basis of its NMR parameters, for example the much
2
larger homonuclear JPP coupling constant (18.5 Hz for
cis-P,P-7 and 238.0 Hz for trans-P,P-7) as well as a broad
triplet at ꢀ13.38 ppm in the hydride region of the 1H NMR
2
2
both to the two P atoms (2JHP1 = 102.3 Hz, JHP2 = 17.2
spectrum with JHP = 19.8 Hz.
Hz) and to one of the four CH protons of COD. 31P
broad-band decoupling collapses/the hydride resonance
2.4. Reactions of [M(PBz3)2(cod)]PF6 and
[M(py)(PBz3)(cod)]PF6 with H2
into
a
slightly broadened doublet (4JHH = 6.3 Hz),
confirming that only one homonuclear H,H coupling is dis-
cernable. A 2D-HMQC NMR experiment showed the met-
allated carbon atom to appear as a doublet at d 146.87
(2JCP = 17.8 Hz) in the 13C NMR spectrum.
Incorporation of the NMR data led us to assign an octa-
hedral coordination to cis-P,P-7 where a terminal hydride
is trans to the P atom of an ortho-metallated PBz3 ligand
(Scheme 3). COD, a phenyl ring and an intact PBz3 com-
plete the coordination geometry.
It is very likely that the intramolecular C–H oxidative
addition leading to cis-P,P-7 is a consequence of the large
steric hindrance exerted by the two cis-disposed PBz3
ligands in the precursor 4 [5]. Indeed, bulky arylphosphines
tend to form o-metallated compounds via intramolecular
C–H bond activation just to relief the steric congestion
with bulky cis ligands [36]. Besides steric effects, o-metalla-
tion could be also promoted by electronic effects,
associated with the enthalpy of formation of new M–C
and M–H bonds as compared to the energy required to
break a C–H bond. In this respect, it is not a case that
the iridium complex 4 undergoes spontaneous o-metalla-
tion, whereas the analogous rhodium derivative 3 is fully
stable in chloroform either even at reflux temperature [37].
Ortho-metallation of a phenyl ring from PPh2Bz has
been previously observed for nickel [15], and suggested
for some ruthenium and palladium complexes with PBz3
When dissolved in coordinating solvents such as ace-
tone, acetonitrile or THF, 3 and 4 reacted rapidly with
H2 at room temperature to give the M(III) cis-dihydrides
[M(H)2(S)2(PBz3)2]PF6 (M = Rh, Ir; S = acetone, MeCN,
THF). The formation of the latter complexes was accom-
panied by the reduction of COD to cyclooctane (COA).
Both the acetone and the acetonitrile Ir adducts
[Ir(H)2(S)2(PBz3)2]PF6 (S = acetone, 8; S = acetonitrile, 9)
could be isolated as cream-colored crystals (Scheme 4).
Due to the better nucleophilic properties of acetonitrile ver-
sus acetone, 8 converted into 9 upon dissolution in acetoni-
trile, while the reverse reaction did not occur. In contrast,
the THF adduct [Ir(H)2(THF)2(PBz3)2]+ (10) was exclu-
sively prepared in situ but could not be isolated in the solid
state.
Octahedral iridium cis-dihydride complexes similar to 8,
9 and 10 have been synthesized by Crabtree and co-work-
ers by reaction of [Ir(PPh3)2(cod)]PF6 with H2 in coordi-
nating solvents [38].
The 31P{1H} NMR spectra of the dihydrides 8–10 exhi-
bit a sharp singlet for the P atoms, as expected for a trans
disposition of the phosphines. In keeping with the presence
of an Ir(III) center, the 31P chemical shift is significantly
low-field shifted with respect to the analogous resonance
+
PBz3
Ir
+
PBz3
PBz3
+
Bz2P
Ir
+
Bz2P
Ir
S
S
H
H
Solvent
COA
Ir
+ 3 H2
+
PBz3
CHCl3
rt
Ir
H
4
PBz3
PBz 3
PBz3
PBz3
H
COA = cyclooctane
4
trans-P,P-7
cis-P,P-7
S = acetone (8); acetonitrile (9), THF (10)
Scheme 3.
Scheme 4.

V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
1043
of the Ir(I) precursor 4. The 1H NMR spectra contain high-
field hydride triplets at ꢀ30.13 ppm (2JHP = 15.3 Hz),
ꢀ21.45 ppm (2JHP = 16.2 Hz); d ꢀ23.5 (JHP = 15.5 Hz).
The 1H NMR spectra of all compounds contain also a vir-
tual triplet for the methylenic PBz3 protons, which is again
consistent with trans-phosphines [39].
of [Rh(H)2(THF)2(PBz3)2]+ (14) and [Rh(THF)2(PBz3)2]+
(15) was detected by NMR analysis under 1 bar H2.
cis-Dihydride bis-THF complexes, [M(H)2(THF)2(py)-
(PBz3)]PF6 [M = Rh (16); Ir (17)], were also obtained
by hydrogenation of [M(py)(PBz3)(cod)]PF6 in THF.
These compounds were exclusively prepared in solution
and characterized in situ by NMR spectroscopy (see
Section 4).
The lower stability of Rh(III) dihydrides versus their
Ir(III) congeners is well known and has been rationalized
on the basis of the greater strength of Ir–H bonds versus
Rh–H bonds [43].
Related iridium hydrido complexes containing PPr3i
exhibit hydride signals with chemical shifts similar to those
found for the present PBz3 derivatives, specially if com-
pared to the acetonitrile complex, 9 [40]. The analogous
compound ½IrðHÞ ðPPr3i ÞðPMe3ÞðCH3CNÞ ꢁBF4 displays a
2
2
unique hydride signal at ꢀ22.26 ppm (dd, JHP = JHPÕ
= 17.0 Hz), indicating similar steric and electronic proper-
ties between our ligand and PPri3 in this complex.
2.5. Reactions of [M(PBz3)2(cod)]PF6 with CO
Unlike iridium, rhodium does not form any bis-solvento
dihydride possible to isolate in the solid state.
[Rh(H)2(CD3CN)2(PBz3)2]+ (11), generated by hydrogena-
tion of 3 in acetonitrile-d3, was stable in solution only
under a protective H2 atmosphere. The hydride signal
The reactions of the dihydrides 8 and 9 with CO were
followed by in situ NMR spectroscopy (Scheme 6). The
replacement of either acetone or MeCN by 1 bar CO was
fast and complete to give [Ir(H)2(CO)2(PBz3)2]+. A bulk
preparative experiment allowed the isolation of the octahe-
dral complex [Ir(H)2(CO)2(PBz3)2]PF6 (18), featured inter
alia by mCO bands at 2002 and 2004 cmꢀ1. A similar com-
pound with P(p-CH3C6H4)3 has been described showing
1
appears as a doublet of triplets in the H NMR spectrum,
while the 31P{1H} spectrum consists of a doublet [30,41].
The formation of COA was put in evidence by a 1H
NMR singlet at 1.39 ppm as well as a GC/MS analysis.
The bis(acetone) derivative [Rh(H)2(Me2CO-d6)2(PBz3)2]+
(12) (dP 32.48; JRhP = 122.1 Hz), was prepared analo-
gously. However, this complex was unstable even under
1 bar H2 and readily equilibrated with the square-planar
Rh(I) cation [Rh(Me2CO-d6)2(PBz3)2]+ (13) (dP 38.36;
JRhP = 149.3 Hz), which apparently forms by reductive
elimination of H2 from 12 (Scheme 5). This behavior has
some precedents in rhodium chemistry, for example
with the couple [Rh(H)2(MeOH)2(PR3)2]+/[Rh(MeOH)2-
(PR3)2]+ (R = Ph, p-tolyl) [34,42]. Increasing the H2 pres-
sure to 10 bar with the use of a HP-NMR sapphire tube
inhibited the reductive elimination of H2 from 12 and no
formation of 13 was observed.
m
CO bands at 2070 and 2040 cmꢀ1 [35]. Also, the monocar-
bonyl dihydride species ½IrH2ðPPri3ÞðCOÞ ðNCCH3Þ2ꢁBF4,
displays a strong mCO band at 2015 cmꢀ1 [40].
The rhodium dihydrides 11, 12 and 14, generated in situ
in the appropriate deuterated solvent, reacted analogously
+
+
PBz
Ir
PBz
3
3
S
S
H
H
H
H
CO
CH Cl
2
2
Ir
CO
3
CO
S
PBz
18
PBz
3
8 or 9
A similar behavior was observed for the hydrogenation
of 3 in THF. Again, an equilibrium concentration (ca. 1:1)
Scheme 6.
+
PBz3
H
+
PBz3
PBz3
MeCN
MeCN
MeCN
COA
Rh
+ H2
Rh
H
3
+ H2
PBz3
11
S = THF or acetone
COA
+
PBz3
Rh
+
+
PBz3
PBz3
PBz3
PBz3
+ H2
- H2
O
O
O
S
H
H
- H2
Rh
Rh
+ H2
S
O
PBz3
15
S = acetone 12; THF 14
13
Scheme 5.

1044
V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
described in this paper highlight the versatility of the
+
+
PBz3
PBz3
Bz3P
OC
CO
PBz3
PBz3 ligand which combines the steric hindrance of triaryl-
phosphines with the basicity of trialkylphosphines, thus
providing a further tool to look for improved activity
and selectivity.
Rh
Rh
COD
CO
3
20
H2
H2
The reactivity of the rhodium and iridium PBz3 com-
plexes towards H2 or CO has been investigated and com-
pared with related complexes bearing either substituted
triphenylphosphines or PPr3i [35,40,45]. Although the reac-
tivity does not generally differ from that reported in the lit-
erature, our complexes are more air and moisture stable
likely due to the presence of PBz3 ligand. In a concomitant
paper, a study of the hydrogenation of imines catalyzed by
Rh and Ir complexes with PBz3, will be reported showing
that the latter is able to generate more efficient catalysts
than the ones known with PPh3 [29].
CH2Cl2
CO
COA
+
+
PBz3
PBz3
S
S
H
H
H
H
CO
Rh
PBz3
Rh
CO
PBz3
CO
S
S = acetone 11; acetonitrile 12; THF 14
COD = 1,5 - cyclooctadiene
COA = cyclooctane
Scheme 7.
4. Experimental
with CO yielding the dicarbonyl dihydride [Rh(H)2(CO)2-
(PBz3)2]+ (19), which was unstable and rapidly converted
to trans-[Rh(CO)2(PBz3)2]PF6 (20) (Scheme7).
All reactions and manipulations were routinely per-
formed under dry nitrogen or argon atmosphere using
standard Schlenk techniques. Unless otherwise stated, all
solvents were distilled just prior to use from appropriate
drying agents. Methanol was distilled from CaSO4, dichlo-
romethane and acetonitrile from P2O5, and tetrahydrofu-
ran (THF) from sodium/benzophenone. Diethylether and
petroleum ether were dried with sodium. Hydrogen was
purified passing it through two columns in series contain-
ing CuO/Al2O3 and CaSO4, respectively. Deuterated sol-
Due to its low solubility in dichloromethane, the latter
complex separated from the solution in almost quantitative
yield. Compound 20 was also independently prepared by
carbonylation of 3 in THF solution. The assignment of
the trans arrangement of the two carbonyl ligands in 20
is confirmed by the presence of a single strong mCO band
at 2022 cmꢀ1 in the solid-state IR spectrum, which slightly
moves to 2019 cmꢀ1 in DMSO solution. The 31P{1H}
˚
vents were dried over 4 A molecular sieves prior to use.
NMR displays a doublet at 48.6 ppm in DMSO-d6 (JRhP
75.1 Hz).
=
All other chemicals were commercial products and used
as received without further purification. Literature meth-
ods were employed for the synthesis of [RhCl(cod)]2 [46],
[IrCl(cod)]2 [47]. The solid complexes were collected on a
sintered glass-frit and washed with ethanol and light petro-
leum ether (b.p. 40–60 ꢁC) or pentane before being dried in
A similar Rh(I) complex with PPh3 has been synthesized
from cationic rhodium-nitrosyl species and shows similar IR
features [44]. Also, a tricarbonyl iridium species with P(p-
CH3C6H4)3 was reported, and the presence of three carbo-
nyls sitting in the equatorial plane of a trigonal-bipyramidal
1
a stream of nitrogen. H, and 13C{1H} NMR spectra were
polyhedron was confirmed by the presence of a unique mCO
-
recorded either on a Bruker ACP 200 (200.13 and
50.32 MHz), a Bruker AM 300 (300.13 and 75.47 MHz)
or a Bruker Avance DRX-500 (500.13 and 125.80 MHz)
spectrometers. Peak positions are relative to tetramethylsi-
lane and were calibrated against the residual solvent reso-
nance (1H) or the deuterated solvent multiplet (13C).
31P{1H} NMR spectra were recorded on the same instru-
ments operating at 81.01, 121.49, and 202.53 MHz, respec-
tively. Chemical shifts were measured relative to external
85% H3PO4, with downfield shifts considered positive. All
the NMR spectra were recorded at room temperature
(25 ꢁC) unless otherwise stated. The high-pressure NMR
(HP-NMR) spectra were recorded by using a standard
band (2010 cmꢀ1) [35]. A computational study carried on a
series of cis- and trans-[Rh(CO)2X2]+ complexes (X = PH3,
PF3, PCl3, PBr3, PI3 or PMe3) suggests that more the ligand
size and the donor properties of the phosphine increase,
more the trans-isomers become stable [45]. mCO frequencies
for these complexes were compared, showing single bands
for trans-compounds ranging from 2083 to 2040 cmꢀ1. Gen-
erally, the CO absorptions move to lower frequencies as the
ligand size increases [45]. These facts, altogether with our
experimental evidence, provide a further strong confirma-
tory evidence of the trans-geometry of 20.
1
3. Conclusions
10-mm probe tuned to 31P and H nuclei on a BRUKER
AC 200 spectrometer operating at 81 MHz. The HPNMR
experiments were performed in a 10 mm-OD sapphire tube
(Saphikon Inc., NH). 2D NMR spectra were recorded on a
Bruker Avance DRX-500, operating at 500.13, 202.46 and
125.77 MHz, respectively, for 1H, 31P and 13C. 2D 1H
DQF-COSY [48], and proton detected 1H–31P and
This paper reports the synthesis and reactivity of a fam-
ily of rhodium and iridium complexes with tribenzylphos-
phine. This ligand has been scarcely investigated in
organometallic chemistry and almost completely ignored
in homogeneous catalysis. The preparations and reactions

V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
1045
1H–13C correlations (HMQC [49] and HMBC [50]) using
nonspinning samples. 2D NMR spectra were recorded
using pulse sequences suitable for phase-sensitive represen-
tations using TPPI. CAUTION: All manipulations involving
high pressures are potentially hazardous. Safety precautions
must be taken at all stages of NMR studies involving high
pressure tubes. Infrared spectra were recorded either on a
Perkin–Elmer 1600 series or a Nicolet Magna IR 560 FT-
IR spectrometers, using samples mulled in Nujol between
KBr plates or in KBr disk. Elemental analyses (C, H, N)
were performed using a Carlo Erba model 1106 elemental
analyser by the Microanalytical Service of the Department
of Chemistry at the University of Florence.
(CH2 COD); d 32.9 (CH2 COD); d 68.8 (CH COD trans
to Cl, d, JCRh = 13.5 Hz); d 103.7 (CH COD trans to P,
dd, JCRh = 11.9 Hz, JCP = 4.7 Hz); d 126.7, d 129.0, d
130.6 (CH aromatic carbons); d 135.0 (C ipso). IR (KBr):
m(Rh–Cl) 478 cmꢀ1(m). Anal. Calc. for C29H33ClPRh: C,
63.22; H, 6.03. Found: C, 63.25; H, 5.95%.
2
4.3. IrCl(PBz3)(cod) (2)
[IrCl(cod)]2 (300 mg; 0.45 mmol) and PBz3 (300 mg;
0.99 mmol) were dissolved in dichloromethane (15 mL)
and stirred vigorously for 30 min. Ethanol (20 mL) was
added, and the solution was concentrated under vacuum
until a shiny yellow solid precipitated. Yield: 437 mg,
77%. 1H NMR (CD2Cl2, 300.13 MHz): d 1.62 (m,
2H, CH2 COD); d 1.84 (m, 2H, CH2 COD); d 2.08
(m, 2H, CH2 COD); d 2.22 (m, 2H, CH2 COD); d 2.86 (m,
2H, CH COD); d 3.22 (d, 6H, CH2 PBz3, JHP = 9.7 Hz);
d 5.11 (m, 2H, CH COD); d 7.25–7.60 (m, 15H, aromatic
protons). 31P{1H} NMR (CD2Cl2, 121.49 MHz): d 8.72
(s, 1P). 13C{1H} NMR (CD2Cl2, 75.47 MHz): d 27.83 (d,
CH2 PBz3, JCP = 25.4 Hz); d 29.3, d 33.5 (CH2 COD); d
52.0 (s, CH COD trans to Cl); d 91.7 (d, CH COD trans
to P, JCP = 14.0 Hz); d 126.6, d 128.2, d 130.8 (s, CH, aro-
4.1. Tribenzylphosphine (PBz3)
PBz3 was prepared using a modification of the reported
method [51]. The Grignard reagent, BzMgCl, was prepared
by slowly adding benzyl chloride (100.0 g, 0.89 mol), to a
cold suspension of magnesium turnings (22.0 g, 0.90 mol)
in dry diethylether (750 mL) under vigorous stirring. The
resulting mixture was slowly brought to the boiling temper-
ature and refluxed for 2 h. To the clear ethereal Grignard
solution, PCl3 (42 g, 0.31 mol) was dropped slowly, while
vigorously stirring, within 2 h. The mixture was left over-
night under a nitrogen atmosphere before 500 mL of aque-
ous saturated solution of NH4Cl (60 g) was added to the
cooled mixture, which caused the separation of two phases.
After separation of the organic layer, the aqueous phase
was washed two times with cold diethyl ether (100 mL
each) and discharged. The organic phase and the two
Et2O washings were combined and dried with NaSO4.
The filtered ethereal solution was concentrated to 250 mL
and left standing overnight to allow for the separation of
ivory colored crystals of the phosphine. The solid was col-
lected on a Buchner funnel by filtration in the air and dried
2
matic carbons); d 134.2 (C ipso, JCP = 4.5 Hz). IR (KBr):
m(Rh–Cl) 479 cmꢀ1(m). Anal. Calc. for C29H33ClIrP: C,
54.40; H, 5.19. Found: C, 54.56; H, 5.11%.
4.4. [Rh(PBz3)2(cod)]PF6 (3)
A solution of RhCl(PBz3)(cod) (1.00 g, 1.81 mmol) in
acetone (20 mL) was treated with AgOSO2CF3 (475 mg,
2.90 mmol), and stirred for 30 min at room temperature.
The AgCl that separated was filtered out, and one equiva-
lent of solid PBz3 (800 mg, 2.63 mmol) was added under
stirring to afford an orange solution. Addition of an excess
of NH4PF6 (700 mg, 4.20 mmol) dissolved in ethanol
(20 mL) and concentration under a brisk current of nitro-
gen precipitated a yellow solid. Yield: 1.56 g, 72%. 1H
NMR (CDCl3, 200.13 MHz): d 1.62 (m, 2H, CH2 COD);
d 1.84 (m, 2H, CH2 COD); d 2.08 (m, 2H, CH2 COD); d
2.22 (m, 2H, CH2 COD); d 2.86 (m, 2H, CH COD);
d 3.22 (d, 6H, CH2 PBz3); d 5.11 (m, 2H, CH COD); d
7.25-7.60 (m, 15H, CH aromatic protons). 31P{1H} NMR
(CDCl3, 81.015 MHz): d 2.75 (d, 2P, JRh–P = 143.5 Hz); d
ꢀ143.6 (sept, PF6, JP–F = 712.1 Hz). 13C{1H} NMR
(CDCl3, 75.47 MHz): d 31.1 (s, CH2 COD); d 33.1 (ps t,
CH2 PBz3,); d 99.0 (CH COD); d 128.5, d 129.9, d 130.7
(CH, aromatic carbons); d 133.3 (C ipso). IR (Nujol mull):
m(P–F) 840 cmꢀ1 (s). Anal. Calc. for C50H54F6P3Rh: C,
62.25; H, 5.64. Found: C, 62.07; H, 5.55%.
1
under vacuum. Yield: 55 g, 60%. H NMR (200.13 MHz;
CDCl3): d 2.78 (s, 6H, CH2), d 7.15–7.32 (m, 15H, aromat-
ics). 31P{1H} (81.01 MHz; CDCl3): d ꢀ11.3 (s, PBz3). Anal.
Calc. for C21H21P: C, 82.87; H, 6.95. Found: C, 82.89; H,
6.75%.
4.2. RhCl(PBz3)(cod) (1)
[RhCl(cod)]2 (500 mg; 1.01 mmol) and PBz3 (680 mg,
2.23 mmol) were dissolved in dichloromethane (15 mL)
and stirred vigorously for 30 min. Ethanol (20 mL) was
added, and the solution was concentrated under vacuum
until a shiny yellow solid precipitated. Yield: 1.00 g, 90%.
1H NMR (CD2Cl2, 300.13 MHz): d 1.85 (m, 2H, CH2
COD); d 2.00 (m, 2H, CH2 COD); d 2.18 (m, 2H, CH2
COD); d 2.35 (m, 2H, CH2 COD); d 3.02 (d, 6H, CH2
PBz3, JHP = 9.3 Hz); d 3.20 (m, 2H, CH COD); d 5.50
(br s, 2H, CH COD); d 7.20–7.80 (m, 15H, CH aromatic
protons). 31P{1H} NMR (CD2Cl2, 121.49 MHz): d 24.2
(d, 1P, JRh–P = 150.5 Hz). 13C{1H} NMR (CD2Cl2,
75.47 MHz): d 28.1 (CH2 PBz3, d, JCP = 19.2 Hz); d 28.5
4.5. [Ir(PBz3)2(cod)]PF6 (4)
A solution of IrCl(PBz3)(cod) (1.00 g, 1.56 mmol) in ace-
tone (40 mL) was treated with AgOSO2CF3(450 mg,
1.73 mmol), and stirred for 30 min. The AgCl that sepa-

1046
V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
rated was filtered out, and one equivalent of solid PBz3
(700 mg, 2.34 mmol) was added to afford a red solution.
Addition of an excess of NH4PF6 (500 mg, 3.13 mmol) dis-
solved in ethanol (20 mL) and concentration under a brisk
current of nitrogen precipitated a carmine red solid. Yield:
31P{1H} NMR (CD2Cl2, 121.49 MHz): d ꢀ3.05 (s, 1P);
ꢀ143.22 (sept, PF6, JP–F = 711.0 Hz). 13C{1H} NMR
(CD2Cl2, 75.47 MHz):
d
29.3 (d, CH2 PBz3,
JCP = 26.7 Hz); d 29.9, d 33.2 (CH2 COD); d 65.0 (CH
COD trans to py); d 93.8 (d, CH COD trans to P,
JCP = 12.3 Hz); d 127, d 128 (CH aromatic + para pyridine
carbons); d 129.5 (CH, aromatic carbons); d 130.4 (d, CH
1
1.52 g, 92%. H NMR (CDCl3, 200.13 MHz): d 1.85 (m,
8H, CH2 COD); d 3.37 (d, 12H, CH2 PBz3, JHP = 7.2 Hz);
d 4.31 (br s, 4H, CH COD); d 7.23–7.40 (m, 30H, CH aro-
matic protons). 31P{1H} NMR (CDCl3, 81.01 MHz): d
ꢀ6.40 (s, 2P); d ꢀ143.6 (sept, PF6). IR (Nujol mull): m(P–
F) 845 cmꢀ1 (s). Anal. Calc. for C50H54F6P3Ir: C, 56.97;
H, 5.16. Found: C, 57.10; H, 5.19%.
3
ortho aromatic carbons, JCP = 6.3 Hz); d 133.0 (d, C ipso,
2JCP = 4.6 Hz); d 138.7 (CH meta pyridine carbons); d
150.3 (CH ortho pyridine carbons). IR (KBr):
m(P–F) 842 cmꢀ1 (s). Anal. Calc. for C34H38NF6IrP2: C,
46.97; H, 4.83; N, 1.77. Found: C, 47.12; H, 4.67; N,
1.68%.
4.6. [Rh(py)(PBz3)(cod)]PF6 (5)
A solution of RhCl(PBz3)(cod) (500 mg, 0.910 mmol) in
methanol (20 mL) was stirred until the solid dissolved com-
pletely and it was then treated with an excess of pyridine
(0.6 mL, 7.58 mmol) in methanol (5 mL) for 60 min to
afford an orange solution. A solution of NH4PF6 in meth-
anol (5 mL) was added. Concentration under vacuum sep-
arated an orange solid which after filtration was washed
with water (5 mL) and methanol (5 mL) before being dried
under vacuum. Yield: 600 mg, 89% 1H NMR (CDCl3,
300.13 MHz): d 2.14 (m, 4H, CH2 COD); d 2.59 (m, 4H,
CH2 COD); d 2.72 (d, 6H, CH2 PBz3, JHP = 7.8 Hz); d
4.16 (br s, 2H, CH COD); d 4.67 (br s, 2H, CH COD);
4.8. [IrH(PBz3)(cod){g2-P,C-(C6H4CH2)PBz2}]PF6 (7)
4.8.1. cis-(P,P)-[IrH(PBz3)(cod){g2-P,C-(C6H4CH2)
PBz2}]PF6 (cis-7)
A solution of [Ir(PBz3)2(cod)]PF6 (500 mg, 0.475 mmol)
in chloroform (5 mL) was left under nitrogen for 3 days.
After this period, the white crystals that separated out were
filtered and washed with cold chloroform and pentane
before being dried in vacuum. Yield: 485 mg, 97%. 1H
NMR (acetone-d6, 500.13 MHz): d 4.93 (td, 1H, CH
3
3
COD, JHP1 = 3JHH = 9.2 Hz, JHH = 5.9 Hz);
d 4.81
(ddd, 1H, CH COD, 3JHP2 = 2.3 Hz, 3JHH = 8.5
3
d
7.10–8.00 (m, 20H, aromatic + pyridine protons).
Hz, JHH = 6.2 Hz);
d
4.40 (dd, 1H, CH2 PBz3,
2
31P{1H} NMR (CDCl3, 121.49 MHz): d 9.30 (d, 2P,
JRhP = 153.3 Hz); d ꢀ142 (sept, PF6, JP–F = 711.0 Hz).
13C{1H} NMR (CDCl3, 75.47 MHz): d 29.0 (d, CH2
PBz3); d 29.4, d 32.4 (CH2 COD); d 79.3 (d, CH COD trans
to py, JCRh = 12.2 Hz); d 104.6 (dd, CH COD trans to P,
JCP = 8.2 Hz, JCRh = 8.0 Hz); d 126.4, d 128 (CH aro-
matic + pyridine carbons); d 129.4 (CH, aromatic + para
pyridine carbons); d 130.14 (d, CH ortho aromatic carbons,
2JHP1 = 6.5 Hz, JHH = 14.5 Hz); d 4.03 (dd, 1H, CH2
PBz3, 2JHP1 = 8.9 Hz, JHH = 14.5 Hz); d 4.17 (m, 1H, CH
2
COD); d 4.01 (m, 1H, CH COD); d 3.41 (dd, 1H, CH2
2
2
PBz3, JHP2 = 9.1 Hz, JHH = 14.6 Hz); d 3.16 (dd, 1H,
2
2
CH2 PBz3, JHP2 = 8.6 Hz, JHH = 14.6 Hz); d 3.96 (dd,
1H, CH2 PBz3, JHP1 = 4.9 Hz, JHH = 14.6 Hz); d 3.95
(dd, 1H, CH2 PBz3, JHP1 = 3.0 Hz, JHH = 14.6 Hz); d
2.76 (m, 1H, CH2 COD); d 1.75 (m, 1H, CH2 COD);
d 1.80 (m, 1H, CH2 COD); d 1.57 (m, 1H, CH2 COD); d
2
2
2
2
2
3JCP = 6.2 Hz); d 133.2 (d, C ipso, JCP = 5.1 Hz); d 138.4
4
(CH meta pyridine carbons); d 151.3 (CH ortho pyridine
carbons). IR (Nujol mull): m(P–F) 847 cmꢀ1 (s). Anal. Calc.
for C34H38NF6P2Rh: C, 52.93; H, 5.44; N, 1.99. Found: C,
52.70; H, 5.33; N, 1.85%.
3.36 (t, 1H, CH2 COD, JHP1 = JHH = 8.6 Hz); d 2.96 (m,
1H, CH2 COD); d 3.13 (m, 1H, CH2 COD); d 2.72 (m,
1H, CH2 COD); d 3.73 (dd, 1H, CH2 PBz3, 2JHP1 = 6.6 Hz,
2JHH = 15.1 Hz); d 3.18 (m, 1H, CH2 PBz3); d ꢀ7.82 (ddd,
2
2
4
1H, hydride, JHP1 = 102.3 Hz, JHP2 = 17.2 Hz, JHH
=
4.7. [Ir(py)(PBz3)(cod)]PF6 (6)
6.3 Hz); d 7.20 (tq, 1H, CH aromatic, JHH = 7.2 Hz,
4JHP1 = JHH = 2.9 Hz); d 7.67 (m, 1H, CH aromatic); d
6.38 (m, 1H, CH aromatic); d 7.43 (m, 1H, CH aromatic).
31P{1H} NMR (acetone-d6, 202.46 MHz): d ꢀ2.86 (d, 1P,
A solution of IrCl(PBz3)(cod) (500 mg, 0.781 mmol) in
methanol (20 mL) was stirred until the solid dissolved com-
pletely and it was then treated with an excess of pyridine
(0.6 mL, 7.58 mmol) in methanol (5 mL) for 60 min to
afford an orange solution. A solution of NH4PF6 in meth-
anol (5 mL) was added. Concentration under vacuum sep-
arated an orange solid which after filtration was washed
with water (5 mL) and methanol (5 mL) before being dried
2
2JPP = 18.5 Hz); d ꢀ9.97 (d, 1P, JPP = 18.5 Hz). 13C{1H}
NMR (acetone-d6, 125.77 MHz): d 26.32 (CH2 COD); d
27.17 (CH2 COD); d 32.11 (d, CH2 PBz3, JCP1 = 20.9 Hz);
d 32.68 (d, CH2 PBz3, JCP2 = 27.5 Hz); d 35.39 (CH2
COD); d 36.70 (d, CH2 PBz3, JCP1 = 18.7 Hz); d 37.68
(CH2 COD); d 37.95 (d, CH2 PBz3, JCP1 = 35.1 Hz); d
1
2
under vacuum. Yield: 550 mg, 85%. H NMR (CD2Cl2,
81.24 (d, CH COD, JCP2 = 15.2 Hz); d 81.81 (CH COD);
300.13 MHz): d 2.12 (m, 4H, CH2 COD); d 2.52 (m, 4H,
CH2 COD); d 2.99 (d, 6H, CH2 PBz3, JHP = 8.9 Hz); d
4.13 (m, 2H, CH COD); d 4.25 (m, 2H, CH COD); d
7.14–7.71 (m, 20H, aromatic + pyridine protons).
d 83.55 (CH COD); d 98.22 (d, CH COD, 2JCP2 = 9.6 Hz);
d 128.88 (C ipso aromatic); d 130.43 (CH aromatic); d
130.59 (CH aromatic); d 131.18 (CH aromatic); d 146.87
2
(d, metalated aromatic C, JCP1 = 17.8 Hz). IR (Nujol

V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
1047
mull): m(Ir–H) 2100 cmꢀ1 (m). Anal. Calc. for C50H54F6P3Ir:
C, 56.97; H, 5.16. Found: C, 57.15; H, 5.12%.
4.11.1. Selected NMR data for 10
1H NMR (THF-d8, 300.13 MHz): d ꢀ23.5 (t, hydrides,
JHP = 15.5 Hz). 31P{1H} NMR (THF-d8, 121.49 MHz): d
9.83 (s).
4.8.2. trans-(P,P)-[IrH(PBz3)(cod){g2-P,C-(C6H4CH2)-
PBz2}]PF6 (trans-7)
4.12. In situ reactions of [Rh(PBz3)2(cod)]PF6 (3) with
H2
Compound trans-7, which forms together with cis-7,
could not be isolated (see text). It was characterized in
solution by NMR spectroscopy: 1H NMR (CDCl3,
200.13 MHz): d ꢀ13.38 (ps t, 1H, hydride, 2JHP = 19.8 Hz).
31P{1H} NMR (CDCl3, 81.014 MHz): d 27.81 (d, 1P,
2JPP = 238.0 Hz); d ꢀ27.61 (d, 1P).
Complex 3 (30 mg; 0.031 mmol) was dissolved in an
NMR tube, under an inert atmosphere, in the appropriate
solvent (acetone-d6, THF-d8 or CD3CN, 1 mL) and cooled
to 0 ꢁC. H2 was gently bubbled into the solution with a long
1
syringe needle for 5 min. H and 31P{1H} NMR spectra
4.9. [Ir(H)2(Me2CO)2(PBz3)2]PF6 (8)
were recorded and showed the formation of the bis-solvento
cis-dihydrides 11, 12, or 14, depending on the solvent used.
All our attempts to isolate 11, 12 or 14 by scaling up the
reactions were unsuccessful. In all cases, mixtures of prod-
ucts were obtained, but no hydride species were detected.
H2 was bubbled through an acetone (40 mL) solution of
[Ir(PBz3)2(cod)]PF6 (1.00 g, 0.950 mmol). After 15 min, the
solution became colorless. At this point the H2 flow was
replaced by nitrogen and the solution was concentrated to
15 mL. Addition of petroleum ether (15 mL), precipitated
1
4.12.1. Selected NMR data for
[Rh(H)2(CD3CN)2(PBz3)2]PF6 (11)
1H NMR (CD3CN, 200.13 MHz): d ꢀ18.21 (dt,
hydrides, JHP = 14.0 Hz; JRhH = 17.2 Hz). 31P{1H} NMR
(CD3CN, 81.01 MHz): d 33.85 (d, JRhP = 113.4 Hz).
a white-off solid. Yield: 920 mg; 91%. H NMR (CD2Cl2,
200.13 MHz): d ꢀ30.13 (t, 2H, hydrides, JHP = 15.3 Hz);
2.00 (s, 12H, CH3 acetone); d 3.20 (t, 12H, CH2 PBz3,
2JHP = 7.4 Hz); d 6.92 (br t, 12H, ortho aromatic protons);
d 7.24–7.32 (m, 18H, meta + para aromatic protons).
31P{1H} NMR (CD2Cl2, 81.015 MHz): d 14.58 (s, 2P); d
ꢀ143.8 (sept, PF6, JP–F = 713.0 Hz). IR (Nujol mull):
m(Ir–H) 2130 cmꢀ1 (s); m(C@O)acetone 1750 cmꢀ1 (s); m(P–
F) 840 cmꢀ1 (s). Anal. Calc. for IrC48H56O2P3F6: C, 54.15;
H, 5.30. Found: C, 54.51; H, 5.14%.
4.12.2. Selected NMR data for
[Rh(H)2(acetone)2(PBz3)2]PF6 (12)
1H NMR (acetone-d6, 200.13 MHz): d ꢀ22.38 (dt,
hydrides, JHP = 15.9 Hz; JRhH = 26.0 Hz). 31P{1H} NMR
(acetone-d6, 81.01 MHz): d 32.48 (d, JRhP = 122.1 Hz).
4.10. [Ir(H)2(MeCN)2(PBz3)2]PF6 (9)
4.12.3. Selected NMR data for
[Rh(H)2(THF)2(PBz3)2]PF6 (14)
Replacing acetone with acetonitrile in the above prepa-
ration gave 9 after identical work-up. Yield: 930 mg; 95%.
1H NMR (CD2Cl2, 300.13 MHz): d ꢀ21.45 (t, 2H,
hydrides, JHP = 16.2 Hz); 1.82 (s, 12H, CH3 acetonitrile);
1H NMR (THF-d8, 300.13 MHz):
d
ꢀ23.30 (dt,
hydrides, JHP = 15.9 Hz; JRhH = 25.8 Hz). 31P{1H} NMR
(THF-d8, 121.49 MHz): d 34.23 (d, JRhP = 122.7 Hz).
2
d 3.29 (t, 12H, CH2 PBz3, JHP = 3.3 Hz); d 6.92 (br t,
4.13. In situ reaction of [Rh(py)(PBz3)(cod)]PF6 (5) with
H2
12H, ortho aromatic protons); d 7.16–7.35 (m, 18H,
meta + para aromatic protons). 31P{1H} NMR (CD2Cl2,
121.5 MHz): d 1.18 (s, 2P); d ꢀ143.22 (sept, PF6,
JP–F = 711.0 Hz). IR (KBr): m(Ir–H) 2150 cmꢀ1 (s);
m(C„N)acetonitrile 2410 cmꢀ1 (s); m(P–F) 850 cmꢀ1 (s). Anal.
Calc. for IrC46H50N2P3F6: C, 53.64; H, 4.89; N, 2.72.
Found: C, 53.81; H, 4.72; N, 2.59%.
Complex 5 (30 mg; 0.045 mmol) was dissolved in THF-
d8 (1 mL) under an inert atmosphere in a 5 mm NMR tube
and cooled to 0 ꢁC, H2 was gently bubbled into the solution
1
for 5 min. H and 31P{1H} NMR spectra at room temper-
ature
showed
the
selective
formation
of
[Rh(H)2(THF)2(py)(PBz3)]+ (16). All our attempts to iso-
late 16 were unsuccessful.
4.11. In situ reaction of [Ir(PBz3)2(cod)]PF6 (4) with H2
in THF
4.13.1. Selected NMR data for 16
1H NMR (THF-d8, 300.13 MHz): d ꢀ22.62 (dd,
hydrides, JHP = 15.7 Hz; JRhH = 26.3 Hz). 31P{1H} NMR
(THF-d8, 121.49 MHz): d 39.23 (d, JRhP = 121.9 Hz).
Complex 4 (30 mg, 0.032 mmol) was dissolved in THF-
d8 (1 mL) and the solution was introduced into a 5 mm
NMR tube under an inert atmosphere. After the tube
was cooled to 0 ꢁC, H2 was gently bubbled into the solution
1
for 5 min. H and 31P{1H} NMR spectra showed the for-
4.14. In situ reaction of [Ir(py)(PBz3)(cod)]PF6 (6) with
H2
mation of [Ir(H)2(THF)2(PBz3)2]+ (10). All our attempts
to isolate 10 by scaling up the reaction were unsuccessful.
In all cases, products without hydride ligands were
detected.
Complex 6 (30 mg; 0.040 mmol) was dissolved in THF-
d8 (1 mL) under an inert atmosphere in a 5 mm NMR tube.

1048
V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
H2 was gently bubbled into the NMR solution for 5 min at
0 ꢁC. 1H and 31P{1H} NMR spectra showed the formation
of [Ir(H)2(THF)2(py)(PBz3)]+ (17). All our attempts to iso-
late 17 by scaling up the reaction were unsuccessful. In all
cases, mixtures of products were obtained, but no hydride
species were detected.
4.18. X-ray diffraction studies
Summary of crystal data and structure refinement
parameters for RhCl(cod)(PBz3) (1) and IrCl(cod)(PBz3)
(2) are reported in Table 1. Selected distances and angles
for both compounds are summarized in Table 2.
4.14.1. Selected NMR data for 17
4.18.1. RhCl(cod)(PBz3) (1)
1H NMR (THF-d8, 200.13 MHz): d ꢀ19.8 (d, hydrides,
JHP = 16.8 Hz). 31P{1H} NMR (THF-d8, 81.01 MHz): d
8.23 (s).
Single crystal structure determination of 1 was carried
out from data collected using graphite monochromated
Mo Ka radiation (k = 0.71073) on a Bruker SMART-
1K CCD area detector diffractometer equipped with a
Cryostream N2 flow cooling device [52]. Series of narrow
x-scans (0.3ꢁ) were performed at several /-settings in
such a way as to cover a sphere of data to a maximum
4.15. [Ir(H)2(CO)2(PBz3)2]PF6 (18)
A solution of 8 (250 mg, 0.24 mmol) in CH2Cl2 (40 mL)
was treated with 1 bar CO for 15 min. After concentration
to ca. 15 mL and addition of petroleum ether (15 mL), 15
˚
resolution of 0.75 A. Data collection was carried out at
260 K. Cell parameters were determined and refined from
the centroids of 956 reflections within the range
5.4ꢁ < 2h < 42.0ꢁ using the SMART software [53]. Raw
frame data were integrated using the SAINT program
[54]. The structure was solved using Direct Methods and
refined by full-matrix least-squares on F2 using SHELXTL
[55]. No absorption correction was applied to data from
(1). All non-hydrogen atoms were refined with anisotropic
displacement parameters (adps). Hydrogens atoms were
geometrically placed and allowed to ride on their parent
C atom with Uiso(H) = 1.2Ueq(C). Idealized C–H dis-
1
separated as a white solid. Yield: 200 mg, 85%. H NMR
(CD2Cl2, 200.13 MHz):
d
ꢀ11.50 (t, 2H, hydrides,
2
JHP = 15.3 Hz); d 3.45 (t, 12H, CH2 PBz3, JHP = 3.7 Hz);
7.24–7.32 (m, 30H, aromatic protons). 31P{1H} NMR
(CD2Cl2, 81.01 MHz): d 10.15 (s, 2P); d ꢀ143.7 (sept, PF6
JP–F = 711.0 Hz). IR (Nujol mull): m(Ir–H) 2120 cmꢀ1
;
m(C„O) 2002 cmꢀ1 (s); m(C„O) 2004 cmꢀ1 (s); m(P–F)
847 cmꢀ1 (s). Anal. Calc. for IrC44H44O2P3F6: C, 52.60;
H, 4.41. Found: C, 52.75; H, 4.35%.
˚
4.16. trans-[Rh(CO)2(PBz3)2]PF6 (20)
tances were fixed at 0.93 A (for C–H in phenyl groups),
˚
˚
0.97 A (for C–H in CH2 groups) and 0.98 A (C–H in
the 1,5-cyclooctadiene group). A phenyl ring from one
of the benzyl groups has been modelled as disordered
over two positions (occupancies of 0.63(4) and 0.37(4)),
with distances between carbon atoms restrained to
A solution of [Rh(cod)(PBz3)2]PF6 (250 mg; 0.26 mmol)
in THF (40 mL) was treated with carbon monoxide at
60 ꢁC for 15 min, and an off-white solid precipitated. This
solid was collected on a frit under nitrogen and washed with
cold THF (5 mL) and petroleum ether (5 mL) before being
dried under vacuum (yield: 200 mg; 85%). 1H NMR
(DMSO-d6, 25 ꢁC, 300.13 MHz): d 3.45 (broad s, 12H,
CH2 PBz3); 6.90–7.73 (m, 30H, aromatics PBz3). 31P{1H}
NMR (CD2Cl2, 25 ꢁC, 121.5 MHz): d 48.6 (d, 2P,
JRhP = 75.1 Hz); d ꢀ143.0 (septuplet, PFꢀ6 ). IR (KBr):
m(CO) = 2022 cmꢀ1 (s). IR (DMSO): m(CO) = 2019 cmꢀ1
(s). Anal. Calc. for RhC44H42O2P3F6: C, 57.91; H, 4.64.
Found: C, 57.25; H, 4.65%.
˚
˚
1.39 A with an s.u. of 0.005 A.
4.18.2. IrCl(cod)(PBz3) (2)
Crystallographic data for 2 were collected on a CAD4
diffractometer using graphite monochromated Mo Ka
˚
radiation (k = 0.7107 A) at room temperature. A set of
25 carefully centered reflections in the range 7ꢁ < h < 9ꢁ
was used for determining the lattice constants. As a general
procedure, the intensity of three standard reflections were
measured periodically every 200 reflections for orientation
and intensity control. This procedure revealed an 8% decay
of intensities during the data collection period, for which
the intensities were corrected. The data were corrected
for Lorentz and polarization effects. Atomic scattering fac-
tors were those tabulated by Cromer and Waber [56] with
anomalous dispersion corrections taken from Ref. [57]. An
empirical absorption correction was applied via w scan
with correction factors in the range 0.8401–0.8977. The
computational work was carried out using the program
SHELX-97 [58]. All non-hydrogen atoms were refined with
anisotropic displacement parameters (adps). Hydrogens
atoms were geometrically placed and refined following
the same procedure described above for the Rh complex
(1).
4.17. In situ reaction of [Rh(cod)(PBz3)2]PF6 (3) with H2
(HP-NMR tube test, PH ¼ 10 bar)
2
Complex 3 (30 mg, 0.031 mmol) was dissolved, under an
inert atmosphere, in acetone-d6 (2 mL) in a sapphire HP-
1
NMR 10 mm tube. H and 31P{1H} NMR spectra were
recorded. Then, the sample was removed from the spectrom-
eter and pressurized with H2 (10 bar). A new series of 1H and
31P{1H} NMR spectra were recorded which confirmed the
quantitative formation of 11. After removal of the sample
from the spectrometer, the HP-NMR tube was depressur-
ized, vented with N2 and checked again by 1H and 31P{1H}
NMR spectroscopy which established the complete loss of
H2 from 11 and the quantitative formation of 12.

V.R. Landaeta et al. / Journal of Organometallic Chemistry 691 (2006) 1039–1050
1049
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Calogero, Inorg. Chem. 37 (1998) 890.
5. Supplementary material
´
[9] A.G. Bell, W. Koz´minski, A. Linden, A.W. von Philipsborn,
Crystallographic data (excluding structure factors) for
the structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplemen-
tary publication nos. CCDC 272989 and 272990. Copies
of the data can be obtained, free of charge, on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44 1223 336 033 or e-mail: deposit@ccdc.cam.ac.uk).
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Acknowledgements
The authors thank FONACIT (Venezuela) for financial
support to V.L. (Doctoral Fellowship and Project S3),
FONACIT and CNR (Italy) for an International Cooper-
ation Grant and the European Community through the
MCRTN program AQUACHEM (Contract MRTN-CT-
2003-503864) for promoting this scientific activity. Thanks
are also expressed to ‘‘FIRENZE HYDROLAB’’, a project spon-
sored by ECRF. We also thank Mr. D. Masi for collecting
the X-ray diffraction data of 2 and Dr. P. Barbaro for run-
ning some NMR spectra.
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