3,5-Bis(diphenylphosphinoethyl)pyrazolate ligand (PNNPC2) and its dirhodium complexes: Comparison with related quadridentate dinucleating diphenylphosphinomethyl (PNNPPy) and phthalazine derivatives (PNNPPh)

Article abstract of DOI:10.1016/j.ica.2011.02.040

Dirhodium carbonyl complex with the 3,5-bis(diphenylphosphinoethyl) pyrazolato ligand (PNNP^C2), [(μ-κ²: κ²-PNNP^C2)Rh₂(CO)₃]BF ₄, is prepared and its reactivity is studied as comp

Full text of DOI:10.1016/j.ica.2011.02.040

Inorganica Chimica Acta 374 (2011) 489–498
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Inorganica Chimica Acta
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3,5-Bis(diphenylphosphinoethyl)pyrazolate ligand (PNNPC2) and its dirhodium
complexes: Comparison with related quadridentate dinucleating
diphenylphosphinomethyl (PNNPPy) and phthalazine derivatives (PNNPPh)
⇑
Akiko Gondoh, Takashi Koike, Munetaka Akita
Chemical Resources Laboratory, Tokyo Institute of Technology, R1-27, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
a r t i c l e i n f o
a b s t r a c t
Dirhodium carbonyl complex with the 3,5-bis(diphenylphosphinoethyl)pyrazolato ligand (PNNPC2),
Article history:
Available online 27 February 2011
[(
reported 3,5-bis(diphenylphosphinomethyl)pyrazolate (PNNP), [(
2-PNNP){Rh(CO)2}2]BF4, and 1,4-
bis(diphenylphosphinomethyl)phthalazine (PNNPPh j2 2-PNNPPh){Rh(CO)2}2](BF4)2.
derivatives, [(l- :j
l- :j
j2 2-PNNPC2)Rh2(CO)3]BF4, is prepared and its reactivity is studied as compared with the previously
l
-
j2
:j
Dedicated to Professor Wolfgang Keim for
his invaluable contribution to
organometallic chemistry
)
The three quadridentate ligands are different in the size of the central ring and the charge; six-membered
ring/neutral (PNNPC2) vs. five-membered ring/mono-negative (PNNP) vs. six-membered ring/neutral
(PNNPPh). The number of the carbonyl ligands (n) in the dirhodium carbonyl complexes, [(
l-
Keywords:
Rhodium
Quadridentate ligand
Carbonyl complex
Acetylide complex
PNNP)Rh2(CO)n](BF4)x, is dependent on the dinucleating ligand: n = 2 (PNNPPh), 3 (PNNPC2) and 4
(PNNPPy). The three dirhodium carbonyl complexes serve as 4e-acceptors, and their reactivities turn
out to be very similar as can be seen from formation of the analogous, unique tetranuclear
([( -PNNP)2{Rh(CO)}4( 4–C„C–R)](BF4)x) and 4-dicarbide complexes ([( -PNNP)2{Rh(CO)}4(l4
C2)](BF4)x).
l4-acetylide
l
l
l
l
–
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
dirhodium-cod complex E affords the tetracarbonyl complex C
(from A) and the dicarbonyl species F (from B). The two carbonyl
species serve as an equivalent to the putative 4e-acceptor D; the
tetracarbonyl species C loses the two inner carbonyl ligands to
form D and the dicarbonyl species F with a formal Rh@Rh bond
is an alternative canonical form of D. The dicarbonyl species F with
the PNNPPh ligand (B) undergoes dimerization to form the tetrahe-
dral tetrarhodium complex G with the intraunit Rh–Rh bonds in
addition to the interunit Rh–Rh bonds. The coordinatively unsatu-
rated species D serves as a 4e-acceptor. 1-Alkynes are incorpo-
rated, via deprotonation, into the dinuclear pocket as the
bridging acetylide ligand (a 4e-donor) to form the dinuclear
Cooperative action of the plural metal centers in polynuclear
species should lead to unique chemical behavior not observed for
mononuclear species [1–9]. Our attention has been focused on
reactivity of dinuclear complexes supported by PNNP-type quad-
ridentate ligands. We first examined the dirhodium carbonyl com-
plex with the 3,5-bis(diphenylphosphinomethyl)pyrazolato ligand
(PNNPPy; A) (Scheme 1) [10]. It has been revealed that, in the case
of the corresponding dirhodium carbonyl complex C, the inner CO
ligands are so labile owing to the influence of the P-donors trans to
CO and the steric reason that the dicarbonyl species D with a
cis-divacant site resulting from decarbonylation of C serves as an
efficient 4e-acceptor to form the adduct E [11]. Later on we
reported the complexes with the neutral 1,4-bis(diphenylphosphi-
nomethyl)phthalazine ligand (PNNPPh; B) [12], which were studied
to compare the characteristic features, i.e. the metal–metal separa-
tion and the charge. The shortened metal–metal separation (l3 < l2)
frequently leads to intraunit metal–metal bond formation (see
below), which has never been observed for the PNNPPy system A.
l– :g
g1 2-acetylide complexes H, which show fluxional behavior
as usually observed for this type of dinuclear species. The dinuclear
adduct H further reacts with another coordinatively unsaturated
species D to give the tetranuclear
l4-acetylide complex I, which
shows dynamic behavior via reversible metal–metal bond scission
and recombination processes and, in the case of the parent ethynyl
complex (R@H), is converted to the
l4-dicarbide complex J upon
deprotonation. In contrast to the formation of the bridging acety-
lide complexes commonly observed for the A and B systems
including the tetranuclear adducts I with the unique structural
features, reaction with internal alkyne depends on the ligand.
Representative reaction behavior of the two
systems is summarized in Scheme 2 [11,12]. Carbonylation of the
(l-PNNP)Rh2
Reaction with the PNNPPy system (A) gives the simply
l– : -
g2 g2
coordinated adduct K, whereas that of the PNNPPh system (B) re-
sults in oxidative addition to give the adduct L, in which the two
⇑
Corresponding author.
E-mail address: makita@res.titech.ac.jp (M. Akita).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.040

490
A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
alkyne molecules span the two metal centers to form the 1,3-dir-
hodacyclohexadiene skeleton. Dependence of the reaction path-
way on the ligand is also observed for reaction with hydrosilane.
Reaction with the PNNPPy species (A) affords the tetrarhodium
4-hydride complex M [11a,b], whereas that of the PNNPPh species
(B) affords the tetrarhodium product G without the hydride ligand.
l
l1
l2
l3
M
M
M
M
M
M
PPh2
Ph2P
N
N
N
N
n
Ph2P
N
N
PPh2
PPh2
Ph2P
PNNPPh
(B)
PNNPC2 (1)
PNNPPy (A)
ligand
PNNPC2
PNNP
(A)
5
PNNPPh
(B)
5
(1)
6
l2 > l1, l3
n
charge
-1
-1
0
m+
m+
m+
Do
(4e-donor)
Do
O
O
O
O
C
O
C
O O
O
C
C
C
C
C
C
- 2CO
Rh
Rh
Rh
Rh
Rh
Rh
D
E
C
(
: vacant site)
Scheme 1.
(cod)
Rh
(cod)
Rh
Charges of the complexes
are omitted for clarity.
E
PNNPPy (A)
PNNPPh (B)
CO
O
O O
O
"
"
O
O
C
O
C
C
C
C
(OC)Rh
C
Rh(CO)
O
C
Rh
C
- 2CO
x 2
Rh
Rh
G
Rh
Rh
Rh
(B)
(OC)Rh
Rh(CO)
C
F
"D"
(
: vacant site)
HSiR3
A
B
R-C≡C-Li (A) R-C≡C-H / H2O (B)
R-C≡C-R
R
(CO)
(CO)
Rh
Rh
C
R
R
R
O
O
R
R
C
C
Rh
C
H
R
C
C
Rh
O
O
Rh
H
C
C
Rh
OC
Rh
OH2
CO
(CO)
Rh
(CO)
Rh
Rh
H2O
M
"D"
K (from A)
L (from B)
R
C
(CO)
Rh
(CO)
Rh
(CO)
Rh
(CO)
Rh
C
[R= H]
base (- H+)
C
C
Rh
Rh
Rh
(CO)
Rh
J
(CO) (CO)
I
(CO)
Scheme 2.

A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
491
Me3SiO
OSiMe3
OMe
O
N
NH
COOMe
(83 %)
MeOOC
+
MeOOC
Cl
1) LiAlH4 2) H3O+
H2N-NH2·H2O
Me3SiOTf
O
N
NH
O
MeOH
(reflux)
OH
HO
Cl
MeOOC
COOMe
(96 %)
SOCl2
PPh2
Ph2P
Cl
N
NH
LiPPh2
HN NH
Cl
(69 %)
1-H (67 %)
Scheme 3.
Although the appearance of the products look dissimilar, the for-
mation of the two products has been interpreted in terms of the
Table 1
Structural parameters for the dirhodium-cod complexes
2
and [(l-
PNNPPh)Rh2(cod)2](BF4)2 E(B).
M-like intermediates [(l-PNNP)Rh4(CO)4(l
x-H)]n+ and has been as-
2a
E(B)b
cribed to the different charge (n) of them. The charges of the M-like
intermediates are +1 (A) and +2 (B), respectively. The more Lewis
acidic dicationic intermediate with the PNNPPh ligands should
undergo deprotonation to form the less positively charged mono-
Molecule 1
Molecule 2
Bond lengths (Å)
Rh1ꢁ ꢁ ꢁRh2
Rh1–N1
Rh1–P1
Rh2–N2
4.1049(8)
2.091(6)
2.320(3)
2.096(7)
2.298(2)
2.139–
Rh3ꢁ ꢁ ꢁRh4
Rh3–N3
Rh3–P3
Rh4–N4
Rh4–P4
Rh3–cod
4.1549(9)
2.094(6)
2.298(3)
2.087(6)
2.298(3)
2.134–
3.949(2)
2.199(2)
2.253(2)
2.110(2)
2.257(1)
2.139–
cationic species G ([(l
-PNNPPh)Rh4(CO)4]+). Thus, while many reac-
tion aspects of the two PNNP systems are similar, the different
reactivity has been ascribed to the ring size as well as the charge
of the intermediates.
Rh2–P2
Rh1–cod
In order to further examine the ring size and charge effects of
the quadridentate ligands we have designed the diphenylphosphi-
noethyl analog of A (PNNPC2; 1) having (1) the six-membered
metallacyclic moieties in place of the five-membered metallacyclic
moieties in the PNNPPy system and (2) ꢀ1 charge similar to the
2.206(10)
2.149–
2.244(9)
2.235(12)
2.150–
2.229(11)
2.279(6)
2.146–
2.236(6)
Rh2–cod
Rh4–cod
Bond angles and torsion angles (°)
N2–N1–Rh1
N1–N2–Rh2
N1–Rh1–P1
N2–Rh2–P2
126.8(5)
125.5(5)
86.2(2)
N4–N3–Rh3
N3–N4–Rh4
N3–Rh3–P3
N4–Rh4–P4
124.3(5)
123.8(5)
87.1(2)
87.2(3)
119.8(3)
121.1(3)
79.1(1)
79.2(1)
53.3
88.43(18)
Rh1–N1–N2– 47.4
Rh2
Rh3–N3–N4– 63.7
Rh4
+
BF4
(cod)
Rh
(cod)
Rh
-
a
A unit cell of 2 contains two independent molecules with essentially the same
geometry.
PPh2
[Rh(cod)2]BF4
NEt3
Ph2P
b
1-H
N
N
Relevant structural parameters. Ref. [12].
2 (77 %)
Scheme 4.
PNNPPy system (Scheme 1). Herein we disclose (1) synthesis of
the PNNPC2 ligand and its rhodium complexes and (2) reactions
of the resultant dirhodium carbonyl species toward alkynes and
HSiEt3 furnishing unique adducts.
2. Results and discussion
2.1. Ligand synthesis
P1
Rh2
N2
Rh1
N1
The PNNPC2 ligand precursor 1-H was prepared following the
synthetic route analogous to that of A (Scheme 3), which includes
pyrazole ring construction [13] via condensation of 1,3-diketone
with hydrazine. The 1,3-diketone precursor for 1, dimethyl dioxo-
pimelate [14], was prepared by acylation of 1-methoxy-1,3-
bis(trimethylsiloxy)butadiene [15] with methyl 3-chloro-3-oxo-
propionate catalyzed by trimethylsilyl triflate as reported by Chan
[16]. The diketone was readily converted to 3,5-di(methoxycar-
bonylmethyl)pyrazole upon treatment with hydrazine hydrate.
P2
C2
Fig. 1. An ORTEP view of the cationic part of 2 drawn with thermal ellipsoids at the
30% probability level. Only one of the two independent molecules with essentially
the same coordination geometry is shown.

492
A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
O
C
+
+
O
O O
O
O
O
C
C
C
C
C
C
CO
CO
2
Rh
Rh
Rh
Rh
THF
PPh2
BF4
PPh2
BF4
Ph2P
Ph2P
N
N
N
N
-
-
3 (99 %)
acetone reflux, 5 h
4
2+
(OC)Rh
Rh(CO)
Rh(CO)
-
= PNNPC2
)
(BF4 )2
(
(OC)Rh
5 (67 %)
Scheme 5.
2.2. Preparation of cod complex 2
Reaction of the obtained PNNPC2 ligand precursor 1-H with the
observed
labile cod complex of rhodium, [Rh(cod)2]BF4, in CH2Cl2 readily
afforded the cationic 1: 2 adduct 2, [(
l- :j :
j2 2-PNNPC2){Rh(g2
g
2-cod)}2]BF4, as yellow crystals (Scheme 4). The composition
and symmetrical structure of the products are confirmed by the
single sets of NMR signals for the CH2CH2P, and cod parts, and
P-coordination is verified by the doublet 31P NMR signal (dP 23.5
(d, JP–Rh = 150.4 Hz)) resulting from coupling with a Rh nucleus.
The 1JRh–P value for 2 is comparable to those of the PNNPPh complex
(E(B); dP 28.0 (d, JP–Rh = 148.4 Hz)) and the PNNPPy complex (E(A);
dP 41.6 (d, JP–Rh = 154.5 Hz)1).
1JRh-Rh'= 11.5 Hz
1JRh-P= 75.7 Hz
2JRh-P'= 1.5 Hz
simulated
The cod complex 2 is also characterized by X-ray crystallogra-
phy (Fig. 1 and Table 1). A unit cell contains two independent
molecules with essentially the same geometry. The structural char-
acterization reveals (1) square-planar geometry of the metal cen-
18.0
17.0
δP / ppm
16.0
ters coordinated by the bridging
l- :j
j2 2-PNNPC2 ligand and the
Fig. 2. Observed and simulated 31P NMR spectra for 3 (observed at 122 MHz in
acetone-d6).
g2
:g
2-cod ligand, (2) a twisted C2-symmetry-like structure with
respect to the axis passing through the C2 atom and the midpoint
of the N1–N2 bond, which is caused by steric repulsion between
the bulky Rh(cod) fragments as is indicated by the large <Rh1–
N1–N2–Rh2 dihedral angles (47.4(9)° and 63.7(8)°), (3) Rhꢁ ꢁ ꢁRh
separations (4.1049(8) Å and 4.1549(9) Å) being substantially
longer than the sum of covalent radius (2.68 Å), and (4) the pseu-
do-chair conformation of the six-membered chelate rings. Compar-
ison with the PNNPPh derivative E(B) (Table 1) reveals the
following features: (1) the bond lengths are comparable, (2) the
N–Rh–P bond angles of 2 closer to the right angle and larger than
that of E(B) by ca. 10° indicate lesser distortion from ideal square-
planar coordination geometry, and (3) the Rhꢁ ꢁ ꢁRh separation and
the Rh–N–N–Rh dihedral angle for 2 are slightly larger than those
of E(B). Although incorporation of the two six-membered chelate
rings in 2 (vs. one six-membered ring in E(B)) may cause shorten-
ing of the Rhꢁ ꢁ ꢁRh separation, this is not the case (feature 3). The
elongation of the Rhꢁ ꢁ ꢁRh separation of 2 may be interpreted in
terms of the more severe steric repulsion between the bulky
Rh(cod) fragments in 2, which are brought closer by the introduc-
tion of the two six-membered metallacyclic ring structures.
O1
C1
O2
C2
P1
Rh1
C3
Rh2
N2
P2
N1
O3
C4
C6
Fig. 3. An ORTEP view of the cationic part of 3 drawn with thermal ellipsoids at the
30% probability level.
Subsequent reduction with LiAlH4, chlorination with thionyl chlo-
ride and nucleophilic substitution with LiPPh2 gave 1-H as color-
less solid. Ligand precursor 1-H is readily characterized on the
basis of its spectroscopic data (dP ꢀ15.3; for other data, see exper-
imental part), which supports the symmetrical structure.
1
The abbreviation X(Y) stands for the X-type complex with the Y ligand.

A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
493
2.3. Carbonylation of cod complex 2: formation of tricarbonyl species 3
and its interconversion with carbonyl species with a more and lesser
number of CO ligands
[(
l
-
j2
:
j
2-PNNPC2)Rh2(CO)2(
l
-CO)]BF4. The presence of a Rh–Rh
1
bond is also supported by the JRh–Rh coupling, which must be ta-
ken into account for successful analysis of the multiplet 31P NMR
1
signals (Fig. 2). In the previous paper [12] we reported that JRh–
Carbonylation of 2 in CH2Cl2 at room temperature gave the or-
ange product 3 in a quantitative yield. (Scheme 5). Single sets of
NMR signals for the PNNPC2 part indicating a symmetrical struc-
coupling is a diagnostic for a Rh–Rh bonding interaction.
Rh
Molecular structure of 3 determined by X-ray crystallography
(Fig. 3 and Table 2) is consistent with the structure proposed on
the basis of the spectroscopic data. The Rh2N2P2 moiety is virtually
planar as is evident from the very small values of the relevant
ture and the IR band for a bridging CO ligand (1897 cmꢀ1 g1
; m( -
CO) 2052, 1986 cmꢀ1) lead to formulation of the product 3 as
Table 2
Selected structural parameters for 3.a
Bond lengths (Å)
Bond angles (°)
Rh1–Rh2
Rh1–P1
Rh1–N1
Rh1–C1
Rh1–C3
Rh2–P2
Rh2–N2
Rh2–C2
Rh2–C3
P1–C8
2.7091(6)
2.3135(16)
2.029(4)
1.859(6)
2.029(5)
2.3007(13)
2.033(5)
1.879(6)
2.016(5)
1.813(6)
1.151(7)
1.133(8)
1.146(6)
Rh2–Rh1–P1
Rh2–Rh1–N1
Rh2–Rh1–C1
Rh2–Rh1–C3
P1–Rh1–N1
P1–Rh1–C1
P1–Rh1–C3
N1–Rh1–C1
N1–Rh1–C3
C1–Rh1–C3
Rh1–Rh2–P2
Rh1–Rh2–N2
Rh1–Rh2–C2
157.13(4)
70.84(13)
105.5(2)
47.75(14)
88.73(13)
93.8(2)
144.95(16)
173.6(2)
88.36(18)
92.9(3)
Rh1–Rh2–C3
P2–Rh2–N2
P2–Rh2–C2
P2–Rh2–C3
N2–Rh2–C2
N2–Rh2–C3
C2–Rh2–C3
N–1–N2–C6
Rh1–C1–O1
Rh2–C2–O2
Rh1–C3–Rh2
Rh1–C3–O3
Rh2–C3–O3
48.15(15)
87.69(13)
93.32(18)
141.06(14)
176.31(19)
90.31(19)
91.1(3)
108.8(5)
179.3(6)
179.4(5)
84.10(18)
137.1(5)
O1–C1
O2–C2
O3–C3
157.36(4)
70.42(12)
108.18(18)
138.2(5)
a
Dihedral angles: hRh1–N1–N2–Rh2 = 6.2°. hC4–N1–Rh1–P1 = 8.0°, hC6–N2–Rh2–P2 = 2.4°.
(a) 3-13CO
31P
13C (CO)
(c) 3
δP 16.7 (d)
δC 190.5 (dm)
(b) 3-13CO / 13CO (3 atm)
(formation of 4-13CO)
(d) 3 / CO (3 atm)
(formation of 4)
δC 188.0 (dd)
δP 26.2 (d)
28 26 24 22 20 18 16
190
188
δC / ppm
δP / ppm
η1-CO
IR (νCO)
μ-CO
(e) 3
(f) 3 / CO (1 atm)
(3 + 4)
4
4
2100
2000
1900
1800
wavenumber / cm-1
Fig. 4. Spectral changes of 3 observed under CO atmosphere (NMR and IR spectra were recorded in acetone-d6 and THF, respectively. 31P and 13C NMR spectra were observed
at 122 MHz and 75 MHz, respectively): (a) A 13C NMR spectrum of 13CO-enriched 3 (3-13CO). (b) A 13C NMR spectrum of 3-13CO observed under 13CO (3 atm). (c) A 31P NMR
spectrum of 3. (d) A 31P NMR spectrum of 3 observed under CO (3 atm). (e) An IR spectrum of 3. (f) An IR spectrum of 3 observed under CO (1 atm).

494
A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
R
+
C
O
C
O
O
O
O
C
Li-C≡C-R
C
C
C
C
Rh
Rh
Rh
Rh
THF
-78°C → r. t.
6 : R= p-tol (6a: 64 %)
SiMe3 (6b: 67 %)
H (6c: 63 %)
BF4
3
HSiEt3
H-C≡C-R
Bu4N·F
3
R
C
in refluxing
acetone
+
(CO)
Rh
(CO)
Rh
(CO)
Rh
+
(CO)
Rh
(CO)
Rh
NEt3
(CO)
Rh
C
C
C
[R= H]
H
Rh
Rh
Rh
BF4
Rh
(CO)
BF4
Rh
Rh
(CO)
BF4
(CO) (CO)
(CO)
(CO)
9 (76 %)
8 (65 %)
7 : R= p-tol (7a: 72 % from 3)
SiMe3 (7b: 69 % from 6b)
H (7c: 70 % from 6c)
Scheme 6.
dihedral angles shown in Table 2. The terminal and bridging CO li-
gands are located virtually in-plane and perpendicular with respect
to the Rh2N2P2 coordination plane, respectively, and the core struc-
ture turns out to be isostructural with that of the Ir-PNNPPh deriv-
ative, [
[12].
A
13C NMR spectrum of 3-13CO observed under 13CO atmo-
sphere (3 atm) (Fig. 4b) showed formation of a new species (dC
188.0 (dd, 1JRh–C = 62.3 Hz, 2JP–C = 14.2 Hz)) assignable to the tetra-
carbonyl species 4 (Scheme 5). 31P NMR measurement of 3 under
CO atmosphere (3 atm) also revealed complete conversion to a
new species (dP 25.0 (1JRh–P = 126.0 Hz)) (Fig. 4c and d). The lack
l l-CO)](BF4)2, reported by us previously
-PNNPPh]Ir2(CO)2(
1
It is notable that the number of the carbonyl ligands (n) of the
dirhodium carbonyl species of the three PNNP systems, [(
of a JRh–Rh coupling suggests disruption of the Rh–Rh bond in 3
l
-
[12]. IR measurement of 3 under CO atmosphere (1 atm) further
confirmed formation of a new species showing CO vibrations at
2081 and 2021 cmꢀ1 (Fig. 4e and f). (Because the IR measurement
was carried out under 1 atm, conversion to the new species was
incomplete.) These spectroscopic behavior is consistent with inter-
conversion between the metal–metal bonded tricarbonyl species 3
and the non-metal–metal bonded tetracarbonyl species 4 (Scheme
5), and the tetracarbonyl species 4 is stable only under CO
pressure.
PNNP)Rh2(CO)n](BF4)x, in other words, the structures of the car-
bonyl species, are dependent on the quadridentate ligand: n = 2
(PNNPPh: F), 3 (PNNPC2: 3), 4 (PNNPPy: C(A)). The results could be
interpreted in terms of the metal–metal distance as well as the
charge. For the PNNPPy complex C(A), the two metal centers are
too much separated to interact with each other, whereas, for the
PNNPPh complex F, the metal–metal distance is short enough for
bond formation but the metal centers can carry a lesser number
of CO ligands because of the weaker back-donation from the more
positively charged metal centers. In the case of the PNNPC2 com-
plex 3, the shorter metal–metal separation and the efficient
back-donation from the less positively charged metal centers
should cause formation of the metal–metal bonded species with
a bridging CO ligand. The tricarbonyl species 3 is a 32 valence elec-
tron species, which is electron-precise as a dinuclear species with a
metal–metal single bond.
On the other hand, refluxing an acetone solution of 3 furnished
the dark red product 5 (Scheme 5). Although crystallographic data
is not available, the spectroscopic data for 5 comparable to those of
G suggest formation of an analogous symmetrical tetrarhodium
species of the formula of [(PNNPC2)2Rh2(CO)4]BF4 as supported by
the ESI-MS data and the single CO vibration. The metal–metal bond
1
formation is supported by the JRh–Rh coupling taken into account
on simulation of the 31P NMR signal. The tetrarhodium species 5
should be formed by dimerization of the dicarbonyl species D(1)
resulting from thermal decarbonylation of 3.
The flexibility of the number of the CO ligand in the PNNP–Rh2
system prompted us to examine interconversion of 3 with species
with a more or lesser number of the CO ligands via carbonylation
or decarbonylation, respectively. First of all, occurrence of inter-
and intra-molecular exchange reactions of the CO ligands is veri-
fied by the 13C NMR experiments: (1) intermolecular process: Pres-
2.4. Reaction of CO complex 3 with lithium acetylide, 1-alkyne and
HSiEt3
3
with 13CO (3 atm) followed by 13C NMR
In order to compare the reactivity of the PNNPC2 complex 3 it
was subjected to reaction with lithium acetylide, 1-alkyne, and
HSiEt3, the reactivity of which toward the PNNPPy and PNNPPh
complexes was already studied (Scheme 2). The reaction products
were characterized by comparison of their spectroscopic features
with those of the PNNPPy derivatives.
urrization of
measurement under N2 (1 atm) revealed 13C-enrichment of the
CO signals of 3 indicating incorporation of external 13CO molecules
(Fig. 4a). (2) intramolecular process: A 13CO-enriched sample
(3-13CO) showed a single dC(CO) signal (dC 190.5 (dm, JRh–C
=
1
63.2 Hz))2 indicative of g1
–l site exchange processes of the CO li-
gands occurring at a rate faster than the NMR timescale (Fig. 4a).
2.4.1. With lithium acetylide and 1-alkyne
The reactivity of the PNNPC2 complex 3 (Scheme 6) turned out
to be essentially the same as that of the PNNPPy complex D(A)
(Scheme 2). Reaction with lithium acetylide gave the dinuclear
2
The multiplet signals should result from coupling with the
g l-
1- and 13CO
ligands.

A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
495
complex 7, which was also obtained by direct treatment of 3 with
1-alkyne. Refluxing in acetone was needed for the formation of 7,
while the reaction of the PNNPPy system proceeded at room tem-
perature. The more harsh conditions may be required for removal
of the bridging ligand. Deprotonation of the C„C–H complex 7c
6a
6b
C5
O1
C3
Rh1
C2
N2
O2
C1
gave the
l
4-dicarbide complex 8 (Scheme 6) in a manner similar
C4
Rh2
P2
to the PNNPPy system (J; Scheme 2). The dinuclear
l-acetylide
complexes 6 were characterized by spectroscopic and crystallo-
graphic methods, while the tetranuclear species 7 and 8 were char-
acterized spectroscopically, in particular, on the basis of their NMR
features (1:2 adducts) and ESI-MS data, as also compared with the
corresponding PNNPPy derivatives (see experimental section).
Complexes 6–8 showed dynamic behavior as observed for the
PNNPPy and PPNPPh complexes H–J (Scheme 2).
P1
N1
The dinuclear
l-acetylide complexes 6a and 6b are character-
ized by X-ray crystallography (Fig. 5 and Table 3). When the two
PNNPC2-acetylide complexes 6a and 6b with essencially the same
core geometry are compared, it is revealed that (1) the Rhꢁ ꢁ ꢁRh
separations are between those for the metal–metal bonded species
3 and the non-metal–metal bonded species 2 and (2) the steric
repulsion between the Rh fragments is released significantly when
compared with 2 as is evident from the Rh–N–N–Rh torsion angles.
For comparison of the coordination properties provided by the
three PNNP ligands selected structural parameters for the p-tolyle-
thynyl complexes with the PNNPC2 (6a), PNNPPy (H(A)) and PNNPPh
ligands (H(B)) are listed in Table 3. Incorporation of the six-mem-
bered ring structure(s) into the central tricyclic chelate-heterocy-
cle-chelate moiety in 6a and H(B) causes shortening of the
Rhꢁ ꢁ ꢁRh distance when compared to the PNNPPy complex H(A)
but the effect is saturated as can be seen from the distances for
6a and H(B). The shortening brings about the dissymmetric
Si1
O1
C3
O2
C4
Rh2
C2
C1
Rh1
N2
P2
N1
(P1)
Fig. 5. ORTEP views of 6a and 6b drawn with thermal ellipsoids at the 30%
probability level.
l– :g
g1 2-acetylide complex 6. Subsequent treatment of the
resultant complex 6 with 3 afforded the tetranuclear l4-acetylide
Table 3
Comparison of structural parameters for the dirhodium
l-acetylide complexes, [(l-L)Rh2(CO)2(l
–C„C–R)](BF4)n (R/L = p-tol/PNNPC2 (6a), SiMe3/
PNNPC2 (H(A)), p-tol/PNNPPy (H(A), and p-tol/PNNPPh (H(B)).
Complex
L/R
6b
6a
H(B)a
H(A)b
PNNPC2/SiMe3
6-5-6/0
PNNPC2/p-tol
6-5-6/0
PNNPPh/p-tol
5-6-5/1
PNNPPy/p-tol
5-5-5/0
ring sizesc/n
Interatomic distances (Å)
Rh1ꢁꢁꢁRh2
C1–C2
Rh1–C1
Rh2–C1
Rh2–C2
Rh1–P1
Rh1–N1
Rh1–C3
Rh2–P2
3.3882(4)
1.224(5)
2.008(3)
2.279(3)
2.387(4)
2.2985(9)
2.055(3)
1.817(4)
2.2533(9)
2.077(3)
1.809(4)
0.108
3.4475(7)
1.216(8)
2.050(6)
2.273(6)
2.364(6)
2.2688(16)
2.063(5)
1.830(7)
2.2637(17)
2.062(6)
1.802(7)
0.091
3.341(1)
1.23(2)
2.001(1)
2.25(1)
2.39(1)
2.270(3)
2.106(2)
1.80(1)
2.226(3)
2.119(7)
1.80(1)
0.14
3.6169(4)
1.205(5)
2.061(3)
2.338(2)
2.338(3)
2.2768(3)
2.030(7)
1.826(3)
2.2405(7)
2.066(2)
1.825(3)
0.000
Rh2–N2
Rh2–C4
D
Bond angles and torsion angles (°)
C1–C2–X
Rh1–C1–Rh2
Rh1–C1–C2
Rh2–C1–C2
C1–Rh2–C2
P1–Rh1–N1
P1–Rh1–C3
N1–Rh1–C1
P2–Rh2–N2
P2–Rh2–C4
N2–Rh2–C1
Rh1–N1–N2–Rh2
X–N1–Rh1–P1
X–N2–Rh2–P2
161.7(3) (Si1)d
104.24(13)
171.5(3)
79.7(2)
30.31(11)
90.43(7)
94.19(10)
85.66(11)
89.23(7)
167.1(6) (C5)d
105.6(3)
167.7(5)
79.0(4)
30.3(2)
90.62(15)
87.0(2)
87.3(3)
86.93(15)
90.7(3)
169(1)
103.6(4)
169.7(8)
80.8(7)
30.6(4)
80.2(2)
96.6(4)
90.3(4)
79.9(2)
90.9(4)
84.7(3)
6.3
164.3(3)
110.5(1)
168.7(3)
77.5(2)
29.5(1)
80.07(8)
99.1(1)
88.2(1)
77.89(6)
93.15(9)
82.55(9)
1.0
90.23(12)
81.50(11)
2.5
81.6(2)
12.7
28.8 (C8)d
33.3 (C10)d
15.8 (C14)d
35.5 (C12)d
22.4
22.3
3.8
11.3
a
b
c
Ref. [12].
Ref. [11d].
The three digits refer to the ring sizes of the chelate–bridging heterocycle–chelate part.
X.
d

496
A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
3. Experimental
observed
simulated
3.1. General methods
All manipulations were carried out under an inert atmosphere
1JRh-H= 31.2 Hz
1JRh-P= 75.5 Hz
2JH-P= 13.6 Hz
by using standard Schlenk tube techniques. THF, ether, hexane
(Na–K alloy), CH2Cl2 (P2O5), acetone (CaH2), and ROH (Mg(OR)2;
R@Me, Et) were treated with appropriate drying agents, distilled,
and stored under argon. Because analytically pure samples of the
products could not be obtained despite several attempts, they were
characterized by spectroscopic methods and, for some cases, crys-
tallographic method as well. 1H and 31P NMR spectra were re-
corded on Bruker AC-200 (1H, 200 MHz; 31P, 81 MHz) and JEOL
JMN-EX-300 spectrometers (1H, 300 MHz; 13C, 75 MHz; 31P,
122 MHz). Chemical shifts are reported in ppm downfield from
-9.5 -9.6 -9.7 -9.8 -9.9 -10.0
δH / ppm
Fig. 6. Observed and simulated 1H NMR spectra (hydride region) for 9 (observed at
400 MHz in acetone-d6).
TMS (1H and 13C) and H3PO4 31P)) and coupling constants are re-
(
ported in Hz. Solvents for NMR measurements containing 0.5%
TMS were dried over molecular sieves, degassed, distilled under re-
duced pressure, and stored under Ar. IR spectra were obtained on a
JASCO FT/IR 5300 spectrometer. ESI-MS spectra were recorded on a
ThermoQuest Finnigan LCQ Duo mass spectrometer. The proce-
dures for X-ray crystallographic analysis were similar to those re-
ported in our previous paper, with the exception of the use of
CrystalStructure ver. 4.0 in place of teXsan [17]. 1-Methoxy-1,3-
bis(trimethylsiloxy)butadiene [15] and [Rh(cod)2]BF4 [10a] were
prepared according to the published procedures. Other chemicals
were purchased and used as received.
g
2-coordination of the C„C part as can be seen from the differ-
ences of the C1–Rh2 and C2–Rh2 distances ( ; Table 3). Strain
D
caused by the dissymmetric coordination may be partly released
by puckering of the flexible chelate rings as is evident from the
X–N1–Rh1–P1 and X–N2–Rh2–P2 torsion angles substantially lar-
ger than those for H(A).
2.4.2. With HSiEt3
Reaction of 3 with HSiEt3 afforded the purple l4-hydride com-
plex 9 in a manner similar to the reaction of D(A) (Scheme 6)
[11a,b]. The formation of 9 has been confirmed by the ESI-MS data
and 1H NMR simulation of the multiplet hydride signal, which has
been successfully analyzed by taking into account coupling with
the four equivalent Rh–P moieties (Fig. 6).
3.2. Preparation of 3,5-bis(diphenylphosphinoethyl)pyrazole (1-H)
3,5-Di(methoxycarbonylmethyl)pyrazole: To a MeOH solution of
dimethyl dioxopimelate [14] (3.31 g, 15.3 mmol) was added hydra-
zine hydrate (1.6 mL, 32 mmol), and the resultant mixture was re-
fluxed for 1 h. After removal of the volatiles the resultant yellow
residue was extracted with ethyl acetate (200 mL). Evaporation
of the volatiles gave the product as dark brown oil, which was used
without further purification. 3,5-Di(methoxycarbonylmethyl)pyra-
zole (3.13 g, 12.7 mmol, 83% yield): dH (CDCl3) 6.14 (1H, s, pyrazole
ring proton), 3.71 (10H, s (overlapped), CH2 + OMe).
2.5. Coordination features of PNNPC2 ligand (1) as compared with
PNNPPy (A) and PNNPPh ligands (B)
The following conclusion can be deduced from the obtained
results.
Many similarities in the reactivity of the dirhodium-carbonyl
species 3, C(A) and C(B) have been noted not only for the conven-
tional species such as the dinuclear
and H(B)) but also for the unique, tetranuclear
compounds (7, I(A), and I(B)) and 4-dicarbide complexes (8, J(A),
and J(B)). The present study reveals that the PNNP ligand set pro-
vides a scaffold for such unique structures, which have never been
observed for other ligand systems.
l
-acetylide complexes (6, H(A),
3.5-Di(2-hydroxyethyl)pyrazole: To a THF suspension (50 mL) of
LiAlH4 (1.83 g, 48.1 mmol) was added a THF solution (150 mL) of
3,5-di(methoxycarbonylmethyl)pyrazole (3.13 g, 12.7 mmol) drop-
wise at room temperature. After being stirred for 30 min at the
same temperature, the reaction mixture was refluxed for 10 h.
The resultant mixture was carefully hydrolyzed with water
(30 mL) and then the volatiles were removed under reduced pres-
sure. The obtained residue suspended in MeOH (200 mL) was bub-
bled with CO2 for 10 min and refluxed for 8 h. Filtration through a
Celite pad followed by evaporation gave the product as brown oil
(2.22 g, 14.2 mmol, 96% yield). 3.5-Di(2-hydroxyethyl)pyrazole:
dH (CDCl3) 5.95 (1H, s, pyrazole ring proton), 3.91 (4H, t,
J = 5.5 Hz, CH2OH), 2.87 (4H, t, J = 5.5 Hz, CH2CH2OH).
l4-acetylide cluster
l
Meanwhile, following dissimilarities are also noted.
(1) Ring size effect: Incorporation of the enlarged six-membered
ring(s) into the chelate-heterocycle-chelate moiety (1 and B)
causes shortening of the metal–metal distance, which fre-
quently leads to the intra-unit M–M bond formation as
exemplified by 5 and G(B).
(2) Charge effect: The coordination properties of the complexes
derived from the two mononegative ligands (1 and A) turn
out to be the very similar, while they differ from those
derived from the neutral ligand (B) to a considerable extent.
(3) The different numbers of the carbonyl ligands in the carbonyl
complexes: This aspect has been interpreted in terms of a
combination of the two factors mentioned above. In the case
of the PNNPC2 complex 2, the shortening of the metal–metal
distance and the effective back donation from the monocat-
ionic (PNNP)Rh2 fragment lead to the formation of the car-
bonyl species 2 with a Rh–Rh single bond as well as three
bridging CO ligands, one of which spans the two metal cen-
ters in a bridging mode.
3,5-Di(chloroethyl)pyrazolium chloride: 3.5-di(2-hydroxy-
ethyl)pyrazole (2.66 g, 17.0 mmol) was dissolved in SOCl2
(25 mL) and refluxed for 30 min. After removal of the volatiles un-
der reduced pressure the residue was extracted with EtOH and fil-
ter through a Celite plug. Evaporation of the solvent gave the
product as dark brown oil (3.19 g, 11.7 mmol, 69% yield). 3,5-
Di(chloroethyl)pyrazolium chloride: dH (CDCl3) 6.46 (1H, s, pyra-
zole ring proton), 3.88 (4H, t, J = 6.2 Hz, CH2Cl), 3.34 (4H, t,
J = 6.2 Hz, CH2CH2Cl).
3,5-Bis(diphenylphosphinoethyl)pyrazole (1-H): To a THF solution
(15 mL) of PPh3 (4.38 g, 16.7 mmol) was added Li wire (241 mg,
34.7 mmol), and the resultant mixture was stirred for 3 h at room
temperature. To the resultant solution of LiPPh2 cooled at ꢀ78 °C

A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
497
was added 3,5-di(chloroethyl)pyrazolium chrolide (952 mg,
4.15 mmol), and the mixture was stirred for 2 h at 0 °C and then
for 30 min at room temperature. Deaerated water was added to de-
stroy the excess LiPPh2. Extraction with ether, drying over Na2SO4,
and filtration, and removal of the volatiles under reduced pressure
left pale yellow solid, which was dissolved in ether (2 mL) and
chromatographed on silica gel under inert atmosphere (eluted
with ether/hexane (1: 1) ? ether) to give 1-H as colorless solid
(1.37 g, 2.78 mmol, 67% yield). 1-H: dH (CDCl3) 7.4–7.3 (20H, m,
Ph), 5.90 (1H, s, pyrazole ring proton), 2.69 (4H, t, J = 8.5 Hz,
CH2P), 2.36 (4H, t, J = 8.5 Hz, CH2CH2P). dP (CDCl3) ꢀ15.3.
ture. Filtration through an alumina pad, evaporation of the vola-
tiles and crystallization of the residue from toluene/ether gave 6a
as yellow crystals (71.6 mg, 0.0842 mmol, 67% yield). 6a (64%
yield): dH (CDCl3) 7.9–7.4 (20H, m, Ph), 7.72, 7.05 (2H ꢂ 2, d ꢂ 2,
J = 8.2 Hz, C6H4), 5.64 (1H, s, pyrazole ring proton), 2.82, 2.33
(4H ꢂ 2, br ꢂ 2, CH2CH2). dP (CDCl3) 30.4 (d, J = 147 Hz). IR (KBr)
1980, 1958 cmꢀ1. FD-MS: m/z = 868 (M+). SiMe3 derivative (6b):
Complex 6b was prepared in a manner similar to the synthesis of
6a. 6b (67% yield): dH (CDCl3) 7.8–7.3 (20H, m, Ph), 5.58 (1H, s, pyr-
azole ring proton), 2.85, 2.27 (4H ꢂ 2, br ꢂ 2, CH2CH2), 0.30 (9H, s,
SiMe3). dP (CDCl3) 29.6 (d, J = 145 Hz). IR (KBr) 1980, 1968,
1932 cmꢀ1. FD-MS: m/z = 850 (M+). H derivative (6c): Treatment
of a THF solution (5 mL) of 6b (54 mg, 0.063 mmol) with Bu4NꢁF
3.3. Preparation of [(
l
-PNNPC2){Rh(cod)}2]BF4 (2)
(a 1M THF solution, 63 lL, 0,0063 mmol) for 2 h at room tempera-
To CH2Cl2 solution (15 mL) of [Rh(cod)2]BF4 (1.01 g,
a
ture followed by evaporation of the volatiles, extraction with
CH2Cl2 and filtration through an alumina pad gave 6c (31 mg,
0.040 mmol, 63% yield) as yellow crystals after removal of the vol-
atiles. 6c: dH (CDCl3) 7.9–7.3 (20H, m, Ph), 5.63 (1H, s, pyrazole ring
proton), 3.38 (1H, s, „CH), 2.81, 2.26 (4H ꢂ 2, br ꢂ 2, CH2CH2). dP
(CDCl3) 30.4 (d, J = 144 Hz).
2.49 mmol) was added 1 (604 mg, 1.23 mmol) dissolved in CH2Cl2
(15 mL). After the mixture was stirred for 2 min NEt3 (0.17 mL,
1.23 mmol) was added. The mixture was further stirred for
30 min at room temperature. The organic phase was washed with
deaerated water three times and dried over Na2SO4. Filtration,
evaporation and crystallization of the residue from THF/ether gave
2 as yellow crystals (951 mg, 0.95 mmol, 75% yield). 2: dH (CDCl3)
8.0–6.8 (20H, m, Ph), 6.00 (1H, s, pyrazole ring proton), 3.9–3.7,
3.5–3.3, 3.0–2.8, 2.7–2.4, 2.25–1.95, 1.95–1.85, 1.85–1.5 (32H, m,
cod + CH2CH2). dP (CDCl3) 23.5 (d, J = 151 Hz).
3.8. Preparation of [(l l-C„C-R)]BF4 (7)
-PNNPC2)2{Rh(CO)}4(
p-Tol derivative (7a): An acetone solution (10 mL) of a mixture of
3 (29 mg, 0.040 mmol) and 6a (33 mg, 0.039 mmol) was refluxed
for 1 h. The obtained dark red solution was concentrated and addi-
tion of hexane caused precipitation of the product 7a (50 mg,
0.029 mmol, 72% yield) as black solid. 7a: dH (CDCl3) 7.67, 7.06
(2H ꢂ 2, d ꢂ 2, J = 7.7 Hz, p-tol), 7.6–6.9 (40H, m, Ph), 5.52 (2H, s,
pyrazole ring proton), 2.8–2.3 (16H, br, CH2), 2.38 (3H, s, CH3). dP
(CDCl3) 29.8 (d, J = 176 Hz). IR (KBr) 2003, 1977 cmꢀ1. ESI-MS: m/
z = 1622 (M+ for the cationic part). SiMe3 derivative (7b): Complex
7b was prepared in a manner analogous to the synthesis of 7a.
7b: dH (CDCl3) 7.9–7.4 (40H, m, Ph), 5.47 (2H, s, pyrazole ring pro-
ton), 3.0–2.4 (16H, br, CH2), 0.21 (9H, s, SiMe3). dP (CDCl3) 28.9 (d,
J = 176 Hz). H derivative (7c): Complex 7c was prepared in a man-
ner analogous to the synthesis of 7a. 7c: dH (CDCl3) 7.5–7.3 (40H,
m, Ph), 7.00 (1H, s, „CH), 5.47 (2H, s, pyrazole ring proton), 2.6–
2.5 (16H, br, CH2). dP (CDCl3) 27.2 (d, J = 170 Hz). IR (KBr) 2007,
1982 cmꢀ1. ESI-MS: m/z = 1531 (M+ for the cationic part).
3.4. Preparation of [(l
-PNNPC2)Rh2(CO)3]BF4 (3)
CO gas was bubbled through a THF suspension (10 mL) of 1
(286 mg, 0.285 mmol) for 1 h. Removal of the volatiles under re-
duced pressure and crystallization of the residue from THF/ether
gave 3 as orange crystals (240 mg,0.276 mmol, 97% yield). 3: dH
(CDCl3) 7.9–7.7 (20H, m, Ph), 6.00 (1H, s, pyrazole ring proton),
2.99, 2.83 (4H ꢂ 2, br ꢂ 2, CH2CH2); dP (CDCl3) 16.7 (d,
J = 153 Hz); IR (KBr) 2063, 2040, 1897 cmꢀ1; ESI-MS: m/z = 781
(M+ for the cationic part).
3.5. Carbonylation of 3 leading to tetracarbonyl species
[(
l
-PNNPC2)Rh2(CO)4]BF4 (4)
An acetone-d6 solution of 3 was prepared in a thick-walled pres-
sure NMR tube equipped with a rubber septum, which was then
capped. CO or 13CO was injected through the rubber septum on
the top via a gastight syringe. In the case of the measurements un-
der 3 atm of CO or 13CO, the amount of the injected gas was calcu-
lated on the basis of the volume of the NMR tube.
3.9. Preparation of [(l l4-C2)] (8)
-PNNPC2)2{Rh(CO)}4(
To an acetone solution (5 mL) of 7c (35 mg, 0.021 mmol) was
added NEt3 (3 mL). After the mixture was stirred for 1 h, the prod-
uct
8 was precipitated by addition of hexane. 8 (22 mg,
0.014 mmol, 65% yield): dH (CDCl3) 7.8–7.2 (40H, m, Ph), 5.68
(2H, s, pyrazole ring proton), 2.8–2.2 (16H, br, CH2). dP (CDCl3)
30.9 (d, J = 150 Hz). IR (KBr) 1982 cmꢀ1. ESI-MS: m/z = 1531 (M+
for the cationic part).
3.6. Thermolysis of 3 giving tetrarhodium complex
[(
l
-PNNPC2)2Rh4(CO)4](BF4) (5)
Refluxing an acetone solution of 3 for 5 h followed by precipita-
tion with hexane gave black solid 5(62% yield). 5: dH (acetone-d6)
3.10. Preparation of [(l l4-H)] (9)
-PNNPC2)2{Rh(CO)}4(
2.55–4.20 (16H, m), 6.70 (2H, s, pz), 7.1–8.0 (40H, m, Ph); dP (ace-
tone-d6) 25.7 (1JRh–P = 140.0 Hz, 1JRh–Rh = 16.0 Hz, 2JRh–P = 6.0 Hz; dC
To a THF solution (5 mL) of 3 (105 mg, 0.12 mmol) was added a
THF solution (5 mL) of HSiEt3 (19.4 mL, 0.120 mmol). After the
mixture was stirred for 1.5 h, the product 9 was precipitated by
addition of ether. 9 (73 mg, 0.046 mmol, 76% yield): dH (CDCl3)
7.8–7.5 (40H, m, Ph), 5.70 (2H, s, pyrazole ring proton), 2.7 (16H,
0
1
2
(acetone-d6) 192.0 (dd, JRh–C = 66.1 Hz, JP–C = 12.3 Hz; IR (KBr)
2008 cmꢀ1 ESI-MS m/z = 1450.8 ([(PNNPC2)2Rh2(CO)2]+; M+
2CO), 1421.9 ([(PNNPC2)2Rh2(CO)]+; M+ – 3CO), 753.3 ([(PNNPC2)2-
Rh2(CO)4]2+; M2+
;
–
)
1
1
2
br, CH2), ꢀ9.77 (1H, m, JRh–H = 31.2 Hz, JRh–P = 75.5 Hz, JH–
3.7. Preparation of [(
l
-PNNPC2){Rh(CO)}2(
l
-C„C-R)]BF4 (6)
P = 13.6 Hz). dP (CDCl3) 37.9 (d, J = 194 Hz). IR (KBr) 1980 cmꢀ1
ESI-MS: m/z = 1507 (M+ for the cationic part).
.
p-Tol derivative (6a): LiC„C-p-tol was generated by treatment
of a THF solution (5 mL) of H–C„C-p-tol (40 L, 0.302 mmol) with
l
Acknowledgments
n-BuLi (1.54 M, 0.18 mL, 0.277 mmol) at ꢀ78 °C for 20 min. To the
resultant mixture was added 3 (109 mg, 0.126 mmol) dissolved in
THF (10 mL) and the mixture was stirred for 2 h at room tempera-
We are grateful to the Ministry of Education, Culture, Sports,
Science and Technology of the Japanese Government and the Japan

498
A. Gondoh et al. / Inorganica Chimica Acta 374 (2011) 489–498
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Society for Promotion of Science and Technology for financial sup-
port of this research (Grants-in-Aid for Scientific Research:
20044007, and 22350026).
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