Dirhodium complexes bridged by bis(diphenylphosphino)phthalazine (PNNP Ph): Central ring size and charge effects as compared with the pyrazolate derivative (PNNPPy)

Article abstract of DOI:10.1021/om100832z

A dirhodium carbonyl complex with 1,4-bis((diphenylphosphino)methyl) phthalazine (PNNP^Ph), [(μ-κ²:κ²- PNNP^Ph){Rh(CO)}₂](BF₄)₂, has been prepared and its reactivity studied as compared with the previously reported 3,5-bis((diphenylphosphino)methyl)pyrazolate (PNNP^Py) analogue [(μ-κ²:κ²-PNNP^Py){Rh(CO) ₂}₂]BF₄. The two quadridentate ligands are different in the size of the central ring and the charge; six-membered ring/neutral (PNNP^Ph) vs five-membered ring/mononegative (PNNP ^Py). The reactivities of the two systems turn out to be very similar, as can be seen from formation of the analogous, unique tetranuclear μ₄-acetylide ([(μ-PNNP^Ph)₂{Rh(CO)} ₄(μ₄-C≡C-p-tol)]BF₄) and μ₄-dicarbide complexes ([(μ-PNNP^Ph) ₂{Rh(CO)}₄(μ₄-C₂)](BF ₄)₂). However, the PNNP^Ph system exhibits the following features. (1) The enlargement of the central ring causes shortening of the metal-metal distance, frequently leading to bond formation between them. For more positively charged PNNP^Ph species, (2) back-donation decreases to facilitate CO dissociation and (3) the rhodium centers become more Lewis acidic. Another feature is that the PNNP^Ph complex undergoes oxidative addition upon treatment with internal alkynes to form stable adducts with unique coordination structures (e.g., 1,4-dimetallacyclohexa-2,5-diene).

Full text of DOI:10.1021/om100832z

Organometallics 2010, 29, 6493–6502 6493
DOI: 10.1021/om100832z
Dirhodium Complexes Bridged by Bis(diphenylphosphino)phthalazine
(PNNPPh): Central Ring Size and Charge Effects As Compared with
the Pyrazolate Derivative (PNNPPy)
Takafumi Yamaguchi, Takashi Koike, and Munetaka Akita*
Chemical Resources Laboratory, Tokyo Institute of Technology, R1-27, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, Japan
Received August 30, 2010
A dirhodium carbonyl complex with 1,4-bis((diphenylphosphino)methyl)phthalazine (PNNPPh),
[(μ-κ2:κ2-PNNPPh){Rh(CO)}2](BF4)2, has been prepared and its reactivity studied as compared
with the previously reported 3,5-bis((diphenylphosphino)methyl)pyrazolate (PNNPPy) analogue
[(μ-κ2:κ2-PNNPPy){Rh(CO)2}2]BF4. The two quadridentate ligands are different in the size of the
central ring and the charge; six-membered ring/neutral (PNNPPh) vs five-membered ring/mono-
negative (PNNPPy). The reactivities of the two systems turn out to be very similar, as can be seen from
formation of the analogous, unique tetranuclear μ4-acetylide ([(μ-PNNPPh)2{Rh(CO)}4(μ4-Ct
C-p-tol)]BF4) and μ4-dicarbide complexes ([(μ-PNNPPh)2{Rh(CO)}4(μ4-C2)](BF4)2). However, the
PNNPPh system exhibits the following features. (1) The enlargement of the central ring causes
shortening of the metal-metal distance, frequently leading to bond formation between them. For
more positively charged PNNPPh species, (2) back-donation decreases to facilitate CO dissociation
and (3) the rhodium centers become more Lewis acidic. Another feature is that the PNNPPh complex
undergoes oxidative addition upon treatment with internal alkynes to form stable adducts with
unique coordination structures (e.g., 1,4-dimetallacyclohexa-2,5-diene).
Introduction
reactivity study of the dirhodium carbonyl adduct [(μ-κ2:κ2-
PNNPPy){Rh(CO)2}2]BF4 (C) were reported by Bosnich in
1985,2 and recently, we revealed the unique reactivity of C: in
particular, the formation of tetranuclear species (see Scheme 1).3
It has been revealed that the inner CO ligands in C are so labile
owing to the influence of the P donors trans to CO as well as
steric reasons that the dicarbonyl species D with a cis-divacant
site resulting from decarbonylation of C serves as an efficient 4e
acceptor.2a,3
Polynuclear species are expected to display unique chemical
behavior arising from cooperation of the plural metal
centers.1 Ourattentionhas been focusedonthe quadridentate,
dinucleating 3,5-bis((diphenylphosphino)methyl)pyrazolate
(PNNPPy) ligand system, which would provide a cis-divacant
coordination site effective for cooperative activation of sub-
strates (e.g., D in Scheme 1). The synthesis and a preliminary
As an extension, we have designed the phthalazine analogue
PNNPPh, having the six-membered pyridazine skeleton in place
of the five-membered pyrazole ring in the PNNPPy ligand
(Scheme 1). The enlargement of the ring part should cause
shortening of the distance between the metal centers (l1 > l2)
and, as a result, the PNNPPh system should have more chances to
form a metal-metal bond between the metal centers within the
(μ-PNNPPh)Rh2 unit (intraunit). For the PNNPPy system, no
intraunit metal-metal bond formation is observed, although
cluster species are formed by interunit metal-metal bond forma-
tion (e.g., F). Furthermore, the change of the ring also causes a
change in the charge of the ligands. PNNPPy is a mononegative
ligand, while PNNPPh is a neutral one. Such a change should
influence the chemical reactivity of the resultant metal complexes.
For the sake of comparison, typical reactions of the
(μ-PNNPPy)Rh2 system are summarized in Scheme 1. The ligand
A-H is readily converted to the dirhodium cod complex B upon
treatment with [Rh(cod)2]þ/NEt3.2a Carbonylation of B affords
the tetracarbonyl complex C, which serves as an equivalent to the
putative 4e acceptor D, upon subsequent in situ decarbonylation.
*To whom correspondence should be addressed. E-mail: makita@
res.titech.ac.jp.
(1) Klingele, J.; Dechert, S.; Meyer, F. Coord. Chem. Rev. 2009, 253,
2698. Braunstein, P.; Oro, L. A.; Raithby, P. R. Metal Clusters in Chemistry;
Wiley-VCH: Weinheim, Germany, 1999 (3 vols.). Dyson, P. J.; McIndoe,
J. S. Transition Metal Carbonyl Cluster Chemistry; Gordon and Breach
Science: Amsterdam, 2000. Shriver, D. F.; Kaesz, H. D.; Adams, R. D. The
Chemistry of Metal Cluster Complexes; VCH: New York, 1990. Abel, E. W.;
Stone, F. G. A.; Wilkinson, G. Comprehensive Organometallic Chemistry
II; Pergamon: Oxford, U.K., 1995; Vols. 3-10. Mingos, D. M. P.;
Crabtree, R. H. Comprehensive Organometallic Chemistry III; Elsevier:
Oxford, U.K., 2007; Vols. 4-8.
(2) (a) Schenk, T. G.; Downs, J. M.; Milne, C. R. C.; Mackenzie,
P. B.; Boucher, H.; Whelan, J.; Bosnich, B. Inorg. Chem. 1985, 24, 2334.
(b) Schenk, T. G.; Milne, C. R. C.; Sawyer, J. F.; Bosnich, B. Inorg. Chem.
1985, 24, 2338. See also (c) Bosnich, B. Inorg. Chem. 1999, 38, 2554.
(3) (a) Tanaka, S.; Akita, M. Angew. Chem., Int. Ed. 2001, 40, 2865.
(b) Tanaka, S.; Dubs, C.; Inagaki, A.; Akita, M. Organometallics 2004, 23,
317. (c) Dubs, C.; Inagaki, A.; Akita, M. Chem. Commun. 2004, 2760.
(d) Tanaka, S.; Dubs, C.; Inagaki, A.; Akita, M. Organometallics 2005, 24,
163. (e) Dubs, C.; Yamamoto, T.; Inagaki, A.; Akita, M. Organometallics
2006, 25, 1344. (f) Dubs, C.; Yamamoto, T.; Inagaki, A.; Akita, M.
Organometallics 2006, 25, 1359. (g) Dubs, C.; Yamamoto, T.; Inagaki, A.;
Akita, M. Chem. Commun 2006, 1962.
r
2010 American Chemical Society
Published on Web 11/03/2010
pubs.acs.org/Organometallics

6494 Organometallics, Vol. 29, No. 23, 2010
Yamaguchi et al.
Scheme 1
Scheme 2
Treatment of C with lithium acetylide provides the dinuclear
μ-η1:η2-acetylide E, which is further converted to the tetranuclear
μ4-acetylide F by treatment with C.3b,d The tetranuclear complex
F has been directly obtained from terminal alkyne upon treat-
ment with C. Interestingly, the tetranuclear μ4-CtCH complex
(F; R = H) is converted to the μ4-dicarbide complex G by depro-
tonation.3b,d The complexes E-Gshow fluxional behavior, and it
is notable that the mechanisms for the fluxional behavior of Fand
G involve reversible metal-metal bond cleavage and recombina-
tion processes. Reaction of C with internal alkyne forms the
unstable μ-η2:η2 adduct H.3d In contrast to the incorporation of
acetylide and alkyne (4e donors), the unique μ4-hydride complex
I is formed by reaction of C with hydrosilane.3b,d
ligand with the phthalazine core developed by Lippard
(Scheme 2).4 Ligand 1 was readily prepared by a two-step
process: (1) overnight reaction of 1,4-dichlorophthalazine with
an excess amount of LiCH2P(dO)Ph2 (generated by treatment
of OdPPh3 with MeLi)5 followed by (2) reduction of the
resultant phosphine oxide derivative 2 with HSiCl3/NEt3.
A shorter reaction time or a smaller amount of the lithium
reagent caused formation of the monosubstituted product 3.
Ligand 1could not be obtained by direct substitution reaction of
1,4-dichlorophthalazine with LiCH2PPh2.6 Ligand 1 is readily
characterized on the basis of its spectroscopic data (δP -18.7;
for other data, see the Experimental Section), which supports
the symmetrical structure.
Herein we disclose (1) the synthesis of the PNNPPh ligand
and its group 9 metal complexes and (2) reactions of the
resultant dirhodium carbonyl species toward alkynes and
HSiEt3, furnishing unique adducts.
Preparation of COD Complexes. Reaction of the obtained
PNNPPh ligand 1 with labile cod complexes of rhodium and
iridium, [M(cod)2]BF4, afforded the dicationic 1:2 adducts 4,
[(μ-κ2:κ2-PNNPPh){M(cod)}2](BF4)2, as yellow (4a) and red
Results and Discussion
(4) Barrios, A. M.; Lippard, S. J. J. Am. Chem. Soc. 1999, 121, 11751.
(5) Seyferth, D.; Welch, D. E.; Heeren, J. K. J. Am. Chem. Soc. 1964,
86, 1100.
Ligand Synthesis. We designed a synthetic route to the
PNNPPh ligand 1 following the relevant hexadentate N6
(6) Peterson, D. J. J. Organomet. Chem. 1967, 8, 199.

Article
Organometallics, Vol. 29, No. 23, 2010 6495
Figure 1. ORTEP views of the cationic parts of 4a (a), 5 (b), and 6 (c) with thermal ellipsoids at the 30% probability level. For 6, phenyl
groups are omitted for clarity.
Scheme 3
crystals (4b), respectively (Scheme 3). The composition and
symmetrical structure of the products are confirmed by the
single sets of NMR signals for the phthalazine, CH2P, and
cod parts, and P coordination is verified for 4a by the doublet
31P NMR signal (δP 28.0 (d, JP-Rh= 148.4 Hz)) resulting
from coupling with the Rh nucleus.
ligand and the η2:η2-cod ligand, (2) twisting of the structure
with respect to the N1-N2 bond (<M1-N1-N2-M2 =
53.3(4)° (4a), 52(1)° (4b)) caused by the bulky M(cod) frag-
˚
˚
ments, and (3) M M separations (3.949(2) A (4a), 3.928(2) A
3 3 3
(4b)) substantially longer than the sum of covalent radii (Rh,
˚
2.68 A; Ir, 2.71 A).
˚
The two cod complexes have also been characterized by
X-ray crystallography (Figure 1a; for 4b, see the Supporting
Information), which reveals (1) square-planar geometry of the
metal centers coordinated by the bridging μ-κ2:κ2-PNNPPh
Carbonylation of COD Complexes. In the case of the
PNNPPy system carbonylation of the cod complex B in
CH2Cl2 afforded the simply substituted tetracarbonyl com-
plex C, without a Rh-Rh bond (Scheme 1).2a Carbonylation

6496 Organometallics, Vol. 29, No. 23, 2010
Yamaguchi et al.
Table 1. Structural Parameters for Tetrahedral Tetrarhodium
Complexes 6 and 10
6
10
˚
Bond Lengths (A)
Rh1-Rh2
Rh1-Rh3
Rh1-Rh4
Rh2-Rh3
Rh2-Rh4
Rh3-Rh4
Rh-P
2.9410(9)
2.814(1)
2.8558(9)
2.875(1)
2.8614(9)
2.905(1)
2.241(2)-2.251(2)
2.065(5)-2.073(5)
1.855(9) (Rh1-C1)
1.854(7) (Rh2-C2)
1.849(8) (Rh3-C3)
1.824(8) (Rh4-C4)
2.860(1)
2.9977(9)
2.7182(9)
2.755(1)
2.881(1)
2.926(1)
2.248(2)-2.289(3)
2.035(8)-2.145(7)
2.00(1) (C11-Rh1)
1.20(2) (C11-C12)
2.01(1) (C21-Rh3)
1.21(1) (C21-C22)
Rh-N
Figure 2. Observed and simulated 31P NMR spectra of 7
(observed in CD3NO2 at 81 MHz at room temperature).
Carbonylation of 4a at -78 °C followed by precipitation
by addition of hexane at the same temperature afforded the
dicarbonyl species 7 as a yellow solid. Complex 7 was also
obtained even in chlorinated solvents, when carbonylation
was carried out at low temperatures. The product 7 was
unstable in the absence of CO. When workup of the reaction
mixture for the carbonylation of 4a was carried out under an
N2 atmosphere, the Rh4 species 6 was obtained instead of 7.
While the instability of 7 hampered its thorough character-
ization, the spectroscopic analysis described below led to
characterization of 7 as the dirhodium dicarbonyl species
Bond Angles (deg)
168.2(7) (Rh1-C1-O1)
169.8(7) (Rh2-C2-O2)
168.0(8) (Rh3-C3-O3)
169.7(9) (Rh4-C4-O4)
172.0(8) (Rh1-C11-C12)
170(1) (C11-C12-C13)
171.5(9) (Rh3-C21-C22)
172(1) (C21-C22-C23)
of the PNNPPh complex 4a in CH2Cl2 in a manner analogous
to that of B (Scheme 2) gave the carbonylated μ-Cl complex 5
˚
(Figure 1b; Rh1 Rh2 = 3.42873(3) A) resulting from car-
bonylation as well as Cl abstraction from the solvent. Similar
Cl abstraction was also observed for the PNNPPy system but
was much slower than that of the PNNPPh system.
3 3 3
1
shown in Scheme 3. The H NMR spectrum of 7 contains
single sets of the phthalazine and CH2 signals, suggesting a
symmetrical structure, and its IR spectrum contains a single
CO vibration at 2045 cm-1. These data are consistent with
the formulation of the product as [(μ-κ2:κ2-PNNPPh){Rh-
(CO)}2]BF4. Crucial information has been obtained from a
31P NMR spectrum, which contains a doublet-of-triplets-
like signal (Figure 2), in sharp contrast to the simple doublet
signal observed for the cod (4a) and μ-Cl complexes (5).
Simulation analysis reveals that the spectrum is best repro-
duced by taking into account three spin-spin couplings,
Then carbonylation was carried out in non-halogenated
solvents such as THF and acetone. The obtained product
was not a monomeric dinuclear species but a dimeric tetra-
nuclear species with a tetrahedral Rh4 core, [(μ-PNNPPh)2-
{Rh(CO)}4](BF4)2 (6), as revealed by X-ray crystallography
(Figure 1c and Table 1). The Rh-Rh distances of ca. 2.8-
˚
2.9 A in 6 are at the longer end of bonding interactions and
are substantially longer than those in the related cluster
7
˚
compound Rh4(CO)12 (∼2.7 A). It is notable that complex 6
contains intraunit Rh-Rh bonds, in contrast to the PNNPPy
1
1
2
0
0
JRhP, JRhRh , and JRhP , as compared in Figure 2. The
system. The distances of the Rh-Rh bonds bridged by the
last two couplings verify bonding interactions between the
two rhodium centers, and such coupling is not observed
for complexes without a Rh-Rh interaction (e.g., 4 and 5).9
On the basis of these data, the dicarbonyl species 7 has
been assigned to the dinuclear species with a RhdRh bond
as shown in Scheme 3,10 which is in resonance with the
coordinatively unsaturated structure 70, analogous to D.
The reactivity of 7 toward alkynes described below is also
consistent with the formulation as a 4e acceptor. In the
following experiments the unstable species 7 was gener-
ated from 4a under a CO atmosphere at -78 °C and used
without isolation at the same temperature because of its
instability.
PNNPPh ligand (∼2.9 A) are slightly longer than those
˚
˚
not supported by the ligand (∼2.8 A). These structural
features suggest that the coordinative unsaturation is delo-
calized over the Rh4 core with an average Rh-Rh bond
order of 7/6. The tetrarhodium species 6 is a coordinatively
unsaturated species with 58 cluster valence electrons (CVE)
(cf. 60 CVE for a coordinatively saturated species). Accord-
ing to the Cambridge Structural Database (CSD), only two
Rh4 species with 58 CVE have been reported and both of
them contain four bridging hydride ligands.8 No hydride 1H
NMR signal is detected for 6 (up to -30 ppm). Simple
dimerization of the dirhodium species 7 (see below) gives a
56-CVE species, and such a highly coordinatively unsatu-
rated species should be stabilized by the 2e reduction to give
the 58-CVE species 6, although the reductant is not clear.
The coordination structural change from a 16e square-planar
geometry as in 4, 5, and 7 to the six-coordinate structure
(preferably with an 18e configuration) should be, in part, the
cause of the electron deficiency of the tetranuclear species,
including those discussed below.
(9) The JRhRh coupling is a useful diagnostic for a Rh-Rh bonding
interaction. Rh-Rh-bonded species such as 6 and 7 do not always show
a sharp doublet 31P NMR signal due to 1JRhRh and/or 2JRhP coupling.
Simulation analysis is not always successful, and in such cases, the 31P
NMR signals are denoted as multiplet signals in this paper. A very small
2JRhP or 3JPP coupling (<3 Hz) is also observed, even for non-Rh-Rh-
bonded species such as 9 and 13 having μ-CtCR and μ-OH ligands,
respectively.
(10) Complex 7 was also examined by VT 13C NMR measurements of
a
13CO-enriched sample. A broad singlet signal observed at room
(7) Wei, C. H. Inorg. Chem. 1969, 8, 2384. Farrugia, L. J. J. Cluster Sci.
2000, 11, 39.
(8) Kulzick, M.; Price, R. T.; Muetterties, E. L.; Day, V. W. Organo-
metallics 1982, 1, 1256. (b) Espinet, P.; Bailey, P. M.; Piraino, P.; Maitlis, P. M.
Inorg. Chem. 1979, 18, 2706.
temperature (δC 184 (in CD2Cl2)) separated into several signals below
-60 °C (δC ∼181 (br), 183.6, 184.0, 184.4, ∼210 (br)). The complicated
behavior should be ascribed to a CO coordination/dissociation equilib-
rium. Because complex 7 decomposed in the absence of CO, however, we
could not obtain a 13C NMR spectrum of 7 in the absence of CO.

Article
Organometallics, Vol. 29, No. 23, 2010 6497
Figure 3. ORTEP views of the cationic part of 9 drawn with thermal ellipsoids at the 30% probability level: (a) top view; (b) side view of
the core part.
Scheme 4
Carbonylation of the iridium analogue 4b resulted in the
formation of the pentacarbonyldiiridium complex 8, which
was characterized on the basis of spectroscopic and prelimi-
nary crystallographic data. The carbonyl complex 8 turned
out to be a coordnatively saturated 34e species with a
metal-metal single bond and a bridging CO ligand (ν(μ-CO)
1751 cm-1), which is totally different from the structures of
the rhodium analogues 5-7.
Reaction of Rhodium CO Complex 7 with HSiEt3 and
Alkynes. The labile rhodium carbonyl species 7 was treated
with hydrosilane and alkynes, which reacted with the PNNPPy
analogue C to afford unique di- and tetranuclear complexes
(Scheme 1).3
Reaction of the carbonyl species 7 or the μ-Cl complex 5
with a lithium acetylide, LiCtC-p-tol, gave a mixture of
products, in contrast to the clean reaction of the PNNPPy
system. Direct reaction of 7 with HCtC-p-tol in the presence
of water afforded the dirhodium μ-η1:η2-acetylide complex 9
(Scheme 4), analogous to the PNNPPy derivative E
(Scheme 1), whereas the reaction in the absence of water
gave an unidentified product.11 In contrast, complex 9 has
been characterized by spectroscopic data and, as usually
observed for the related complexes, it shows fluxional behav-
ior by way of a windshield wiper like motion, which leads to
mirror-symmetrical NMR features for the (μ-PNNPPh)Rh2
moiety at room temperature.12 Complex 9 was also char-
acterized by X-ray crystallography (Figure 3 and Table 2)
and is a good sample for comparison of the structural
features of the two PNNP ligand systems. For the (μ-L)Rh2-
(i). With HSiEt3. In contrast to the reaction of the
PNNPPy complex C with hydrosilane, giving the tetranuclear
μ4-hydride complex I (Scheme 1),3a,d the analogous reaction
of 7 with HSiEt3 gave the tetrarhodium complex 6 without
the hydride ligand (Scheme 4). The reaction may initially
(CO)2 part, first of all, the Rh Rh separation in 9 is shorter
3 3 3
˚
than that in E (R = p-tol) by ca. 0.27 A, as we expected. The
form
a
hydride species, [(μ-PNNPPh)Rh2(CO)2(μ-H)]þ,
Rh-N distances of 9 are slightly shortened compared to
those of E (R = p-tol), presumably reflecting the different
charges of L (PNNPPy negative vs PNNPPh neutral), whereas
the Rh-P distances are comparable. On the other hand, no
which couples with a second molecule of 7 to form a
tetrarhodium μ-hydride intermediate analogous to I,
[(μ-PNNPPh)2Rh4(CO)4(μx-H)]3þ. The resultant þ3 spe-
cies, however, is so acidic that it may undergo deprotona-
tion to form the non-hydride tetrarhodium cluster compound 6
with þ2 charge.
(11) The unidentified product presumably contains
a
(ii). With Terminal Alkyne. Reaction of the PNNPPh
species 7 with terminal alkyne was dependent on the reaction
conditions, and core parts of some of the reaction products
turned out to be isostructural with those of the PNNPPy
derivatives.
Rh-C(dO)C(p-tol)dC(H) -C(dO) fragment like that found in 13
and a μ-acetylide functional group like that in 9.
(12) VT measurements (∼-90 °C) were carried out for the fluxional
complexes, but a spectrum at the slow exchange limit was not obtained,
although broadening of the spectra was observed for some of the
complexes.

6498 Organometallics, Vol. 29, No. 23, 2010
Yamaguchi et al.
Table 2. Comparison of Structural Parameters for the Dirhodium
μ-p-Tolylacetylide Complexes [(μ-L){Rh(CO)}2(μ-CtC-
p-tol)](BF4)n (L/n = PNNPPh/1 (9), PNNPPy/0 (E (R = p-tol))a
Rh-CtC linkages (172.0(8)° (Rh1-C11-C12), 171.5(9)°
(Rh3-C21-C22)). This is a rare example of a σ-bonded
acetylide cluster compound without π interaction.13 Taking
into account the electron-deficient configuration of the Rh4
cores with 58 CVE, 2e short of a saturated configuration
(60 CVE), it should be noted that the cluster part remains
coordinatively unsaturated even in the presence of the
π donor (acetylide) in the vicinity. Decarbonylation of 9
forms a coordinatively unsaturated monocarbonyl inter-
mediate, [(μ-PNNPPh)Rh2(CO)(CtC-p-tol)]þ, which captures
another molecule of 9 via metal-metal bond formation to
furnish 10.3b,d
The tetrarhodium μ4-acetylide cluster compound 11 was
prepared by following a synthetic route analogous to that of
F (Scheme 1; E þ C f F).3b,d Simple mixing of equimolar
amounts of 9 and 7 in THF at room temperature gave 11
(Scheme 4). The spectroscopic properties of 11, including
fluxional behavior via reversible metal-metal bond cleavage
and recombination processes, are very similar to those of
F;3b,d,12 single sets of 1H and 31P NMR signals for the CH2P
parts are observed. The coordinatively unsaturated species 7
readily couples with 9 to form the tetranuclear adduct 11.
Structural features of 11 (Figure 4b and Table 3) also turn
out to be very similar to those of F. The acetylide ligand
is coordinated to the folded Z-shaped metal array in a
μ4-η1(Rh1):η1(Rh3):η1(Rh4):η2(Rh2) fashion.
9
E (R = p-tol)b
˚
Bond Lengths (A)
Rh1 Rh2
3 3 3
3.341(1)
2.270(3)
2.106(7)
1.81(1)
2.226(3)
2.119(7)
1.80(1)
2.00(1)
2.25(1)
2.39(1)
1.23(2)
1.46(2)
3.6169(4)
2.2768(8)
2.030(2)
1.826(3)
2.2405(7)
2.066(2)
1.825(3)
2.061(3)
2.338(2)
2.388(3)
1.205(5)
1.448(5)
Rh1-P1
Rh1-N1
Rh1-C01
Rh2-P2
Rh2-N2
Rh2-C02
C11-Rh1
C11-Rh2
C12-Rh2
C11-C12
C12-C13
Bond Angles (deg)
P1-Rh1-N1
80.2(2)
96.6(4)
90.3(4)
92.9(5)
79.9(2)
90.9(4)
84.7(3)
104.7(4)
103.6(4)
169.7(8)
80.8(7)
68.6(7)
169(1)
80.07(8)
99.1(1)
88.2(1)
P1-Rh1-C01
N1-Rh1-C11
C01-Rh1-C11
P2-Rh2-N2
92.7(1)
77.89(6)
93.15(9)
82.55(9)
105.22(9)
110.5(1)
168.7(3)
77.5(2)
P2-Rh2-C02
N2-Rh2-C11
C02-Rh2-C11
Rh1-C11-Rh2
Rh1-C11-C12
Rh2-C11-C12
Rh2-C12-C11
C11-C12-C13
The tetrarhodium μ4-dicarbide complex 12,14,15 analogous
to the PNNPPy derivative G, was obtained by treatment of 7
with Me3SiCtCH. In contrast to the PNNPPy system, the
μ4-C2 complex 12 was formed directly, and no μ4-acetylide
intermediate 11 (R = SiMe3, H) analogous to F was detected.
The molecular structure of the fluxional molecule 1212 has been
determined by X-ray crystallography (Figure 4c). The C-C
73.0(2)
164.3(3)
a A unit cell of 9 contains two independent molecules with essentially
the same geometry, and the parameters for one of them are shown.
b References 3b,3d.
˚
˚
significant differences are noted for the Rh2(μ-CtC) part. This
would result from the fact that the strain of the Rh2(μ-CtC)
part can be released by twisting the square-planar Rh coordi-
nation planes, as can be seen from a side view (Figure 3b). The
five-membered Rh-N-C-C-P ring adopts an envelope-like
conformation by puckering of the Rh-P-C moieties.
The notable effect of water suggests the following formation
mechanism of 9: coordination of water to 7 followed by
deprotonation forms the μ-hydroxo intermediate [(μ-PNNPPh)-
{Rh(CO)}2(μ-OH)]þ, which undergoes dehydrative condensa-
tion with terminal alkyne to produce 9. Similar deprotonation
occurs for the PNNPPy system during the formation of the
tetranuclear species F from the carbonyl precursor C.3c,d
In contrast to the PNNPPy system (C f F), the tetranuclear
μ4-acetylide cluster compound 11, like F, cannot be obtained
directly from 8by a one-pot reaction but by another method (see
below).
distance of 1.24(2) A is similar to that of G (1.249(7) A), as
compared in Table 4, but the coordination structure of the
central C2 part is changed from a double μ-η1:η2 coordination
(μ4-η1:η1:η2:η2) (G) to a μ4-η1:η1:η1:η1 coordination (12),15 as
indicated by the significant difference in the distances between
˚
the Rh2 atom and the two C2 atoms (0.54 A (12); cf. 0.03-
0.04 A (G)). The more η coordination character in G is evident
2
˚
(13) Cherkas, A. A.; Taylor, N. J.; Carty, A. J. Chem. Commun. 1990,
385. Yamagata, T.; Okiyama, H.; Imoto, H.; Saito, T. Acta Crystallogr.,
Sect. C 1997, 53, 859. Kizas, O. A.; Krivykh, V. V.; Vorontsov, E. V.; Tok,
O. L.; Dolgushin, F. M.; Koridze, A. A. Organometallics 2001, 20, 4170.
Wong, W.-Y.; Ting, F.-L.; Lam, W.-L. Eur. J. Inorg. Chem. 2001, 623. For
planar Pt cluster compounds, see: Smith, D. E.; Welch, A. J.; Treurnicht, I.;
Puddephatt, R. J. Inorg. Chem. 1986, 25, 4616. Che, C.-M.; Yip, H.-K.; Lo,
W.-C.; Peng, S.-M. Polyhedron 1994, 13, 887. Leoni, P.; Marchetti, F.;
Marchetti, L.; Pasquali, M. Chem. Commun. 2003, 2372. Albinati, A.; de
Biani, F. F.; Leoni, P.; Marchetti, L.; Pasquali, M.; Rizzato, S.; Zanello, P.
Angew. Chem., Int. Ed. 2005, 44, 5701. Cavazza, C.; de Biani, F. F.;
Funaioli, T.; Leoni, P.; Marchetti, F.; Marchetti, L.; Zanello, P. Inorg. Chem.
2009, 48, 1385.
(14) Bruce, M. I.; Low, P. J. Adv. Organomet. Chem. 2004, 50, 180.
(15) μ4-η1:η1:η1:η1-C2 complexes: (a) Griffith, C. S.; Koutsantonis,
G. A.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2005, 690,
3410. (b) Akita, M.; Sugimoto, S.; Tanaka, M.; Moro-oka, Y. J. Am. Chem.
Soc. 1992, 114, 7581. (c) Akita, M.; Sugimoto, S.; Hirakawa, H.; Kato, S.;
Terada, M.; Tanaka, M.; Moro-oka, Y. Organometallics 2001, 20, 1555.
(d) Terada, M.; Higashihara, G.; Inagaki, A.; Akita, M. Chem. Commun.
2003, 2984. (e) Terada, M.; Akita, M. Organometallics 2003, 22, 355.
(f) Higashihara, G.; Terada, M.; Inagaki, A.; Akita, M. Organometallics
2007, 26, 439. Double μ-η1:η2-C2 complexes: (g) Bruce, M. I.; Snow, M. R.;
Tiekink, E. R. T.; Williams, M. L. Chem. Commun. 1986, 701. (h) Yam, V.
W.-W.; Fung, W. K.-M.; Cheung, K.-K. Angew. Chem., Int. Ed. 1996, 35,
1100. (i) Mihan, S.; Sunkel, K.; Beck, W. Chem. Eur. J. 1999, 5, 745.
(j) Song, H.-B.; Wang, Q.-M.; Zhang, Z.-Z.; Mak, T. C. W. Chem. Commun.
2001, 1658. (k) Hooper, T. N.; Green, M.; Russell, C. A. Chem. Commun.
2010, 46, 2313.
The dinuclear μ-acetylide complex 9 was not so stable as to
be gradually converted to the tetranuclear diacetylide cluster
complex 10 via decarbonylation associated with dimeriza-
tion of the Rh2(μ-CtCR) core of 9. X-ray crystallography of
10 reveals the presence of a tetrahedral Rh4 core with Rh-
˚
Rh distances between 2.7182(9) and 2.9977(9) A (Figure 4a
and Table 1). The Rh-Rh bonds, except the Rh1-Rh3
bond, are associated with the bridging ligands (PNNPPh or
˚
CO), and accordingly, the Rh1-Rh3 bond (2.9977(9) A)
is the longest among them. The two acetylide groups are
σ-bonded to the rhodium centers, as indicated by no appar-
ent π interaction with the neighboring rhodium centers
˚
˚
(2.517(9) (C11-Rh3), 2.640(9) A (C11-Rh4), 2.579(9) A
˚
(C21-Rh1), 2.53(1) A (C21-Rh2)) as well as the linear

Article
Organometallics, Vol. 29, No. 23, 2010 6499
Figure 4. ORTEP views of the cationic parts of 10 (a), 11 (b), and 12 (c) drawn with thermal ellipsoids at the 30% probability level.
Phenyl groups are omitted for clarity.
˚
Table 3. Comparison of Structural Parameters (Bond Lengths in A)
˚
Table 4. Comparison of Structural Parameters (Bond Lengths in A)
for the Tetrarhodium μ4-p-Tolylacetylide Cluster Compounds
for the Tetrarhodium μ4-Dicarbide Cluster Compounds
[(μ-L)2{Rh(CO)}4(μ-C2)](BF4)n (L/n = PNNPPh/2 (12),
PNNPPy/0 (G))a
[(μ-L)2{Rh(CO)}4(μ-CtC-p-tol)](BF4)n (L/n = PNNPPh
3 (11), PNNPPy/1 (F (R = p-tol))a
/
11
F (R = p-tol)b
12b
Gc,d
Rh1-Rh3
Rh1-Rh4
Rh2-Rh3
Rh-P
2.856(1)
2.894(1)
2.967(3)
2.211(3)-2.245(2)
2.116(8)-2.142(7)
2.18(1)
2.246(9)
2.17(1)
2.313(9)
2.47(1)
2.8925(4)
2.9474(5)
2.9732(5)
2.218(1)-2.264(1)
2.042(4)-2.062(4)
2.151(4)
2.309(4)
2.223(4)
2.335(4)
2.386(5)
Rh1 Rh2
3 3 3
3.1967(9)
3.009(3)
2.254(2)
2.234(2)
2.088(6)
2.110(6)
1.82(1)
1.80(1)
1.23(1)
2.015(6)
2.195(8)
2.737(7)
3.815(2), 3.849(1)
3.173(2)
Rh2 Rh2*
3 3 3
Rh1-P1
Rh2-P2
Rh1-N1
Rh2-N2
Rh1-C01
Rh2-C02
C1-C1*
C1-Rh1
C1-Rh2
C1*-Rh2
2.259(2), 2.258(2)
2.230(4), 2.219(3)
2.03(1), 2.042(9)
2.079(5), 2.069(6)
1.82(2), 1.81(1)
1.83(1), 1.810(8)
1.22(1)
2.042(9), 2.062(9)
2.44(2), 2.44(1)
2.396(9), 2.41(1)
Rh-N
C1-Rh1
C1-Rh2
C1-Rh3
C1-Rh4
C2-Rh2
C2 Rh4
2.55(1)
1.24(2)
1.44(2)
2.555(5)
1.249(7)
1.441(7)
3 3 3
C1-C2
C2-C3
a Bond angles (in deg): 12, Rh1-C1-Rh2 = 98.7(3), Rh1-C1-
C1* = 159.0(5), Rh2-C1-C1* = 102.2(4); G, Rh1-C1-Rh2 =
116.5(4), 117.2(3), Rh1-C1-C1* = 163.4(7), 164.0(8), Rh2-C1-
C1* = 74(1), 73.3(7). b Imposed on a crystallographic C2 axis. c With
no crystallographic symmetry within the molecule. d References 3b,3d.
a Bond angles (in deg): 11, Rh3-Rh1-Rh4 = 75.49(3), Rh1-Rh3-
Rh2 = 74.54(3), C1-C2-C3= 173(1); F, Rh3-Rh1-Rh4 = 80.13(2),
Rh1-Rh3-Rh2 = 77.62(1), C1-C2-C3 = 172.3(5). b References 3b,3d.
from the similar Rh-C bond distances. Accordingly, the C2
carbon atoms become planar, as judged by the sum of the
bond angles (359.9° (12) vs 353.9, 354.5° (G)). However, the
(μ4-C2)Rh4 part still deviates from a D2h-symmetrical,
planar tetrametalated ethylene structure, M2CdCM2,15 as
is evident from (1) the unsymmetrical bonding of the C1
and one of the two metal centers. Because back-donation from
the dicationic (μ-PNNPPh)Rh2(CO)2 fragment is weaker than
that from the monocationic (μ-PNNPPy)Rh2(CO)2 fragment,
the μ-η1:η2-acetylide coordination features are less apparent for
the PNNPPh system. The Rh1 Rh2 (3.1967(2) A) and
˚
3 3 3
˚
˚
Rh2 Rh2* separations (3.009(3) A) are out of the range of
atom to the two rhodium centers (C1-Rh1 = 2.015(6) A,
3 3 3
˚
˚
C1-Rh2 = 2.195(8) A; difference 0.18 A) and (2) the
dihedral angle Rh2-C2-C2*-Rh2* (58.3°). The deviation
may result from the following two factors. One is steric
repulsion between the bulky metal fragments, as can be seen
from the overall molecular structure. The other is intrinsic
preference of the M2(μ-C2) part to a μ-η1:η2-acetylide co-
ordination structure with an unsymmetrical CRM2 triangle,
resulting from π interaction between the C-C multiple bond
bonding interactions, and the Rh2 Rh2* separation is short-
3 3 3
˚
er than that in G (3.173(2) A). However, formation of the C2-
symmetrical structure of 12 in preference to the isomeric
centrosymmetrical structure 120 (Chart 1) suggests that there
may be a weak bonding interaction between Rh2 and Rh2*,
although the conformation may result from packing in the
single crystal. Complex 12 should be formed via mechanisms
analogous to those for G:3b,d i.e., desilylation of the Me3SiCtC

6500 Organometallics, Vol. 29, No. 23, 2010
Yamaguchi et al.
Figure 5. ORTEP views of the cationic parts of 13 (a) and 14 (b) with thermal ellipsoids at the 30% probability level. Phenyl groups are
omitted for clarity.
Chart 1
Scheme 5
derivative of 11 followed by spontaneous deprotonation of the
resultant μ4-C2H intermediate.
(iii). With Internal Alkyne. The PNNPPh complex 7 reacted
with internal alkynes to afford stable adducts with unique
coordination structures (Scheme 5) in contrast to the PNNPPy
system, giving unstable μ-η2:η2 adducts (Scheme 1).3d
substituents couple with dinuclear species to form adducts with
a tetrahedral M2C2 core, whereas those with electron-with-
drawing substituents undergo insertion into the metal-metal
bond.16 A 1,4-dimetallacyclohexa-2,5-diene structure as in 14
has several precedents.17 Coordination of water gives the six-
coordinate structure.
Reaction of 7 with di-p-tolylacetylene in acetone gave the
yellow product 13 in moderate yield. The 31P NMR spectrum
of 13, containing a pair of doublet of multiplets signals,9 sug-
gests an unsymmetrical structure, and the dimeric structure
has been characterized by X-ray crystallography (Figure 5a).
The structure contains a 2,5-dioxorhodacyclopent-3-ene
ring and a bridging hydroxo ligand, and coordination of the
CdO group to the rhodium center in the other unit furnishes
the cyclic, dimeric structure. The metallacycle results from
oxidative metallacyclization of one molecule of the alkyne
and two molecules of CO. As a result, one of the two rhodium
centers (Rh2 included in the metallacycle) is a six-coordinate
Rh(III) center, while Rh1 remains Rh(I). In accord with this
change, the Rh-P/N distances associated with the Rh(III)
center are slightly longer than those associated with the Rh(I)
Coordination Features of the PNNPPh Ligand As Com-
pared with Those of the PNNPPy Ligand. The following
conclusion can be deduced from the obtained experimental
results.
Many similarities in the structures of the reaction products of
the carbonyl species C and 7 have been observed, not only for
conventional species such as the dinuclear μ-acetylide com-
plexes (E and 9) but also for unique, tetranuclear μ4-acetylide
cluster compounds (F and 11) and μ4-dicarbide complexes (G
and 12). The present study reveals that the PNNP ligand set
provides a scaffold for such unique structures, which have never
been observed for other ligand systems.
Meanwhile, the following dissimilarities are also noted.
˚
˚
center (Rh1-P1 = 2.194(2) A, Rh2-P2 = 2.241(2) A; Rh1-
(1) Ring size effect. The enlarged six-membered ring in
PNNPPh causes shortening of the metal-metal distance,
which frequently leads to intraunit M-M bond formation
as exemplified by 6.
˚
˚
N1 = 2.143(6) A, Rh2-N2 = 2.226(5) A). The intraunit
Rh-Rh separation (3.5980(8) A) is far beyond the range of
bonding interactions.
˚
Reaction of 7 with diethyl acetylenedicarboxylate, an alkyne
molecule with electron-withdrawing substituents, afforded the
totally different 1:2 adduct 14, which was confirmed by X-ray
crystallography (Figure 5b). Two molecules of the alkyne
oxidatively add across the Rh-Rh linkage to form the bicyclic
structure. In general, alkyne molecules with electron-releasing
(16) Hoffman, D. M.; Hoffmann, R.; Fisel, C. R. J. Am. Chem. Soc.
1982, 104, 3858.
(17) Clemens, J.; Green, M.; Kuo, C. M.; Fritchie, J. C., Jr.; Mague,
T. J.; Stone, F. G. A. Chem. Commun. 1972, 53. Smart, E. L.; Green, M.;
Laguna, A.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1977, 1777.
Jenkins, A. J.; Cowie, M. Organometallics 1992, 11, 2774.

Article
Organometallics, Vol. 29, No. 23, 2010 6501
(2) Charge effects. (i) Complexation of the neutral PNNPPh
ligand with cationic metal species provides more positively
charged species, in which back-donation decreases when com-
pared with the corresponding less positively charged PNNPPy
analogues. The lesser number of CO ligands on the dinuclear
carbonyl species 7 (vs C) should result from decreased back-
donation to CO ligands (i.e., the Rh centers in 7 cannot support
two CO ligands), and the less unsymmetrical μ-η1:η2 coordina-
tion structure in the μ4-dicarbide complex 12 (vs G) arises from
weaker back-donation from the dicationic [(μ-PNNPPh){Rh-
(CO)2}2]2þ moiety. (ii) More positively charged species are more
Brønsted and Lewis acidic. For example, Me3SiCtCH can be
incorporated into both of the (μ-PNNP)Rh2 systems but, in the
case of the PNNPPh system, subsequent desilylation and depro-
tonation leading to the μ4-C2 complex 12 occur spontaneously,
owing to the enhanced electrophilicity at the Si center in the
more Lewis acidic PNNPPh derivative and the increased
Brønsted acidity of the μ4-C2H moiety.
and dried over MgSO4. Evaporating the volatiles and washing
with a mixture of CH2Cl2 (30 mL) and ether (45 mL) gave 1 as a
colorless solid (1.45 g, 2.75 mmol, 51% yield). 1: δH (CDCl3)
8.23-8.18, 7.83-7.78 (2H ꢁ 2, m ꢁ 2, phthalazine), 7.54-7.46
(8H, m, Ph), 7.31-7.28 (12H, m, Ar), 4.10 (4H, s, CH2P); δP
(CDCl3) -18.7. Anal. Calcd for C34H28N2P2: C, 77.36; H, 5.36;
N, 5.32. Found: C, 77.04; H, 5.29; N, 5.21.
(iii) Preparation of Monosubstituted Ligand 3. A 1:1.5 reaction
between LiCH2P(dO)Ph2 and 1,4-dichlorophthalazine as de-
scribed for (i) was quenched just after the temperature of the
mixture reached room temperature. Analogous workup and
subsequent deoxygenation with HSiCl3/NEt3 gave 3 as a color-
less solid (69% yield). 3: δH (CDCl3) 8.31-8.18, 8.00-7.88 (2H
ꢁ 2, m ꢁ 2, Ar), 7.52-7.47 (4H, m, Ph), 7.30 (6H, m, Ph), 4.11
(2H, s, CH2P); δP (CDCl3) -18.2. Ligand 3 was converted to the
Rh adduct [3 Rh(cod)]BF4 by treatment with [Rh(cod)2]BF4 as
3
described for 4a, and the Rh adduct was characterized by X-ray
crystallography (see the Supporting Information).
Preparation of COD Complexes, [(μ-PNNPPh){M(cod)}2]-
(BF4)2 (4). (i) Rhodium Complex 4a (M = Rh). To a CH2Cl2
solution (15 mL) of [Rh(cod)2]BF4 (2.34 g, 5.76 mmol) was
added 2 (1.45 g, 2.75 mmol) dissolved in CH2Cl2 (70 mL) over 1
h. After the mixture was stirred for 1 h at room temperature, the
resultant red-brown solution was evaporated and the obtained
residue was washed with a mixture of acetone (30 mL) and
hexane (40 mL) three times to give 4a (2.68 g, 2.39 mmol, 87%
yield) as an orange powder. 4a: δH (CDCl3) 8.54-8.49,
8.25-8.20 (2H ꢁ 2, m ꢁ 2, phthalazine), 7.63-7.49 (20H, m,
Ph), 5.15 (4H, d, J = 8.5 Hz, CH2P), 4.04 (4H, br, dCH in cod),
(3) Oxidative addition reactions (13 and 14). These are
observed only for the PNNPPh system.
Experimental Section
General Methods. All manipulations were carried out under
an inert atmosphere 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. 1H
and 31P NMR spectra were recorded on a Bruker AC-200
instrument (1H, 200 MHz; 31P, 81 MHz; chemical shifts down-
field from TMS (1H) and H3PO4 (31P)), and resonances and
coupling constants are reported in ppm and in Hz, respectively.
Solvents for NMR measurements containing 0.5% TMS were
dried over molecular sieves, degassed, distilled under reduced
pressure, and stored under Ar. IR and UV-vis-near-IR spectra
were obtained on JASCO FT/IR 5300 and JASCO V-570
spectrometers, respectively. ESI-MS spectra were recorded on
a ThermoQuest Finnigan LCQ Duo mass spectrometer. 1,4-
Dichlorophthalazine18 and [M(cod)2]BF4 (M = Rh, Ir)2a were
prepared according to the published procedures. Other chemi-
cals were purchased and used as received. Details of X-ray
crystallography are included in the Supporting Information.
Ligand Synthesis (1). (i) Preparation of 2. To OdPPh3 (28.3g,
102 mmol) suspended in ether (80 mL) was added an ethereal
solution of MeLi (1.0 M, 100 mL, 100 mol, 2.5 equiv) dropwise at
room temperature, and the resultant mixture was stirred for
2 h to afford a brown solution.5 To the mixture cooled to -78 °C
was added dropwise a THF solution of 1,4-dichlorophthalazine
(4.02 g, 20.2 mmol), and the mixture was stirred overnight. Then the
reaction was quenched with water (500 mL) and the product was
extracted with CH2Cl2 (1.2 L). Evaporation of the extract gave a
yellowish solid, which was washed with toluene (100 mL) and then
ether (50 mL). After drying under reduced pressure 2 was obtained
as a colorless solid (6.78 g, 12.1 mmol, 60% yield). 2: δH (CDCl3)
8.41-8.36 (2H, m, phthalazine), 7.87-7.73 (10H, m, Ar), 7.44-
7.35 (12H, m, Ar), 4.41 (4H, d, J = 14.0 Hz, CH2P); δP (CDCl3)
22.0; FAB-MS m/z 559 (M þ H).
2.48, 1.63 (8H ꢁ 2, br ꢁ 2, CH2 in cod); δP 28.0 (d, JP-Rh =
148.4 Hz); ESI-MS m/z 737 (Mþ - 2 BF4). Anal. Calcd for
C50.75H53.5B2Cl1.5F8N2P2Rh2 (4a 0.75CH2Cl2): C, 51.39; H,
4.55; N, 2.36. Found: C, 51.47; H, 4.67; N, 2.38.
3
(ii) Iridium Complex 4b (M = Ir). Complex 1 (197.2 mg, 0.375
mmol) dissolved in CH2Cl2 (70 mL) was added to a CH2Cl2
solution (7 mL) of [Rh(cod)2]BF4 (376.9 mg, 0.76 mmol) over
1 h. After the mixture was stirred for 1 h at room temperature,
the resultant deep red solution was evaporated. Dissolution of
the obtained residue in hot EtOH (60 °C) followed by cooling to
room temperature gave red crystals, which were collected by
filtration and dried under reduced pressure. 4b (309.0 mg, 0.238
mmol, 63% yield): δH (CDCl3) 9.01-8.96, 8.52-8.48 (2H ꢁ 2,
m ꢁ 2, phthalazine), 7.86 (8H, br, Ph), 7.63-7.59 (12H, m, Ph),
5.73 (4H, d, J = 8.5 Hz, CH2P), 4.02 (4H, br, dCH in cod), 2.26,
1.80 (8H ꢁ 2, br ꢁ 2, CH2 in cod); δP (CDCl3) 24.1; ESI-MS m/z
827 (Mþ - 2 BF4). Anal. Calcd for C51.5H55B2Cl3F8N2P2Ir2
(4a 1.5CH2Cl2): C, 43.31; H, 3.88; N, 1.96. Found: C, 43.02; H,
3
3.78; N, 1.88.
Preparation of the μ-Cl Complex [(μ-PNNPPh){Rh(CO)}2(μ-
Cl)]BF4 (5). CO was bubbled through a MeOH suspension
(10 mL) of 4a (121.4 mg, 0.0990 mmol) and NaCl (33.0 mg,
0.565 mmol) for 1 h. Addition of Et2O (60 mL) gave a yellow
precipitate, to which was added CH2Cl2 (15 mL) and water
(15 mL). The organic layer was collected, dried over MgSO4,
and evaporated to afford 5 (71.7 mg, 0.0718 mmol, 73% yield) as
a yellow powder. 5: δH (CDCl3) 8.52-8.48, 8.01-7.98 (2H ꢁ 2,
m ꢁ 2, phthalazine), 7.88-7.78 (8H, m, Ph), 7.50-7.46 (12H,
m, Ph), 4.82 (4H, d, J = 11.3 Hz, CH2P); δP (CDCl3) 57.1 (d,
JP-Rh = 168.3 Hz); IR (νCO) 2022 cm-1 (KBr). Anal. Calcd
(ii) Preparation of 1. Addition of NEt3 (5.1 g, 50 mmol) and
HSiCl3 (13.4 g, 99 mmol) to 2 (3.01 g, 5.39 mmol) suspended
in toluene (300 mL) caused a rapid color change to yellow.
Refluxing the mixture caused a change from a yellow suspension
to a yellow solution. The mixture was cooled in an ice-water
bath, and water (250 mL) and 20% aqueous NaOH (200 mL)
were added. The product was extracted with CH2Cl2 (150 mL)
for C36.25H28.5BCl1.5F4NPRh2 (5 0.25CH2Cl2): C, 46.72; H, 3.08;
3
N, 3.01. Found: C, 46.73; H, 3.08; N, 3.01. Complex 5 was also
obtained by carbonylation of 4a in CH2Cl2, as described in
the text.
Preparation of the Tetrarhodium Complex [(μ-PNNPPh)2{Rh-
(CO)}4](BF4)2 (6). A THF suspension (4 mL) of 4a (51.8 mg,
0.0462 mmol) cooled to -78 °C was bubbled with CO for
30 min. After addition of HSiEt3 (3.2 mg, 0.028 mmol) via a
microsyringe the mixture was warmed to room temperature and
further stirred for 1 h. Addition of hexane to the resultant black
mixture gave black precipitates (6), which were collected by
(18) Amberg, W.; Bennani, Y. L.; Chada, R. K.; Crispino, G. A.;
Davis, W. D.; Hartung, J.; Jeong, K.-S.; Ogino, Y.; Shibata, T.; Sharpless,
K. B. J. Org. Chem. 1993, 58, 844.

6502 Organometallics, Vol. 29, No. 23, 2010
Yamaguchi et al.
filtration and dried under reduced pressure. 6 (33.7 mg, 0.020
mmol, 88% yield): δH (acetone-d6) 8.88-8.83, 8.41-8.36 (4H ꢁ
2, m ꢁ 2, phthalazine), 7.82-7.44 (40H, m, Ph), 5.21 (8H, d, J =
9.8 Hz, CH2P); δP (acetone-d6) 49.6 (dq-like, J = 73 and 6 Hz);9
IR (νCO) 1924 cm-1 (KBr), 1936 cm-1 (CH2Cl2); ESI-MS m/z
1663 (Mþ - BF4), 1576 (Mþ - 2 BF4). Anal. Calcd for C73.5H58-
Preparation of Tetrarhodium Monoacetylide Cluster Com-
pound 11. CO was bubbled through a THF suspension (4 mL)
of a mixture of 9 (26.3 mg, 0.0266 mmol) and 4a (29.8 mg, 0.0266
mmol) cooled to -78 °C for 1 h. Then the mixture was wormed
to room temperature and further stirred for 1.5 h to give a black
precipitate, which was collected and dried under reduced pres-
sure. 11 (43.5 mg, 0.0223 mmol, 84% yield):19a δH (CD2Cl2)
8.40-8.35 (2H, m, phthalazine), 8.23 (2H, d, J = 8.0 Hz, tol),
8.08-8.04 (4H, m, phthalazine), 7.63-7.30 (42H, m, Ph and
tol), 7.78 (2H, d, J = 8.0 Hz, tol), 4.85 (8H, d, JHP = 11.2 Hz,
B2Cl2F8N4P4Rh4 (6 CH2Cl2): C, 47.77; H, 3.19; N, 3.05.
3
Found: C, 47.48; H, 3.39; N, 3.08. Complex 6 was also obtained
by carbonylation of 4a in non-halogenated solvents such as
THF and acetone, as described in the text.
Carbonylation of 4a in THF at -78 °C: Formation of [(μ-
PNNPPh){(Rh(CO))}2](BF4)2 (7). CO was bubbled through a
THF suspension (4 mL) of 4a (51.7 mg, 0.0461 mmol) cooled to
-78 °C for 30 min. Addition of hexane to the resultant black
mixture at -78 °C gave a yellow powder (7), which was collected
by filtration and dried under reduced pressure. 7 (32.5 mg,
0.0338 mmol, 73% yield):19b δH (CD3NO2) 8.65-8.50, 8.45-
8.41 (2H ꢁ 2, m ꢁ 2, phthalazine), 7.90-7.79 (8H, m, Ph),
7.72-7.60 (12H, m, Ph), 5.08 (4H, d, J = 10.4 Hz, CH2P); δP
(CD3NO2) 48.4 (m);9 IR (νCO) 2008 cm-1 (KBr), 2098, 2078,
2045 cm-1 (CDCl3 under CO).
CH2P), 2.55 (3H, s, Me in tol); δP (CD2Cl2) 58.6 (d, JPRh =
160.0 Hz); IR (νCO) 2005 cm-1 (KBr); ESI-MS m/z 903 (Mþ - 2
BF4 - 2 CO).
Preparation of Tetrarhodium Dicarbide Cluster Compound 12.
A THF solution of 7 (5 mL) was generated from 5a (96.5 mg,
0.0860 mmol) at -78 °C as described for 9. After addition of
Me3SiCtCH (50.7 mg, 0.516 mmol) the mixture was warmed to
room temperature and stirred for 1.5 h. The resultant black
precipitate 12 was collected and washed with acetone (3 mL). 12
(42.7 mg, 0.0241 mmol, 60% yield): δH (CD3CN) 8.36-8.29
(8H, m, phthalazine), 7.63-7.29 (40H, m, Ph and tol), 4.55 (8H,
d, JHP = 10.6 Hz, CH2P); δP (CD3CN) 57.2 (d, JPRh = 144.1
Hz); IR (νCO) 2006 cm-1 (KBr); ESI-MS: m/z 1687 (Mþ - BF4),
801 (Mþ - 2 BF4; dication). Anal. Calcd for C72H56B2F8N4-
O4P4Rh4 (12): C, 49.41; H, 3.22; N, 3.20. Found: C, 49.70; H,
3.47; N, 3.31.
Reaction of 7 with Di-p-tolylacetylene To Give 13. A THF
solution of 7 (5 mL) was generated from 5a (96.6 mg, 0.0861
mmol) at -78 °C as described for 9. To the resultant solution
was added di-p-tolylacetylene (53.3 mg, 0.258 mmol) dissolved
in acetone (2 mL), and the mixture was gradually warmed to
room temperature and stirred for 2 h to give a dark brown
solution. Addition of hexane (30 mL) formed a precipitate,
which was collected and dried under reduced pressure. Recrys-
tallization from acetone (3 mL)-Et2O (1 mL) gave 13 as a
yellow powder (34.0 mg, 0.0151 mmol, 35% yield). 13:19a δH
(CD3CN) 8.70-8.66, 8.54-8.51, 8.36-8.21, 7.83-7.71, 7.53-
7.41, 7.05-6.97 (aromatic), 6.65 (8H, d, J = 7.9 Hz, tol), 5.15-
4.75 (8H, m, CH2P), 2.26, 2.25 (3H ꢁ 2, s ꢁ 2, Me in tol); δP
(CD3CN) 53.5 (dd, 1JPRh = 146.2 Hz, 3JPRh = 3.2 Hz), 36.4 (dd,
1JPRh = 157.3 Hz, 3JPRh = 3.2 Hz); IR (νCO) 1992, 1638 cm-1
(KBr); ESI-MS m/z 1039 (Mþ - 2 BF4; dication).
Carbonylation of [(μ-PNNPPh){(Ir(cod))}2](BF4)2 (4b) To
Give [(μ-PNNPPh)Ir2(CO)5](BF4)2 (8). CO was bubbled through
an acetone solution of 4a (29.8 mg, 0.0229 mmol) for 1 h. The
solution immediately changed from red to yellow. After 1.5 h Et2O
(17 mL) was added under a CO atmosphere to precipitate the
product, which was collected by filtration and dried under reduced
pressure. 8 (22.3 mg, 0.0181 mmol, 79% yield): δH (acetone-d6)
8.87-8.83, 8.47-8.42 (2H ꢁ 2, m ꢁ 2, phthalazine), 8.10-7.79
(8H, m, Ph), 7.72-7.50 (12H, m, Ph), 5.45 (4H, br, CH2P); δP
(acetone-d6) 23.3 (m);9 IR (νCO) 2085, 2023, 1751 cm-1 (KBr);ESI-
MS m/z 995 (Mþ - 2 BF4), 967 (Mþ - 2 BF4 - CO). Anal. Calcd
for C39H28B2F4Ir2N2P2 (8): C, 38.25; H, 2.30; N, 2.29. Found: C,
38.38; H, 2.10; N, 2.50.
Preparation of Dirhodium μ-Acetylide Complex 9. CO was
bubbled through a THF suspension (10 mL) of 4a (200.5 mg,
0.179 mmol) cooled to -78 °C for 30 min. To the resultant
solution of the carbonyl species 7 was added water (3.2 mg, 0.180
mmol) and p-tol-CtCH (64.4 mg, 0.554 mmol), and then the
mixture was warmed to room temperature. The solution color
darkened. Stirring the mixture for 1 h caused precipitation of an
orange solid, which was collected and washed with THF (2 mL ꢁ
3) to afford 9 after drying under reduced pressure. 9 (110.7 mg,
0.102 mmol, 57%): δH (acetone-d6) 8.80-8.75, 8.39-8.34 (2H ꢁ
2, m ꢁ 2, phthalazine), 7.97-7.87 (8H, m, Ph), 7.78 (2H, d, J =
8.0 Hz, tol), 7.59-7.55 (12H, m, Ph), 7.22 (2H, d, J = 8.0 Hz,
Reaction of 7 with Diethyl Acetylenedicarboxylate To Give 14.
The reaction was carried out as described for 13 using 5a (72.0
mg, 0.0539 mmol) and diethyl acetylenedicarboxylate (96.1 mg,
0.565 mmol). After the mixture was stirred for 2 h, a yellow
precipitate appeared, were collected, which was washed with
THF (2 mL) and dried under reduced pressure. 14 (yellow powder,
72.0 mg, 0.0539 mmol, 58% yield):19a δH (CD3CN) 8.67-8.62,
8.45-8.40, 8.36-8.27, 7.90-7.87, 7.44-7.08 (aromatic), 5.40 (2H,
tol), 5.26 (4H, d, JHP = 10.6 Hz, CH2P), 2.36 (3H, s, Me in tol);
1
δP (acetone-d6) 59.6 (1JPRh = 139.0 Hz, JRhRh = 2.5 Hz,
0
JPRh = 0.8 Hz); IR (νCO) 2003 cm-1 (KBr); ESI-MS m/z 903
2
9
0
(Mþ - 2 BF4), 967 (Mþ - 2 BF4 - CO). Anal. Calcd for C46H37-
BCl2F4N2O2P2Rh2 (9 CH2Cl2): C, 51.77; H, 3.85; N, 2.67.
Found: C, 51.38; H, 3.47; N, 2.61.
dd, JHH = 18.5 Hz, JHP = 12.5 Hz, CH2P), 5.09 (2H, dd, JHH =
3
18.5 Hz, JHP = 5.5 Hz, CH2P), 4.08-3.92 (4H, m, Et), 3.74-3.64,
3.43-3.31 (2H ꢁ 2, m ꢁ 2, Et), 1.21-1.13, 0.87-0.80 (6H ꢁ 2, Et);
δP (CD3CN) 22.1 (d, J = 73.7 Hz); IR (νCO) 2085, 1677 cm-1
(KBr); ESI-MS m/z 1145 (Mþ - 2 BF4; dication).
Formation of Tetrarhodium Diacetylide Cluster Compound 10.
When an acetone solution of 9 was stirred under an N2 atmo-
sphere for 24 h at room temperature, the solution darkened.
Addition of hexane caused precipitation of 10 (68% yield),
which was collected and dried under reduced pressure. 10:19a
δH (CD3NO2) 8.63-8.22, 7.97-7.12 (m, aromatic), 6.05, 5.37
(2H ꢁ 2, d ꢁ 2, J = 8.2 Hz, C6H4 in p-tol), 1.76 (3H, s, Me in
tol).20
Acknowledgment. We are grateful to the Ministry of
Education, Culture, Sports, Science and Technology of
the Japanese Government and the Japan Society for
Promotion of Science and Technology for financial sup-
port of this research (Grants-in-Aid for Scientific Re-
search Nos. 18065009, 20044007, and 22350026).
(19) (a) An analytically pure sample could not be obtained despite
several attempts, presumably because of tarry impurities. (b) An an-
alytically pure sample could not be obtained because of the instability.
(20) A 31P NMR signal and the 1H NMR signals for the CH2P part
could not be located, presumably owing to some fluxional process. VT
analysis was hindered by the lower solubility of 10 in organic solvents
and the higher melting point of CD3NO2 (Figure S12, Supporting
Information).
Supporting Information Available: Text, tables, figures, and
CIF files giving crystallographic data and additional character-
ization data. This material is available free of charge via the
Internet at http://pubs.acs.org.