Neutralization of palladium hydroxides, [L2Pd2(R)2(μ-OH)2], by M-H acids, [CpM(CO)3H] (M = W, Mo, Cr)

Article abstract of DOI:10.1021/om9605138

The reaction of [L₂Pd₂(Ph)₂(μ-OH)₂] (L = Ph₃P, Cy₃P) with an equimolar amount of [CpM-(CO)₃H] (M = W, Mo, Cr) afforded the organometallic hydroxo clusters [L₂Pd₂(Ph)₂(μ-OH)-(μ-CO) ₂(μ₃-CO)MCp) (1-3) in high yield. These reactions can be regarded as the neutralization of an acidic transition-metal hydride by a basic transition-metal hydroxide. The structure of the Pd₂Cr cluster 3 was established by a single-crystal X-ray diffraction study. The trinuclear hydroxo clusters are stable in the solid state but slowly decompose in solution, the decomposition path being strongly dependent on the nature of M. Facile and selective decomposition of 1 (M = W) resulted in the formation of [(Ph₃P)₂Pd₂(Ph)₂(μ-OH) ₂], biphenyl, and the tetranuclear Pd₂W₂ cluster 4. Similar tetranuclear clusters 4-8 were obtained in high yield when the palladium hydroxo dimers were neutralized with excess [CpM(CO)₃H] or [Cp*W(CO)₃H]. However, these reactions proceed by a different pathway involving Ph/H exchange processes, and resulted in the formation of benzene and [CpM(CO)₃Ph] or [Cp*W-(CO)₃Ph], respectively. Labeling experiments suggested that H atoms of the hydrido and hydroxo ligands underwent an exchange which was faster than the neutralization and the concomitant formation of the metal-metal bond. Infrared and NMR studies show that the structures of the trinuclear hydroxo clusters were more rigid than those of the tetranuclear species. Tetranuclear systems containing three different metals, Pd₂WMo (9) and Pd₂WCr (10), were prepared and characterized.

Full text of DOI:10.1021/om9605138

Organometallics 1997, 16, 97-106
97
“Neu tr a liza tion ” of P a lla d iu m Hyd r oxid es,
[L2P d 2(R)2(µ-OH)2], by M-H Acid s, [Cp M(CO)3H] (M ) W,
Mo, Cr )
Vladimir F. Kuznetsov,† Corinne Bensimon,† Glenn A. Facey,†
Vladimir V. Grushin,†,‡ and Howard Alper*,†
Departments of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario,
Canada K1N 6N5, and Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5
Received J une 26, 1996X
The reaction of [L2Pd2(Ph)2(µ-OH)2] (L ) Ph3P, Cy3P) with an equimolar amount of [CpM-
(CO)3H] (M ) W, Mo, Cr) afforded the organometallic hydroxo clusters [L2Pd2(Ph)2(µ-OH)-
(µ-CO)2(µ3-CO)MCp) (1-3) in high yield. These reactions can be regarded as the “neutral-
ization” of an acidic transition-metal hydride by a basic transition-metal hydroxide. The
structure of the Pd2Cr cluster 3 was established by a single-crystal X-ray diffraction study.
The trinuclear hydroxo clusters are stable in the solid state but slowly decompose in solution,
the decomposition path being strongly dependent on the nature of M. Facile and selective
decomposition of 1 (M ) W) resulted in the formation of [(Ph3P)2Pd2(Ph)2(µ-OH)2], biphenyl,
and the tetranuclear Pd2W2 cluster 4. Similar tetranuclear clusters 4-8 were obtained in
high yield when the palladium hydroxo dimers were neutralized with excess [CpM(CO)3H]
or [Cp*W(CO)3H]. However, these reactions proceed by a different pathway involving Ph/H
exchange processes, and resulted in the formation of benzene and [CpM(CO)3Ph] or [Cp*W-
(CO)3Ph], respectively. Labeling experiments suggested that H atoms of the hydrido and
hydroxo ligands underwent an exchange which was faster than the neutralization and the
concomitant formation of the metal-metal bond. Infrared and NMR studies show that the
structures of the trinuclear hydroxo clusters were more rigid than those of the tetranuclear
species. Tetranuclear systems containing three different metals, Pd2WMo (9) and Pd2WCr
(10), were prepared and characterized.
In tr od u ction
The Brønsted acidity of some transition-metal hy-
drides has been established beyond any doubt and is
now well-documented.1 One of the most exciting ap-
plications of acidic transition-metal hydrides is their
“neutralization” with hydroxo complexes of transition
metals, resulting in metal-metal bond formation. To
our knowledge, this approach had not been used for the
synthesis of heterobimetallic and polymetallic com-
plexes.2,3 We have recently reported4 that treatment
of the rhodium hydroxo dimer [(Ph3P)4Rh2(µ-OH)2] with
acidic5 [CpM(CO)3H] (M ) Cr, Mo, W) results in the
(1)
plexes as a result of neutralization of organopalladium
binuclear hydroxo complexes by [CpM(CO)3H].
smooth formation of [CpM(CO)(µ-CO)2Rh(PPh3)2] and
water, according to eq 1. In this paper we report the
formation of tri- and tetranuclear heterometallic com-
Syn th esis a n d Ch a r a cter iza tion of Tr in u clea r
P d 2M (M ) Cr , Mo, W) Hyd r oxo Com p lexes 1-3:
X-r a y Str u ctu r e of 3
† University of Ottawa.
‡ Wilfrid Laurier University.
X Abstract published in Advance ACS Abstracts, December 1, 1996.
(1) (a) Pearson, R. G. Chem. Rev. 1985, 85, 41. (b) Kristja´nsdo´ttir,
S. S.; Norton, J . R. Acidity of Hydrido Transition Metal Complexes in
Solution. In Transition Metal Hydrides; Dedieu, A., Ed.; VCH: New
York, 1991; p 309. (c) J essop, P. G.; Morris, R. H. Coord. Chem. Rev.
1992, 121, 155. (d) Grushin, V. V. Acc. Chem. Res. 1993, 26, 279.
(2) Cotton, F. A.; Walton, R. A. Multiple Bonds Between Metal Atoms,
2nd ed.; Clarendon Press: Oxford, U.K., 1993.
Treatment of the hydroxo-bridged Pd dimers [L2Pd2-
Ph2(µ-OH)2] (L ) Ph3P, Cy3P)6,7 with 1 molar equiv of
the acidic hydrides [CpM(CO)3H] (M ) W, Mo, Cr)
affords the corresponding trinuclear monohydroxo com-
plexes by neutralization of one of the two OH ligands
(eq 2). These trinuclear complexes were isolated in high
yield as yellow (M ) W, Mo) or orange (M ) Cr)
crystalline materials. Not only do complexes 1-3
belong to the still very limited group of neutral orga-
(3) (a) The formation of heterobimetallic complexes with concomitant
loss of alcohol has been reported in the reactions of [CpW(CO)3H] with
[L2Re(CO)3(OMe)]3b and of [HMn(CO)5] with [(i-PrO)4Ti].3c (b) Simp-
son, R. D.; Bergman, R. G. Organometallic 1992, 11, 3980. (c) Belyi,
A. A.; Kuznetsov, V. F.; Blumenfeld, A. L. Russ. Chem. Bull. 1993, 42,
130 (English translation of Izv. Acad. Nauk, Ser. Khim.-Moskva).
(4) Grushin, V. V.; Kuznetsov, V. F.; Bensimon, C.; Alper, H.
Organometallics 1995, 14, 3927.
(5) For [CpM(CO)3H] (where M ) Cr, Mo, W), pKa(MeCN, 25 °C) )
13.3(1), 13.9(1), and 16.1(1), respectively. See: Moore, E. J .; Sullivan,
J . M.; Norton, J . R. J . Am. Chem. Soc. 1986, 108, 2257.
(6) Grushin, V. V.; Alper, H. Organometallics 1993, 12, 1890.
(7) In solution, [(Ph3P)2Pd2Ph2(µ-OH)2] and [(Cy3P)2Pd2Ph2(µ-OH)2]
exist as 4:1 and 6:1 mixtures of trans and cis isomers, respectively.6
S0276-7333(96)00513-4 CCC: $14.00 © 1997 American Chemical Society

98 Organometallics, Vol. 16, No. 1, 1997
Kuznetsov et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta for
[(P h 3P )2P d (µ-OH)(µ-CO)2(µ3-CO)Cr Cp ]‚MeOH
formula
fw
C57H46CrO5P2Pd2
1137.72
cryst shape
cryst dimens
cryst syst
lattice params
plate
0.3 × 0.2 × 0.1
monoclinic
a ) 32.9701(4) Å
b ) 10.6761(1) Å
c ) 28.9941(2) Å
â ) 108.405(1)°
C2/c
space group
Z
V
dcalcd
T, K
8
9683.71(16) Å3
1.561 g/cm3
123
(2)
radiation (λ)
Mo KR1 (0.709 30 Å)
µ
1.03 mm-1
R (Rw)a
6.1% (7.8%)
a
R ) ∑(Fo - Fc)/∑(Fo); Rw ) [∑(w(Fo - Fc)2)/∑(wFo2)]1/2
.
nopalladium hydroxo comnplexes6,8-11 but they also
represent the first examples of heteropolymetallic spe-
cies containing a Pd-OH unit. These compounds can
be regarded as the simplest soluble models for hetero-
geneous hydroxopalladium catalysts, e.g. Pearlman’s
catalyst (palladium hydroxide on carbon),12 which pos-
sesses interesting catalytic properties in some pro-
cesses.13 Pearlman’s catalyst has proven successful
even when other Pd/C systems exhibit no catalytic
activity. It is also worth noting that soluble hydroxo
complexes of Pd are catalytically active in various
processes,14 including the water-gas shift reaction15 and
the hydroxycarbonylation of organic halides.6,16
It is remarkable that complexes 1-3 are stable,
despite the fact that their palladium centers bear OH,
σ-Ph, and CO ligands in the same coordination sphere.
To our knowledge, no Pd complexes have been described
in the literature containing a set of OH, CO, and σ-aryl
(alkyl) ligands situated around one Pd center.17 In fact,
σ-alkyls (aryls) and especially hydroxo ligands on Pd are
prone to migratory insertion reactions with carbonyls
F igu r e 1. ORTEP drawing of complex 3 with adopted
numbering scheme. Hydrogen atoms (except for O-H) are
omitted for clarity.
coordinated to the metal.14,18-22 The striking stability
of 1-3 may be due to their rigidity, which prevents
these compounds from adopting the conformations
required for migratory insertion. Perhaps more impor-
tant is that the OH and Ph ligands are coordinated
entirely to the Pd centers, whereas the semibridging
carbonyls are bound primarily to Cr, Mo, and W (see
below). Therefore, migratory insertion in such systems
would, in fact, require ligand transfer from one metal
to a carbonyl group on another metal, which is unlikely.
Complexes 1-3 were characterized by elemental
1
analysis, IR spectra, and H, 13C, and 31P NMR spectra.
In addition, the structure of 3 (methanol solvate) was
determined by single-crystal X-ray diffraction. Crystal-
lographic data and the structure of 3‚MeOH are pre-
sented in Table 1 and Figure 1, respectively. Selected
bond distances and bond angles are given in Table 2.
(8) Gilje, J . W.; Roesky, H. W. Chem. Rev. 1994, 94, 895.
(9) (a) Lo´pez, G.; Ruiz, J .; Garcia, G.; Vicente, C.; Marti, J . M.;
Santana, M. D. J . Organomet. Chem. 1990, 393, C53. (b) Ruiz, J .;
Vicente, C.; Marti, J . M.; Cutillas, N.; Garcia, G.; Lo´pez, G. J .
Organomet. Chem. 1993, 460, 241.
(10) Ruiz, J .; Cutillas, N.; Torregrosa, J .; Garcia, G.; Lo´pez, G.;
Chaloner, P. A.; Hitchcock, P. B.; Harrison, R. M. J . Chem. Soc., Dalton
Trans. 1994, 2353.
The molecule of 3 contains an open triangular Pd-
Cr-Pd fragment. The Pd‚‚‚Pd separation (3.381(6) Å)
(11) Grushin, V. V.; Bensimon, C.; Alper, H. Organometallics 1995,
14, 3295.
(12) Pearlman, W. M. Tetrahedron Lett. 1967, 17, 1663.
(13) Fieser, M. Fieser and Fiesers Reagents for Organic Synthesis;
Wiley: New York, 1992; Vol. 16, p 269.
(18) Maitlis, P. M. The Organic Chemistry of Palladium; Academic
Press: New York, 1971; Vols. 1 and 2.
(19) Tsuji, J . Organic Synthesis with Palladium Compounds;
Springer-Verlag: New York, 1980.
(20) Heck, R. F. Palladium Reagents in Organic Synthesis; Academic
Press: New York, 1985.
(21) Colquhoun, H. M.; Thompson, D. J .; Twigg, M. V. Carbonyla-
tion: Direct Synthesis of Carbonyl Compounds; Plenum Press: New
York, 1991.
(14) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163.
(15) Kullberg, M. L.; Kubiak, C. P. C1 Mol. Chem. 1984, 1, 171.
(16) Grushin, V. V.; Alper, H. J . Am. Chem. Soc. 1995, 117, 4305.
(17) (a) Palladium complexes containing a set of both CO and OH
(e.g., [(µ-dmpm)2Pd2(OH)2(µ-CO)]15,17b or both CO and σ-aryl ligands
(e.g., cis-[PdCl2(CO)(Ar)])17c) in the inner coordination sphere are very
rare.14 (b) Kullberg, M. L.; Kubiak, C. P. Organometallics 1984, 3,
632. (c) Vicente, J .; Arcas, A.; Borrachero, M. V.; Tiripicchio, A.;
Camellini, M. T. Organometallics 1991, 10, 3873.
(22) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
Wiley: New York, 1992.

“Neutralization” of Palladium Hydroxides
Organometallics, Vol. 16, No. 1, 1997 99
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for
[(P h 3P )2P d 2(µ-OH)(µ-OH)2(µ3-CO)Cr Cp ]‚MeOH
Pd(1)-Cr
2.7523(15)
2.7604(15)
2.3035(23)
2.125(6)
2.324(8)
2.305(9)
Pd(1)-C(5)
C(2)-O(3)
C(3)-O(4)
Cr-C(2)
1.998(9)
1.182(10)
1.184(10)
1.846(9)
1.889(9)
1.842(5)
Pd(2)-Cr
Pd(1)-P(1)
Pd(1)-O(1)
Pd(1)-C(3)
Pd(1)-C(2)
Cr-C(3)
Cr-centroid Cp
C(3)-Pd(1)-O(1)
79.8(3)
Pd(1)-Cr-C(3)
C(2)-Cr-C(1)
C(2)-Cr-C(3)
O(2)-C(1)-Cr
56.5(3)
79.7(4)
112.4(4)
164.1(8)
Pd(1)-O(1)-Pd(2) 105.4(3)
Pd(1)-C(3)-Pd(2)
Cr-Pd(1)-P(1)
Cr-Pd(1)-C(5)
O(1)-Pd(1)-C(5)
P(1)-Pd(1)-O(1)
P(1)-Pd(1)-C(5)
Pd(1)-Cr-Pd(2)
93.3(3)
178.93(7)
92.28(24) O(2)-C(1)-Pd(2) 113.0(6)
174.7(3)
Pd(1)-C(2)-Cr
82.3(3)
161.6(7)
97.54(17) O(4)-C(3)-Cr
87.74(25) O(4)-C(3)-Pd(1) 110.7(6)
75.68(4) Pd(1)-C(3)-Cr 80.9(3)
Ta ble 3. Bon d Dista n ces (Å) a n d An gles (d eg) for
th e P d 2M(µ-CO)2(µ3-CO) Un its in 3 a n d Releva n t
Clu ster s (See Text)
bond distance/angle
Pd2Cr23
Pd2Mo24
3
Pd-C (µ-CO)
2.30(1)
2.34(1)
2.34(1)
2.26(1)
1.84(1)
1.92(1)
114.7(6)
117.9(6)
118.1(8)
117.7(6)
165.7(7)
159.8(7)
156.6(5)
2.304(7)
2.243(6)
2.311(8)
2.321(7)
NAa
2.305(9)
sharper, as compared to the analogous bands in the IR
spectra of 4-6, measured under similar conditions. This
observation indicates structural rigidity of the trinuclear
clusters, which is supported by the NMR studies de-
scribed below.
Pd-C (µ3-CO)
2.324(8)
Cr-C (µ-CO)
Cr-C (µ3-CO)
Pd-C-O (µ-CO)
1.846(9)
1.889(9)
113.0(6)
NA
116.7(5)
116.8(7)
118.3(5)
119.2(5)
NA
1
The H NMR spectra of 1-3, while not informative
Pd-C-O (µ3-CO)
Cr-C-O (µ-CO)
Cr-C-O (µ3-CO)
110.7(6)
164.1(8)
161.6(7)
in the aromatic region, exhibit sharp, well-resolved
triplets at -3.7 to -4.0 ppm (J H-P ) ca. 2 Hz) due to
the OH ligand trans to the phosphines. Since the Cp
1
protons occur as sharp singlets in the H NMR spectra
NA
(CDCl3, recorded from -25 to +20 °C), the rotation of
the cyclopentadienyl rings across the M-Cp axis in the
trinuclear hydroxides must have a low activation bar-
rier.
a
NA ) not applicable.
is much longer than the sum of the two covalent radii
(2.98 Å), suggesting that there is no Pd-Pd bond in the
complex. The four-membered Pd(1)-O(1)-Pd(2)-C(3)
metallacycle is slightly puckered (the torsion angles lie
in the range of 9.5-10.8(3)°), and it assumes a dihedral
angle of 49.25(22)° with the Pd2Cr frame. The two
phosphines are syn, the Pd-P bonds are collinear with
the corresponding Pd-Cr bond. The two µ-carbonyls
are situated above and the µ3-carbonyl is located below
the CrPd2 plane in a manner analogous to that found
in Braunstein’s23 tetranuclear Pd2M2 (M ) W, Mo, Cr;
see below) and Werner’s24 trinuclear Pd2Mo clusters. As
can be seen from Table 3, the metal-carbonyl cores are
structurally similar in [(Et3P)2Pd2Cp2Cr2(µ-CO)4(µ3-
CO)2],23 [(i-Pr3P)2Pd2Mo(µ-CO)2(µ3-CO)Cp2],24 and 3.
This indicates similar bonding for the semibridging and
semi-triply-bridging µ- and µ3-carbonyls25 to the metals
in all three complexes. However, from our IR and NMR
studies (see below) it is clear that the metal-carbonyl
units in 1-3 are remarkably rigid, whereas that in
Braunstein’s Pd2Cr2 cluster was found to be fluxional.23
The solid-state IR carbonyl bands for 1-3 are very
similar in shape, frequency, and intensity to those of
the tetranuclear complexes 4-6.23 This is in line with
the X-ray structural data, which demonstrate that the
[MPd2(CO)3] frameworks in 1-6 are similar in struc-
ture. However, the carbonyl bands in 1-3 are obviously
Narrow singlet resonances at 23.4, 18.5, and 18.0 ppm
were observed in the 31P NMR spectra of 1, 2, and 3,
respectively. The symmetry of complexes 1-3 dictates
that the two phosphorus atoms be chemically equiva-
lent. Although these atoms are magnetically non-
equivalent, singlet resonances were observed in the 31
P
NMR spectra of 1-3. This situation makes it impossible
to measure J P-P in the 31P NMR spectrum. However,
in certain instances, this parameter can be measured
indirectly via the 13C NMR spectrum, where 31P-31P
coupling can lead to second-order effects. Such an
example is the Pd2Cr complex 3, where the 13C NMR
spectrum has second-order properties in both the car-
bonyl and aromatic regions.
The carbonyl region of the 13C spectrum of 3 consists
of two signals in a 2:1 intensity ratio. The downfield
signal centered at 244.6 ppm is due to the two chemi-
cally equivalent µ-carbonyl groups bridging the Pd and
Cr centers. It is a second-order pattern of the AXX′
type. The pattern can be simulated26 with the following
parameters: δX ) δX′, J A-X ) (19 Hz, J A-X′ ) -5 Hz,
and |J X-X′| ) 5 Hz. The relative signs of the coupling
constants between the carbon and each magnetically
nonequivalent phosphorus must be different in order to
reproduce the experimental spectrum (see Figure 2).
The upfield carbonyl resonance centered at 243.2 ppm
appears as a first-order triplet (J C-P ) 12.3 Hz). The
ortho and meta carbons of the triphenylphosphine
(23) Bender, R.; Braunstein, P.; J ud, J .-M.; Dusausoy, Y. Inorg.
Chem. 1983, 22, 3394.
(24) Werner, H.; Thometzek, P.; Kru¨ger, C.; Kraus, H.-J . Chem. Ber.
1986, 119, 2777.
(25) Colton, R.; McCormic, M. J . Coord. Chem. Rev. 1980, 31, 1.
(26) The PC-based program DSYM-PC by S. Goudetsidis and G.
Ha¨gele was used for the simulation.

100 Organometallics, Vol. 16, No. 1, 1997
Kuznetsov et al.
decomposition and obtain a well-resolved pattern in the
carbonyl region. It was noticed that, at -25 °C, both
ortho and meta carbons of the σ-phenyls were magneti-
cally nonequivalent within each pair, probably because
of the hindered rotation across the Pd-Ph bond. More-
over, the ortho carbon resonances were noticeably
broadened. At ambient temperature, this nonequiva-
1
lence vanished for 1-3 but was still observed in the H
and 13C NMR spectra of the tricyclohexylphosphine
complex 1a , due to the bulkiness of Cy3P.
Decom p osition of 1-3 in Solu tion
In the solid state, complexes 2 and 3 can be stored in
air for months. Although the tungsten counterpart 1
is less stable and should be kept under nitrogen in a
freezer, it can be handled in air for hours, without any
sign of decomposition. In solution, however, the hydroxo
clusters decompose even in the absence of air, with their
stability decreasing in the order 3 (Cr) > 2 (Mo) > 1
(W). At ambient temperature, the tungsten-palladium
hydroxide 1 decomposes completely within ca. 20 h in
benzene or toluene, to give exclusively the tetranuclear
complex 4, the original binuclear organopalladium di-
hydroxide [(Ph3P)2Pd2Ph2(µ-OH)2], and biphenyl, all
being formed in quantitative yield. The absence of
benzene and bibenzyl among the decomposition prod-
ucts, when the reaction is run in toluene, points to a
nonradical mechanism for this process.27 Perhaps, the
decomposition of 1 involves disproportionation, followed
by reductive elimination of biphenyl (Scheme 1). Ex-
amples of binuclear reductive elimination from Pd
complexes have been reported previously.28 Usually,
these processes involve migration of one of the two
groups from one metal center to the other, which
eventually leads to the reductive elimination from one
metal. The intermediate shown in Scheme 1 might
exhibit similar behavior, provided the carbonyl ligands
would serve as a channel for the transfer of the Ph
ligands from one Pd to the other via a series of
migratory insertion-deinsertion processes. Considering
the steric strain and coordinative saturation of the
intermediate, the transfer of a phenyl group and the
reductive elimination of the Ph2 could be facile enough
to prevent an observation of the intermediate by NMR.
The decomposition of 1 is convenient to monitor by
31P NMR spectroscopy, by following the gradual disap-
pearance of the resonance due to 1 (23.4 ppm) and the
growth of signals for 4 (21.0 ppm)23 and [(Ph3P)2Pd2-
Ph2(µ-OH)2] (33.9 and 33.2 ppm due to the trans and
cis isomers, respectively).6,7
F igu r e 2. 13C{1H} NMR of 3 (carbonyl region): (a, bottom)
experimental spectrum of 3 at -20 °C in CDCl3; (b, middle)
simulated spectrum with J C-P1 ) -19 Hz, J C-P2 ) 5 Hz,
and J P1-P2 ) 5 Hz; (c, top) simulated spectrum with J C-P1
) 19 Hz, J C-P2 ) 5 Hz, and J P1-P2 ) 5 Hz.
ligands are also second-order patterns, consistent with
|J P-P| ) 5 Hz. The 13C NMR carbonyl regions of
complexes 1 and 2 appear to be first order, suggesting
that the 31P-31P coupling is much weaker in these
compounds. The ortho and meta carbon signals of the
PPh3 ligands show only very small second-order effects.
From the NMR data it is clear that there is no positional
exchange between the carbonyl ligands in 1-3. In
contrast, carbonyls in the closely related tetranuclear
clusters 4-6 undergo fast (on the NMR time scale)
exchange even at -90 °C.23 Both the IR (see above) and
NMR studies point to the fact that the trinuclear
hydroxo clusters 1-3 possess considerably more rigid
structures than Braunstein’s tetranuclear complexes
4-6. This remarkable difference in fluxionality may be
due to the presence of the Pd-Pd bond in 4-6 and its
absence in the trinuclear hydroxo complexes. As carbon
monoxide is known to insert into Pd-Pd bonds of some
complexes,15,17b the coordinated CO ligands in 4-6 may
reversibly do so, thus undergoing facile positional
exchange. Obviously, such a mechanism is inconceiv-
able for 1-3, which have no bonding Pd-Pd interaction.
As the hydroxo clusters slowly decompose in solution
at room temperature (see below), their 13C NMR spectra
were measured at -25 °C in order to slow down the
Unlike the smooth and straightforward dispropor-
tionation of 1, the decomposition of the chromium
counterpart 3 is much more sluggish, taking days and
resulting in complex mixtures of products which were
neither isolated nor identified. It is remarkable that
neither 6 nor [(Ph3P)2Pd2Ph2(µ-OH)2] emerged from the
decomposition of 3 (31P NMR). The Pd2Mo hydroxo
cluster 2 decomposed faster than 3 and slower than 1;
the reaction took approximately 2 days at room tem-
(27) (a) According to GC and GC-MS analyses, less than 0.5% of
bibenzyl formed when 1 was disproportionated in toluene. (b) Non-
hebel, D. C.; Walton, J . C. Free-Radical Chemistry; Cambridge
University Press: Cambridge, U.K., 1974.
(28) See, for example: Young, S. J .; Kellenberger, B.; Reibenspies,
J . H.; Himmel, S. E.; Manning, M.; Anderson, O. P.; Stille, J . K. J .
Am. Chem. Soc. 1988, 110, 5744.

“Neutralization” of Palladium Hydroxides
Organometallics, Vol. 16, No. 1, 1997 101
Sch em e 1
perature. Both 5 and [(Ph3P)2Pd2Ph2(µ-OH)2] (1:1 molar
ratio) were formed, among other unidentified products.
Rea ction s of Or ga n op a lla d iu m Hyd r oxo Dim er s
w ith Excess [Cp M(CO)3H]
According to eq 2 and Scheme 1, the tetranuclear
Pd2W2 cluster 4 can be prepared from [(Ph3P)2Pd2Ph2-
(µ-OH)2] and 2 molar equiv of [CpW(CO)3H]. However,
the 2:1 stoichiometry was observed only if the hydride
was added to the hydroxo dimer very slowly. Fast
addition of the of the tungsten hydride to 1 or to
[(Ph3P)2Pd2Ph2(µ-OH)2], while affording 4 in quantita-
tive yield, did so by a totally different reaction pathway.
When 3 molar equiv or more of [CpW(CO)3H] was
added, in one portion, to [(Ph3P)2Pd2Ph2(µ-OH)2] in
toluene, complex 4 (90% isolated yield), benzene (83%
GC yield; see Experimental Section), and [CpW(CO)3Ph]29
(91% isolated yield) were formed (eq 3), but no biphenyl
or bibenzyl was found among the reaction products.
Monitoring reaction 3 by 31P NMR spectroscopy
revealed the rapid (seconds) formation of 1 upon addi-
tion of the W hydride to the Pd dihydroxide, followed
by the gradual disappearance of 1 and concomitant
formation of 4. The spontaneous disproportionation of
1 (Scheme 1) was much slower (20 h) than the interac-
(3)
tion between 1 and the tungsten hydride (eq 3), which
took less than 30 min under similar conditions. Clearly,
reaction 3 proceeded through the formation of 1, which
then interacted with 2 equiv more of the hydride to give
4, benzene, and [CpW(CO)3Ph] (Scheme 2). Indeed, the
addition of 2 equiv of [CpW(CO)3H] to 1 resulted in the
formation of 4, benzene, and the (σ-phenyl)tungsten
(29) (a) Nesmeyanov, A. N.; Chapovsky, Yu. A.; Lokshin, B. V.; Kisin,
A. V.; Makarova, L. G. Dokl. Akad. Nauk SSSR 1966, 171, 637. (b)
Mahmond, K. A.; Rest, A. J .; Alt, H. G.; Eichner, M. E.; J ansen, B. M.
J . Chem. Soc., Dalton Trans. 1984, 175.

102 Organometallics, Vol. 16, No. 1, 1997
Kuznetsov et al.
Sch em e 2
Sch em e 3
derivative, in high yield. It is conceivable that the
formation of benzene and the (σ-phenyl)tungsten com-
plex is due to a Ph/H exchange between the W hydride
and one of the two Pd-Ph centers in an intermediate
binuclear species. For instance (Scheme 3), the pro-
posed tetranuclear intermediate (also presented in
Scheme 1) may form upon neutralization of both OH
ligands in [(Ph3P)2Pd2Ph2(µ-OH)2] with 2 equiv of the
hydride. If one of the two σ-Ph ligands in this inter-
mediate exchanged for H from the still-present [CpW-
(CO)3H], binuclear reductive elimination of PhH from
the resulting Pd(H)Pd(Ph) species would give benzene
and complex 4. Should both organic ligands be replaced
by hydrides, the elimination might result in the forma-
tion of H2 due to reductive elimination. Indeed, the
formation of both CH4 and H2 was experimentally
observed in a similar reaction between [(Ph3P)2Pd2(Me)2-
(µ-OH)2] and excess [CpW(CO)3H]. When [(Ph3P)2Pd2-
(Me)2(µ-OH)2]11 was treated with an excess of [CpW-
(CO)3H], 4 and [CpW(CO)3Me]30 were formed as the only
organometallic products in high yield, with both CH4
and H2 (6:1 molar ratio) being found in the gas phase
(GC). These results can be rationalized in terms of the
mechanism outlined in Scheme 3. The mechanism of
the W-H/Pd-R exchange remains unclear; perhaps it
involves oxidative addition of the W-H bond to the Pd
(30) (a) The resulting [CpW(CO)3Me] was identified by comparison
of its 1H and 13C NMR spectra with the literature data.30b,c 1H NMR
(C6D6): δ 0.6 (s, 3H, Me), 4.4 (s, 5H, Cp). 13C NMR (C6D6): δ -34.2
(s, J C-W ) 28.8 Hz, Me), 91.6 (s, Cp). (b) For the 1H NMR spectrum,
see: McFarlane, H. C.; McFarlane, W.; Rycroft, D. C. J . Chem. Soc.,
Dalton Trans. 1976, 1616. (c) For the 13C NMR spectrum, see:
Elschenbroich, C.; Salzer, A. Organometallics: A Concise Introduction,
2nd ed.; VCH: New York, 1992; p 297.
center, followed by reductive elimination of the W-R
complex.31 If so, this reaction sequence might involve
significant changes in the cluster structures, due to

“Neutralization” of Palladium Hydroxides
Organometallics, Vol. 16, No. 1, 1997 103
8: R ) Ph, M ) W, Cp ) Cp* ) η5-C5Me5
steric requirements for the oxidative addition. At-
tempted preparation of the σ-methyl analog of 1 failed,
apparently because the desired hydroxo complex and the
starting hydroxide, [(Ph3P)2Pd2(Me)2(µ-OH)2], exhibited
similar reactivity toward the hydride.32
reaction between [(Ph3P)2Pd2(Ph)2(µ-OH)2] and [Cp*W-
(CO)3H] (Cp* ) η5-C5Me5) furnished, as anticipated,
[(Ph3P)2Pd2Cp*2W2(µ-CO)4(µ3-CO)2] (8) along with
[Cp*W(CO)3Ph] in 60% and 72% isolated yields, respec-
tively. The [CpM(CO)3Ph] byproducts were not isolated
in all these cases, but their formation was confirmed
Treating [(Ph3P)2Pd2(Ph)2(µ-OH)2] with 3 equiv of
[CpW(CO)3D] in dry toluene gave benzene, with the
ratio of C6H6 to C6H5D being approximately 1:1 (GC-
MS). When [(Ph3P)2Pd2(Ph)2(µ-OD)2] was used for the
reaction with [CpW(CO)3D], the benzene product con-
tained 90% C6H5D. Both experiments demonstrated
that, in the course of the reaction, extensive exchange
occurred between the hydrido and hydroxo hydrogens
of the organometallic reactants. In line with the
proposed mechanism (Scheme 2), the hydrido/hydroxo
H/D exchange was found to occur noticeably faster than
the neutralization reactions. When 1 equiv of [CpW-
(CO)3D] (90% D) was added to nondeuterated 1 in
toluene-d8 at -40 °C, neither H/D exchange nor forma-
tion of 4 was observed (1H NMR) over 30 min. The
hydrido region of the spectrum contained a triplet (-3.7
ppm) due to the µ-OH and the residual resonance of the
tungsten hydride (-7.2 ppm). The sample was then
quickly warmed and kept at room temperature for ca.
1 min, and the spectrum was again recorded at -40 °C.
This brief exposure at room temperature was sufficient
for complete scrambling of the D label over the hydrido/
hydroxo sites. At the same time, it was clear (from the
1H NMR spectrum) that less than 5% of 1 underwent
conversion to 4. An independent experiment was
conducted to show that the H/D exchange between
[CpW(CO)3D] (in benzene or toluene) and H2O is very
slow, taking days at room temperature.33 Therefore, the
above H/D scrambling observed was due to the direct
hydrido/hydroxo exchange and required no water. The
above experiments account for the formation of both
C6H6 and C6H5D in the reaction between [CpW(CO)3D]
and [(Ph3P)2Pd2(Ph)2(µ-OH)2], according to Schemes 2
and 3.
1
by TLC and H NMR spectral data.
Spectral (IR, NMR) parameters obtained for com-
plexes 4-6 were identical with those previously re-
ported by Braunstein and co-workers.23 The new clus-
ters 7 and 8 were characterized by elemental analysis
and IR and NMR spectral data (see Experimental
Section).
F or m a tion of Tetr a n u clea r Tr im eta llic P d 2MM′
Clu ster s
Having established the fact that the reactions be-
tween [(Ph3P)2Pd2(Ph)2(µ-OH)2] and excess [CpM(CO)3H]
occur via the intermediate formation of trinuclear
hydroxo clusters 1-3, we attempted the synthesis of
tetranuclear trimetallic Pd2MM′ systems. It is worth
noting that such clusters cannot be prepared by Braun-
stein’s method.23 First, we found that a 1:1 mixture of
4 and 5 in benzene did not exhibit any sign of a W/Mo
exchange (weeks at room temperature; 31P NMR con-
trol). Nonetheless, when 1 was treated with 2 equiv of
[CpMo(CO)3H], the three clusters 4, 5, and the mixed
Pd2MoW species 9 were found in the reaction mixture
in a ca. 1:10:2 ratio. The reaction between 2 and [CpW-
(CO)3H] also resulted in the formation of 4, 5, and 9,
although in a ratio of 7:1:10. From this experiment,
complex 9 was isolated by column chromatography (55%
yield) and characterized by elemental analysis and IR
and NMR spectral data. Having been kept in benzene
for 24 h, 9 did not disproportionate or decompose,
suggesting that the observed scrambling cannot be
explained by the instability of the mixed species. We
also tried to prepare the Pd2WCr and Pd2MoCr mixed
clusters by applying the above techniques. None of the
reactions gave the desired complexes selectively; mix-
tures of all three possible clusters were obtained instead.
It is worth mentioning that the reaction between [L2-
Pd2(µ-Cl)(µ-CO)2(µ3-CO)MCp] and [CpM′(CO)3]- (M, M′
) W, Mo, Cr) also gave mixtures of all possible clusters,
which were not isolated.24
Complexes 5, 6, and [(Cy3P)2Pd2Cp2W2(µ-CO)4(µ3-
CO)2] (7) were prepared by neutralization of the hy-
droxopalladium complexes with the corresponding hy-
drides using a 1:3 molar ratio (eq 4). Similarly, the
[(R3P)2Pd2(Ph)2(µ-OH)2] + 3[CpM(CO)3H] f
[(R3P)2Pd2M2Cp2(CO)6]
(4)
4-8
Clearly, the unexpected M/M′ scrambling observed did
not result from exchange between the Pd2M2 and Pd2M′2
units or disproportionation of Pd2MM′ (see above).
Neither could it be accounted for by exchange between
the already formed Pd2MM′ and the as yet unreacted
[CpM(CO)3H]. In fact, although some W/Cr exchange
was observed when 6 was mixed with [CpW(CO)3H] in
benzene, the reaction was very sluggish, taking several
hours at room temperature before the Pd2WCr (10) and
Pd2W2 species (4) formed in concentrations observable
by 31P NMR techniques. The palladium-tungsten-
chromium cluster was obtained in this manner and
isolated in 34% yield after 70 h of reaction. In contrast,
all reactions of 1-3 and various [CpM(CO)3H] com-
plexes were significantly more facile, reaching comple-
tion in less than 30 min. Therefore, the M/M′ scram-
bling obviously occurred at earlier steps of the reaction.
Unlike [CpM(CO)3H] (M ) W, Mo, Cr), the corre-
sponding potassium salts K+[CpM(CO)3]- readily and
4: R ) Ph, M ) W
5: R ) Ph, M ) Mo
6: R ) Ph, M ) Cr
7: R ) Cy, M ) W
(31) Fukuoka, A.; Sadashima, T.; Endo, I.; Ohashi, N.; Kambara,
Y.; Sugiura, T.; Miki, K.; Kasai, N.; Komiya, S. Organometallics 1994,
13, 4033.
(32) When [CpW(CO)3H] was gradually added to [(Ph3P)2Pd2(Me)2-
(µ-OH)2] in benzene (the reaction was monitored by 31P NMR), a singlet
was observed at 32 ppm in the spectrum which could be assigned to
the σ-methyl analog of 1. This singlet rapidly disappeared.
(33) (a) In contrast, [(Ph3P)2Pd2(Ph)2(µ-OH)2] readily exchanges with
D2O within seconds under similar conditions. For instance, adding 1
drop of D2O to a solution of this Pd hydroxo dimer in CDCl3 (ca. 1 mL
in a 5 mm NMR tube) and shaking the mixture for 5 s resulted in
complete deuteration of the OH ligands (1H NMR).33b (b) Grushin, V.
V. Unpublished observations, 1993.

104 Organometallics, Vol. 16, No. 1, 1997
Kuznetsov et al.
reduced in volume under vacuum until it became slightly
turbid. The clear yellow solution was decanted from the dark
solid and evaporated until yellow crystals were formed and
the liquid phase became colorless. The crystals were sepa-
rated, washed with pentane (3 × 10 mL), and dried under
vacuum. The yield of analytically and spectroscopically pure
1 was 103 mg (81%). Anal. Calcd for C56H46O4P2Pd2W: C,
54.2; H, 3.7. Found: C, 54.3; H, 3.8. 1H NMR (CDCl3, 20 °C):
δ -3.7 (t, J H-P ) 2.1 Hz, 1H, PdOH), 4.4 (s, 5H, C5H5), 6.5-
7.4 (m, 40H, C6H5). 31P NMR (C6D6, 20 °C): δ 23.4 (s). 13C
NMR (CDCl3, -25 °C): δ 91.2 (s, C5H5), 122.0 (s, p-C6H5Pd),
126.4 (s, m-C6H5Pd), 127.0 (s, m-C6H5Pd), 128.3 (d, J C-P ) 10.4
Hz, m-C6H5P), 129.5 (d, J C-P ) 40.0 Hz, q-C6H5P), 130.0 (s,
p-C6H5P), 133.8 (d, J C-P ) 12.9 Hz, o-C6H5P), 135.5 (br s,
o-C6H5P), 139.4 (m, q-C6H5Pd), 225.8 (t, J C-P ) 14.0 Hz, µ3-
rapidly exchanged with 4-6 in 30 min. Trinuclear
hydroxo clusters 1-3 also underwent exchange with the
potassium carbonylates (eq 5), equilibria being reached
in less than 30 min at ambient temperature (31P NMR).
[CpM(CO)3Pd2L2Ph2OH] + K[CpM′(CO)3] a [CpM′
(CO)3Pd2L2Ph2OH] + K[CpM(CO)3] (5)
M ) W, M′ ) Mo; M ) Mo, M′ ) W; M ) Cr,
M′ ) W; L ) PPh3
Remarkably, two sharp singlets were observed in the
carbonyl region of the 13C NMR spectra of 9 and 10,
indicating that the positional exchange of the carbonyl
ligands takes place only within each Pd2M unit, with
no CO exchange occurring between the two Pd2M
frameworks. This is probably true for clusters 4-8,
which exhibit only one carbonyl 13C NMR resonance due
to symmetry.
CO), 228.0 (d, J C-P ) 15.5 Hz, µ-CO). IR (KBr): νCO (cm-1
)
1861 (vs), 1785 (vs), 1750 (vs).
Syn th esis of [(Cy3P )2P d 2(P h )2(µ-OH)W(CO)3Cp ] (1a ).
Solid [CpW(CO)3H] (38 mg; 0.114 mmol) was added to a
vigorously stirred solution of [(Cy3P)2Pd2(Ph)2(µ-OH)2] (130 mg;
0.116 mmol) in a mixture of CH2Cl2 (15 mL), heptane (15 mL),
and toluene (2 mL), at 0 °C. The resulting clear yellow solution
was stirred at 0 °C for 10 min, reduced in volume under
vacuum to ca. 10 mL, and kept at -78 °C for 3 days. The
yellow crystals that precipitated were separated, washed with
cold (-78 °C) pentane, and dried under vacuum. The yield of
spectroscopically pure [(Cy3P)2Pd2(Ph)2(µ-OH)W(CO)3Cp]‚C6H5-
CH3 was 110 mg (70%). The compound was recrystallized from
Con clu sion s
The above reactions (eqs 2 and 3) represent the first
examples of palladium-transition-metal bond formation
due to acid-base interaction between a hydroxo Pd
species and an acidic metal hydride. Although reactions
2 and (to a certain degree) 3 could be regarded as simple
neutralization processes, their mechanisms may be
more sophisticated than the simple hydrido and hydroxo
ligands coming together to form a molecule of water.
At this moment, not enough data have been accrued to
draw any conclusions regarding the mechanisms of this
unusual neutralization chemistry, which may involve
a series of oxidative-addition and reductive-elimination
processes. Another aspect which merits emphasis is the
“peaceful coexistence” of the OH, σ-phenyl, and carbonyl
ligands, all attached to each of the palladium centers
in molecules of 1-3. We are unaware of any other
palladium complexes bearing CO, OH, and σ-aryl (alkyl)
ligands on one metal atom. From this perspective,
“polyfunctional” complexes 1-3 are of potential interest
in inorganic and organometallic synthesis, as well as
in the chemistry of catalytic carbonylation of organic
substrates in the presence of alkali-metal and homoge-
neous Pd catalysts.19-22
a
1:1 mixture of toluene-pentane (8 mL) for elemental
analysis. Anal. Calcd for C63H90O4P2Pd2W: C, 55.2; H, 6.6.
Found: C, 55.5; H, 6.6. 1H NMR (C6D6, 20 °C): δ -1.4 (s, 1H,
PdOH), 1.0-2.2 (m, 69H, C6H11 + Me), 4.4 (s, 5H, C5H5), 6.8
(t, J H-H ) 7.1 Hz, 2H, 4-C6H5Pd), 7.0 (m, 4H, 3-C6H5Pd), 7.1-
7.2 (m, 5H, C6H4Me), 7.8 (d, J H-H ) 8.0 Hz, 2H, 2-C6H5Pd),
8.2 (d, J H-H ) 7.7 Hz, 2H, 2-C6H5Pd). 31P NMR (CDCl3, 20
°C): δ 28.1 (s). 13C NMR (CDCl3, -40 °C): δ 23.4 (s, Me), 26.2
(s, C6H11), 27.5 (br s, C6H11), 29.0 (m, C6H11), 31.2 (br s, C6H11),
91.3 (s, C5H5), 122.0 (s, p-C6H5Pd), 125.3 (s, C6H5Me), 125.9
(s, m-C6H5Pd), 126.7 (s, m-C6H5Pd), 128.4 (s, C6H5Me), 129.2
(s, C6H5Me), 134.7 (s, o-C6H5Pd), 128.4 (s, C6H5Me), 129.2 (s,
C6H5Me), 134.7 (s, o-C6H5Pd), 135.3 (s, o-C6H5Pd), 137.2 (s,
C6H5Me), 140.1 (s, q-C6H5Pd), 226.7 (t, J C-P ) 14.0 Hz, µ3-
CO), 230.4 (d, J C-P ) 16.5 Hz, µ-CO). IR (KBr): νCO (cm-1
1856 (vs), 1783 (vs), 1744 (vs).
)
Syn th esis of [(P h 3P )2P d 2(P h )2(µ-OH)Mo(CO)3Cp ] (2). A
solution of freshly purified [CpMo(CO)3H] (33 mg; 0.134 mmol)
in heptane (4 mL) was added to a vigorously stirred solution
of [(Ph3P)2Pd2(Ph)2(µ-OH)2] (128 mg; 0.138 mmol) in benzene
(20 mL). Heptane (20 mL) was added, and the clear yellow
solution was reduced in volume under vacuum to ca. 20 mL.
The yellow crystals were separated, washed with pentane (3
× 10 mL), and dried under vacuum. The yield of analytically
and spectroscopically pure 2 was 138 mg (89%). Anal. Calcd
for C56H46MoO4P2Pd2: C, 58.3; H, 4.0. Found: C, 58.7; H, 3.9.
1H NMR (CDCl3, 20 °C): δ -3.8 (t, J H-P ) 2.1 Hz, 1H, PdOH),
4.3 (s, 5H, C5H5), 6.6-7.4 (m, 40H, C6H5). 13P NMR (C6D6, 20
°C): δ 18.5 (s). 13C NMR (CDCl3, -25 °C): δ 102.2 (s, C5H5),
121.7 (s, p-C6H5Pd), 126.2 (s, m-C6H5Pd), 126.8 (s, m-C6H5-
Pd), 128.0 (second-order m, J C-P ) ca. 10.6 Hz, m-C6H5P),
129.4 (d, J C-P ) 40.1 Hz, q-C6H5P), 130.7 (s, p-C6H5P), 133.7
(second-order m, J C-P ) ca. 13.0 Hz, o-C6H5P), 134.0 (s, o-C6H5-
Exp er im en ta l Section
The following instruments were used: Varian Gemini-200
(1H NMR), Varian XL 300 (1H, 13C, and 31P NMR), Bruker
AMX 500 (1H, 13C, and 31P NMR), Hewlett-Packard 5890 Series
II-Kratos Concept II H (GC-MS), Bomem MB-100 (FT-IR),
and Perkin-Elmer 2400 Series II (combustion microanalysis).
All chemicals were purchased from Aldrich, Strem, Organo-
metallics, and MSD Isotopes and used as received. The metal
complexes [(Ph3P)2Pd2(Ph)2(µ-OH)2],6 [(Cy3P)2Pd2(Ph)2(µ-OH)2],6,16
[(Ph3P)2Pd2(Me)2(µ-OH)2],11 [CpW(CO)3H],29 [CpMo(CO)3H],34
Hg[CpCr(CO)3]2,35 and [Cp*W(CO)3H]36 were prepared as
described in the literature.
Syn th esis of [(P h 3P )2P d 2(P h )2(µ-OH)W(CO)3Cp ] (1).
Solid [CpW(CO)3H] (34 mg; 0.102 mmol) was added to a
vigorously stirred solution of [(Ph3P)2Pd2(Ph)2(µ-OH)2] (100 mg;
0.108 mmol) in benzene (20 mL). Heptane (20 mL was added
to the resulting yellow-brown mixture, and the solution was
Pd), 135.5 (s, o-C6H5Pd), 139.3 (m, q-C6H5Pd), 233.4 (t, J C-P
)
17.1 Hz, µ3-CO), 236.1 (d, J C-P ) 20.5 Hz, µ-CO). IR (KBr):
νCO (cm-1) 1867 (vs), 1799 (vs), 1762 (vs).
Syn th esis of [(P h 3P )2P d 2(P h )2(µ-OH)Cr (CO)3Cp ] (3). A
mixture of [CpCr(CO)3]2Hg (210 mg; 0.348 mol), THF (5 mL),
and a Na/K alloy (1 mL) was stirred for 1 h. The THF solution
was filtered and treated with AcOH (1 mL). After it was
stirred for 10 min, the mixture was evaporated to dryness, and
the residue was washed with water (10 mL). The bright yellow
solid ([CpCr(CO)3H]) was dried under vacuum and dissolved
in pentane (5 mL). The solution was filtered, and evaporation
(34) Fischer, E. O. Inorg. Synth. 1963, 7, 136.
(35) Burtlitch, J . M.; Ferrari, A. Inorg. Chem. 1970, 9, 563.
(36) Kubas, G. J .; Wasserman, H. J .; Ryan, R. R. Organometallics
1985, 4, 2012.

“Neutralization” of Palladium Hydroxides
Organometallics, Vol. 16, No. 1, 1997 105
of pentane gave 60 mg (42%) of yellow [CpCr(CO)3H]. The
prepared chromium hydride was dissolved in heptane (4.0 mL),
and an aliquot of this solution (1.8 mL; 0.133 mmol of [CpCr-
(CO)3H]) was added to a vigorously stirred solution of [(Ph3P)2-
Pd2(Ph)2(µ-OH)2] (135 mg; 0.146 mmol) in benzene (20 mL).
Heptane (20 mL) was added; the mixture was reduced in
volume to ca. 20 mL and kept first at room temperature (30
min) and then at -17 °C (1 h). The resulting orange crystals
were separated, washed with pentane (3 × 10 mL), and dried
under vacuum. The yield of analytically and spectroscopically
pure 3 was 133 mg (90%). Anal. Calcd for C56H46CrO4P2Pd2:
C, 60.6; H, 4.2. Found: C, 60.4; H, 4.3. 1H NMR (CDCl3, 20
°C): δ -4.0 (t, J H-P ) 2.0 Hz, 1H, PdOH), 3.7 (s, 5H, C5H5),
6.5-7.6 (m, 40H, C6H5). 13P NMR (C6D6, 20 °C): δ 18.0 (s).
13C NMR (CDCl3, -25 °C): δ 89.4 (s, C5H5), 121.8 (s, p-C6H5-
Pd), 126.4 (s, m-C6H5Pd), 127.1 (s, m-C6H5Pd), 128.1 (second-
order m, J C-P ) ca. 10.2 Hz, m-C6H5P), 129.4 (d, J C-P ) 41.5
Hz, q-C6H5P), 129.9 (s, p-C6H5P), 133.7 (second-order m, J C-P
) ca. 12.8 Hz, o-C6H5P), 135.3 (s, o-C6H5Pd), 142.2 (m, q-C6H5-
Pd), 243.2 (t, J C-P ) 12.3 Hz, µ3-CO), 244.6 (second-order m,
µ-CO; see text). IR (KBr pellet): νCO (cm-1) 1859 (vs), 1792
(vs), 1760 (vs).
benzene-containing distillates were analyzed by GC-MS. The
composition of C6H5D/C6H6 mixtures was calculated from the
abundances of isotopic peaks in the electron impact mass
spectra, using an ISONETA program.37
(c) Syn th esis of [(P h 3P )2P d 2Cp 2W2(µ-CO)4(µ3-CO)2] (4).
A mixture of [CpW(CO)3H] (240 mg; 0.72 mmol), [(Ph3P)2Pd2-
(Ph)2(µ-OH)2] (139 mg; 0.15 mmol), and benzene (10 mL) was
stirred for 30 min, treated with MeOH (10 mL), and left
overnight. The precipitated dark green crystals of 423 were
separated, washed with MeOH (3 × 10 mL), pentane (3 × 10
mL), and dried under vacuum. The yield of the analytically
and spectroscopically pure 4 thus obtained was 190 mg (90%).
Anal. Calcd for C52H40O6P2Pd2W2: C, 44.5; H, 2.9. Found:
C, 44.3; H, 2.9. 1H NMR (CDCl3, 20 °C): δ 4.7 (s, 10H, C5H5),
7.4 (m, 18H, 3,4,5-C6H5), 7.6 (m, 12H, 2,6-C6H5). 31P NMR
(CDCl3, 20 °C): δ 20.7 (s). IR (KBr pellet): νCO (cm-1) 1916
(m), 1853 (s), 1821 (vs), 1784 (s).
Syn th esis of [(P h 3P )2P d 2Cp 2Mo2(µ-CO)4(µ3-CO)2] (5). A
mixture of [CpMo(CO)3H] (155 mg; 0.63 mmol), [(Ph3P)2Pd2-
(Ph)2(µ-OH)2] (140 mg; 0.15 mmol), and benzene (4 mL) was
stirred for 30 min. The resulting deep green solutions were
treated with MeOH (8 mL), stirred for 10 min, and filtered.
The green solid was thoroughly washed with acetone and
pentane and dried under vacuum to give 155 mg (84%) of
analytically and spectroscopically pure 5.23 Anal. Calcd for
Disp r op or tion a tion of 1. The gradual disappearance of
1 (benzene or toluene solutions) and concomitant formation
of 4 and [(Ph3P)2Pd2(Ph)2(µ-OH)2] was monitored by 31P NMR
spectroscopy (see text).
C
52H40Mo2O6P2Pd2: C, 50.9; H, 3.3. Found: C, 50.7; H, 3.2.
1H NMR (CDCl3, 20 °C): δ 4.6 (s, 10H, C5H5), 7.4 (m, 18H,
3,4,5-C6H5), 7.6 (m, 12H, 2,6-C6H5). 31P NMR (CDCl3, 20 °C):
δ 24.5 (s). IR (KBr): νCO (cm-1) 1915 (m), 1852 (s), 1829 (vs),
1784 (s).
(b) Solid [CpW(CO)3H] (16 mg; 0.048 mmol) was added to a
stirred mixture of [(Ph3P)2Pd2(Ph)2(µ-OH)2] (64 mg; 0.069
mmol) and toluene (4 mL) at -78 °C. The mixture was
warmed to room temperature and left overnight. The volatiles
were transferred (vacuum) to a small flask and mixed with
n-butylbenzene (internal standard, 5 µL). The residue, after
distillation, was stirred with hexane (4 mL) containing n-
butylbenzene (internal standard, 5 µL), and the pale yellow
liquid phase was decanted from the dark blue precipitate of
4. Analysis of the liquids by GLC indicated that biphenyl was
formed in 73% yield.
Syn th esis of [(P h 3P )2P d 2Cp 2Cr 2(µ-CO)4(µ3-CO)2] (6).
Solid [(Ph3P)2Pd(Ph)2(µ-OH)2] (100 mg; 0.108 mmol) was added
to a solution of [CpCr(CO)3H] (73 mg; 0.363 mmol) in benzene
(3 mL), and the mixture was stirred for 30 min. The resulting
solution was reduced in volume to ca. 1 mL, treated with
pentane (8 mL), and left overnight. The precipitated solid was
separated, washed with MeOH (3 × 6 mL) and pentane (3 ×
6 mL), dried, and recrystallized from CH2Cl2/MeOH to give
96 mg (78%) of spectroscopically pure 6.23 1H NMR (CDCl3,
20 °C): δ 4.1 (s, 10H, C5H5), 7.4 (m, 18H, 3,4,5-C6H5), 7.5 (m,
12H, 2,6-C6H5). 31P NMR (CDCl3, 20 °C): δ 26.8 (s). IR (KBr
pellet): νCO (cm-1) 1902 (m), 1847 (vs), 1824 (vs), 1789 (s).
Syn th esis of [(Cy3P )2P d 2Cp 2W2(µ-CO)4(µ3--CO)2] (7). A
mixture of [(Cy3P)2Pd2(Ph)2(µ-OH)2] (50 mg; 0.052 mmol),
[CpW(CO)3H] (80 mg; 0.239 mmol), and benzene (4 mL) was
stirred for 30 min, diluted with MeOH (5 mL), and left
overnight. The precipitated solid was separated, washed with
MeOH (3 × 5 mL) and pentane (2 × 5 mL), and dried under
vacuum to give 71 mg (95%) of analytically and spectroscopi-
cally pure, dark blue 7. Anal. Calcd for C52H76O6P2Pd2W2:
C, 43.4; H, 5.3. Found: C, 43.2; H, 5.0. 1H NMR (C6D6, 20
°C): δ 1.2-2.2 (m, 66H, C6H11), 5.2 (s, 10H, C5H5). 31P NMR
(CH2Cl2, 20 °C): δ 33.8 (s). IR (KBr pellet): νCO (cm-1) 1895
(m), 1820 (vs), 1795 (vs).
P r ep a r a tion of [Cp W(CO)3D]. A mixture of [CpW(CO)3H]
(173 mg; 0.518 mmol), THF (5 mL), and Na/K alloy (0.2 mL)
was stirred for 1 h. The resulting THF solution was filtered,
treated with AcOD (0.5 mL), stirred for 10 min, and evaporated
to dryness. The residue was washed with D2O (2 mL), dried
under vacuum, and dissolved in pentane (4 mL). The pentane
solution was filtered through cotton and evaporated to give
1
130 mg of white crystals of [CpW(CO)3D] (95% D, H NMR).
P r ep a r a tion of [(P h 3P )2P d 2(P h )2(µ-OD)2]. A mixture of
[(Ph3P)2Pd2(Ph)2(µ-OH)2] (100 mg; 0.108 mmol), CH2Cl2 (5 mL),
and D2O (1 mL) was stirred for 15 min. The organic layer
was separated, filtered through cotton, and evaporated to
dryness to give 94 mg of white [(Ph3P)2Pd2(Ph)2(µ-OD)2].
R ea ct ion of [(P h 3P )2P d 2(P h )2(µ-OH )2] w it h E xcess
[Cp W(CO)3H]. (a ) Isola tion of [Cp (CO)3WP h ] a n d De-
ter m in a tion of th e Am ou n t of Ben zen e. A mixture of
[(Ph3P)2Pd2(Ph)2(µ-OH)2] (41 mg; 0.044 mmol), [CpW(CO)3H]
(52 mg; 0.155 mmol), and toluene (2 mL) was stirred for 1 h.
The volatiles were vacuum-transferred, n-butylbenzene (in-
ternal standard) was added, and the distillate was analyzed
by GLC. The amount of benzene formed was 37 mmol (83%).
Trace amounts of cyclopentadiene, biphenyl, and bibenzyl were
also found (GC-MS). The residue after distillation was
extracted with pentane (3 × 1 mL), and the resulting yellow
solution was chromatographed on silica (toluene/heptane) to
give pure [CpW(CO)3Ph]29 (16.6 mg; 91%). 1H NMR (CDCl3,
20 °C): δ 5.5 (s, 5H, C5H5), 7.0 (m, 3H, 3,4,5-C6H5), 7.7 (m,
2H, 2,6-C6H5). 13C NMR (CDCl3, 20 °C): δ 92.4 (s, C5H5), 124.4
(s, q-C6H5), 124.5 (s, p-C6H5), 128.4 (s, m-C6H4), 147.3 (s,
o-C6H5), 218.3 (s, J W-C ) 158 Hz, CO), 228.2 (s, J W-C ) 112
Hz, CO). IR (KBr pellet): νCO (cm-1) 2017 (m), 1915 (vs), 1896
(vs).
Syn th esis of [(P h 3P )2P d 2Cp *2W2(µ-CO)4(µ3-CO)2] (8). A
mixture of [Cp*W(CO)3H] (179 mg; 0.443 mmol), [(Ph3P)2Pd2-
(Ph)2(µ-OH)2] (116 mg; 0.125 mmol), and benzene (4 mL) was
stirred for 1 h, and the resulting emerald green solution was
chromatographed on a silica gel column (toluene/CH2Cl2). The
orange-yellow and green fractions were collected, and evapora-
tion of the latter gave 182 mg of 8 (90% purity according to
31P NMR). Crude 8 was dissolved in CH2Cl2 (2 mL), pentane
(10 mL) was added, and the mixture was kept at -17 °C
overnight, forming long green needles of 8, which was sepa-
rated, washed with cold pentane (2 × 5 mL), and dried under
vacuum. The yield of 8 was 115 mg (60%). Anal. Calcd for
C
62H60O6P2Pd2W2: C, 48.2; H, 3.9. Found: C, 49.0; H, 4.0. 1H
NMR (CDCl3, 20 °C): δ 1.4 (s, 30H, CH3), 7.3-7.7 (m, 30H,
C6H5). 31P NMR (C6D6, 20 °C): δ 15.1 (s). 13C NMR (CDCl3,
(b) Rea ction of [Cp W(CO)3D] w ith [(P h 3P )2P d 2(P h )2(µ-
OH)2] a n d w ith [(P h 3P )2P d 2(P h )2(µ-OD)2]. These reactions
were conducted in absolute toluene, as described above. The
(37) Sukharev, Yu. N.; Nekrasov, Yu. S. Org. Mass Spectrom. 1976,
11, 1239.

106 Organometallics, Vol. 16, No. 1, 1997
Kuznetsov et al.
20 °C): δ 9.8 (s, CH3), 100.5 (s, C5), 128.0 (virtual t, J C-P
)
(m, 18H, 3,4,5-C6H5), 7.6 (m, 12H, 2,6-C6H5). 31P NMR (C6H6,
20 °C): δ 24.2 (s). 13C NMR (CDCl3, 20 °C): δ 86.8 (s, C5H5-
Cr), 89.8 (s, C5H5W), 128.2 (virtual t, J C-P ) 4.8 Hz, m-C6H5),
129.9 (s, p-C6H5), 134.3 (virtual t, J C-P ) 7.1 Hz, o-C6H5), 134.3
(virtual t, J C-P ) 17.5 Hz, q-C6H5), 227.6 (s, CrCO), 251.9 (s,
WCO). IR (KBr pellet): νCO (cm-1) 1922 (m), 1849 (s), 1822
(s), 1792 (s). Evaporation of the violet fraction gave 10 mg
(8%) of 4 (identified by 31P NMR).
4.8 Hz, m-C6H5), 129.2 (s, p-C6H5), 134.3 (virtual t, J C-P ) 7.2
Hz, o-C6H5), 135.6 (virtual t, J C-P ) 16.1 Hz, q-C6H5), 236.1
(s, CO). IR (KBr): νCO (cm-1) 1887 (m), 1836 (sh), 1811 (sh),
1795 (vs). The orange-yellow fraction was evaporated and
chromatographed on silica (heptane/toluene) to give 43 mg
(72%) of spectroscopically pure [Cp*W(CO)3Ph]. The com-
pound was recrystallized from pentane for elemental analysis.
Anal. Calcd for C19H20O3W: C, 47.5; H, 4.2. Found: C, 47.8;
H, 3.9. 1H NMR (CDCl3, 20 °C): δ 1.9 (s, 15H, CH3), 7.1 (m,
3H, 3,4,5-C6H5), 7.7 (m, 2H, 2,6-C6H5). 13C NMR (CDCl3, 20
°C): δ 10.6 (s, CH3), 104.5 (s, C5), 124.6 (s, p-C6H5), 128.5 (s,
m-C6H5), 136.8 (s, q-C6H5), 145.8 (s, o-C6H5), 222.4 (s, CO),
233.1 (s, CO). IR (KBr): νCO (cm-1) 1999 (s), 1912 (s), 1892
(vs).
Sin gle-Cr ysta l X-r a y Diffr a ction Stu d y of [(P h 3P )2-
P d2(P h )2(µ-OH)Cr (CO)3Cp]‚MeOH (3‚MeOH). Well-shaped,
transparent orange crystals of the complex were obtained by
slow diffusion of pentane into a solution of 3 in dichlo-
romethane containing traces of methanol, over 1 week at -17
°C. One of the crystals (ca. 0.3 × 0.2 × 0.1 mm) was mounted
on a glass capillary. All measurements were made at -150
°C on a Siemens SMART CCD diffractometer with Mo KR1
radiation. During the data collection, standards were mea-
sured after every 150 reflections. No crystal decay was
noticed. A total of 17 590 reflections were collected. The
unique set contained 6379 reflections. Using the criterion I
> 2.5σ(I), where σ(I) is the estimated standard deviation
derived from the counting statistics, 5328 reflections were
used. The data were corrected for Lorentz and polarization
effects.38 No absorption correction was made. The structure
was solved by direct methods. All atoms were refined aniso-
tropically, except for hydrogens. The refinement was made
on F. The hydrogen atoms were calculated. The final cycle
of full-matrix least-squares refinement was based on 5328
observed reflections and 605 variable parameters. Weights
based on calculated statistics were used. The maximum and
minimum peaks on the final difference Fourier map cor-
responded to +0.820 and -0.720 e/Å3, respectively. All the
calculations were performed using the NRCVAX crystal-
lographic software package.39
Syn th esis of [(P h 3P )2P d 2Cp 2MoW(µ-CO)4(µ3-CO)2] (9).
Solid [CpW(CO)3H] (65 mg; 0.195 mmol) was added to a stirred
solution of 2 (101 mg; 0.088 mmol) in benzene (20 mL), causing
the color to change first to brown and then to green. The
mixture was stirred for 1 h, reduced in volume, and chromato-
graphed on a silica column (25 × 250 mm; toluene-CH2Cl2).
The first pink-brown band was discarded, and the subsequent
bright green, green-blue, and violet bands were collected. The
green-blue band was evaporated to dryness under vacuum,
affording 57 mg (49%) of [(Ph3P)2Pd2Cp2MoW(µ-CO)4(µ3-CO)2]
as a green solid. Anal. Calcd for C52H40MoO6P2Pd2W: C, 47.5;
H, 3.1. Found: C, 47.4; H, 2.9. 1H NMR (CDCl3, 20 °C): δ
4.65 (s, 5H, MoC5H5), 4.7 (s, 5H, WC5H5), 7.4 (m, 18H, 3,4,5-
C6H5), 7.6 (m, 12H, 2,6-C6H5). 31P NMR (CH2Cl2, 20 °C): δ
22.9 (s). 13C NMR (CDCl3, 20 °C): δ 87.3 (s, C5H5Mo), 90.9 (s,
C5H5W), 128.1 (virtual t, J C-P ) 4.5 Hz, m-C6H5), 129.8 (s,
p-C6H5), 134.3 (virtual t, J C-P ) 7.0 Hz, o-C6H5), 134.4 (virtual
t, J C-P ) 17.7 Hz, q-C6H5), 228.6 (s, MoCO), 240.3 (s, WCO).
IR (KBr): νCO (cm-1) 1916 (m), 1854 (s), 1825 (vs), 1781 (s).
The bright green and violet fractions gave 5 and 4, respectively
(identified by 31P NMR), whose yields were not determined.
Syn th esis of [(P h 3P )2P d 2Cp 2Cr W(µ-CO)4(µ3-CO)2] (10).
A mixture of 6 (105 mg; 0.089 mmol), [CpW(CO)3H] (77 mg;
0.229 mmol), and benzene (15 mL) was stirred at room
temperature (the reaction was monitored by 31P NMR spec-
troscopy). After 70 h, when the solution contained 10 and 4
in a ca. 3:1 ratio and only trace amounts of 6, the mixture
was chromatographed on a silica column (25 × 250 mm;
toluene-CH2Cl2). The first pink-brown band was discarded,
and the following green and violet fractions were collected. The
green fraction was evaporated to dryness under vacuum to give
40 mg (34%) of analytically and spectroscopically pure [(Ph3P)2-
Pd2Cp2CrW(µ-CO)4(µ-CO)2] (10). Anal. Calcd for C52H40CrO6-
P2Pd2W: C, 49.1; H, 3.2. Found: C, 48.9; H, 2.9. 1H NMR
(CDCl3, 20 °C): δ 4.0 (s, 5H, CrC5H5), 4.7 (s, 5H, WC5H5), 7.4
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada (NSERC)
for support of this research.
Su p p or tin g In for m a tion Ava ila ble: Listings of crystal-
lographic details, atomic parameters, bond distances and
angles, torsion and dihedral angles, and isotropic and aniso-
tropic thermal parameters and ORTEP drawings for 3‚MeOH
(27 pages). Ordering information is given on any current
masthead page.
OM9605138
(38) Grant, D. F.; Gabe, E. J . J . Appl. Crystallogr. 1978, 11, 114.
(39) Gabe, E. J .; Lee, F. L.; Lepage, Y. J . Appl. Crystallogr. 1989,
22, 384.