Reductive formation of straight linear metal-metal bonded tetranuclear complexes X-M-Mo-Mo-M-X from X2M···Mo-Mo···MX2 supported by four tridentate 6-diphenylphosphino-2-pyridonate ligands (M = Pd, Pt; X = Cl, Br, I)

Article abstract of DOI:10.1021/ja960606g

Straight linear tetranuclear complexes have been prepared by using pyphos ligand (pyphos = 6-diphenylphosphino-2-pyridonate), which has unique coordinating sites comprised of three kinds of elements, i.e., phosphine, nitrogen, and oxygen atoms, in almost linear fashion. The starting complex is the quadruply bonded dinuclear molybdenum(II) complex, Mo₂(pyphos)₄ (1),which was prepared by the reaction of Mo₂(OAc)₄ with sodium salt of pyphos. Single crystal X-ray analysis revealed that 1 consists of quadruply-bonded Mo₂ and trans-arranged diphosphine at both axial position of Mo₂ core. Thus, transition metal can be expected to be placed at both axial positions of Mo₂ core. Thus, treatment of 1 with Pd(II) and Pt(II) complexes gave rise to tetranuclear complexes of the general formula, Mo₂Pd₂X₄(pyphos)₄ (2) and Mo₂Pt₂X₄(pyphos)₄ (4) (a: X = Cl; b: X = Br; c:X = I). Single crystal X-ray analysis of 2a, 2b, and 4a revealed the structure of complexes 2 and 4 that consist of M(II)···MoMo···M(II) skeleton supported by four pyphos ligands. They have quadruply-bonded Mo₂ core and no bonding between a M(II) atom and a Mo atom. Treatment of 2 and 4 with reducing reagents, photoirradiation, or thermal reduction resulted in the formation of metal-metal bonded tetranuclear complexes Mo₂Pd₂X₂(pyphos)₄ (6) and Mo₂Pt₂X₂(pyphos)₄ (7) (a: X = Cl; b: X = Br; c: X = I), respectively. All of them were characterized by single crystal X-ray analysis, which revealed that they consist of M(I)-MoMo-M(I) skeleton supported by pyphos ligands. The bond lengths between M(I) and Mo are short enough to be formally regarded as a single M(I)-Mo bond, while the longer Mo-Mo distance compared to that of 1, 2, and 4 indicated that the Mo-Mo bond of 6 and 7 are formally triple (π²δ component). The electrochemical study indicates that all the atoms in the M-Mo-Mo-M system are electronically strongly coupled to allow an effective 2-electron redox process, and thus the chemical reduction of 2 and 4 readily gives 6 and 7, respectively.

Full text of DOI:10.1021/ja960606g

J. Am. Chem. Soc. 1996, 118, 9083-9095
9083
Reductive Formation of Straight Linear Metal-Metal Bonded
Tetranuclear Complexes X-M-Mo-Mo-M-X from
X2M‚‚‚Mo-Mo‚‚‚MX2 Supported by Four Tridentate
6-Diphenylphosphino-2-pyridonate Ligands (M ) Pd, Pt; X )
Cl, Br, I)
Kazushi Mashima,*,† Hiroshi Nakano,‡ and Akira Nakamura*,‡
Contribution from the Department of Chemistry, Faculty of Engineering Science, Osaka
UniVersity, Toyonaka, Osaka 560, Japan, and Department of Macromolecular Science, Faculty of
Science, Osaka UniVersity, Toyonaka, Osaka 560, Japan
ReceiVed February 26, 1996X
Abstract: Straight linear tetranuclear complexes have been prepared by using pyphos ligand (pyphos ) 6-diphe-
nylphosphino-2-pyridonate), which has unique coordinating sites comprised of three kinds of elements, i.e., phosphine,
nitrogen, and oxygen atoms, in almost linear fashion. The starting complex is the quadruply bonded dinuclear
molybdenum(II) complex, Mo2(pyphos)4 (1), which was prepared by the reaction of Mo2(OAc)4 with sodium salt of
pyphos. Single crystal X-ray analysis revealed that 1 consists of quadruply-bonded Mo2 and trans-arranged diphosphine
at both axial position of Mo2 core. Thus, transition metal can be expected to be placed at both axial positions of
Mo2 core. Thus, treatment of 1 with Pd(II) and Pt(II) complexes gave rise to tetranuclear complexes of the general
formula, Mo2Pd2X4(pyphos)4 (2) and Mo2Pt2X4(pyphos)4 (4) (a: X ) Cl; b: X ) Br; c: X ) I). Single crystal
X-ray analysis of 2a, 2b, and 4a revealed the structure of complexes 2 and 4 that consist of M(II)‚‚‚MoMo‚‚‚M(II)
skeleton supported by four pyphos ligands. They have quadruply-bonded Mo2 core and no bonding between a
M(II) atom and a Mo atom. Treatment of 2 and 4 with reducing reagents, photoirradiation, or thermal reduction
resulted in the formation of metal-metal bonded tetranuclear complexes Mo2Pd2X2(pyphos)4 (6) and Mo2Pt2X2-
(pyphos)4 (7) (a: X ) Cl; b: X ) Br; c: X ) I), respectively. All of them were characterized by single crystal
X-ray analysis, which revealed that they consist of M(I)-MoMo-M(I) skeleton supported by pyphos ligands. The
bond lengths between M(I) and Mo are short enough to be formally regarded as a single M(I)-Mo bond, while the
longer Mo-Mo distance compared to that of 1, 2, and 4 indicated that the Mo-Mo bond of 6 and 7 are formally
triple (π2δ component). The electrochemical study indicates that all the atoms in the M-Mo-Mo-M system are
electronically strongly coupled to allow an effective 2-electron redox process, and thus the chemical reduction of 2
and 4 readily gives 6 and 7, respectively.
Introduction
a linear array of few metal atoms have been reported so far,4-15
the polymerization of metal-to-metal multiple bond, similar to
the polymerization of alkenes and alkynes, would be the most
rational synthetic method to preparing one-dimensional transi-
tion-metal-based materials (eq 1), thereafter (n) and (n-1)
denote the order of multiplicity of metal-metal bond, though
this approach has been unsuccessful with oppressive difficulty.
Low-dimensional materials have attracted much interest in
view of their magnetic, electronic, and optical properties.1-3 In
this field, inorganic as well as organometallic compounds have
been studied since they are the molecular precursors for
constructing such materials. Although compounds containing
† Faculty of Engineering Science, Osaka University.
‡ Faculty of Science, Osaka University.
X Abstract published in AdVance ACS Abstracts, September 1, 1996.
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S0002-7863(96)00606-3 CCC: $12.00 © 1996 American Chemical Society

9084 J. Am. Chem. Soc., Vol. 118, No. 38, 1996
Mashima et al.
The chemistry of multiply-bonded dinuclear complexes, which
are monomers in eq 1, has been developed for last two decade,
and a great variety of the quadruply bonded dinuclear complexes
including the δ bonding has been synthesized.16,17 With an
intent for assembling one-dimensional binary systems from
organic and inorganic molecules, the interaction of multiply-
bonded M2 complexes with bidentate organic donor ligands has
also been actively investigated (eq 2).18-21 On the other hand,
the direct metal-to-metal axial interaction among multiply
bonded M2 units (eq 3) has not been achieved.5
We are interested in the reaction shown in eq 4, in which the
addition of two metal atoms to the axial positions of a multiple
metal-metal bond, as one of the preparative routes to metal
chains.23 For preparing the required complexes, it is strategically
important to choose a ligand supporting metal atoms at the
specified positions. Many multinuclear complexes have already
been synthesized by using different kinds of bidentate ligands,
i.e., O-N bridging9-11,24-28 and N-P bridging8,29 ligands. We
used a tridentate ligand of 6-diphenylphosphino-2-pyridonate
(abbreviated pyphos), which has three coordination sites, O, N,
and P, supported linearly by the rigid pyridone ring.30 Thus,
the pyphos ligand is found to be one of the most suitable ligands
for arranging transition metals in linear manner. Here, we fully
describe the syntheses and characterization of a dinuclear Mo2
complex and then the tetranuclear complexes having specified
linear structures, e.g., M(II)‚‚‚MoMo‚‚‚M(II) and M(I)-MoMo-
M(I) (M ) Pd and Pt), supported by the pyphos ligands.
Results
The multiply bonded M2 complexes are now found to undergo
a variety of the reactions cognate to that of carbon-carbon
multiple bonds, namely, substitution, oxidative addition, reduc-
tive elimination, metathesis and [2 + 2] cycloaddition of metal-
metal multiply bonded dinuclear complexes.16,22
Synthesis and Structure of Mo2(pyphos)4 (1). Dinuclear
molybdenum(II) complex, Mo2(pyphos)4 (1) (pyphos ) 6-diphe-
nylphosphino-2-pyridonate), was obtained by the ligand ex-
change reaction of a quadruply-bonded dinuclear complex,
Mo2(O2CCH3)4,31 with 6-diphenylphosphino-2-pyridone (ab-
breviated as pyphosH) in the presence of sodium methoxide in
dichloromethane (eq 5). The yellow color of the reaction
mixture immediately turned red. Removal of sodium acetate
followed by crystallization from dichloromethane-diethyl ether
afforded 1 as red plates in 53% yield. The 31P{1H} NMR
spectrum of 1 displayed a singlet at δ -7.8, indicating that four
phosphorus atoms of the four pyphos ligands of 1 are equivalent
in solution. The chemical shift value lies in the range of
conventional triaryl-substituted phosphorus nuclei. Thus, the
four phosphorus atoms are free from coordination to transition
metal, and the dinuclear structure consists of bridged N and O
chelation of the four pyphos ligands.
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Figure 1 shows the crystal structure of 1. Selected atomic
distances and angles are given in Table 1. Complex 1
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Straight Linear Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 118, No. 38, 1996 9085
Two vacant coordination sites at both axial positions of the
Mo-Mo quadruple bond are sufficient to have a transition metal
atom since the distances between two phosphorus atoms
arranged at each mutually trans position are 3.826(6) Å and
3.753(6) Å. Complex 1 has an eclipsed structure with two pairs
of pyridonates placed at right angles, which is an important
general feature of quadruply-bonded dinuclear complexes.16 The
vector of P‚‚‚N‚‚‚O of pyphos ligands does not parallel with
that of Mo-Mo bond, and thus dihedral angles between the
plane defined by P‚‚‚N-Mo and the plane defined by N-Mo-
Mo in four pyphos ligands are 9°, 179°, 4°, and 179°.
Syntheses and Structures of Mo2Pd2X4(pyphos)4 (2) and
Mo2Pt2X4(pyphos)4 (4) (a: X ) Cl; b: X ) Br; c: X ) I).
The dinuclear complex 1 reacted immediately with 2 equiv of
PdCl2(PhCN)2 in dichloromethane to give a tetranuclear com-
plex, Mo2Pd2Cl4(pyphos)4 (2a) (eq 6), in which two PdCl2
moieties are coordinated by two sets of trans arranged phos-
phorus atoms of the pyphos ligands and thus are placed at both
axial positions of Mo2 core, but there is no direct bonding
interaction between two PdCl2 and Mo2 core. The 31P{1H}
NMR spectrum of 2a displayed a singlet peak at δ 16.1, a value
which is close to that (δ 17.1) of the related Pd(II) mononuclear
complex, PdCl2(pyphosH)2 (3a).36 A bromo derivative, Mo2-
Pd2Br4(pyphos)4 (2b), was also synthesized by the reaction of
1 and 2 equiv of PdBr2(cod) (cod ) 1,5-cyclooctadiene). In
contrast, when we measured the 31P{1H} NMR spectrum of a
reaction mixture of 1 and 2 equiv of PdI2(cod) in CDCl3, no
signal assignable to the corresponding iodo derivative was
observed. This is ascribed to the spontaneous formation of a
reduced Pd-Mo bonded product, Mo2Pd2I2(pyphos)4 (6c) (Vide
infra), under this reaction condition.
Figure 1. Two ORTEP drawings of 1: a perspective perpendicular to
the MosMo vector (top) and a view down the metal-metal bond
(bottom). Thermal ellipsoids are drawn at the 30% probability.
Table 1. Selected Bond Distances (Å) and Angles (deg) of
Mo2(pyphos)4 (1)
distances
Å
angles
deg
Mo(1)sMo(2)
Mo(1)sO(1)
Mo(1)sO(3)
Mo(1)sN(2)
Mo(1)sN(4)
Mo(2)sO(2)
Mo(2)sO(4)
Mo(2)sN(1)
Mo(2)sN(3)
P(1)‚‚‚P(3)a
P(2)‚‚‚P(4)a
2.098(2)
2.086(8)
2.075(8)
2.18(1)
Mo(2)sMo(1)sO(1)
Mo(2)sMo(1)sO(3)
Mo(2)sMo(1)sN(2)
Mo(2)sMo(1)sN(4)
O(1)sMo(1)sO(3)
O(1)sMo(1)sN(2)
O(1)sMo(1)sN(4)
O(3)sMo(1)sN(2)
O(3)sMo(1)sN(4)
N(2)sMo(1)sN(4)
Mo(1)sMo(2)sO(2)
Mo(1)sMo(2)sO(4)
Mo(1)sMo(2)sN(1)
Mo(1)sMo(2)sN(3)
O(2)sMo(2)sO(4)
O(2)sMo(2)sN(1)
O(2)sMo(2)sN(3)
O(4)sMo(2)sN(1)
O(4)sMo(2)sN(3)
N(1)sMo(2)sN(3)
95.9(3)
94.4(2)
89.8(3)
90.4(3)
169.6(4)
91.6(3)
86.9(3)
87.8(3)
93.6(3)
178.6(3)
95.7(3)
95.2(3)
89.8(3)
90.9(3)
169.0(4)
90.5(3)
87.1(3)
88.4(4)
93.9(3)
177.5(3)
2.17(1)
2.077(8)
2.071(9)
2.193(9)
2.163(9)
3.754(6)
3.826(5)
This synthetic method was applied to the synthesis of the
corresponding platinum complexes. Platinum(II) complexes
such as PtCl2(cod) react with 1 slower than the palladium(II)
analogues. A reaction mixture of 1 and 2 equiv of PtCl2(cod)
at 40 °C for 4 days resulted in the quantitative formation of a
a Nonbonded contact.
approximates closely to D2d symmetry, and its structural feature
is similar to that of Mo2(mhp)4 (mhp ) 6-methylpyridonate).24
The Mo-Mo distance (2.098(2) Å) of 1 is unexceptional for
tetranuclear complex, Mo2PtII Cl4(pyphos)4 (4a), whose structure
2
is the same as that of 2. The 31P{1H} NMR spectrum of 4a
displayed a singlet peak at δ 12.6 (JPt-P ) 3592 Hz) due to the
four equivalent phosphorus atoms coordinating to platinum(II).
This chemical shift value and the Pt-P coupling constant are
the same as those (δ 12.6 ppm, JPt-P ) 3592 Hz) found for a
that of σ2π4δ2 quadruply-bonded MoII and is comparable to
2
that of Mo2(O2CCH3)4 (2.0934(8) Å)32 and Mo2(mhp)4 (2.065-
(1) Å)24 but is shorter than that of typical triply-bonded MoIII
2
complexes such as Mo2(OCH2CMe3)6 (2.222(2) Å),33 Mo2-
(OCHMe2)4(mhp)2 (2.206(1) Å),34 and Mo2(O2CMe)4(CH2-
CMe3)2 (2.130(1) Å).35
mononuclear platinum(II) complex, PtCl2(pyphosH)2 (5a).36
A
bromo derivative, Mo2Pt2Br4(pyphos)4 (4b), and an iodo deriva-
tive, Mo2Pt2I4(pyphos)4 (4c), were synthesized similarly by
reaction of 1 with 2 equiv of PtBr2(cod) and PtI2(cod),
respectively, in dichloromethane. The 31P{1H} NMR spectra
of 4b (δ 11.4, JPt-P ) 3534 Hz) and 4c (δ 7.9, JPt-P ) 3283
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(35) Chisholm, M. H.; Huffman, J. C.; Van Der Sluys, W. G. Inorg.
Chim. Acta 1986, 116, L13.
(36) Nakano, H.; Nakamura, A.; Mashima, K. Inorg. Chem. 1996, 35,
4007.

9086 J. Am. Chem. Soc., Vol. 118, No. 38, 1996
Mashima et al.
[91.61(9)-95.0(1)°] are obtuse. This distortion might be
resulted from longer Pd‚‚‚Mo distances than the distance of
PsN chelation.
Syntheses of Mo2Pd2X2(pyphos)4 (6) and Mo2Pt2X2-
(pyphos)4 (7) (a: X ) Cl; b: X ) Br; c: X ) I). In the
presence of Et4NBH4, treatment of 1 with 2 equiv of PtI2(cod)
for 2 days resulted in the formation of a tetranuclear complex
Mo2Pt2I2(pyphos)4 (7c) in 36% yield (eq 7). Spectral data as
well as elemental analysis revealed that 7c has two Pt(I) ions,
Figure 2. Molecular structure of 2b with a labeling scheme. Thermal
ellipsoids are drawn at the 30% probability.
Table 2. Selected Bond Distances (Å) and Angles (deg) of 2a, 2b,
and 4aa
2a
Distances, Å
2b
4a
Mo1sMo1*
Mo1sM1
M1sX1
M1sX2
M1sP1
2.096(3)
2.943(2)
2.287(4)
2.282(5)
2.341(5)
2.333(6)
2.06(1)
2.095(4)
2.902(3)
2.427(3)
2.433(3)
2.344(7)
2.347(7)
2.08(2)
2.101(2)
2.9292(9)
2.307(3)
2.304(3)
2.320(3)
2.323(3)
2.110(7)
2.096(7)
2.160(8)
2.152(8)
4.615(5)
M1sP2
Mo1sO1
Mo1sO2
Mo1sN1
Mo1sN2
P(1)‚‚‚P(2)b
2.10(1)
2.07(2)
2.14(1)
2.15(1)
2.12(2)
2.16(2)
and thus two platinum ions are reduced to Pt(I) in the reaction
course. The 31P{1H} NMR spectrum of 7c in CDCl3 displayed
a peak at δ 26.7 (JPt-P ) 3331 Hz) and was different from that
of 4c, indicating that all phosphorus atoms coordinated to
4.638(8)
4.666(9)
Angles, deg
179.2(1)
82.8(1)
83.0(1)
95.0(1)
92.4(1)
1
M1sMo1sMo1*
Mo1sM1sP1
Mo1sM1sP2
Mo1sM1sX1
Mo1sM1sX2
177.4(1)
84.6(2)
83.4(2)
91.61(9)
94.7(1)
179.43(5)
83.54(7)
83.73(7)
94.35(8)
93.27(8)
platinum(I) atoms. In the H NMR spectrum of 7c, 3-H and
5-H resonances of the pyphos ligand are found to have an upfield
shift (ca. 1.0 ppm) from those of 4c, but 4-H resonance is
displayed by downfield shift (0.6 ppm). Such a change in the
chemical shift of pyridone protons upon formation of 7c from
4c could be due to the decrease of magnetic anisotropy around
Mo2 core.37 During a reaction course, complex 4c was detected
by 31P{1H} NMR spectroscopy. Thus, complex 7c was prepared
alternatively by the reduction of 4c by using Et4NBH4 in
dichloromethane, but chemical yield was low (11%) (eq 8). The
most convenient method for the preparation of 7c is heating at
300 °C in Vacuo of solid sample derived from 1 and 2 equiv of
PtI2(cod) without any reductant (eq 8). This reaction is
accompanied by an elimination of iodine (see Experimental
Section). Complex 7a and 7b were synthesized by reaction of
1 with 2 equiv of PtCl2(cod) and PtBr2(cod), respectively. At
the early stage of these reactions, 4a and 4b were also detected
by 31P{1H} NMR spectroscopy.
a M denotes the metal atom at the axial position of Mo 4 Mo, and X
denotes halogen atoms bound to M; M ) Pd, X ) Cl for 2a, M ) Pd,
X ) Br for 2b, and M ) Pt, X ) Cl for 4a. b Nonbonded contact.
Hz) are quite similar to those of the related Pt(II) mononuclear
complexes, trans-PtBr2(pyphosH)2 (5b) (δ 11.4, JPt-P ) 3534
Hz) and trans-PtI2(pyphosH)2 (5c) (δ 7.9, JPt-P ) 3381 Hz),
respectively.36 The H NMR spectra of 4 are also similar to
1
those of 5.
The complexes 2a, 2b, and 4a were crystallized in C2/c space
group. Their structural features are essentially the same, and
thus the crystal structures of 2b and 4a are shown in Figures 2
and 3, respectively. Interatomic distances and angles of 2a,
2b, and 4a are given in Table 2. In these complexes, a C2 axis
is passing through the center of two molybdenum atoms and
therefore the half of them, i.e., the moiety of MoMX2(pyphos)2,
is a crystallographically unique part. The Pd-Mo distances of
2a [2.943 (2) Å] and 2b [2.902(3) Å] and the Pt-Mo distance
of 4a [2.9292 (9) Å] are too long for both atoms to interact
strongly. This is consistent with the fact that the MosMo
distance [2.095(4)-2.101(2) Å] of 2a, 2b, and 4a is almost the
same as that of 1. Both M(II) atoms are in a square-planar
configuration comprised of two halogen atoms and two phos-
phorus atoms in trans arrangement. Two MX2P2 planes are
oriented perpendicular to the vector of MosMo bond. Each
of the palladium and the platinum atoms is somewhat deviated
outside from the position expected for a normal square
coordination plane and close to tetrahedral. The coordination
geometry of M(II) approaches to tetrahedron. The acute angles
were observed for MosMsP (M ) Pd for 2a and 2b, M ) Pt
for 4a) [82.8(1)-84.6(2) degree, while the angles of MosMsX
Palladium derivatives 6a-c were prepared by the similar
reactions (eqs 7 and 8). Treatment of 1 with 2 equiv of
PdCl2(PhCN)2 in the presence of Et4NBH4 for 2 h led to the
(37) Cotton, F. A.; Ren, T. J. Am. Chem. Soc. 1992, 114, 2237.

Straight Linear Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 118, No. 38, 1996 9087
Table 3. Selected Bond Distances (Å) of 6 and 7a
6a 6b
2.1208(9) 2.1221(9)
6c
Mo1sMo2
Mo1sPd1
Mo2sPd2
Pd1sX1
Pd2sX2
Pd1sP2
Pd1sP4
Pd2sP1
Pd2sP3
Mo1sO1
Mo1sO3
Mo1sN2
Mo1sN4
Mo2sO2
Mo2sO4
Mo2sN1
Mo2sN3
P‚‚‚Pb
2.119(2)
2.711(2)
2.687(2)
2.695(2)
2.680(2)
2.274(6)
2.277(6)
2.275(6)
2.284(6)
2.03(1)
2.08(1)
2.16(2)
2.17(1)
2.05(1)
2.06(1)
2.19(2)
2.20(2)
4.539(8)
4.541(9)
2.689(4)
2.679(4)
2.42(1)
2.42(1)
2.283(6)
2.687(4)
2.690(4)
2.562(5)
2.511(4)
2.282(6)
2.287(6)
2.04(1)
2.15(2)
2.05(2)
2.25(2)
2.285(7)
2.04(1)
2.19(2)
2.06(2)
2.22(1)
Figure 3. Molecular structure of 4a with a labeling scheme. Thermal
ellipsoids are drawn at the 30% probability.
4.57(1)
4.56(1)
4.57(1)
4.56(1)
P‚‚‚Pb
7a
7b
7c
Mo1sMo2
Mo1sPt1
Mo2sPt2
Pt1sX1
Pt2sX2
Pt1sP2
Pt1sP4
Pt2sP1
Pt2sP3
2.134(1)
2.687(3)
2.639(4)
2.42(1)
2.44(1)
2.247(8)
2.135(2)
2.647(1)
2.668(1)
2.534(2)
2.542(2)
2.253(5)
2.263(5)
2.256(4)
2.261(4)
2.06(1)
2.07(1)
2.19(1)
2.20(1)
2.07(1)
2.06(1)
2.17(1)
2.18(1)
4.510(6)
4.499(6)
2.135(2)
2.682(2)
2.669(2)
2.703(1)
2.695(2)
2.260(5)
2.256(5)
2.266(6)
2.258(6)
2.05(1)
2.04(1)
2.16(2)
2.18(1)
2.06(1)
2.07(1)
2.20(1)
2.22(1)
4.508(7)
4.512(8)
2.284(7)
2.03(2)
2.23(2)
2.09(1)
2.18(2)
Mo1sO1
Mo1sO3
Mo1sN2
Mo1sN4
Mo2sO2
Mo2sO4
Mo2sN1
Mo2sN3
P‚‚‚Pb
Figure 4. Molecular structure of 6b. Thermal ellipsoids are drawn at
the 30% probability.
tetranuclear complex, Mo2Pd2Cl2(pyphos)4 (6a), in 40% yield
(eq 7). The formation of 6a also proceeded stepwise since 6a
was readily prepared by the reaction of 2a with Et4NBH4 in
dichloromethane (60% yield) (eq 8). Complex 6b was prepared
by treatment of 1 with 2 equiv of PdBr2(cod) in the presence
of Et4NBH4 and reduction of 2b by Et4NBH4. Gentle heating
up to 300 °C in attempts to determine the melting points for 2a
and 2b did not cause melting, but the complexes were converted
to the palladium(I) complexes, 6a and 6b (eq 8). Reaction of
1 with 2 equiv of PdI2(cod) at room temperature gave rise to
Mo2Pd2I2(pyphos)4 (6c) in 50% yield without any reducing
reagent since PdI2(cod) is easily reducible.
4.57(1)
4.49(2)
P‚‚‚Pb
a X denotes halogen atoms bound to M, X ) Cl for 6a and 7a, X )
Br for 6b and 7b, and X ) I for 6c and 7c. b Distances between two
atoms arranged at a mutually trans position.
atom and one molybdenum atom. The coordination planes of
two Pd(I) atoms are coplanar to the MosMo bond. The
MosMo bond length (2.1221(9) Å) of 6b is longer than that
found for 1, 2a, 2b, and 4a, indicating that the MosMo bond
is elongated by the coordination of two Pd(I) atoms. The
complex 6b has two MosPd distances, i.e., 2.687(4) Å and
2.690(4) Å, values which are short enough to be regarded as a
single bond.
The chloro complex 6a has the same arrangement with 6b.30
Complex 6c crystallized in the P21/n space group. Complex
6c has the quite similar disposition to 6b although the entire
molecule constitutes an asymmetric unit and no crystallographic
symmetry is imposed on it.
The platinum complexes 7 have essentially the same stere-
ochemical arrangement as the palladium analogue. Complex
7c is isomorphous with 7b and 6c, while complex 7a is
isomorphous with 6a and 6b. Figure 5 shows the drawing of
7b. The MosMo distance of 7 lies in a range of 2.134(1)-
2.135(2) Å , which is longer than that of 1 and is significantly
longer than those (2.119(2)-2.1221(9) Å) of palladium com-
plexes 6. The PtsMo distances (2.639(4)-2.687(3) Å) of 7
are shorter than the PdsMo distances (2.679(4)-2.711(2) Å)
of 6. The bonding interaction between the platinum atom and
the molybdenum atom is stronger than that between the
palladium atom and the molybdenum atom.
When we measured Raman spectra of 2 and 4 (Vide infra),
photochemical reduction of 2 and 4 readily proceeded, and
thereby the peak of photo reduction product 6 and 7 was detected
concurrently (eq 8).
Crystal Structures of 6 and 7. Crystal structure of 6a was
previously communicated.30 The crystal structures of 6b, 6c,
and 7 were determined by X-ray analysis, and structural feature
of all 6 and 7 are described. Complexes 6 and 7 crystallized in
two series of the isomorphous packing structures; one is
tetragonal space group I41, and the other is monoclinic space
group P21/n. Complexes 6a, 6b, and 7a crystallized in I41 space
group which possesses a C2 axis in the molecule, while 6c, 7b,
and 7c crystallized in P21/n without any crystallographic
symmetry within the molecule.
Figure 4 shows two drawings of 6b. The interatomic
distances and bond angles of 6 and 7 are listed in Tables 3 and
4, respectively. Four metal atoms and two bromine atoms are
aligned on a C2 axis and thus the BrsPdsMosMosPdsBr
skeleton supported by four pyphos ligands is linear. Two Pd-
(I) atoms occupy both axial positions of the Mo2 moiety, and
each palladium atom has the square planar geometry comprised
of two phosphorus atoms in trans arrangement, one bromine

9088 J. Am. Chem. Soc., Vol. 118, No. 38, 1996
Table 4. Selected Bond Angles (deg) of 6 and 7a
Mashima et al.
Table 5. UV-vis Absorption Maxima of 1, 2, 4, 6, and 7
6a
6b
6c
complex
λ
max (nm) (ꢀ (M-1 cm-1))
Pd1sMo1sMo2
Pd2sMo2sMo1
X1sPd1sMo1
X2sPd2sMo2
Mo2sPd2sP1
Mo2sPd2sP3
Mo1sPd1sP2
Mo1sPd1sP4
Mo2sMo1sO1
Mo2sMo1sO3
Mo1sMo2sO2
Mo1sMo2sO4
Mo1sMo2sN1
Mo1sMo2sN3
Mo2sMo1sN2
Mo2sMo1sN4
180.00
180.00
180.00
180.00
87.5(2)
180.00
180.00
180.00
180.00
87.9(2)
179.6(1)
176.4(1)
177.9(1)
174.83(9)
86.7(1)
88.1(1)
86.1(1)
85.5(1)
94.5(3)
94.3(3)
93.6(3)
96.3(3)
88.3(4)
89.6(4)
90.0(4)
88.8(4)
1
465 (9.0 × 103)
482 (3.2 × 103)
486 (2.5 × 103)
485 (4.6 × 103)
515 (4.3 × 103)
504 (a)
2a
2b
4a
4b
4c
6a
6b
6c
7a
7b
7c
87.1(2)
93.8(5)
97.4(5)
89.0(4)
88.3(4)
86.7(2)
96.6(5)
94.3(5)
87.5(4)
89.5(4)
458 (1.3 × 104)
470 (1.3 × 104)
489 (5.3 × 103)
409 (1.4 × 104)
414 (1.4 × 104)
418 (1.6 × 104)
642 (3.0 × 104)
662 (4.7 × 104)
706 (4.0 × 104)
506 (3.1 × 104)
523 (4.7 × 104)
564 (7.4 × 104)
a Contamination of complex 7c.
distance found for these complexes. The MosMo distance
(2.065(1) Å) of Mo2(mhp)4 is shorter than that of 1, 2, 4, 6,
and 7, although Mo2(mhp)4 has almost the same distance (ca.
2.3 Å) of four N‚‚‚O chelations as these complexes.24 This
indicates that the MosMo distance is not affected by the N‚‚‚O
chelation. Moreover, no significant variation is found for the
P‚‚‚N distances among 1, 2, 4, 6, and 7. Thus the coordination
of two M(I) atoms to both ends of the Mo2 core in 6 and 7
elongates the MosMo distance and shortens the MosM bond,
resulting in the new addition reaction of two metals to a metal-
to-metal multiple bond.
Dihedral angles between the planes defined by P‚‚‚NsMo
and the planes defined by NsMosMo indicate the degree of
the deviation of pyphos ligands from the line of MosMo. The
dihedral angles of 2 and 4 are around 21°, and the averaged
dihedral angles of 6 and 7 lie in the range 12 and 16°. All
these values are larger than those of 1, indicating that the
direction of diphenylphosphino moiety of pyphos ligand in 2,
4, 6, and 7 turned aside from that observed for 1. This
divergence might be ascribed to the insertion of M atoms
between the each trans phosphorus atoms. This insertion of
M atoms between two phosphorus atoms makes the P‚‚‚P
distances (ca. 4.5-4.6 Å) in 2, 4, 6, and 7 considerably longer
than those in 1 (3.8 Å). In spite of the observed deviation of
pyphos ligands from the original position, the linearity of the
MsMosMosM fragment is maintained. Thus the pyphos
ligand has a remarkable ability to align metal atoms linear.
Electronic Spectra. The spectral data of 1, 2, 4, 6, and 7
are numerically shown in Table 5. The dinuclear complex 1
exhibited one distinct peak at 465 nm, which is typical of δ-δ*
excitation due to the MosMo quadruple bond.38,39 Each
electronic spectrum of 2 and 4 showed one distinct peak at 482-
486 and 485-515 nm, respectively, indicating that these have
the quadruply bonded MosMo bond.
7a
7b
7c
Pt1sMo1sMo2
Pt2sMo2sMo1
X1sPt1sMo1
X2sPt2sMo2
Mo2sPt2sP1
Mo2sPt2sP3
Mo1sPt1sP2
Mo1sPt1sP4
Mo2sMo1sO1
Mo2sMo1sO3
Mo1sMo2sO2
Mo1sMo2sO4
Mo1sMo2sN1
Mo1sMo2sN3
Mo2sMo1sN2
Mo2sMo1sN4
180.00
180.00
180.00
180.00
88.8(2)
177.03(8)
179.41(8)
173.61(7)
176.83(7)
86.7(1)
87.4(1)
88.2(1)
89.5(1)
94.1(3)
93.5(3)
94.0(3)
93.1(3)
88.5(3)
89.5(3)
89.2(3)
90.0(3)
179.57(9)
177.51(9)
177.96(7)
174.76(6)
88.7(1)
87.6(1)
86.6(1)
87.1(1)
93.4(3)
95.0(3)
93.9(3)
93.4(3)
90.1(3)
89.4(4)
89.0(4)
89.4(3)
87.6(2)
92.5(6)
97.2(5)
91.8(6)
86.1(5)
a X denotes halogen atoms bound to M, X ) Cl for 6a and 7a, X )
Br for 6b and 7b, and X ) I for 6c and 7c.
In the reaction course of formation of the linear tetranuclear
complexes 6 and 7, the color of the solution changed from red
to green (M ) Pd) or to purple (M ) Pt). The tetranuclear
complexes 6 and 7 show two characteristic visible absorption
maxima, both of which serve as a sensitive probe for MosM
(M ) Pd, Pt) and MosMo bonding. The peak at the higher
energy is assignable to δ-δ* excitation of the MosMo bond.
The other absorption of 6 and 7 is observed in the ranges of
506-564 and 642-706 nm, respectively, while 1, 2, and 4 have
no peak in these regions. Accordingly, the latter peak is ascribed
to the excitation at MosM bond, i.e., essentially charge transfer
from Mo atom to M atom.
Figure 5. Two ORTEP drawings of 7b; perspective perpendicular to
the PtsMosMosPt vector (top) and a view down the metal-metal
bond (bottom). Thermal ellipsoids are drawn at the 30% probability.
The position of MMCT band observed for 6 and 7 is in
accordance with the spectrochemical series of halo ligands, I
(38) Martin, D. S.; Newman, R. A.; Fanwick, P. E. Inorg. Chem. 1979,
18, 2511.
(39) Martin, D. S.; Huang, H.-W. Inorg. Chem. 1990, 29, 3674.
The distance of N‚‚‚O chelation (2.3 Å) of pyphos ligands
in 1, 2, 4, 6, and 7 is moderately longer than the Mo 4 Mo bond

Straight Linear Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 118, No. 38, 1996 9089
Table 6. Selected Raman Frequencies of 1, 2, 4, 6, and 7
ν(MosMo)
complex
(cm-1
)
others (cm-1
)
d(MosMo) (Å)a
1
394
403
403
403
395
395
386
386
387
381
382
381
2.098(2)
2.096(3)
2.095(4)
2.101(2)
2a
2b
4a
4b
4c
6a
6b
6c
7a
7b
7c
122
122
116
126
127
120
84
82
73
81
81
73
2.1208(9)
2.1221(9)
2.119(2)
2.134(1)
2.135(2)
2.135(2)
a Distance of MosMo multiple bond.
< Br < Cl, depending on electronegativities of halogen atoms.
Both complexes 6 and 7 have the same tendency, i.e., the
differences between a (X ) Cl) and b (X ) Br) are smaller
than those between b (X ) Br) and c (X ) I). On the
comparison of CT band between 6 and 7 with the same halo
ligand set, 6 have 140 nm longer wavelength than 7. The
maxima of δ-δ* excitation are also in accordance with the
spectrochemical series of halogen atoms. Comparing the
influence of M atoms to δ-δ* of MosMo, the excitation in 7
requires higher energy than that of 6. The differences of peak
wavelengths between 6a and 6b and between 6b and 6c are 12
and 19 nm, respectively, while those for 7 equal 5 nm. These
indicate that the MosMo multiple bonding of 6 is more
delicately influenced by the halogen ligands than that of 7.
Raman Spectra. The Raman active ν(MosMo) mode has
provided a highly useful spectroscopic probe of the nature of
bonding in many of the dimolybdenum complexes.40,41 The
wavenumbers of ν(MosMo) together with the MosMo distance
for 1, 2, 4, 6, and 7 are listed in Table 6. Complex 1 has a
ν(MosMo) peak at 394 cm-1 which is consistent with the
Figure 6. Photoreduction process of 2b with 514.5 nm laser irradiation
monitored by Raman spectra at moderate time intervals.
Scheme 1
24
frequency of ν(MosMo) observed for Mo2(mhp)4 and
Mo2(O2CCH3)4.42-45 The ν(MosMo) of 2 and 4 is observed
at slightly higher frequency (395-403 cm-1) than that of 1.
This is consistent with the crystallographic result that the
MosMo bond distance of 2 and 4 is almost the same as that of
1. The effects of halo ligands of 2 were too small to be detected,
and all three complexes 2 have the same value (403 cm-1) of
ν(MosMo). As mentioned above, photochemical reduction of
2 and 4 proceeded. Figure 6 shows time-dependent spectra of
2b upon irradiation of 514.5 nm laser. The intensity of
ν(MosMo) (386 cm-1) of 6b increased at the expense of the
intensity of that (403 cm-1) of 2b. For platinum complexes 4,
the ν(MosMo) peak was observed at the range of 395-403
cm-1 accompanied with the signal of each reduction product
of 7, whose intensity increased with irradiation time.
The resonance Raman spectra were measured for 6 and 7.
The most probable frequency assignable to ν(MosMo) in 6
and 7 was observed at 381-387 cm-1, lower wavenumber than
those in 1, 2, and 4. The assignment of this peak is strongly
supported by the excitation profiles of resonance Raman spectra.
The example of 6c is shown in Figure 7, in which eight
wavelengths of excitation were used. The excitation profiles
of these spectra are shown in Figure 8. The most effective
enhancement of the ν(MosMo) peak strength was observed
with the excitation of 454.5 nm. The spectrum with longer
wavelength of laser excitation gave the ν(MosMo) peak with
lower intensity, and the peak excited by 632.8 nm laser line
had the lowest peak intensity. This is attributed to the closest
wavelength of excitation (454.5 nm) to the absorption at 416
nm. On the other hand, two peaks at 116 and 73 cm-1 are
enhanced by the excitation whose wavenumber was the closest
to the longer wavelength absorption maximum at 706 nm.
A similar situation was observed for five other complexes of
6a, 6b, and 7a-c. The resonance Raman spectra of these
complexes were measured with three wavelengths (457.9, 514.5,
and 632.8 nm) of laser excitation. In the spectra of these
complexes, the most effective enhancement of the ν(MosMo)
peak strength was generally observed when the laser excitation
of 457.9 nm was used since this excitation has the closest
wavelength to the δ-δ* absorption around 400-500 nm. The
514.5 nm excitation gave the ν(MosMo) peak with lower
intensity and the peak excited by 632.8 nm laser line had the
(40) Clark, R. J. H.; Franks, M. L. J. Am. Chem. Soc. 1975, 97, 2691.
(41) Manning, M. C.; Holland, G. F.; Ellis, D. E.; Trogler, W. C. J.
Phys. Chem 1983, 87, 3093.
(42) Bratton, W. K.; Cotton, F. A.; Debeau, M.; Walton, R. A. J. Coord.
Chem. 1971, 1, 121.
(43) San Filippo, J. J.; Sniadoch, H. J. Inorg. Chem. 1973, 12, 2326.
(44) Ketteringham, A. P.; Oldham, C. J. Chem. Soc., Dalton Trans. 1973,
1067.
(45) Clark, R. J. H.; Hempleman, A. J.; Kurmoo, M. J. Chem. Soc.,
Dalton Trans. 1988, 973.

9090 J. Am. Chem. Soc., Vol. 118, No. 38, 1996
Mashima et al.
Figure 7. Resonance Raman spectra of 6c using various wavelengths
of laser excitation.
Figure 9. Cyclic voltammograms of 1 (top), 4a (middle), and 7c
(bottom). Condition: 1.0 mM dichloromethane solution, 0.2 M tetra-
n-butylammonium perchlorate as supporting electrode, Ag/AgCl, the
scan rate of 100 mV/s.
stretching and MosMosM bending, respectively. As shown
in Figure 7, two Raman peaks (116 and 73 cm-1) of 6c are
enhanced by the irradiation whose wavelength is close to the
absorption maximum of MoM charge transfer band. Thus these
peaks are ascribed to the vibrations related MsMo bonding;
however, the strict assignment is difficult at present.
Electrochemistry. Cyclic voltammetry of each complex is
performed in dichloromethane solution containing tetra-n-
butylammonium perchlorate as supporting electrode and data
were referred to Ag/AgCl. The dinuclear complex 1 displayed
a quasi-reversible redox wave at E1/2 ) +80 mV (Figure 9)
assignable to one-electron oxidation at the filled δ-bonding level
of the MosMo quadruple bond.48-52 Cyclic voltammetry of
complexes 2a-c, 4b, and 4c gave rather complicated waves,
which could not be assigned; however, the CV of complex 4a
afforded two quasi-reversible waves at E1/2 ) +270 mV and
Figure 8. UV-vis spectrum and excitation profiles of 6c. Relative
intensity of peaks at 387 cm-1 for b, at 116 cm-1 for O, and at 73
cm-1 for 2.
(46) Durig, J. G.; Lau, K. K.; Nagarajan, G. N.; Walker, M. J. B. J.
Chem. Phys. 1969, 50, 2130.
(47) Stein, P.; Dickson, M. K.; Max Roundhill, D. J. Am. Chem. Soc.
1983, 105, 3489.
(48) Cotton, F. A.; Pedersen, E. Inorg. Chem. 1975, 14, 399.
(49) Zeitlow, T. C.; Klendworth, D. D.; Nimry, T.; Salmon, D. J.; Walton,
R. A. Inorg. Chem. 1981, 20, 947.
(50) Santure, D. J.; Huffman, J. C.; Sattelberger, A. P. Inorg. Chem.
1985, 24, 371.
(51) Chisholm, M. H.; Clark, D. L.; Huffman, J. C.; Van Der Sluys, W.
G.; Kober, E. M.; Lichtenberger, D. L.; Bursten, B. E. J. Am. Chem. Soc.
1987, 109, 6796.
lowest peak intensity, while two peaks at 120-126 and 73-84
cm-1 are enhanced by the excitation whose wavenumber was
the closest to the CT band, i.e., 632.8 nm laser excitation for
6a and 6b, 514.5 nm for 7a-7f.
Analyzing with linearly linked four atoms model,
MsMosMosM, which is assumed to be in D∞h point group,
five of the symmetry coordinates exist.46,47 The Raman active
vibration results from three modes of Σg+, Σg+, and Πg, which
are described approximately by MosMo stretching, MsMo
(52) Lin, C.; Protasiewicz, J. D.; Smith, E. T.; Ren, T. J. Chem. Soc.,
Chem. Commun. 1995, 2257.

Straight Linear Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 118, No. 38, 1996 9091
Table 7. E1/2 [mV] Values for 6 and 7 by Cyclic Voltammograma
PdCl2(pyphos)2(O2CCH3)2]2 (9)30 and [Mo2PtX2(pyphos)2(O2-
CR)2]2 [R ) CH3 (10), R ) CMe3 (11)]36 in which M(II) (M
) Pd, Pt) atoms are square-planar and are coordinated by two
phosphorus atoms and two halogen atoms in cis-fashion. The
MsMo distances of 9 and 10 is comparable to those of 2 and
4 and longer than those of 6 and 7.
complex
E1/2 [mV]
complex
E1/2 [mV]
6a
6b
6c
+530, +350
+560, +360
+520, +350
7a
7b
7c
+490, +270
+510, +290
+510, +290
a All compounds were studied as 1.0 mM solutions in dichlo-
romethane containing 0.2 M tetra-n-butylammonium perchlorate as
supporting electrode at the scan rate of 100 mV/s.
The key step of the formation of 6 and 7 is the reduction of
two M(II) atoms in 2 and 4, resulting in the elimination of two
halo ligands and the coordination of a Mo atom of Mo2 core to
each M(I) atom. The molybdenum atom is formally acting as
a ligand of square-planar M(I) ions. The most interesting feature
of this reaction is that the orientation of two coordination planes
of M atoms has changed from perpendicular to coplanar to the
MosMo line, which is schematically shown in Scheme 1. The
complexes 2 and 4 are also easily reduced by heating or
photoirradiation. The platinum derivatives, 4a-c are somewhat
more stable than the corresponding palladium complexes, and
thus the reduction of 4 takes longer times than that of 2. Thus,
it is generally concluded that the initially formed 2 and 4 are
reduced to 6 and 7, respectively. The odd oxidation state of
group 10 metal atoms, i.e., +1 and +3, are generally important
to generate metal-metal bond and thus the reduction or
oxidation is accompanied by the formation of MsM bond. Some
multimetal complexes without any metal-to-metal bond were
oxidized to give the metal-metal bonded ones. Representative
examples are the Pt2Pd complexes such as cis-[(NH3)2Pt(1-
MeU)2Pd(1-MeU)2Pt(NH3)2]2+ (MeU ) 1-methyluracilato)10b
and Pt2 complexes such as [Pt2H(µ-dppm)2(η1-dppm)]Cl,53 [Pt2-
Cl2(pyt)4] (pyt ) anion of pyridine-2-thiol),54 and [Pt(C8-
doH)2Cl2]2 (C8doH represents C8 carbocyclic R-dioximate ligand
{C8H12(dNO)2H}-).55
-330 mV (Figure 9). The first process is the same as 1, and
the second one is attributed to a reduction process for generating
7a.
In contrast, the tetranuclear complexes 6 and 7 display two
quasi-reversible redox waves, and the electrochemical data are
summarized in Table 7. Figure 9 shows representative cyclic
voltammograms of 7c. These E1/2 values indicate that the
substitution of palladium atoms with platinum atoms provides
redox waves with ca. 50 mV negative shift, which is reasonable
on taking account of the M+ f M2+ ionization energies (Pd:
1875 kJ/mol; Pt: 1791 kJ/mol). The variation of halo ligands
bound to metals hardly influences the redox process.
We examined the electrooxidation of 7c at the sufficiently
higher potential than that of the second oxidation process (+0.51
V) by using a platinum disk electrode. The electrolysis of 7c
at +0.70 V for 10 min afforded the corresponding platinum(II)
complex 4c in ca. 70% yield (monitored by 31P{1H} NMR
spectrum together with electronic spectrum). The formation of
4c may indicate that each of the two redox processes of 6 and
7 in cyclic voltammetry is a one electron oxidation process.
This assignment is supported by the following experimental
results to some extent. At the potential between the first redox
(+0.29 V) and that of the second redox (+0.51 V), the
electrolysis of 7c in dichloromethane was carried out. After
the electrolysis at +0.45 V for 1 h was performed, the UV-vis
spectrum of the electrolysis solution did not indicate distinct
change, and its 31P{1H}NMR spectrum displayed a sharp singlet
at δ 25.6 due to the starting complex of 7c. When 7c was
electrolyzed at +0.50 V, no change was observed in UV-vis
spectrum, however, the 31P{1H}NMR spectrum displayed a
broad signal centered at δ 25.6 with the peak width at half height
of 31.8 Hz on a 109 MHz spectrometer. These results would
indicate that a paramagnetic species was formed by one electron
oxidation, and the resulting paramagnetic species broadened the
31P{1H}NMR signal. Unfortunately, all attempts to isolate and
perceive the paramagnetic species have been unsuccessful due
to its rapid conversion to 7c and unidentified materials.
It has been conceived that the construction of the straight
linear tetrametal system including a metal-metal multiple bond
is difficult. Chisholm and co-workers found that a tetranuclear
complex bearing two quadruply-bonded Mo2 moieties, [Mo2(O2C-
tBu)3]2(µ-2,7-O2N2C8H4) (8),5,56 has no direct metal-to-metal
interaction between two units of Mo 4 Mo which are aligned
parallel. In complex 8, each internal molybdenum atom is
coordinated by the oxygen atom of its neighboring µ-carboxy-
lates at the axial position of the Mo 4 Mo core. The oxygen
bridged Mo2O2 geometry results in no direct bonding interaction
between Mo atoms and the slip of two Mo2 moieties out of the
straight line. Such a Mo‚‚‚O interaction prevents the straight
linear alignment of four metals from two M2 core in dinuclear
M2(O2CR)4 complexes32,39,57,58 as well as in the dimer of the
trinuclear complexes such as 9,30 10,36 and 11.36
Discussion
Bonding Considerations. The MosMo bond of 6 and 7
may be considered as formally π4δ2 triple bond and is related
to the π4δ2 MosMo triple bond of Mo2(O2CMe)4(CH2CMe3)2
(12),35 where the MosMo distance [2.130(1) Å] is quite close
to that found for 6 and 7. The σ-bonding interaction between
two M(I) atoms and the Mo2 moiety in 6 and 7 elongates the
MosMo bond by 0.02-0.03 Å from that of 1, 2a, 2b, and 4a.
The MosMo bond length of 6 and 7 is shorter than that of the
MosMo triple bond in Mo2(OCH2CMe3)4(MeCOCHCOMe)2
[2.237(1) Å] and is much shorter than that of the triple bond
Formation of Multiply Bonded MsMosMosM Systems.
The trans-arrangement of each two phosphorus atoms in the
Mo2(pyphos)4 skeleton has superior ability to bind two other
metal atoms, which are allowed to interact with the terminals
of the MosMo quadruple bond. The distances between each
trans phosphorus atoms are sufficiently long to have platinum
ions or palladium ions at each site.
As shown in Figures 2 and 3, the complexes 2 and 4 have
two square planes comprised of M (M ) Pd, Pt), two halogen
atoms, and two phosphorus atoms. These planes are perpen-
dicular to the MosMo axis. The MosMo bond distance
indicates that they have quadruple as just found for 1. The
Raman spectra also suggested that 2 and 4 have the MosMo
quadruple bond based on the values of the ν(MosMo) peak.
Thus two M(II) atoms of 2 and 4 interact only weakly with the
molybdenum atoms. The comparable situation has already been
found in the dimer of trinuclear complexes such as [Mo2-
(53) Umakoshi, K.; Kinoshita, I.; Ichimura, A.; Ooi, S. Inorg. Chem.
1987, 26, 3551.
(54) Krevor, J. V. Z.; Yee, L. Inorg. Chem. 1990, 29, 4305.
(55) Baxter, L. A. M.; Heath, G. A.; Raptis, R. G.; Willis, A. C. J. Am.
Chem. Soc. 1992, 114, 6499.
(56) Cayton, R. H.; Chisholm, M. H.; Putilina, E. F.; Folting, K.
Polyhedron 1993, 12, 2627.
(57) Cotton, F. A.; Extine, M.; Gage, L. D. Inorg. Chem. 1978, 17, 172.
(58) Robbins, G. A.; Martin, D. S. Inorg. Chem. 1984, 23, 2086.

9092 J. Am. Chem. Soc., Vol. 118, No. 38, 1996
Mashima et al.
Table 8. Torsion Angles of OsMosMosO for 1, 2a, 2b, 4a, 6,
and 7
found for Mo2(OCH2CMe3)4(MeCOCHCOMe)2(CNCMe3)2
[2.508(2) Å].59-61
complex
OsMosMosN (deg)
The interaction between molybdenum and M(I) (M ) Pd,
Pt) is a novel aspect of our complexes. Some examples of
dinuclear complexes containing the PdsMo single bond have
been reported, e.g., [(t-BuNC)(OC)3Mo(µ-dpm)2PdI]+ (dpm )
bis(diphenylphosphino)methane)62 and (CO)4Mo(µ-PCy2)2Pd-
(PPh3).63 These PdsMo distances (2.870(2) and 2.760(1) Å,
respectively) are longer than that of 6. Compared with the
reported Mo(0)sPt(II) bond distance of (OC)4Mo(µ-PPh2)2Pt-
(PEt3), 2.766(1) Å,64 the corresponding values of 7 are shorter
by 0.1 Å.
1
1.2(4)
0.1(3)
-0.5(3)
-0.2(3)
2a
2b
4a
6a
6b
6c
7a
7b
7c
11.0(5)
-12.4(7)
12.1(3)
4.6(6)
-2.6(6)
10.0(6)
4.8(7)
11.8(5)
-9.9(6)
11.3(3)
-1.8(6)
3.1(6)
10.1(5)
-1.9(6)
11.5(4)
9.8(6)
9.3(5)
10.4(6)
10.6(4)
9.6(5)
10.3(4)
11.5(5)
8.9(4)
10.5(5)
The X-ray analysis clearly shows that the PtsCl distances
of 7a are longer than those in 4a and are comparable to that of
[Pt2(µ-dppm)2Cl(PPh3)](PF6) [2.403(14) Å].65 Generally, MsX
bonds of 6 and 7 are longer than those of the corresponding
complexes 2 and 4 as well as those of the conventional MsX
covalent bonds. This elongation might be explained in term of
the trans influence of the MosPt bond to the PtsCl one. For
the metal-metal single bond, similar trans influence of metal-
metal bond was reported in dinuclear platinum(I) complexes,
K4[Pt2(P2O5H2)4L2] (L ) SCN, NO2, and so on),66 and [Pt2(µ-
dppm)2Cl(PPh3)](PF6),65 in which the PtsCl bond length [2.403-
(14)Å] trans to PtsPt bond is close to that of 7a.
CR)4 by Cotton et al.67 It is also found that the MosMo bond
is only slightly extended by the axial coordination of organic
ligands.57
The torsion angle of OsMosMosN provides information
to the strength of the δ bond in the Mo2 core. The torsion angles
for all complexes are listed in Table 8. The torsion angles (0.1-
(3)-1.2(4)°) of 1 are nearly zero, indicating that 1 has the
eclipsed geometry around Mo2 core and the maximum of the
δ-bonding interaction. When two M(II) ions are introduced,
the torsion angles of complexes 2a, 2b, and 4a are deviated by
ca. 10 degree from the desired eclipsed geometry. In complexes
6 and 7, the iodo complexes 6c and 7c are deformed by 10
degree, while the torsion angles of chloro ones, 6a and 7a, are
small. Thus, the presence of metal atoms at both axial positions
of the Mo2 core might affect slightly the δ-δ* overlapping.
As this influence is not severe, these complexes have a
considerable amount of the δ bonding on the Mo2 core.
It is interesting to compare the influence of a halo ligand in
a series of complexes 6 and 7. The inductive effects exerted
by the halo ligand are evaluated by the comparison of the bond
lengths in 6 and 7. Structural data of 6 and 7 indicate that the
MosMo distance is insensitive to the identity of halogen, while
the mean value of the MsMo distances is affected by changing
halogen atoms, i.e., 6a (2.684 Å) ≈ 6b (2.685 Å) < 6c (2.699
Å) in Mo2Pd2 complexes and 7a (2.662 Å) ≈ 7b (2.658 Å) <
7c (2.676 Å) in Mo2Pt2 complexes.
Conclusion
The tetranuclear complexes of 2, 4, 6, and 7 are the first
example of dinuclear multiply bonded molybdenum(II) com-
plexes having later transition metal atoms as the axial ligands.
The linearity of MsMosMosM (M ) Pd, Pt) moieties is
enforced by the Mo2(pyphos)4 skeleton. We have elucidated
by single crystal X-ray analyses that 6 and 7 have the novel
structure possessing four metal atoms aligned straight linearly
and bonded directly each other, while there is essentially no
bonding interaction between Mo(II) and M(II) in complexes 2
and 4. The complexes 6 and 7 formally have two single
M(I)sMo(II) bonds and one triple MosMo bond (π4δ2). The
chemical reduction of 2 and 4 readily gives 6 and 7, respectively.
Thus, the reduction is essential to the formation of the MsMo
bond. The electrochemical study indicates that all the atoms
in the MsMosMosM system are electronically strongly
coupled to allow two well distinguished one electron redox
processes. In the Mo2M2X2(pyphos)4 system, the absorption
maxima are tunable by substitution of M atoms and X atoms.
The tetrametal skeleton of 6 and 7 is thermally and photo-
chemically very stable and not easily collapsed, and thus this
unit provides a unique part for constructing low dimensional
materials, which is of our current interest.
In contrast to the small effect by halo ligands bound to a
M(I) ion, we found distinct influence of axial metal substitution
to the MosMo bond length. The MosMo distances in Mo2-
Pd2 complexes, 6a-c [2.119(2)-2.127(2) Å], are shorter by
0.01 Å than those of Mo2Pt2 complexes, 7a-c (2.134(1)-2.135-
(2) Å). Compared with the MsMo distances of 6a-c with
those in 7a-c, the former distances are ca. 0.02 Å longer than
the latter ones, nonetheless the ionic radii of both metals are
almost the same. These indicate that the MsMo bonds for M
) Pt are stronger than those for M ) Pd. Stronger MosPt
interaction might be attributed to the relativistic effect for 5d
metals. Thus, it is concluded that the MosMo and MosM
(M ) Pd, Pt) bond lengths are inversely related, i.e., the longer
MosMo distance of 7 is attended by the shorter MsMo
distances. This is comparable to the relation between CrsCr
and CrsL (L ) axial ligands) distances reported for Cr2(O2-
(59) Chisholm, M. H.; Folting, K.; Huffman, J. C.; Ratermann, A. L.
Inorg. Chem. 1984, 23, 613.
(60) Chisholm, M. H.; Corning, J. F.; Folting, K.; Huffman, J. C.;
Ratermann, A. L.; Rothwell, I. P.; Streib, W. E. Inorg. Chem. 1984, 23,
1037.
Experimental Section
(61) Chisholm, M. H. Angew. Chem., Int. Ed. Engl. 1986, 25, 21.
(62) Balch, A. L.; Noll, B. C.; Olmstead, M. M.; Toronto, D. V. Inorg.
Chem. 1993, 32, 3613.
(63) Loeb, S. J.; Taylor, H. A.; Gelmini, L.; Stephan, D. W. Inorg. Chem.
1986, 25, 1977.
(64) Powell, J.; Couture, C.; Gregg, M. R.; Sawyer, J. F. Inorg. Chem.
1989, 28, 3437.
(65) Blau, R. J.; Espenson, J. M.; Kim, S.; Jacobson, R. A. Inorg. Chem.
1986, 25, 757.
General Methods. All manipulations for air- and moisture-sensitive
compounds were carried out by the use of the standard Schlenk
techniques under argon atmosphere. Each solvent was purified by
distillation under argon after drying over the desiccant shown below:
dichloromethane, calcium hydride or phosphorus pentaoxide; diethyl
ether, sodium benzophenone ketyl; chloroform-d, phosphorus pentaox-
ide; benzene-d6, sodium/potassium alloy. PdCl2(PhCN)2,68a PdX2(cod)
(66) Che, C.-M.; Lee, W.-M.; Mak, T. C. W.; Gray, H. B. J. Am. Chem.
Soc. 1986, 108, 4446.
(67) (a) Cotton, F. A.; Extine, M. W.; Rice, G. W. Inorg. Chem. 1978,
17, 176. (b) Cotton, F. A.; Wang, W. NouV. J. Chim. 1984, 8, 331.

Straight Linear Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 118, No. 38, 1996 9093
Table 9. Crystallographic Data of 1, 2, and 4a,b
complex
formula
solvent molecules
fw
cryst system
space group
1
2a
C69H54O4N4P4Mo2Cl2
dichloromethane (one)
1389.89
monoclinic
P21/c
C74H64O4N4P4Mo2Pd2Cl16
dichloromethane (six)
2169.17
monoclinic
C2/c
a, Å
b, Å
c, Å
14.755 (9)
24.96(1)
19.58(1)
111.56(4)
6709 (9)
4
1.376
MoKR
296
24.262(4)
12.300(3)
31.521(6)
112.86(1)
8667(3)
4
1.662
MoKR
296
â, deg
V, Å3
Z
Dcalc, g cm-3
radiation
temp, K
linear abs coeff, cm-1
cryst. size, mm
GOF
5.86
13.05
0.3 × 0.4 × 0.5
0.1 × 0.3 × 0.5
2.38
2.97
no. of unique data
no. of data with I >3σ(I)
no. of variables
R
12540
5308
920
0.062
11716
3468
496
0.084
Rw
0.082
0.064
complex
formula
2b
4a
C71H58O4N4P4Mo2Pd2Br4Cl6
C72H60O4N4P4Mo2Pt2Cl12
solvent molecules
fw
cryst system
space group
dichloromethane (three)
2092.17
monoclinic
C2/c
dichloromethane (four)
2176.68
monoclinic
C2/c
a, Å
b, Å
c, Å
32.540(5)
12.461(4)
19.759(3)
104.25(1)
7765(2)
4
1.789
MoKR
296
24.273(2)
12.278(3)
31.545(6)
112.87(1)
8662(2)
4
1.669
MoKR
296
â, deg
V, Å3
Z
Dcalc, g cm-3
radiation
temp, K
linear abs coeff, cm-1
cryst. size, mm
GOF
31.73
39.78
0.1 × 0.1 × 0.5
0.3 × 0.5 × 0.7
2.85
2.73
no. of unique data
no. of data with I >3σ(I)
no. of variables
R
7621
2556
446
0.068
13159
8292
452
0.054
Rw
0.058
0.090
2
a R ) ∑||Fo| - |Fc||/|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑wFo ]1/2. w ) 1/σ2(Fo); function minimized: ∑w(| Fo| - |Fc|)2.
(X ) Br, I),68b PtX2(cod) (X ) Cl, Br, I),68c and 6-diphenylphosphino-
2-pyridone (pyphosH)69 were prepared according to the literature.
Physical Measurements. Nuclear magnetic resonance (1H, 31P
NMR) spectra were measured on a JEOL JNM-GSX-270 spectrometer.
the working electrode was a glassy-carbon electrode, and the counter
electrode was a platinum wire. The measurements were recorded on
1.0 mM dichloromethane solution that contained 0.2 M tetra-n-
butylammonium perchlorate as supporting electrode at the scan rate of
100 mV/s. Under our experimental conditions the ferrocenium/
ferrocene couple was observed at E1/2 ) 520 mV vs Ag/AgCl.
The electrolysis was performed in stirred dichloromethane solution
(1.0 mM) of 7c containing 0.2 M tetra-n-butylammonium perchlorate
as supporting electrode. The working electrode and counter electrode
were 0.5 × 10 × 20 mm platinum plates. The Ag/AgCl electrode was
used as reference electrode.
Crystallographic Data Collections and Structure Determination.
Data Collection. Each suitable crystal was mounted in glass capillaries
under argon atmosphere. Data for all complexes were collected by a
Rigaku AFC-5R diffractometer with a graphite monochromated Mo
KR radiation and a 12 kW rotating anode generator. The incident beam
collimator was 1.0 mm, and the crystal to detector distance was 285
mm. Cell constants and an orientation matrix for data collection,
obtained from a least-squares refinement using the setting angles of
25 carefully centered reflections, corresponded to the cells with
dimensions listed in Tables 9 and 10, where details of the data collection
were summarized. The weak reflections (I < 10σ(I)) were rescanned
(maximum of two rescans), and the counts were accumulated to assure
good counting statistics. Stationary background counts were recorded
on each side of the reflection. The ratio of peak counting time to
1
All H NMR chemical shifts were reported in ppm relative to proton
impurity resonance in chloroform-d at δ 7.27 and benzene-d6 at δ 7.20.
The 31P NMR chemical shifts were reported in ppm relative to external
reference of 85% H3PO4 at δ 0.00. Mass spectra were recorded on a
JEOL SX-102 spectrometer. Raman spectra were recorded at 298 K
on a Jasco NR-1800 and R-800 spectrometer equipped with a LN-
CCD 1152E and a HTV-R649 photomultiplier with Ar+ or He-Ne laser,
or Spectra-Physics R6G dye laser excitation using KBr disk samples
sealed in glass tubes under argon atmosphere. IR spectra were recorded
on a Jasco FT/IR-3 spectrometer with use of KBr discs. Elemental
analyses were performed at Elemental Analysis Center of Osaka
University. UV-vis spectra were taken on a Jasco Ubest-30 in a sealed
1 mm cells. All melting points were measured in sealed tubes and
were not corrected.
Cyclic Voltammetry and Electrolysis. Cyclic votammetry and
electrolyses were carried out with a BAS100B electrochemical worksta-
tion referenced to a Ag/AgCl electrode. In the cyclic voltammetry,
(68) (a) Doyle, J. R.; Slade, P. E.; Jonassen, H. B. Inorg. Synth. 1960,
6, 218. (b) Drew, D.; Doyle, J. R. Inorg. Synth. 1972, 13, 52. (c) Drew, D.;
Doyle, J. R. Inorg. Synth. 1972, 13, 47.
(69) Newkome, G. R.; Hager, D. C. J. Org. Chem. 1978, 43, 947.

9094 J. Am. Chem. Soc., Vol. 118, No. 38, 1996
Table 10. Crystallographic Data of 6 and 7a,b
Mashima et al.
complex
formula
solvent molecules
fw
6a
6b
C72H60O4N4P4Mo2Pd2Cl10
dichloromethane (four)
1928.40
C70H56O4N4P4Mo2Pd2Br2Cl4
dichloromethane (two)
1847.43
cryst system
space group
tetragonal
I41
tetragonal
I41
a, Å
17.388(4)
17.455(3)
b, Å
c, Å
25.748(5)
25.971(6)
â, deg
V, Å3
7784(4)
4
1.645
MoKR
296
12.32
0.3 × 0.4 × 0.4
1.19
7913(3)
4
1.693
MoKR
296
21.69
0.6 × 0.6 × 0.6
2.09
Z
Dcalc, g cm-3
radiation
temp, K
linear abs coeff, cm-1
cryst. size, mm
GOF
no. of unique data
no. of data with I >3σ(I)
no. of variables
R
5840
3112
445
0.032
0.035
3270
2162
445
0.029
0.027
Rw
complex
formula
solvent molecules
fw
cryst system
space group
6c
7a
C69H54O4N4P4Mo2Pd2I2Cl2
C72H60O4N4P4Mo2Pt2Cl10
dichloromethane (four)
2105.77
tetragonal
I41
dichloromethane (one)
1856.50
monoclinic
P21/n
a, Å
b, Å
c, Å
16.074(7)
16.807(7)
28.194(4)
94.97(2)
7587(3)
4
1.625
MoKR
296
17.407(2)
25.798(3)
â, deg
V, Å3
7817(2)
4
1.789
MoKR
296
43.85
0.3 × 0.4 × 0.4
1.095
5854
3319
445
0.028
0.031
Z
Dcalc, g cm-3
radiation
temp, K
linear abs coeff, cm-1
cryst. size, mm
GOF
18.03
0.4 × 0.4 × 0.5
5.28
no. of unique data
no. of data with I >3σ(I)
no. of variables
R
21237
9689
802
0.069
Rw
0.084
complex
formula
7b
7c
C69H54O4N4P4Mo2Pt2Br2Cl2
C69H54O4N4P4Mo2Pt2I2Cl2
solvent molecules
fw
cryst system
space group
dichloromethane (one)
1939.88
monoclinic
P21/n
dichloromethane (one)
2033.88
monoclinic
P21/n
a, Å
b, Å
c, Å
16.077(3)
16.592(3)
27.861(2)
96.10(1)
7390(2)
4
1.743
MoKR
296
16.137(3)
16.815(3)
28.274(1)
94.888(8)
7644(2)
4
1.767
MoKR
296
â, deg
V, Å3
Z
Dcalc, g cm-3
radiation
temp, K
linear abs coeff, cm-1
cryst. size, mm
GOF
54.13
49.97
0.3 × 0.3 × 0.5
0.4 × 0.5 × 0.5
1.817
2.22
no. of unique data
no. of data with I >3σ(I)
no. of variables
R
22378
8564
891
0.053
23120
8475
920
0.060
Rw
0.069
0.078
2
a R ) ∑||Fo| - |Fc||/|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑wFo ]1/2. w ) 1/σ2(Fo); function minimized: ∑w(|Fo| - |Fc|)2.
background counting time was 2:1. Three standard reflections were
chosen and monitored every 100 reflections and not shown any
significant change in intensity over the data collection period.
Data Reduction. An empirical absorption correction based on
azimuthal scans of several reflections was applied. The data were
corrected for Lorentz and polarization effects.

Straight Linear Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 118, No. 38, 1996 9095
Structure Determination and Refinement. The structure of 1, 6a,
6b, 7a, 7b, and 7c were solved by direct methods, MITHRIL, and the
structure of 2b by direct method, SIR88. The structure of 2a, 4a, and
6c was solved by heavy-atom Patterson methods, PATTY. These were
expanded using Fourier techniques. Measured nonequivalent reflections
with I > 3.0 σ(I) were used for the structure determination. The non-
hydrogen atoms were refined anisotropically. The crystal of all
compounds contain some solvent molecules, CH2Cl2. In the final
refinement cycle, hydrogen atom coordinates were included at idealized
positions and were given the same temperature factor as that of the
carbon atom to which they were bonded. All calculations were
performed using a TEXSAN crystallographic software package of the
Molecular Structure Corporation.
Preparation of 1. To a mixture of Mo2(O2CCH3)4 (1.31 g, 3.06
mmol), pyphosH (3.42 g, 12.3 mmol), and NaOMe (0.669 g, 12.4
mmol) was added dichloromethane (150 mL). After stirring the mixture
for 6 days, the insoluble products were removed by filtration. The
solvent was removed in Vacuo, and the resulting product was recrystal-
lized from dichloromethane-diethyl ether at room temperature to afford
1 as red crystals (2.14 g, 53% yield), mp 140-150 °C (dec). 1H NMR
(C6D6, 30 °C): δ 6.36 (d, JHH ) 6.9 Hz, 4H), 6.58 (d, JHH ) 8.7 Hz,
4H), 6.76 (dd, JHH ) 6.9 Hz, JHH ) 8.7 Hz, 4H), 7.07-7.14 (m, 24H),
7.40-7.46 (m, 16H). 31P{1H} NMR (CDCl3, 30 °C): δ -7.8 (s). FAB-
MS for 98Mo m/z 1309 (MH+). Anal. Calcd for C68H52N4O4P4Mo2:
C, 62.59; H, 4.02; N, 4.29. Found: C, 61.99; H, 4.15; N, 4.28.
Preparation of 2a. A mixture of 1 (0.293 g, 0.225 mmol) and PdCl2-
(PhCN)2 (0.174 g, 0.454 mmol) in dichloromethane (60 mL) was stirred
for 1 day at room temperature, and then supernatant was removed to
give red brown powder (50% yield). 1H NMR (CDCl3, 30 °C): δ
5.95 (d, JHH ) 8.1 Hz, 4H), 6.52 (m, 4H), 7.11 (m, 4H), 7.30-7.33
(m, 16H), 7.40-7.50 (m, 24H). 31P{1H} NMR (CDCl3, 30 °C): δ
16.1 (s). Anal. Calcd for C68H52Cl4Mo2N4O4P4Pd2(CH2Cl2): C, 47.51;
H, 3.12; N, 3.21. Found: C, 47.78; H, 3.11; N, 3.37.
Preparation of 2b. A mixture of PdBr2(cod) (cod ) 1,5-cyclooc-
tadiene) (0.050 g, 0.144 mmol) and 1 (0.083 g, 0.064 mmol) in
dichloromethane (20 mL) was stirred for a few minutes, and then the
solution was left undisturbed at room temperature for 3 days to give
brown microcrystals (32% yield). 1H NMR (CD2Cl2, 30 °C): δ 6.01
(d, JHH ) 8.6 Hz, 4H), 6.18 (m, 4H), 7.17 (m, 4H), 7.22-7.26 (m,
16H), 7.28-7.33 (m, 24H). 31P{1H} NMR (CDCl3, 30 °C): δ 16.5
(s). Anal. Calcd for C68H52Br4Mo2N4O4P4Pd2(CH2Cl2): C, 43.11; H,
2.83; N, 2.91. Found: C, 43.16; H, 2.82; N, 3.06.
Preparation of 4a. A mixture of PtCl2(cod) (0.321 g, 0.619 mmol)
and 1 (0.404 g, 0.310 mmol) was dissolved in dichloromethane (20
mL). After stirring for 3 days at 40 °C, the supernatant was removed
to give quantitatively 4a as gray powder. 1H NMR (CDCl3, 30 °C):
δ 6.49 (t, 4H), 6.73 (d, 4H), 7.20-7.59 (m, 44H). 31P{1H} NMR
(CDCl3, 30 °C): δ 12.6 (JPt-P ) 3592 Hz). Anal. Calcd for
C68H52Cl4Mo2N4O4P4Pt2‚6(CH2Cl2): C, 37.88; H, 2.75; N, 2.39.
Found: C, 37.36; H, 3.06; N, 2.87.
solid, and then recrystallization of the resulting solid from dichlo-
romethane-diethyl ether gave 6a as red crystals in 69% yield, mp 237-
243 °C. 1H NMR (CDCl3, 30 °C): δ 6.03 (d, JHH ) 8.2 Hz, 4H), 6.25
(d, JHH ) 7.0 Hz, 4H), 7.2 (dd, 4H), 7.33-7.46 (m, 24H), 7.50-7.57
(m, 16H). 31P{1H} NMR (CDCl3, 30 °C): δ 15.7 (s). FAB-MS for
98Mo106Pd m/z 1521 (MH+-Cl2). Anal. Calcd for C68H52Cl2Mo2N4-
O4P4Pd2(CH2Cl2): C, 49.52; H, 3.25; N, 3.35. Found: C, 49.97; H,
3.38; N, 3.50.
Preparation of 6b. To a Schlenk tube containing PdBr2(cod) (0.193
g, 0.515 mmol) and 1 (0.265 g, 0.203 mmol) was added dichlo-
romethane (20 mL). After stirring for 14 h at room temperature, all
volatiles were removed under reduced pressure to give deep green
powder. Recrystallization of the resulting powder from dichlo-
romethane-diethyl ether gave red crystals of 6b in 63% yield, mp >
300 °C. 1H NMR (CDCl3, 30 °C): δ 6.06 (d, 4H), 6.22 (d, 4H), 7.16
(d, 4H), 7.34-7.47 (m, 24H), 7.50-7.57 (m, 16H). 31P NMR (CDCl3,
30 °C): δ 15.7(s). FAB-MS for 98Mo 106Pd m/z 1600 (MH+ - Br2).
Anal. Calcd for C68H52N4O4P4Mo2Pd2Br2: C, 44.45; H, 2.85; N, 3.05.
Found: C, 44.12; H, 3.50; N, 2.76.
By the similar procedure, complexes 6c and 7a-c were prepared
and characterized.
6c: 50% yield, mp > 300 °C. 1H NMR (CDCl3, 30 °C): δ 6.00 (d,
4H), 6.17 (d, 4H), 7.14 (t, 4H), 7.33-7.54 (m, 40H). 31P NMR (CDCl3,
30 °C): δ 15.8 (s). Anal. Calcd for C68H52N4O4P4I2Mo2Pd2(CH2Cl2):
C, 44.64; H, 2.93; N, 3.02. Found: C, 44.35; H, 3.15; N, 2.91.
7a: 40% yield, mp > 300 °C. 1H NMR (CDCl3, 30 °C): δ 5.77
(d, 4H), 6.21 (m, 4H), 7.15 (m, 4H), 7.34-7.47 (m, 24H), 7.51-7.59
(m, 16H). 31P NMR (CDCl3, 30 °C): δ 27.9 (JPt-P ) 3391 Hz). FAB-
MS for 98Mo 195Pt m/z 1699 (MH+ - Cl2). Anal. Calcd for
C68H52N4O4P4Mo2Pt2Cl2(CH2Cl2) C, 44.77; H, 2.94; N, 3.03. Found:
C, 45.21; H, 2.95; N, 3.12.
7b: 28% yield, mp > 300 °C. 1H NMR (CDCl3, 30 °C): δ 5.79 (d,
4H), 6.17 (m, 4H), 7.15 (m, 4H), 7.34-7.47 (m, 24H), 7.51-7.60 (m,
16H). 31P NMR (CDCl3, 30 °C): δ 27.3 (JPt-P ) 3363 Hz). FAB-
MS for 98Mo 195Pt m/z 1699 (MH+ - Br2). Anal. Calcd for
C68H52N4O4P4Mo2Pt2Br2(CH2Cl2) C, 42.72; H, 2.81; N, 2.89. Found:
C, 42.18; H, 2.81; N, 2.89.
7c: 36% yield, mp > 300 °C. 1H NMR (CDCl3, 30 °C): δ 5.77 (d,
4H), 6.13 (m, 4H), 7.15 (m, 4H), 7.34-7.47 (m, 24H), 7.51-7.59 (m,
16H). 31P NMR (CDCl3, 30 °C): δ 26.7 (JPt-P ) 3331 Hz). FAB-
MS for 98Mo 195Pt m/z 1699 (MH+ - I2). Anal. Calcd for C68H52N4O4P4-
Mo2Pt2I2(CH2Cl2)2 C, 39.68; H, 2.66; N, 2.64. Found: C, 39.49; H,
3.15; N, 2.45.
Complex 7c was prepared alternatively as follows: To a Schlenk
tube containing 1 (215 mg, 0.156 mmol) and PtI2(cod) (0.186 g, 0.334
mmol) was added dichloromethane (20 mL). After stirring for several
days at 30 °C, all volatiles were removed under reduced pressure to
give a deep red powder. The resulting powder was placed in an
apparatus for sublimation with a cold finger, and then it was heated at
300° C in reduced pressure for 12 h to give a purple solid of 7c in
quantitative yield. In this process, iodine was sublimed on the cold
finger.
A similar procedure was used in the preparation of bromo and iodo
complexes.
4b: quantitative yield. 1H NMR (CDCl3, 30 °C): δ 6.52 (t, 4H),
6.72 (d, 4H), 7.20-7.60 (m, 44H). 31P{1H} NMR (CDCl3, 30 °C): δ
12.6 (JPt-P ) 3592 Hz). Anal. Calcd for C68H52Br4Mo2N4O4P4Pt2:
C, 40.54; H, 2.60; N, 2.78. Found: C, 40.97; H, 3.44; N, 2.43.
4c: quantitative yield. 1H NMR (CDCl3, 30 °C): δ 6.55 (m, 4H),
6.71 (d, 4H), 7.20-7.63 (m, 44H). 31P{1H} NMR (CDCl3, 30 °C): δ
7.9 (JPt-P ) 3383 Hz). The contamination of 7c prevented elemental
analysis.
Preparation of 6a. A mixture of 1 (0.097 g, 0.074 mmol),
PdCl2(PhCN)2 (0.057 g, 0.15 mmol), and Et4NBH4 (0.006 g, 0.04 mmol)
in dichloromethane (40 mL) was stirred for 2 h at room temperature.
All volatiles were removed under reduced pressure to give a deep green
Acknowledgment. K.M. and A.N. are grateful for financial
support from the Ministry of Education, Science and Culture
of Japan (Specially Promoted Research No. 06101004).
Supporting Information Available: Final positional pa-
rameters, final thermal parameters, bond distances, bond angles,
and ORTEP drawings for 1, 2a, 2b, 4a, 6a-c and 7a-c (75
pages). See any current masthead page for ordering and Internet
access instructions.
JA960606G