Synthesis of a new multidentate phosphane ligand C6H2(CH2PPh2)4-1,2,4,5 - X-ray structure of a dinuclear ruthenium(II)-bridged complex: [{RuCl2(PPh3)}2{C6H 2(CH2PPh2) 4-1,2,4,5-P,P′,P″,P?}]

Article abstract of DOI:10.1002/(sici)1099-0682(199804)1998:4<477::aid-ejic477>3.0.co;2-u

The tetrakis(phosphane oxide) C₆H₂{CH₂P(O)Ph₂}4-1,2,4,5 (5), has been prepared in high yield from the Arbuzov reaction of C₆H₂(CH₂Br)₄-1,2,4,5 (4), with excess (7 equiv.) of Ph₂POEt. Subsequent reduction of 5 with HSiCl₃ (12 equiv.) in C₆H₄Cl₂-1,2 afforded the new tetraphosphane C₆H₂(CH₂PPh₂)₄-1,2,4,5 (6), in high yield. The reaction of 6 with [RuCl₂(PPh₃)₄] in CH₂Cl₂ afforded the green dinuclear ruthenium(II) coordination complex [{RuCl₂(PPh₃)}₂[C₆H ₂-(CH₂PPh₂) ₄-1,2,4,5-P,P′,P″,P?}]·0.5 CH₂Cl₂ (8), in 39percent isolated yield. The solid-state molecular geometry of 8, determined by X-ray analysis, shows that the tetraphosphane is ortho-P,P′-chelated to each of the two [Ru^IICl₂(PPh₃)] units.

Full text of DOI:10.1002/(sici)1099-0682(199804)1998:4<477::aid-ejic477>3.0.co;2-u

FULL PAPER
Synthesis of a New Multidentate Phosphane Ligand C6H2(CH2PPh2)4-1,2,4,5
؊ X-ray Structure of a Dinuclear Ruthenium(II)-Bridged Complex:
[{RuCl2(PPh3)}2{C6H2(CH2PPh2)4-1,2,4,5-P,PЈ,PЈЈ,PЈЈЈ}]
Pablo Steenwinkela, Sebastiaan Kolmschota, Robert A. Gossagea, Paulo Dania, Nora Veldmanb, Anthony L. Spekb[°], and
Gerard van Koten*a
Debye Institute, Department of Metal-Mediated Synthesis, Utrecht Universitya,
Padualaan 8, NL-3584 CH Utrecht, The Netherlands
Fax: (internat.) ϩ 31-30/252-3615
E-mail: g.vankoten@chem.ruu.nl
Bijvoet Center for Biomolecular Research, Department of Crystal and Structural Chemistry, Utrecht Universityb,
Padualaan 8, NL-3584 CH Utrecht, The Netherlands
Received November 14, 1997
Keywords: Ruthenium / Bridging bis(bidentate) tetraphosphane ligand / Diruthenium(II) coordination complex /
Cyclometallation versus o-P,PЈ chelation
The tetrakis(phosphane oxide) C6H2{CH2P(O)Ph2}4-1,2,4,5
(5), has been prepared in high yield from the Arbuzov reac-
with [RuCl2(PPh3)4] in CH2Cl2 afforded the green dinuclear
ruthenium(II) coordination complex [{RuCl2(PPh3)}2{C6H2-
tion of C6H2(CH2Br)4-1,2,4,5 (4), with excess (7 equiv.) of (CH2PPh2)4-1,2,4,5-P,PЈ,PЈЈ,PЈЈЈ}]·0.5 CH2Cl2 (8), in 39% iso-
Ph2POEt. Subsequent reduction of 5 with HSiCl3 (12 equiv.)
in C6H4Cl2-1,2 afforded the new tetraphosphane
C6H2(CH2PPh2)4-1,2,4,5 (6), in high yield. The reaction of 6
lated yield. The solid-state molecular geometry of 8, determi-
ned by X-ray analysis, shows that the tetraphosphane is or-
tho-P,PЈ-chelated to each of the two [RuIICl2(PPh3)] units.
Introduction
(ϭ PCP-R-4) (Figure 2). The use of these ligands, which
can be derived from the aryl compounds C6H3(CH2ERЈ2)2-
1,3-R-5 (1), either by transmetallation (of 1a-Li) or direct
cyclometallation (of 1b), has resulted in a new series of
In recent years there has been an increasing interest in
dinuclear organometallic complexes and such species have
been used to model fundamental properties of multi- and
polymeric organometallic materials[1] that have potential
optical and/or electronic applications. Recently, we reported
on the selective synthesis of 4,4Ј-biphenylene- and 1,4-phen-
ylene-bridged bimetallic complexes of some platinum-group
metals containing anionic N,C,NЈ-terdentate ligands (Fig-
ure 1)[2]. In addition to their interesting photochemical be-
havior[2a], these complexes have potential in the develop-
ment of multimetallic materials, such as “molecular wires”.
stable organoruthenium complexes (see Scheme 1)[3]
.
Figure 2. Schematic representation of the monoanionic aryl ligands
NCN-R-4 (R ϭ H, Ph, Me3SiCϵC, Me3Si) and PCP-R-4 (R ϭ H,
Ph) and the dianionic C2N4 ligand
Figure 1. Some examples of 4,4Ј-biphenylene- and 1,4-phenylene-
bridged organometallic complexes containing ligands with anionic
N,C,NЈ-terdentate coordination moieties
The PCP-R-4 ruthenium(II) complexes 2b can be ob-
tained directly by cyclometallation[4] of the corresponding
diphosphanes 1b with [RuCl2(PPh3)4]. In contrast, the
NCN-R-4 ruthenium(II) complexes 2a were prepared by
transmetallation of organolithium reagents [LiC6H2-
(CH2NMe2)2-2,6-R-4]2 derived from the aryldiamines 1a.
Some NCN-R-4 and PCP-R-4 ruthenium(II) complexes
have also been used as catalysts in various hydrogen-trans-
We have also investigated the synthesis of ruthenium(II)
complexes of monoanionic (functionalized) N,C,NЈ-terden-
tate ligands [C6H2(CH2NMe2)2-2,6-R-4]Ϫ (ϭ NCN-R-4)
and P, C, P Ј -terdentate ligands [C6H2(CH2PPh2)2-2,6-R-4]Ϫ
fer reactions[5]
.
Recently, we have also developed a synthetic strategy for
the preparation of homo- and heterodinuclear organomet-
allic complexes of the bis(N,C,NЈ-terdentate) coordinating
dianionic 1,4-phenylene-bridging ligand [C6(CH2NMe2)4-
2,3,5,6]2Ϫ (ϭ C2N4; Figure 2)[6] and extension of this re-
[°]
Address correspondence pertaining to crystallographic studies
to this author; E-mail: spea@xray.chem.ruu.nl
Eur. J. Inorg. Chem. 1998, 477Ϫ483
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1434Ϫ1948/98/0404Ϫ0477 $ 17.50ϩ.50/0
477

P. Steenwinkel et al.
FULL PAPER
Scheme 1. Synthesis of ruthenium(II) complexes 2 and 3 derived the latter case, a new product formed in ca. 10% yield with
from (functionalized) N,C,NЈ- and P, C, PЈ-terdentate-
over 85% of the starting material still present. This new
coordinating ligands 1, by transmetallation (of 1a-Li) or
product has not been isolated in a pure form but on the
basis of 31P-NMR data of the crude material, its air sta-
bility and its water solubility we believe that it is likely to
be an ionic phosphonium species (vide infra). It was felt
that the poor reactivity of 5 in the attempted reduction re-
actions was possibly due to its inherent low solubility.
Therefore, alternative solvents were examined and it has
been found that for the reduction of 5 with HSiCl3, hot 1,2-
dichlorobenzene was the solvent of choice. In practice, a
suspension of 5 in 1,2-dichlorobenzene was heated to 180°C
and kept at this temperature for 10 min to dissolve all solid
material. The solution temperature was then reduced to
140°C and HSiCl3 was added by syringe. The reaction mix-
ture was kept for 1 h at this temperature and, after appro-
priate work-up, the desired tetraphosphane 6 was obtained
as a white solid in very good yield (96%). Compound 6 is
air-sensitive and reasonably soluble in aromatic and chlori-
nated solvents. Analytically pure crystals of 6 can be ob-
tained by slow diffusion of MeOH into a solution of 6 in
benzene.
direct cyclometallation (of 1b)
search has been aimed at the generation of the related di-
anionic 1,4-phenylene ligand with two potentially P, C, P Ј -
terdentate coordination motifs, i.e., an analog to the tetra-
aminophenylene dianion C2N4 shown in Figure 2. As part
of this research we have explored the synthesis of the tetra-
phosphane C6H2(CH2PPh2)4-1,2,4,5 (6), which is a poten-
tial precursor to the ligand [C6(CH2PPh2)4-1,2,4,5]2Ϫ. We
now report the successful synthesis of 6 and its com-
plexation reaction with [RuCl2(PPh3)4].
Scheme 2. Synthesis of the tetraphosphane C6H2(CH2PPh2)4-
1,2,4,5 (6). Ϫ i: Ph2POEt, m-xylene, 140°C, ϪEtBr. Ϫ
ii: HSiCl3, C6H4Cl2Ϫ1,2, 140°C, 1 h.
Results
The target compound of this study is tetraphosphane-
substituted benzene C6H2(CH2PPh2)4-1,2,4,5 (6). The syn-
thetic protocol used involves an Arbuzov reaction[7] of a
phosphanic ester (i.e., Ph2POEt) with a benzylic bromide
[i.e., C6H2(CH2Br)4-1,2,4,5 (4)] to afford a PV oxide com-
pound, 5[8]. The latter is then reduced to the corresponding
desired tetraphosphane 6 (see Scheme 2).
Reaction of Tetraphosphane 6 with [RuCl2(PPh3)4]
It was anticipated that phosphane 6 would be susceptible
to cyclometallation and that with [RuCl2(PPh3)4][12] the
product of this reaction would be a bimetallic species re-
lated to the ruthenium(II) complex 3b (Scheme 1) obtained
when C6H3(CH2PPh2)2-1,3-R-5 (1b), is used as the phos-
phane[3c][3d]. To test the reactivity of the new tetraphos-
Synthesis of C6H2(CH2PPh2)4-1,2,4,5 (5)
Compound 5 can be obtained in high yield, as a white phane 6 towards [RuCl2(PPh3)4], these two species were
solid, by treatment of the known C6H2(CH2Br)4-1,2,4,5 mixed in a 1:2 molar ratio in CH2Cl2 (Scheme 3) at room
(4)[9] with excess of ethyldiphenylphosphanite (Ph2POEt) in temperature and after 1 h a green precipitate had been
m-xylene at 140°C in a slight modification of a previously formed. After appropriate work-up, this precipitate was iso-
described procedure that gives an improved yield[8]. The lated as a green solid, whose poor solubility in common
1H-NMR data of the poorly soluble tetrakis(phosphane ox- organic solvents (benzene, toluene, THF, CH2Cl2, etc.) has
ide) 5 (in warm CD3OD solution) were identical to those prevented us from identifying this material, 8, by solution-
reported previously[8]
.
NMR spectroscopy and also prevented successful recrystal-
Typical procedures described for the reduction of phos- lization. However, elemental microanalysis data suggested
phane oxides to phosphanes failed to completely reduce that this crude product has an overall formula
compound 5 to phosphane 6. For example, HSiCl3 re- [{RuCl2(PPh3)}2(6)]·0.5 CH2Cl2.
duction of 5 in benzene, toluene or xylene at reflux tem-
In a second experiment, aimed at directly obtaining a
perature[10] did not result in the formation of the desired purer, more crystalline product 8, we carried out the orig-
phosphane. Similarly, LiAlH4 (or LiAlH4 ·CeCl3) re- inal reaction under slightly different conditions. To this end,
ductions[11] in THF also failed to reduce 5 selectively. In a CH2Cl2 solution of two equivalents of [RuCl2(PPh3)4] was
478
Eur. J. Inorg. Chem. 1998, 477Ϫ483

New Multidentate Phosphane Ligand C6H2(CH2PPh2)4-1,2,4,5
FULL PAPER
carefully layered with a solution of tetraphosphane 6 in gle of 160.96(9)°, are similar to those reported for related
CH2Cl2 and the reaction mixture was left undisturbed for complexes with the general formula [RuCl2(Ph2-
24 h at room temperature. This produced analytically pure PR)3][13a][13b] (see Discussion). The PϪCaryl bond lengths
˚
green crystals of 8 (isolated yield: 38%) which were suitable fall in the range of 1.815(10) to 1.853(9) A and the RuϪPϪ
for an X-ray crystallographic study. This study afforded a Caryl bond angles vary from 100.0(3) to 124.7(3)°. Interest-
solid-state structure (vide infra) which shows this prod- ingly, the proton H(31) situated on triphenylphosphane or-
uct to be [{RuCl2(PPh3)}2{C6H2(CH2PPh2)4-1,2,4,5- tho-carbon atom C(31) is fairly close to the ruthenium(II)
˚
P, P Ј ,PЈЈ,PЈЈЈ}]·0.5 CH2Cl2 (8); the molecular geometry is center with a Ru(1)···H(31) distance of 2.82 A that is sub-
depicted in Figure 3 and selected geometrical details are stantially shorter than the sum of the van der Waals radii
˚
collected in Table 1. Complex 8 has a composition that (3.40 A).
corresponds to the original microanalytical data and it can
In further experimental studies aimed at promoting
be seen to be a dinuclear coordination complex of 6 in cyclometallation of the neutral phosphane 6 present in
which this tetraphosphane functions as a bridging ligand complex 8, this latter complex was suspended in 1,2-di-
that coordinates in a P, P Ј -bidentate manner to each of the chlorobenzene and heated to 140°C together with PPh3 and
identical metal centers. Thus, under the experimental con- trioctylamine as a base. Although NMR-spectroscopic
ditions used or at reflux temperature in CH2Cl2, compound studies of the resulting solution indicated that a new ortho-
6 does not undergo cyclometallation with the ruthenium(II) metallated product had been formed, it was in fact the coor-
center to afford a product such as 7. This behavior is differ- dinated PPh3 ligand, and not 6, that had been cyclometal-
ent to that of aryldiphosphane C6H4(CH2PPh2)2-1,3 which lated. Unfortunately, a pure sample of this new cyclometal-
cyclometallates with [RuCl2(PPh3)4] under identical con- lated product could not be separated for further identifi-
ditions to afford [RuCl{C6H3(CH2PPh2)2-2,6}(PPh3)][3]
.
cation.
Scheme 3. Reactivity of 6 with [RuCl2(PPh3)4] in CH2Cl2 to afford
coordination complex 8 rather than the cyclometallated
species 7. Ϫ i: 2 equiv. [RuCl2(PPh3)4], CH2Cl2, room
temp., 1 h, Ϫ6 equiv. PPh3.
Discussion
Synthesis of the Tetraphosphane
The choice of the Arbuzov-reaction/reduction sequence
for the synthesis of tetraphosphane 6 is a consequence of
the poor results that we achieved in preliminary experi-
ments using the tetrabromide 4 as starting material in the
well-known nucleophilic substitution of a benzylic bromide
with NaPPh2 in liquid ammonia[3c][14]. The main product
of this latter reaction is not the desired phosphane 6, but a
mixture of phosphonium salts. These phosphonium salts
are probably formed as a result of an intramolecular nucle-
ophilic substitution reaction of a CH2Br group with an or-
tho-positioned CH2PPh2 group that has been produced by
an initially successful intermolecular nucleophilic substi-
tution (see Scheme 4). The success of the route we employ
to form 6 (Scheme 2) comes from the fact that the product
of the Arbuzov reaction is a non-nucleophilic phosphane
oxide and the initially formed CH2P(O)Ph2 unit is inert to
intramolecular attack by an ortho-positioned benzylic bro-
mide.
In the X-ray crystallographic structure of 8, the tetra-
phosphane ligand bridges between the two identical 5-coor-
dinate ruthenium(II) metal centers that have approximate
square-pyramidal geometries; the molecule has a center of
inversion positioned in the central aromatic ring of this
tetraphosphane. The square pyramidal ligand array com-
prises in the basal plane plane two trans-Cl atoms [Cl(1)
and Cl(2)] and two trans-P atoms [P(2) of the bridging li-
gand and P(3) of PPh3] and at the apex there is a phos-
phorus atom P(1) of the bridging ligand. The bridging
phosphane employs two mutually ortho-CH2PPh2 substitu-
ents for ortho-P,PЈ chelation to each metal center, thus for-
ming a 7-membered chelate ring in which the bite angle
P(1)ϪRu(1)ϪP(2) is 97.46(9)°. The geometrical parameters
The solvent used in the HSiCl3-mediated reduction reac-
tion of the tetrakis(phosphane oxide) 5 to the tetraphos-
phane 6 was found to be crucial and the best experimental
conditions that we found was the use of 1,2-dichloroben-
zene at high temperature. It appears that for phosphane ox-
ides like 5, which have poor solubility characteristics, it is
important to use a solvent that not only has a high boiling
point but also one that has a good degree of polarity, and
this combination of physical properties is found in 1,2-di-
chlorobenzene.
Solid-State Structure of 8
The complex formed by the undisturbed reaction of
found for 8, including RuϪP bond lengths in the range of [RuCl2(PPh3)4] with 6 in CH2Cl2 was not one containing
˚
2.208(3) to 2.391(2) A and a Cl(1)ϪRu(1)ϪCl(2) bond an- the expected cyclometallated tetraphosphane ligand 7. In-
Eur. J. Inorg. Chem. 1998, 477Ϫ483
479

P. Steenwinkel et al.
FULL PAPER
Figure 3. ORTEP drawing (50% probability atomic displacement ellipsoids) of [{RuCl2(PPh3)}2{C6H2(CH2PPh2)4-1,2,4,5-P, PЈ,PЈЈ,PЈЈЈ}]
(8); hydrogen atoms and cocrystallized CH2Cl2 molecules have been omitted for clarity
Table 1. Selected bond parameters of [{RuCl2(PPh3)}2- the central aromatic ring cannot approach the metal center
{C6H2(CH2PPh2)4-1,2,4,5-P, PЈ,PЈЈ,PЈЈЈ}] (8)
for intramolecular activation and subsequent CϪRu bond
formation.
˚
Bond lengths [A]
Bond angles [°]
Bisruthenium(II) complex 8 is one of only a few structur-
ally characterized 5-coordinate ruthenium(II) species in
which the ligand array comprises two halide atoms and
three phosphanes. Moreover, in complex 8 the presence of
a close contact between the metal center and an ortho H
atom of one of the PPh3 CarylϪH units is a noteworthy
feature; interestingly, the structure of [RuCl2(PPh3)3] has a
similar interaction which was concluded to be substantially
repulsive,[13a] and not to be an agostic interaction[13c][13d]
of this CarylϪH bond with the metal center. The authors
described the overall structure of this complex as a dis-
torted square pyramid with this ortho-H atom occupying
the open coordination site of an octahedral ligand array.
More recently, Cotton and Matusz[13b] have reported the
solid-state structure of another square-pyramidal ru-
thenium complex, [RuCl2(Ph2PCH2SiMe3)3], in which this
type of M···HϪC interaction was not found and the bulky
benzylic substituent would appear to be shielding the vac-
ant sixth coordination site in this 16-electron species. Com-
parison of some selected bond lengths and interbond angles
collected in Table 2, shows that the overall solid-state struc-
tures of bimetallic 8 with P, P Ј -chelation and the mononu-
clear complexes [RuCl2(Ph2PR)3] (R ϭ Ph, CH2SiMe3) with
monodentate-bonded phosphanes are surprisingly similar.
Ru(1)ϪCl(1)
Ru(1)ϪCl(2)
Ru(1)ϪP(1)
Ru(1)ϪP(2)
Ru(1)ϪP(3)
P(1)ϪC(4)
2.389(2)
2.383(2)
2.208(3)
2.318(2)
2.391(2)
1.846(8)
1.853(9)
1.834(9)
1.847(9)
1.815(10)
1.816(10)
1.844(10)
1.828(8)
1.821(9)
2.8118
Cl(1)ϪRu(1)ϪCl(2)
P(1)ϪRu(1)ϪP(2)
P(1)ϪRu(1)ϪP(3)
P(2)ϪRu(1)ϪP(3)
Ru(1)ϪP(1)ϪC(4)
Ru(1)ϪP(1)ϪC(18)
Ru(1)ϪP(1)ϪC(24)
Ru(1)ϪP(2)ϪC(5)
Ru(1)ϪP(2)ϪC(6)
Ru(1)ϪP(2)ϪC(12)
Ru(1)ϪP(3)ϪC(30)
Ru(1)ϪP(3)ϪC(36)
Ru(1)ϪP(3)ϪC(42)
P(3)ϪC(30)ϪC(31)
P(3)ϪC(30)ϪC(35)
P(3)ϪC(36)ϪC(37)
P(3)ϪC(36)ϪC(41)
P(3)ϪC(42)ϪC(43)
P(3)ϪC(42)ϪC(47)
160.96(9)
97.46(9)
101.74(9)
160.49(9)
114.8(3)
120.1(3)
116.3(3)
118.3(3)
100.0(3)
124.7(3)
103.1(3)
120.2(3)
121.5(3)
116.9(7)
123.5(7)
120.8(7)
120.6(7)
122.9(7)
118.9(7)
P(1)ϪC(18)
P(1)ϪC(24)
P(2)ϪC(5)
P(2)ϪC(6)
P(2)ϪC(12)
P(3)ϪC(30)
P(3)ϪC(36)
P(3)ϪC(42)
Ru(1)···H(31)
Scheme 4. Schematic formation of phosphonium species from the
reaction of NaPPh2 with ortho-bis(bromomethyl)arenes
P,PЈ-Chelation versus Cyclometallation
stead, the product is a bimetallic coordination complex of
neutral tetraphosphane 6 in which two ortho-positioned
Cyclometallation of aryldiphosphanes with ru-
phosphane donor substituents are coordinated to a ru- thenium(II) species is a well-known reaction and has been
thenium(II) metal center. The related tetraphosphane ligand successfully employed by us[3c] and others[3e] in earlier stud-
1,2,4,5-tetrakis(diphenylphosphano)benzene has been re- ies to form
a
series of complexes containing
ported to form similar, non-metallated, bridged bimetallic [C6H2(CH2PPh2)2-2,6-R-4]Ϫ, PCP-R-4 (Scheme 1). How-
(and polymeric) coordination complexes with several tran- ever, as reported here, the neutral tetraphosphane 6 has to
sition metals[15]. It appears that this type of initial P, P Ј - date not been found to undergo such cyclometallation reac-
chelation forms a species that is relatively inert to RuϪP tions and it is worthwhile considering the unique aspects of
bond cleavage and as a consequence the CarylϪH bond of this compound that result in it having a different reactivity
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Eur. J. Inorg. Chem. 1998, 477Ϫ483

New Multidentate Phosphane Ligand C6H2(CH2PPh2)4-1,2,4,5
FULL PAPER
Table 2. Selected bond parameters of 8 and the known rutheni- that in 8 there is chelation of two ortho-positioned
um(II) complexes [RuCl2(Ph2PR)3] (R ϭ Ph, CH2SiMe3)
CH2PPh2 groups, whereas in A there is chelation two meta-
positioned CH2PPh2 groups.
8
[RuCl2-
[RuCl2(Ph2-
(PPh3)3][a]
PCH2SiMe3)3][b]
Figure 5. Schematic representation of two different coordination
complexes
8
and
A
which could be formed from
[RuCl2(PPh3)]4
6 and
˚
Bond lengths [A]
Ru(1)ϪCl(1)
Ru(1)ϪCl(2)
2.389(2)
2.383(2)
2.208(3)
2.318(2)
2.391(2)
2.8118
2.387(7)
2.388(7)
2.230(8)
2.374(6)
2.412(6)
2.59
2.395(2)
2.390(2)
2.210(2)
2.348(2)
2.379(2)
not present
[c]
Ru(1)ϪPA
[c]
Ru(1)ϪPB
Ru(1)···H
Bond angles [°]
Cl(1)ϪRu(1)ϪCl(2) 160.96(9)
157.2(2)
156.4(2)
101.1(2)
101.4(2)
163.93(7)
165.91(7)
96.83(7)
99.24(7)
[c]
PBϪRu(1)ϪPB[c]
160.49(9)
97.46(9)
101.74(9)
PAϪRu(1)ϪPB
[a]
[b]
Data obtained from ref.[12a]. Ϫ
Data obtained from ref.[12b]
.
Ϫ
tively.
[c] PA and PB are the apical and basal phosphorus atoms, respec-
In complex A, there are two 8-membered chelate rings
that allow the metal centers to be brought close to the aryl
CϪH bonds at positions 3 and 6 on the central aromatic
ring; as a result of geometric (steric) restraints each ring has
limited flexibility. In contrast, complex 8 contains two 7-
membered chelate rings that have a good degree of confor-
mational flexibility, and therefore this situation is energeti-
cally more favorable than that in A. However, unlike the
situation in A the ruthenium(II) centers in 8 are unable to
approach the central CϪH bonds to undergo cyclometal-
lation and form complex 7 (Scheme 3). The favorable situ-
ation found in complex 8 is emphasized by the fact that
this complex does not undergo cycloruthenation during the
synthetic procedure. In principle, the excess of free PPh3
present in the reaction mixture (see Scheme 2) could induce
the formation of an η1-P-coordinated ligand 6 in complex
8, and this would be sufficient to generate a situation where
the an aryl CϪH bond (as in A) is close enough to the
metal center for cyclometallation to occur. However, the
poor solubility characteristics of 8 in common organic sol-
vents prevents the possibility of this situation.
pattern. For reaction of the neutral aryldiphosphanes
C6H3(CH2PPh2)2-1,3-R-5 (1b), with [RuCl2(PPh3)4] we pro-
posed that prior to cyclometallation an 8-membered cyclic
coordination complex is formed by replacement of PPh3 li-
gands of [RuCl2(PPh3)3] (vide supra) by the more basic
phosphorus donor substituents of 1b[3c]. In this resulting
intermediate complex the two meta-positioned CH2PPh2
substituents are coordinated to the ruthenium(II) metal
center in a bidentate P, P Ј -chelate mode. As a consequence
the metal center is brought into proximity to the CϪH
bond which can then be activated. Because this intermedi-
ate has not been detected by NMR-spectroscopic methods
we assume that the formation of this intermediate is rate-
determining and that the following step, i.e. CϪH bond
cleavage and generation of the new RuϪC σ bond, is a
much faster process. In one rare and unique case, an ex-
ample of an agostic interaction of a CarylϪH bond of an
aryldiphosphane, 1b (R ϭ H), at an RuII center afforded
by P, P Ј -chelate bonding has been confirmed by an X-ray
crystallographic study[3d]; the molecular geometry of the
monocationic complex reported in this study is sche-
matically presented in Figure 4.
Conclusion
In this report we have shown that the new neutral tetra-
phosphane ligand C6H2(CH2PPh2)4-1,2,4,5 (6) can be easily
prepared in high yield. The synthetic strategy, which in-
volves an Arbuzov reaction, has great potential as an
alternative (and less hazardous) route to many other aryl-
and alkylphosphanes. In this strategy the choice of 1,2-di-
chlorobenzene as a high-temperature solvent for the re-
duction of the corresponding phosphane oxide was crucial.
With ruthenium(II) centers the new tetraphosphane 6 af-
fords P, P Ј -bidentate chelation from two ortho-positioned,
rather than meta-positioned, CH2PPh2 substituents such
that CϪH bond activation and formation of a P, C, P Ј -ter-
dentate-coordinated ruthenium(II) species does not occur.
Figure 4. Schematic representation of aryl CϪH bond activation
at a RuII center in an intermediate whose structure has been deter-
mined by an X-ray crystallographic study
Tetraphosphane 6 should, like diphosphanes 1b, displace
PPh3 from [RuCl2(PPh3)3] since the CH2PPh2 groups are
more basic P donors than PPh3. Several different coordi-
nation complexes could be formed, and two of these based
on P, P Ј -chelation are the observed dinuclear coordination
complex 8 as well as the alternative chelation complex A
This work was supported in part (P. S., N. V., A. L. S.) by the
Netherlands Foundation for Chemical Research (SON) with finan-
cial aid from the Netherlands Organization for Scientific Research
(See Figure 5). The difference between these complexes is (NWO).
Eur. J. Inorg. Chem. 1998, 477Ϫ483
481

P. Steenwinkel et al.
FULL PAPER
Table 3. Crystal Data and Details of the Structure Determination for [{RuCl2(PPh3)}2{C6H2(CH2PPh2)4-1,2,4,5-P, PЈ,PЈЈ,PЈЈЈ}] (8)
Crystal Data
empirical formula
formula weight
crystal system
C94H80Cl4P6Ru2 ·8 CH2Cl2
2418.92
crystal size [mm]
space group
0.15 ϫ 0.15 ϫ 0.63
¯
triclinic
P1 (no. 2)
˚
a [A]
10.2378(13)
106.139(10)
14.227(2)
97.707(10)
20.237(2)
106.822(11)
2635.4(6)
1
α [°]
˚
b [A]
β [°]
˚
c [A]
γ [°]
V [A3]
Dcalcd. [g cmϪ3
F(000) [e]
]
1.524
1226
˚
Z
µ(Mo-Kα) [cmϪ1
]
9.3
Data Collection
150
T [K]
θmin, θmax [°]
1.1, 25.0
0.71073
˚
wavelength (Mo-Kα) [A]
hor. aperture
scan range [°]
vert. aperture
1.10 ϩ 0.00 tanθ
4.00
3.00
data set
total data
Ϫ8/12, Ϫ17/17, Ϫ25/25
10839
total unique data
observed data [I > 2.0 σ(I)]
9273
5094
Refinement
9273, 586
0.1660
Nref, Npar
final R1[a]
0.0748
1.01
final wR2[b]
goodness of fit
2
wϪ1
σ2(F2) ϩ (0.0474P)2 ϩ 1.8922P, where P ϭ (Fo2ϩ2Fc )/3
(∆.σ)av, (∆.σ)max
min. and max.
0.00, 0.00
resid. density [e AϪ3
˚
]
Ϫ0.74, 0.64
[a]
[b]
R1 ϭ ΣʈFo͉Ϫ͉Fcʈ/Σ͉Fo͉. Ϫ wR2 ϭ [(͉Fo͉2Ϫ͉Fc͉2)2/Σw(͉Fo͉2)2]1/2
.
was then allowed to cool to 140°C and HSiCl3 (2.46 ml, 24.4
mmol) was carefully added through the septum over a period of 5
min by means of a syringe. The reaction mixture was then stirred
at 140°C for 1 h, after which a clear solution was obtained. This
solution was then cooled to 0°C with an ice bath. Degassed aque-
ous NaOH (50 ml, 4 ) was carefully added through the septum
over a period of 5 min by means of a syringe while the mixture was
stirred vigorously. This resulted in the formation of a two-layer
system, from which the organic layer was collected. The aqueous
layer was extracted with CH2Cl2 (2 ϫ 25 ml) and the combined
organic fractions were dried with MgSO4 and filtered. The filtrate
was concentrated in vacuo to ca. 10 ml. Hexane (50 ml) was slowly
added, which induced the crystallization of a white solid. This solid
was collected by filtration, washed with hexane (2 ϫ 25 ml) and
dried in vacuo to afford analytically pure tetraphosphane 6 as white
Experimental Section
General: All synthetic procedures were performed under dry di-
nitrogen. Hexane and benzene were freshly distilled from sodium
benzophenone ketyl, CH2Cl2 from CaH2, and xylenes and 1,2-di-
˚
chlorobenzene from molecular sieves (5 A). Ϫ Spectroscopic meas-
urements (1 H, 13C{1H} and 31P{1H} NMR) were performed with
a Bruker AC200 or AC300 spectrometer, with chemical shifts refer-
enced to either Me4Si or 85% H3PO4. Ϫ Elemental analyses were
carried out by Dornis und Kolbe, Mikroanalytisches Laborato-
rium, Mülheim, Germany. Ϫ The compounds C6H2(CH2Br)4-
1,2,4,5 (4)[9], Ph2POEt[16], and [RuCl2(PPh3)4][17] were prepared ac-
cording to previously described methods. RuCl3 ·3 H2O was pur-
chased from Degussa.
C6H2(CH2P(O)Ph2)4-1,2,4,5 (5): A modification of a procedure
described in the literature[8] was used. In a two-necked 100-ml
round bottom flask, a stirred colorless solution of Ph2POEt (20.52
g, 89 mmol) and C6H2(CH2Br)4-1,2,4,5 (5.35 g, 11.9 mmol) in xy-
lenes (20 ml) was heated at 140°C for 0.5 h, while a gentle stream
of nitrogen was bubbled through the reaction mixture. After this
time, the reaction mixture was cooled to 50°C (ice bath) and the
white solid which had precipitated was filtered off. This solid was
washed once with hot benzene (100 ml), filtered off and dried in
vacuo to afford the tetraphosphoryl compound 5 as a white solid
which was sufficiently pure for further synthesis. Yield: 9.53 g
(86%), mp > 220°C (ref.[8]: 315Ϫ317°C). Ϫ 1H NMR (CD3OD,
200 MHz, 335 K): δ ϭ 7.62 (m, 40 H, ArH), 6.42 (s, 2 H, ArH),
1
crystals. Yield: 1.68 g (96%), mp 125°C. Ϫ H NMR (CDCl3, 300
MHz, 298 K): δ ϭ 7.28 (m, 40 H, ArH), 6.22 (s, 2 H, ArH), 2.96
(s, 8 H, CH2P). Ϫ 13C{1H} NMR (CDCl3, 75 MHz, 298 K ): δ ϭ
1
2
138.4 (d, JP-C ϭ 16 Hz, Ar), 133.0 (d, JP-C ϭ 19 Hz, Ar), 131.2
(d, JP-C ϭ 12 Hz, Ar), 128.4 (d, 3JP-C ϭ 23 Hz, Ar), 32.6, 32.4 (d,
3
1JP-C ϭ 15 Hz, CH2P). Ϫ 31P{1H} NMR (CDCl3, 81 MHz, 298
K): δ ϭ Ϫ12.3 (s). Ϫ C58H50P4: calcd. C 79.99, H 5.79; found C
79.84, H 5.72.
[{RuCl2(PPh3)}2{C6H2(CH2PPh2)4-1,2,4,5-P,PЈ,PЈЈ,PЈЈЈ}]·0.5
CH2Cl2 (8): A colorless solution of tetraphosphane 6 (0.38 g, 0.44
mmol) in CH2Cl2 (20 ml) was added to a brown solution of
[RuCl2(PPh3)4] in CH2Cl2 (20 ml) at room temperature and the
resulting reaction mixture was stirred for 2 h at this temperature.
During this time a green precipitate formed. After 2 h, the green
precipitate was filtered off, washed with CH2Cl2 (2 ϫ 20 ml) and
dried in vacuo to afford the pure bisruthenium(II) complex 8 in
2
3.52 (d, 8 H, JP-H ϭ 12 Hz, CH2P). Ϫ 31P{1H} NMR (CD3OD,
81 MHz, 335 K): δ ϭ 32.4 (s).
C6H2(CH2PPh2)4-1,2,4,5 (6): In a two-necked 100-ml round
bottom flask equipped with a reflux condensor and a septum, was
heated a stirred suspension of the tetraphosphoryl compound 5
(1.89 g, 2.02 mmol) in 1,2-dichlorobenzene (50 ml) at reflux tem-
38% yield as
a green insoluble solid (mp > 200°C). Ϫ
C94H78Cl4P6Ru2 ·0.5 CH2Cl2: calcd. C 63.69, H 4.58; found C
perature until all solids had dissolved. The resulting clear solution 63.83, H 4.65. Ϫ When a CH2Cl2 solution of [RuCl2(PPh3)4] was
482 Eur. J. Inorg. Chem. 1998, 477Ϫ483

New Multidentate Phosphane Ligand C6H2(CH2PPh2)4-1,2,4,5
FULL PAPER
A. L. Spek, G. van Koten, J. Am. Chem. Soc. 1997, 119, 11317.
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sulting reaction mixture was left undisturbed for 24 h, green-brown
X-ray quality crystals (mp > 200°C) of bisruthenium complex 8
were obtained. These crystals were collected by filtration, washed
with CH2Cl2 (2 ϫ 20 ml), dried in vacuo and subsequently sub-
jected to an X-ray structure determination.
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483