Conditioned P-CH2 bond cleavage of a μ-DPPM ligand in a cationic diruthenium system

Article abstract of DOI:10.1021/om960572l

Thermal reactions of [Ru₂(CO)₄(μ-O₂CMe)(μ-DPPM) ₂]⁺ ([1]⁺) with an excess amount of neutral two-electron nucleophiles in MeCN have been studied. The P-CH₂ bond of one coordinated DPPM ligand can be cleaved, depending on the choice of the nucleophiles used. Reactions of [1]⁺ with MeCN and phosphite P(OMe)₃ afford only substituted products [Ru₂(CO)₂L₂(μ-O ₂CMe)(μ-DPPM)₂]⁺ (L = MeCN ([2a]⁺), P(OMe)₃ ([2b]⁺)) via intermediates [Ru₂(CO)₃L(μ-O₂CMe)(μ-DPPM) ₂]⁺ (L = MeCN ([3a]⁺), P(OMe)₃ ([3b]⁺)). Compounds [2a]⁺ and [3a]⁺ can be prepared alternatively from decarbonylation reaction Of [1]⁺ with a suitable amount of Me₃NO in MeCN at ambient temperature, and the structure of [3a][BPh₄] has been determined by X-ray diffraction. Reactions Of [1]⁺ with phosphines (PR₃) PPh₃, PPh₂-Me, and PEt3, however, yield unexpected products, [Ru₂(CO)₂(PR₃)₂(μ-O ₂CMe)(μ-DPPM)(μ-PPh₂)] (4) and [Ph₂PCH₂PR₃][BPh₄] (5). The triphenylphosphine products, 4a and [5a]⁺, can be prepared alternatively from the thermal reaction of either [2a]⁺ or [3a]⁺ with excess PPh₃. Reaction of [1]⁺ with a stoichiometric amount of PPh₃ helped to reveal the presence of a cationic intermediate [Ru₂(CO)₂(PR₃)(μ₁,η ²-CH₂PPh₂)(μ-O ₂CMe)(μ-DPPM)(μ-PPh₂)]⁺ ([6]⁺) produced apparently from [Ru₂(CO)₃(PR₃)(μ-O ₂CMe)(μ-DPPM)₂]⁺ ([3c]⁺). An electronic supersaturation rather than a transient unsaturation is proposed to account for the observed P-CH² bond cleavage taking place for [3c]⁺. Both the spectroscopic and the X-ray structural results of the triphenylphospine intermediate [6a][BPh₄] indicate the presence of two isomeric forms in an approximate ratio of 1:5, differing probably in the relative orientation of the CH₂PPh₂ group with respect to the carboxylato bridge.

Full text of DOI:10.1021/om960572l

114
Organometallics 1997, 16, 114-119
Con d ition ed P -CH2 Bon d Clea va ge of a µ-DP P M Liga n d
in a Ca tion ic Dir u th en iu m System
Kom-Bei Shiu,* Shih-Wei J ean,† and Hsiang-J en Wang
Department of Chemistry, National Cheng Kung University, Tainan 701,
Taiwan, Republic of China
Sue-Lein Wang and Fen-Ling Liao
Department of Chemistry, National Tsing Hua University, Hsinchu 300,
Taiwan, Republic of China
J u-Chun Wang and Lin-Shu Liou
Department of Chemistry, Soochow University, Taipei 111, Taiwan, Republic of China
Received J uly 10, 1996X
Thermal reactions of [Ru2(CO)4(µ-O2CMe)(µ-DPPM)2]+ ([1]+) with an excess amount of
neutral two-electron nucleophiles in MeCN have been studied. The P-CH2 bond of one
coordinated DPPM ligand can be cleaved, depending on the choice of the nucleophiles used.
Reactions of [1]+ with MeCN and phosphite P(OMe)3 afford only substituted products
[Ru2(CO)2L2(µ-O2CMe)(µ-DPPM)2]+ (L ) MeCN ([2a ]+), P(OMe)3 ([2b]+)) via intermediates
[Ru2(CO)3L(µ-O2CMe)(µ-DPPM)2]+ (L ) MeCN ([3a ]+), P(OMe)3 ([3b]+)). Compounds [2a ]+
and [3a ]+ can be prepared alternatively from decarbonylation reaction of [1]+ with a suitable
amount of Me3NO in MeCN at ambient temperature, and the structure of [3a ][BPh4] has
been determined by X-ray diffraction. Reactions of [1]+ with phosphines (PR3) PPh3, PPh2-
Me, and PEt3, however, yield unexpected products, [Ru2(CO)2(PR3)2(µ-O2CMe)(µ-DPPM)(µ-
PPh2)] (4) and [Ph2PCH2PR3][BPh4] (5). The triphenylphosphine products, 4a and [5a ]+,
can be prepared alternatively from the thermal reaction of either [2a ]+ or [3a ]+ with excess
PPh3. Reaction of [1]+ with a stoichiometric amount of PPh3 helped to reveal the presence
of a cationic intermediate [Ru2(CO)2(PR3)(µ1,η2-CH2PPh2)(µ-O2CMe)(µ-DPPM)(µ-PPh2)]+ ([6]+),
produced apparently from [Ru2(CO)3(PR3)(µ-O2CMe)(µ-DPPM)2]+ ([3c]+). An electronic
supersaturation rather than a transient unsaturation is proposed to account for the observed
P-CH2 bond cleavage taking place for [3c]+. Both the spectroscopic and the X-ray structural
results of the triphenylphospine intermediate [6a ][BPh4] indicate the presence of two isomeric
forms in an approximate ratio of 1:5, differing probably in the relative orientation of the
CH2PPh2 group with respect to the carboxylato bridge.
In tr od u ction
saturation6 rather than a transient unsaturation. The
cleavage pattern is quite unusual, involving a difficult
P-C(sp3) bond breaking7 from Ph2PCH2PPh2 into Ph2P-
and CH2PPh2-coordinated fragments. Importantly, the
latter fragment was found to adopt a side-on coordina-
tion mode on only one of the two metal centers in an
isolated key intermediate. Further reaction with a
phosphine, releases this fragment as a cation [PR3CH2-
PPh2]+.
Bis(diphenylphosphino)methane (DPPM), one of the
most commonly used diphosphine ligands in “stabiliz-
ing” the integrity of di- and polynuclear transition-metal
frameworks,1 is known to undergo a thermally oxidative
P-C bond cleavage.2-4 It is normally reported that
carbonyl loss is a key step, creating electron deficiency
and then leading to the cleavage. However, this is
largely unsubstantiated.
In an extended study of the thermal substitution
reactions5 of a cation [Ru2(CO)4(µ-O2CMe)(µ-DPPM)2]+
([1]+) with various neutral two-electron nucleophiles,
described below, we found some evidence indicating that
the cleavage is more sensitive to an electronic super-
(2) (a) Lavigne, G.; Bonnet, J .-J . Inorg. Chem. 1981, 20, 2713. (b)
Lugan, N.; Bonnet, J .-J .; Ibers, J . A. J . Am. Chem. Soc. 1985, 107,
4484. (c) Bergounhou, C.; Bonnet, J .-J .; Fompeyrine, P.; Lavigne, G.;
Lugan, N.; Mansilla, F. Organometallics 1986, 5, 60. (d) Lugan, N.;
Bonnet, J .-J .; Ibers, J . A. Organometallics 1988, 7, 1538.
(3) (a) Doherty, N. M.; Hogarth, G.; Knox, S. A. R.; Macpherson, K.
A.; Melchior, F. M.; Orpen, A. G. J . Chem. Soc., Chem. Commun. 1986,
540. (b) Grist, N. J .; Hogarth, G.; Knox, S. A. R.; Lloyd, B. R.; Morton,
D. A. V.; Orpen, A. G. J . Chem. Soc., Chem. Commun. 1988, 673. (c)
Hogarth, G.; Knox, S. A. R.; Turner, M. L. J . Chem. Soc., Chem.
Commun. 1990, 145.
(4) Riera, V.; Ruiz, M. A.; Villafane, F.; Bois, C.; J eannin, Y. J .
Organomet. Chem. 1989, 375, C23.
(5) Shiu, K.-B.; Guo, W.-N.; Chan, T.-J .; Wang, J .-C.; Liou, L.-S.;
Peng, S.-M.; Cheng, M.-C. Organometallics 1995, 14, 1732.
(6) Geiger, W. E. Acc. Chem. Res. 1995, 28, 351.
* To whom correspondence should be addressed. Fax: (+886) 6 274
0552. E-mail: kbshiu@mail.ncku.edu.tw.
† Deceased April 1, 1996.
X Abstract published in Advance ACS Abstracts, December 15, 1996.
(1) (a) Puddephatt, R. J . Chem. Soc. Rev. 1983, 12, 99. (b) Balch, A.
L. In Homogeneous Catalysis with Metal Phosphine Complexes; Pigno-
let, L. H., Ed.; Plenum: New York, 1983; pp 167-213. (c) Chaudret,
B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev. 1988, 86, 191. (d)
Shriver, D. F.; Kaesz, H. D.; Adams, R. D. The Chemistry of Metal
Cluster Complexes; VCH: New York, 1990.
(7) Garrou, P. E. Chem. Rev. 1985, 85, 171.
S0276-7333(96)00572-9 CCC: $14.00 © 1997 American Chemical Society

Conditioned P-CH2 Bond Cleavage
Organometallics, Vol. 16, No. 1, 1997 115
two linkages, O-Ru-CO, formed by two acetate oxygen
atoms, two Ru atoms, and two trans-equatorial carbo-
nyls, are almost collinear with O(4)-Ru(1)-C(4) )
173.1(14)° and O(5)-Ru(2)-C(5) ) 174.5(12)°. With
ligation of a softer but bulkier ligand, either a phosphite
such as P(OMe)3 or a phosphine (PR3), relative to MeCN,
the collinear feature will not be kept, especially for the
equatorial carbonyl group closer to the phosphite or
phosphine ligand in [Ru2(CO)3(L)(µ-O2CMe)(µ-DPPM)2]+
(L ) P(OMe)3 ([3b]+) or PR3 ([3c]+)); this carbonyl would
be forced to bend back from the ligand and from the
collinearity more than the other one. In other words,
structures [3b]+ and [3c]+ are believed to be more
distorted than structure [3a ]+. With this distortion, the
equatorial carbonyl groups may not dissipate the ac-
cumulated electron density in the diruthenium center
due to the ligation of the trans-acetate group in [3b]+
or [3c]+ as efficiently as in [3a ]+.
In contrast to the straightforward reaction of [1]+ with
MeCN or P(OMe)3, those of [1]+ with an excess amount
of various phosphines in MeCN appeared complicated,
as shown in the 31P{1H} NMR spectra of the reaction
solution measured sequentially. However, isolation of
a key intermediate and all the final products formed
enlightens our understanding about the reactions. The
reaction products are unexpected to have two compo-
nents with and without metals, including neutral
compounds in a general formula of [Ru2(CO)2(PR3)2(µ-
O2CMe)(µ-DPPM)(µ-PPh2)] (PR3 ) PPh3 (4a ), PPh2Me
(4b), and PEt3 (4c)) and salts [Ph2PCH2PR3][BPh4] (PR3
) PPh3 (5a ), PPh2Me (5b), and PEt3 (5c)). Compounds
4a and [5a ]+ can be obtained alternatively from the
thermal reaction of either [2a ]+ or [3a ]+ with excess
PPh3, indicating that these two cations are probably
involved in the formation of 4 and [5]+ from [1]+ in
MeCN. The structures of 4a -c can be deduced as
shown in Scheme 1 on the basis of the observed
diamagnetic property, 31P NMR spectral data,3,4,11,12 and
the structure of one of the precursor compounds
[Ru2(CO)2(PPh3)(µ1,η2-CH2PPh2)(µ-O2CMe)(µ-DPPM)(µ-
PPh2)][BPh4] (6a or [6a ][BPh4]), the key intermediate
(Figure 2) which can be easily separated from a trace
amount of an insoluble by-product, 4a , in the reaction
between [1]+ and a stoichiometric amount of PPh3.
Conversion from [6a ]+ to 4a and [5a ]+ by reacting with
excess PPh3 was found almost quantitatively. Appar-
ently, the increased electron density accumulated in the
diruthenium center after the ligation of one phosphine
ligand, softer than MeCN or P(OMe)3, in the presumed
intermediate, [3c]+, accompanied with the worse dis-
sipation of this electron density in [3c]+ by the distorted
carbonyls as described above, may cause an electronic
supersaturation,6 initiating the oxidative Ph2P-CH2-
PPh2 bond cleavage to produce Ph2P- and CH2PPh2-
coordinated fragments in [6a ]+. The former fragment
was found to act as a bridging ligand for the two Ru
atoms, whereas the latter one coordinates with only one
Ru atom in a side-on geometry. The O-Ru-CO link-
ages in [6a ]+ regain collinearity from those in [3c]+, with
O(3)-Ru(1)-C(1) ) 173.7(5)° and O(4)-Ru(2)-C(2)
) 178.8(4)° (Figure 2). The intermediates, [6a ]+, [6b]+,
F igu r e 1. ORTEP plot of [3a ]+ with 50% thermal el-
lipsoids. Selected bond lengths: Ru(1)-Ru(2) ) 2.830(4),
Ru(1)-P(1) ) 2.402(10), Ru(1)-P(3) ) 2.380(10), Ru(1)-
O(4) ) 2.150(22), Ru(1)-C(3) ) 1.914(42), Ru(1)-C(4) )
1.805(42), Ru(2)-P(2) ) 2.367(10), Ru(2)-P(4) ) 2.349(10),
Ru(2)-O(5) ) 1.764(37), Ru(2)-N(1) ) 2.125(30), Ru(2)-
C(5) ) 1.764(37) Å. Selected bond angles: Ru(2)-Ru(1)-
P(1) ) 89.6(2), Ru(2)-Ru(1)-P(3) ) 92.0(3), Ru(2)-Ru(1)-
C(3) ) 172.7(13), Ru(2)-Ru(1)-C(4) ) 93.3(12), Ru(2)-
Ru(1)-O(4) ) 80.5(6), Ru(1)-Ru(2)-P(2) ) 93.0(2), Ru(1)-
Ru(2)-P(4) ) 90.9(2), Ru(1)-Ru(2)-N(1) ) 165.5(7), Ru(1)-
Ru(2)-C(5) ) 93.4(12), Ru(1)-Ru(2)-O(5) ) 81.2(5), N(1)-
C(6)-C(7) ) 177.9(46), O(4)-Ru(1)-C(4) ) 173.1(14),
O(5)-Ru(2)-C(5) ) 174.5(12)°.
Resu lts a n d Discu ssion
The specific thermal lability of two axial carbonyls
in bimetallic Ru(I) complexes has been recently observed
in many instances.8 Hence, it is not surprising to
observe that thermal reaction of [1]+ with MeCN or
P(OMe)3 follows a similar route, producing [Ru2(CO)2L2(µ-
O2CMe)(µ-DPPM)2]+ (L ) MeCN ([2a ]+) or P(OMe)3
([2b]+)). However, as reflected in the IR spectra mea-
sured sequentially for the reactions in solution, the
presumed intermediate, [Ru2(CO)3(MeCN)(µ-O2CMe)(µ-
DPPM)2]+ ([3a ]+), should have enough thermal stability
to be isolated or prepared via an alternative route.
Indeed, this intermediate can be obtained almost im-
mediately and quantitatively by treatment of [1]+ with
1 equiv of Me3NO in MeCN at ambient temperature.
The structure of [3a ]+ was also confirmed by X-ray
diffraction methods to have the MeCN ligand at one
axial position (Figure 1). Subsequent reaction of [3a ]+
with MeCN either at reflux or with addition of another
1 equiv of Me3NO allows formation of [2a ]+.
The Ru-Ru distance of 2.830(4) Å found in [3a ]+ is
slightly shorter than that of 2.841(1) Å observed in [1]+,9
but the difference between these two values is not
significant. The slightly longer Ru-N distance of 2.125-
(30) Å in [3a ]+ relative to the typical values between
2.097(6) and 2.107(6)9,10 and the bended Ru-Ru-N
skeleton with Ru(1)-Ru(2)-N(1) ) 165.5(7)° reflect
the weak coordination between the hard MeCN ligand
and the soft Ru(I) metal center in [3a ]+. As a result,
(8) Neuman, F.; Su¨ss-Fink, G. J . Organomet. Chem. 1989, 367, 175.
(9) Sherlock, S. J .; Cowie, M.; Singleton, E.; Steyn, M. M. d. V.
Organometallics 1988, 7, 1663.
(10) Shiu, K.-B.; Li, C.-H.; Chan, T.-J .; Peng, S.-M.; Cheng, M.-C.;
Wang, S.-L.; Liao, F.-L.; Chiang, M. Y. Organometallics 1995, 14, 524.
(11) (a) Albers, M. O.; Liles, D. C.; Singleton, E.; Stead, J . E.; Steyn,
M. M. d. V. Organometallics 1986, 5, 1262. (b) Bohle, D. S.; Chris-
tensen, A. N.; Goodson, P. A. Inorg. Chem. 1993, 32, 4173.
(12) Shyu, S.-G.; Hsiao, S.-M.; Lin, K.-J .; Gau, H.-M. Organometal-
lics 1995, 14, 4300.

116 Organometallics, Vol. 16, No. 1, 1997
Shiu et al.
Sch em e 1
F igu r e 2. ORTEP plot of [6a ]+ with 50% thermal el-
lipsoids. Selected bond lengths: Ru(1)-Ru(2) ) 2.999(1),
Ru(1)-C(72) ) 2.204(13), Ru(1)-P(1) ) 2.386(3), Ru(1)-
P(2) ) 2.329(3), Ru(1)-P(3) ) 2.395(3), Ru(2)-P(3) )
2.299(3), Ru(2)-P(4) ) 2.361(3), Ru(2)-P(5) ) 2.423(2),
P(2)-C(72) ) 1.742(12), Ru(1)-O(3) ) 2.113(7), Ru(2)-O(4)
) 2.135(8), Ru(1)-C(1) ) 1.833(14), Ru(2)-C(2) ) 1.833-
(13) Å. Selected bond angles: Ru(2)-Ru(1)-P(1) ) 79.5-
(1), Ru(2)-Ru(1)-P(2) ) 145.8(1), Ru(2)-Ru(1)-P(3) )
48.9(1), Ru(2)-Ru(1)-C(1) ) 105.8(5), Ru(2)-Ru(1)-O(3)
) 80.1(2), Ru(1)-Ru(2)-P(3) ) 51.7(1), Ru(1)-Ru(2)-P(4)
) 158.6(1), Ru(1)-Ru(2)-P(5) ) 98.9(1), Ru(1)-Ru(2)-C(2)
) 100.2(3), Ru(1)-Ru(2)-O(4) ) 79.2(2), P(2)-Ru(1)-C(72)
) 45.1(3), Ru(1)-C(72)-P(1) ) 71.3(4), Ru(1)-P(2)-C(72)
) 63.6(4), O(3)-Ru(1)-C(1) ) 173.7(5), O(4)-Ru(2)-C(2)
) 178.8(4)°.
and the ORTEP shown in this figure is probably the
major isomeric form B having less repulsive interactions
between the CH2PPh2 group and the nearby carbonyl.
Two similar isomers are believed to be present also for
the presumed intermediate, 6b or 6c. The nonbonded
distances between the µ-PPh2 phosphorus atom, P(3),
and the DPPM phosphorus atoms, P(1) and P(5), are
different, with d(P(3)‚‚‚P(1)) ) 4.296 Å and d(P(3)‚‚‚P-
(5)) ) 4.558 Å. If we assume that the coupling constant
J P(3),P(1) is smaller than J P(3),P(5), an NMR simulation
and [6c]+, display electrophilic behavior, reacting with
excess phosphine (PR3) to afford 4 and [5]+ (Scheme 1).
Although a 1H NMR spectrum of 6a , measured in
acetone-d6, indicates apparently one isomeric form, the
corresponding IR and 31P{1H} NMR solution spectra
show the possible presence of two different isomers, A
and B, illustrated by four carbonyl stretching bands in
program may help to give J P(1),P(2) ) 43.35, J P(1),P(3)
17.49, J P(1),P(4) ) 47.52, J P(1),P(5) ) -113.42, J P(2),P(3)
35.36, J P(2),P(4) ) 15.70, J P(2),P(5) ) -101.27, J P(3),P(4)
)
)
)
175.64, J P(3),P(5) ) 22.00, and J P(4),P(5) ) 33.03 Hz and
δP(1) ) 26.3, δP(2) ) -10.5, δP(3) ) 179.5, δP(4) ) 11.8,
and δP(5) ) 51.4.13
The Ph2P-CH2 bond length (i.e., d(P(2)-C(72)) of
1.742(12) in 6a is much shorter than that of 1.787(6) Å
in [Fe2(CO)4(µ-DPPM)(µ-PPh2)(µ2,η2-CH2PPh2)]3a or that
of 1.81(1) Å in [Mo2(η-C5H5)2(CO)(µ-I)(µ-PPh2)(µ2,η2-CH2-
PPh2)].4 By comparison with the singly bonded P-CH3
distance of 1.843 Å,14 the three P-CH2 distances are
indicative of a P-C bond order greater than unity. As
shown by various multiplets in NMR spectra, compound
6a is diamagnetic. It is hence evident that the formal
oxidation state for each Ru atom is two. Thus, the
ligated “(diphenylphosphino)carbene” group should bet-
ter be viewed as a four-electron anionic donor (i.e.,
PPh2CH2-) in [6a ]+, and a conventional electron-count-
the IR spectrum and two similar sets of phosphorus
multiplets with different intensity and slightly different
chemical shifts in this NMR spectrum. If an inverse-
gated 31P{1H} NMR spectrum was recorded (i.e., with-
out NOE), the integration of the multiplets shows a ratio
of A/B close to 1:5. The spectrum (Figure S1) is
deposited as Supporting Information. Attempts to
separate the two isomers for further characterization
unfortunately failed. However, with the structure of one
isomer determined by X-ray diffraction methods (Figure
2), it is probable true that the difference between the
two isomeric forms is in the relative orientation of the
CH2PPh2 group with respect to the carboxylato bridge,
(13) Spectral Simulation gNMR, version 3.6; Cherwell Scientific
Publishing Limited: Oxford, U.K., 1995.
(14) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Oxford:
New York, 1984; p 846.

Conditioned P-CH2 Bond Cleavage
Organometallics, Vol. 16, No. 1, 1997 117
intermediate, [6a ]+ (Figure 2), the Ph2P-CH2PPh2 bond
cleavage produces µ-Ph2P- and µ1,η2-(CH2PPh2)-coordi-
nated fragments. By reaction with excess phosphine,
the latter fragment can be released as a cation [5a ]+,
with concomitant formation of a neutral phosphido
complex, [4a ] (Scheme 1). Thermal reactions of other
cationic diruthenium compounds containing different
bidentate ligands with two-electron nucleophiles are
currently being carried out in our laboratory.
Sch em e 2
Exp er im en ta l Section
Gen er a l Com m en ts. All solvents were dried and purified
by standard methods [ethers, paraffins, and arenes from
potassium with benzophenone as indicator; halocarbons and
acetonitrile from CaH2; alcohols from the corresponding alkox-
ide] and were freshly distilled under nitrogen immediately
before use. All reactions and manipulations were carried out
in standard Schlenk ware, connected to a switchable double
manifold providing vacuum and nitrogen. Reagents were used
as supplied by Aldrich. 1H and 31P NMR spectra were
measured on a Bruker AMC-400 or a Varian Unity Plus-400
(1H, 400 MHz; 31P, 162 MHz) or a Bruker AC-200 (1H, 200
MHz) NMR spectrometer. 1H chemical shifts (δ in ppm, J in
Hz) are defined as positive downfield relative to internal MeSi4
(TMS) or the deuterated solvent, while 31P chemical shifts are
defined as positive downfield relative to external 85% H3PO4.
The IR spectra were recorded on a Hitachi Model 270-30 or
Bio-Rad FTS 175 instrument. The following abbreviations
were used: vs, very strong; s, strong; m, medium; w, weak; s,
singlet; d, doublet; t, triplet; dd, doublet of doublet; dt, doublet
of triplet; dq, doublet of quartet; m, multiplet; br, broad
unresolved signal. Microanalyses were carried out by the staff
of the Microanalytical Service of the Department of Chemistry,
National Cheng Kung University.
ing system would predict a single Ru-Ru bond for this
34-electron species. This view appears compatible with
the more upfield P(1) relative to P(5). The long Ru-
Ru bond with d(Ru-Ru) ) 2.999(1) Å may be classified
as a dative bond, donating an electron pair from the 18-
electron Ru(1) center to the 16-electron Ru(2) center.5,15
However, reactions of [6]+ toward PR3 are not typical
for a dinuclear compound with a “dative” metal-metal
bond,12 as demonstrated by that of [6a ]+ with PPh3 not
to give a Ru(II) adduct such as [Ru2(CO)2(PR3)2(µ-O2-
CMe)(µ-DPPM)(µ-PPh2)(µ1,η2-CH2PPh2)]+ ([7]+) but to
give a reduced Ru(I) product with PPh2CH2 eliminated,
[Ru2(CO)2(PR3)2(µ-O2CMe)(µ-DPPM)(µ-PPh2)] ([4]). The
elimination of the PPh2CH2 group as phosphonium salt
[Ph2PCH2PR3][BPh4] with the reduction of the metal
center in [6]+ is somewhat surprising, but similar cases
were either reported or proposed previously.16 Lack of
formation of an adduct such as [7]+ is probably caused
by the sterically unfavorable impedance, especially
between two bulky phosphine groups (Scheme 2).
Syn th esis of [Ru 2(CO)2(MeCN)2(µ-O2CMe)(µ-DP P M)2]
[BP h 4]2 (2a ). Meth od 1. A stirred solution of [Ru2(CO)4(µ-
O2CMe)(µ-DPPM)2][BF4] (1)9 (0.110 g, 0.090 mmol) in MeCN
(15 mL) was heated under reflux for 12 h, and 0.080 g of
NaBPh4 (0.234 mmol) was then added to the mixture. The
resultant solution was stirred at ambient temperature for 0.5
h to effect the metathesis reaction. The solvent was removed
under vacuum. Recrystallization from CH2Cl2/MeOH gave a
yellow product (0.124 g, 93%).
Meth od 2. To a stirred solution of 1 (0.306 g, 0.249 mmol)
in MeCN (10 mL) was added dropwise 5 mL solution of Me3-
NO‚2H2O (0.062 g, 0.550 mmol) dissolved in MeCN. After 2
h, 0.200 g of NaBPh4 (0.585 mmol) was added to the solution.
The solvent was removed under vacuum. Recrystallization
from CH2Cl2/MeOH gave a yellow product (0.322 g, 87%).
Alternatively, compound 2a can be prepared by a procedure
similar to method 2 but in a shorter period of time (ca. 1.5 h),
using equimolar amounts of 3a , described below, and Me3NO‚-
2H2O in MeCN at ambient temperature. The yield is 94%.
Anal. Calcd for C82H73BN2O4P4Ru2: C, 66.22; H, 4.95; N, 1.88.
Found: C, 65.82; H, 5.15; N, 1.89. 1H NMR (25 °C, acetone-
d6, 400 MHz): 1.27 (3 H, s), 2.02 (6 H, s), 3.75 (2 H, m), 4.37
(2 H, m), 6.74-7.66 (60 H, m). 31P{1H} NMR (25 °C, acetone-
d6, 162 MHz): 25.72 (4 P, s). IR (CH2Cl2): vCO, 1927 s; 1885
Con clu sion s
The thermal oxidative P-C(sp3) bond cleavage of a
bridging DPPM ligand from a cationic dinuclear complex
[1]+ can be made to occur by addition of a phosphine,
but not a phosphite or MeCN, indicating apparently that
the cleavage is more sensitive to an electronic super-
saturation6 rather than a transient unsaturation de-
scribed previously.2-4 As revealed in an isolated key
(15) (a) Langebach, H.-J .; Vahrenkamp, H. Chem. Ber. 1979, 112,
3390, 3773. (b) Breen, M. J .; Duttera, M. R.; Geoffroy, G. L.; Novotnak,
G. C.; Roberts, D. A.; Shulman, P. M.; Steinmetz, G. R. Organometallics
1982, 1, 1008. (c) Roberts, D. A.; Steinmetz, G. R.; Breen, M. J .;
Shulman, P. M.; Morrison, E. D.; Duttera, M. R.; DeBrosse, C. W.;
Whittle, R. R.; Geoffroy, G. L. Organometallics 1983, 2, 846. (d) Mercer,
W. C.; Whittle, R. R.; Burkhardt, E. W.; Geoffroy, G. L. Organometallics
1985, 4, 68. (e) Shyu, S.-G.; Wojcicki, A. Organometallics 1985, 4, 1457.
(f) Powell, J .; Coutoure, C.; Gregg, M. R. J . Chem. Soc., Chem.
Commun. 1988, 1208. (g) Baker, R. T.; Calabrese, J . C.; Krusic, P. J .;
Therien, M. J .; Trogler, W. C. J . Am. Chem. Soc. 1988, 110, 8392. (h)
J enkins, H. A.; Loeb, S. J .; Stephan, D. W. Inorg. Chem. 1989, 28, 1998.
(i) Powell, J .; Sawyer, J . F.; Stainer, M. V. R. Inorg. Chem. 1989, 28,
4461. (j) Shyu, S.-G.; Hsu, J .-Y.; Lin, P.-J .; Wu, W.-J .; Peng, S.-M.;
Lee, G.-H.; Wen, Y.-S. Organometallics 1994, 13, 1699.
(16) (a) Friedel, H.; Renk, I. W.; Dieck, H. T. J . Organomet. Chem.
1971, 26, 247. (b) Weinberg, E. L.; Baird, M. C. J . Organomet. Chem.
1979, 179, C61. (c) Huggins, J . M.; Bergman, R. G. J . Am. Chem. Soc.
1979, 101, 4410. (d) Kampmeier, J . A.; Harris, S. H.; Rodehorst, R. M.
J . Am. Chem. Soc. 1981, 103, 1478. (e) Kampmeier, J . A.; Rodehorst,
R. M. J . Am. Chem. Soc. 1981, 103, 1847.
w cm-1
Syn t h esis
.
of
[R u 2(CO)2(P (OMe)3)2(µ-O2CMe)(µ-
DP P M)2][BP h 4]2 (2b). To a stirred solution of 1 (0.142 g,
0.116 mmol) in MeCN (25 mL) was added excess P(OMe)3 (ca.
0.5 mL). The solution was heated under reflux for 7 h, and
0.212 g of NaBPh4 (0.619 mmol) was then added to the
mixture. The resultant solution was stirred at ambient
temperature for 0.5 h to effect the metathesis reaction. The
solvent was removed under vacuum. Recrystallization from
CH2Cl2/MeOH gave a yellow product (0.148 g, 77%). Anal.
Calcd for C84H85O10P6Ru2: C, 61.02; H, 5.18. Found: C, 60.69;
H, 5.28. 1H NMR (25 °C, CDCl3, 200 MHz): 0.97 (3 H, s), 2.79
(18 H, t, J ) 5.3), 4.28 (2 H, m), 4.45 (2 H, m), 6.85-7.59 (60

118 Organometallics, Vol. 16, No. 1, 1997
Shiu et al.
H, m). 31P{1H} NMR (25 °C, acetone-d6, 162 MHz): 21.45 (4
P, t, J ) 24.7), 119.88 (2 P, quintet). IR (CH2Cl2): vCO, 1929
Ta ble 1. Cr ysta l Da ta
compd
formula
fw
color, habit
diffractometer used
space group
a, Å
3a ‚1/2C6H14‚H2O
C84H76BNO6P4Ru2
1532.29
6a ‚2CH3OH‚H2O
C98H92BO7P5Ru2
1739.4
s; 1886 w cm-1
.
Syn th esis of [Ru 2(CO)3(MeCN)(µ-O2CMe)(µ-DP P M)2]-
[BP h 4]2 (3a ). To a stirred solution of 1 (0.133 g, 0.108 mmol)
in MeCN (10 mL) was added dropwise 2 mL solution of Me3-
NO‚2H2O (0.0121 g, 0.109 mmol) dissolved in MeCN. After
10 min, 0.194 g of NaBPh4 (0.567 mmol) was added to the
solution. The solvent was then removed under vacuum.
Recrystallization from CH2Cl2/MeOH gave a yellow product
(0.145 g, 91%). Anal. Calcd for C81H70BNO5P4Ru2: C, 65.99;
H, 4.79; N, 0.95. Found: C, 65.68; H, 4.81; N, 0.96. 1H NMR
(25 °C, CD3CN, 400 MHz): 0.80 (3 H, s), 1.95 (3 H, s), 3.88 (1
H, m), 4.13 (1 H, m), 4.34 (1 H, m), 4.58 (1 H, m), 5.41-7.48
(60 H, m). 31P{1H} NMR (25 °C, acetone-d6, 162 MHz): 27.96
(2 P, m), 28.53 (2 P, m). IR (CH2Cl2): vCO, 2006 s; 1950 s;
orange irregular
Siemens P4
monoclinic, P21/c
17.605(7)
20.434(4)
21.558(2)
90
orange-yellow bladed
Siemens SMART-CCD
triclinic, P1h
15.681(2)
16.233(2)
21.548(2)
89.67(2)
b, Å
c, Å
R, deg
â, deg
97.870(1)
90
71.09(2)
62.27(2)
γ, deg
V, Å3
7682(4)
4
4524.1(9)
2
Z
Dcalcd, gcm-3
λ(Mo KR), Å
F(000)
1.325
1.277
0.710 73
3152
0.710 73
1788
1902 w cm-1
.
unit cell detn
no.; 2θ range, deg 25; 15-16
whole data
hemisphere
3-52
R ea ct ion of [R u 2(CO)4(µ-O2CMe)(µ-DP P M)2][BF 4] (1)
w ith Excess P h osp h in e. With P P h 3. A stirred solution of1
(0.174 g, 0.142 mmol) and PPh3 (0.311 g, 1.187 mmol) in MeCN
(40 mL) was heated under reflux for 61 h. The orange-yellow
precipitate formed during the reaction was filtered out, washed
with MeCN (5 mL) three times, and dried under vacuum to
give 0.168 g (84%) of compound 4a . A 0.107 g amount of
NaBPh4 (0.313 mmol) was added to the filtrate, and the
solution was stirred for 0.5 h to effect the metathesis reaction.
The solvent was removed under vacuum. Recrystallization
from CH2Cl2/MeOH gave a pale yellow product 5a (0.087 g,
78%).
With P P h 2Me. A stirred solution of 1 (0.144 g, 0.117 mmol)
and PPh2Me (ca. 0.2 mL) in MeCN (15 mL) was heated under
reflux for 3 h. The solvent was removed under vacuum. The
solid residue was extracted with Et2O six times. The remain-
ing residue was dissolved in 5 mL of MeOH. Upon addition
of 0.100 g of NaBPh4 (0.292 mmol), a pale yellow precipitate
formed, which was collected, washed with 5 mL of MeOH and
5 mL of Et2O, and dried under vacuum to give 5b (0.058 g,
69%). The ether solvent was then removed from the extract.
Recrystallization from CH2Cl2/MeOH gave a yellow product
4b (0.110 g, 73%).
scan type
θ-ω
2θ range, deg
h,k,l range
3-45
18,22,(23
(18,(19,26
µ(Mo KR), cm-1
cryst size, mm
temp, K
5.3
4.75
0.2 × 0.2 × 0.3
298
0.22 × 0.11 × 0.05
296
no. of measd reflns
no. of unique reflns
10 390
10 011
36 133
15 390
no. of obsd reflns (No) 2314 (>5σ)
8705 (>3σ)
0.077, 0.075
1.43
R,a Rw
0.084, 0.092
1.26
a
GOFa
refinement program
no. of ref params (Np) 308
SHELXTL-PLUS
SHELXTL-PLUS
993
2
-1
2 -1
weighting scheme
[σ2(Fo) + 0.0015Fo
0.61
]
[σ2(Fo) + 0.0005Fo
]
(∆F)max, e Å-3
1.33
(∆F)min, e Å-3
-0.65
-1.02
R ) [∑||Fo| - |Fc||/∑|Fo]. Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
a
2
GOF ) [∑w(|Fo| - |Fc|)2/(No - Np)]1/2
.
Rea ction of 1, 2a , or 3a w ith a Stoich iom etr ic Am ou n t
of P h osp h in e. Since the reactions gave a similar mixture of
different products, only one typical reaction for 2a was
described below. A stirred solution of 2a (0.142 g, 0.096 mmol)
and PPh3 (0.252 g, 0.096 mmol) in MeCN (15 mL) was heated
under reflux for 7 h. About 0.0021 g (2%) of the orange-yellow
precipitate 4a , formed during the reaction, was filtered out,
washed with MeCN (5 mL) several times until a colorless
filtrate was obtained, and dried under vacuum. A 0.198 g
amount of NaBPh4 (0.579 mmol) was added to the filtrate, and
the resultant solution was stirred for 0.5 h to effect the
metathesis reaction. The solvent was then removed under
vacuum. Recrystallization from CH2Cl2/MeOH gave an orange-
yellow compound 6a . The compound was washed with cool
MeCN (2 mL) to be rid of any 5a and dried under vacuum to
give 0.101 g (63%). Anal. Calcd for C96H82BO4P5Ru2: C, 69.15;
H, 4.96. Found: C, 69.46; H, 5.18. 1H NMR (25 °C, acetone-
d6, 400 MHz): 0.87 (2 H, m), 1.27 (3 H, s), 4.65 (1 H, m), 4.78
(1 H, m), 6.74-7.60 (75 H, m). 31P{1H} NMR (25 °C, acetone-
d6, 162 MHz): multiplets for isomer B, 179.5, 51.4, 26.3, 11.8,
-10.5; for minor isomer A, 167.9, 47.1, 13.6, 9.1, -17.3. IR
With P Et3. Compounds 4c and 5c were prepared in yields
of 63% and 78%, respectively, by a procedure similar to that
used for 4b and 5b. Anal. Calcd for C77H65O4P5Ru2 (4a ): C,
65.53; H, 4.64. Found: C, 65.64; H, 4.65. 1H NMR (25 °C,
CDCl3, 400 MHz): 0.86 (3 H, s), 3.42 (1 H, m), 3.78 (1 H, br),
6.46-7.53 (60 H, m). 31P{1H} NMR (25 °C, CDCl3, 162 MHz):
24.5 (2 P, d, J ) 182), 31.4 (2 P, s), 153.7 (1 P, t). IR (CH2Cl2):
v
CO, 1904 s; 1869 w cm-1
. Anal. Calcd for C67H61O4P5Ru2
(4b): C, 62.52; H, 4.78. Found: C, 62.64; H, 4.90. 1H NMR
(25 °C, CDCl3, 200 MHz): 0.86 (3 H, s), 1.51 (6 H, br), 4.01 (2
H, m), 6.75-7.44 (50 H, m). 31P{1H} NMR (25 °C, acetone-d6,
162 MHz): 12.0 (2 P, s), 26.6 (2 P, d, J ) 181), 150.7 (1 P, t).
IR (CH2Cl2): vCO, 1903 s; 1866 w cm-1
.
Anal. Calcd for
C
53H65O4P5Ru2 (4c): C, 55.68; H, 5.83. Found: C, 55.68; H,
5.98. 1H NMR (25 °C, acetone-d6, 400 MHz): 0.77 (18 H, m),
1.39 (3 H, m), 1.60 (12 H, m), 4.06 (2 H, m), 7.07-7.58 (30 H,
m). 31P{1H} NMR (25 °C, acetone-d6, 162 MHz): 11.8 (2 P, s),
27.7 (2 P, d, J ) 182), 148.5 (1 P, t). IR (CH2Cl2): vCO, 1900
s; 1862 w cm-1. Anal. Calcd for C55H47BP2 (5a ): C, 84.61; H,
6.07. Found: C, 83.93; H, 6.02. 1H NMR (25 °C, CD3CN, 400
MHz): 4.00 (2 H, dd, J ) 14.4, 0.8), 6.80-7.73 (45 H, m).
31P{1H} NMR (25 °C, CD3CN, 162 MHz): -29.0 (1 P, d, J )
62), 21.9 (1 P, d). Anal. Calcd for C50H45BP2 (5b): C, 83.56;
H, 6.31. Found: C, 83.33; H, 6.38. 1H NMR (25 °C, acetone-
d6, 400 MHz): 2.67 (2 H, d, J ) 13.6), 4.08 (2 H, d, br, J )
15.2), 6.74-7.90 (40 H, m). 31P{1H} NMR (25 °C, CD3CN, 162
MHz): -29.0 (1 P, d, J ) 62), 21.9 (1 P, d). Anal. Calcd for
(MeCN): vCO, 2001 w; 1968 w; 1945 w; 1925 s cm-1
.
Sin gle-Cr ysta l X-r a y Diffr a ction Stu d ies of 3a a n d 6a .
Suitable single crystals were grown from CH2Cl2/hexane or
MeCN/Et2O at room temperature to do the single-crystal
structure determination. The X-ray diffraction data for 3a
were measured on a Siemens P4 four-circle diffractometer, and
those for 6a were measured in frames with increasing ω (0.30°/
frame) and with the scan speed at 10.00 s/frame on a Siemens
SMART-CCD instrument, equipped with a normal focus and
3 kW sealed-tube X-ray source. For data collected on the four-
circle diffractometer, three standard reflections were moni-
tored every 500 reflections through the collection. The varia-
tion for 3a was less than 6%. Empirical absorption corrections
were carried out on the basis of an azimuthal scan. The
structures of 3a and 6a were solved by direct methods and
refined by a full-matrix least-square procedure using SHELX-
TL-
C
43H47BP2 (5c): C, 81.13; H, 7.44. Found: C, 81.20; H, 7.44.
1H NMR (25 °C, acetone-d6, 400 MHz): 1.22 (9 H, dt, J ) 18.8,
7.6), 2.33 (6 H, dq, J ) 12.8, 7.6), 3.34 (2 H, d, J ) 14.8), 6.75-
7.54 (30 H, m). 31P{1H} NMR (25 °C, CD3CN, 162 MHz):
-30.2 (1 P, d, J ) 48), 40.5 (1 P, d).

Conditioned P-CH2 Bond Cleavage
Organometallics, Vol. 16, No. 1, 1997 119
PLUS.17 In order to keep an optimum data-to-parameter ratio,
only non-hydrogen and -carbon atoms were refined anisotro-
pically for 3a . The other essential details of single-crystal data
measurement and refinement are given in Table 1. In the
asymmetric unit of the crystals used were found one molecule
of water and a half-molecule of hexane in 3a and two molecules
of MeOH and one molecule of water in 6a . The three hydrogen
atoms of MeCN in 3a were not found in a difference map and
not included in the final cycle of the refinement.
Ack n ow led gm en t. We thank the National Science
Council of the Republic of China for financial support
of this research (Contract NSC86-2113-M006-007).
Su p p or tin g In for m a tion Ava ila ble: The 162-MHz in-
verse-gated 31P{1H} NMR spectrum of 6a in acetone-d6 (Figure
S1) and tables of non-hydrogen atomic coordinates and equiva-
lent isotropic displacement coefficients, complete bond lengths
and angles, anisotropic displacement coefficients, and hydro-
gen coordinates and B values for 3a and 6a (14 pages).
Ordering information is given on any current masthead page.
(17) (a) Sheldrick, G. M. SHELXTL-Plus Crystallographic System,
release 4.21; Siemens Analytical X-ray Instruments: Madison, WI,
1991. (b) Siemens Analytical X-ray Instruments Inc., Karlsruhe,
Germany, 1991.
OM960572L