Hydrodimetalation of tert-butylphosphaethyne by a diruthenium complex: Crystal and molecular structure of [Ru2(CO)4(μ-PBu 2t)(μ-Ph2PCH2PPh 2){μ-PC(H)But}]

Article abstract of DOI:10.1021/om049777h

The reaction of [Ru₂(CO)₃(PBu_{3 n})(μ-H)(μ-PBu₂^t)(μ-dppm)] (1a) with tert-butylphosphaethyne leads under hydrodimetalation to the novel phosphaethenyl complex [Ru₂CO)₄-(μ-PBu₂ ^t)(μ-dppm){μ-PC(H)Bu^t}] (2), which has been characterized by spectroscopic methods as well as by X-ray diffraction. Compound 2 represents the first structurally characterized complex with a phosphaalkenyl ligand of the type μ-PC(H)R bridging two metal centers.

Full text of DOI:10.1021/om049777h

5314
Organometallics 2004, 23, 5314-5316
Hyd r od im eta la tion of ter t-Bu tylp h osp h a eth yn e by a
Dir u th en iu m Com p lex: Cr ysta l a n d Molecu la r Str u ctu r e
of [Ru 2(CO)4(µ-P Bu t )(µ-P h 2P CH2P P h 2){µ-P C(H)Bu t}]
2
Hans-Christian Bo¨ttcher*
Institute of Inorganic Chemistry, Martin Luther University Halle-Wittenberg,
Kurt-Mothes-Strasse 2, D-06120 Halle/ Saale, Germany
Daniel Himmel and Manfred Scheer*
Institute of Inorganic Chemistry, University of Karlsruhe (TH), Engesserstrasse 15,
D-76128 Karlsruhe, Germany
Received March 30, 2004
The reaction of [Ru2(CO)3(PBun )(µ-H)(µ-PBut )(µ-dppm)] (1a ) with tert-butylphosphaethyne
3
2
leads under hydrodimetalation to the novel phosphaethenyl complex [Ru2(CO)4(µ-PBut )(µ-
2
dppm){µ-PC(H)But}] (2), which has been characterized by spectroscopic methods as well as
by X-ray diffraction. Compound 2 represents the first structurally characterized complex
with a phosphaalkenyl ligand of the type µ-PC(H)R bridging two metal centers.
Within our studies on the reactivity of the coordina-
(CO)5].6 Furthermore, two interesting transformations
on [Fe2(µ-CO)(CO)6(µ-dppm)] in the presence of PtCBut
were reported: UV irradiation in toluene for 9 h yielded
[Fe2(CO)5(µ-dppm){µ,η2-PC(CO)But}], whereas under
prolonged UV irradiation (12-30 h) a mixture of prod-
ucts was obtained containing [Fe2(µ-CO)(CO)4(µ,η2-
PCBut)].7 Moreover, a few hydrometalation reactions of
phosphaalkynes induced by transition metal complexes
were reported.8,9 Thus, the reaction of [RuH(CO)Cl-
(PPh3)3] with PtCBut results in insertion of the phos-
phaalkyne into the M-H bond to give the phosphaal-
kenyl complex [Ru(CO)Cl(PPh3)2{PdC(H)But}].8 To our
knowledge for dinuclear complexes and metal clusters,
respectively, this kind of hydrodimetalation of PtCR
resulting in a bridging phosphaalkenyl ligand, µ-PC-
(H)R, has not been reported until now. An “indirect”
hydrodimetalation was described during the reaction of
[HIr4(CO)10(µ-PPh2)] with [Pt(dppe)(η2-PCBut)], yielding
the clusters [Ir4Pt(dppe)(CO)n(µ-PPh2){µ-PC(H)But}] (n
) 9, 10; dppe ) Ph2PC2H4PPh2).9 The structures of
these compounds, isolated as a mixture only, were
proposed on the basis of NMR and mass spectrometry
experiments. Herein we describe reactions of the com-
tively unsaturated complexes [M2(CO)4(µ-H)(µ-PBut )-
2
(µ-dppm)] (M ) Fe, Ru; dppm ) Ph2PCH2PPh2)1 we
observed a facile insertion of carbon disulfide into the
dimetal hydrido core of [Ru2(CO)4(µ-H)(µ-PBut )(µ-
2
dppm)] (1), resulting in the dithioformato compound
[Ru2(CO)4(µ-S2CH)(µ-PBut )(µ-dppm)].2 Terminal alkynes
2
such as PhCtCH did not insert into the Ru2(µ-H) core
of 1, because the starting complex is a strong base and
on the other hand the alkyne is too acidic; therefore the
acetylide-bridged species [Ru2(CO)4(µ,η1:η2-CtCPh)(µ-
PBut )(µ-dppm)] was obtained.3 In light of more inser-
2
tion reactions we were interested in the reaction be-
havior of 1 toward phosphaalkynes. Since the develop-
ment of preparative pathways to stable phosphaalkynes,4
several types of reactions involving these compounds
have been observed in the coordination sphere of transi-
tion metals such as oligomerizations, cyclizations, and
insertions.5 Therefore phosphaalkynes show a complex
coordination behavior dominated by bonding modes
involving mainly the phosphorus carbon triple bond. An
analogous reaction pattern to the alkynes has been
observed in several cases. Thus, we could show that a
kind of heteroalkyne metathesis can be realized, wherein
the alkoxide complexes [(RO)3WtW(OR)3] reacted with
phosphaalkynes in the presence of [W(CO)5THF], yield-
ing the products [(RO)3WtCR] and [(RO)3WtPfW-
plexes [Ru2(CO)3L(µ-H)(µ-PBut )(µ-dppm)] (L ) CO, 1;
2
L ) PBun3, 1a ) with PtCBut resulting in the synthesis
and structural characterization of the novel complex
[Ru2(CO)4(µ-PBut )(µ-dppm){µ-PC(H)But}] (2).
2
Treatment of the coordinatively unsaturated [Ru2-
(CO)4(µ-H)(µ-PBut )(µ-dppm)] (1) with an excess of Pt
2
CBut in DME solution under reflux for 8 h does not
result in any conversion. As described for the reaction
of 1 with phenylethyne, long reaction times in refluxing
* To whom correspondence should be addressed. E-mail: boettcher@
chemie.uni-halle.de and mascheer@chemie.uni-karlsruhe.de.
(1) Bo¨ttcher, H.-C.; Graf, M.; Merzweiler, K.; Wagner, C. Inorg.
Chim. Acta 2003, 350, 399, and references therein.
(2) Bo¨ttcher, H.-C.; Graf, M.; Merzweiler, K.; Wagner, C. Z. Anorg.
Allg. Chem. 2000, 626, 597.
(3) Bo¨ttcher, H.-C.; Graf, M.; Merzweiler, K.; Wagner, C. Z. Anorg.
Allg. Chem. 2000, 626, 1335, and references therein.
(4) Becker, G.; Gesser, G.; Uhl, W. Z. Naturforsch. 1981, 36b, 16.
(5) (a) Nixon, J . F. Coord. Chem. Rev. 1995, 145, 201. (b) Nixon, J .
F. Chem. Soc. Rev. 1995, 24, 319. (c) Dillon, K. B.; Mathey, F.; Nixon,
J . F. In Phosphorus, The Carbon Copy; Wiley: Chichester, 1998; p 40.
(d) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578.
(6) Scheer, M.; Kramkowski, P.; Schuster, K. Organometallics 1999,
18, 2874.
(7) Hitchcock, P. B.; Madden, T. J .; Nixon, J . F. J . Organomet. Chem.
1993, 463, 155.
(8) Bedford, R. B.; Hill, A. F.; J ones, C. Angew. Chem., Int. Ed. Engl.
1996, 35, 547, and references therein.
(9) Araujo, M. H.; Avent, A. G.; Hitchcock, P. B.; Nixon, J . F.; Vargas,
M. D. Organometallics 1998, 17, 5460, and references therein.
10.1021/om049777h CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/18/2004

Hydrodimetalation of tert-Butylphosphaethyne
Organometallics, Vol. 23, No. 22, 2004 5315
ways can be considered: (i) the dimetal complexes 1 and
1a exhibit formal Ru-Ru double bonds; therefore an
addition of the triple bond of the phosphaethyne to the
Ru-Ru double bond could be taken into account. The
LUMO of the RudRu bond exhibits π* character and
could interact with the HOMO π orbital of the phos-
phaethyne. Thus, by this way the “clean” addition
product [Ru2(CO)3(PBun3)(µ-PBut )(µ-dppm){µ-PC(H)-
2
But}] should be obtained, which is however not the case.
Therefore we have to assume that due to the steric
hindrance of the tributylphosphine a simultaneous
dissociation occurs that is followed by a CO addition.
The CO must be produced in side reactions of this
thermolysis, which occur with certainty because the
formation of the complexes [Ru(CO)4(PBun3)] and [Ru-
(CO)3(PBun3)2] was indicated by 31P NMR. Since these
speculations about a possible reaction pathway are not
very convincing, the following pathway seems to us to
be the more realistic one. (ii) Here, in a first step the
dissociation of the phosphine occurs followed by an “end-
on” coordination of the phosphaethyne via the phospho-
rus lone pair. Furthermore, the phosphaethyne under-
goes a bridging of the Ru-Ru bond with a simultaneous
migration of the hydride to the phosphaethyne carbon
to form the phosphaethenyl ligand. Finally, the remain-
ing free coordination site is occupied by the sterically
less demanding and better π acceptor ligand CO (com-
pared to PBun3). Obviously, the free phosphine leads to
a degradation of the dinuclear core of the starting
material under the employed thermolytic conditions.
Thus, 31P{1H} NMR investigations of crude reaction
mixtures indicate additionally the presence of free
F igu r e 1. Molecular structure of [Ru2(CO)4(µ-PBut )(µ-
2
dppm){µ-PC(H)But}] (2) showing 30% thermal displace-
ment ellipsoids. Selected bond distances (Å) and angles
(deg): Ru(1)-Ru(2) 2.854(1), Ru(1)-P(1) 2.286(2), Ru(1)-
P(2) 2.362(1), Ru(1)-P(3) 2.361(1), Ru(2)-P(1) 2.311(2),
Ru(2)-P(2) 2.376(2), Ru(2)-P(4) 2.350(1), P(1)-C(5) 1.662(7);
Ru(1)-P(1)-Ru(2) 76.77(5), Ru(1)-P(1)-C(5) 132.0(2),
Ru(2)-P(1)-C(5) 148.8(3), Ru(1)-Ru(2)-P(1) 51.21(4),
Ru(2)-Ru(1)-P(1) 52.02(4).
Sch em e 1
PBun as well as mononuclear complexes such as [Ru-
3
(CO)4(PBun3)] and [Ru(CO)3(PBun3)2] to some extent.
Similar degradation reactions were described during the
thermal treatment of the complexes [Ru2(CO)4(PBun3)2(µ-
O2CMe)2] in heptane solution for example.10
The 31P{1H} NMR spectrum of 2 reveals an AMXY
spectrum due to the chemical inequivalence of the two
phosphorus nuclei of the bridging dppm ligand. These
groups appear as two signals that couple with the P
nucleus of the phosphido bridge and the phosphorus of
the bridging phosphaethenyl ligand. For 2 the signal
at δ 255.9 can be assigned with certainty to the
toluene were necessary to afford a noticeable transfor-
mation of the reactants.3 However due to the labile
phosphine ligand, the complex [Ru2(CO)3(PBun3)(µ-H)-
(µ-PBut )(µ-dppm)] (1a ) is much more reactive, which
phosphido bridge µ-PBut .1,11 Therefore, the downfield
2
2
resulted in a drastic decrease in reaction time and in a
remarkable increase in the yield of the main product in
the course of this reaction. Thus, treatment of 1a with
an excess of PtCBut in refluxing DME afforded a
complete conversion after 3 h. Workup of the reaction
mixture gave yellow crystals, which were subjected to
X-ray structure analysis, revealing the dinuclear com-
signal at δ 378.4 is attributable to the P atom of the
µ-PdC(H)But group and correlates with observations
for, for example, [Ru(CO)Cl(PPh3)2{PdC(H)But}] (δ
450.4).8 The assignment of this signal was confirmed
additionally by a selective phosphorus decoupled proton
NMR experiment: irradiation at δ 378.4 resulted in the
disappearance of the doublet at δ 3.34 in the proton
spectrum to give a singlet instead. Furthermore, the
proton coupled 31P NMR spectrum of 2 showed a doublet
at δ 379.5 (2J PH ) 40.0 Hz), confirming the correct
plex [Ru2(CO)4(µ-PBut )(µ-dppm){µ-PC(H)But}] (2). Fig-
2
ure 1 shows an ORTEP view of the molecule. The
molecule consists of a diruthenium core bridged by a
phosphido group, the dppm, and a phosphaethenyl
group as a 3e- ligand. The coordination sphere of the
two ruthenium atoms is completed by four carbonyl
ligands, and therefore by electron counting 2 exhibits
34 cluster valence electrons. The result of the X-ray
structure analysis showed that no direct insertion of the
phosphaethyne in 1a occurred, because four carbonyl
ligands were found in the product 2 (Scheme 1).
Although there is no experimental evidence for a pos-
sible formation pathway of 2, the following two path-
1
assignment of the signal. The H NMR spectrum of 2
exhibits, in addition to the other signals for µ-PBut2 and
dppm, a resonance at δ 3.34 (d) attributable to the
proton of the phosphaethenyl ligand (H5) with a large
coupling to the phosphaethenyl phosphorus (40 Hz). No
(10) Frediani, P.; Bianchi, M.; Salvini, A.; Piacenti, F. J . Chem. Soc.,
Dalton Trans. 1990, 3663.
(11) Carty, A. J .; MacLaughlin, S. A.; Nucciarone, D. In Phosphorus-
31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J . G., Quin,
L. D., Eds.; VCH: Weinheim, 1987; pp 559-619.

5316 Organometallics, Vol. 23, No. 22, 2004
Bo¨ttcher et al.
dppm)] (1a ) (306 mg, 0.3 mmol) in DME (25 mL) was treated
with a 0.4 M solution of PtCBut in hexane (0.5 mmol) and
refluxed with stirring for 3 h. During this time the color of
the solution changed from deep violet to orange brown. After
cooling to room temperature the solvent was removed in vacuo
and the remaining residue extracted three times with 10 mL
portions of hexane. The combined extracts were reduced to 5
mL in vacuo and stored at -28 °C overnight to obtain 2 as
yellow crystals (156 mg, 55% yield based on 1a ). Anal. Calcd
for C42H50O4P4Ru2: C, 53.39; H, 5.33. Found: C, 53.05; H, 4.97.
IR (KBr, cm-1): ν(CO) 1983s, 1965vs, 1924vs. 1H NMR (THF-
d8): δ 8.02-6.77 (m, 20H, PC6H5), 4.27-3.80 (m, 2H, P-CH2-
further coupling of this H to the other P nuclei is found.
For [Ir4Pt(dppe)(CO)10(µ-PPh2){µ-PC(H)But}] a reso-
nance at δ 4.2 (dd) is reported with corresponding
2
4
couplings J PH ) 12 Hz and J PH ) 3 Hz, respectively.9
The H atoms of the But substituent of the latter
compound resonate at δ 0.50 as a multiplet, and in
accordance with this we assign the signal at δ 0.57 (d,
4J PH ) 1.1 Hz) to the tert-butyl substituent of the
phosphaethenyl group.
The bonding characteristics of the bridging phospha-
ethenyl ligand in the structure of 2 have no precedent.
Therefore a comparison with some bonding parameters
found for the related compounds [Fe2(CO)6{µ-PdC(Si-
Me3)2}2] (3)12 and [Fe2(CO)6(µ-SBut){µ-PdC(SiMe3)2}]
(4)13 should be given. In this light the most interesting
feature refers to the P-C distance exhibiting these
species as phosphaalkenyl complexes. For 3 and 4 the
corresponding P-C bond lengths were found to be
1.650(4) and 1.621(9) Å and are in good accordance with
the distance P(1)-C(5) found for 2 (Figure 1). In a
similar context the corresponding distance in [Ru-
{P(Me)dC(H)But}Cl(I)(CO)(PPh3)2] was reported to be
1.657(8) Å and discussed clearly as multiple in nature.14
Furthermore, the angles M-P-M of compounds 2-4
are in good agreement: 3, 75.0°; 4, 73.0° (for 2 see
Figure 1). Moreover, the angle between the planes of
Ru(1)-P(1)-Ru(2) and Ru(1)-P(2)-Ru(2) is 70.05(5)°,
and the planes between the almost planar arrangement
of the phosphaethenyl ligand (av deviation from the
idealized plane: 0.0374 Å) and the Ru(1)-P(1)-Ru(2)
plane is 8.7°. The Ru-Ru distance in 2 corresponds to
a single bond, and the other structural parameters agree
well with those found for similarly constituted diruthen-
ium complexes reported by us.1
2
3
P), 3.34 (d, 1H, J PH ) 40.2 Hz, PdCH), 1.67 (d, 9H, J PH
)
13.6 Hz, PC4H9), 1.42 (d, 9H, 3J P,H ) 13.0 Hz, PC4H9), 0.57 (d,
4J P,H ) 1.1 Hz, PdC-But). 31P{1H} NMR (THF-d8): δ 378.4
(ddd, 2J P1,P2 ) 95 Hz, 2J P1,P3 ) 49 Hz, 2J P1,P4 ) 56 Hz, P1), 255.9
2
2
2
(ddd, J P2,P1 ) 95 Hz, J P2,P3 ) 124 Hz, J P2,P4 ) 134 Hz, P2),
2
2
2
34.9 (ddd, J P3,P1 ) 49 Hz, J P3,P2 ) 124 Hz, J P3,P4 ) 79 Hz,
2
2
2
P3), 29.5 (ddd, J P4,P1 ) 56 Hz, J P4,P2 ) 134 Hz, J P4,P3 ) 79
Hz, P4). EI MS: m/z (%) 946 (2.1) M+, 918 (3.1) [M - CO]+,
890 (36.8) [M - 2CO]+.
X-r a y Str u ctu r e Deter m in a tion a n d Deta ils of Refin e-
m en t. Crystals of 2 were obtained from hexane by cooling to
-28 °C. X-ray data were collected on a Stoe IPDS diffracto-
meter using graphite-monochromated Ag KR radiation (λ )
0.56087 Å). Corrections for Lorentz and polarization effects,
for crystal decay, and for absorption were applied. The
structure was solved by direct methods using the program
SHELXS-97.16a Structure solution by full-matrix least-squares
refinement on F2 was carried out with the program SHELXL-
9716b with anisotropic displacement for non-hydrogen atoms.
Hydrogen atoms were placed in idealized positions and refined
isotropically according to the riding model. Residue electron
density for H5 was found, for which the distance was fixed
and freely refined. The methyl groups of the But substituent
at C5 were found to be disordered over two different positions.
[Ru 2(CO)4(µ-P Bu t2)(µ-d p p m ){µ-P C(H)Bu t}] (2): C42H50
-
O4P4Ru2, M ) 944.84, crystal dimensions 0.30 × 0.16 × 0.04
mm, monoclinic, space group C2/c, unit cell parameters a )
35.639(7) Å, b ) 16.820(2) Å, c ) 16.730(2) Å, â ) 97.11(2)°, Z
) 8, V ) 9952(3) Å3, T ) 210(2) K, Dc ) 1.261 mg m-3, µ(Ag
KR) ) 0.408 mm-1, 25 753 independent reflections, θ range
for data collection 1.66-20.00°, 9097 unique reflections (Rint
In conclusion, these results stimulate further studies
of the general type of reaction of polynuclear hydrido-
metal complexes with phosphaalkynes.
Exp er im en ta l Section
) 0.0613), goodness-of-fit on F2 ) 1.055, R1 ) 0.0550, wR2
0.1481 (I > 2σ(I)), R1 ) 0.0878, wR2 ) 0.1671 (all data).
)
Gen er a l Com m en ts. All reactions were performed under
an atmosphere of dry argon using conventional Schlenk
techniques. Solvents were dried over sodium-benzophenone
ketyl or molecular sieves and were distilled under argon prior
to use. The phosphaethyne PtCBut 15 as well as the complexes
Ack n ow led gm en t. The authors are grateful to the
Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie for financial support. Further-
more we thank the Degussa AG for a generous loan of
RuCl3‚3H2O.
[Ru2(CO)3L(µ-H)(µ-PBut )(µ-dppm)] (L ) CO, 1; L ) PBun3, 1a )3
2
were prepared according to the reported procedures. IR spectra
were recorded as KBr pellets on a Bruker FT-IR spectrometer
IFS 28. Mass spectra were obtained on a Varian MAT 711
spectrometer (70 eV). NMR spectra were recorded on Bruker
AC 250 equipment (1H, 250.133 MHz; 31P, 101.256 MHz).
Chemical shifts are given in ppm relative to SiMe4 (1H) or 85%
H3PO4 (31P).
Su p p or tin g In for m a tion Ava ila ble: Listings of atomic
coordinates, H atom parameters, anisotropic temperature
factors, and bond lengths and angles for 2. This material is
available free of charge via the Internet at http://pubs.acs.org.
Syn t h esis of [R u 2(CO)4(µ-P Bu t 2)(µ-d p p m ){µ-P C(H )-
OM049777H
Bu t }] (2). A solution of [Ru2(CO)3(PBun3)(µ-H)(µ-PBut )(µ-
2
(15) Ro¨sch, W.; Alspach, T.; Bergstra¨sser, U.; Regitz, M. In Synthetic
Methods of Organometallic and Inorganic Chemistry; Herrmann, W.
A., Ed.; Thieme Verlag: Stuttgart, 1996; p 13.
(16) (a) Sheldrick, G. M. SHELXS-97: Program for the Solution of
Crystal Structures; University of Go¨ttingen: Germany, 1997. (b)
Sheldrick, G. M. SHELXL-97: Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Germany, 1997.
(12) Arif, A. M.; Cowley, A. H.; Quashie, S. J . Chem. Soc., Chem.
Commun. 1985, 428.
(13) Wisian-Neilson, P.; Onan, K. D.; Seyferth, D. Organometallics
1988, 7, 917.
(14) Bedford, R. B.; Hill, A. F.; J ones, C.; White, A. J . P.; Wilton-
Ely, J . D. E. T. J . Chem Soc., Dalton Trans. 1997, 139.