Reactive hydroxo and hydroxycarbyne cyclopentadienyl complexes. Proton transfer and oxidative addition of O-H bonds at unsaturated Ditungsten centers [4]

Full text of DOI:10.1021/ja9818203

1960
J. Am. Chem. Soc. 1999, 121, 1960-1961
Scheme 1
Reactive Hydroxo and Hydroxycarbyne
Cyclopentadienyl Complexes. Proton Transfer and
Oxidative Addition of O-H Bonds at Unsaturated
Ditungsten Centers
M. Esther Garc´ıa, V´ıctor Riera, M. Teresa Rueda, and
Miguel A. Ruiz*
Departamento de Qu´ımica Orga´nica e Inorga´nica/IUQOEM
UniVersidad de OViedo, 33071 OViedo, Spain
Sabine Halut
Laboratoire de Chimie des Me´taux de Transition
URACNRS 419, UniVersite´ P. et M. Curie
4 Place Jussieu, 75252 Paris, Cedex 05 France
ReceiVed May 26, 1998
Recently we reported the preparation and some reactions of
the binuclear hydroxycarbyne complex [W2(µ-COH)Cp2(CO)2(µ-
Ph2PCH2PPh2)]BF4 (Cp ) η5-C5H5).1 Interest in hydroxycarbyne
complexes arises from two main considerations. In the first place,
their chemistry is virtually unexplored due to the lack of available
compounds with enough thermal stability. Second, their trans-
formations can be of relevance in the context of some important
reactions as, for example, carbon monoxide reduction.1,2 Thus,
we sought to prepare new thermally stable binuclear hydroxy-
carbyne complexes to better study their chemical behavior. In
this paper we report the preparation of the new compound [W2-
(µ-COH)Cp2(µ-PPh2)2]BF4 (2), and some unusual transformations
derived thereof (Scheme 1). This hydroxycarbyne complex readily
reacts with oxygen to afford, after proton transfer, the hydroxo
carbonyl derivative [W2Cp2(OH)(µ-PPh2)2(CO)]BF4 (4), which
in turn experiences an intramolecular oxidative addition of the
O-H bond at rt to give the oxohydrido complex [W2Cp2(µ-H)-
(O)(µ-PPh2)2(CO)]BF4 (6). The latter represents a rare example
of oxidative O-H bond addition occurring at a dimetal center.
In fact, we are aware of just one previous complex experiencing
this rearrangement in a detectable way.3 More importantly, the
unsaturated nature of 4 makes the terminal hydroxo ligand quite
reactive toward organic substrates having acidic protons, a
property held by different late metal hydroxo complexes,4 and
this gives a considerable synthetic potential to this compound.
We note here that the chemistry of hydroxo complexes is of
relevance in the context of different metal-catalyzed reactions of
organic substrates such as oxidation or hydrolysis, the latter
including a large number of biological transformations such as
those induced by zinc enzymes.4d,5
method can be equally used with other primary or secondary
phosphines HPRR′, whereby a wide range of mixed phosphido
complexes with tunable steric and electronic characteristics can
be prepared. We recall here that the dimolybdenum analogue of
1 has been previously prepared in a two-step reaction starting
from [Mo2Cp2(CO)6] and P2Ph4.8
Compound 1 has a bridging CO ligand, and it is therefore
expected to experience electrophilic attack at the oxygen atom
of this ligand. Indeed, 1 is easily protonated with HBF4‚OEt2 or
methylated with MeSO3CF3 to give with good yields the corre-
sponding hydroxycarbyne 2 or methoxycarbyne analogue [W2-
(µ-COMe)Cp2(µ-PPh2)2]SO3CF3 (3). Although quite reactive in
general, both compounds are stable at room temperature. More-
over, spectroscopic data for these species indicate that they have
the same structure,9,10 confirmed through an X-ray study carried
out on the latter (Figure 1).11 This 30-electron complex formally
retains a triple W-W bond, which is consistent with the
intermetallic distance of 2.5324(8) Å (for comparison, M-M
distances are 2.5144(5) Å for [W2Cp2(µ-Ph2PCH2PPh2)(CO)2]12
or 2.515(2) Å for [Mo2(µ-CO)Cp2(µ-PPh2)2]).8 As for the carbyne
ligand, its C-donor atom is placed on a C2 axis of the crystal,
and therefore, the methoxy group is disordered in two positions
(only one of them is shown in Figure 1). Interatomic distances
The triply bonded dimer [W2(µ-CO)Cp2(µ-PPh2)2] (1) can be
obtained in high yield through the photochemical reaction of the
hydride [W2Cp2(µ-H)(µ-PPh2)(CO)4] and HPPh2.6,7 This synthetic
(7) [W2Cp2(µ-H)(µ-PPh2)(CO)4] is synthesized from PPh2H and [W2Cp2-
(CO)4] (prepared in situ from [W2Cp2(CO)6] as described in ref 20) at 333 K.
Selected spectroscopic data: ν(CO) (CH2Cl2) 1947 (vw, sh), 1926 (vs), 1853
(1) Alvarez, M. A.; Bois, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Angew.
Chem., Int. Ed. Engl. 1996, 35, 102-104.
(2) (a) Miller, R. L.; Toreki, R.; LaPointe, R. E.; Wolczanski, P. T.; Van
Duyne, G. D.; Roe, D. C. J. Am. Chem. Soc. 1993, 115, 5570-5588. (b)
Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1982, 21, 117-130.
(3) Tahmassebi, S. K.; McNeil, W. S.; Mayer, J. M. Organometallics 1997,
16, 5342-5353.
(s) cm-1 31P{1H}NMR (121.50 MHz, CD2Cl2) δ 109.2 [s, J(PW) 209]. 1H
.
NMR (300.13 MHz, CD2Cl2) δ -14.83 [d, J(HP) 27, J(HW) 39].
(8) Adatia, T.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby, P. R.
J. Chem. Soc., Dalton Trans. 1989, 1555-1564.
(9) Selected spectroscopic data for 2: 31P{1H}NMR (81.01 MHz, CD2-
Cl2) δ 186.8 [s, J(PW) 364]. 1H NMR (400.13 MHz, CD2Cl2, 233 K) δ 13.71
(br, 1H, µ-COH), 6.25 (s, 10H, Cp). 13C{1H}NMR (75.48 MHz, CD2Cl2) δ
367.9 [t, J(CP) 6, µ-COH].
(4) (a) Ritter, J. C. M.; Bergman, R. G. J. Am. Chem. Soc. 1997, 119,
2580-2581. (b) Kaplan, A. W.; Bergman, R. G. Organometallics 1997, 16,
1106-1108. (c) Gilje, J. W.; Roesky, H. W. Chem. ReV. 1994, 94, 895-910.
(d) Bryndza, H. E.; Tam, W. Chem. ReV. 1988, 88, 1163-1188.
(5) (a) Mayer, J. M. Polyhedron 1995, 22, 3273-3292. (b) Bergman, R.
G. Polyhedron 3227-3237. (c) Bertini, I.; Luchinat, C. In Bioinorganic
Chemistry; Bertini, I., Gray, H. B., Lippard, S. J., Valentine, J. S., Eds.;
University Science Books: Mill Valley, CA, 1994; pp 37-106.
(10) Selected spectroscopic data for 3: 31P{1H}NMR (121.49 MHz, CD2-
Cl2) δ 191.5 [s, J(PW) 364]. 13C{1H}NMR (75.48 MHz, CD2Cl2) δ 366.9 (s,
µ-COMe).
(11) X-ray data: black crystals of 3, monoclinic (C2/c), a ) 15.458(2) Å,
b ) 13.507(2) Å, c ) 19.326(3) Å, â ) 113.90(1)°, V ) 3689(1) Å3, Z ) 4,
R ) 0.044, GOF ) 0.8.
(6) Selected spectroscopic data for 1: ν(CO) (CH2Cl2) 1635 cm-1 31P-
.
{1H}NMR (81.03 MHz, CD2Cl2) δ 144.7[s, J(PW) 389]. 13C{1H}NMR (75.47
MHz, CD2Cl2) δ 303.9 (s, µ-CO).
(12) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Falvello, L.
R.; Bois, C. Organometallics 1997, 16, 354-364.
10.1021/ja9818203 CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/18/1999

Communications to the Editor
J. Am. Chem. Soc., Vol. 121, No. 9, 1999 1961
irreversibly above ca. 273 K to yield quantitatively the oxohydrido
complex 6,17 which can be also deprotonated with base to give
selectively 5 (cis isomer). Thus, both 4 and 6 are thought to
display a cis disposition of their CO and oxygen-donor ligands.
The isomerization 4/6 equally occurs in the solid state at room
temperature. On that basis, we trust that a genuinely intramolecular
R-migration of the hydroxylic H atom (from oxygen to tungsten)
takes place in this substrate. In CH2Cl2 solution, isomerization is
complete in ca. 15 min at 291 K, a rate far higher than that
measured for the R-migration in [Re(OH)(C2Et2)3].3 This differ-
ence can be possibly ascribed to the electronic and (specially)
coordinative unsaturation of 4.
Although thermally quite unstable, complex 4 can be safely
handled by working below 253 K, so that its chemistry can be
explored in detail. Preliminary studies indicate that it readily reacts
with a variety of molecules having acidic hydrogens such as thiols,
carboxylic acids, or ketones such as acetone or acetylacetone.
The reaction seems to proceed analogously in all cases, and it is
exemplified for the latter reagent: the hydroxo ligand deprotonates
the incoming molecule and the corresponding 3-e donor anion
(acac) occupies the vacant position after water elimination. The
resulting complex, i.e., [W2Cp2(O,O′-acac)(µ-PPh2)2(CO)]BF4
(7),18,19 is presumably isoelectronic with the starting material and
also retains a cis disposition of the new ligand relative to the
carbonyl group.
In summary, we have described efficient synthetic methods
for new binuclear hydroxycarbyne and hydroxo complexes which
experience unusual H rearrangements. Moreover, these complexes
are highly unsaturated molecules and therefore quite reactive
under mild conditions, with the hydroxo derivative displaying a
useful nucleophilic behavior. All of these properties allow us to
anticipate a wide chemistry to be developed around these species,
and further studies in this direction are now in progress.
Figure 1. View of the molecular structure of the cation in complex 3
(ellipsoids at 20% probability and H atoms omitted; only symmetry-
independent atoms labeled). Selected bond distances (Å) and angles
(deg): W(1)-P(1) ) 2.372(3), W(1)-C(1) ) 1.97(1), C(1)-O(1) )
1.390(9), O(1)-C(110) ) 1.40(1); W(1)-P(1)-W(1)′ ) 64.44(7), W(1)-
C(1)-W(1)′ ) 80.2(5), C(1)-O(1)-C(110) ) 113.8(14).
involving this group are otherwise similar to those measured at
the 32-electron species [W2(µ-COMe)Cp2(µ-Ph2PCH2PPh2)(CO)2]-
BF4.1 To our knowledge, compound 3 is the first complex having
an alkoxycarbyne ligand bridging a triple metal-metal bond to
be structurally characterized.
Acknowledgment. We thank the DGICYT of Spain for financial
support and the FICYT of Asturias for a grant (to M.T.R.).
In the presence of small amounts of oxygen, the hydroxycar-
byne 2 readily transforms into the hydroxo derivative 4.13 In this
way, compound 4 can be isolated from the solution, provided
the reaction is carried out below 253 K, otherwise further
transformation occurs rapidly (see below). The unusual formation
of this hydroxo complex possibly involves electrophilic attack
of oxygen on the carbyne (a similar reaction has been previously
observed between sulfur and arylcarbyne-bridged complexes),14
followed by H transfer between oxygen atoms, an hypothesis
which is under current study. It is clear, in any case, that the
hydroxycarbyne ligand can act as an H reservoir for molecules
approaching the unsaturated dimetal center.
As expected, the hydroxo complex 4 can be deprotonated with
base to afford quantitatively the corresponding oxo complex [W2-
Cp2(O)(µ-PPh2)2(CO)] (5), which is selectively formed as the cis
isomer.15,16 This reaction can be reversed by just adding HBF4‚
OEt2 at 253 K to the latter. However, compound 4 isomerizes
Supporting Information Available: Experimental procedures for the
preparation of new complexes and microanalytical data. Data collection,
refinement details and listings of atomic coordinates, thermal parameters,
bond lengths and bond angles for the X-ray study on complex 3 (PDF).
JA9818203
(15) Selected spectroscopic data for 5: ν(CO) (CH2Cl2) 1851 cm-1. ν-
(W-O) (Nujol mull) 888 cm-1 31P{1H}NMR (81.01 MHz, CD2Cl2) δ 102.2
.
[s, J(PW) 381, 322]. 13C{1H}NMR (75.47 MHz, CD2Cl2) δ 224.0 (s, CO),
100.4, 83.7 (2 × s, Cp).
(16) A mixture of cis and trans isomers of the dimolybdenum analogue of
5 has been reported from the reaction of [Mo2Cp2(µ-PPh2)2(µ-CO)] with
oxygen.8
(17) Selected spectroscopic data for 6: ν(CO) (CH2Cl2) 1977 cm-1. ν-
(W-O) (Nujol mull) 964 cm-1
.
31P{1H}NMR (81.01 MHz, CD2Cl2) δ 31.3
1
[s, J(PW) 280, 246]. H NMR (400.13 MHz, CD2Cl2) δ -9.83 [t, J(HP) 52,
J(HW) 38, 6, µ-H].
(18) Selected spectroscopic data for 7: ν(CO) (CH2Cl2) 1882 cm-1 31P-
.
{1H}NMR (121.49 MHz, CD2Cl2) δ 123.7 [s, J(PW) 346, 199]. 1H NMR
(300.13 MHz, CD2Cl2) δ 5.80, 5.30 (2 × s, 2 × 5H, Cp), 5.47 (s, 1H, CH),
1.09 (s, 6H, CH3).
(13) Selected spectroscopic data for 4: IR (Nujol mull) 3500 [vbr, ν(OH)],
1893 [ν(CO)] cm-1
.
31P{1H}NMR (161.99 MHz, CD2Cl2, 263 K) δ 109.9 [s,
1
J(PW) 372, 281]. H NMR (400.13 MHz, CD2Cl2, 263 K) δ 5.92, 5.51(2 ×
s, 2 × 5H, Cp); the resonance of the O-H proton could not be identified.
(14) Byrne, P. G.; Garc´ıa, M. E.; Jeffery, J. C.; Sherwood, P.; Stone, F. G.
A. J. Chem. Soc., Dalton Trans. 1987, 1215-1219.
(19) The analogous dimolybdenum complex has been characterized through
an X-ray study (results to be published).
(20) Curtis, M. D.; Fotinos, N. A.; Messerle, L.; Sattelberger, A. P. Inorg.
Chem. 1983, 22, 1559-1561.