Chemistry of the phosphinidene oxide ligand

Article abstract of DOI:10.1021/ja045487g

Reaction of [Mo₂Cp₂(μ-H)(μ-PHR*)(CO)₄] with DBU followed by O₂ gives the first anionic phosphinidene oxide complex (H-DBU)[MoCp{P(O)R*}(CO)₂] (1) (DBU = 1,8-diazabicyclo [5.4.0] undec-7-ene; R* = 2,4,

Full text of DOI:10.1021/ja045487g

Published on Web 09/30/2004
Chemistry of the Phosphinidene Oxide Ligand
Mar´ıa Alonso,† M. Esther Garc´ıa,† Miguel A. Ruiz,*,† Hayrullo Hamidov,‡ and John C. Jeffery‡
Departamento de Qu´ımica Orga´nica e Inorga´nica/IUQOEM, UniVersidad de OViedo, 33071 OViedo, Spain, and
School of Chemistry, UniVersity of Bristol, Bristol BS8 1TS, UK
Received July 27, 2004; E-mail: mara@fq.uniovi.es
Scheme 1a
The chemistry of transition metal complexes having the versatile
phosphinidene (PR) ligand is an active research area of interest to
both organic and inorganic chemists. This is particularly the case
for terminal bent complexes, in which the metal-P bond has
considerable multiple character and exhibits carbene-like reactivity.
As a result, these complexes are useful synthetic reagents in
organophosphorus and cluster chemistry.1,2 In contrast, the chemical
behavior of the phosphinidene oxide (RsPdO) complexes remains
virtually unexplored to date.
Uncoordinated phosphinidene oxides are unstable molecules
isolobally related to carbenes3 and are thought to be generated in
reactions such as the thermal or photochemical decomposition of
phospholene, phosphirane or phophanorbornadiene oxides, and
others.4 These transient species undergo processes such as addition
to dienes and diones or insertion into OsH and SsS bonds and
are therefore interesting synthons for new organophosphorus
derivatives.4a As for the coordinated RsPdO ligand, we must
remark that only a few complexes have been reported. These display
terminal (A),5a,b µ2-P,O-bridging (B),5c µ2-P-bridging (C),5d,e or
µ3-P,O-bridging (D)5f coordination modes (Chart 1), but their
reactivity has not been explored. Interestingly, we note that terminal
RsPdO complexes have been proposed as intermediates in the
formation of dioxaphospholanes.6
+
a HBF4, [Me3O]BF4 or PhC(O)Cl for R1+. MeI or C3H5Br for R2
.
Following our studies on the synthesis and reactivity of phos-
phinidene-bridged complexes,7 we accidentally discovered the
t
formation of [MoCp{P(O)R*}(CO)2]- (1) (R* ) 2,4,6-C6H2 Bu3;
Cp) η5-C5H5), the first anionic phosphinidene oxide complex
reported to date. More importantly, this anion is nucleophilic enough
to react with a wide variety of electrophiles at room temperature.
Herein we report our initial results on the reactivity of 1, which is
Figure 1. Molecular structure of the anion 1 (left) and compound 2c (right).
also the first report on the chemistry of a phosphinidene oxide
complex. As will be shown, complex 1 exhibits a unique reactivity,
with three different nucleophilic sites (at O, P, and Mo), which
leads to new compounds that have not yet been prepared otherwise
(Scheme 1).
Methyl groups are omitted for clarity.
Chart 1
Complex 1 [as the (H-DBU)+ salt]8 is cleanly formed by the
controlled action of air on (H-DBU)[Mo2Cp2(µ-PHR*)(CO)4], a
salt prepared in turn from [Mo2Cp2(µ-H)(µ-PHR*)(CO)4]7a and
DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). No other P- or CO-
containing product was formed in significant amounts, and the fate
of the lost MoCpH(CO)2 moiety has not been yet determined. The
anion 1 displays a terminally bound phosphinidene oxide ligand
lying in the plane bisecting the MoCp(CO)2 moiety; the terminal
oxygen atom is involved in a hydrogen bond with the (H-DBU)+
cation and is placed anti with respect to the cyclopentadienyl ligand
(Figure 1).9 The PsMo [2.239(1) Å] and PsO [1.514(3) Å] bond
lengths are short and comparable to the corresponding values in
the two reported neutral compounds with terminal RsPdO
ligands.5a,b This supports the formulation of double ModP and
PdO bonds for the P(O)R* ligand in 1. Besides, the low frequencies
of the CsO stretching bands of 1 are indicative of substantial
delocalization of the negative charge all over the complex, in
agreement with the nucleophilic behavior discussed next.
Anion 1 is protonated by HBF4‚OEt2 at the oxygen atom, which
is consistent with the H‚‚‚O interaction present in the crystal. The
resulting hydroxophosphide complex [MoCp{P(OH)R*}(CO)2] (2a)
is easily deprotonated upon manipulation. A similar reaction occurs
between 1 and carbon-based electrophiles such as [Me3O]BF4 or
PhC(O)Cl to give related alkoxyphosphide compounds [MoCp-
{P(OR)R*}(CO)2] (R ) Me, 2b; C(O)Ph, 2c).10 An X-ray study
on 2c revealed that the phosphide ligand retains the geometry of
the parent phosphinidene oxide group (Figure 1).11 The most
† Universidad de Oviedo.
‡ University of Bristol.
9
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J. AM. CHEM. SOC. 2004, 126, 13610-13611
10.1021/ja045487g CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
sites allows the rational synthesis of novel and unusual derivatives
that cannot be prepared otherwise.
Acknowledgment. We thank the MCYT/MECD of Spain for
a grant (to M.A.) and financial support (BQU2003-05471).
Supporting Information Available: Experimental procedures and
spectroscopic data for new compounds (PDF); crystallographic data
for compounds 1, 2c, 3, and 4b (CIF). This material is available free
of charge via the Internet at http://pubs.acs.org.
Figure 2. Molecular structure of compounds 3 (left) and 4b (right). Methyl
groups are omitted for clarity.
relevant changes are a substantial increase in the PsO distance
[1.671(3) Å, a value typical of single PsO bonds], and a slight
decrease in the MosP distance [2.196(1) Å]. These structural
features are similar to those found for [MoCp{PCH(SiMe3)2}(OEt)-
(CO)2], a related complex prepared by reaction of EtOH on a
phosphavinylidene precursor.12
References
(1) (a) Lammertsma, K.; Vlaar, M. J. M. Eur. J. Org. Chem. 2002, 1127-
1138. (b) Mathey, F.; Tran Huy, N. H.; Marinetti, A. HelV. Chim. Acta
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G.; Knoll, K. Angew. Chem., Int. Ed. Engl. 1987, 26, 743-759.
The hydroxoderivative 2a can be further protonated with HBF4‚
OEt2 to give the fluorophosphide complex [MoCp(PFR*)(CO)2]
(3), after elimination of water and fluoride abstraction from the
(2) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy.
Wiley: New York, USA, 1998.
(3) Schoeller, W. W.; Niecke, E. Chem. Commun. 1982, 569-570.
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BF4 anion.13 The structure of this molecule is similar to that of
(4) (a) Gaspar, P. P.; Qian, H.; Beatty, A. M.; d’Avignon, D. A.; Kao, J. L.
F.; Watt, J. C.; Rath, N. P. Tetrahedron 2000, 56, 105-119 and references
therein. (b) Cowley, A. H.; Gabba¨ı, F. P.; Corbelin, S.; Decken, A. Inorg.
Chem. 1995, 34, 5931-5932. (c) Wang, K.; Emge, T. J.; Goldman, A. S.
Organometallics 1994, 13, 2135-2137. (d) Niecke, E.; Zorn, H.; Krebs,
B.; Henkel, G. Angew. Chem., Int. Ed. Engl. 1980, 19, 709-710.
(5) (a) Niecke, E.; Engelmann, M.; Zorn, H.; Krebs, B.; Henkel, G. Angew.
Chem., Int. Ed. Engl. 1980, 19, 710-712. (b) Hitchcock, P. B.; Johnson,
J. A.; Lemos, M. A. N. D. A.; Meidine, M. F.; Nixon, J. F.; Pombeiro, A.
J. L. J. Chem. Soc., Chem. Commum. 1992, 645-646. (c) Johnson, M. J.
A.; Odom, A. L.; Cummins, C. C. Chem. Commum. 1997, 1523-1524.
(d) Kourkine, V.; Glueck, D. S. Inorg. Chem. 1997, 36, 5160-5164. (e)
Schmitt, G.; Ullrich, D.; Wolmersha¨user, G.; Regitz, M.; Scherer, O. J.
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G.; Imhof, W. J. Organomet. Chem. 1990, 388, 307-320.
the alkoxyphosphide 2c, displaying a quite short MosP distance
[2.2037(12) Å] (Figure 2).14 Compound 3 appears to be the first
complex reported with a trigonal fluorophosphide (PFR) ligand,
although a few related chlorophosphide complexes are known.15
Carbon-based electrophiles can alternatively attack the P site in
1. This is the dominant reaction pathway when using milder
electrophiles such as MeI or C3H5Br, which then give the respective
phosphinite derivatives [MoCp(κ2-OPRR*)(CO)2] (R ) Me, 4a;
C3H5, 4b).16 These are the first complexes reported to have a P,O-
bound phosphinite ligand. Separate experiments showed that the
isomeric methyl derivatives 2b and 4a did not interconvert even in
refluxing toluene. This proves that compounds 2 and 4 arise from
independent reaction pathways. An X-ray study on 4b revealed an
unusual environment in the phosphinite ligand, with the P(3), C(3),
and C(31) atoms almost placed in a plane and close to that one
bisecting the MoCp(CO)2 moiety, and the O(3) atom also bonded
to molybdenum (Figure 2).17 This results in a strained MoPO ring
with internuclear separations suggesting single (MosO) or inter-
mediate (between single and double) bonds (MosP and PsO).
Similar structural effects have been reported for related thiophos-
phinite complexes.18
(6) Marinetti, A.; Mathey, F. Organometallics 1987, 6, 2189-2191.
(7) (a) Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Sa´ez, D.; Vaissermann, J.;
Jeffery, J. C. J. Am. Chem. Soc. 2002, 124, 14304-14305. (b) Garc´ıa,
M. E.; Riera, V.; Ruiz, M. A.; Sa´ez, D.; Hamidov, H.; Jeffery, J. C.;
Riis-Johannessen, T. J. Am. Chem. Soc. 2003, 125, 13044-13045.
(8) Selected spectroscopic data for 1: νCO (CH2Cl2) 1874 (vs), 1790 (s) cm-1
.
31P{1H} NMR (CD2Cl2) δ 385.0 ppm.
(9) X-ray data for 1: Yellow-orange crystals, orthorhombic. (P212121), a )
9.5709(15), b ) 17.391(3), c ) 20.501(3) Å, V ) 3412.4(9) Å3, T ) 173
K, Z ) 4, R ) 4.42, GOF ) 0.933.
(10) Selected spectroscopic data for 2b: νCO (CH2Cl2) 1935 (vs), 1856 (s)
cm-1 31P{1H} NMR(CD2Cl2) δ 350.5 ppm. 13C{1H} NMR(CD2Cl2) δ
.
238.5 (d, JCP ) 20, CO), 55.7 (s, OCH3) ppm.
(11) X-ray data for 2c: dark red crystals, orthorhombic (Pbca), a ) 17.1829-
(15), b ) 13.0958(11), c ) 27.663(2) Å, V ) 6224.8(9) Å3, T ) 173 K,
Z ) 8, R ) 6.51, GOF ) 0.944.
Anion 1 also displays dual behavior when reacting with metal-
based electrophiles, as illustrated through the reactions with [ZrCl2-
Cp2] and SnClPh3. The zirconium fragment binds to the O atom
giving the P,O-bridged [MoCp{P(OZrClCp2)R*}(CO)2] (5).19 The
tin fragment, however, binds to the Mo atom to give [MoCp{P(O)-
R*}(CO)2(SnPh3)] (6), which displays a terminal P(O)R* ligand
and trans-dicarbonyl geometry.20 The formation of 5 provides a
new route to heterometallic complexes bridged by the phosphinidene
oxide ligand, of which only one compound has been reported so
far.5c In addition, the formation of 6 indicates that 1 has a third
nucleophilic position located at the metal atom, and this allows
the preparation of new neutral complexes with terminal RsPdO
groups. Because of the multiple nature of the MosP bond in these
species, it is expected that they can display some carbene-like
reactivity. Currently we are exploring this possibility and extending
the electrophiles under study to unravel the factors governing the
complex nucleophilicity of anion 1.
(12) Arif, A. M.; Cowley, A. H.; Nunn, C. M.; Quashie, S. Organometallics
1989, 8, 1878-1884.
(13) Selected spectroscopic data for 3: νCO (CH2Cl2) 1959 (vs), 1884 (s) cm-1
.
31P{1H} NMR δ 323.8 (d, JPF ) 1132 Hz) ppm.
(14) X-ray data for 3: Red crystals, monoclinic (P21/c), a ) 20.947(2), b )
10.4889(10), c ) 11.5591(12) Å, â ) 102.708(2)°, V ) 2477.4(4) Å3, T
) 173 K, Z ) 4, R ) 5.67, GOF ) 0.969.
(15) (a) Cowley, A. H.; Giolando, D. M.; Nunn, C. M.; Pakulski, M.;
Westmoreland, D.; Norman, N. C. J. Chem. Soc., Dalton Trans. 1988,
2127-2134. (b) Malisch, W.; Hirth, U. A.; Gru¨n, K.; Schmeuâer, M. J.
Organomet. Chem. 1999, 572, 207-212.
(16) Selected spectroscopic data for 4a: νCO (CH2Cl2) 1940 (vs), 1850 (s) cm-1
.
31P{1H} NMR(CD2Cl2) δ 28.3 ppm. 13C{1H} NMR(CD2Cl2) δ 255.8 (d,
JCP ) 26, CO), 246.0 (s, CO), 23.8 [d, JCP ) 27, PCH3] ppm.
(17) X-ray data for 4b: Red crystals, triclinic P1h, a ) 9.2708(3), b ) 12.0224-
(4), c ) 14.3208(5) Å, R ) 84.8940(10), â ) 77.0620(10), γ ) 75.5350-
(10)°, V ) 1505.40(9) Å3, T ) 173 K, Z ) 2, R ) 2.41, GOF ) 0.982.
(18) (a) Alper, H.; Einstein, F. W. B.; Hartstock, F. W.; Jones, R. H.
Organometallics 1987, 6, 829-833. (b) Malisch, W.; Gru¨n, K.; Hirth, U.
A.; Noltemeyer, M. J. Organomet. Chem. 1996, 513, 31-36. (c) Reisacher,
H. U.; McNamara, W. F.; Duesler, E. N.; Paine, R. T. Organometallics
1997, 16, 449-455.
(19) Selected spectroscopic data for 5: νCO (CH2Cl2) 1921 (vs), 1841 (s) cm-1
.
The present work is the first study on the reactivity of a
coordinated phosphinidene oxide ligand. The anion 1 has a
terminally bound RsPdO ligand and displays unique acid/base
properties, with three different nucleophilic sites located at the O,
P, and Mo atoms. The binding of different electrophiles to these
1H NMR (CD2Cl2) δ 6.39 (s, 10H, ZrCp) 5.12 (s, 5H, MoCp) ppm. 31P-
{1H} NMR (CD2Cl2) δ 350.3 ppm.
(20) Selected spectroscopic data for 6: νCO (CH2Cl2) 1947 (s), 1889 (vs) cm-1
31P{1H} NMR (CD2Cl2) δ 468.1 (J119SnP ) J117SnP ) 116 Hz) ppm.
.
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