A polyoxometalate transfer reagent: Synthesis, structure, and reactivity of zirconocene polyoxometalate [(PNbW11O40)2ZrCp2]6- [7]

Full text of DOI:10.1021/ja9905039

J. Am. Chem. Soc. 1999, 121, 8953-8954
Scheme 1. The Formation and Chemistry of
8953
A Polyoxometalate Transfer Reagent: Synthesis,
6
a
2 2
[(LNbO) ZrCp ] -
Structure, and Reactivity of Zirconocene
Polyoxometalate [(PNbW11O40)2ZrCp2]6-
†
‡
,§
Emil V. Radkov, Victor G. Young Jr., and Robert H. Beer*
Departments of Chemistry
Fordham UniVersity, Bronx, New York 10458
Columbia UniVersity, New York, New York 10027
UniVersity of Minnesota, Minneapolis, Minnesota 55455
ReceiVed February 17, 1999
1
The rising popularity of polyoxometalates in catalysis, materi-
als, and biological studies has increased efforts to both modify
their properties and prepare new compounds.1 To date, synthetic
,2
3
methods that functionalize complete, intact polyoxometalates
4
have relied largely on the use of electrophilic organic or
organometallic species5 to bind to polyoxometalate surface
oxygen atoms. Although studies have investigated many aspects
of their reactivity, functionalized complete polyoxometalates have
not themselves been used generally as reagents to prepare new
-7
8
derivatives. Polyoxometalate supported cyclopentadienyl com-
plexes5 are potential candidates for such a reagent. Among this
derivative class, the monocyclopentadienyl organometallic adducts
of complete polyoxometalates have been prepared and thoroughly
,6
6
studied. Far less, however, is known about the biscyclopentadi-
enyl adducts. In this communication, we describe the synthesis
9
a
The lacunary Keggin ion, L ) {R-PW O }7-, is represented by a
11
39
of the first polyoxometalate supported biscyclopentadienyl com-
curvilinear shape.
6-
2 2
plex of Group 4, [(PW11O39NbO) ZrCp ] , and use this complex
to demonstrate the transfer of the complete polyoxometalate
†
Columbia University.
[PW11O
39NbO]4 to several molecular species.
-
‡
University of Minnesota.
Fordham University.
§
Previous syntheses of polyoxometalate supported organome-
tallic complexes have taken advantage of the enhanced Lewis
basicity of oxygen atoms bound to Group 5 metals in mixed-
(
1) (a) Pope, M. T. Heteropoly and Isopoly Oxometalates; Springer-
Verlag: New York, 1983. (b) Pope, M. T.; M u¨ ller, A. Angew. Chem., Intl.
Ed. Engl. 1991, 30, 34. (c) Polyoxometalates: from Platonic Solids to Retro-
Viral ActiVity; Pope, M. T., M u¨ ller, A., Eds.; Kluwer Academic Publishers:
Dodrecht, The Netherlands, 1994. (d) Thematic issue on polyoxometalates
metal polyoxometalates to coordinate to cationic organometallic
2
fragments. Using this synthetic strategy, the reaction of Cp
2
Zr-
(
Hill, C. L., Ed.): Chem. ReV. 1998, 98, 1-390.
2) (a) Day, W. G.; Klemperer, Science 1985, 228, 533. (b) Gouzerh, P.;
Proust, A. Chem. ReV. 1998, 98, 77 and references therein.
-
-
(
(OTf)
2
‚THF (Cp ) C
niobium-substituted polytungstate (n-Bu
5
H
5
, OTf ) O
3
SCF
N)
39} ) in acetonitrile forms (n-Bu
3
) with 2 equiv of the
1
0
4
4
[LNbO] (where L
N) [(LNbO)
When the reaction is
1
b
(
3) Complete (plenary) polyoxometalate derivatives are defined herein
7-
)
R-{PW11
O
4
6
2
-
as being Group 5 and Group 6 isopoly- or heteropolyoxometalates that bind
to molecular compounds or fragments via surface oxygen atoms. This definition
excludes syntheses that involve oxygen ligand substitution reactions or add
1
1,12
ZrCp
2
] in 91% yield (eq 1, Scheme 1).
4-
carried out with [LNb*O] in which the terminal ONb oxygen
n+
metal fragments into vacancies created by removing {MO} units.
(
17
atom is enriched selectively with H *O (*O ) O, 10%
2
4) (a) Knoth, W. H.; Harlow, R. L. J. Am. Chem. Soc. 1981, 103, 4265.
enriched),13 quantitative retention of the isotopic label in (n-
(
1
b) Siedle, A. R.; Lyon, P. A.; Hunt, S. L.; Skarjune, A. P. J. Am. Chem. Soc.
986, 108, 6430. (c) Day, V. W.; Klemperer, W. G.; Schwartz, C. J. Am.
Chem. Soc. 1987, 109, 6030. (d) Ma, L.; Liu, S.; Zubieta, J. Inorg. Chem.
989, 28, 175.
5) (a) Besecker, C. J.; Day, V. W.; Klemperer, W. G.; Thompson, M. R.
4 6 2 2
Bu N) [(LNbO) ZrCp
] is observed by 17O NMR spectroscopy
17
6-
2 2
asshownineq1.The ONMRchemicalshiftof[(LNb*O) ZrCp ]
1
displays an upfield chemical shift to 554 ppm compared to 831
(
4- 13
Inorg. Chem. 1985, 24, 44. (b) Besecker, C. J.; Klemperer, W. G.; Day, V.
W. J. Am. Chem. Soc. 1982, 104, 6158. (c) Day, V. W.; Klemperer, W. G.;
Main, D. J. Inorg. Chem. 1990, 29, 2345. (d) Klemperer, W. G.; Main, D. J.
Inorg. Chem. 1990, 29, 2355. (e) Day, V. W.; Eberspacher, T. A.; Klemperer,
W. G.; Planalp, R. P.; Schiller, P. W.; Yagasaki, A.; Zhong, B. Inorg. Chem.
ppm for [LNbO] , consistent with the presence of a Nb-O-
2a,12b,14
Zr oxygen bridge.
O NMR chemical shifts reported for related oxo-bridged niobium
This resonance is in the range of the
17
1
7
1
1
993, 32, 1629. (f) Lin, Y.; Nomiya, K.; Finke, R. G. Inorg. Chem. 1995, 34,
67. (g) Attanasio, D.; Bachechi, F.; Suber, L. J. Chem. Soc., Dalton Trans.
993, 2373. (h) Abe, M.; Isobe, K.; Kida, K.; Yagasaki, A. Inorg. Chem.
996, 35, 5114. (i) Nagata, T.; Pohl, M.; Weiner, H.; Finke, R. G. Inorg.
(10) Radkov, E.; Beer, R. H. Polyhedron 1995, 14, 2139.
(11) Synthesis and characterization details are given in Supporting Informa-
tion.
(12) Related Group 4 metallocene-metal oxoanion conjugates have been
2
-
Chem. 1997, 36, 1366.
6) (a) Besecker, C. J.; Day, V. W.; Klemperer, W. G.; Thompson, M. R.
prepared by halide displacement reactions: (a) Cp
2
TiCl
2
with [WO
4
]
or
2
-
(
[Mo O ] : Carofiglioi, T.; Floriani, C.; Rosi, M.; Chiesi-Villa, A.; Rizzoli,
2 7
-
J. Am. Chem. Soc. 1984, 106, 4125. (b) Chae, H. K.; Klemperer, W. G.; Day,
V. W. Inorg. Chem. 1989, 28, 1483. (c) Hayashi, Y.; Ozawa, Y.; Isobe, K.
Inorg. Chem. 1991, 30, 1025. (d) Rapko, B. M.; Pohl, M.; Finke, R. G. Inorg.
Chem. 1994, 33, 3625 and references therein. (e) Pohl, M.; Lin, Y.; Weakley,
T. J. R.; Nomiya, K.; Kaneko, M.; Werner, H.; Finke, R. G. Inorg. Chem.
C Inorg. Chem. 1997, 30, 33245. (b) Cp
2
M′Cl
2
(M′ ) Ti, Zr) with Cp*M(O)
3
(M ) Mo, W.; Cp* ) C Me ): Rau, M. S.; Kretz, C. M.; Geoffroy, G. L.
5 5
Organometallics 1994, 13, 1624.
(13) Radkov, E.; Lu, Y.-J.; Beer, R. H. Inorg. Chem. 1996, 35, 551.
17
(14) The O NMR chemical shift is sensitive to the electronic environment
around the oxygen atom and can demarcate terminal and bridging coordination
modes. (a) Klemperer, W. G. Angew. Chem., Int. Ed. Engl. 1978, 17, 246.
(b) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds; J. Wiley
and Sons: New York, 1988; pp 127-129.
1
995, 34, 767 and references therein.
7) Day, V. W.; Klemperer, W. G.; Maltbie, D. J. Organometallics 1985,
, 104.
(
4
(
8) Derivatization of polyoxometalates which incorporate organometallic
n+
fragments into {MO} vacancies: (a) Day, V. W.; Fredrich, M. F.; Thompson,
M. R.; Klemperer, W. G.; Liu, R.-S.; Shum, W. J. Am. Chem. Soc. 1981,
(15) Lu, Y.-J.; Lalancette, R.; Beer, R. H. Inorg. Chem. 1996, 35, 2524.
3
(16) Colorless needles grown from CH CN solution by vapor diffusion of
1
03, 3597. (b) Klemperer, W. G.; Zhong, B. Inorg. Chem. 1993, 32, 5821.
2 2
Et O in a vial under N : crystal system, space group: triclinic, P 1h , Z ) 2.
(
9) Polyoxometalate bis(cyclopentadienyl) metallocene compounds: (a)
Cell constants: a ) 14.3725(2) Å, R ) 73.468(1)°, b ) 26.2888(1) Å, â )
4-
3
[
(Cp
D. J. J. Am. Chem. Soc. 1985, 107, 8262. (b) [Mo
Stark, J. L.; Young, V. G.; Maata, E. A. Angew. Chem., Int. Ed. Engl. 1995,
4, 2547.
2 2 5 19 2
U) (TiW O ) ]
: Day, V. W.; Earley, C. W.; Klemperer, W. G.; Maltbie,
76.193(1)°, c ) 26.5749(4) Å, γ ) 84.178(1)°. V ) 9341.7(3) Å . Z ) 2. R
2
-
2
6
O
18(NR)] (R ) Cp
2
Fe):
(I >2σ(Ι)): R
1
) 0.0818, wR
2
) 0.1622. GOF(F ) ) 1.132. The presence of
disordered solvent molecules is likely. X-ray crystallographic details are
provided in the Supporting Information.
3
1
0.1021/ja9905039 CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/14/1999

8954 J. Am. Chem. Soc., Vol. 121, No. 38, 1999
Communications to the Editor
*O]6 detected by 17O NMR spectroscopy
2
-
tion product [(LNb)
(
17
24
O δ, 512 ppm).4 These results are consistent with hydrolysis
-
+
studies of [LNbO] with the noncoordinating counterion n-Bu
4
N
which undergoes oxo ligand exchange with H *O only in the
2
1
3
presence of a catalytic amount of acid. Presumably the
Zr}2 fragment hydrolyzes initially to form
+
coordinated {Cp
2
25
zirconium hydroxide or aquo species which, acting as source
of protons, mediate the oxo ligand exchange reaction. The lability
of [LNbO]4 in [(LNbO)
-
ZrCp
of the rapid exchange of [MW
]
6-
corroborates earlier studies
2
2
-
]6 with selected
Figure 1. ORTEP Representation of [(LNbO)
2
ZrCp
2
-
5
O
19]3 (7M ) Nb, Ta) fragments
atom labels omitted for clarity.
3-
in [Cp
3
M′(MW
5
O
19
)
2
]
(M′ ) Th, U).
polyoxometalates4c,7,15 and heterobimetallic complexes [Cp
Zr]-
]6- with main group covalent
2
Reactions of [(LNbO)
halides result in transfer of [LNbO] to form main group
2
ZrCp
2
(M ) Mo, W).1
2b
(µ-O)
2
[Cp*M(O)
2
]
2
4-
derivatives functionalized solely on the terminal ONb oxygen
4
2
[LNb*O] - + Cp Zr(OTf) f
6-
2
2
atom also shown in Scheme 1. The reaction of [(LNbO)
with excess R
quantitative formation of Cp
2 2
ZrCp ]
6
-
-
3
SiX (R ) Me; X ) Cl, Br, I) resulted in
[(LNb*O) ZrCp ] + 2OTf (1)
2
2
3
-26
2
ZrX
2
and [LNbOSiR
3
],
an
4
c
example of a silyl derivative of a complete polyoxometalate.
A crystal structure of (n-Bu
the anion contains two complete [LNbO] ions acting as ligands
4
N)
6
[(LNbO)
2
2
ZrCp ] reveals that
An 17O NMR spectroscopic study of the reaction with enriched
4
-
2
+
6-
coordinated to the {Cp
2
Zr} center by the formerly terminal ONb
[(LNb*O)
[LNb*OSiMe
to the {R
2
ZrCp
2
3-
]
confirmed complete retention of the label in
oxygen atom in [LNbO]4 as shown in Figure 1. The two bent
Nb-O-Zr bond angles of 159(1)° and 148(1)° fall within the
range (142.5-161.5°) reported for two related complexes
-
16
4-
3
+
]
consistent with transfer of the [LNbO] group
3
Si} group. In contrast, no reaction is observed between
trialkylsilyl halides and (n-Bu N) [LNbO]. The monosubstituted
4
4
1
2
3-
[(MeCp)
2
Ti(µ
-MoO )]
2 4 2
2
and [{Cp Zr}(µ-O)
2
{Cp*W(O)
2
}
2
]. The
2
product [LNbOZrClCp ] , a putative intermediate in the reaction,
SiCl to form [LNbOSiMe
Preliminary results indicate that the reaction of [(LNbO)
Nb-O-Zr bond angle is likely to be influenced largely by steric
3-
also reacted with Me
3
3
]
cleanly.
ZrCp ]
2
Zr}2
+
interactions due to the lack of π bonding by the {Cp
2
6-
2
fragment.17 The Zr-O bond lengths in [(LNbO)
6-
of 2.04-
2 2
ZrCp ]
with PcAlCl (Pc
[
phthalocyanine conjugate [LNbOAlPc] .
)
29H,31H-phthalocyaninato) yields
12,17,18
(
2) and 2.07(2) Å are consistent with single bond lengths.
]3- and the novel blue polyoxometalate
LNbOZrClCp
2
A short Nb-O bond distance of 1.80(1) Å in both {NbOZr}
fragments is observed, indicative of considerable multiple bond
character. A similar Nb-O bond distance of 1.78 Å was reported
3 5 19 2
inapolyoxometalatewithaNb-O-Ubridge,[Cp U(NbW O ) ] .
The structural data suggest that the multiply bonded terminal ONb
oxygen atom of each [LNbO]4- anion acts as a two-electron
donor, i.e., Zr r :ONbL, to yield an 18-electron zirconocene
complex.20 Aside from the NbO and NbOZr metrical data,
3- 27
19
The reactions in Scheme 1 feature the activation of the terminal
ONb oxygen atom toward derivatization by coordination to the
3
- 7
2+
2
strong Lewis acid fragment {Cp Zr} . The ready displacement
6-
2 2
of this group from [(LNbO) ZrCp ]
illustrates a potential general
method for derivatizing polyoxometalates with a larger variety
of main group and transition metal reagents than investigated
previously and exemplifies the lability of the Zr-O bond when
4-
2+
2
coordination of [LNbO] to {Cp Zr} has no apparent affect
on the structure of either moiety.2
1,22
2+
12b
the {Cp Zr} fragment coordinates to a metal oxo species.
2
-
]6 and
Both the lability of the Zr-O bond in [(LNbO)
2
ZrCp
2
Since polyoxometalate surface oxygens resemble solid-state metal
its ability to act as a [LNbO]4 transfer reagent are borne out by
-
1,2,5i
oxide surfaces,
metallocene chemistry and functionalization of oxide materi-
als.
these reactions could be applied to the Group
the reactions summarized in Scheme 1. Facile Zr-O bond
cleavage occurs when [(LNbO)
28
29
4
6
-
2
ZrCp
2
]
reacts with excess
4
-
n-Bu
ZrX
between n-Bu
4
2
NX (X ) Cl, Br) to form quantitatively [LNbO] and Cp -
1
2
as observed by H NMR and IR spectroscopy. The reaction
Acknowledgment. The authors thank Fordham and Columbia Uni-
versity and the Kanagawa Academy of Science and Technology for
financial support. We thank Dr. Robert Cody (JEOL USA, Inc., Peabody,
MA) for positive ion FAB mass spectra.
4
NCl and the singly substituted species
3
- 23
4-
[
[
LNbOZrClCp
(LNbO) ZrCp
2
]
also yielded [LNbO] and Cp
2
ZrCl
2
. The
NOAc and
]6 ion reacts likewise with n-Bu
-
2
2
4
4-
n-Bu
Hydrolysis of [(LNbO)
*O in acetonitrile produces [LNb*O] and the acid condensa-
4
NF to produce [LNbO] .
ZrCp
2
]6 with excess 17O enriched
-
2
4
-
Supporting Information Available: Preparative and spectroscopic
data (PDF) plus additional crystallographic tables and figures (CIF). This
material is available free of charge via the Internet at http://pubs.acs.org.
H
2
(
17) Howard, W. A.; Trnka, T. M.; Parkin, G. Inorg. Chem. 1995, 34, 5900
and references therein.
18) The Zr-O bond distance is 2.091(3) Å in Cp
Thewalt, U. J. Organomet. Chem. 1986, 302, 201.
19) Average terminal Nb-O bond distances for (a) Mn(Nb
Å): Flynn, C. M.; Stucky Inorg. Chem. 1969, 8, 178 335. (b) [C
(
2 2
Zr(OTs) : Lasser, W.;
JA9905039
1
2-
(
6
O
19
)
2
(1.77
12)Ir] H-
(1.78 Å) (ref 5c). (c) 16 mononuclear compounds (1.71 Å):
8
H
2
(24) Radkov, E., Ph.D. Dissertation, Columbia University, 1997.
(25) Hillhouse, G. L.; Bercaw J. E. J. Am. Chem. Soc. 1984, 106, 5472
6-
(Nb
2
W
O
4 19
)
2
Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds; J. Wiley and
Sons: New York, 1988; pp 162-3.
and references therein.
-
(26) Spectroscopic data for the formation of [LNbOSiR
3
]3 are given in
1
(
20) This asymmetric bridging mode by multiply bonded metal oxo species
the Supporting Information. The Cp
2
ZrX
2
products were identified by H NMR
is described in: West, B. O. Polyhedron 1989, 8, 219.
21) The O-Zr-O bond angle of 95.9(7)°, Zr-to-Cp centroid distances
and mass spectroscopy.
1
ZrCl(ONbL)]3- at 6.65 ppm and the Pc
(
(27) The Cp H resonance of [Cp
H AA′XX′ multiplets at 8.38 ppm (4,5-H) and 9.68 ppm (3,6-H) were detected
2
6-
1
(
2.195, 2.213 Å), and Cp centroid-to-centroid angle (131.1°) in [(LNbO)
2
ZrCp
2
]
compare favorably with Cp ZrX
2
2
complexes (X ) monoanion): Cardin, D.
(Janson, T. R.; Katz, J. J. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: 1979; Vol. 4, p 17). IR (KBr, cm- ): 1334, 1289, 1262, 1168, 1121,
1075, 972, 893, 810, 736, 709. The FAB-MS show prominent peak envelopes
1
J.; Lappert, M. F.; Raston, C. L.; Riley, P. I. In ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon
Press: 1982; Vol. 3, p 568 and references therein.
4 3 4 4
for the {(n-Bu N) N)
[LNbOAlPc]}+ and {(n-Bu [LNbOAlPc]}+ ions near
3-
(
22) Metrical parameters of L are nearly identical with the parent ion
4050 and 4300 m/z, correspondingly. A schematic of [LNbOAlPc] is given
in the Supporting Information.
3-
[
LWO] : (a) D’Amour, H.; Allman, R. Z. Kristallogr. 1976, 143, 1. (b)
Brown, G. M.; Noe-Spirlet, M. R.; Busing, W. R.; Levy, H. A. Acta
(28) Metallocenes; Togni, A., Halterman, R. L., Eds.; Wiley-VCH: Wein-
Crystallogr. 1977, B33, 1038.
heim, Germany, 1998; Vols. 1 and 2.
(
23) Preparative details for [LNbOZrClCp
2
]3 from Cp
-
2
Zr(OTf)Cl and
2
(29) {Cp Ti} on silica: Maschmeyer, T.; Rey, F.; Sankar, G.; Thomas,
2+
4-
[
LNbO] and spectroscopic data are given in the Supporting Information.
J. M. Nature 1995, 378, 159.