Preparation and reactivity of zirconium(III), niobium(III), and molybdenum(III) complexes stabilized by a cyclopentadienyl unit with pendant phosphine donors

Article abstract of DOI:10.1021/om990096+

This paper deals with the organometallic chemistry of the trivalent second-row transition metals of groups 4-6, namely, Zr, Nb, and Mo, with the cyclopentadienyldiphosphine ligand [η⁵-C₅H₃-1,3-(SiMe₂CH ₂PR₂)₂], abbreviated as [^RP₂Cp] (where R = i-Pr and Ph). The Zr(IV) complex [^i-PrP₂Cp]ZrCl₃ undergoes reduction with Na/Hg to form the trivalent Zr derivative, [^i-PrP₂Cp]ZrCl₂, which undergoes a metathetical reaction with MeMgBr to yield the monomethyl derivative [^i-PrP₂Cp]Zr(CH₃)Cl. The reaction of the Zr(III) complex [^i-PrP₂Cp]ZrCl₂ with excess carbon monoxide results in disproportionation to the Zr(IV) complex, [^i-PrP₂Cp]ZrCl₃, and the Zr(II) compound [^i-PrP₂Cp]Zr(CO)₂Cl. This reaction is reversible, and upon removal of CO the starting material, [^i-PrP₂Cp]ZrCl₂ is formed. The preparation of the diamagnetic Nb(III) complex [^RP₂Cp]NbCl₂ is achieved by the reaction of NbCl₃(DME) with [^RP₂Cp]Li. [^RP₂Cp]NbCl₂ complexes react with excess CO to form the CO adducts whose solid-state structures have been determined. The Nb(IV) derivatives [^RP₂Cp]NbCl₃ are formed via the reaction of [^RP₂Cp]NbCl₂ with PbCl₂. These complexes can also be produced when Nb(O)-Cl₃(THF)₂ is allowed to react with excess [^RP₂Cp]Li. These Nb(IV) derivatives are ESR active, and their solid-state molecular structures show distorted octahedral geometries around the Nb center. MoCl₃(THF)₃ reacts with [^RP₂Cp]Li to generate the corresponding Mo(III) complexes [^RP₂Cp]MoCl₂. These compounds are low-spin, paramagnetic complexes as evidenced by their ESR spectra.

Full text of DOI:10.1021/om990096+

4050
Organometallics 1999, 18, 4050-4058
P r ep a r a tion a n d Rea ctivity of Zir con iu m (III),
Niobiu m (III), a n d Molybd en u m (III) Com p lexes Sta bilized
by a Cyclop en ta d ien yl Un it w ith P en d a n t P h osp h in e
Don or s
Michael D. Fryzuk,* Laleh J afarpour, and Steven J . Rettig†
Department of Chemistry, University of British Columbia, 2036 Main Mall,
Vancouver, British Columbia, Canada V6T 1Z1
Received February 16, 1999
This paper deals with the organometallic chemistry of the trivalent second-row transition
metals of groups 4-6, namely, Zr, Nb, and Mo, with the cyclopentadienyldiphosphine ligand
[η5-C5H3-1,3-(SiMe2CH2PR2)2], abbreviated as [RP2Cp] (where R ) i-Pr and Ph). The Zr(IV)
complex [i-PrP2Cp]ZrCl3 undergoes reduction with Na/Hg to form the trivalent Zr derivative,
[
i-PrP2Cp]ZrCl2, which undergoes a metathetical reaction with MeMgBr to yield the
monomethyl derivative [i-PrP2Cp]Zr(CH3)Cl. The reaction of the Zr(III) complex [i-PrP2Cp]ZrCl2
with excess carbon monoxide results in disproportionation to the Zr(IV) complex, [i-PrP2Cp]ZrCl3,
and the Zr(II) compound [i-PrP2Cp]Zr(CO)2Cl. This reaction is reversible, and upon removal
of CO the starting material, [i-PrP2Cp]ZrCl2 is formed. The preparation of the diamagnetic
Nb(III) complex [RP2Cp]NbCl2 is achieved by the reaction of NbCl3(DME) with [RP2Cp]Li.
[RP2Cp]NbCl2 complexes react with excess CO to form the CO adducts whose solid-state
structures have been determined. The Nb(IV) derivatives [RP2Cp]NbCl3 are formed via the
reaction of [RP2Cp]NbCl2 with PbCl2. These complexes can also be produced when Nb(O)-
Cl3(THF)2 is allowed to react with excess [RP2Cp]Li. These Nb(IV) derivatives are ESR active,
and their solid-state molecular structures show distorted octahedral geometries around the
Nb center. MoCl3(THF)3 reacts with [RP2Cp]Li to generate the corresponding Mo(III)
complexes [RP2Cp]MoCl2. These compounds are low-spin, paramagnetic complexes as
evidenced by their ESR spectra.
In tr od u ction
use of bulky cyclopentadienyl derivatives has allowed
for the preparation of the mononuclear Zr(III) complexes
Complexes that contain zirconium in the trivalent
state are not particularly common.1 Generally, one finds
that attempts to prepare Zr(III) derivatives result in the
formation of diamagnetic dinuclear species2-14 unless
sufficiently bulky ligands are utilized. For example, the
(η5-C5Me5)Zr(η8-C8H8),15 (η5-1,3-C5H3But ) ZrCl,16 and
2 2
Bu4N[{(η5-1,3-C5H3(SiMe3)2}2ZrCl2].14 We recently re-
ported17 that mononuclear Zr(III) complexes could also
be stabilized by the use of the bulky tridentate ligand
N(SiMe2CH2P(i-Pr)2)2. In these systems, complexes of
the formula (η5-C5H5)ZrX[N(SiMe2CH2P(i-Pr)2)2] (X )
Cl, H, or hydrocarbyl) could be isolated by virtue of the
fact that the pendant phosphine arms can coordinate
to the Zr(III) center and prevent dimerization.
† Professional Officer: UBC X-ray Structural Laboratory (Deceased
October 27, 1998).
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A few years ago we reported the synthesis of a
modified cyclopentadienyl ligand that contains pendant
phosphine arms; the use of [η5-C5H3-1,3-(SiMe2CH2P-
(i-Pr)2)2], abbreviated as [i-PrP2Cp], allowed for the first
structurally characterized zirconium alkylidene complex
[η5-C5H3-1,3-(SiMe2CH2P(i-Pr)2)2]ZrdCHPh(Cl).18 More
recent work19 with this ligand has shown that the
presence of pendant phosphines attached to a cyclopen-
tadienyl ligand generates systems that are fluxional due
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L. R. Polyhedron 1996, 15, 689.
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1995, 14, 11.
10.1021/om990096+ CCC: $15.00 © 1999 American Chemical Society
Publication on Web 08/28/1999

Zr, Nb, and Mo Complexes with Cyclopentadienyl
Organometallics, Vol. 18, No. 20, 1999 4051
to the fact that these pendant phosphine arms bind only
weakly to Zr(IV). To fully assess the coordination
chemistry of these modified cyclopentadienyl ligands,
we have examined their ability to stabilize the relatively
rare Zr(III) state. In addition, we also expanded this
study to include groups 5 and 6 and report on the
coordination chemistry of [RP2Cp] (R ) i-Pr, Ph) with
the related trivalent species Nb(III)20-26 and Mo(III).27-30
Resu lts a n d Discu ssion
Syn t h esis a n d R ea ct ivit y of [i-P r P 2Cp ]Zr (III)
Com p lexes. The reduction of the Zr(IV) precursor
[
i-PrP2Cp]ZrCl3 (1)18 with excess sodium amalgam (Na/
F igu r e 1. Room-temperature ESR spectrum of [i-PrP2Cp]-
ZrCl2, 2 (solution in toluene).
Hg) in the absence of molecular nitrogen generates the
Zr(III) complex [i-PrP2Cp]ZrCl2 (2); during the reduction,
the solution changes from a pale yellow to a dark green,
which, after workup, leads to the isolation of dark green
crystals of 2 (eq 1). If the reduction is performed under
monomethyl derivative [i-PrP2Cp]Zr(CH3)Cl (3) as dark
green microcrystals after workup. The elemental analy-
sis is consistent with the exchange of only one chloride
of 2 for methyl in the product 3. ESR spectroscopy shows
a 10-line spectrum (Figure 2): a triplet of quartets
centered at g ) 2.01, due to coupling to two 31P nuclei,
a(31P) ) 23.0 G, the three methyl protons, a(1H) ) 8.0
G, and satellites due to one 91Zr nucleus (not simulated).
Unfortunately, despite many attempts, suitable crystals
for X-ray analysis could not be obtained.
N2, the same green coloration is observed, but after a
period of time, the green solution gradually turns deep
brown due to the formation of a dinuclear dinitrogen
complex.31 The 1H NMR spectrum of 2 shows only broad
resonances, and no signals are observed in the 31P{1H}
NMR spectrum; both observations are in agreement
with the fact that the complex is paramagnetic. The
ESR spectrum of 2 (Figure 1) shows a binomial triplet
at g ) 1.96 with coupling to two 31P nuclei, a(31P) )
22.7 G, and satellites due to one magnetically dilute Zr
nucleus, a(91Zr) ) 13.6 G, 91Zr ) 11.23%, I ) 5/2.
Magnetic measurements in solution by Evans’ method32,33
and the solid-state magnetic measurement give values
of 1.8 and 2.0 µB for µeff, respectively, corresponding to
one unpaired electron. Mass spectrometry also confirms
that 2 is mononuclear. Unfortunately, single crystals
suitable for X-ray analysis could not be obtained.
Metathetical reactions of this complex have been
examined. Complex 2 reacts with either 1 or 2 equiv of
CH3MgCl in toluene at -78 °C (eq 2) to yield the
As already mentioned, even in the presence of 2 equiv
of Grignard reagent, there is no evidence for the
formation of any dimethyl derivative [i-PrP2Cp]Zr(CH3)2,
just monomethyl 3. While we have no rationalization
for this, we note that the related Zr(IV) precursor,
[
i-PrP2Cp]ZrCl3 (1), can be converted quantitatively to
the corresponding trimethyl, [i-PrP2Cp]Zr(CH3)3, and
other trialkyl derivatives.19,34 Although dichloride 2 is
consumed upon reaction with other alkylating agents
such as LiCH2SiMe3, EtMgCl, or PhMgCl, the isolation
of pure materials was not possible. Apparently, for
hydrocarbyl species bulkier than methyl groups, the
reaction is not straightforward and decomposition to
intractable materials occurs.
(20) Fettinger, J . C.; Keogh, D. W.; Kraatz, H. B.; Poli, R. Organo-
metallics 1996, 15, 5489.
(21) Siemeling, U.; Gibson, V. C. J . Organomet. Chem. 1992, 424,
159.
(22) Bunker, M. J .; Green, M. L. H. J . Organomet. Chem. 1980, 192,
C6.
(23) de la Mata, J .; Galakov, M. V.; Gomez, M.; Royo, P. Organo-
metallics 1993, 12, 1189.
(24) Curtis, M. D.; Real, J .; Kwon, D. Organometallics 1989, 8, 1644.
(25) Andreu, A. M.; J alon, F. A.; Otero, A.; Royo, P.; Manotti
Lanfredi, A. M.; Tiripicchio, A. J . Chem. Soc., Dalton Trans. 1987, 953.
(26) Burt, R. J .; Leigh, G. J . J . Organomet. Chem. 1978, 148, C19.
(27) Krueger, S. T.; Poli, R.; Rheingold, A. R.; Staley, D. L. Inorg.
Chem. 1989, 28, 4599.
Treatment of a solution of 2 with carbon monoxide (1
atm, 25 °C) results in a rapid color change from dark
1
green to deep brown. If the reaction is monitored by H
and 31P{1H} NMR spectroscopy, one observes the for-
mation of two diamagnetic species; the ESR spectrum
of this same sample showed only a very weak signal.
On the basis of the NMR data, the solution contains a
mixture of [i-PrP2Cp]Zr(CO)2Cl (4) and [i-PrP2Cp]ZrCl3
(1); in other words, disproportionation of Zr(III) to
Zr(II) and Zr(IV) has occurred. The resonances of
trichloride 1 are easily assigned; what is also evident
are two additional Cp resonances at 5.19 ppm (2H) and
5.21 ppm (1H) along with expected peaks for the SiMe2-
CH2P portion of the pendant arms in the 1H NMR
(28) Krueger, S. T.; Owens, B. E.; Poli, R. Inorg. Chem. 1990, 29,
2001.
(29) Grebenik, P. D.; Green, M. L. H.; Izquierdo, A.; Mtetwa, V. S.;
Prout, K. J . J . Chem. Soc., Dalton Trans. 1987, 9.
(30) Green, M. L. H.; Izquierdo, A.; Martin-Polo, J . J .; Mtetwa, V.
S.; Prout, K. J . J . Chem. Soc., Chem. Commun. 1983, 538.
(31) Fryzuk, M. D.; J afarpour, L.; Duval, P. B. Unpublished results.
(32) Sur, S. K. J . Magn. Reson. 1989, 82, 169.
(33) Evans, F. D. J . Chem. Soc. 1959, 2003.
(34) Fryzuk, M. D.; Duval, P. B.; Mao, S. S. H.; Zaworotko, M. J .;
MacGillivray, L. R. J . Am. Chem. Soc. 1999, 121, 2478.

4052 Organometallics, Vol. 18, No. 20, 1999
Fryzuk et al.
F igu r e 2. (a) Room-temperature ESR spectrum of [i-PrP2Cp]Zr(CH3)Cl, 3 (solution in toluene). (b) Simulated spectrum
(see Results and Discussion for details).
spectrum, and a sharp singlet at 31.6 ppm is observed
in the 31P{1H} NMR spectrum. The solution IR spec-
trum shows νjCO stretches at 1888 and 1978 cm-1. The
bromide derivative, [i-PrP2Cp]Zr(CO)2Br, has been pre-
viously prepared,35 and it displays very similar chemical
shifts: 5.16 ppm (2H) and 5.19 ppm (1H) in the 1H NMR
spectrum and 29.1 ppm in the 31P{1H} NMR spectrum.
However, upon removal of the CO from the aforemen-
tioned reaction mixture, the color changed from dark
brown to deep green, and the ESR and NMR spectra of
the resulting product were identical to the paramagnetic
dichloro derivative, 2; this is summarized in eq 3. Such
were isolated. Presumably, the phenyl groups attached
to phosphorus in the [PhP2Cp] ligand are more electron
withdrawing than the i-Pr groups of the corresponding
derivative [i-PrP2Cp], and this combined with the fact
that Zr(IV) is an electron-poor, d0 metal center renders
this combination ineffective.
Syn th esis a n d Rea ctivity of [RP 2Cp ]Nb(III) Com -
p lexes. When NbCl3(DME) is allowed to react with [RP2-
Cp]Li at room temperature in toluene, the initial brown
color of the solution changes to brown-red after 4 h.
Upon workup of the reaction mixture, one obtains
cherry-red, microcrystalline solids in good yield, which
are formulated as [RP2Cp]NbCl2 (5, R ) i-Pr; 6, R ) Ph)
(eq 4) according to the elemental analysis. 1H NMR
studies show that 5 and 6 are diamagnetic complexes
with the Cp resonances at 4.70 ppm (1H) and 5.60 ppm
(2H) for 5 and 5.25 ppm (2H) and 5.5 ppm (1H) for 6.
31P{1H} NMR spectroscopy shows quadrupolar-broad-
ened singlets at 24.6 ppm for 5 and 22.5 ppm for 6
(93Nb, I ) 9/2, 100%). Mass spectrometry and molecular
weight determinations indicate that 5 and 6 are mono-
nuclear. The 16-electron monocyclopentadienyl Nb(III)
compounds reported in the literature either are para-
magnetic, such as (η5-C5Me5)NbCl2(PMe3)2,21 or show
contact-shifted NMR signals, such as (η5-C5Me5)-
NbCl2(PMe2Ph)2 and (η5-C5H4Me)NbCl2(PEt3)2.20 The
only example of a diamagnetic species of this type is
the complex (η5-C5H5)NbCl2(dppe).20 There are of course
diamagnetic Nb(III) dimers with Nb-Nb bonds such as
an equilibrium between Zr(III) and its disproportion-
ation products does have precedent; for example, it has
been shown that CpZrCl[N(SiMe2CH2P(i-Pr)2)2] reacts
with CO in a similar manner.36
To investigate the electronic and steric effects of the
ligand on the stability and reactivity of the Zr(III)
complexes, the synthesis of the corresponding Zr(IV)
starting material [PhP2Cp]ZrCl3 was attempted by the
reaction of [PhP2Cp]Li with ZrCl4(THT)2. However, no
reaction was observed even after prolonged reaction
times and with heating to 65 °C; only starting materials
(35) Fryzuk, M. D.; Duval, P. B. Unpublished results, 1998.
(36) Mylvaganam, M. Dinitrogen and Paramagnetic Complexes of
Zirconium. Ph.D. Thesis, University of British Columbia, 1994.

Zr, Nb, and Mo Complexes with Cyclopentadienyl
Organometallics, Vol. 18, No. 20, 1999 4053
{(η5-C5Me5)NbCl2}2.23 Although 5 and 6 can be crystal-
lized from toluene, the crystals obtained were not
suitable for X-ray analysis.
When 5 and 6 are dissolved in toluene and placed
under 1 atm of CO, the color of the solution changes
from dark red to orange and microcrystalline solids can
be isolated. Elemental analysis identifies the compounds
as [RP2Cp]Nb(CO)Cl2 (7, R ) i-Pr; 8, R ) Ph; eq 5). Both
are 18-electron complexes with the νjCO stretching vibra-
tion at 1914 cm-1 for 7 and 1927 cm-1 for 8, typical for
Nb(III) derivatives.21,22,37,38 Compounds 7 and 8 are
diamagnetic, with 1H NMR resonances for the unique
Cp at 4.4 ppm (2H) and 6.0 ppm (1H) for 7 and 4.5 ppm
(2H) and 6.4 ppm (1H) for 8. The chemical shifts for
the resonances due to the silylmethyls and the meth-
ylene protons of the ligand are very similar in both
compounds. 31P{1H} NMR spectra show quadrupolar-
broadened singlets at 25.85 ppm for 7 and 18.20 ppm
for 8. All mononuclear carbonyl derivatives of (η5-C5H5)-
NbCl2L2 described in the literature are also dia-
magnetic.21,23-26,37-39 One curious point is that the
monocarbonyl complexes are all formed stereoselec-
tively, with the carbonyl ligand bound on the side
opposite the unique carbon of the cyclopentadienyl unit.
In solution, no isomers are detected, and the stereo-
chemistry of the final products 7 and 8 is evident from
the crystal structures described below.
F igu r e 3. Molecular structure and numbering scheme of
[
i-PrP2Cp]Nb(CO)Cl2, 7.
Crystals suitable for X-ray analysis were grown from
toluene. The crystal structures of 7 and 8 are shown in
Figures 3 and 4, respectively. Both show pseudo-
octahedral arrangements, fairly common in monocyclo-
pentadienyl Nb(III) 18-electron complexes, where CO,
Cl, and both phosphines occupy pseudoequatorial posi-
tions and the Cp ring and the other Cl atom occupying
the apical positions. The Nb atom in each complex is
not found in the equatorial plane, but is located ap-
proximately 0.61 Å above it. The Nb-C (CO) bond
(2.0823(3) Å) is shorter in 7 than in 8 (2.138(4) Å), and
consequently the C-O bond length (1.149(4) Å) in 7 is
longer than in 8 (1.044(4) Å). This is not surprising,
because the phosphine substituents in 7 are more
electron-releasing (i-Pr) than those in 8 (Ph). The
additional electron density in 7 results in increased
M-C-O π-back-bonding, thus resulting in stronger
M-C and weaker C-O bonds. This is consistent with
the observed CO stretching frequencies for both com-
plexes. Both Nb-P bond distances are identical (within
experimental error) in 8, but in 7 one is 0.013 Å longer
than the other. The Nb-Cl (axial) bond distances are
similar in both structures, but the Nb-Cl (equatorial)
Figu r e 4. Molecular representation and numbering scheme
of [PhP2Cp]Nb(CO)Cl2, 8.
Ta ble 1: Selected Bon d Len gth s in
[
i-P r P 2Cp ]NbCl2(CO), 7
atom
atom
distance (Å)
atom
atom
distance (Å)
Nb
Nb
Nb
Nb
Nb
Nb
Cl(1)
Cl(2)
P(1)
P(2)
C(1)
C(2)
2.5021(8)
2.5867(7)
2.7020(8)
2.7150(9)
2.382(3)
2.458(3)
Nb
Nb
Nb
Nb
Nb
C(24)
C(3)
C(4)
C(5)
Cp
C(24)
O(1)
2.483(3)
2.384(3)
2.330(3)
2.081
2.082(3)
1.149(4)
bond lengths are different because the chlorides are
trans to CO and are affected by variations in M-C (CO)
bond lengths. Selected bond lengths and bond angles
are collected in Tables 1-4.
Attempts to introduce alkyl groups at niobium via the
reaction with Grignard reagents were examined with
(37) Antinolo, A.; de IIarduya, J . M.; Otero, A.; Royo, P.; Manotti
Lanfredi, A. M.; Tiripicchio, A. J . Chem. Soc., Dalton Trans. 1988, 2685.
(38) J alon, F. A.; Otero, A.; Balcazar, J . L.; Florencio, F.; Garcia-
Blanco, S. J . Chem. Soc., Dalton Trans. 1989, 79.
(39) Bunker, M. J .; Green, M. L. H. J . Chem. Soc., Dalton Trans.
1981, 85.

4054 Organometallics, Vol. 18, No. 20, 1999
Fryzuk et al.
Ta ble 2: Selected Bon d An gles in
[
i-P r P 2Cp ]NbCl2(CO), 7
atom atom atom angle (deg) atom atom atom angle (deg)
Cl(1) Nb Cl(2)
P(1) Nb P(2)
Cl(1) Nb P(1)
Cl(2) Nb P(2)
Cl(1) Nb C(24)
85.29(3) P(2)
152.45(3) Cl(1) Nb Cp
76.49(3) Cl(2) Nb Cp
86.98(2) P(1)
75.54(9) P(2)
Nb C(24)
92.61(9)
171.1
103.6
103.9
103.5
95.6
Nb Cp
Nb Cp
Cl(2) Nb C(24) 160.39(9) C(24) Nb Cp
P(1)
Nb C(24)
88.21(9)
Ta ble 3: Selected Bon d Len gth s in
P h P 2Cp ]NbCl2(CO), 8
[
F igu r e 5. Room-temperature ESR spectrum of [i-PrP2Cp]-
NbCl3, 9 (solution in toluene).
atom
atom
distance (Å)
atom
atom
distance (Å)
Nb
Nb
Nb
Nb
Nb
Nb
Cl(1)
Cl(2)
P(1)
P(2)
C(1)
C(2)
2.5724(9)
2.4927(10)
2.6822(10)
2.6849(9)
2.436(4)
Nb
Nb
Nb
Nb
Nb
C(36)
C(3)
C(4)
C(5)
Cp
C(36)
O(1)
2.458(3)
2.364(3)
2.353(3)
2.090
2.138(4)
1.049(4)
2.462(3)
Ta ble 4: Selected Bon d An gles in
P h P 2Cp ]NbCl2(CO), 8
[
atom atom atom angle (deg) atom atom atom angle (deg)
Cl(1) Nb Cl(2)
P(1) Nb P(2) 152.73(3) Cl(1) Nb Cp
Cl(1) Nb P(1)
Cl(2) Nb P(2)
Cl(1) Nb C(36) 159.77(11) P(2)
85.83(3) P(2)
Nb C(36)
89.32(9)
103.4
170.8
104.2
102.9
96.7
92.83(3) Cl(2) Nb Cp
77.48(3) P(1)
Nb Cp
Nb Cp
Cl(2) Nb C(36) 74.10(11) C(36) Nb Cp
P(1) Nb C(36) 84.62(9)
both Nb(III) compounds. When 5 was allowed to react
with 2 equiv of MeMgBr, only mixtures of products were
obtained; a similar result was observed with 6. The
NMR spectra of the crude material indicated that the
product consisted of a mixture of two compounds. All
attempts to separate these two complexes have failed
due to their similar solubilities in common solvents. In
the absence of strong evidence, we can only speculate
that these species are the mono- and dimethyl deriva-
tives, [RP2Cp]NbMeX (X ) Cl or Br) and [RP2Cp]NbMe2.
Both 5 and 6 react with LiCH2SiMe3 to produce brown
oils that are mixtures of two compounds based on their
NMR spectra; presumably, these mixtures are also
mono- and dialkylated derivatives.
F igu r e 6. Molecular structure and numbering scheme of
[
i-PrP2Cp]NbCl3, 9.
although this process is difficult to control and overoxi-
dation complicates isolation of the Nb(IV) derivatives,
ESR spectroscopy clearly shows that the Nb(IV) species
are formed (eq 7). For 9, a decet of triplets centered at
g ) 2.035 is observed, while for 10 this pattern is found
at g ) 2.036. The unpaired electron on each Nb(IV)
center is coupled to two equivalent phosphines, a(31P)
) 26 and 21 G, and one Nb atom, a(93Nb) ) 124 and
117 G (93Nb, I ) 9/2, 100%), for 9 and 10, respectively.
The ESR spectrum of 9 is shown in Figure 5. The same
complexes are produced when NbCl3(O)(THF)2 reacts
with [RP2Cp]Li (eq 7). The yield of this latter reaction
is 45% and 37% for 9 and 10, respectively. This reaction
was performed originally to synthesize Nb(V) deriva-
tives of the [RP2Cp] ligand, but the dark green color of
the reaction mixture, the ESR spectrum, and the X-ray
analysis of 9, all attest to the formation of 9 and 10.
The mechanism for the reaction in eq 7 is not obvious.
Since a reduction from Nb(V) to Nb(IV) is observed, one
possible rationale is that the reducing agent is the
phosphine ligand (used in excess); unfortunately, no
corroborating evidence was obtained.
Oxidation of the Nb(III) derivatives [RP2Cp]NbCl2
with PbCl2 results in the formation of the niobium(IV)
complexes [RP2Cp]NbCl3 (9, R ) i-Pr; 10, R ) Ph);
The crystal structure of 9 is shown in Figure 6 and
indicates a pseudo-octahedral geometry around the
metal center. Assuming that the Cp ring occupies only
one site, two chlorides and both phosphines form a
pseudoequatorial plane, while the Cp ring and the third
Cl occupy the apical positions. The molecule is distorted

Zr, Nb, and Mo Complexes with Cyclopentadienyl
Organometallics, Vol. 18, No. 20, 1999 4055
Ta ble 5: Selected Bon d Len gth s in
[
i-P r P 2Cp ]NbCl3, 9
atom
atom
distance (Å)
atom
atom
distance (Å)
Nb
Nb
Nb
Nb
Nb
Nb
Cl(1)
Cl(2)
Cl(3)
P(1)
P(2)
C(1)
2.5121(6)
2.5284(7)
2.4771(7)
2.7365(6)
2.7194(6)
2.442(3)
Nb
Nb
Nb
Nb
Nb
C(2)
C(3)
C(4)
C(5)
Cp
2.481(3)
2.503(3)
2.414(3)
2.391(3)
2.13
Ta ble 6: Selected Bon d An gles in [i-P r P 2Cp ]NbCl3,
9
atom atom atom angle (deg) atom atom atom angle (deg)
Cl(1) Nb Cl(2) 160.53(3) Cl(3) Nb
P(2)
Cp
Cp
75.93(2)
100.3
98.9
F igu r e 7. Room-temperature ESR spectrum of [i-PrP2Cp]-
MoCl2, 11 (solution in toluene).
Cl(1) Nb Cl(3)
Cl(2) Nb Cl(3)
Cl(1) Nb P(1)
Cl(1) Nb P(2)
Cl(2) Nb P(1)
Cl(2) Nb P(2)
Cl(3) Nb P(1)
83.03(2) Cl(1) Nb
77.87(3) Cl(2) Nb
83.62(2) Cl(3) Nb
Cp
176.5
88.23(2) P(1)
90.73(2) P(1)
90.73(2) P(2)
77.53(2)
Nb
Nb
Nb
P(2) 152.98(2)
Cp
Cp
103.8
103.0
because both Cl(1)-Nb-Cl(2) (160.53(3)°) and P(1)-
Nb-P(2) (152.98(3)°) angles depart by 20° and 30° from
180°. The Nb atom lies 0.5391 Å above the equatorial
plane toward the Cp ring. Nb-Cl (equatorial) and Nb-P
bond lengths are longer than those found in CpNbCl3-
dppe.40,41 The structure compares very well with the
structure of the zirconium(IV) analogue, [i-PrP2Cp]ZrCl3
(1), which has a similar geometry and comparable bond
lengths and angles.19 Selected bond lengths and bond
angles are shown in Tables 5 and 6.
Syn th esis an d Reactivity of [RP 2Cp]Mo(III) Com -
p lexes. MoCl3(THF)3 reacts with [RP2Cp]Li in toluene
at 65 °C to form brown solutions, which upon workup
yield brown microcrystalline solids (eq 8). These com-
pounds have the molecular formula [RP2Cp]MoCl2 (11,
R ) i-Pr; 12, R ) Ph).
F igu r e 8. Molecular structure and numbering scheme of
[
i-PrP2Cp]MoCl2, 11.
for 12) and satellites due to one magnetically dilute Mo
nucleus (a(95,97Mo) ) 39.1 G for 11 and 43.4 G for
12: 95Mo and 97Mo, 25% total, I ) 5/2). The ESR
spectrum for 11 is shown in Figure 7. Since most
Mo(III) complexes are in a S ) 3/2 spin state, they show
unresolved singlets in their room-temperature ESR
spectra. There are some examples of low-spin Mo(III)
complexes that show well-resolved ESR spectra with
hyperfine couplings; for example, (η5-C5H5)MoCl2(PMe3)2
and (η5-C5H5)MoX2(dppe), X ) halide, have g values of
about 1.98.27
The crystal structure of 11 is shown in Figure 8. A
comparison of the bond angles around the Mo center
suggests that the coordination environment can be
described as a distorted square pyramid with the
phosphine donor atoms and both chlorides in the same
plane, which is capped by the Cp ring. The Mo atom
lies 0.9465 Å above the Cl2P2 plane toward the Cp ring.
The geometry of the molecule can be referred to as a
“four-legged piano stool”. The Mo-C (Cp) distances
(average 2.301 Å) are slightly longer than those of (η5-
C5H5)MoCl2(PMe3)2 (2.272 Å), but Mo-Cl distances are
very similar (average 2.479 Å vs 2.471 Å).27 The
lengthening of the Mo-P bond distances in 11 (average
Mo-P bond distance 2.5645(7) Å) as compared to those
in (η5-C5H5)MoCl2(PMe3)2 (2.482(2) Å)27 is probably
caused by the steric bulk of the [P2Cp] ligand that
Solutions of 11 and 12 show broad, unresolved signals
in their respective NMR spectra; both solution magnetic
studies by the Evans’ method and magnetic susceptibil-
ity measurements on solid samples show that the
effective magnetic moments 1.98 and 2.10 µB are
consistent with one unpaired electron on 11 and 12,
respectively. Magnetic studies for low-spin Mo(III)
complexes are rare, because most pseudo-octahedral
Mo(III) compounds have high-spin (S ) 3/2) electronic
ground states.27 The effective magnetic moment for the
closely related compound (η5-C5H5)MoCl2(PMe3)2 is 1.72
µB.27 Room-temperature solution ESR spectra of 11 and
12 in toluene are observed as broad triplets at g ) 1.97
and 1.98, respectively, due to coupling to two equivalent
phosphorus nuclei (a(31P) ) 15.2 G for 11 and 11.0 G
(40) Daran, J . C.; Prout, K.; De Gian, A.; Green, M. L. H.; Siganporia,
N. J . Organomet. Chem. 1977, 136, C4.
(41) Prout, K.; Daran, J . Acta Crystallogr. B 1979, 35, 2882.

4056 Organometallics, Vol. 18, No. 20, 1999
Fryzuk et al.
Ta ble 7: Selected Bon d Len gth s in
free dinitrogen or argon by means of standard Schlenk or
glovebox techniques.48 Hexanes, toluene, Et2O, and THF were
refluxed over CaH prior to a final distillation from either
sodium metal or sodium benzophenone ketyl under an Ar
atmosphere. Deuterated solvents were dried over potassium
and vacuum transferred. They were then degassed by three
“freeze-pump-thaw” cycles. The solid-state magnetic mea-
surements were determined from Gouy measurements per-
formed on a J ohnson Matthey MSB-1 apparatus at room
temperature. The magnetic measurements in solution were
performed using Evans’ method with ferrocene as standard.32,33
[
i-P r P 2Cp ]MoCl2, 11
atom
atom
distance (Å)
atom
atom
distance (Å)
Mo
Mo
Mo
Mo
Mo
Cl(1)
Cl(2)
P(1)
P(2)
C(1)
2.4899(8)
2.4678(8)
2.5380(7)
2.5910(8)
2.254(3)
Mo
Mo
Mo
Mo
Mo
C(2)
C(3)
C(4)
C(5)
Cp
2.339(3)
2.395(3)
2.301(3)
2.216(3)
1.955
Ta ble 8: Selected Bon d An gles in [i-P r P 2Cp ]MoCl2,
11
Rea gen t Syn th eses. 1,1-C5H4(SiMe3CH2Cl)2,34
[
i-PrP2Cp]-
atom atom atom angle (deg) atom atom atom angle (deg)
ZrCl3,19 i-PrP2Cp]Li,18 NbCl3(DME),49 Nb(O)Cl3(THF)2,50 and
[
Cl(1) Mo Cl(2) 135.40(3) Cl(1) Mo
P(1) Mo P(2) 136.28(3) Cl(2) Mo
Cp
Cp
Cp
Cp
110.3
114.3
113.0
110.5
51
MoCl3(THF)3 were prepared using literature procedures.
Mercury was purchased from BDH and purified following a
literature procedure.52 Sodium amalgam was made under a
nitrogen atmosphere and washed with toluene until the
washing showed no gray coloration. MeMgCl and MeMgBr (3
M solutions in diethyl ether) were purchased from Aldrich.
CO was purchased from Praxair and used as received.
Syn th esis of [P h P 2Cp ]Li. A solution of 1,1-C5H4(SiMe3CH2-
Cl)2 (10 g, 36 mmol) in THF (120 mL) and toluene (20 mL)
was heated to 65 °C and added dropwise to a solution of Ph2-
PLi (20.63 g, 107 mmol) in THF (120 mL) at 65 °C. The
reaction mixture was allowed to cool to room temperature, and
the solvent and excess Ph2PH were removed in vacuo. The
white residue was then extracted with toluene and filtered
through Celite. Removal of the solvent produced a yellow air-
and moisture-sensitive oil (yield ) 65%, 13.3 g). 1H NMR
(C6D6): δH ) 0.05 (s, 12H, Si(CH3)2); 1.30 (m, 4H, SiCH2P);
6.7 (m, 3H, C5H3); 7.00 (m, 20H, C6H5). 31P{1H}: δP ) -22.12
(1:1:1:1 quartet, J PLi ) 84 Hz).
Cl(1) Mo P(1)
Cl(2) Mo P(2)
79.75(3) P(1)
84.20(3) P(2)
Mo
Mo
pushes the phosphines slightly away from the Mo(III)
center, since the electronic factors in these two com-
pounds are very similar; confirmation of this is apparent
from the longer Mo-P bond distances in (η5-C5Me5)-
MoCl2(PMe3)2 of 2.5104(8) and 2.5080(8) Å.42 An exami-
nation of C-C bond distances of the Cp ring and Mo-
C(Cp) bond lengths shows that the bonding of Cp to the
metal is consistent with η2,η3 character. The carbons of
the η3 system, C(2), C(3), and C(4), are further away
from the metal than C(1) and C(5), which belong to the
η2 system. In many piano-stool complexes a slight tilting
of the Cp ring from a plane perpendicular to the Cp-M
axis is observed.27 Selected bond lengths and bond
angles are show in Tables 7 and 8.
Complex 11 reacts with MeMgBr at -78 °C, to yield
a brown oil, which shows a broad singlet in its ESR
Syn th esis of [i-P r P 2Cp ]Zr Cl2, 2. To an intimate mixture
of Na/Hg (92 g, 0.012 mol) and [i-PrP2Cp]ZrCl3 (1 g, 1.56 mmol)
was added toluene (100 mL) under N2. The reaction mixture
was degassed by three “freeze-pump-thaw” cycles and was
stirred for 48 h under vacuum, during which the solution
turned green. It then was filtered through Celite, and the
solvent was evaporated under reduced pressure to yield a dark
green microcrystalline solid (yield ) 85%, 0.8 g). ESR (tolu-
ene): g ) 1.96; a(31P) ) 22.7 G, 2P, a(91Zr) ) 13.6 G, 1Zr. Anal.
1
spectrum. The product is NMR active, and both H and
31P{1H} NMR spectra indicate that the crude product
is a mixture of compounds. All attempts to separate and
characterize these species have proved futile.
Con clu sion s
The use of a cyclopentadienyl ligand with pendant
donors is not a new approach to ligand design. Indeed,
there are many examples of this in the literature.43,44
What is significant about this work is that the examples
of complexes of the general type CpMCl2(PR3)2 have
been prepared for M ) Zr, Nb, and Mo with a modified
cyclopentadienyl with two pendant phosphine donors.
Other cyclopentadienyl units with one pendant phos-
phine are known.43,45-4745-47 However, our approach to
using two pendant phosphine donors is unique to our
knowledge. These complexes are reactive, as evidenced
by their reactivity with carbon monoxide. Attempts to
generate alkyl derivatives of these second-row trivalent
metal complexes have only been partially successful. In
general complicated mixtures result that have so far
eluded purification.
Calcd for
C23H47Cl2P2Si2Zr‚(NaCl)0.1: C, 45.31; H, 7.77.
Found: C, 45.13; H, 7.99. MS: m/e 603 (M+). µ (solid) ) 2.0
µB, µ (solution in C6D6) ) 1.8 µB.
Syn t h esis of [i-P r P 2Cp ]Zr ClMe, 3. To a solution of
[
i-PrP2Cp]ZrCl2 (0.25 g, 0.41 mmol) in toluene was added
MeMgCl (0.32 mL, 0.45 mmol) dropwise at -78 °C. The
solution was then warmed to room temperature and stirred
for 4 h, during which a white precipitate formed. The reaction
mixture was then concentrated under reduced pressure and
filtered through Celite, and the solvent was evaporated,
yielding a green powder (yield ) 70%, 0.17 g). ESR (toluene):
g ) 2.01; a(31P) ) 23.0 G, 2P, a(1H) ) 8.0 G, 3H, a(91Zr) ) 8.0
G, 1Zr. Anal. Calcd for C24H50ClP2Si2Zr: C, 49.41; H, 8.64.
Found: C, 49.33; H, 8.93.
Rea ction of [i-P r P 2Cp ]Zr Cl2, 2, w ith CO; F or m a tion of
[
i-P r P 2Cp]Zr (CO)2Cl, 4. A degassed solution of [i-PrP2Cp]ZrCl2,
2 (0.05 g, 0.09 mmol), in C6D6 was stirred under 1 atm of CO
for 24 h, during which the color changed from dark green to
1
brown. H NMR (C6D6): δH ) 0.12 and 0.28 (s, 6H, Si(CH3)2),
Exp er im en ta l Section
2
2
0.51 and 0.82 (dd, 2H, J HH ) 15 Hz, J PH ) 9 Hz, SiCH2P),
Gen er a l P r oced u r es. Unless otherwise stated all manipu-
lations were carried out under an atmosphere of dry, oxygen-
3
3
0.97, 1.22, 1.29, 1.32 (dd, 6H, J HH ) 7 Hz, J PH ) 7 Hz, CH-
(CH3)2), 1.95 and 2.48 (sept, 2H, J HH ) 7 Hz,CH(CH3)2), 5.19
3
(42) Baker, R. T.; Calabrese, J . C.; Harlow, R. L.; Williams, I. D.
Organometallics 1993, 12, 830.
(43) Charrier, C.; Mathey, F. Tetrahedron Lett. 1978, 27, 2407.
(44) J utzi, P.; Redeker, T. Eur. J . Inorg. Chem. 1998, 663.
(45) Schore, N. E. J . Am. Chem. Soc. 1979, 101, 7410.
(46) Schore, N. E.; Benner, L. S.; LaBelle, B. E. Inorg. Chem. 1981,
20, 3200.
(48) Brown, T. L.; Dickerhoof, D. W.; Bafus, D. A.; Morgan, G. L.
Rev. Sci. Instrum. 1962, 33, 491.
(49) Roskamp, E. J .; Pedersen, S. F. J . Am. Chem. Soc. 1987, 109,
6551.
(50) Gibson, V. C.; Kee, T. P.; Shaw, A. Polyhedron 1988, 7, 2217.
(51) Dilworth, J . R.; Richards, R. L. Inorg. Synth. 1980, 20, 121.
(52) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3 ed.; Butterworth-Heinemann Ltd.: Oxford, 1994.
(47) Bensley, D. M., J r.; Mintz, E. A. J . Organomet. Chem. 1988,
353, 93.

Zr, Nb, and Mo Complexes with Cyclopentadienyl
Organometallics, Vol. 18, No. 20, 1999 4057
Ta ble 9: Cr ysta llogr a p h ic Da ta
[
i-PrP2Cp]NbCl2(CO)(7)
[
PhP2Cp]NbCl2(CO) (8)
[
i-PrP2Cp]NbCl3 (10)
[
i-PrP2Cp]MoCl2 (11)
formula
fw
color, habit
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C
24H47Cl2NbOP2Si2
C36H39Cl2NbOP2Si2
769.63
red, irregular
orthorhombic
Pca21
28.5375(4)
9.6009(8)
13.1317(3)
90
C23H47Cl3NbP2Si2
641.01
dark, prism
monoclinic
P21/n
17.0192(14)
11.6262(13)
17.0176(3)
90
116.4187(5)
90
3015.6(3)
4
C23H47Cl2MoP2Si2
608.59
dark brown, irregular
monoclinic
P21/a
15.4113(12)
9.4576(12)
20.4912(5)
90
104.3124(5)
90
663.57
orange, prism
monoclinic
P21/c
12.718(2)
16.609(3)
14.739(8)
90
101.6445(6)
90
3049.3(5)
4
90
90
3597.9(3)
4
2894.0(3)
4
Z
T, °C
D
-93
1.380
-93
1.421
-93
1.412
-93
1.397
calc, g/cm3
F000
radiation
1328.00
Mo
1584.00
Mo
1340.00
Mo
1276.00
Mo
λ, Å
0.71069
7.69
0.5670-1.0015
60.1
28614
7291
0.030
0.71069
6.66
0.6362-1.0000
60.1
32169
5537
0.045
0.71069
8.61
0.7064-1.0082
60.1
28555
7744
0.052
0.71069
8.41
0.8883-1.0000
60.1
23795
7130
0.027
µ, cm-1
correction factors
2θmaz, deg
total no. of reflns
no. of unique reflns
Rint
no. with I > 3σ(I)
no. of variables
Ra
5389
289
0.075
0.089
5988
396
0.065
0.054
6092
280
0.062
0.111
4661
271
0.060
0.064
a
Rw
gof
2.53
1.38
1.19
1.36
max ∆/σ
0.016
-1.64-1.73
0.0003
-2.17-2.47
0.001
-3.31-3.39
0.001
-0.97-1.03
residual density, e/Å3
a
2
R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) (∑w(|Fo| - |Fc|)2/∑w|Fo| )1/2
.
(s, 2H, Cp), 5.21 (s, 1H, Cp). 31P{1H}: δP ) 31.6 (s). IR
For 8: 1H NMR (C6D6): δH ) 0.02 (s, 6H, Si(CH3)2); 0.25 (s,
(benzene, cm-1): 1888 (s, CO), 1978 (s, CO).
6H, Si(CH3)2); 0.9 (dd, 2H, J HH ) 14 Hz, SiCH2P); 1.20 (dd,
3
Syn th esis of [RP 2Cp ]NbCl2, R ) i-P r , P h , 5, 6. To a slurry
of NbCl3(DME) (1 g, 3.89 mmol) in toluene (20 mL) was added
the solution of [RP2Cp]Li (3.89 mmol) in toluene (10 mL) at
room temperature. The reaction mixture was stirred for 4 h,
during which the solution turned brown-red. It was then
filtered through Celite, and the solvent was evaporated under
reduced pressure to produce a cherry-red microcrystalline solid
(yield ) 80%).
2H, SiCH2P); 4.60 (s, 2H, C5H3); 6.40 (s, 1H, C5H3); 7.0 (m,
16H, Ph); 7.60 (m, 2H, p-Ph); 8.20 (m, 2H, p-Ph). 31P{1H}: δP
) 18.19 (br s). Anal. Calcd for C36H39Cl2P2Si2NbO: C, 56.18;
H, 5.11. Found: C, 56.48; H, 5.14. IR (toluene, cm-1): 1927
(s, CO).
Syn th esis of [RP 2Cp ]NbCl3, 9, 10. A solution of [RP2Cp]-
Li (0.64 mmol) in toluene (5 mL) was added dropwise to a
slurry of Nb(O)Cl3(THF)2 (0.25 g, 0.7 mmol) in toluene (10 mL)
at -40 °C. The color changed from yellow to green im-
mediately. The reaction mixture was allowed to warm to room
temperature and stirred for 10 h. It then was filtered through
Celite and the solvent evaporated under reduced pressure to
produce a green microcrystalline solid (yield ) 60%).
For 9: Dark green crystals suitable for X-ray analysis were
grown from slow evaporation of the toluene solution. ESR
(toluene): g ) 2.35, a(31P) ) 26 G, 2P, a(93Nb) ) 124 G, 1Nb.
Anal. Calcd for C23H47Cl3P2Si2Nb: C, 43.10; H, 7.39. Found:
C, 43.42; H, 7.51.
For 5: 1H NMR (C6D6): δH ) 0.00 (s, 6H, Si(CH3)2); 0.28 (s,
3
6H, Si(CH3)2); 0.50 (br s, 6H, CH(CH3)2); 0.51 (dd, 2H, J HH
)
16 Hz, PCH2Si); 0.65 (dd, 2H, PCH2Si); 0.91 (br s, 6H, CH-
(CH3)2); 1.33 (d, J PH ) 7 Hz, 6H, CH(CH3)2); 1.63 (d, J PH ) 7
3
Hz, 6H, CH(CH3)2); 2.90 (sept, 4H, J HH ) 6 Hz, CHMe); 4.70
(s, 1H, C5H3); 5.60 (s, 2H, C5H3). 31P{1H}: δP ) 24.62 (br s).
Anal. Calcd for C23H47Cl2P2Si2Nb: C, 45.62; H, 7.82. Found:
C, 45.52; H, 7.73. MS: m/e 604 (M+).
For 6: 1H NMR (C6D6): δH ) -0.10 (s, 6H, Si(CH3)2); 0.04
(s, 6H, Si(CH3)2); 0.80 (ABX, 2H, SiCH2P); 1.30 (ABX, 2H,
SiCH2P); 5.20 (s, 2H, C5H3); 5.80 (s, 1H, C5H3); 6.95 (m, 8H,
Ph); 7.2 (m, 8H, Ph); 7.80 (m, 2H, p-Ph), 7.95 (m, 2H, p-Ph).
31P{1H}: δP ) 22.50 (br s). Anal. Calcd for C35H39Cl2P2Si2Nb-
(C7H8)0.75: C, 59.63; H, 5.59. Found: C, 59.84; H, 5.60.
Syn th esis of [RP 2Cp ]NbCl2(CO), R ) i-P r , P h , 7, 8. A
degassed solution of [RP2Cp]NbCl2 (1 mmol) in toluene (20 mL)
was stirred under 1 atm of CO for 24 h, during which the color
changed from dark red to orange. The solvent was then
removed under vacuum to yield an orange microcrystalline
solid (yield ) 80%). Crystals suitable for X-ray analysis were
grown by slow evaporation from a saturated toluene solution.
For 7: 1H NMR (C6D6): δH ) -0.05 (s, 6H, Si(CH3)2); 0.25
For 10: ESR (toluene): g ) 2.04, a(31P) ) 21 G, 2P, a(93Nb)
) 117 G, 1Nb.
Rea ction of [i-P r P 2Cp ]NbCl2 w ith P bCl2. To a solution
of [i-PrP2Cp]NbCl2 (0.1 g, 0.17 mmol) in toluene (5 mL) cooled
to -40 °C was added PbCl2 (0.14 g, 0.51 mmol) in solid form.
The reaction mixture was warmed to room temperature and
stirred for 5 h, during which most of the PbCl2 slurry was
dissolved and the color changed from red to green. Filtration
through Celite and evaporation of the solvent yield a yellow-
green solid which gave ESR signals identical to [i-PrP2Cp]NbCl3.
Syn th esis of [RP 2Cp ]MoCl2, R ) i-P r , P h , 11, 12. To a
slurry of MoCl3(THF)3 (1 g, 2.39 mmol) in toluene (30 mL) was
added the solution of [RP2Cp]Li (2.39 mmol) in toluene (10 mL).
The reaction flask was covered with aluminum foil and heated
to 65 °C for 24 h, during which the color slowly changed from
orange to brown. After the reaction mixture cooled to room
temperature, it was filtered through Celite and the solvent
evaporated to yield a brown microcrystalline solid (yield ) 85%
and 65% for 11 and 12, respectively).
3
(s, 6H, Si(CH3)2); 0.80 (dd, 2H, J HH ) 16 Hz, SiCH2P); 0.90
(dd, 2H, SiCH2P); 1.10 (m, 12H, CH(CH3)2); 1.30 (m, 12H, CH-
3
(CH3)2); 2.60 (sept. 2H, J HH ) 8 Hz, CHMe); 3.30 (sept. 2H,
3J HH ) 8 Hz, CHMe) 4.40 (s, 2H, C5H3); 6.05 (s, 1H, C5H3).
31P{1H}: δP ) 25.66 (br s). Anal. Calcd for C24H47Cl2P2Si2-
NbO: C, 45.50; H, 7.48. Found: C, 45.02; H, 7.29. IR (toluene,
cm-1): 1914 (s, CO).

4058 Organometallics, Vol. 18, No. 20, 1999
Fryzuk et al.
For 11: Brown crystals suitable for X-ray analysis were
grown from slow evaporation of the toluene solution. ESR
(toluene): g ) 1.97, a(31P) ) 15.2 G, 2P, a(95Mo) ) 39.1 G,
1Mo, a(97Mo) ) 23 G, 1Mo. Anal. Calcd for C23H49Cl2P2Si2Mo:
C, 45.24; H, 8.09. Found: C, 45.54; H, 7.93. µ(solid) ) 1.98 µB.
For 12: ESR (toluene): g ) 1.98, a(31P) ) 11 G, 2P, a(95Mo)
fied statistical weights (w ) 1/σ2(Fo)2) were employed for all
four structures. Neutral atom scattering factors and anoma-
lous dispersion corrections were taken from the International
Tables for X-ray Crystallography.54,55
Selected bond lengths and bond angles appear in Tables
1-8. Tables of final atomic coordinates and equivalent isotropic
thermal parameters, anisotropic thermal parameters, bond
lengths and angles, torsion angles, intermolecular contacts,
and least-squares planes are included as Supporting Informa-
tion.
) 43.4 G, 1Mo, a(97Mo) ) 23 G, 1Mo. Anal. Calcd for C35H39
-
Cl2P2Si2Mo: C, 56.45; H, 5.28. Found: C, 56.92; H, 5.40.
µ(solid) ) 2.10 µB.
X-r ay Cr ystallogr aph ic An alyses of {η5-C5H3-1,3-(SiMe2-
CH2P -i-P r 2)2}NbCl2(CO)(7),{η5-C5H3-1,3-(SiMe2CH2P P h 2)2}-
NbCl2(CO) (8), {η5-C5H3-1,3-(SiMe2CH2P -i-P r 2)2}NbCl3 (9),
a n d {η5-C5H3-1,3-(SiMe2CH2P -i-P r 2)2}MoCl2 (11). Crystal-
lographic data were collected on a Rigaku/ADSC CCD diffrac-
tometer and appear in Table 9. The final unit cell parameters
were obtained by least squares on the setting angles for 28614
reflections (7), 32169 reflections (8), 28555 reflections (9), and
23795 reflections (11) with 2θ ) 4.0-60.1°. The data were
processed53 and corrected by Lorentz and polarization effects
and absorption (empirical: based on a three-dimensional
analysis of a symmetry-equivalent data).
Ack n ow led gm en t. We thank NSERC of Canada for
generous financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of final
atomic coordinates and equivalent isotropic thermal param-
eters, anisotropic thermal parameters, bond lengths and
angles, torsion angles, intermolecular contacts, and least-
squares planes. This material is available free of charge via
the Internet at http://pubs.acs.org.
The structures were solved by heavy-atom Patterson meth-
ods. All non-hydrogen atoms were refined with anisotropic
thermal parameters. Hydrogen atoms were fixed in calculated
positions with C-H ) 0.98 Å and BH ) 1.2bonded atom. Unmodi-
OM990096+
(54) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV, pp 99-102.
(55) International Tables for X-ray Crystallography; Kluwer Aca-
demic Publishers: Boston, MA, 1992; Vol. C, pp 200-206.
(53) teXsan Crystal Structure Analysis Package, 1.8 ed.; Molecular
Structure Corp.: The Woodlands, TX, 1996.