Coordination and Reductive Chemistry of Tetraphenylborate Complexes of Trivalent Rare Earth Metallocene Cations, [(C5Me5) 2Ln][(μ-Ph)2BPh2]

Article abstract of DOI:10.1021/ic2000409

The reactivity of the tetraphenylborate salts of the rare earth metallocene cations [(C₅Me₅)₂Ln][(μ-Ph) ₂BPh₂] (Ln = Y, 1; Sm, 2) has been investigated with substrates that undergo reduction with f element complexes to probe metal-substrate interactions prior to reduction. Results with NaN₃, 1-adamantyl azide, acetone, benzophenone, phenanthroline, pyridine, azobenzene, and phenazine are described. Not only were coordination complexes isolated, but substrate reduction by (BPh₄)^- was also observed. Complex 1 reacts with NaN₃ to form the azide [(C₅Me ₅)₂YN₃]_x, 3, which crystallizes as [(C₅Me₅)₂Y(μ-N₃)]₃, 4, when obtained from 1 and 1-adamantyl azide. The samarium analogue [(C ₅Me₅)₂SmN₃]_x, 5, can be produced similarly from 2 and NaN₃ and crystallized from MeCN as [(C₅Me₅)₂Sm(NCMe)(μ-N₃)] ₃, 6, and {[(C₅Me₅)₂Sm(μ-N ₃)][(C₅Me₅)₂Sm(NCMe)(μ-N ₃)]}_n, 7. Complexes 1 and 2 react with stoichiometric amounts of acetone and benzophenone to form the ketone adducts [(C ₅Me₅)₂Ln(OCMe₂)₂] [BPh₄] (Ln = Y, 8; Sm, 9) and [(C₅Me₅) ₂Ln(OCPh₂)₂][BPh₄] (Ln = Y, 10; Sm, 11), respectively. Phenanthroline (phen) coordinates to 1 to form [(C ₅Me₅)₂Y(phen)][BPh₄], 12. Complexes 1 and 2 react with pyridine (py) to form [(C₅Me₅) ₂Ln(py)₂][BPh₄], (Ln = Y, 13; Sm, 14). Complexes 3, 8, 10, and 12 can also be made from the solvated cation [(C ₅Me₅)₂Y(THF)₂][BPh₄]. The reaction of 1 with PhNNPh yields the diamagnetic adduct [(C₅Me ₅)₂Y(PhNNPh)][BPh₄], 15, which transforms in benzene to the radical anion complex (C₅Me₅) ₂Y(PhNNPh), 16, via a one electron reduction by (BPh ₄)^-. Complex 1 similarly reacts with phenazine (phz) to produce the first rare earth phenazine radical anion complex {[(C ₅Me₅)₂Y]₂(phz)}{BPh₄}, 17. Further reduction of phenazine by (BPh₄)^- in 17 yields [(C₅Me₅)₂Y]₂(phz), 18, which contains the common (phz)^2- dianion. The reduction of fluorenone by (BPh₄)^- is also reported.

Full text of DOI:10.1021/ic2000409

ARTICLE
pubs.acs.org/IC
Coordination and Reductive Chemistry of Tetraphenylborate
Complexes of Trivalent Rare Earth Metallocene Cations,
[(C5Me5)2Ln][(μ-Ph)2BPh2]
Matthew R. MacDonald, Joseph W. Ziller, and William J. Evans*
Department of Chemistry, University of California, Irvine, California 92697-2025, United States
S Supporting Information
b
ABSTRACT:
The reactivity of the tetraphenylborate salts of the rare earth metallocene cations [(C5Me5)2Ln][(μ-Ph)2BPh2] (Ln = Y, 1; Sm, 2) has
been investigated with substrates that undergo reduction with f element complexes to probe metal-substrate interactions prior to
reduction. Results with NaN3, 1-adamantyl azide, acetone, benzophenone, phenanthroline, pyridine, azobenzene, and phenazine are
described. Not only were coordination complexes isolated, but substrate reduction by (BPh4)ꢀ was also observed. Complex 1 reacts with
NaN3 to form the azide [(C5Me5)2YN3]x, 3, which crystallizes as [(C5Me5)2Y(μ-N3)]3, 4, when obtained from 1 and 1-adamantyl azide.
The samarium analogue [(C5Me5)2SmN3]x, 5, can be produced similarly from 2 and NaN3 and crystallized from MeCN as
[(C5Me5)2Sm(NCMe)(μ-N3)]3, 6, and {[(C5Me5)2Sm(μ-N3)][(C5Me5)2Sm(NCMe)(μ-N3)]}n, 7. Complexes 1 and 2 react with
stoichiometric amounts of acetone and benzophenone to form the ketone adducts [(C5Me5)2Ln(OCMe2)2][BPh4] (Ln = Y, 8; Sm, 9)
and [(C5Me5)2Ln(OCPh2)2][BPh4] (Ln = Y, 10; Sm, 11), respectively. Phenanthroline (phen) coordinates to 1 to form [(C5Me5)2Y-
(phen)][BPh4], 12. Complexes 1and 2react with pyridine (py) to form [(C5Me5)2Ln(py)2][BPh4], (Ln=Y, 13;Sm, 14). Complexes3,
8, 10, and 12 can also be made from the solvated cation [(C5Me5)2Y(THF)2][BPh4]. The reaction of 1 with PhNNPh yields the dia-
magnetic adduct [(C5Me5)2Y(PhNNPh)][BPh4], 15, which transforms in benzene to the radical anion complex (C5Me5)2Y(PhNNPh),
16, via a one electron reduction by (BPh4)ꢀ. Complex 1 similarly reacts with phenazine (phz) to produce the first rare earth phenazine
radical anion complex {[(C5Me5)2Y]2(phz)}{BPh4}, 17. Further reduction of phenazine by (BPh4)ꢀ in 17 yields [(C5Me5)2Y]2(phz),
18, which contains the common (phz)2ꢀ dianion. The reduction of fluorenone by (BPh4)ꢀ is also reported.
’ INTRODUCTION
The unsolvated metallocene tetraphenylborate salts,
[(C5Me5)2M][(μ-Ph)2BPh2] (M = lanthanides,1,2 Y,2 U3), are
highly reactive precursors to f element complexes that have
expanded our knowledge in fundamental areas such as sterically
induced reduction,4 CꢀH bond activation,2,5ꢀ7 and multielec-
tron reduction via metal- and ligand-based processes.8ꢀ10 For
example, these complexes provide facile access to unsolvated
alkyl complexes, (C5Me5)2LnR,5ꢀ7 eq 1, that are highly reactive
in CꢀH bond activation. The [(C5Me5)2Ln][(μ-Ph)2BPh2]
complexes also provide one of the primary routes to the sterically
crowded tris(pentamethylcyclopentadienyl) complexes, (C5Me5)3-
Ln,1,2,4 via reactions with KC5Me5, eq 2.
In contrast, the reaction of KC5Me5 with the tetrahydrofuran
metallocene is only loosely ligated with the tetraphenylborate ion
(THF)-solvatedanalogue, [(C5Me5)2M(THF)2][BPh4], formsring-
opened products, (C5Me5)2M[(O(CH2)4(C5Me5)](THF).1,11,12
The latter reaction is thought to occur because the THF ligands
are strongly activated by the Ln3þ center for nucleophilic attack.
In the unsolvated [(C5Me5)2M][(μ-Ph)2BPh2] complexes, the
via long M HC(aryl) interactions.
3 3 3
Received: January 7, 2011
Published: March 25, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/ic2000409 Inorg. Chem. 2011, 50, 4092–4106
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ARTICLE
redox. Here we report that a redox active metal is not needed to
effect reduction by (BPh4)ꢀ in rare earth metal compounds.
’ EXPERIMENTAL SECTION
The syntheses and manipulations described below were conducted
under nitrogen with rigorous exclusion of air and water using Schlenk,
vacuum line, and glovebox techniques. Solvents were sparged with argon
and dried over columns containing Q-5 and molecular sieves. NMR
solvents were dried over NaK alloy, degassed by three freezeꢀ
pumpꢀthaw cycles, and vacuum transferred before use. Acetone
(Fisher) and pyridine (Aldrich) were dried over molecular sieves and
degassed by three freezeꢀpumpꢀthaw cycles before use. NaN3, 1-ada-
mantyl azide, PhNNPh, phenanthroline, fluorenone, and Ph2CO were
purchased from Aldrich and placed under 10ꢀ3 Torr for 12 h before
use. Phenazine was purchased from Aldrich and sublimed before
use. The unsolvated metallocene cation complexes [(C5Me5)2Ln][(μ-
Ph)2BPh2] (Ln = Y,2 1; Sm,1 2) were prepared as previously described.
1H, 13C, and 11B NMR spectra were obtained on a Bruker DRX 500
MHz spectrometer at 25 ꢀC, unless otherwise specified. 11B NMR
Because of the ease of displacement of the (BPh4)ꢀ group in
the [(C5Me5)2M][(μ-Ph)2BPh2] complexes, they seemed to be
ideal for investigating the initial interaction between metallocene
cations and substrates. As part of our study of f element reduc-
tion, we have examined the reactions of these unsolvated metal-
locene cations with substrates that previously have been reduced
by f element metallocene reductants such as (C5Me5)2Sm,13ꢀ16
[(C5Me5)2Ln]2(μ-η2:η2-N2),17,18 and the U3þ complex [(C5-
Me5)2U][(μ-Ph)2BPh2].8,19 Displacement of the (BPh4)ꢀ coun-
ter-anions by the substrate could provide [(C5Me5)2Ln-
(substrate)x][BPh4] complexes that would reveal how these
species bind to the metallocene prior to reduction. Reactions
with the THF-solvated analogues, [(C5Me5)2M(THF)2][BPh4],
were also examined for comparison.
A broad range of substrates previously shown to be reduced in
f element based reduction systems was examined. These include
PhNdNPh,8,17,20ꢀ24 phenazine,4,14,17,18,25ꢀ28 benzophenone,29,30
phenanthroline,31 pyridine,32 and fluorenone.29,30,33,34 Acetone was
also included in the study for comparison with benzophenone.
Inorganic azides were also examined as substrates in light of
the reduction of NaN3 by [(C5Me5)2U][(μ-Ph)2BPh2] to form the
azide-nitride oligomer, [(C5Me5)2U(μ-N)U(μ-N3)(C5Me5)2]4.19
This reaction presumably proceeds through a “(C5Me5)2UN3”inter-
mediate, but such a species was not isolated with uranium. With a
nonredox active Ln3þ ion, such an intermediate should be isolable by
this cation route. The existence of the La3þ azide complex, {(C5Me5)2-
La[CNN(SiMe3)2](μ-N3)}3,35 and the Sm3þ azide complex, {Li-
(DME)3}{[(C5H5)3Sm]2(μ-N3)},36 suggested that this was viable.
This study focused on [(C5Me5)2Y][(μ-Ph)2BPh2], 1, and
[(C5Me5)2Sm][(μ-Ph)2BPh2], 2. Complex 1 was chosen since
Y3þ is diamagnetic and has a nuclear spin of I = 1/2 that assists in
making NMR and EPR assignments. Complex 2 was chosen
because of the extensive reductive chemistry of (C5Me5)2Sm and
the significant knowledge base that exists on the trivalent
(C5Me5)2SmX products. These two metals also represent med-
ium- and small-sized trivalent lanthanides37 so that reactivity can
also be examined as a function of metal size.
resonances were referenced with BF3 Et2O (δ = 0 ppm) as an external
3
standard, and the presence of BPh3 was associated with a 11B NMR
resonance at 68 ppm.47 IR samples were prepared as KBr pellets, and the
spectra were obtained on a Varian 1000 FT-IR spectrophotometer.
Elemental analyses were performed with a Perkin-Elmer 2400 Series II
CHNS analyzer. Electrospray ionization mass spectrometry (ESI-MS)
spectra were obtained from a Waters (Micromass) LCT Premier
orthogonal time-of-flight mass spectrometer. Electron paramagnetic
resonance (EPR) spectra were collected using a Bruker EMX spectro-
meter equipped with an ER041XG microwave bridge. The magnetic
field was calibrated with DPPH, and all experiments were conducted at
room temperature. EPR spectra were simulated using the PEST
WinSIM program.48
[(C5Me5)2YN3]x, 3. NaN3 (8 mg, 0.1 mmol) was stirred in THF
(10 mL) for 10 min and then combined with a solution of
[(C5Me5)2Y][(μ-Ph)2BPh2], 1 (83 mg, 0.12 mmol) in THF (10 mL).
The reaction mixture was allowed to stir for 24 h. The resulting white
slurry was centrifuged, and the colorless supernatant was discarded. The
white insoluble product was washed twice with THF and dried under
vacuum to yield 3 as a white powder (43 mg, 88%). 1 H NMR (CD3CN):
δ 1.90 (br s, C5Me5, 30H). 13C NMR (CD3CN): δ 116.5 (C5Me5), 11.0
(C5Me5). IR: 3532w, 3391w, 2972s, 2909s, 2861s, 2726w, 2164vs,
2116vs, 1493m, 1439s, 1384m, 1165w, 1061m, 1022m, 729w, 639 m,
606w cmꢀ1. Anal. Calcd for C20H30N3Y: C, 59.85; H, 7.53; N, 10.47.
Found: C, 59.33; H, 7.25; N, 10.30. MS (ESI, MeCN) m/z (rel intensity):
443.1 (100) {[(C5Me5)2Y(N3)](N3)}ꢀ, 844.2 (68) {[(C5Me5)2Y(N3)]2-
(N3)}ꢀ, 1245.4 (28) {[(C5Me5)2Y(N3)]3(N3)}ꢀ, 1646.5 (9) {[(C5Me5)2Y-
(N3)]4(N3)}ꢀ.
[(C5Me5)2Y(μ-N3)]3, 4. A solution of 1-adamantyl azide (15 mg,
0.085 mmol) in benzene (1 mL) was added to a slurry of 1 (59 mg, 0.087
mmol) in benzene (1 mL). The mixture immediately became a yellow
solution. After 3 d at room temperature, colorless crystals of 4 suitable
for X-ray diffraction were deposited from the reaction mixture (30 mg,
88%). The IR spectrum of these crystals was identical to that of the
powder sample of 3 obtained above. The mother liquor was found to
contain BPh3 by 1H and 11B NMR spectroscopy. The mother liquor was
passed through a column of silica gel to obtain a colorless solution.
Analysis of the solution by GC-MS gave mass spectra consistent with the
presence of C5Me5H and fragments of Ph2 and adamantane.
We report the new coordination complexes isolated from
these reactions as well as reduction chemistry for the (BPh4)ꢀ
anion. Although the redox reactivity of (BPh4)ꢀ has been
known for decades,38ꢀ46 eq 3, it has only recently been
ðBPh4Þꢀ f BPh3 þ 1=2Ph2 þ eꢀ
ð3Þ
[(C5Me5)2SmN3]x, 5. Following the procedure for 3, NaN3 (6 mg,
0.09 mmol) was combined with [(C5Me5)2Sm][(μ-Ph)2BPh2], 2,
(70 mg, 0.095 mmol) to yield 5 as a yellow powder (29 mg, 68%).
1H NMR (CD3CN): δ 1.17 (br s, C5Me5, 30H). 13C NMR (CD3CN): δ
112.9 (C5Me5), 16.7 (C5Me5). IR: 3495w, 2970s, 2908s, 2860s, 2726w,
found to be a useful method to enhance reductive reactivity in
f element complexes. In reactions of [(C5Me5)2U][(μ-Ph)2-
BPh2]8 and [(C5Me5)Sm][(μ-Ph)2BPh2],25 the (BPh4)ꢀ reduc-
tion combines with a metal-based reduction to give multielectron
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2142vs, 2097vs, 1494w, 1438s, 1385m, 1163w, 1061m, 1022m, 801w,
729w, 639m, 610m cmꢀ1. Anal. Calcd for C20H30N3Sm: C, 51.90; H,
6.53; N, 9.08. Found: C, 51.81; H, 6.43; N, 9.08. MS (ESI, MeCN) m/z
(rel intensity): 506.2 (100) {[(C5Me5)2Sm(N3)](N3)}ꢀ, 967.3 (28)
{[(C5Me5)2Sm(N3)]2(N3)}ꢀ, 1429.6 (8) {[(C5Me5)2Sm(N3)]3-
(N3)}ꢀ, 1894.9 (8) {[(C5Me5)2Sm(N3)]4(N3)}ꢀ.
[(C5Me5)2Sm(NCMe)(μ-N3)]3, 6. Yellow X-ray quality crystals of
6 were grown from a saturated solution of 5 in acetonitrile at ꢀ30 ꢀC.
When the mother liquor was removed and the crystals were allowed to
dry by evaporation, they became dull and dark yellow in color. These
dried solids were indistinguishable from 5 when analyzed by 1H NMR
and IR spectroscopy.
{[(C5Me5)2Sm(μ-N3)][(C5Me5)2Sm(NCMe)(μ-N3)]}n, 7. Yel-
low X-ray quality crystals of 7 were grown over 3 d by allowing a
concentrated solution of 5 in hot acetonitrile to cool slowly to room
temperature. The IR spectrum of these crystals was identical to that of
crude 5 isolated as a powder, except that an additional shoulder was
observed at 2090 cmꢀ1 in the azide stretching region.
[(C5Me5)2Y(OCMe2)2][BPh4], 8. A 100 mL Schlenk flask was
charged with a solution of 1 (70 mg, 0.10 mmol) in benzene (20 mL) in
the glovebox and transferred to a Schlenk line. The flask was connected
via a T-joint to another 100 mL Schlenk flask containing a 10:1 benzene/
acetone mixture (20 mL). Under a static atmosphere of dinitrogen, both
flasks were opened to allow slow diffusion of acetone into the solution of
1. Over 2 d, light yellow needle-like crystals formed in the colorless
solution. The crystals were collected by filtration, washed with benzene
and hexane, and dried under vacuum to obtain 8 (74 mg, 91%). 1H NMR
(THF-d8): δ 7.32 (br s, o-BPh4, 8H), 6.88 (t, 3JHH = 7.0 Hz, m-BPh4,
8H), 6.74 (t, 3JHH = 7.0 Hz, p-BPh4, 4H), 2.24 (s, Me2CO, 12H), 1.85 (s,
C5Me5, 30H). 13C NMR (THF-d8): δ 204.3 (Me2CO), 165.4 (BPh4),
137.4 (BPh4), 126.0 (BPh4), 122.1 (BPh4), 119.9 (C5Me5), 32.5
(Me2CO), 11.2 (C5Me5). IR: 3055s, 2984s, 2906s, 2863s, 1942w,
1881w, 1814w, 1772w, 1678vs, 1581s, 1480s, 1427s, 1370s, 1247s,
1183m, 1148m, 1067m, 1031m, 914w, 848m, 734vs, 706vs,
613s cmꢀ1. Anal. Calcd for C50H62BO2Y: C, 75.56; H, 7.86. Found:
C, 75.16; H, 7.42. MS (ESI, THF) m/z (rel intensity): 359.1 (26)
[(C5Me5)2Y]þ, 417.2 (100) [(C5Me5)2Y(OCMe2)]þ, 431.2 (97)
[(C5Me5)2Y(THF)]þ, 489.2 (3) [(C5Me5)2Y(OCMe2)(THF)]þ.
[(C5Me5)2Y(OCMe2)2][BPh4], 8, from [(C5Me5)2Y(THF)2]-
[BPh4] and Acetone. Two equivalents of acetone were vacuum
transferred to a frozen (ꢀ196 ꢀC) colorless solution of [(C5Me5)2Y-
(THF)2][BPh4] prepared from 1 (10 mg, 0.015 mmol) in THF-d8
(0.5 mL) in a J-Young NMR tube. The reaction mixture was warmed to
room temperature and over 15 min turned pale yellow. Complex 8 was
observed by 1H NMR spectroscopy as the only product.
solution immediately became red, and after 15 min of stirring the red
slurry was centrifuged and the supernatant discarded. The insoluble
material was washed with benzene and hexane and dried under vacuum
to yield 10 as a red orange powder (84 mg, 86%). When the reaction
mixture was filtered immediately after combining reagents and layered
with hexane, slow evaporation over 5 d yielded X-ray quality crystals. 1H
NMR (THF-d8, 5 ꢀC): δ 7.78 (d, 3JHH = 7.5 Hz, o-Ph2CO, 8H), 6.64 (br
s, m-Ph2CO, 4H), 7.60 (t, 3JHH = 7.5 Hz, m-Ph2CO, 4H), 7.50 (t, 3JHH
=
7.5 Hz, p-Ph2CO, 4H), 7.30 (m, o-BPh4, 8H), 6.86 (t, 3JHH = 7.0 Hz, m-
BPh4, 8H), 6.72 (t, 3JHH = 7.0 Hz, p-BPh4, 4H), 1.92 (s, C5Me5, 30H).
13C NMR (THF-d8, 5 ꢀC): δ 196.1 (Ph2CO), 165.3 (BPh4), 137.3
(BPh4), 133.2 (Ph2CO), 130.9 (Ph2CO), 129.2 (Ph2CO), 125.9 (BPh4),
122.0 (BPh4), 121.1 (C5Me5), 11.9 (C5Me5). 11B NMR (THF-d8,
ꢀ70 ꢀC): δ ꢀ5.99 (BPh4). IR: 3055m, 3033m, 3000m, 2982m,
2941m, 2905m, 2859m, 2156w, 1939w, 1879w, 1819w, 1656w, 1603s,
1558s, 1480s, 1448s, 1381m, 1327s, 1294s, 1160s, 1078m, 1032m,
999s, 941s, 842s, 810m, 771s, 734s, 705s, 636s, 613s cmꢀ1. Anal. Calcd
for C70H70BO2Y: C, 80.61; H, 6.76. Found: C, 80.64; H, 6.91.
[(C5Me5)2Y(OCPh2)2][BPh4], 10, from [(C5Me5)2Y(THF)2]-
[BPh4] and Benzophenone. A solution of [(C5Me5)2Y(THF)2]-
[BPh4] prepared from 1 (18 mg, 0.027 mmol) in THF (3 mL) was
combined with a solution of benzophenone (12 mg, 0.067 mmol) in
THF (1 mL). A red solution immediately formed, and the solvent was
removed under vacuum. Analysis of the resulting tacky red residue by 1H
NMR spectroscopy showed residual Ph2CO and 10 as the only
organometallic product.
[(C5Me5)2Sm(OCPh2)2][BPh4], 11. A solution of 2 (22 mg, 0.030
mmol) in benzene (5 mL) was added to a stirred solution of benzo-
phenone (12 mg, 0.067 mmol) in benzene (5 mL). The maroon red
solution quickly turned dark red and then to red orange. After 15 min of
stirring, the red slurry was centrifuged and the supernatant discarded.
The insoluble material was washed with benzene and hexane and dried
1
under vacuum to yield 11 as a red orange powder (25 mg, 75%). H
NMR (THF-d8, 5 ꢀC): δ 7.54 (t, 3JHH = 7.5 Hz, p-Ph2CO, 4H), 7.38 (br
s, o/m-Ph2CO, 16H), 7.20 (m, o-BPh4, 8H), 6.83 (t, 3JHH = 7.0 Hz, m-
BPh4, 8H), 6.73 (t, 3JHH = 7.0 Hz, p-BPh4, 4H), 0.92 (s, C5Me5, 30H).
13C NMR (THF-d8, 5 ꢀC): δ 165.2 (BPh4), 137.2 (BPh4), 134.0
(Ph2CO), 130.8 (Ph2CO), 129.2 (Ph2CO), 125.9 (BPh4), 122.0
(BPh4), 119.0 (C5Me5), 18.7 (C5Me5). The 13C resonance for Ph2CO
was not located. 11B NMR (THF-d8, ꢀ70 ꢀC): δ ꢀ6.06 (BPh4). IR:
3055m, 3034m, 2982m, 2905m, 2859m, 2728w, 2332w, 2239w, 1940w,
1818w, 1759w, 1656w, 1603s, 1554s, 1480s, 1448s, 1426s, 1383m,
1326s, 1291s, 1180s, 1159s, 1077s, 1032s, 999s, 976m, 941s, 923s, 842s,
811m, 770s, 734s, 704s, 636s, 613 cmꢀ1. Anal. Calcd for C70H70BO2Sm:
C, 76.12; H, 6.39. Found: C, 76.00; H, 6.31.
[(C5Me5)2Sm(OCMe2)2][BPh4], 9. As described for 8, acetone
was allowed to diffuse slowly into a solution of 2 (55 mg, 0.070 mmol) in
benzene (6 mL) yielding red orange needle-like crystals. The crystals
were washed with benzene and hexane and dried under vacuum to
obtain 9 (55 mg, 91%). 1H NMR (THF-d8): δ 7.17 (br s, o-BPh4, 8H),
6.79 (t, 3JHH = 7.0 Hz, m-BPh4, 8H), 6.68 (t, 3JHH = 7.0 Hz, p-BPh4, 4H),
1.18 (s, Me2CO, 12H), 0.77 (s, C5Me5, 30H). 13C NMR (THF-d8): δ
217.1 (Me2CO), 165.2 (BPh4), 137.2 (BPh4), 125.8 (BPh4), 122.0
(BPh4), 118.1 (C5Me5), 30.2 (Me2CO), 18.5 (C5Me5). IR: 3054s, 2984s,
2906s, 2861s, 1942w, 1880w, 1814w, 1772w, 1676vs, 1581s, 1480s,
1427s, 1370s, 1246s, 1183m, 1148m, 1067m, 1031m, 914w, 847m,
734vs, 706vs, 606s cmꢀ1. Anal. Calcd for C50H62BO2Sm: C, 70.14; H,
7.30. Found: C, 69.45; H, 7.28. MS (ESI, THF) m/z (rel intensity):
422.1 (22) [(C5Me5)2Sm]þ, 480.2 (33) [(C5Me5)2Sm(OCMe2)]þ,
494.2 (100) [(C5Me5)2Sm(THF)]þ, 552.2 (5) [(C5Me5)2Sm(OCMe2)-
(THF)]þ.
[(C5Me5)2Y(phen)][BPh4], 12. A solution of phenanthroline (10
mg, 0.055 mmol) in benzene (3 mL) was added to a stirred solution of 1
(36 mg, 0.053 mmol) in benzene (10 mL). The mixture immediately
turned cloudy yellow. After 15 min, the insoluble material was obtained
by centrifugation and removal of the supernatant. The solids were dried
under vacuum to yield 12 as a bright yellow powder (43 mg, 94%).
Crystals suitable for X-ray diffraction were grown over several days from
a concentrated THF solution at ꢀ35 ꢀC. 1H NMR (THF-d8, 5 ꢀC): δ
8.47 (m, phen, 4H), 7.92 (s, phen, 2H), 7.81 (dd, phen, 2H), 7.40 (br s, o-
BPh4, 8H), 6.87 (t, 3JHH = 7.0 Hz, m-BPh4, 8H), 6.72 (t, 3JHH = 7.0 Hz, p-
BPh4, 4H), 1.63 (s, C5Me5, 30H). 13C NMR (THF-d8, 5 ꢀC): δ 165.4
(BPh4), 150.2 (phen), 143.2 (phen), 142.8 (phen), 137.4 (BPh4), 131.7
(phen), 129.5 (phen), 126.4 (phen), 126.1 (BPh4), 122.3 (BPh4), 120.3
(C5Me5), 11.0 (C5Me5). 11B NMR (THF-d8, ꢀ70 ꢀC): δ ꢀ5.96 (BPh4).
IR: 3056m, 3035m, 2907m, 2860m, 2730w, 1944w, 1881w, 1819w, 1764w,
1625m, 1580m, 1523s, 1479s, 1425s, 1380 m, 1340w, 1301w, 1266m,
1221w, 1184w, 1146m, 1105m, 1065w, 1032 m, 912w, 849s, 803w, 777w,
731s, 705s, 682s, 644 m, 613s, 509w cmꢀ1. Anal. Calcd for C56H58BN2Y:
C, 78.32; H, 6.81; N, 3.26. Found: C, 78.60; H, 6.89; N, 2.99.
[(C5Me5)2Y(OCPh2)2][BPh4], 10. A solution of 1 (72 mg, 0.11
mmol) in benzene (10 mL) was added to a stirred solution of
benzophenone (34 mg, 0.19 mmol) in benzene (4 mL). The combined
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Inorganic Chemistry
ARTICLE
[(C5Me5)2Y(phen)][BPh4], 12, from [(C5Me5)2Y(THF)2]-
[BPh4] and Phenanthroline. A solution of [(C5Me5)2Y(THF)2]-
[BPh4] prepared by dissolving 1 (26 mg, 0.038 mmol) in THF (3 mL)
was combined with a solution of phenanthroline (7 mg, 0.04 mmol) in
THF (1 mL). A yellow solution immediately formed, and the solvent
was removed under vacuum. Analysis of the resulting tacky yellow
residue by 1H NMR spectroscopy showed residual phenanthroline and
12 as the only organometallic product.
(ESI, C6H6) m/z (rel intensity): 359.1 (20) [(C5Me5)2Y]þ, 541.2 (100)
[(C5Me5)2Y(PhNNPh)]þ; 319.2 (100) [BPh4]ꢀ. IR: 3600w, 3056m,
3034m, 2985m, 2909m, 2861m, 2732w, 1938w, 1876w, 1810w, 1760w,
1581s, 1479s, 1440s, 1382m, 1316w, 1268w, 1164m, 1066m, 1032m,
999m, 938w, 902w, 846m, 772s, 730vs, 703vs, 680s, 606s, 518w cmꢀ1
.
Anal. Calcd for C56H60BN2Y: C, 78.14; H, 7.03; N, 3.25. Found: C,
77.15; H, 6.86; N, 3.02.
(C5Me5)2Y(PhNNPh), 16. A dark brown suspension of 15 (112
mg, 0.128 mmol, from several preparations as described above) in
benzene (15 mL) was heated at reflux for 1 h, during which time it
became a green solution. The solvent was removed under vacuum to
yield a tacky mixture of green and colorless solids. Extraction of this
mixture with hexane and removal of solvent gave an oily green residue
containing 16. Complex 16 is NMR silent, but the green oil was found to
[(C5Me5)2Y(py)2][BPh4], 13. Pyridine (24 mg, 0.30 mmol) was
diluted with benzene (5 mL) and was added to a stirred solution of 1 (74
mg, 0.11 mmol) in benzene (7 mL). A white precipitate immediately
formed. After stirring for 15 min, the reaction mixture was centrifuged
and the supernatant removed. The solids were washed with benzene and
hexane and dried under vacuum to yield 13 as a white powder (71 mg,
77%). The 1H NMR spectrum of 13 in THF-d8 showed three (C5Me5)ꢀ
resonances, one of which was attributed to [(C5Me5)2Y(THF)2][BPh4]
at 1.92 ppm, and several sets of pyridine peaks, including free pyridine.
1H NMR (pyridine-d5): δ 8.15 (br s, o-BPh4, 8H), 7.35 (t, 3JHH = 7.0 Hz,
m-BPh4, 8H), 7.17 (t, 3JHH = 7.0 Hz, p-BPh4, 4H), 1.67 (s, C5Me5, 30H).
The 1H and 13C resonances of the pyridine ligands were not observed
because of exchange with pyridine-d5. 13C NMR (pyridine-d5): δ 165.5
(BPh4), 137.6 (BPh4), 126.1 (BPh4), 122.8 (BPh4), 120.9 (C5Me5), 11.0
(C5Me5). 11B NMR (pyridine-d5): δ ꢀ5.96 (BPh4). IR: 3055m, 2983m,
2908m, 2862m, 2731w, 2472w, 1942w, 1884w, 1817w, 1764w, 1702w,
1638w, 1602s, 1580s, 1480s, 1441s, 1381m, 1307w, 1267m, 1217s,
1182m, 1158m, 1067s, 1030s, 1008s, 948m, 915w, 846s, 802w, 733s,
708s, 614s cmꢀ1. Anal. Calcd for C54H60BN2Y: C, 77.51; H, 7.23; N,
3.35. Found: C, 76.98; H, 7.55; N, 3.32.
1
contain BPh3 and Ph2 by H and 11B NMR spectroscopy. MS (ESI,
hexane) m/z (rel intensity): 541.2 (100) [(C5Me5)2Y(PhNNPh)]þ.
EPR (hexane): g = 2.004; aN = 8.25 G (2N); aH = 2.40 G (6H), 0.95 G
(4H); aY = 1.95 G (1Y).
{[(C5Me5)2Y]2(phz)}{BPh4}, 17. Phenazine (7 mg, 0.04 mmol)
and 1 (52 mg, 0.077 mmol) were combined in benzene (10 mL) and
stirred for 2 d, during which time the amber solution turned dark green.
After the solvent was removed under vacuum, the brown tacky solids
were washed with hexane and dried under vacuum. The solids were
dissolved in hot benzene (4 mL), and hexane was slowly diffused into the
solution over 2 d to yield 17 as dark green X-ray quality crystals (35 mg,
74%). When the reaction was monitored by 1H NMR spectroscopy in
C6D6, the resonances of the starting materials gradually diminished and
resonances for BPh3 and Ph2 grew in. Complex 17 is NMR silent as there
were no resonances attributable to (C5Me5)ꢀ or (phz)ꢀ in the 1H NMR
spectrum. EPR (benzene): g = 2.005; aN = 5.44 G (2N); aH = 1.68 G
(4H), 0.95 G (4H); aY = 1.18 G (2Y). IR: 3033m, 2965m, 2909m,
2861m, 1935w, 1876w, 1813w, 1759w, 1655w, 1604m, 1579m, 1532m,
1480m, 1429m, 1381m, 1326s, 1261m, 1185w, 1153m, 1064m, 1031m,
901s, 824m, 800w, 732s, 703s, 679s, 613s cmꢀ1. Anal. Calcd for
C76H92BN2Y: C, 74,69; H, 7.59; N, 2.29. Found: C, 74.93; H, 7.48;
N, 2.19.
[(C5Me5)2Sm(py)2][BPh4], 14. As described for 13, pyridine (17
mg, 0.21 mmol) was combined with 2 (50 mg, 0.068 mmol) to produce
an orange reaction mixture, from which 14 was isolated as a light orange
powder (41 mg, 67%). X-ray quality crystals of 14 were grown by slow
diffusion of pyridine into a benzene solution of 2 over 4 d. The 1H NMR
spectrum of 14 in THF-d8 showed [(C5Me5)2Sm(THF)2][BPh4]11 as
the major component and several sets of pyridine peaks, including free
pyridine. 1H NMR (pyridine-d5): δ 8.11 (br s, o-BPh4, 8H), 7.33 (t, 3JHH
=
3
[(C5Me5)2Y]2(phz), 18. A solution of 17 (15 mg, 0.012 mmol) in
C6D6 (0.5 mL) was sealed in a J-Young NMR tube and heated at 70 ꢀC
over 2 d. The dark green solution slowly turned red and two different
diamagnetic phenazine-containing products were identified along with
BPh3, Ph2, and 5,10-dihydrophenazine (phzH2) in the 1H NMR
spectrum. The assignments of 5,10-dihydrophenazine were confirmed
by comparison to an independently synthesized sample.49 Red crystals
of 18 suitable for X-ray diffraction were grown at room temperature over
several weeks via slow evaporation of an NMR sample of 17 in C6D6. 1H
NMR (C6D6): 18, δ 6.07 (m, phz, 4H), 4.88 (m, phz, 4H), 2.11 (s,
C5Me5, 60H); (C5Me5)2Y(phzH), δ 6.24 (m, phzH, 4H), 5.42 (m,
phzH, 2H), 4.94 (m, phzH, 2H), 3.74 (br s, phzH, 1H), 1.98 (s, C5Me5,
30H); phzH2, δ 6.46 (m, phzH2, 4H), 5.70 (m, phzH2, 4H), 3.94 (br s,
phzH2, 2H).
7.0 Hz, m-BPh4, 8H), 7.16 (t, JHH = 7.0 Hz, p-BPh4, 4H), 0.87 (s,
C5Me5, 30H). The 1H and 13C resonances of the pyridine ligands were
not observed because of exchange with pyridine-d5. 13C NMR (pyridine-
d5): δ 165.6 (BPh4), 137.6 (BPh4), 126.1 (BPh4), 122.8 (BPh4), 118.5
(C5Me5), 17.9 (C5Me5). 11B NMR (pyridine-d5): δ ꢀ5.64 (BPh4). IR:
3055m, 2983m, 2907m, 2860m, 2731w, 2361w, 1944w, 1884w, 1818w,
1767w, 1635w, 1600s, 1580m, 1479s, 1441s, 1384m, 1267m, 1217m,
1182m, 1158m, 1068s, 1041m, 1007s, 946w, 915w, 846 m, 802w, 733s,
704s, 606s cmꢀ1. Anal. Calcd for C54H60BN2Sm: C, 72.21; H, 6.73; N,
3.12. Found: C, 71.96; H, 6.80; N, 3.08.
[(C5Me5)2Y(PhNNPh)][BPh4], 15. PhNdNPh (4.2 mL of a 0.023
M solution in methylcyclohexane, 0.097 mmol) was added via syringe to
a slurry of 1 (65 mg, 0.096 mmol) in methylcyclohexane (15 mL). After
42 h, the orange mixture had turned brown, and the brown solids were
collected by centrifugation, washed twice with benzene and twice with
hexane, and dried under vacuum to yield 15 as a fine brown powder (40
mg, 48%). 1H NMR (C6D6): δ 8.10 (br s, NPh, 10H), 7.67 (d, 3JHH = 5.5
Reaction of 1 with Fluorenone. A solution of fluorenone,
C7H8O, (15 mg, 0.083 mmol) in benzene (5 mL) was added to a
stirred solution of 1 (55 mg, 0.081 mmol) in benzene (5 mL). The
mixture quickly became dark burgundy in color. After 20 min of stirring,
the resulting precipitate was collected by centrifugation, washed with
benzene, and dried under vacuum to yield a dark burgundy powder (34
mg). The supernatant contained unreacted 1 and BPh3 when analyzed
by 1H and 11B NMR spectroscopy. The solids were dissolved in THF-d8,
and both diamagnetic and paramagnetic species, consistent with
[(C5Me5)2Y(OC7H8)(THF)x][BPh4] and (C5Me5)2Y(OC7H8)n-
Hz, o-BPh4, 8H), 7.32 (m, 3JHH = 5.5, 7.0 Hz, m-BPh4, 8H), 7.25 (t, 3JHH
=
7.0 Hz, p-BPh4, 4H), 1.59 (s, C5Me5, 30H); (THF-d8, ꢀ70 ꢀC): δ 7.60
(m, NPh, 1H), 7.53 (m, NPh, 2H), 7.51 (br s, NPh, 2H), 7.34 (s, NPh,
2H), 7.28 (t, 3JHH = 8.0 Hz, NPh, 1H), 7.25 (br s, o-BPh4, 8H), 7.15 (t,
3JHH = 7.5 Hz, NPh, 1H), 6.86 (t, 3JHH = 7.5 Hz, m-BPh4, 8H), 6.83 (m,
NPh, 1H), 6.73 (t, 3JHH = 7.0 Hz, p-BPh4, 4H), 1.91 (s, C5Me5, 30H).
13C NMR (THF-d8, ꢀ70 ꢀC): δ 164.9 (BPh4), 154.7 (NPh), 150.0
(NPh), 137.1 (BPh4), 136.0 (NPh), 132.8 (NPh), 132.2 (NPh), 131.1
(NPh), 129.7 (NPh), 127.9 (NPh), 127.1 (NPh), 125.8 (BPh4), 122.0
1
(THF)x (n = 1, 2), respectively, were observed by H, 13C, and 11B
NMR and EPR spectroscopy. The EPR spectrum of the THF solution
supports the formation of a fluorenone radical complex. 1H NMR (THF-d8,
ꢀ70 ꢀC): δ 7.76 (d, 3JHH = 7.5 Hz, C7H8O, 2H), 7.63 (d, 3JHH = 7.5 Hz,
(BPh4), 121.3 (NPh), 120.9 (NPh), 119.6 (C5Me5), 12.0 (C5Me5). 11
NMR (C6D6): δ ꢀ5.85 (BPh4); (THF-d8, ꢀ70 ꢀC): ꢀ6.07 (BPh4). MS
B
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Inorganic Chemistry
ARTICLE
Table 1. X-ray Data Collection Parameters for [(C5Me5)2Y(μ-N3)]3, 4, [(C5Me5)2Sm(NCMe)(μ-N3)]3, 6, {[(C5Me5)2Sm(μ-
N3)][(C5Me5)2Sm(NCMe)(μ-N3)]}n, 7, [(C5Me5)2Y(OCMe2)2][BPh4], 8, and [(C5Me5)2Sm(OCMe2)2][BPh4], 9
4
6
7
8
9
empirical formula
fw
C60H90N9Y3
1204.14
93(2)
C66H99N12Sm3 6(CH3CN)
[C42H63N7Sm2]¥
966.69
C50H62BO2Y
794.72
C50H62BO2Sm
856.16
3
1757.95
148(2)
trigonal
P3
temp (K)
crys syst
space group
a (Å)
93(2)
93(2)
98(2)
monoclinic
C2/c
triclinic
monoclinic
P2/c
monoclinic
P2/c
P1
22.2813(8)
14.5879(6)
19.2893(7)
90
27.1898(15)
27.1898(15)
19.8371(11)
90
10.8241(4)
14.1064(5)
14.3236(5)
86.1256(4)
79.4371(4)
83.4938(4)
2133.70(13)
2
10.3246(4)
14.1253(6)
15.5657(7)
90
10.3283(3)
14.1678(5)
15.6546(5)
90
b (Å)
c (Å)
R (deg)
β (deg)
γ(deg)
105.7323
90
90
105.1600(10)
90
105.3136(4)
90
120
volume (Å3)
6034.9(4)
4
12700.5(12)
6
2191.07(16)
2
2209.39(12)
2
Z
F
calcd (mg/m3)
μ (mmꢀ1
1.325
1.379
1.505
1.205
1.287
)
2.905
2.103
2.761
1.368
1.366
R1a (I > 2.0σ(I))
0.0247
0.0252
0.0236
0.0321
0.0155
wR2b (all data)
0.0642
0.0623
0.0564
0.0782
0.0389
a R1 = ∑||Fo| ꢀ |Fc||/∑|Fo|. b wR2 = [∑w(Fo ꢀ Fc2)2/∑w(Fo ) ]
.
2
2 2 1/2
C7H8O, 2H), 7.60 (t, 3JHH = 7.5 Hz, C7H8O, 2H), 7.39 (t, 3JHH = 7.5 Hz,
C7H8O, 2H), 7.28 (br s, o-BPh4, 8H), 6.88 (t, 3JHH = 7.5 Hz, m-BPh4, 8H),
6.75 (t, 3JHH = 7.5 Hz, p-BPh4, 4H), 1.92 (br s, C5Me5, 30H). 13C NMR
(THF-d8, 5 ꢀC): δ 165.4 (BPh4), 137.4 (BPh4), 125.9 (BPh4), 122.0
(C5Me5), 11.8 (C5Me5), the 13C resonances of fluorenone could not be
located. 11B NMR (THF-d8): δ ꢀ6.1 (BPh4). EPR (THF): g = 2.003; aH =
3.36 G (2H), 0.73 G (2H), 2.76 G (2H), 0.61 G (2H); aY = 0.63 G (1Y).
X-ray Data Collection, Structure Determination, and Re-
finement. Crystallographic information for complexes 4, 6, 7, 8, 9, 10,
12, 14, 17, and 18 is summarized in the Supporting Information and
Tables 1 and 2.
Elemental analyses of 3 and 5 were consistent with their
expected elemental compositions. The negative ESI-MS spectra
of millimolar solutions of 3 and 5 in MeCN, Figure 1, show
several mass peaks that correspond to the exact masses of mono-,
bi-, tri-, and tetra-metallic species containing (C5Me5)ꢀ and
1
(N3)ꢀ ligands. Variable-temperature H NMR studies of 5 in
CD3CN revealed only one (C5Me5)ꢀ resonance between ꢀ30
and 60 ꢀC.
Analysis of these complexes by IR spectroscopy revealed two
strong absorptions at 2164 and 2116 cmꢀ1 for 3 and 2142 and
2097 cmꢀ1 for 5. These absorptions are in the region typical for
the asymmetric stretch observed in coordinated azides.50 These
sharp absorption bands differ from the broad absorption band of
NaN3 at 2129 cmꢀ1, but are similar to the 2115 cmꢀ1 band for
’ RESULTS
35
Synthesis of Lanthanide Metallocene Azides. The reaction
of 1 and 2 with 1 equiv of NaN3 yields [(C5Me5)2LnN3]x (Ln =
Y, 3; Sm, 5), eq 4. The reaction proceeds slowly in benzene,
most likely because of the insolubility of NaN3. The reaction
time is greatly reduced when THF is used as the solvent and
[(C5Me5)2Ln(THF)2][BPh4], formed in situ, is the starting
material. Even in THF, the same unsolvated complexes, 3 and
5, are isolated.
{(C5Me5)2La[CNN(SiMe3)2](μ-N3)}3 and the 2111 and
2073 cmꢀ1 bands for [(C5Me5)2U(N3)(μ-N3)]3.51 The pre-
sence of two azide stretches in each complex suggests that there
are multiple azide sites in these solids.
A crystalline derivative of 5 was obtained from MeCN at
ꢀ30 ꢀC and was found to be the cyclic trimer [(C5Me5)2Sm(NCMe)-
(μ-N3)]3, 6, by X-ray diffraction, Figure 2. The structure of 6 in the
solid state has a 3-fold rotational axis down the center of the 12-
membered ring, and the bridging azides are in the plane of the three
metals. Similar arrangements of bridging azides are found in
35
{(C5Me5)2La[CNN(SiMe3)2](μ-N3)}3 and [(C5Me5)2U(N3)
(μ-N3)]3.51 In these complexes, as well as 6, the metal is fully
saturated with a formal coordination number of nine.
Complex 5 crystallized with only one MeCN per two samar-
ium ions when a hot acetonitrile solution was allowed to cool to
room temperature. X-ray diffraction revealed that these yellow
crystals existed as a polymeric samarium azide chain, {[(C5Me5)2-
Sm(μ-N3)][(C5Me5)2Sm(NCMe)(μ-N3)]}n, 7. Figure 3 shows
two repeat units of this polymer, in which the two crystallographi-
cally independent samarium positions are arranged (Sm1ꢀSm1ꢀ
Sm2ꢀSm2)n rather than (Sm1ꢀSm2ꢀSm1ꢀSm2)n. The equiva-
lent metallocene units are symmetry related by inversion at N1 and
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Inorganic Chemistry
ARTICLE
Table 2. X-ray Data Collection Parameters for [(C5Me5)2Y(OCPh2)2][BPh4], 10, [(C5Me5)2Y(phen)][BPh4], 12,
[(C5Me5)2Sm(py)2][BPh4], 14, {[(C5Me5)2Y]2(phz)}{BPh4}, 17, and [(C5Me5)2Y]2(phz), 18
10
12
14
17
18
empirical formula
fw
C
70 H70BO2Y
C64H74BN2O2Y
1002.97
143(2)
orthorhombic
P212121
11.0392(5)
15.5736(8)
31.0265(15)
90
C54H60BN2Sm
898.20
[C52H68N2Y2] [C24H20B](C6H6)
C52H68N2Y2(C6H6)
977.01
1042.98
143(2)
monoclinic
P21/c
1296.22
93(2)
temp (K)
crys syst
space group
a (Å)
93(2)
148(2)
monoclinic
P2/c
orthorhombic
P212121
13.6157(5)
18.4964(7)
27.1343(10)
90
triclinic
P1
10.9624(5)
14.7189(7)
34.3027(17)
90
10.3569(4)
14.1863(5)
16.1998(6)
90
10.5327(5)
10.9558(5)
11.2847(5)
79.5057(6)
75.6293(6)
85.1580(6)
1239.29(10)
1
b (Å)
c (Å)
R (deg)
β (deg)
γ(deg)
92.5507(7)
90
90
106.8571(4)
90
90
90
90
volume (Å3)
5529.4(5)
4
5334.1(4)
4
2277.90(15)
2
6833.5(4)
4
Z
F
calcd (mg/m3)
μ (mmꢀ1
1.253
1.249
1.310
1.260
1.309
)
1.101
1.139
1.326
1.735
2.368
R1a (I > 2.0σ(I))
wR2b (all data)
0.0413
0.0400
0.0182
0.0335
0.0729
0.0282
0.0956
0.0980
0.0464
0.0725
a R1 = ∑||Fo| ꢀ |Fc||/∑|Fo|. b wR2 = [∑w(Fo ꢀ Fc2)2/∑w(Fo ) ]
.
2
2 2 1/2
Figure 1. Negative ESI-MS spectra of (a) 3 and (b) 5 in MeCN. Mass peaks corresponding to (BPh4)ꢀ, [Na(BPh4)2]ꢀ, and [K(BPh4)2]ꢀ ions were
omitted for clarity.
N7. Complex 7 contains both solvated nine coordinate and
unsolvated eight coordinate samarium centers.
Surprisingly, a crystalline unsolvated cyclic trimeric derivative
of 3, namely, [(C5Me5)2Y(μ-N3)]3, 4, could also be isolated and
characterized by X-ray diffraction, Figure 4. The crystals were
obtained from the reaction of 1 with 1-adamantyl azide, eq 5, a
reaction that involves reduction of the organic azide. Since the
1
mother liquor contained BPh3, identified by H and 11B NMR
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Inorganic Chemistry
ARTICLE
Figure 2. ORTEP52 of [(C5Me5)2Sm(NCMe)(μ-N3)]3, 6, shown at the 50% probability level from the (a) axial and (b) equatorial viewpoints. The
hydrogen atoms have been omitted for clarity.
spectroscopy, and GC-MS analysis revealed peaks for adaman-
tane, adamantylbenzene, and biphenyl, the (BPh4)ꢀ anion was
presumably the component that reduced 1-adamantyl azide
according to eq 3. The IR spectrum of the crystals was identical
to that of samples of 3 isolated as a powder. The solid-state
structure of the unsolvated 4, shown in Figure 4, has major
differences from that of 6. Complex 4 has a 2-fold rotational axis
between Y1 and N5, and only the central nitrogen atoms of the
bridging azides are in the trimetallic plane (within 0.06 Å).
Figure 3. ORTEP of two repeat units of {[(C5Me5)2Sm(μ-N3)]-
[(C5Me5)2Sm(NCMe)(μ-N3)]}n, 7, shown at the 50% probability level.
Only one component of the disordered (C5Me5)ꢀ ligands is shown. The
hydrogen atoms have been omitted for clarity.
The N(azide)ꢀLnꢀN(azide) angles for the eight coordinate
metals in these complexes are in the range of 88.42(8)ꢀ90.89-
(9)ꢀ, but they are smaller for nine coordinate metals, 74.20-
(7)ꢀ76.47(9)ꢀ. The absence of an additional coordinating
ligand in 4 not only affects these N(azide)ꢀLnꢀN(azide) angles
but it also allows 4 to adopt the more regular triangular shape
than found in 6 and 19. In the latter molecules, the presence of
the extra ligand to one side of the wedge leads to asymmetry in
the location of the two azide ligands: one azide is in the center
and one is at the side of the wedge. This results in a more kinked
structure shown in Figure 2a. A similar arrangement is found in
[(C5Me5)2U(N3)(μ-N3)]3.51 The NꢀN bond distances within
the azide ligands in 4, 6, and 7 are within the conventional range,
1.163(1)ꢀ1.182(3) Å, and the NꢀNꢀN angles were measured
to be between 177.4(3) and 179.997(2)ꢀ.
Reactivity of [(C5Me5)2Ln][(μ-Ph)2BPh2] with Ketones.
Slow diffusion of acetone into a solution of 1 in benzene
produced pale yellow crystals of [(C5Me5)2Y(OCMe2)2][BPh4],
8, eq 6. The reaction was repeated in the same manner with 2
and acetone to produce the analogous product [(C5Me5)2Sm
Structural Analysis of [(C5Me5)2Y(μ-N3)]3, 4, [(C5Me5)2Sm-
(NCMe)(μ-N3)]3, 6, and {[(C5Me5)2Sm(μ-N3)][(C5Me5)2Sm-
(NCMe)(μ-N3)]}n, 7. Crystallographic data on 4, 6, and 7 are
presented in Table 3 along with a comparison to {(C5Me5)2La-
[CNN(SiMe3)2](μ-N3)}3,35 19. The Lnꢀ(C5Me5 ring cen-
troid) and LnꢀN(azide) distances in these complexes are all
similar when the differences in ionic radii are considered: eight
coordinate Y3þ, 1.019 Å; eight coordinate Sm3þ, 1.079 Å; nine
coordinate Sm3þ, 1.132 Å; and nine coordinate La3þ, 1.216 Å.37
The (C5Me5 ring centroid)ꢀLnꢀ(C5Me5 ring centroid) angles
are all very similar to each other and to other known examples.53
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Figure 4. ORTEP of [(C5Me5)2Y(μ-N3)]3, 4, shown at the 50% probability level from the (a) axial and (b) equatorial viewpoints. The hydrogen atoms
have been omitted for clarity.
2.261(1) Å YꢀO(benzophenone) distances in 10. Hence, both
ketones bind similarly. However, within 10 there are surprising
differences. Despite equivalent YꢀO(benzophenone) bond
lengths, the Y1ꢀO2ꢀC34 and analogous Y1ꢀO1ꢀC21 bond
angles are very different: 172.4(1)ꢀ and 164.7(1)ꢀ. This is
another good example of the lack of correlation of bond angle
and bond length with oxygen bound ligands.54,55
The structure of 9 allows comparisons with [(C5Me5)2Sm-
(THF)2][BPh4], 20.11 The two equivalent 2.363(1) Å SmꢀO-
(acetone) distances in 9 are significantly shorter than the 2.46(1)
Å SmꢀO(THF) distance measured in 20.11 However, the 2.423 Å
Smꢀ(C5Me5 ringcentroid) distance and the92.9(4)ꢀ OꢀSmꢀO
and 134.2ꢀ (C5Me5 ring centroid)ꢀSmꢀ(C5Me5 ring centroid)
angles in 20 are very similar to those of 9. The shorter distances
suggest tighter binding of the ketone compared to THF, which
is consistent with the THF ligands being displaced by the
ketones.
(OCMe2)2][BPh4], 9, as red-orange crystals. The crystalline
Reactivity of [(C5Me5)2Ln][(μ-Ph)2BPh2] with Nitrogen
products were identified by X-ray crystallography, Figure 5a, and
Donor Atom Substrates. One equivalent of phenanthroline
characterized by 1H and 13C NMR and IR spectroscopy, as well
(phen) reacts with 1 to make yellow [(C5Me5)2Y(phen)][BPh4],
as by mass spectrometry and elemental analysis. Complex 8 was
12, eq 7, which can be crystallized from THF at ꢀ35 ꢀC, Figure 6a.
also formed by reacting acetone with the solvated cation,
Phenanthroline also reacts with [(C5Me5)2Y(THF)2][BPh4] in
[(C5Me5)2Y(THF)2][BPh4], in THF.
THF to form 12 as identified by 1H NMR spectroscopy. Pyridine
Benzophenone reacts with the unsolvated cation complexes 1
and 2 to form the analogous bis(ketone) adducts, [(C5Me5)2Ln-
(OCPh2)2][BPh4] (Ln = Y, 10; Sm, 11), eq 6. Slow evaporation
of the filtered reaction solution of 1 and benzophenone depos-
ited red orange crystals of 10, which were analyzed by X-ray
diffraction, Figure 5b. Addition of benzophenone to a THF solution
of 1 also yields 10, as identified by 1H NMR spectroscopy.
Structural Analysis of [(C5Me5)2Y(OCMe2)2][BPh4], 8,
[(C5Me5)2Sm(OCMe2)2][BPh4], 9, and [(C5Me5)2Y(OCPh2)2]-
[BPh4], 10. Table 4 summarizes structural information for 8ꢀ10.
These formally eight coordinate complexes display metrical
parameters typical for lanthanide metallocenes with two addi-
tional ligands. Complexes 8 and 9 have very similar structures
and the lanthanide based bond distances vary by the difference in
ionic radii of eight coordinate Sm3þ, 1.079 Å, and Y3þ, 1.019 Å.37
Complex 10 has slightly larger Yꢀ(C5Me5 ring centroid)
distances and a larger (C5Me5 ring centroid)ꢀYꢀ(C5Me5 ring
centroid) angle compared to 8, presumably because of the larger
(py) reacts with 1 and 2 to form the bis(pyridine) adducts
[(C5Me5)2Ln(py)2][BPh4] (Ln = Y, 13; Sm, 14), eq 8. Orange
size of the benzophenone ligands versus acetone. The 2.271(1) Å
YꢀO(acetone) distance in 8 is very similar to the 2.268(1) and
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Table 3. Selected Bond Distances (Å) and Angles (deg) for [(C5Me5)2Y(μ-N3)]3, 4, [(C5Me5)2Sm(NCMe)(μ-N3)]3, 6,
{[(C5Me5)2Sm(μ-N3)][(C5Me5)2Sm(NCMe)(μ-N3)]}n, 7, and {(C5Me5)2La[CNN(SiMe3)2](μ-N3)}3, 19
4
6
7
19
LnꢀCnt
2.345, 2.348
2.470, 2.454
2.460, 2.459
2.454, 2.461
2.435(2)
2.474(2)
2.444(2)
2.474(2)
2.455(2)
2.480(2)
2.588(2)
2.568(2)
2.582(2)
138.7, 138.1
136.9
2.428, 2.413
2.443, 2.440
2.572, 2.544
LnꢀN(N3)
2.335(1)
2.397(2)
2.400(2)
2.473(2)
2.484(2)
2.535(2)
2.556(3)
2.335(1)
2.321(1), 2.335(1)
LnꢀLa
2.600(2)
2.811(3)
CntꢀLnꢀCnt
139.0, 140.4
137.5, 140.8
139.0
N(N3)ꢀLnꢀN(N3)
88.42(8)
88.46(6)
74.87(7)
74.20(7)
74.32(7)
90.89(9),
75.35(8)
76.47(9)
a For 6 and 7, L = N(NCMe); for 19, L = C[CNN(SiMe3)2].
Figure 5. ORTEP of (a) [(C5Me5)2Sm(OCMe2)2][BPh4], 9, and (b) [(C5Me5)2Y(OCPh2)2][BPh4], 10, shown at the 50% probability level. Only
one component of the disorder in the structure of 9 is shown. The hydrogen atoms have been omitted for clarity. The yttrium acetone analog, 8,
crystallized in a different space group, but has a molecular structure very similar to 9.
Table 4. Selected Bond Distances (Å) and Angles (deg) for
[(C5Me5)2Y(OCMe2)2][BPh4], 8, [(C5Me5)2Sm(OCMe2)2]-
[BPh4], 9, and [(C5Me5)2Y(OCPh2)2][BPh4], 10
[(C5Me5)2Ln(L)x][BPh4]
8
9
10
LnꢀCnt
LnꢀO
2.328
2.391
2.358, 2.366
2.271(1) 2.3633(9), 2.268(1),
2.363(1) 2.261(1)
133.6 140.3
CntꢀLnꢀCnt
OꢀLnꢀO
LnꢀOꢀC
133.6
91.88(7) 92.55(6)
176.1(1) 174.8(1)
95.11(5)
164.7(1), 172.4(1)
crystals of 14 were obtained by diffusion of pyridine into a
benzene solution of 2, Figure 6b. In contrast to the reactions
above, 13 and 14 cannot be isolated cleanly from the THF
solvated cations.11 When 13 and 14 are dissolved in THF,
[(C5Me5)2Ln(THF)2][BPh4] is formed, along with free
pyridine.
The reaction of 1 with 1 equiv of PhNdNPh in methylcyclo-
hexane yields a brown precipitate over 2 days. The H NMR
spectrum of this product in C6D6 shows a single resonance for
1
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Figure 6. ORTEP of (a) [(C5Me5)2Y(phen)][BPh4], 12, and (b) [(C5Me5)2Sm(py)2][BPh4], 14, shown at the 50% probability level. Only one
component of the disorder in the structure of 14 is shown. The hydrogen atoms have been omitted for clarity.
two (C5Me5)ꢀ groups, a broad aromatic resonance which
integrates to 10 protons, and new (BPh4)ꢀ resonances. A sharp
resonance at ꢀ5.85 ppm in the 11B NMR spectrum indicates that
(BPh4)ꢀ is present and not BPh3 (68.0 ppm47). The data are
consistent with the formation of the azobenzene salt,
[(C5Me5)2Y(PhNNPh)][BPh4], 15, eq 9. Complex 15 was also
characterized by ESI-MS, IR spectroscopy, and elemental
analysis.
The EPR spectrum of 16, Figure 7a, shows five major
resonances separated by 8.25 G, which is the splitting pattern
expected for an unpaired electron coupled to two 14N nuclei (I =
1). Typical 14N hyperfine coupling constants for free
(PhNNPh)ꢀ are around 4 to 5 G.56,57 The EPR spectrum also
shows hyperfine splitting attributable to coupling of an unpaired
electron with the protons on the phenyl rings of (PhNNPh)ꢀ.
The 1H coupling constants were determined through simulation
to be 0.95 and 2.40 G. Proton hyperfine coupling constants of
K(PhNNPh) are found to be in the range of 0.61 to 3.20 G.57,58
Coupling to a single 89Y nucleus is also observed, with a coupling
constant of 1.95 G. The simulated EPR spectrum with these
parameters, Figure 7b, agrees well with the experimental data. An
isotropic g value of 2.004 was measured for 16 using DPPH as a
calibrant. This suggests that the radical is mainly ligand-centered.
The NMR and EPR data are consistent with a (PhNNPh)ꢀ
radical and the formation of (C5Me5)2Y(PhNNPh) according to
eq 10.
Complex 15 is sparingly soluble in benzene, and the solution
changes color to dark green over 12 h in benzene at room
temperature, or upon heating for 2 h in aromatic or aliphatic
solvents. The formation of (C5Me5)2Y(PhNNPh), 16, eq 10,
is postulated on the basis of the NMR and EPR spectra of
the green crude product mixture. The conversion of 15 to 16 was
1
monitored over the course of 1 day by H and 11B NMR
spectroscopy. A decrease in the PhNNPh and (C5Me5)ꢀ reso-
nances in the 1H NMR spectrum of 15 was observed, along with
the conversion of (BPh4)ꢀ to BPh3 in the 11B NMR spectrum.
Complex 16 can be separated from residual, less soluble 15 by
alkane extraction, but the BPh3 and Ph2 byproducts are difficult
to separate from 16 because of their similar solubilities. BPh3
could be separated by sublimation of the mixture at 100 ꢀC under
high vacuum (10ꢀ5 Torr), but azobenzene also sublimed, which
suggested that 16 is not stable under these conditions.
The reaction of 1 with phenazine in benzene is similar to the
azobenzene reaction above, in that
a radical product
{[(C5Me5)2Y]2(phz)}{BPh4}, 17, is formed, eq 11. Complex
17 is NMR silent, and its EPR spectrum strongly supports the
presence of the radical monoanion (phz)ꢀ. The EPR spectrum,
Figure 7c, also shows five major resonances attributable to
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Figure 7. EPR spectra of (a) (C5Me5)2Y(PhNNPh), 16, in hexane at room temperature, (b) simulation of 16, (c) {[(C5Me5)2Y]2(phz)}{BPh4}, 17, in
benzene at room temperature, and (d) simulation of 17.
solution showed 18 to be the major product along with reso-
nances for BPh3 and Ph2. Resonances for 5,10-dihydrophena-
zine, phzH2, were also identified by independent synthesis49 and
1
determination of its H NMR spectrum in C6D6. The slow
conversion of 17 to 18 can be described by a second one-electron
reduction of the phenazine radical anion in 17 by (BPh4)ꢀ, eq 12.
coupling with two 14N nuclei in phenazine. A 14N coupling
constant of 5.44 G was determined by simulation, which is in the
3.6 to 6.8 G range for 14N coupling constants of known
phenazine radical anions.59,60 The hyperfine splitting in the
spectrum shows a pattern consistent with an unpaired electron
coupled to eight protons and two yttrium nuclei. The 1H
coupling constants were determined via spectral simulation to
be 1.68 and 0.95 G, which are in the 0.72 to 2.53 G range for
proton coupling constants of coordinated phenazine radical
anions.59 A coupling constant of 1.18 G for both 89Y nuclei was
also determined in the simulation process. The simulated EPR
spectrum, Figure 7d, agrees well with the experimental data. The g
value for this spectrum was measured to be 2.005, consistent with a
ligand-centered radical. No reaction occurs between the solvate,
[(C5Me5)2Y(THF)2][BPh4], and phenazine.
Table 5. Selected Bond Distances (Å) and Angles (deg) for
[(C5Me5)2Y(phen)][BPh4], 12, [(C5Me5)2Sm(py)2][BPh4],
14, and [(C5Me5)2Yb(phen)][I], 21
[(C5Me5)2Ln(L)x][BPh4]
12
14
21
LnꢀCnt
LnꢀN
2.343, 2.354
2.403(2),
2.413(2)
144.2
2.417
2.540(1)
2.339(8),
2.382(8)
Slow diffusion of hexane into a concentrated green solution of
17 in benzene yielded dark green X-ray quality crystals, Figure 8a.
Red crystals of the phenazine dianion complex [(C5Me5)2Y]2(phz),
18, formed from an NMR sample of 17 in benzene-d6 over several
weeks at room temperature. Complex 18 was characterized by X-ray
crystallography, Figure 8b.
CntꢀLnꢀCnt
NꢀLnꢀN
137.2
69.46(7)
90.98(6)
70.3(3)
Structural Analysis of Nitrogen-Donor Complexes. Table 5
shows the metrical data for [(C5Me5)2Y(phen)][BPh4], 12, and
[(C5Me5)2Sm(py)2][BPh4], 14, along with comparison data for
Complex 18 can also be formed by heating 17 at 70 ꢀC in
C6D6 over 2 days. The 1H NMR spectrum of the resulting red
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Figure 8. ORTEP of (a) {[(C5Me5)2Y]2(phz)}{BPh4}, 17, and (b) [(C5Me5)2Y]2(phz), 18, shown at the 50% probability level. The hydrogen atoms
have been omitted for clarity.
Table 6. Selected Bond Distances (Å), Angles (deg), and Metal Displacements out of the Phenazine Plane for
{[(C5Me5)2Y]2(phz)}{BPh4}, 17, [(C5Me5)2Y]2(phz), 18, [(C5Me5)2Sm]2(phz), 22, and [(C5Me4H)2Lu]2(phz), 23
17
18
22
23
LnꢀCnt
LnꢀN
2.318, 2.325
2.320, 2.326
2.358(2)
2.366, 2.346
2.421, 2.436
2.301, 2.272
2.275, 2.299
2. 248(2)
2.298(1)
2.817(2)
2.785(2)
2.360(2)
2.877(2)
2.866(3)
2.3545(19)
2.231(2)
a
LnꢀCR
3.062(2) 3.060(2)
2.755(3)
2.762(3)
b
LnꢀCβ
3.028(2) 3.028(2)
2.719(3)
2.762(3)
CntꢀLnꢀCnt
142.8, 142.4
160.9, 158.9
0.8486, 0.8150
137.0
144.5
1.3523
136.4
140.4
1.5249
133.5, 133.7
148.6, 149.9
1.2223, 1.0990
LnꢀNꢀ(phz plane)c
Ln displacement
a CR = C41, C47 for 17; C21 for 18. b Cβ = C42, C48 for 17; C22 for 18. c Plane defined by the 6 atoms in the central ring of phenazine.
[(C5Me5)2Yb(phen)][I], 21.31 The structures of 12 and 21 have
similar metalꢀligand bond distances within the error limits when
the difference in the eight coordinate ionic radii is considered:
expected, the phenazine dianion in 18 interacts more strongly
with yttrium than does the monoanion in 17. In addition, the
metal atoms in 17 approach the phenazine plane at a more
obtuse angle, that is, the LnꢀNꢀ(phz plane) angles are
158.9ꢀ160.9ꢀ in 17 versus 140.4ꢀ149.9ꢀ in the (phz)2ꢀ
examples in Table 6. This is consistent with the fact that as
phenazine is successively reduced by one and then two
electrons, aromaticity decreases and the hybridization of the
nitrogen atoms is shifted from sp2 toward sp3.
1.019 Å for Y3þ versus 0.985 Å for Yb3þ 37
. The bond distances in
the neutral phenanthroline ligands are also quite similar. How-
ever, the plane of the phenanthroline ligand in 12 is tilted only 1ꢀ
from the plane that bisects the metallocene wedge, whereas the
analogous angle is 15ꢀ in 21.
The symmetry equivalent neutral pyridine molecules coordi-
nated to samarium in complex 14 have a 2.540(1)Å SmꢀN
distance that is similar to the 2.576(3) Å value in
[(C5Me2)Sm(py)]2(μ-O).61 The SmꢀN distances in 14 are,
on average, 0.132 Å longer than the YꢀN distances in 12, which
is 0.072 Å more than expected when only the differences in ionic
radii are considered. It may be the chelating ability of phenan-
throline that allows it to bind more tightly than two separate
pyridine ligands.
Fluorenone. The combination of 1 and fluorenone produces a
1
dark burgundy precipitate in benzene within 20 min. The H
NMR spectrum of the isolated product in THF-d8 is consistent
with a mono(fluorenone) adduct salt, [(C5Me5)2Y(OC7H8)-
(THF)x][BPh4]. The same NMR sample gave an EPR spectrum
that is consistent with a fluorenone radical, Figure 9a. A simulated
EPR spectrum, Figure 9b, agrees well with the experimental data,
displaying 1H coupling constants due to 8 protons, 3.36 G (2H),
0.73 G (2H), 2.76 G (2H), 0.61 G (2H), and an 89Y coupling
constant due to one yttrium nucleus, 0.63 G. The measured g
value is 2.003, which is characteristic of a ligand-based radical.
Crystallographic data on the structures of {[(C5Me5)2Y]2(phz)}-
{BPh4}, 17, and [(C5Me5)2Y]2(phz), 18, are presented in Table 6,
along with that of [(C5Me5)2Sm]2(phz),14 22, and [(C5Me4-
H)2Lu]2(phz),18 23. The structures of 17 and 18 allow the first
comparison of a phenazine monoanion and a phenazine dianion in
rare earth metallocenes. Significant differences exist between 17 and
the other structures. The 2.354(2) and 2.358(2) Å YꢀN distances
in 17 are longer than the 2.298(1) Å YꢀN distance in 18, and the
BPh3 was identified in the dark burgundy THF solution by 11
B
NMR spectroscopy, suggesting the same type of (BPh4)ꢀ
reduction observed with azobenzene and phenazine may be
occurring with fluorenone to form a complex such as
“(C5Me5)2Y(OC7H8).” However, attempts to isolate such a
complex in pure crystalline form were unsuccessful.
Y
C(phz) distances are over 0.2 Å longer in 17. Hence, as
3 3 3
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[(C5Me5)2Ln][(μ-Ph)2BPh2] and [(C5Me5)2Ln(THF)2][BPh4],
eq 6. However, the reactions with phenanthroline and pyridine differ
in terms of their sensitivity to the presence of THF. [(C5Me5)2-
Y(phen)][BPh4], 12, can be made from 1 or its THF adduct, but
addition of THF to the pyridine complexes, [(C5Me5)2Ln(py)2]-
[BPh4], 13 and 14, forms the THF adducts, [(C5Me5)2Ln(THF)2]-
[BPh4]. The chelating effect of phenanthroline could explain why it
is not displaced by THF in 12 as pyridine is in 13 and 14.
Reductive reactivity facilitated by the tetraphenylborate ion via
eq 3 was also observed in the reaction of 1 with azobenzene.
Lanthanide based reductions of azobenzene have been exten-
sively studied.17,20ꢀ24 Although evidence for the azobenzene
adduct, [(C5Me5)2Y(PhNNPh)][BPh4], 15, was obtained, this
product is not stable with respect to the neutral complex free of
(BPh4)ꢀ, namely, (C5Me5)2Y(PhNNPh), 16. An analogous
complex of samarium had previously been obtained through
reduction of PhNdNPh by the divalent complex, (C5Me5)2Sm-
(THF)2, and fully characterized by X-ray crystallography as the
THF adduct, (C5Me5)2Sm(PhNNPh)(THF).20 However, this
species could not be fully characterized by EPR spectroscopy
because of the paramagnetic 4f5 Sm3þ ion. In contrast, the EPR
spectrum of 16 clearly indicated the presence of the (PhNNPh)ꢀ
radical anion.
Figure 9. (a) EPR spectrum of
“[(C5Me5)2Y(OC7H8)(THF)x][BPh4]” in THF at room temperature.
(b) Simulated spectrum.
a millimolar solution of
’ DISCUSSION
[(C5Me5)2Y][(μ-Ph)2BPh2], 1, and [(C5Me5)2Sm][(μ-Ph)2-
BPh2], 2, readily react with NaN3 to provide the [(C5Me5)2Ln-
(N3)]x compounds that were desired as models for the postulated
[(C5Me5)2UN3]x intermediate in the formation of [(C5Me5)2U-
(μ-N)U(μ-N3)(C5Me5)2]4 from NaN3 and [(C5Me5)2U][(μ-Ph)2-
BPh2].19 The unsolvated azide complexes are not very soluble, as
is typical with [(C5Me5)2Ln(bridging ligand)]x complexes where
the bridging ligand is a halide4,62 or a pseudohalide63ꢀ68 like
cyanide. This is generally attributed to extended bridging struc-
tures. Complexes of this type are often crystallographically
characterizable as Lewis base (L) adducts, and they are usually
obtained as trimers, that is, [(C5Me5)2Ln(L)(bridging ligand)]3.
This is the case with the samarium azide, [(C5Me5)2Sm(μ-N3)]x,
5, that could be crystallographically characterized as the acetoni-
trile adduct, [(C5Me5)2Sm(NCMe)(μ-N3)]3, 6. Interestingly,
complex 5 could also be crystallized in a different solvated form,
one in which there is only one coordinating ligand per two metals,
{[(C5Me5)2Sm(μ-N3)][(C5Me5)2Sm(NCMe)(μ-N3)]}n, 7. In
the absence of 1:1 Lewis base to metal ligation, an extended polymer
is formed in 7 via SmꢀNNNꢀSm bridges.
Since phenazine (ꢀ0.36 V vs SCE)70 and fluorenone (ꢀ1.30 V
vs SCE)71 are more easily reduced than azobenzene (ꢀ1.35 to
ꢀ1.41 V vs SCE),72 it was not surprising that they too are reduced
by 1 via eq 3. The EPR spectra of these products suggested
formation of the radical monoanions (phz)ꢀ and (OC7H8)ꢀ,
respectively. In the phenazine case, the structure was confirmed by
X-ray crystallography as {[(C5Me5)2Y]2(phz)}{BPh4}, 17.
Hence, the reductive reactivity of the tetraphenylborate anion
in [(C5Me5)2Y][(μ-Ph)2BPh2] has some generality. Although
the long known (BPh4)ꢀ reductive reactivity38ꢀ46 had recently
been observed in f element complexes, it was generally in
combination with a redox active metal such as uranium or
samarium. In 1, the (BPh4)ꢀ effects reduction without any
concomitant metal redox reaction.
’ CONCLUSION
The unsolvated cations, [(C5Me5)2Y][(μ-Ph)2BPh2], 1, and
[(C5Me5)2Sm][(μ-Ph)2BPh2], 2, have provided a useful ap-
proach to examine the initial coordination of Lewis basic sub-
strates to lanthanide metallocenes. They react readily with a
variety of substrates by displacement of the weakly coordinated
(BPh4)ꢀ anion. Although this type of reactivity was expected, it
was not anticipated that (BPh4)ꢀ would also show reductive
reactivity in these complexes. The one electron redox chemistry
of this anion in the presence of the metallocene cation has
provided complexes of radical anions that were previously
unavailable from reductions with Ln2þ reagents like (C5Me5)2Ln-
(THF)x, Ln = Eu, Yb, and Sm. The isolation of the first rare earth
(phenazine)ꢀ complex, {[(C5Me5)2Y]2(phz)}{BPh4}, shows the
power of combining the reductive reactivity of the (BPh4)ꢀ anion
with the coordinating and stabilizing capacity of rare earth metallo-
cene cations.
In the yttrium case, crystals of an unsolvated complex,
[(C5Me5)2Y(μ-N3)]3, 4, were fortuitously obtained when this
complex was synthesized via a reduction reaction involving
1-adamantyl azide and 1. This was the first example in this study
whereby a tetraphenylborate ligand acts as a non-innocent
counter-anion: it can act as a reductant as shown in eq 3.
Additional examples are discussed below.
Formation of the azide complexes 3 and 5 did not require the
unsolvated cations, 1 and 2, since these reactions could also be
conducted in THF. The fact that an inorganic azide reacts with
[(C5Me5)2Ln(THF)2][BPh4] (Ln = Y, Sm) to form unsolvated
[(C5Me5)2Ln(N3)]x species contrasts sharply with the reaction
of (C5Me5)ꢀ with the solvated cations that leads to nucleophilic
ring-opening of the bound THF to make (C5Me5)2Ln[O-
(CH2)4C5Me5](THF).69
The reactions of the lanthanide metallocene cations with
ketones are also unaffected by the absence or presence of
THF. Hence the acetone adducts, [(C5Me5)2Ln(OCMe2)2]-
[BPh4], 8 and 9, and the benzophenone complexes [(C5Me5)2Ln-
(OCPh2)2][BPh4], 10 and 11, can be generated from both
’ ASSOCIATED CONTENT
S
Supporting Information. X-ray data collection, structure
b
solution, and refinement (PDF) and X-ray diffraction details of
compounds 4, 6, 7, 8, 9, 10, 12, 14, 17, 18 (CIF, CCDC No.
4104
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Inorganic Chemistry
ARTICLE
803836ꢀ803845). This material is available free of charge via the
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’ AUTHOR INFORMATION
(27) Evans, W. J.; Takase, M. K.; Ziller, J. W.; DiPasquale, A. G.;
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Corresponding Author
*Fax: 949-824-2210. E-mail: wevans@uci.edu.
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