A naphthyl-substituted pentamethylcyclopentadienyl ligand and its Sm(ii) bent-metallocene complexes with solvent-induced structure change

Article abstract of DOI:10.1039/c1dt11844g

A naphthyl-substituted pentamethylcyclopentadienyl ligand (Cp ^Naph = η⁵-C₅Me₄CH ₂C₁₀H₇) and its Sm(ii) complexes [Sm(Cp ^Naph)₂(THF)_x] (1: x = 2, 2: x = 0) have been prepared and characterised. The solvent-induced reversible conversion between the di-THF solvated purple complex 1 and the un-solvated dark green complex 2 is presented.

Full text of DOI:10.1039/c1dt11844g

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 354
www.rsc.org/dalton
COMMUNICATION
A naphthyl-substituted pentamethylcyclopentadienyl ligand and its Sm(II)
bent-metallocene complexes with solvent-induced structure change†
Takeshi Yatabe,a,b Masaki Karasawa,a Kiyoshi Isobe,a,b Seiji Ogob,c,d and Hidetaka Nakai*a,c,d
Received 29th September 2011, Accepted 8th November 2011
DOI: 10.1039/c1dt11844g
5
A naphthyl-substituted pentamethylcyclopentadienyl ligand
tuted Cp* ligand (CpOlefin = h -C5Me4SiMe2CH2CH CH2), but
a corresponding di-solvated complex has been elusive in this
system.5
5
(CpNaph = g -C5Me4CH2C10H7) and its Sm(II) complexes
[Sm(CpNaph)2(THF)x] (1: x = 2, 2: x = 0) have been prepared
and characterised. The solvent-induced reversible conversion
between the di-THF solvated purple complex 1 and the un-
solvated dark green complex 2 is presented.
We have now found that, by using a naphthyl-substituted Cp*
ligand (CpNaph = h -C5Me4CH2C10H7), both di- and un-solvated
5
complexes [Sm(CpNaph)2(THF)x] (1: x = 2, 2: x = 0) can be
readily prepared and isolated. The di-solvated purple complex
1 reversibly converts to the un-solvated dark green complex 2
with conformational change of the CpNaph ligands (Scheme 1).
The naphthyl substituent having considerably negative reduction
potential (-2.60 V vs. SCE) is crucial to show the solvent-induced
reversible conversion between 1 and 2, because the un-solvated
Sm(II) complex [Sm(Cp*)2] reduces polycyclic aromatic hydrocar-
bons with reduction potentials more positive than -2.22 V to form
Sm(III) complexes irreversibly.6 Herein we report the synthesis,
structure, and properties of 1, 2, and a potassium salt of the CpNaph
ligand (KCpNaph).
Chemical modification of ligands is a useful approach to control
properties of metal complexes. A pentamethylcyclopentadienyl
5
anion (Cp* = h -C5Me5), which is a common and important ligand
in organometallic chemistry,1 is one of the fascinating frameworks
for modification and functionalization. In this context, we have
recently demonstrated that the substituted Cp* ligands provide
a new strategy to construct functional metal complexes.2 For
instance, a highly luminescent organoterbium(III) complex has
been successfully prepared by using an N-phenylcarbazolyl-
5
substituted Cp* ligand (CpPhCar = h -C5Me4CH2C18H12N).2b Thus,
the CpPhCar ligand can efficiently sensitize the f–f emission from the
terbium metal centre of the complex.
With regard to Sm(II) bent-metallocene complexes with Cp*
ligands, [Sm(Cp*)2(THF)x] (x = 2, 1, or 0), it is known
that complete removal of the coordinated THF is not easy:
the conversion from the ◦di- to un-solvated complex is only
achieved by heating to 80 C under high vacuum (~10-5 Torr).3,4
Since the physical and chemical properties of the di- and un-
solvated complexes are different, the mutual conversion be-
tween the complexes by convenient methods is useful to con-
struct switching materials. Intriguingly, an un-solvated complex
[Sm(CpOlefin)2] is readily prepared by using the olefin substi-
aDepartment of Chemistry, Graduate School of Natural Science & Technol-
ogy, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan
bCore Research for Evolutional Science and Technology (CREST), Japan
Science and Technology Agency (JST), Kawaguchi Centre Building, 4-1-8
Honcho, Kawaguchi-shi, Saitama, 332-0012, Japan
cDepartment of Chemistry and Biochemistry, Graduate School of Engineer-
ing, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan.
E-mail: nakai@mail.cstm.kyushu-u.ac.jp; Fax: +81 92 802 2823; Tel: +81
92 802 2822
Scheme 1 Preparation of the potassium salt KCpNaph and Sm(II) complexes
1 and 2.
5
dInternational Institute for Carbon-Neutral Energy Research (I2CNER),
744 Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan
The substituted Cp* or Cp (h -C5H5) ligands with an aromatic
hydrocarbon have been scarcely known because of troublesome
synthesis and isolation.2b,7 The naphthyl-substituted Cp* ligand
(CpNaph) was synthesized by a method used to synthesize other
types of C5Me4R ligands (R = NMe2, allyl, indenyl, dithianyl,
† Electronic supplementary information (ESI) available: Further exper-
imental details and characterisation data. CCDC 846172, 846173, and
846174. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c1dt11844g
354 | Dalton Trans., 2012, 41, 354–356
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
and N-phenylcarbazolyl).2b,8 The CpNaph ligand was isolated as the
potassium salt [K(CpNaph)(THF)] (KCpNaph) in 22% overall yield
from 1-bromonaphthalene (Scheme 1).
Solid-state structural information for the Cp* or Cp deriva-
tive alkali-metal salts is comparatively limited.1a,9 Fortunately,
colourless crystals suitable for X-ray diffraction analysis were
obtained from a saturated THF solution of KCpNaph at room
temperature (rt). The solid-state structure of KCpNaph consists
of polymeric zigzag chains of composition [K(CpNaph)(THF)]•
(Fig. 1).‡ The K–ringcen(1) and K–ringcen(2) distances are 2.763 and
2.758 A, respectively (ringcen: the centroid of the five membered
˚
ring). The ringcen(1)–K–ringcen(2) and K–ringcen(2)–K angles are
143.53(5) and 177.80(4)◦, respectively. The structural parameters
of [K(CpNaph)(THF)]• are comparable to those of the mono-THF
˚
solvated potassium salts of Cp* derivatives (2.746–2.808 A for
the distance of K–r◦ingcen, 141.7–145.5◦ for the angle of ringcen–K–
ringcen, 174.0–176.6 for the angle of K–ringcen–K).2b,9 Intriguingly,
a weak interaction between the potassium ion and the tethered
naphthyl substituent was observed. The K ◊ ◊ ◊ C12 distance of
Fig. 2 ORTEP drawing of 1 with 50% probability ellipsoids. Front
view (left) and top view (right). Hydrogen atoms are omitted for clarity.
˚
Selected bond distances (A) and angles (deg): Sm–C(ring) average: 2.8455,
Sm–ringcen(1) = 2.576, Sm–ringcen(2) = 2.582, Sm–O1 = 2.646(2), Sm–O2 =
2.590(2); ringcen(1)–Sm–ringcen(2) = 138.97(3), O1–Sm–O2 = 98.70(7).
“ringcen” indicates the centroid of the five membered ring.
˚
3.231(2) A is short compared to the K ◊ ◊ ◊ C(tethered arene or
alkene) distances found in [K(CpPhCar)(THF)]• (3.495(2) A) and
2b
˚
5
[K(CpOlefin)(THF)]• (3.58(3) A).
˚
◦
(2.8455 A) and the ringcen(1)–Sm–ringcen(2) angle (138.97(3) ) of 1
˚
are comparable to those found in [Sm(Cp*)2(THF)2] (Sm–ringave
=
◦
2.86(3) A, ringcen–Sm–ringcen = 137 ).3c
˚
The un-solvated dark green complex 2 was isolated by evap-
oration of toluene solutions of 1 in quantitative yield (Scheme
1). In the 13C NMR spectrum of 2 in benzene-d6 at 22 ◦C, the
characteristic resonances of the ring carbons in the CpNaph ligands
are observed at -74.0, -78.3, and -86.1 ppm, which are in the
range for Sm(II) complexes found from -73 to -99 ppm rather
than in the range for Sm(III) complexes found from 113 to 121
ppm.10,11 Fig. 3 displays the UV-vis-NIR absorption spectra of 1
and 2 in THF and benzene, respectively. The colours of 1 and
2 are consistent with the colours of [Sm(Cp*)2(THF)x] (x = 2
or 0): the di- and un-solvated Sm(II) complexes are purple and
green, respectively.3,5 The colour of 1 changes from purple to dark
green on dissolving in non-polar solvents such as pentane, hexane,
benzene, or toluene, due to elimination of the THF on the Sm(II)
centre. As expected, dissolution of the dark green complex 2 in
Fig. 1 ORTEP drawing of a zigzag [K(CpNaph)(THF)]• chain. Hy-
drogen atoms are omitted for clarity, thermal ellipsoids are at 50%
probability. Selected bond lengths (A) and angles (deg): K–ringcen(1) =
˚
2.763, K–ringcen(2) = 2.758, K–O = 2.664(2), K ◊ ◊ ◊ C12 = 3.231(2);
ringcen(1)–K–ringcen(2) = 143.53(5), K–ringcen(2)–K = 177.80(4). “ringcen
”
indicates the centroid of the five membered ring.
The reaction of two equivalent KCpNaph with SmI2(THF)2 in
THF at rt led to the formation of the Sm(II) complex 1 in good
yield (56%) as a purple powder (Scheme 1). The 1H NMR spectrum
of 1 in THF-d8 at 22 ◦C exhibits the expected 10 paramagnetically
shifted and broadened signals from CpNaph between -4 and
11 ppm.10 Crystals of 1 suitable for X-ray diffraction analysis
were grown from a saturated THF solution at -22 ◦C. The solid-
state molecular structure of 1 is typical of a bent-metallocene
species that contains two additional ligands (Fig. 2).‡ The ligand
arrangements around the formally eight-coordinate Sm atom are
pseudo-tetrahedral with the two C5 rings of CpNaph and two oxygen
atoms of the THF ligands. The Sm–C(ring) average distance
Fig. 3 Absorption spectra of 1 (purple) and 2 (green) in THF and
benzene, respectively. The inset shows photographs of solutions of 1 (left)
and 2 (right) in THF and benzene, respectively.
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 354–356 | 355
©

View Article Online
THF results in a back-formation of the purple di-THF solvated
complex 1 (Scheme 1). Thus, complexes 1 and 2 exhibit reversible
solvatochromic behavior.12
Dark green crystals of 2 suitable for X-ray diffraction analysis
were grown from a saturated benzene solution at rt. The solid-
state molecular structure of 2 is depicted in Fig. 4.‡ The Sm
atom is coordinated to the two cyclopentadienyl rings in a typical
bent-metallocene fashion and no coordinated THF is present. The
cation, Culture, Sports, Science and Technology (MEXT) (Japan)
and the Basic Research Programs CREST Type “Development
of the Foundation for Nano-Interface Technology” from JST
(Japan).
Notes and references
‡ Crystal data for KCpNaph: C24H29KO, M = 372.59, colourless block, T = 123
˚
1 K, monoclinic, space group P21/n, a = 14.092(2) A, b = 10.4839(15)
˚
Sm–C(ring) average distance of 2.8038 A is consistent with those
◦
3
˚
˚
˚
A, c = 15.135(2) A, b = 109.3371(11) , V = 2110.0(6) A , Z = 4, 22242
reflections measured, 4815 unique (Rint = 0.031), R1 = 0.0642 ([I > 2s(I)],
wR2 = 0.2101 (all data), GOF = 1.013. CCDC 846172. Crystal data for 1:
C48H58O2Sm, M = 817.38, purple plate, T = 123 1 K, monoclinic, space
11
˚
for divalent Sm(Cp*)2 complexes (2.79–2.86 A). Both of the
naphthyl substituents in 2 are oriented toward the Sm(II) centre to
fill the coordination sphere in the solid state. It should be noticed
that Sm(II) displays short contacts with one of the carbon atoms
of the naphthyl substituent (Sm ◊ ◊ ◊ C12 = 3.015(4), Sm ◊ ◊ ◊ C32 =
˚
˚
˚
group P21/a, a ◦= 15.8327(15) A, b = 14.1300(13) A, c = 18.3007(18) A,
3
˚
b = 104.2865(5) , V = 3967.5(7) A , Z = 4, 42712 reflections measured,
8979 unique (Rint = 0.033), R1 = 0.0341 [I > 2s(I)], wR2 = 0.0735 (all
data), GOF = 1.084. CCDC 846173. Crystal data for 2: C40H42Sm, M =
673.17, dark green block, T = 123 1 K, monoclinic, space group P21/n,
1
˚
2.925(5) A). The Sm(II) ◊ ◊ ◊ C(h -arene) distances in 2 are com-
1
parable to those reported for the Sm(II) ◊ ◊ ◊ C(alkene or h -arene)
◦
˚
˚
˚
a = 15.9579(17) A, b = 12.1851(12) A, c = 16.6516(18) A, b = 109.624(3) ,
distances found in [Sm(CpOlefin)2] (3.004(3) and 3.249(4) A) and
5
˚
3
˚
V = 3049.8(6) A , Z = 4, 32774 reflections measured, 6923 unique (Rint
=
[Sm(Cp*)(BPh4)(THF)] (2.933(4) A).13 The solid-state structure of
˚
0.047), R1 = 0.0499 [I > 2s(I)], wR2 = 0.1351 (all data), GOF = 1.096.
CCDC 846174.
2 suggests that the unusual metal–p-arene (naphthyl) interactions
play an important role in the easy removal of the coordinated THF
from 1 and the formation of 2.
1 (a) S. Harder, Coord. Chem. Rev., 1998, 176, 17; (b) P. Jutzi and G.
Reumann, J. Chem. Soc., Dalton Trans., 2000, 2237; (c) W. J. Evans
and B. L. Davis, Chem. Rev., 2002, 102, 2119; (d) Comprehensive
organometallic chemistry III, ed. R. H. Crabtree and D. M. P. Mingos,
Elsevier, 2007, Vol. 4.
2 (a) H. Nakai, M. Hatake, Y. Miyano and K. Isobe, Chem. Commun.,
2009, 2685; (b) T. Yatabe, H. Nakai, K. Nozaki, T. Yamamura and K.
Isobe, Organometallics, 2010, 29, 2390.
3 (a) W. J. Evans, I. Bloom, W. E. Hunter and J. L. Atwood, J. Am.
Chem. Soc., 1981, 103, 6507; (b) W. J. Evans, L. A. Hughes and T.
P. Hanusa, J. Am. Chem. Soc., 1984, 106, 4270; (c) W. J. Evans, J. W.
Grate, H. W. Choi, I. Bloom, W. E. Hunter and J. L. Atwood, J. Am.
Chem. Soc., 1985, 107, 941; (d) W. J. Evans, G. Kociok-Ko¨hn, S. E.
Foster, J. W. Ziller and R. J. Doedens, J. Organomet. Chem., 1993, 444,
61.
4 The preparation of [Sm(Cp*)2] from [Sm(Cp*)2(OEt2)] has been
reported: D. J. Berg, C. J. Burns, R. A. Andersen and A. Zalkin,
Organometallics, 1989, 8, 1865.
5 W. J. Evans, J. M. Perotti, J. C. Brady and J. W. Ziller, J. Am. Chem.
Soc., 2003, 125, 5204.
6 W. J. Evans, S. L. Gonzales and J. W. Ziller, J. Am. Chem. Soc., 1994,
116, 2600.
7 (a) M. Bjo¨rgvinsson, S. Halldorsson, I. Arnason, J. Magull and D.
Fenske, J. Organomet. Chem., 1997, 544, 207; (b) F. Cicogna, M.
Colonna, J. L. Houben, G. Ingrosso and F. Marchetti, J. Organomet.
Chem., 2000, 593–594, 251; (c) M. Carano, F. Cicogna, I. D’Ambra, B.
Gaddi, G. Ingrosso, M. Marcaccio, D. Paolucci, F. Paolucci, C. Pinzino
and S. Roffia, Organometallics, 2002, 21, 5583; (d) S. K. S. Tse, T. Guo,
H. H.-Y. Sung, I. D. Williams, Z. Lin and G. Jia, Organometallics, 2009,
28, 5529; (e) S. K. S. Tse, W. Bai, H. H.-Y. Sung, I. D. Williams and G.
Jia, Organometallics, 2010, 29, 3571.
Fig. 4 ORTEP drawing of 2 with 50% probability ellipsoids. Front
view (left) and top view (right). Hydrogen atoms are omitted for clarity.
˚
Selected bond distances (A) and angles (deg): Sm–C(ring) average: 2.8038,
Sm–ringcen(1) = 2.533, Sm–ringcen(2) = 2.529, Sm ◊ ◊ ◊ C12 = 3.015(4),
Sm ◊ ◊ ◊ C32 = 2.925(5); ringcen(1)–Sm–ringcen(2) = 138.05(6), C12–Sm–C32 =
102.02(13). “ringcen” indicates the centroid of the five membered ring.
In conclusion, we have unequivocally demonstrated that the
tethered naphthyl unit of CpNaph can function as both an interact-
ing and non-interacting group with the Sm(II) centre. In the present
system, the solvent effect on the THF coordination is controlled by
the proximal effect on the metal–p-arene interaction (vice versa).
Thus, the newly prepared CpNaph ligand provides a new strategy to
construct novel solvent-responsive organometallic compounds. In
addition, the photofunctional naphthyl unit of CpNaph may bring
out a novel photoreactivity. In this line, further work is currently
in progress.
8 P. Jutzi, T. Heidemann, B. Neumann and H. G. Stammler, Synthesis,
1992, 1096.
9 W. J. Evans, J. C. Brady, C. H. Fujimoto, D. G. Giarikos and J. W. Ziller,
J. Organomet. Chem., 2002, 649, 252.
1
10 In order to obtain information on the Sm–THF and Sm–C(h -arene)
1
interaction in solution, the variable temperature H NMR spectra of
1 and 2 were measured at -80 to 100 ◦C in toluene-d8. The obtained
results are complicated by the paramagnetic nature of Sm(II) and are
not suitable for detailed analysis.
Acknowledgements
11 W. J. Evans and D. K. Drummond, J. Am. Chem. Soc., 1989, 111,
3329.
This work was supported by grants-in-aid: 21021011, 21750059
and 23655054, the Global COE Program “Science for Future
Molecular Systems”, and the World Premier International Re-
search Centre Initiative (WPI Program) from the Ministry of Edu-
12 Inorganic Chromotropism, ed. Y. Fukuda, Kodansha/Springer, Tokyo,
2007, pp. 18–27 and pp. 143–198.
13 W. J. Evans, T. M. Champagne and J. W. Ziller, Organometallics, 2007,
26, 1204.
356 | Dalton Trans., 2012, 41, 354–356
This journal is
The Royal Society of Chemistry 2012
©