Synthesis of [Ti(η6-1,3,5-C6H3iPr 3)2][BAr4] (Ar = C6H5, p-C6H4F, 3,5-C6H3(CF3)2), the fir

Article abstract of DOI:10.1021/om970155o

The oxidation of Ti(η⁶-1,3,5-C₆H₃ⁱPr ₃)₂ with FeCp₂[BAr₄], Ar = C₆H₅, p-C₆H₄F, 3,5-C₆H₃(CF₃

Full text of DOI:10.1021/om970155o

3100
Organometallics 1997, 16, 3100-3101
i
Syn th esis of [Ti(η6-1,3,5-C6H3 P r 3)2][BAr 4] (Ar ) C6H5,
p-C6H4F , 3,5-C6H3(CF 3)2), th e F ir st Tita n iu m (I)
Der iva tives
Fausto Calderazzo, Isabella Ferri, and Guido Pampaloni*
Dipartimento di Chimica e Chimica Industriale, Universita` di Pisa,
Via Risorgimento 35, I-56126 Pisa, Italy
Ulli Englert
Institut fu¨r Anorganische Chemie der Rheinisch-Westfa¨lischen Technischen Hochschule,
Professor-Pirlet-Strasse 1, D-52074 Aachen, Germany
Malcolm L. H. Green
Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, U.K.
Received February 27, 1997X
i
7b
Summary: The oxidation of Ti(η6-1,3,5-C6H3 Pr3)2 with
FeCp2[BAr4], Ar ) C6H5, p-C6H4F, 3,5-C6H3(CF3)2, af-
fords good yields of the paramagnetic derivatives of
radical anions7a or KC10H8 or by sonication in the
presence of both KBEt3H and arene.8
Reduction to the [Ti(η6-arene)2]- anion (arene )
benzene, toluene) was achieved with potassium or
potassium hydride,9 while loss of the coordinated aro-
matic ligand results from oxidation of the metal cen-
ter: Ti(acac)3, Ti2S3, or [TiCp2Cl]2 have been obtained
by reaction of Ti(η6-toluene)2 with acacH, H2S (or S8),
or TiCp2Cl2, respectively.10 With CO2, Ti(η6-toluene)2
was mentioned to give a low-valent titanium oxalate in
an unspecified oxidation state.11
i
titanium(I), [Ti(η6-1,3,5-C6H3 Pr3)2][BAr4]; these com-
pounds have been characterized by conventional meth-
ods, including single-crystal X-ray diffractometry of
i
[Ti(η6-1,3,5-C6H3 Pr3)2][B(p-C6H4F)4].
Ti(η6-arene)2 (arene ) benzene, toluene, and mesity-
lene) complexes were first prepared in 1975 by co-
condensation of metal atoms with the required aromatic
hydrocarbon;1 by a similar procedure, bis(η6-naphtha-
lene)titanium(0) was also obtained.2 Some years later,
X-ray diffractometry of Ti(η6-arene)2, arene ) benzene
and toluene, showed the titanium atom to be sand-
wiched between the two aromatic rings with eclipsed
ring carbon atoms and diametrically opposed methyl
groups.3
To expand upon the earlier results by some of us on
the one-electron oxidation of bis(arenes) of vanadium-
(0) or niobium(0) with ferricinium cations to the corre-
sponding monovalent cations,12 we now wish to report
the oxidation by a ferricinium derivative FeCp2[BAr4],
Ar ) Ph, p-C6H4F, 3,5-C6H3(CF3)2, of the new, thermally
stable (both in the solid state and in solution) bis(arene)
t
More recently, Ti(η6-1,3,5-C6H3 Bu3)2 has been pre-
i
derivative of titanium(0), Ti(η6-1,3,5-C6H3 Pr3)2.13
pared,4 and thermochemical and ab initio quantum
chemical studies on this molecule have appeared.5
Although Ti(η6-arene)2, arene ) toluene and mesity-
lene, can also be obtained by reducing TiCl3(THF)3 with
potassium in THF in the presence of the parent aro-
matic hydrocarbon,6 conventional syntheses of bis(η6-
arene) derivatives of titanium(0) were achieved only
recently by Ellis and co-workers7 and by Bo¨nnemann
and co-workers8 by reducing TiCl4(THF)2 with arene
The paramagnetic (µeff (293 K) ) 2.01 µB (Ar )
p-C6H4F), 1.94 µB (3,5-C6H3(CF3)2) derivatives of tita-
nium(I), namely [Ti(η6-1,3,5-iPr3C6H3)2][BAr4],14 which
are the first examples of fully characterized derivatives
of titanium(I),15 were obtained according to eq 1. The
solubility in toluene and the stability of these com-
pounds strongly depend on the substituents on the
(9) Bandy, J . A.; Berry, A.; Green, M. L. H.; Perutz, R. N.; Prout,
K.; Verpeaux, J .-N. J . Chem. Soc., Chem. Commun. 1984, 729.
(10) Young, D. Ph.D. Thesis, University of Oxford, Oxford, U.K.,
1974.
(11) Kvashina, E. F. Russ. Chem. Bull. 1994, 43, 2121; Chem. Abstr.
1995, 123, 314110m.
X Abstract published in Advance ACS Abstracts, J une 1, 1997.
(1) Anthony, M. T.; Green, M. L. H.; Young, D. J . Chem. Soc., Dalton
Trans. 1975, 1419.
(2) Morand, P. D.; Francis, C. G. Inorg. Chem. 1985, 24, 56.
(3) Tairova, G. G.; Krasochka, O. N.; Ponomaryov, V. I.; Kvashina,
E. F.; Shvetsov, Yu. A.; Lisetsky, E. M.; Kiryukhin, D. P.; Atovmyan,
L. O.; Borod’ko, Yu. G. Transition Met. Chem. 1982, 7, 189. Tairova,
G. G.; Kvashina, E. F.; Krasochka, O. N.; Kichigina, G. A.; Shvetsov,
Yu. A.; Lisetsky, E. M.; Atovmyan, L. O.; Borod’ko, Yu. G. Nouv. J .
Chim. 1981, 5, 603.
(4) Cloke, F. G. N.; Lappert, M. F.; Lawless, G. A.; Swain, A. C. J .
Chem. Soc., Chem. Commun. 1987, 1667. Cloke, F. G. N.; Courtney,
K. A. E.; Sameh, A. A.; Swain, A. C. Polyhedron 1989, 8, 1641.
(5) King, W. A.; Di Bella, S.; Lanza, G.; Khan, K.; Duncalf, D. J .;
Cloke, F. G. N.; Fragala, I. L.; Marks, T. J . J . Am. Chem. Soc. 1996,
118, 627.
(6) Hawker, P. N.; Ku¨ndig, E. P.; Timms, P. L. J . Chem. Soc., Chem.
Commun. 1978, 730. Hawker, P. N.; Timms, P. L. J . Chem. Soc., Dalton
Trans. 1983, 1123.
(7) (a) Blackburn, D. W.; Britton, D.; Ellis, J . E. Angew. Chem., Int.
Ed. Engl. 1992, 31, 1495. (b) Ellis, J . E.; Blackburn, D. W.; Yuen, P.;
J ang, M. J . Am. Chem. Soc. 1993, 115, 11616.
(12) Calderazzo, F.; Pampaloni, G.; Rocchi, L.; Englert, U. Organo-
metallics 1994, 13, 2592. Ferri, I. Ph.D. Thesis, Scuola Normale
Superiore, Pisa, Italy, 1996.
(13) Synthesis of Ti(η6-1,3,5-C6H3iPr3)2. In a typical experiment,
titanium (2.3 g, 48 mmol) from an ingot of ca. 24 g at a power input of
0.58 kW was co-condensed with an excess of 1,3,5-triisopropylbenzene
at 77 K over a 3 h period. After the reaction mixture was allowed to
warm to room temperature, the reactor walls were washed with light
petroleum ether (400 mL) and the resultant deep purple solution was
filtered at 193 K. The light petroleum ether was evaporated under
reduced pressure, and the excess ligand was removed by condensation
on a cold finger cooled with liquid nitrogen under vacuum (10-5 atm).
The residue was extracted with light petroleum ether, and the solution
was filtered and cooled at 193 K, giving a black-purple solid. The solid
was recovered by filtration and dried in vacuo (4.11 g, 19% yield with
respect to the evaporated titanium). Anal. Calcd for C30H48Ti: C, 78.9;
H, 10.6. Found: C, 79.5; H, 10.8. 1H NMR (benzene-d6, 500 MHz, 25
°C): δ 4.81 (s, 3 H), 2.67 (septet, J HH ) 7.0 Hz, 6 H), 1.20 (d, J HH ) 7.0
Hz, 18 H) ppm. 13C{1H} NMR (benzene-d6, 125.7 MHz, 25 °C): δ 107.93
(C-CH(CH3)2), 82.29 (ring CH), 35.03 (CH(CH3)2), 25.75 (CH(CH3)2)
ppm.
(8) Bo¨nnemann, H.; Korall, B. Angew. Chem., Int. Ed. Engl. 1992,
31, 1490.
S0276-7333(97)00155-6 CCC: $14.00 © 1997 American Chemical Society

Communications
Organometallics, Vol. 16, No. 14, 1997 3101
i
Ti(η6-1,3,5-C6H3 Pr3)2 + FeCp2[BAr4] f
i
[Ti(η6-1,3,5-C6H3 Pr3)2][BAr4] + FeCp2
Ar ) Ph, p-C6H4F, 3,5-C6H3(CF3)2
aromatic rings of the tetraarylborato anion; thus, [Ti-
i
(η6-1,3,5-C6H3 Pr3)2][B(C6H5)4] decomposes at about 50
°C and has a limited solubility in aromatic hydrocar-
i
bons; [Ti(η6-1,3,5-C6H3 Pr3)2][B(p-C6H4F)4] undergoes
partial decomposition in boiling toluene and can be
recrystallized from this medium. The substantially
i
insoluble [Ti(η6-1,3,5-C6H3 Pr3)2][B(3,5-C6H3(CF3)2)4] is
stable in boiling toluene and can be handled in air over
short periods of time in the solid state.
i
Recrystallization of [Ti(η6-1,3,5-C6H3 Pr3)2][B(p-C6H4F)4]
from toluene gave small orange platelets suitable for a
single-crystal X-ray diffraction experiment.16 Although
the poor quality of the crystals did not allow accurate
data collection to be carried out, the atom connectivity
can be definitely established. The structure consists of
i
F igu r e 1. Structure of the [Ti(η6-1,3,5-C6H3 Pr3)2]+ cation
i
in [Ti(η6-1,3,5-C6H3 Pr3)2][B(p-C6H4F)4]. Selected bond dis-
tances and angles: Ti-C, 2.27(2)-2.33(2) Å; C-C (ring),
i
[Ti(η6-1,3,5-C6H3 Pr3)2]+ cations (Figure 1) and [B(p-
1.34(3)-1.51(3) Å; Cring-C Pr, 1.49(3)-1.54(3) Å; C-C (iPr),
i
C6H4F)4]- anions with two independent cationic moi-
eties on inversion centers, i.e., with necessarily coplanar
arene ligands, and a tetrakis(p-fluorophenylborate)
anion in a general position. The cation has an inversion
center on the titanium atom and, therefore, a staggered
conformation of the alkyl substituents on the aromatic
rings. The ring centroid-to-titanium bond distance is
1.81 Å, compared with the values observed for [V(η6-
1.49(3)-1.61(3); C-C-C (ring), 115(3)-123(2)°; Cring
-
i
Cring-C Pr, 117(2)-126(2)°.
i
1,3,5-C6H3Me3)2][AlCl4] (1.73.Å),17 [Cr(η6-1,3,5-C6H3 -
Pr3)2]I (1.65 Å),18 and [Mn(η6-C6H5Me)2]I (1.56 Å).19 The
larger distance observed in the titanium(I) complex of
the 3d3 configuration with respect to the systems of
chromium(I), 3d5, or manganese(I), 3d6, is believed to
be consistent with the presumably larger radius of
titanium, due to a lower effective nuclear charge.
The paramagnetic behavior of titanium is in agree-
ment with the presence of one unpaired electron and
may suggest the existence of a small orbital contribution
consistent with the energy level scheme for sandwiched
bis(arene) metal complexes characterized by a low-
energy degenerate level.6,20,21
(14) Synthesis of [Ti(η6-1,3,5-C6H3iPr3)2][BAr4], Ar ) C6H5, p-C6H4F;
3,5-C6H3(CF3)2. Only the preparation of [Ti(η6-1,3,5-C6H3iPr3)2][B(p-
C6H4F)4] is described in detail, the other compounds were prepared in
a similar manner. Ti(η6-1,3,5-C6H3iPr3)2 (0.33 g, 0.73 mmol) was added
to a suspension of FeCp2[B(p-C6H4F)4] (0.40 g, 0.69 mmol) in toluene
(40 mL) at 243 K. An immediate reaction took place. After 12 h of
stirring at room temperature, the solid was recovered by filtration,
washed with toluene (5 mL) and heptane (5 mL), and dried in vacuo.
It was analytically and spectroscopically identified as [Ti(η6-1,3,5-C6H3
-
i
The compounds reported in this paper completes the
series of the bis(η6-arene)metal(I) cations from the d6
manganese(I) to the d4 vanadium(I) through the chro-
mium(I) derivatives.
Pr3)2][B(p-C6H4F)4] (0.37 g, 63% yield). Anal. Calcd for C54H64BF4Ti:
C, 74.6; H, 7.5; Ti, 5.6. Found: C, 75.9; H, 7.2; Ti, 5.2. IR (poly(chlo-
rotrifluoroethylene), PCTFE and Nujol mull): 2965 (s), 2930 (m), 2873
(w), 1594 (s), 1582 (m s), 1493 (s), 1461 (m), 1385 (w), 1365 (w), 1232
(m s), 1207 (m), 1157 (m s), 837 (w), 812 (s), 548 (w m) cm-1. The
compound readily loses included solvent (toluene) by drying in vacuo.
[Ti(η6-1,3,5-C6H3iPr3)2][B(C6H5)4]: red-orange, 63% yield. Anal. Calcd
for C54H68BTi): C, 83.5; H, 8.8; B, 1.5; Ti, 6.2. Found: C, 82.9; H, 8.0;
B, 1.5; Ti, 5.7. IR (PCTFE and Nujol mull): 3055 (w m), 3032 (w), 2968
(s), 2929 (m), 2872 (w), 1601 (vw), 1581 (w), 1484 (w m), 1461 (m),
Ack n ow led gm en t. Financial support by the Min-
istero dell’Universita` e della Ricerca Scientifica e Tec-
nologica (MURST) and the Consiglio Nazionale delle
Ricerche (CNR, Roma) is gratefully acknowledged. The
stay of I.F. at the Inorganic Chemistry Laboratory was
financed by Ente Nazionale Idrocarburi (ENI, Roma) in
the framework of an ENI-SNS agreement within a
Ph.D. research program.
1424 (w), 1306 (m), 1262 (m), 1068 (m), 733 (s), 704 (s), 613(m) cm-1
.
1H NMR (acetonitrile-d3 in the presence of air, 200 MHz, 25 °C):
δ
7.3 (m, 26 H), 2.86 (septet, J HH ) 7.0 Hz, 6 H), 1.21 (d, J HH ) 7.0 Hz,
36 H) ppm. µeff (293 K): 2.01 µB (øM ) 1710 × 10-6 cgsu, diamagnetic
corr
correction ) -553 × 10-6 cgsu). [Ti(η6-1,3,5-C6H3iPr3)2][B(3,5-C6H3-
(CF3)2)4]: green-brown, 50% yield. Anal. Calcd for C62H60BF24Ti: C,
56.4; H, 4.5; Ti, 3.6. Found: C, 55.2; H, 4.3; Ti, 4.5. IR (PCTFE and
Nujol mull): 3050 (w), 3030 (w), 2967 (m), 2928 (m), 2873 (w), 1610
(w), 1580 (w), 1354 (s), 1279 (vs), 1228 (m), 1168 (vs), 1138 (vs), 896
(m), 723 (s), 683 (s) cm-1. µeff (293 K): 1.94 µB (øM
cgsu, diamagnetic correction ) -729 × 10-6 cgsu).
) 1593 × 10-6
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters of non-hydrogen atoms, positional parameters of
hydrogen atoms, and bond distances and angles (9 pages).
Ordering information is given on any current masthead page.
corr
(15) Thewalt, U. Organotitanium Compounds, Part 4. In Gmelin
Handbook of Inorganic Chemistry, 8th ed.; Springer-Verlag: Berlin,
1984; p 61.
(16) Crystals of [Ti(η6-1,3,5-C6H3iPr3)2][B(p-C6H4F)4] were obtained
from toluene as thin elongated platelets (0.9 × 0.2 × 0.06 mm) and
quickly transferred in a stream of cold nitrogen (T ) -90 °C). Intensity
data collection determination resulted in mostly weak reflections. Due
to the limited number of observations, phenyl carbon atoms were
refined isotropically. Crystal data for [Ti(η6-1,3,5-C6H3iPr3)2]-
[B(p-C6H4F)4]‚C7H8: C61H72BF4Ti, fw 939.96, orange platelets, T ) 183
K, P1h (No. 2), Z ) 2, a ) 10.74(1) Å, b ) 12.66(1) Å, c ) 21.26(2) Å, R
) 102.06(5)°, â ) 97.20(8)°, γ ) 109.25(8)°, V ) 2608(4) Å3, λ (Cu KR)
) 1.5418 Å, µ ) 17.89 cm-1, Dc ) 1.197 g‚cm-3, F(000) ) 1002. Of the
8759 measured and empirically absorption-corrected reflections (ω-θ
scan type; scan range 4°< θ < 49°), 1651 independent reflections with
I > 1.5σ(I) and 267 variables for 140 atoms were considered for the
refinement (R ) 0.147, Rw ) 0.116, GOF ) 1.830).
OM970155O
(17) Calderazzo, F.; Invernizzi, R.; Marchetti, F.; Masi, F.; Moalli,
A.; Pampaloni, G.; Rocchi, L. Gazz. Chim. Ital. 1993, 123, 53.
(18) Li, T. T.-T.; Kung, W.-J .; Ward, D. L.; McCulloch, B.; Brubaker,
C. H., J r. Organometallics 1982, 1, 1229.
(19) O’Hare, D.; Murphy, V.; Bland, A.; Scott, P. J . Organomet.
Chem. 1993, 443, C37.
(20) Muetterties, E. L.; Bleeke, J . R.; Wucherer, E. J .; Albright, T.
A. Chem. Rev. 1982, 82, 499.
(21) Figgis, B. N.; Lewis, J . The Magnetochemistry of Complex
Compounds. In Modern Coordination Chemistry; Lewis, J ., Wilkins,
R. G., Eds.; Interscience: New York, 1960; Chapter 6.