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Ether-Soluble Ti0 and Bis(6-arene)titanium(0) Complexes from the Reduction of TiCl4 with Triethylhydroborate.

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Ether-Soluble Ti0 and Bis(q6-arene)titanium(o)
Complexes from the Reduction of TiCI, with
Fc (C 013
By Helmut Bonnernann* and Barbara Korall
Scheme 2. E = COOMe
localized on the more substituted double bond. The stereochemistry of 7c, in the absence of any secondary orbital
interaction, is determined by steric interactions. The formation of 8 c follows the same pattern.
Structures 7c and 8c have five and seven linearly fused
cyclobutane rings, respectively, as well as many ester groups
positioned on one face. This “polarofacial” disposition should
confer special properties on these compounds and make
them interesting as spacers and new materials. We are actively pursuing these aims, particularly the synthesis of even
higher ladderanes.
Received: June 29, 1992 [Z 5437 IE]
German version: AngeN,. Chem. 1992, 104, 1557.
CAS Registry numbers:
5c, 1120-53-2; 6c, 143859-21-6;7c, 143859-22-7;8c, 143859-23-8
[l] M. A. Miller, J. M. Schulman, J. Mol. Slrurt. 1988, 163, 133.
[2] Related literature for systems with the bicyclo[2.2.0]hexane([2]-ladderane)
as spacers: M. N. Paddon-Row, Acc. Chem. Res. 1982, is,245; H. Overing, M. N. Paddon-Row, M. Heppener, A. M. Oliver, E. Cotsaris, J. W.
1987, 109, 3258; D. C. Craig,
Verhoeven, N. S . Hush. J. Am. Chem. SOC.
J. M. Lawson, A . M . Oliver, M. N. Paddon-Row, J. Chem. SOC.Perkin
Trans. 1 1990, 3305; R. N. Warrener, P. Groundwater, I. G. Pitt, D. N.
Butler, R. A. Russell, Tetrahedron Lett. 1991, 32, 1885.
[3] E. Osawa, J. M. Rudzinski, D. A. Barbiric, E. D. Jemmis in Strain and its
Implications in Organic Chemistrv, (Eds.: A. de Meijere, S. Blechert),
NATO-AS1 Series, Kluwer, London, 1989, p. 259.
[4] G. Dinsburg, Nouv. J. Chim. 1982, 6, 175.
[5] A. Nickon, E. F. Silversmith, Organic Chemistry: The Name Game, Pergamon Press, New York, 1987, p. 87. A stepwise approach to an [11]-ladderane en route to 3 and 4, conceptualized by A. Eschenmoser, is mentioned
in this book.
[6] H. D. Martin, M. Hekman, Angew. Chem. 1973, 8.5, 615. Angew. Chem.
Int. Ed. Engl. 1973, 12, 572; J. Meinwald, J. Mioduski, Tetrahedron Lett.
1974, 3839; H. D. Martin, M. Hekman, ibid. 1978, 1183; H. D. Martin, B.
Mayer, M. Putter, H. Hochstetter, Angew. Chem. 1981, 90, 695; Angew.
Chem. Int. Ed. Engl. 1981, 20, 677. For an annulated derivative. see G.
Mehtd, M. B. Viswanath, M. Nethaji, K. Venkatesan, J. Chem. Soc. Chem.
Commun. 1992, 82.
17) T. Bally, S . Masamune, Tetrahedron 1980,36, 343; G . Maier, K. Euler, H.
Irngartinger, M. Nixdorf, Chem. Ber. 1985, 118, 409; I. G. Pitt, R. A.
Russell, R. N. Warrener, Syn. Commun. 1986, 16, 1627; G. Maier, Angew.
Chem. 1988, 100, 311; Angew. Chem. Int. Ed. Engl. 1988, 27, 309.
[8] M. J. S . Dewar, E. G. Zoebisch, E. F. Healy, J. J. P. Stewart, J. Am. Chem.
SOC.1985, 107, 3902.
[9] I. Fleming, Frontier Orbitals and Organic Chemical Reactions, Wiley, New
York, 1976.
[lo] G. Berens, F. Kaplan, R. Rimerman, B. W. Roberts, A. Wissner. J. Am.
Chem. Soc. 1975,97,7076.
Verlogsgesellschaft mbH. W-6940 Weinheim, 1992
The reduction of transition metal salts with alkali metal
triethylhydroborates in THF yields finely divided, noncrystalline metal powders.[’] We have found that the analogous
reaction of titanium or zirconium halides leads surprisingly
to ether-soluble metal species.
Within 2 hours TiC1;2 THF and TiCI, ‘ 3THF reacted in
THF with K[BEt,H] with evolution of H, to give brownblack solutions from which roughly 90 % of the precipitated
KCI could be removed by filtration. Solvent and BEt, (identified by “B NMR spectroscopy) were removed under vacuum (10 Pa) leaving a black residue which was extracted with
THE This THF solution was treated with pentane to give a
brown-black precipitate, which according to elemental analysis was composed of 23.7% C, 4.4% H, 7.9% 0, 0.3% B,
8.5% C1, 8.8% K, and 46.7% Ti; after thorough drying
under vacuum this solid was pyrophoric. The K and C1 components were identified as KCI by X-ray diffraction measurements. The material contained almost no boron. It dissolved in THF and ether but was insoluble in pentane and in
arene solvents. Complete dissolution in THF provided a
0.5 M solution which could be concentrated without formation of a precipitate to approximately 2.5 M by distilling off
During the reduction only about one mol of H, was released per mol of titanium. The hydrogen which is not accounted for, approximately one mol, should be found bound
to titanium. To test this hypothesis we conducted the reduction with K[BEt,D]. During the reaction, 48% of the
amount of D, theoretically anticipated was released. In the
protonolysis of the reaction mixture with 2 N HCI a mixture
of HD and H, formed [Eq.(a)]. Following Equation (a) the
D/Ti ratio in “TiD,” was determined to be m = 2 from the
amount of HD produced from material with a known titanium content.
+ ( n - m)/2 H i + Ti”
After workup and drying, the product had a D/Ti ratio of
only m = 0.3. Thus, compound 1is found in solution, but it
loses hydrogen under vacuum. Our results are best summarized in Scheme 1.
TiCI, . 2 T H F
+ 4K[BEt,H]
. xTHF),,,,,,,
+ 4BEt, + 4KC1, + (2 - 4 2 ) H I
Ti . 0.5 T H F
Scheme 1. The course of the reduction of TiCI, with K[BEt,H] in THE
[*] Prof. Dr. H. Bonnemann, Dr. B. Korall
Max-Planck-Institut fur Kohlenforschung
Postfach 101353, D-W-4330 Miilheim an der Ruhr (FRG)
[**I We thank Dr. K. Seevogel for recording the IR spectra on a Nicolet FT-IR
spectrometer 7199 and interpreting them, Dr. G. Block (Krupp Industrietechnik GmbH, Essen) for X-ray diffractograms, Prof. Dr. R. Courths
(Universitat-Gesamthochschule Duisburg) for XPS spectra with ESCALAB Mark 11, and Prof. Dr. P Kleinschmit (Degussa AG, ZN Wolfgang)
for the gift of the metal sponges.
0570-OS33~92jllll-1490$3.50+ .2S/0
Angew. Chem. l n t . Ed. Engl. 1992, 31, No. lf
The protonolysis of 2 with 2 N HC1 provided 1.5-2 mol of
H, per mol of titanium. Theoretically, 1.5 mol H, are expected for Ti'. This shows that in 2 Ti' has various amounts of
residual hydrogen.
According to the IR spectrum of 2 intact T H F is coordinated to the metal center. Neither the IR nor 'HNMR spectra give evidence of Ti-bound hydrogen. Likewise, there is no
spectroscopic proof of a cleavage of THF by Ti'. In the
X-ray diffractogram of 2 besides the reflections of the KCl
impurity only a diffuse, small peak at 20 = 30" is seen, the
position of which matches that of the peak of amorphous
titanium. The accompanying lattice distance, approximately
0.3 nm, corresponds to that in metal. In the XPS spectrum of
2 (Fig. Id) the Ti2p peak is found 2.3 eV higher in energy
than in the spectrum of TiO, (Fig. la). Although metallic
titanium as finely divided as 2 was not available for control
experiments, it can be deduced from the XPS spectra (Fig. 1)
that titanium in 2 is almost as reduced as titanium metal. The
Table 1. Comparison of the Ti-Ti distances in 2 , @-Tiand P-TiH,.,,,
( a = 2.952, c = 4.689 8, 131)
P-TiH, 9 7 1
(a = 4.440 A [31)
2.90 A}2.925 8,
2.95 A
3.14 A
4.21 8,
2.95 8,
4.44 A
5.44 A
5.2% CI, 17.9% K, and 19.4% Zr. The purification and
closer characterization are not yet complete.
When the reduction of TiCI, with K[BEt,H] was conducted in arene solvents (benzene, toluene, p-xylene, and
mesitylene) instead of THF, the corresponding bis(V6arene)titanium complexes were obtained under standard
conditions in up to 20% yield.[51Previously these compounds could be prepared only by the metal-atom vapor
technique.16] The two-step synthesis of the bis(q6arene)titanium complexes by reaction of 2 with the appropriate arene did not succeed.
Complex 2 and the bis($-arene)titaniurn complexes may
find application as dopants for noble metal hydrogenation
catalysts; this should increase the catalytic activity and the
2 and the analogous zirlifetime ~ o n s i d e r a b l y71. ~Complex
conium compound catalyze the hydrogenation of titanium
and zirconium sponges as well as of a hydride battery alloy.
Experimental Procedure
Synthesis of 2: To a stirred solution of TiCI;2THF (6.68 g, 20 mmol) in THF
(250 mL) at 40°C was added 70 mL o f a 1 . 1 5 solution
of K[BEt,H] (80 mmol)
in T H F over 2h. Approximately 20 mmol of H, were released during the reaction. After the addition was complete, the reaction mixture was stirred another
30min at 40°C. The precipitated KC1 was removed by filtration with a D4 kit.
BEt, ("B NMR (THF, 300K):b =76.73) and T H F were removed from the
brown filtrate under vacuum (10 Pa), and the residue extracted with T H F
(100mL). Insoluble material was removed by filtration, and the filtrate was
concentrated under vacuum to a volume of roughly 20 mL. The brown-black
precipitate formed by addition of pentane to this solution was filtered and dried
under vacuum for 16h. Yield: 1.68 g (82%) 2 , 5.24g (88%) KCI. - IR:
<[cm-'] = 867 s, 915 vw, 1035 s, 1340 br, 1455 w; ' H N M R ([DJTHF, 300K.
TMS): 6 =1.77 (m. 2H), 3.61 (m. 2H); MS: m/z 72 (C,H,O+); X-ray diffraction: KCI, titanium portion is amorphous (small diffuse peak at 26-30");
DSC: exothermic reaction at 73 and 147°C; protonolysis of 2 with 2 N HCI
provides a H/Ti ratio of 1.7:1.
Reduction of ZrCI,: Procedure analogous to that described for 2 ; yield of
Zr-containing product: 31.93 g (81 %),
Synthesis of the bis(q6-arene)titanium complexes:
a)Bis($-benzene)titanium: To a solution of TiCI, (2.2 mL, 20 mL) in benzene
(50 mL) in an ultrasonic bath at room temperature was added 160 mL of a 0.5 M
solution of K[BEt,H] (80 mmol) in benzene over 1 h. After the addition was
complete the reaction mixture was left in the ultrasonic bath another 1h. A
black precipitate was filtered away from the clear, red solution with a D4 frit
and then washed with benzene (3 x 50 mL). The filtrate and the washes were
combined and concentrated to dryness. The residue was taken up in pentane,
and insoluble material was removed from the red solution by filtering through
a D4 frit. The pentane was removed under vacuum, and the residue was recrystallized from pentane. Bis(q6-benzene)titanium was obtained as deep red, shiny
plates. Yield: 0.449 g (1 1 O h ) . 'H NMR ([DJbenzene, 300K. TMS): 6 = 4.92 (s,
6H, CH) (according to ref@]: 6 (in [DJbenzene) = 5.04); IR (KBr):
;[cm-'] = 673 vs, 694 vs, 943 s, 973 s, 1406 w, 1478 w (according to ref@]:
S[cm-'] = 946 s, 979 s).
b) Bis(q6-toluene)titanium: Procedure analogous to that described in a);
toluene was used as the solvent. Yield: 1.014g (22%). satisfactory C,H,Ti
analysis. 'H NMR([D,]benzene. 300K,TMS): 6 = 2.13 (s, 3H, CH,), 5.01 (m,
5H, CH) (according to ref.@]: 6 (in [D,,]SiMe,) = 2.15, 4.89); MS m / i 232
[(H,,C,,)48T~', 52%], 140 [(H,C,48Ti', 1001, 138 [(H,C,48Tit, 351, 116
[(H,,C,,)48Tiz+t,61, 70 [(H,C,)48TiZt, 41, 48 [48Ti+,13).
c) Bis(q6-p-xylene)titanium: Procedure analogous to that described in a); p xylene was used as the solvent, reaction mixture treated for 4 h in the ultrasonic
bath. Yield: 0.462 g, (9%). ' H N M R ([D,]benzene, 300K, TMS): b =1.96 (s,
6H, CH,), 4.84 (s, 4H, CH); MS: m / r 260 [(H,,C,,)48Ti+, 100%], 154
Fig. 1. XPS spectra (double peak Ti 2p,,, and Ti 2p,,,) of a) TiO,,b) TiO, from
2, c) a sample of 2 with an oxidized surface, d) Ti.0.5THF 2. n = Number of
recorded pulses.
lack of the typical broad peak between 990 and 1010 eV for
2 indicates the absence of TiO, (no oxidation of the sample
during the measurement). As a comparison for the measured
values, the curves from TiO, produced from 2 (Fig. lb) and
from an oxidized sample (Fig. lc) are also displayed.
Two titanium-hydrogen compounds are known. a-TiH,
( x < 0.46) can be described as elemental titanium with incorporated hydrogen, whereas p-TiH, (ca. 1 < y < 2)[21has a
CaF,-type structure. The radial distribution function of an
initial EXAFS analysis fitted with the experimentally determined titanium phase function (of titanium metal) shows
three shells of titanium for 2 with the Ti-Ti distances listed
in Table 1 . A hexagonal structure type similar to that of
a-titanium can be deduced from these values. The lattice is
somewhat expanded!41 possibly by the included hydrogen.
The characterization of 2 up to this point supports its
description as colloidal titanium stabilized by complexed
T H F and containing included residual hydrogen. The determination of the particle size by transmission electron microscopy has not been conducted.
The analogous reduction of ZrC1, with K[BEt,H] in THF
also provided a product soluble in THF; its composition was
determined to be 34.1% C, 8.0% H, 11.4% 0, 3.7% B,
AngeM. Chem. I n f . Ed. Engl. 1992, 31, N o . 11
VerhgsgeselIschafi mbH. W-6940 Weinheim, 1992
0570-0833i92jllll-1491 $3.50+.25/0
851, 152 [(H8C,)4'Ti+. 411, 130 [(H,,C,,)48Ti2+. 141, 77
[(H,,C,)48Ti2t, 91, 48 [4*TiZ+,
d) Bis(s6-mesitylene)titanium: Procedure analogous to that described in a);
mesitylene was used as the solvent, reaction mixture treated for 16h in the
ultrasonic bath. Yield: < 5%. ' H N M R ([DJbenzene, 300K. TMS): S =1.99
(s, 9H, CH,), 4.74 (s, 3H, CH); (according to ref.[S]; S (in [D,,]SiMe,) =1.96,
4.69); MS: m/: 288 [(H,4C,,)48Ti+, loo%], 168 [(H,,C,)48Ti', 421, 166
[(H,,C,)48Ti', 381. 144[(H,,C,,)"'Ti",
211, 48[48Ti+,41.
Received: June 27, 1992
Revised: July 28, 1992 [Z5436IE]
German version: Angen.. Chem. 1992, 104. 1506
CAS Registry numbers:
2, 143746-11-6; TiHm. 11140-68-4; TiDm, 53095-13-9; ZrHm. 11105-16-1;
[(C,H,),TI]. 52462-43-8; [(C,H,Me),Ti], 55527-82-7;[(C,H,Me,),Ti], 14374612-7; [(C,H,Me,),Ti], 57347-27-0;TiC14.2THF, 3101 1-57-1; ZrCI,, 10026-116; C,H,, 71-43-2; C,H,Me, 108-88-3; C,H,Me,, 106-42-3; C,H,Me,, 108.678; K[BEt,H], 22560-21-0; K[BEt,D], 143773-88-0.
[l] H. Bonnemann, W Brijoux, T. JouOen, Angew. Chem. 1990, 102,324-326;
Angew. Chem. Int. Ed. Engl. 1990,29, 273-275.
[2] A. Chretien, W. Freundlich, M. Bichara, C. R. Hebd. Seances Acad. Sri.
1954, 238, 1423.
[3] S. S. Sidhu, L. Heaton, D. D. Zauberis. Acta Crystallogr. 1956, 9, 607.
[4] Dr. L. Aleandri, Max-Planck-Institut fur Kohlenforschung, Miilheim an
der Ruhr, 1991. The X-ray absorption spectrum was recorded on the Ti
K-edge (77K) with an EXAFS 3 spectrometer in DCI (French Synchrotron
Facility in Lure) with monochromatic X-ray radiation.
[5] H. Bonnemann, W. Brijoux, R. Brinkmann, E. Dinjus, R. Fretzen, T.
Mol. Calul., 1992. 74. 323-333.
JouRen, B. Korall, .l
[6] F. Benfield, M. L. H. Green, J. S. Ogden, D. Young, J. Chem. Soc. Chpm.
Commun. 1973, 866-867; P. N. Hawker, E. P. Kiindig, P. L. Timms, ibid.
1978, 730-731. See also D. W Blackburn, D. Britton, J. E. Ellis, Angen.
Chem. 1992, 104, 1520; Angew. Chem. Int. Ed. Engl. 1992, 31, 1495.
[7] H. Bonnemann, W Brijoux, R. Brinkmann, E. Dinjus, T. JouRen, B. Korall,
Angew. Chem. 1991,103,1344-1346; Angew. Chem. Int. Ed. Engl. 1991.30,
[8] M. T. Anthony, M. L. H. Green, D. Young, 1 Chem. Soc. Dalton Trans.
1975, 1419-1422.
intriguing question required the synthesis of "giant rings" up
to 72 atoms in size.[41Any synthesis chosen to construct the
macrocyclic lipids15]had to proceed in high yields if we were
to secure sufficient amounts for subsequent physical/chemical studies.[', 31 And the route had to be flexible enough to
give, in addition to the looped diesters, the diether analogues
(interesting molecules because of their similarity to lipids of
archaebacterial thermophiles).[61Our answer to the synthetic
challenge is described in the ensuing text.
Our method is based on Glaser oxidation of dialkynyl
compounds [Eq. (a)]. When the reaction was carried out by
slow addition of the dialkynyl compound (syringe pump,
4-5 h), and at higher than usual temperatures (140"C),
yields were consistently and reproducibly high (Table 1). The
procedure seems preferable to those used in the only two
previously reported syntheses of cyclic lipids.[51
Table 1. Yields for high-temperature Glaser cyclization of seven giant-ring
lipids [a].
Lipid type
Ring size
Yield [YO]
60, 68
78, 79
77, 78, 85
[a] Reactions were conducted with 0.9 to 2.8 g diyne as described in the text.
Yields refer to the amounts of material after purification by column chromatography.
High-Yield Synthesis of Lipid Systems
with Giant Rings**
By Fredric M . Menger,* Stephen Brocchini,
and Xiangyang Chen
Phospholipids, a major constituent of biological membranes, possess two alkyl chains each made up of 14-18
carbon atoms (see e.g. I). Since the chains are connected only
at the ester ends, they have a certain amount of freedom
within the membrane bilayer to bend, reorient, and interdigitate."] We wondered how membrane behavior (e.g. thermotropic properties,[2]permeability,t31etc.) would be affected when the two distal ends are joined as in 11, thereby
restricting independent motion. Answering this simple but
- ;:I
I 0
( ( C H 2 ) , 0 1 OP c
[*I Prof. Dr. F. M. Menger, S. Brocchini, X. Chen
Department of Chemistry, Emory University
Atlanta, GA 30322 (USA)
[**I The authors gratefully acknowledge the support of the Dow Chemical Co.
and the National Institutes of Health.
0 VCH Verlagsgesellsrhaft mbH, W-6940 Weinheim. 1992
Scheme 1. a) Dihydropyran (DHP), p-TsOH, 90%; b) 1. 1-alkyne, nBuLi,
hexamethylphosphoric triamide (HMPA); 2. MeOH, p-TsOH, pH = 3-4,
75%; c) 1. nBuLi, HMPA; 2. (CH,O),, 84%; d) 1. Li, H,N(CH,),NH,;
tBuOK, (from 3), 44% (from 5), 70%; e) MesCl, Et,N, 90%; f) 1. PhCH,CI,
dimethylsulfoxide (DMSO), powdered KOH; 2. 10% HOAc, 9 0 T , 6 6 % ;
g) powdered KOH, DMSO, 7.76%; h) O,, CuCI, TMEDA, 140°C 71-85%;
i) H,, 10% Pd/C, 60-74%; j) 1. 2-chloro-2-oxo-l,3,2-dioxaphospholane,
Et,N, benzene, 2 h; 2. Me,N, MeCN, 60-65"C, 48 h, 35-66%.
0570-0833i92jllll-1492 S 3 . 5 0 i .25/0
Angew. Chem. Int. Ed. Engl. 1992, 31, No. 11
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titanium, ethers, ti0, triethylhydroborat, reduction, arena, soluble, bis, complexes, ticl
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