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Nickelacyclobutabenzene Compounds by Oxidative Addition of Cyclopropabenzene to Nickel(0) Compounds.

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I51 13a: MS (70 ev): m/z 268 (M'), 178 (Cp2Ti): 'H-NMR (for numbering
,
(s, 2 H ; C H 2 ) ,
see Scheme I ) : 6 (CD2C12)=5.85 (s, 1OH: C 5 H S ) 3.17
+E+&
cz
CP5
Fig. I Crystal structure of 17a. R = H
Experimental
A suspension of dovbly sublimed magnesium (576 mg, 24 mmol, particle size
1-2 mm) in T H F (4 mL) was treated with dibromoethane (21 mg, 0.1 mmol),
and the mixture stirred for 15 min. A solution of 10 (492 mg, 2.4 mmol)'I2' in
T H F (30 mL) was then added dropwise to the mixture within 2 h, and stirring
continued for a further 1 h. To remove excess magnesium, the mixture was
filtered through glass wool. This furnished a suspension of a green precipitate in a greenish-yellow solution, with the precipitate containing the greater
part of the organomagnesium compound. The yield of 11 was almost quantitative. This was ascertained by hydrolysis and titration of the base and the
magnesium ions with HCI and ethylenediamine tetraacetate (EDTA), respectively, and by determination of the a,o-dideuteriotoluene (99%) after deuteriolysis (GC/MS). Derivatization with C 0 2 , Me,GeCI, and Me,SnCI also afforded the expected disubstitution products in 92-94% yield.
For the synthesis of 13a, 12 (198 mg, 0.795 mmol) was added to a THFsuspension of a molar equivalent of 11 (0.0199 M) at -20°C in a sealed glass
system and stirred for 2 h. The grey precipitate dissolved and a deep red
solution resulted. After removal of the T H F by distillation at 4°C the solution was treated with dioxane (10 mL): after 15 minutes' stirring and removal
of a white precipitate (magnesium salts), the filtrate was evaporated to dryness. The residue was virtually pure 13a (red powder; 93% yield, determined
by 'H-NMR spectroscopy with cyclopentane as standard).
Received: March 4. 1986;
revised: May 15, 1986 [ Z 1690 IE]
German version: Angew. Chem. 98 (1986) 641
[ I ] a) J. B. Lee, G. L. Gajda, W. P. Schaefer, T. R. Howard, T. Ikariya, D. A.
Straus, R. H. Grubbs, J . Am. Chem. Soc. 103 (1981) 7358; A. K. Rappe,
W A. Goddard 111, ibid. 104 (1982) 297; W. R. Tikkanen, J. W. Egan, Jr.,
J. L. Petersen, Organometallics 3 (1984) 1646; b) F. N. Tebbe, G. W.
Parshall, D. W. Ovenall, J . Am. Chem. SOC.I01 (1979) 5074; T. R. Howard, J. B. Lee, R. H. Grubbs ,;bid. 102 (1980) 6876: D. A. Straus, R. H.
Grubbs, J . Mol. Cutal. 28 (1985) 9; c) K. A. Brown-Wensley, S. L. Buchwald, L. Cannizzo, L. Clawson, S. Ho, D. Meinhardt, J. R. Stille, D.
Straus, R. H. Grubbs, Pure Appl. Chem. 58 (1983) 1733, and references
cited therein.
[2] a) J. W. F. L. Seetz, B. J. J. van de Heisteeg, G. Schat, 0. S. Akkerman,
F. Bickelhaupt, J . Mol. Catul. 28 (1985) 71, and references cited therein:
B. 1. J. van d e Heisteeg, G. Schat, 0. S. Akkerman, F. Bickelhaupt, Tetrahedron Lett. 25 (1984) 5191; Orgonometallics4 (1985) 1141; b) W. R.
Tikkanen, J. Z . Liu, J. W. Egan, Jr., J. L. Petersen, ibid. 3 (1984) 825: c)
for other modes of formation of metallacyclobutanes see, e.g., P. Foley,
G. M. Whitesides, J. Am. Chem. Soc. 101 (1979) 2732: M. Ephritikhine,
M. L. H. Green, R. E. MacKenzie, J . Chem. SOC.Chem. Commun. 1976.
619.
[3] G. Erker, P. Czisch, C. Kriiger, J. M. Wallis, Organometallics 4 (1985)
2059.
[4] T. H. Tulip, D. L. Thorn, J . Am. Chem. SOC.103 (1981) 2448; L. Dahlenburg, V. Sinnwell, D. Thoennes, Chem. Ber. 111 (1978) 3367; V. F. Traven, M. Yu. Eismont, V. V. Redchenko, B. 1. Stepanov, Zh. Obshch. Khim.
50 (1980) 2007; Chem. Abstr. 94 (1981) 29681 2: T. Behling, G. S. Girolami, G. Wilkinson, R. G. Somerville, M. B. Hursthouse, J. Chem. SOC.
Dolron Trans. 1984, 877; J. A. Stotler, G. Wilkinson, M. Thornton-Pett,
M 8. Hursthouse, ibid. 1731; R. Neidlein, A. Rufinska, H. Schwager, G.
Wilke, Angew. Chem. 98 (1986) 643; Angew. Chem. Int Ed. Engl 25
(1986) 640.
640
0 VCH Verlagsgesellschafr mbH. 0-6940 Wernherm, 1986
7.06, 7.28 (d, in each case 'Jblc,=7 Hz, each I H: H3. H6), 6.90 (m, 2 H ;
H4, H 5 ) : 6 (ChD6)=5.50 (CSH,), 3.30 (CH2); "C-NMR (CD2C12):
6 - I 11.8 (d, 'Jcli= 174 Hz; CSHS),63.4 (t. ' J ~ H = 140 Hz: CHZ), 105.1 ( s ;
CI), 208.9 (s; a),
128.9 (d; C6). 132.6 (d, 'JcBt= 157 Hz: C3), 125.5,
125.2 (d, 'Jcli= 158 Hz; C4, C5).
161 a) G. Erker, P. Czisch, R. Mynott, Y:H. Tsay, C. Kruger, Organometallics 4 (1985) 13 10: b) for further examples of this type of compound see:
G. Erker, P. Czisch, R. Mynott, Z . Naturforsch. B 4 0 (1985) 1177; H.
Schmidbaur, R. Pichl, ibid. 352; R. E. Cramer, R. B. Maynard, J. W.
Gilje, Inorg. Chem. 20 (1981) 2466: K. 1. Cell, J. Schwartz, ibid. 19
(1980) 3207; c) J. C. Baldwin, N. L. Keder, C. F. Strouse, W. C. Kaska,
Z . Naturforsch. 835 (1980) 1289.
171 A mixture of 3.6g (10.9 mmol) of Cp2TiPh2 and 3 3 g (12 mmol) of
H2C=PPh, in 250 mL of heptane after heating at 70°C for 7 h and subsequent crystallization afforded 3.6g (95%) of pure 17a. The solution
contained u p to 80-90% of pure 13a together with PPh, ( 1 : 1). 17a: M.p.
163°C; correct elemental analysis: MS (70 ev): m / z 530 (Ma), 453
(M' - Ph), 275 (CHPPh?): IR (KBr): 5=3040, 1430, 1100, 800 (C,H,),
920 (C-P) c m - ' ; 'H-NMR (C,D,, for numbering see Scheme I ) :
6=5.71 (5, IOH: CsHs), 8.78 (d, ' J H P =Hz,
~ 1 H; CH=P), 6.85-7.20 and
7.40-7.85 (m. 20H; 4C6H,); "C-NMR (CD2C12): 6=108.8 (d,
' J c H = 173 Hz; CSH,), 165.2 (dd, 'JcH= 122 Hz, 'Jcp=20 Hz; CH=P),
187.7 (S; CI), 144.0 (d, ' J c H = 156 Hz; C2), 125.5 (d, ' J , - H = 153 Hz; C3),
121.5 (d, 'JCH=
157 Hz; C4). signals of the PPh, group: 6 = 133.7 (d,
'Jcp=80.5 Hz; i-C), 133.7 (dd, ' J C - H = 163 Hz, *Jcp=9 2 Hz; 0-c), 128.8
(dd, ' J c H = l 6 3 Hz, ' J c ~ , = I l . l Hz; m-C), 131.4 (dd, IJrH=160 Hz,
4Jrp=2.6 Hz; p-C).
181 Starting from bis@-tolyl)titanocene, the aryltitanocene ylides 17a (methyl at C3) and 17a' (methyl at C4) were obtained in a 60:40 ratio together with a mixture of the substituted titanacyclobutabenzenes 13a
(methyl at C5) and 13a' (methyl at C4). I n this particular case, H-transfer is favored over CH,-transfer to the extent of 3 : I .
[9] crystal structure analysis of 17a : a = l0.872( I), b = 17.928(3),
c=28.643(4)A: V=5583.1 A3;p,,,,,=1.26 g cm-'.p=3.79 c m - ' , Z = 8 ;
space group Pbca, 2151 of 6290 independent reflections observed, 458
parameters refined, R = 0.049, R , =0.042. Selected bond lengths [A] and
angles ["I: Ti-CI 2.254(5), Ti-C7 2.033(6), P-C7 1709(6); CI-Ti-C7
95.5(2), Ti-C7-P 138.5(3): C6-CI-Ti-C7 31.5, CI-Ti-C7-P 99.5. Further
details of the crystal structure investigation are available on request
from the Fachinformationszentrum Energie, Physik, Mathematik
GmbH, D-75 14 Eggenstein-Leopoldshafen2, on quoting the depository
number CSD-51937, the names of the authors, and the full citation of
the journal.
[lo] For the special stereoelectronic properties of the bent metallocene
moiety see J. W. Lauher, R. Hoffmann, J. Am. Chem SOC.98 (1976)
1729; C Erker, F. Rosenfeldt, Angew. Chem. 90 (1978) 640; Angew.
Chem. I n / . Ed. Engl. 17 (1978) 605.
[l I] Almost identical with d(Ti-C) in dicdrbonyltitanocene (2.030(1 1)
J.
L. Atwood, K. E. Stone, H. G. Alt, D. C. Hrncir, M. D Rausch, J. Organomef. Chem. 132 (1977) 367; Ti-C bond lengths: W. E. Hunter, J. L.
Atwood, G. Fachinetti, C. Floriani, ibid. 204 (1981) 67: I. W. Bassi, G.
Allegra, R. Scordamaglia, G. Chiccola, J. Am. Chem. Sot. 93 (1971)
3787: J. L. Calderon, F. A. Cotton, B. G. De Boer, J. Takats, ibid. 3592;
G. P. Pez, ibid. 98 (1976) 8072.
[I21 Prepared from o-bromobenzyl alcohol according to the method described by D. Landin, F. Monetari, F. Rolla, Synthestr 1974, 37.
A):
Nickelacyclobutabenzene Compounds by
Oxidative Addition of Cyclopropabenzene to
Nickel(o) Compounds**
By Richard Neidlein,* Anna Rufitiska, Harald Schwager,
and Gunther Wilke*
Dedicated to Professor Hans-Herloff Inhoffen on the
occasion of his 80th birthday
Metallacyclobutanes, which are so far known for only a
few transition metals,['' have developed into an important
~
[*I Prof. Dr. G. Wilke, Dr. A. Rufinska, DiplLChem. H. Schwagel
Max-Planck-Institut fur Kohlenforschung
Kaiser-Wilhelm-Platz 1, D-4330 Miilheim a.d. Ruhr (FRG)
Prof. Dr. R. Neidlein
Pharmazeutisch-chemisches Institut der Universitat
Im Neuenheimer Feld 364, D-6900 Heidelberg (FRG)
[**I
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
0570-0833/86/0707-0640 $ 02 SO/O
Angew. Chem. Int. Ed. Engl. 28 (1986) No. 7
class of organometallic compounds on account of their importance as intermediates in olefin metathesis reactions.'21
Metallacyclobutenes, on the other hand, have not yet been
isolated, although metallacyclobutabenzene compounds of
some transition metals (but not of nickel) are known.I3I
Higher-membered, multiply unsaturated metallacycles
may be prepared, for example, by oxidative addition of biphenyls to nickel(@)compounds, whereby a CC o-bond
that is activated by ring strain undergoes cleavage.[41As we
recently showed, oxidative addition of cyclopropabenzene
1 to [(Me, P)2Ni(cod)] (COD = cis,cis-1,5-cyclooctadiene)
results in the formation of a bis-methano-bridged nicke l a [ l 2 ] a n n ~ l e n e . 'Here
~ ~ we report a novel and flexible approach to metallacyclobutabenzenes, which was discovered in the course of those investigations.
When lf6Iis allowed to react with the nickel(0) complexes 2'' and 3I9I [Eq. (a) and (b), respectively] o r with a
1 : 1 mixture of trisethenenickel(0) 4"" and tetramethylethylenediamine (TMEDA)L''l[Eq. (c)], the corresponding
nickelaannulenes are not formed."] Instead, the crystalline
nickel(i1) compounds 5, i.e., nickelacyclobutabenzene derivatives, are produced in high yields as the result of insertion of a Ni atom into one of the CC o-bonds of the threemembered ring of 1. The ligands thereby released can be
removed by recrystallization o r under high vacuum. The
complexes with (nBu),P and Ph3P ligands (5b and 5c, respectively) are stable at room temperature, whereas those
with the ligands Et3P and TMEDA (5a and Sd, respectively) decompose slowly, turning black."21
(6= -0.24 and
- 0.34, 25=9 Hz). The N M R spectra of 5d
differ clearly from those of 5a-c in the high-field shifts of
the atoms C-1 and C-7, which are directly bonded to the
Ni atom, as well as of the proton H-7. We ascribe this to
the stronger shielding of these nuclei on account of the
large electron density at the Ni atom; the ligand TMEDA
acts only as an electron donor without taking part in back
bonding.
Table I . 'H-NMR data for the nickelacyclobutabenzene fragment of the
compounds 5 (400 MHz [a], [D,]THF, -80°C [b], 6 values with respect to
TMS).
~~
H-2
IH
5a 7.17(m)
5b 7.18(m)
5c 6.17(m)
5d 7.03(dd)
H-3
1H
H-4
IH
H-5
IH
H-7
2H
6.58(m)
6.59(m)
6.57(m)
6.34(dt)
6.70(m)
6.70(rn)
6.l6(m)
6.53(dt)
6.24(m)
6.23(m)
5.99(m)
6.00(dd)
041(d)
0.38(br. d )
0 55(dd)
-0.26(br.s)
[a] 5a at 200 MHz. [b] 5c at
- 10°C.
Table 2. "C-NMR data for the nickelacyclobutabenzene fragment of the
compounds 5 (75.5 MHz, [DdTHF, -80°C [a]).
5b
5a
_
_
_
_
_
_
_
~
~
~
5c
5d
~
6 values relative to TMS, J(C,H) multiplicities in parentheses
c-I
134.7 (s)
134.2 (s)
134.5 (s) [b]
c-2
122.4 (d)
122.5 (d)
122.8 (d)
I:
C-5
C-6
c-7
124.3 (d)
125.4 (d)
129.4 {d)
160.5 (s)
-6.3 (t)
124.2 (d)
125.6 (d)
129.5 (d)
160.7 (s)
-7.1 (t)
124.3 (d)
123.8 (d)
[c]
158.0 (s)
0.5 (t)
~
128.6 (s)
121.7 (d)
122.3 (d)
123.4 (d)
128.1 (d)
159.1 (s)
-17.8 (t)
IJ(P,C)I in Hz
2a,b
1
5a,b
'J ( P,C- 1)
'J(P,C- I )
*J(P,C-7)
*J(P',C-7)
a,R=Et; b.R=nBu
25.0
78.2
23.0
55.4
24.9
78.8
23.4
56.0
-PI
- [bl
18.3
50.9
[a] 5c at -40°C. 5d at -60°C. [b] Signal not identified unequivocally [c]
Signal overlapped.
3
4
5c
5d
The nuclear magnetic resonance spectra are in agreement with the structures givenft3'(Tables 1 and 2). The following features were observed for each of the compounds
5a-c. In the "P-NMR spectrum, the splitting pattern of an
AX spin system is observed. In the '-?C('H)-NMRspectrum, the signal of the Ni-bonded C atom of the methylene
group (C-7) is a doublet of doublets at high field; the differing magnitudes of the coupling constants 'J(P,C-l) and
'J(P',C-i) (as well as 'J(P,C-7) and 'J(P,C-7)) (see Table
2) indicate a square-planar geometry at the Ni atom. The
C-6 atom of the aromatic ring gives rise to a signal at
markedly low field (6= 158-160). In the ' H - N M R spectrum, the nonequivalent, aromatic protons (H-2 to H-5) appear as an ABCD spin system, and the protons of the CH2
group appear as a broad signal at 6=0. For Sd, the chelating ligand assumes a preferred conformation at
T = - 120°C. This causes the Ni atom to become a center
of chirality, and the protons on C-7 are thus diastereotopic
Angew. Chem. In/. Ed. Engl. 25 (1986) No. 7
Evidence for the structures of 5a-d is also provided by
chemical reactions. Protolysis of 5b with HCl in ether results in the nearly quantitative formation of toluene. As expected on account of the ring strain, 5a-d readily undergo
ring expansion: 5b already undergoes reaction at -78°C
6
with carbon dioxide to form the six-membered cyclic carboxylate 6 in high yield [Eq. (d)], which could be characterized u n e q u i ~ o c a l l y . Protolysis
~'~~
of 6 with HCI in ether
affords o-methylbenzoic acid in nearly quantitative yield.
Received: March 6, 1986 [Z 1694 IEJ
German version: Angew. Chem. 98 (1986) 643
[I] a) P. W. Hall, R. J. Puddephatt, C. F. H. Tipper, J . Organomer. Chem. 84
(1975) 407, and references cited therein: b) M. Ephrithikine, M. L. H.
Green, J . Chem SOC.Chem. Commun. 1976. 926, and references cited
therein; c) G. Erker, P. Czisch, C. Kriiger, J. M. Wallis, Organome/alhcs
4 (1985) 2059, and references cited therein.
121 R. H. Grubbs, h o g . Inorg. Chem. 24 (1978) I .
0 V C H Verlagsgesellschafi mbH. 0-6940 Weinheim. 1986
0570-0833/86/0707-064l$ 02.56'0
641
131 T. H. Tulip, D. L. Thorn, J . Am. Chem. SOC.103 (1981) 2448; L. Dahlenburg, V. Sinnwell, D Thoennes, Chem. Ber. 111 (1978) 3367; V. F. Traven, M. Yu. Eismont, V. V. Redchenko, B. I. Stepanov, Zh. Obshch. Khim.
50 (1980) 2007; Chem. Abstr. 94 (1981) 296812; T. Behling, G. S . Girolami, G. Wilkinson, R. G. Somerville, M. B. Hursthouse, J. Chem. SOC.
Dalton Trans. 1984, 877; J. A. Statler, G. Wilkinson, M. Thornton-Pett,
M. B. Hursthouse, 1. Chem. SOC.Dalfon Trans. 1984. 1731; H. J. R. de
Boer, 0. S . Akkerman, F. Bickelhaupt, G. Erker, P. Czisch, R. Mynott, J.
M. Wallis, C. Kriiger, Angew. Chem. 98 (1986) 641 ; Angew. Chem. I n t .
Ed. Engl. 25 (1986) 639.
14) J. J. Eisch, A. M. Piotrowski, K. 1. Han, C. Kriiger, Y.-H. Tsay, OrganomefaNics 4 (1985) 224.
151 R. Mynott, R. Neidlein, H. Schwager, G. Wilke, Angew. Chem. 98 (1986)
374; Angew. Chem. Int. Ed. Engl. 25 (1986) 367.
161 W. E. Billups, A. J. Blakeney, W. Y. Chow, Org. Synth. 55 (1976) 12.
171 5a: 1 (0.5 mL, 4.85 mmol) was added to a vigorously stirred solution of
2a (1.67 g, 4.14 mmol) in 60 mL of pentane under argon at - 20°C. The
reaction mixture was then allowed to warm to room temperature and
stirred for 30 min. After the reaction mixture had been concentrated to
20 mL and a slightly amorphous precipitate removed, the filtrate was
cooled slowly to -78°C and allowed to stand for 1 week at this temperature. The crystals that separated out were filtered off, washed once with
cold pentane, and dried at a maximum temperature of -20°C under
high vacuum. Yield: 1.21 g (3.14 mmol, 76%) greenish brown crystals.
[8] 5b: Synthesized analogously to 5a. Green crystals, yield 68%.
191 5 c : 1 (0.5 mL, 4.85 mmol) was added to a solution of 3 (1.92 g,
1.74 mmol) in 50 mL of toluene at -20°C under argon. The reaction
mixture was then stirred over night at room temperature, during which
time a finely crystalline, yellow precipitate separated out. After 1 d at
-20°C. the yellow crystals were collected on a D, frit, washed with ether, and then dried at room temperature under high vacuum. Yield: 936 g
(1.39 mmol, 8OYo) of yellow microcrystals.
K. Fischer, K. Jonas, G. Wilke, Angew. Chem. 85 (1973) 620; Angew.
Chem. 1st. Ed. Engl. 12 (1973) 525.
TMEDA (0.62 mL, 4.15 mmol) was added to a freshly prepared solution
of CDT-Ni (CDT=all-trans-l,5,9-cyclododecatriene)
[IS] 4 in 20 mL of
E t 2 0 at -78°C. 1 (0.75 mL, 5.03 mmol) was then added to the clear
solution at -78°C and the reaction mixture was allowed t o warm over
3 h to -20°C. The reaction mixture turned cloudy and ethylene
evolved. I n order to achieve complete crystallization, the mixture was
cooled for 1 d at -78°C. The precipitate was filtered under suction
while still cold, washed twice with cold Et20, and dried at - 20°C under
high vacuum. Yield: 770 mg (2.91 mmol, 70%) of greenish brown microcrystals.
The elemental analyses are in agreement with the empirical formulas.
NMR data collection, NMR-Labor, Max-Planck-Institut fur Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-4330 Mulheim a. d. Ruhr (FRG).
6 : 5b (770 mg, 1.39 mmol) was dissolved in 5 0 m L of pentane under
argon and allowed to react at -78°C with 200 mL (8.9 mmol) of C 0 2 .
During the course of C 0 2 addition, a yellow, crystalline material separated out. In order to achieve complete crystallization, the reaction mixture was allowed to stand for I d at -78°C. The crystals were then collected o n a cooled frit by suction filtration, washed twice with cold pentane, and dried under high vacuum. Yield: 670 mg (1.12 mmol, 81%) of
yellow crystals; correct elemental analysis. 'H-NMR (400 MHz,
[D,]THF, - S O T , selected): 6=7.49 (d, 1 H ; H-3), 7.0 (m,3 H ; H-4, H-5,
H-6), 2.29 (br, 2 H ; H-8); "C-NMR (75.5 MHz, [Ds]THF, - S O T , selected): & = I 6 9 3 (s, G I ) , 138.2 (s, C-2), 129.4 (d, C-3), 123.1 (d, C-4),
129.9 (d, C-S), 125.9 (d, C-6), 145.0 (s, C-7), 27.4 (t, C-8, 2J(P,C)=28.0
Hz, 2J(P',C)=53.9 Hz); "P-NMR (32 MHz, [DaITHF, -80°C): 6=9.3,
18.4 (2J(P,P)= 13.4 Hz); IR (KBr): =
;
1631 (s, C = O ) cm-'.
B. Bogdanovic, M. Kroner, G. Wilke, Justus Liebigs Ann. Chem. 699
(1966) 1.
hexadienes 2, the 1,2-diboratabenzene ions 3, and transition-metal complexes in which 2 and 3 are stabilized as
ligands. We report here on the first entry to 1,2-diboratabenzene derivatives.
[OER]"
R
2
1
3
The diborane(4) CI(Me2N)BB(NMe2)CI~'1 smoothly
reacts with C,H6Mg(THF)2[2' (THF= tetrahydrofuran) to
give the liquid 1,2-dibora-4-cyclohexenederivative 4.[3,41
Metalation of 4 with lithium 2,2,6,6-tetramethylpiperidide
(LiTMP) affords the sparingly soluble lithium 1,2-diboratabenzene derivative 5 ;[4.51 this can be converted by
reaction
with
N,N,N',N'-tetramethylethylenediamine
(TMEDA)
into
the
readily
crystallizable salt
[Li(TMEDA)],[ I,2-C4H4(BNMe2)216 , which is soluble in
TH F.
4
5
The salt 6 has a triple-decker structure with crystallographic C2 symmetry (Fig. 1).16' The structure can be interpreted as a contact ion triple. The 1,2-diboratabenzene ring
is virtually planar (twist conformation; maximum vertical
deviation 4.2 pm). The bonding pattern in the C4Bz ring is
that of a delocalized 6n-electron system. As can be expected, the Li(TMEDA) groups are shifted from the B
atoms in the direction of the atoms C2 and C2'; the acentricity of the bonding (slip distortion) is 14.9 pm.['I
A 1,2-Diboratabenzene: Lithium Salt and
Transition Metal Complexes**
By Gerhard E. Herberich,* Bernd Hessner, and
Mariin Hostalek
1,2-Diborabenzene 1 and its derivatives have so far
never been reported in the literature. Possibly the most important representatives of 1 are the 1,2-dibora-3,5-cyclo[*] Prof. Dr. G. E. Herberich, Dr. B. Hessner, DipLChem. M. Hostalek
lnstitut fur Anorganische Chemie der Technischen Hochschule
Professor-Pirlet-Strasse 1, D-5100 Aachen (FRG)
[**I Derivatives of 1,2-Diborabenzene, Part 1. This work was supported by
the Fonds der Chemischen Industrie.
642
0 VCH Verlagsgesellschaft mbH, 0-6940 Weinheim. 1986
Fig. I . Structure of 6. Selected bond lengths [pm]: LiK2 228.8(9), Li-C2'
226.3(8), Li-CI 235.1(8), Li-C1' 236.8(7), Li-B 247.1(8), Li-B' 255.3(8), Li-N2
216.4(7), Li-N3 216.2(8); in the anion: B-B' 170.6(8), B-C1 150.5(6), C1-C2
141.3(6), C2-C2' 141.7(8), B-N1 149.5(5).
0570-0833/86/0707-0642 $! 02.50/0
Angew. Chem. Int. Ed. Engl. 25 (1986) No. 7
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nickell, nickelacyclobutabenzene, cyclopropabenzene, compounds, oxidative, additional
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