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Monomeric Mononuclear Enediolate Complexes of Zirconium Molecular Geometry and Electronic Structure of the Products of Reductive CO Coupling on the Metal.

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CAS Registry numbers:
Za, 90295-66-2: Zb, 97486-15-2; 3, 3131-54-2: 4a, 97486-08-3; 4a (hydrate),
97486-09-4; 4b, 97486-10-7; 5, 97486.1 1-8; 6, 97486-12-9; 7, 97486-13-0; 8,
97486-14-1.
[ I ] B. Steffan, W. Steglich, Angew. Chem. 96 (1984) 435; Angew. Chem. Int.
Ed. Engi. 23 (1984) 445. For the isolation of another natural product containing this partial structure, see W. A. Ayer, Y . Hoyano, 1. van Altena, Y.
Hiratsuka, Reu. Latinoam. Quim. 1982, 84.
[21 L. Horner, W. Durckheimer, Z . Naturforsch. 8 1 4 (1959) 742. N o further
details are given on the regioselectivity of the dimerization of 3.
[3] R. Willstatter, F. Muller, Ber. Dlsch. Chem. Ges. 44 (1911) 2171.
[4] The structure of 4a-hydrate was confirmed by X-ray structure determination: W. H. Watson, private communication. The formation of rhe hydrate is probably due to the presence of traces of water in the solvent. For
endo-ri.y ring junction of the 1,2-benzoquinone dimers, see L. Horner, W.
Diirckheimer, Chem. Ber. 95 (1962) 1219.
[51 4a-Hydrate: light yellow needles, m.p. 128- 130°C; 'H-NMR (CDC13,
400 MHz): 6 = 1.91 (d, J = 1.8 Hz, 6-CH3), 2.28 (br. s, 12-CH3), 3.49 (dd,
J=8.8, 2.8 Hz, 8-H), 3.58 (br. d, J = 8 . 8 Hz, 7-H), 3.71 (dd, J=1.8, 1.8 Hz,
I-H), 3.98 (dd, J=6.4, 2.8 Hz, 4-H), 6.16 (ddq, J=6.4, 1.8, 1.8 Hz, 5-H),
6.57 (dq, J = I , I Hz, Il-Hj.--5, gold-yellow resin.-6, dark red needles,
m.p. above 225°C (decornp.); 'H-NMR ([DJDMSO): S=2.10 (d, J = 1.8
Hz, 6-CHI), 2.20 (d, J = 1.0 Hz, I2-CHI), 4.42 (d, J = 1.8 Hz, I-H), 4.54 (d,
J = 6 . 4 Hz, 4-H), 6.30 (9, J = 1.0 Hz, 11-H), 6.45 (ddq, J=6.4, 1.8, 1.8 Hz,
S-Hj.-S, dark red microcrystals, m.p. =244--248"C; UV/VIS (MeOH):
2.,,,,,=275, 360, 458 nm; 'H-NMR ([Da]DMSO): S=2.54 (br. s, 6-CH3),
2.59 (d, J = 0 . 8 Hz, 4-CH3), 7.14 (q, J = O . X Hz, 3-H), 8.10 (br. d, J = 1.5 Hz,
5-H), 8.18 (br. s , J = 1 . 5 Hz, 7-H), 10.62 (br., OH); "C-NMR
([D,]DMSOj:~7=I8.00(Qd,J=127.4,5.3
Hz,4-CH1),20.84(Qt,J=127.4,
4.5 Hz, 6-CH3j, 120.51 (t, J = 6 . 6 Hz, CXa), 120.99(Dq, J = 158.4, 5 Hz, C 3), 125.57 (s, C-8), 126.54 (m,C-6), 129.51 (Ddq, J = 164, 7.2, 4 Hz, C-7),
129.64 (d, J = 7 . 0 Hz, C - I ) , 132.52 (dq, J = 5 , 4 Hz, C-4), 132.61 (Ddq,
J = 164, 6.9, 4 Hz,C-S), 133.69 (m.C-4a), 142.33 (br. s , C-2), 154.37 (s, Cla), 172.76 (d, J = 4 . 4 Hz, C-9); MS: m/r=242.0575 (lo%, M i , calcd. for
C,,H,,,O, 242.0579), 214 (loo), 186 (6), 158 (49), 130 (14). I 1 5 (29).
[6] L. Horner, W. Diirckheimer, Z . Naturforc-ch.B l 4 (1959) 741.
[7] A. 6. Neill, E. D. Amstutz, J. Am. Chrm. SOC.73 (1951) 3687, obtained
traces of a substance that was assigned a naphtho[l,X-bclpyrandione
structure on reaction of 1,s-naphthalenediol with ethyl cyanoformate.
2a, R=Me
2b, R = t B u
A
\
B
2a was synthesized by the method of Bercuw et al.14a1by
carbonylation of 1. The X-ray structure analysisr6' confirms the monomeric structure of the compound (Fig. I ,
left). The ZrOZC2chelate ring of 2a in the crystal is not
planar, but rather folded around the 0-0 axis so that the
ZrOz and the OzCz planes form an angle of 16.8" (Fig. 1,
bottom left).
c2
Monomeric, Mononuclear Enediolate Complexes
of Zirconium: Molecular Geometry and Electronic
Structure of the Products of Reductive CO Coupling
on the Metal**
By Peter Hofmann, * Martin Frede, Peter Stauffert,
Wiltraud Lasser, and Ulf Thewalt
Dedicated to Professor Helmut Behrens on the occasion
of his 70th birthday
Insertion reactions of CO into transition-metal-carbon
bonds are of great interest.l'I Carbonylation of dialkylbis(cyclopentadieny1) complexes of early transition metals
[Cp,MR2] and [CptMRZ](Cp=q5-C5H5,Cp* =q5-CsMe,;
M =Ti, Zr, Hf) in some cases results in direct reductive
coupling of two CO building blocks to yield mononuclear
enediolate complexes (e.g. 1-+ 2a)'41; the initially formed
q*-acyl complexes and their chemistry have been intensely
studied both experimentally'21and theoretically.[']
The mechanism of this remarkable synthetic reaction is
not yet known with certainty."' In order to elucidate it,
among other things, a knowledge of the ground state
geometry and electronic structure of complexes 2 is important. We report here relevant results for 2a and 2b that
confirm the predictions of MO calculations.
[*] Prof. Dr. P. Hofmann, Dipl.-Chem. M. Frede, Dip1.-Chem. P. Stauffert
Anorganisch-chemisches Institut der Technischen Universitat Miinchen
Lichtenbergstrasse 4, D-8046 Garching (FRG)
(**I
7 12
Dip1.-Chem. W. Lasser, Prof. Dr. U. Thewalt
Sektion fur Rontgen- und Elektronenbeugung der Universitat
Oberer Eselsberg, D-7900 Ulm (FRG)
This work was supported by the Fonds der Chemischen Industrie.
0 VCH Verlagsgesellschafl mbH. 0-6940
Weinhelm. I985
Fig. I . Lett: Structure of 2a in the crystal; above. top view; below, aide blew.
Selected bond lengths [A]and angles ["I: Zr-Ol 2.031(4), Zr-02 2.048(6),
01-C1 1.371(10), 02-C6 1.367(9), CI-C6 1.315(13). Zr-C(CSMei) 2,5192.570, C-C ( C , rings) 1.357- 1.435; 01-Zr-02
79.2(2j, Zr-01-CI
111.2(5j, Zr-02-C6
110.0(6), OI-CI-C6
117.3(7), O2-C6-CI
118.7(8),
21-Zr-22 137.0(3) (ZI, 2 2 : centers of [he C5 rings). Right: Structure of Zb
in the crystal; above, top view; below, side view. Selected bond lengths
and angles ["I: Zr-OI 2.022(6), Zr-02 2.011(6), 01-CI 1.372(11), 02-C6
1.400(1I), C I L C 6 1.357(131, Zr-C(C5MeS) 2.525-2.616, C-C (C, rings)
1.372-1.458; 01-Zr-02 75.9(2), Zr-01-CI
I18.4(5), Zr-02-C6 I 18.0(5),
01-CI-C6
I14.2(9), 02-C6-CI
113.5(8), ZI-Zr-Z2
136.1(4) (ZI, 22:
centers of the C , rings).
[A]
Thus, 2a exhibits a geometry that deviates clearly from
A and a 5 2structure toward B and a 02,zbonding mode,
in analogy to enedithiolate complexes[71or s-cis-diene complexes of Cp2Zr fragments.[x1We conclude from this finding for CpTZr, which is a weaker Lewis acid and makes the
ring folding sterically more difficult, that the nonplanar
geometry is a general structural feature"'' of monomeric
do-Cp,M enediolate complexes.'y1 MO model calculations["] for 2a, with a planar geometry corresponding to
0570-0833/XS/0X08-07/2S 02.50/0
Angew Chem lnt Ed. Enyl. 24 (1985) No 8
E
Fig. 2. Frontier orbital energies for? r and &,n geometries (only main contributions to the wave functions of the C=C part and on Zr shown).
Figure 2, give the n orbital of the C=C bond as the H O M O
(b,) and an M O with yz character ( a , ) on the metal as the
LUMO.
Only the folding of the ring['z1allows the n and y2 orbitals to interact, thus causing an increase of the frontier orbital gap: the decrease in n back-bonding of the oxygen
lone pairs to the metal with increasing folding of the chelate ring opposes the frontier-orbital-based trend toward a
02,n geometry. The deep violet color of solutions of 2a
(AmLIx(pentane) = 495 nm, E = 299, band extending far into
the visible), which is unusual for d o systems (Zr'"), may be
ascribed to an electronic transition from the HOMO(n) to
the LUMO (y') and, according to Figure 2, should be more
shifted to longer wavelengths the less the Zr02Czring is
folded. In order to test this, and because explicit calculations for 2a only gave energy differences of a few kcal between A and (even strongly folded) B, we have attempted
to prepare a model system with a planar chelate ring and
pure oz bonding of the enediolate ligand. Accordingly, 2b
was prepared from the nitrogen complex 3[2a1
and the diketone 4. The complex 2b crystallizes in the form of intensely blue crystals;["] its electronic spectrum exhibits a
long-wavelength maximum with a considerable bathochromic shift (Amax(pentane) = 5 7 0 , =
~ 120) as compared to
2a, and its X-ray structure analysis['41(Fig. 1 , right) shows
a sterically constrained, completely planar metallacycle in
the crystal. The distances between the C atoms of the double bond and Zr are 0.1 1 A longer than in nonplanar 2a. It
is thus shown experimentally that 02,n structures on d o CpzM or CpTM fragments are electronically preferred also
for enediolate ligands, but that the extent to which this
bonding mode is found is easily influenced. The preference for such nonplanar ground-state geometries may be
of significance for both stereochemistry and the mechanism of CO coupling on the metal.
[4] a) J . M. Manriquez, D. R. McAlister, R. D. Sanner, J. E. Bercaw, J . A m .
Chem. Soc. 100 (1978) 2716; h) the reaction proceeds similarly for C p in
place of Cp*: G. Erker, private communication; c) for R=CH,SiMel
and Th, U : J. M. Manriquez, P. J. Fagan, T. J. Marks, C. S. Day, V. W.
Day, J . A m . Chem. SOC. 100 (1978) 7112; d) the hydridochloride
(Cp'ZrHCI), can also be carhonylated to an (albeit dimeric) enediolate
complex of type 2 ( R = H , C p instead of Cp*): S . Gamharotta, C. Floriani, A. Chiesi-Villa, C. Guastini, J. Am. Chem. Soc. I05 (1983) 1690.
[5] Crossover experiments with [Cp$Zr(CH,),l and [CpfZr(CD&] confirm
the clean intramolecular course of the reaction l a - 2 a : P. Hofmann, P.
Stauffert, unpublished results.
(61 pi,
a = 13.732(4),
h=10.375(2),
c=9.760(2) A,
a = 114.12(2).
fl= 104.46(2), y=98.89(3)", 2 = 2 ; R = 0 . 0 6 8 , R,(F)=0.075 for 2906 reflections (Philips PW- I100 single-crystal diffractometer, MoK<,radiation; & t 2 0 ( F n ) , 0 5 2 3 " ) . We thank J . Riede for technical assistance.
Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Energie Physik Mathematik,
D-7514 Eggenstein-Leopoldshafen 2, by quoting the depository number
CSD 5 I 296, the names of the authors, and the journal citation.
[7] A. Kutoglu, Acta Crj~slaNogr.Sect. 8 2 9 (1973) 2891.
[S] a) C. Kruger, G. Muller, G. Erker, U. Dorf, K. Engel, Organomerallic.~4
(1985) 215 and references cited therein; h) K. Tatsumi, H. Yasuda, A.
Nakamura, Isr. J . Chem. 23 (1983) 145.
[9] Dimerization may he possible (as described in [4dl) for C p derivatives
analogous to 2a; this would eliminate the tendency toward 02,n coordination as well as remove the origin of the deep color of the systems.
[lo] The o',n-type coordination should therefore also be exhibited by enediamide and enearnidolate complexes of this type: cf. A. K. McMullen,
I. P. Rothwell, J. C. Huffman, J . A m . Chem. Soc. 107 (1975) 1072.
[ I I ] Of the extended Huckel type. For parameters see [3al.
[I21 J. W. Lauher, R. Hoffmann, J. Am. Chem. Sac. 98 (1976) 1729.
[ 131 Experimental procedure: 4 (0.75 g), dissolved in 20 mL of toluene, was
added to 3 (1.8 g) in 40 m L of toluene at -60°C. Upon warming the
mixture to room temperature, N 2 started to evolve and the solution
turned from violet to dark blue. The crude product, which crystallized
out upon concentration of the solution to 10 mL at -8O"C, was recrystorr). Yield 1.7 g
tallized from pentane or sublimed. ( 120-I3O0C,
(76%): m.p.= 150°C (decomp.); correct C,H analysis; ' H - N M R (60
MHz, C,H,): 8=1.4 (s, IXH), 1.9 (s, 3 0 H ) ; I R (Nujol): v = 1700 c m - '
(GC).
[I41 P2,/n, a = 15.288(2), h = 18.937(3), c=9.980(1) A. 8=96.96(1J0, 2 = 4 ;
R=0.072, R,(F)=0.073 for 2477 reflections, ( F c , 2 u ( F < , )0;5 2 3 " ) ; see
also [6].
Can 1,2,3-Oxadiazole be Stable?**
By Minh Tho Nguyen, Anthony F. Hegarty.* and
JosP Elguero
Although 1,2,3-oxadiazoles 1 were first postulated as intermediates in the 1,3-dipolar cycloaddition of dinitrogen
oxide ( N 2 0 ) to alkynes almost thirty-five years ago,[" this
class of heterocycles was unknown until recently. The
weakness of the NO o-bond, which provides a thermodynamic driving force for ring opening to form the more stable acyldiazomethanes 2 was considered as the main reason for the nonexistence of stable l ,2,3-0xadiazoles.~~~
1
2
3
Received: March 26, 1985 [Z 1240 1El
German version: Angew. Chem. 97 (1985) 693
In 1979, Schulz and Schweig reported spectroscopic evidence for the existence of the 1,2,3-benzoxadiazole 3 in
the gas phase (by PE spectroscopy);''] more recently, they
[I] a) F. Calderazzo. Angew. Chem. 89 (1977) 305; Angew. Chem. Int. Ed.
Engl. 16 (1977) 299; b) J. P. Collman, L. S. Hegedus: Principles a n d A p plications of Organorransition Metal Chemistry. University Science
Books, Mill Valley, C A 1980, p. 259ff.
121 a) P. T. Wolczanski, J. E. Bercaw, Acc. Chem. Res. 13 (1980) 21; b) G.
Erker, i h d 17 (1984) 103, and references cited therein.
[3] a) P. Hofmann, P. Stauffert, K. Tatsumi, A. Nakamura, R. Hoffmann,
Organometallics 4 (1985) 404; h) K. Tatsumi, A. Nakamnra, P. Hofmann, P. Stauffert, R. Hoffmann, J . Am. Chem. Soc. I 0 7 (1985) 4440.
[*I Prof. Dr. A. F. Hegarty, Dr. M. T. Nguyen
Department of Chemistry, University College
Belfield, Dublin 4 (Ireland)
Prof. Dr. J. Elguero
Instituto d e Quimica Medica, CSlC
Juan d e la Cierva 3, E-28006 Madrid (Spain)
[**I M . T. N . and A. F. H . thank the Department of Education (Irish
Government) for financial support.
Angew. Cheni Int. Ed. Engl. 24 ( I U S S ) N o .
Y
0 VCH VerlagsgesellschaJi mhH. 0 - 6 9 4 0 Wemherm, 1985
0570-0833/85/0808-0713
S
02.50/0
7 13
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molecular, enediolate, electronica, couplings, complexes, geometry, structure, monomeric, metali, reductive, product, zirconium, mononuclear
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