Organometallic reactivity on a calix[4]arene oxo surface. Synthesis and rearrangement of Zr-C functionalities anchored to a calix[4]arene moiety

DOI: 10.1021/ja970821c

Source and publish data:

Journal of the American Chemical Society p. 9198 - 9210 (1997)

Update date:2022-08-05

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Authors:

Giannini, Luca

Caselli, Alessandro

Solari, Euro

Floriani, Carlo

Chiesi-Villa, Angiola

Rizzoli, Corrado

Re, Nazzareno

Sgamellotti, Antonio

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Article abstract of DOI:10.1021/ja970821c

This report concerns the formation and the main properties of Zr-C functionalities supported by the O₄ matrix of either the monoalkylated (trianionic) or dialkylated (dianionic) forms of [p-Bu(t)-calix[4]arene] (1). The synthesis of the starting materials [p-Bu(t)-calix[4]-(OMe)₂(O)₂ZrCl₂] (4) and [{μ-p-Bu(t)-calix[4]-(OMe)(O)₃}₂ Zr₂Cl₂] (10) has been performed via the lithiation of the corresponding protic forms, [p-Bu(t)-calix[4]-(OMe)₂(OH)₂]] (2) and [p-Bu(t)-calix[4]-(OMe)(OH)₃] (8), followed by reaction with ZrCl₄·(thf)₂. Complex 4 undergoes a facile base-induced (base = Et₃N, Py) demethylation, leading to the monomethoxy derivative [p-Bu(t)-calix[4]-(OMe)(O)₃ZrCl₂]^-[MeNEt₃]⁺ (5) and ionization of the Zr-Cl bond to give [p-Bu(t)-calix[4]-(OMe)₂(O)₂Zr(OTf)₂] (6). The alkylation of 4 led to the corresponding dialkylaryl derivatives [p-Bu(t)-calix[4]-(OMe)₂(O)₂ZrR₂] (R = Me, 12; R = CH₂Ph, 13; R = CH₂-SiMe₃, 14 R = p-MeC₆H₄, 15]. They undergo a base-induced demethylation and dealkylation illustrated by the obtention of [p-Bu(t)-calix[4]]-(OMe)(O)₃Zr(CH₂Ph)(Py)] (18), while the thermal decomposition gave a particularly interesting result in the case of 15, with the formation of the corresponding η²-benzyne, [p-Bu(t)-calix[4]-(OMe)₂(O)₂-Zr(η²-MeC₆H₃) (16). Cationic alkyl derivatives of zirconium have been obtained, in the case of 13, using the monoelectronic oxidizing agent [Cp₂Fe]⁺ or a strong Lewis acid such as [B(C₆F₅)₃], [p-Bu(t)-calix [4]-(OMe)₂(O)₂-Zr(CH₂Ph)]⁺BPh₄^- (19); [p-Bu(t)-calix[4]-(OMe)₂(O)₂Zr(CH₂Ph)(thf)]⁺BPh₄^- (20); and [p-Bu(t)-calix[4]-(OMe)₂(O)₂-Zr(CH₂Ph)]⁺ [B(C₆F₅)₃(CH₂Ph)]^- (21). The cationic alkyl derivatives undergo easy demethylation by pyridine to give 18. The alkylation of 10 with LiPh led to a dimeric dimetallic aryl compound, [{μ-p-Bu(t)-calix[4]-(OMe)(O)₃}₂-Zr₂Ph₂] (22), where the calix[4]arene unit bridges two metal atoms and the methoxy groups are only weakly bound to the metal. The spectator methoxy group binds strongly to the metal in the monomeric η²-iminoacyl [p-Bu(t)-calix[4]-(OMe) (O)₃Zr(Bu(t)N=CPh)] (23), formed from the migratory insertion of Bu(t)NC into the Zr-Ph in 22. The proposed structures have been supported by X-ray analyses carried out on 4, 6, 13, 16, 22, and 23.

Full text of DOI:10.1021/ja970821c

9198

J. Am. Chem. Soc. 1997, 119, 9198-9210

Organometallic Reactivity on a Calix[4]arene Oxo Surface.

Synthesis and Rearrangement of Zr-C Functionalities

Anchored to a Calix[4]arene Moiety

Luca Giannini,^†Alessandro Caselli,^†Euro Solari,^†Carlo Floriani,*^,†

Angiola Chiesi-Villa,^‡Corrado Rizzoli,^‡Nazzareno Re,^§and Antonio Sgamellotti^§

Contribution from the Institut de Chimie Mine´rale et Analytique, BCH, UniVersite´ de Lausanne,

CH-1015 Lausanne, Switzerland, Dipartimento di Chimica, UniVersita` di Parma,

I-43100 Parma, Italy, and Dipartimento di Chimica, UniVersita` di Perugia,

I-06100 Perugia, Italy

ReceiVed March 13, 1997^X

Abstract: This report concerns the formation and the main properties of Zr-C functionalities supported by the O₄

matrix of either the monoalkylated (trianionic) or dialkylated (dianionic) forms of [p-Bu^t-calix[4]arene] (1). The

synthesis of the starting materials [p-Bu^t-calix[4]-(OMe)₂(O)₂ZrCl₂] (4) and [{µ-p-Bu^t-calix[4]-(OMe)(O)₃}₂Zr₂Cl₂]

(10) has been performed Via the lithiation of the corresponding protic forms, [p-Bu^t-calix[4]-(OMe)₂(OH)₂] (2) and

[p-Bu^t-calix[4]-(OMe)(OH)₃] (8), followed by reaction with ZrCl₄‚(thf)₂. Complex 4 undergoes a facile base-induced

(base ) Et₃N, Py) demethylation, leading to the monomethoxy derivative [p-Bu^t-calix[4]-(OMe)(O)₃ZrCl₂]^-[MeNEt₃]⁺

(5) and ionization of the Zr-Cl bond to give [p-Bu^t-calix[4]-(OMe)₂(O)₂Zr(OTf)₂] (6). The alkylation of 4 led to

the corresponding dialkylaryl derivatives [p-Bu^t-calix[4]-(OMe)₂(O)₂ZrR₂] (R ) Me, 12; R ) CH₂Ph, 13; R ) CH₂-

SiMe₃, 14; R ) p-MeC₆H₄, 15]. They undergo a base-induced demethylation and dealkylation illustrated by the

obtention of [p-Bu^t-calix[4]-(OMe)(O)₃Zr(CH₂Ph)(Py)] (18), while the thermal decomposition gave a particularly

interesting result in the case of 15, with the formation of the corresponding η²-benzyne, [p-Bu^t-calix[4]-(OMe)₂(O)₂-

Zr(η²-MeC₆H₃)] (16). Cationic alkyl derivatives of zirconium have been obtained, in the case of 13, using the

monoelectronic oxidizing agent [Cp₂Fe]⁺or a strong Lewis acid such as [B(C₆F₅)₃], [p-Bu^t-calix[4]-(OMe)₂(O)₂-

Zr(CH₂Ph)]⁺BPh₄^-(19); [p-Bu^t-calix[4]-(OMe)₂(O)₂Zr(CH₂Ph)(thf)]⁺BPh₄^-(20); and [p-Bu^t-calix[4]-(OMe)₂(O)₂-

Zr(CH₂Ph)]⁺[B(C₆F₅)₃(CH₂Ph)]^-(21). The cationic alkyl derivatives undergo easy demethylation by pyridine to

give 18. The alkylation of 10 with LiPh led to a dimeric dimetallic aryl compound, [{µ-p-Bu^t-calix[4]-(OMe)(O)₃}₂-

Zr₂Ph₂] (22), where the calix[4]arene unit bridges two metal atoms and the methoxy groups are only weakly bound

to the metal. The spectator methoxy group binds strongly to the metal in the monomeric η²-iminoacyl [p-Bu^t-

calix[4]-(OMe)(O)₃Zr(Bu^tNdCPh)] (23), formed from the migratory insertion of Bu^tNC into the Zr-Ph in 22. The

proposed structures have been supported by X-ray analyses carried out on 4, 6, 13, 16, 22, and 23.

Introduction

Chart 1

The use of a preorganized O₄set of oxygen donor atoms as

a single ancillary ligand in organometallic chemistry does not

have precedent, except for some very recent preliminary

reports.^1-3The p-Bu^t-calix[4]arene and its alkylated forms⁴(see

Chart 1) allowed us to enter this new area.

The few previous reports concern exclusively the complex-

ation of a transition metal ion by the calix[4]arene tetraanion

without any focus on the organometallic functionalization of

the metal center.^3ef,5A, B, and C provide a coordination

environment very different, in terms of geometry and coordina-

tion number, from that determined by the use of monodentate

phenoxo groups. As shown in Chart 1, we can tune the charge

of the calix macrocycle and, consequently, the degree of

functionalization of the [O₄M] fragment Via the alkylation of

the calix[4]arene tetraanion. The major peculiarities in the use

of A, B, or C (Chart 1) as ancillary ligands are (i) the calix[4]-

arene skeleton limits the adaptability of the O₄set to certain

^†Universite´ de Lausanne.

^‡Universita` di Parma.

^§Universita` di Perugia.

^XAbstract published in AdVance ACS Abstracts, September 15, 1997.

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Villa, A.; Rizzoli, C. Angew. Chem., Int. Ed. Engl. 1996, 35, 2825. (b)

Giannini, L.; Solari, E.; Zanotti-Gerosa, A.; Floriani, C.; Chiesi-Villa, A.;

Rizzoli, C. Angew. Chem., Int. Ed. Engl., in press. (c) Gardiner, M. G.;

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Cambridge, U.K., 1989. (b) Calixarenes, A Versatile Class of Macrocyclic

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Netherlands, 1991.

Zr-C Functionalities on a Calix[4]arene Oxo Surface

J. Am. Chem. Soc., Vol. 119, No. 39, 1997 9199

Experimental Section

arrangements around the metal, the square-planar being the

favored one (such a geometrical constraint affects the M-O π

bonding interaction and the frontier orbitals of the [O₄M]

fragment) and (ii) methoxy groups in B and C can play the

role of a spectator donor atom, thus adapting the coordination

number requested by the metal along the reaction pathway.

All operations were carried out under an atmosphere of purified

nitrogen. All solvents were purified by standard methods and freshly

distilled prior to use. NMR spectra were recorded on 200-AC and 400-

dpx Bruker instruments. The syntheses of 1 and 2 have been performed

as reported in the literature.¹¹

Synthesis of 4. BuLi (69 mL, 1.65 M in hexane, 114 mmol) was

added dropwise over 30 min to a stirred solution of 2 (39.3 g, 58.0

mmol) in THF (400 mL). The resulting orange solution was transferred

to a dropping funnel and added dropwise to a suspension of ZrCl₄‚

(thf)₂(22.6 g, 60.0 mol) in THF (200 mL), yielding a yellow solution.

Volatiles were removed in Vacuo, the flask was charged with fresh

benzene (400 mL), and the reaction mixture was refluxed for 3 h. The

mixture was stirred overnight and then extracted over 12 h. Volatiles

were removed in Vacuo, benzene (400 mL) was added, and the mixture

was extracted over 2 h, to yield a white suspension. Volatiles were

removed in Vacuo, benzene (100 mL) and hexane (300 mL) were then

added, and the mixture was stirred for 5 h. The white microcrystalline

4‚(C₆H₆)₂was collected and dried in Vacuo (43.07 g, 75%). ¹H NMR

(CD₂Cl₂, 298 K): δ 7.37 (s, 12H, benzene), 7.16 (s, 4H, ArH), 7.11

(s, 4H, ArH), 4.53 (s, 6H, MeO), 4.34 (d, J ) 13.0 Hz, 4H, endo-

CH₂), 3.44 (d, J ) 13.0 Hz, 4H, exo-CH₂), 1.30 (s, 18H, Bu^t), 1.17 (s,

18H, Bu^t). Anal. Calcd for 4‚(C₆H₆)₂, C₅₈H₇₀Cl₂O₄Zr: C, 70.13; H,

7.10. Found: C, 70.12, H, 7.44. Crystals suitable for X-ray analysis

were obtained at room temperature from supersaturated benzene

solutions of 4.

Synthesis of 5. Et₃N (1 mL) was added at room temperature to a

solution of 4·(C₆H₆)₂(1.61 g, 1.62 mmol) in toluene (100 mL), yielding

a white suspension. 5·(C₇H₈)₂was collected as a white powder (1.14

g, 65%). ¹H NMR (CD₂Cl₂, 298 K): δ 7.22 (m, 10H, C₇H₈), 7.04 (m,

6H, ArH), 6.94 (m, 2H, ArH), 4.53 (d, J ) 12.6 Hz, 2H, endo-CH₂),

4.33 (d, J ) 12.6 Hz, 2H, endo-CH₂), 4.26 (s, 3H, MeO), 3.38 (m, 6H,

CH₂), 3.25 (d, J ) 12.6 Hz, 2H,exo-CH₂), 3.12 (d, J ) 12.6 Hz, 2H,

exo-CH₂), 3.01 (s, 3H, CH₃), 2.34 (s, 6H, C₇H₈), 1.35 (m, 9H, CH₃),

1.26 (s, 9H, Bu^t), 1.15 (s, 9H, Bu^t), 1.34 (s, 18H, Bu^t). Anal. Calcd

for 5·(C₇H₈)₂, C₆₃H₈₃Cl₂NO₄Zr: C, 70,03; H, 7.74; N, 1.30. Found:

C, 69.82; H, 8.12; N, 1.10.

The oxygen donor atoms are particularly appropriate for the

oxophilic, early transition metals. We chose to investigate zir-

conium due to its relevant role in organic synthesis and cataly-

sis.^6-8To this end, we took advantage of the contributions made

by groups such as Rothwell and Wolczanski^9,10in using alkoxo

functionalities as ancillary ligands in organometallic chemistry

and catalysis assisted by early transition metals.

Herein we report full details on the synthesis and the chemical

behavior of the Zr-C bond functionalities bonded to the O₄

skeleton shown in Chart 1 (see anions B and C). This approach

has been developed through the synthesis and the organometallic

functionalization of [calix[4]-(OMe)(O)₃ZrCl]₂and [calix[4]-

(OMe)₂(O)₂ZrCl₂], which give rise to two classes of derivatives

related by the base-induced demethylation of one of the meth-

oxy groups. The experimental and theoretical studies reported

here will emphasize the major differences between the [O₄Zr]²⁺

[O₄Zr]⁺, and [Cp₂Zr]²⁺[Cp ) η⁵-C₅H₅] fragments. The

organometallic derivatization of [calix[4]-(OMe)₂(O)₂ZrCl₂] has

been briefly communicated.¹

(6) (a) Negishi, E.-I.; Takahashi, T. Acc. Chem. Res. 1994, 27, 124 and

references therein. (b) Reetz, M. T. In Organometallics in Synthesis;

Schlosser, M., Ed.; Wiley: New York, 1994; Chapter 3. (c) Erker, G.; Pfaff,

R. Organometallics 1993, 12, 1921. (d) Negishi, E.-I. In ComprehensiVe

Organic Synthesis; Paquette, L. A., Ed.; Pergamon: Oxford, 1991; Vol. 5,

p 1163. (e) Schore, N. E. In ComprehensiVe Organic Synthesis; Paquette,

L. A., Ed.; Pergamon: Oxford, 1991; Vol. 5, p 1037. (f) Buchwald, S. L.;

Nielsen, R. B. Chem. ReV. 1988, 88, 1047.

(7) Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Organozir-

conium and Hafnium Compounds; Wiley: New York, 1986.

(8) (a) Ryan, E. J. In ComprehensiVe Organometallic Chemistry II;

Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford,

1995; Vol. 4, Chapter 9. (b) Coates, G. W.; Waymouth, R. M. In

ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F. G.

A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol. 12, Chapter 12.1.

Organometallics 1989, 8, 2892 and references therein. (d) Buchwald, S.

L.; La Maire, S. J.; Nielsen, R. B.; Watson, B. T.; King, S. M. Tetrahedron

Lett. 1987, 28, 3895. (e) Neghishi, E.; Takahashi, T. Aldrichim. Acta 1985,

18, 31. (f) Neghishi, E.; Miller, J. A.; Yoshida, T. Tetrahedron Lett. 1984,

25, 3407. (g) Neghishi, E.; Yoshida, T. Tetrahedron Lett. 1980, 21, 1501.

(h) Schwartz, J. Pure Appl. Chem. 1980, 52, 733. (i) Carr, D. B.; Yoshifuji,

M.; Shoer, L. I.; Gell, K. I.; Schwartz, J. Ann. N. Y. Acad. Sci. 1977, 295,

127. (j) Schwartz, J.; Labinger, J. A. Angew. Chem., Int. Ed. Engl. 1976,

15, 333.

(9) Parkin, B. C.; Clark, J. R.; Visciglio, V. M.; Fanwick, P. E.; Rothwell,

I. P. Organometallics 1995, 14, 3002. Clark, J. R.; Fanwick, P. E.; Rothwell,

I. P. J. Chem. Soc., Chem. Commun. 1995, 553. Bonanno, J. B.; Lobkovsky,

E. B.; Wolczanski, P. T. J. Am. Chem. Soc. 1994, 116, 11159. Miller, R.

L.; Toreki, R.; LaPointe, R. E.; Wolczanski, P. T.; Van Duyne, G. D.; Roe,

D. C. J. Am. Chem. Soc. 1993, 115, 5570. Yu, J. S.; Ankianiec, B. C.;

Rothwell, I. P., Nguyen, M. T. J. Am. Chem. Soc. 1992, 114, 1927. Chesnut,

R. W.; Jacob, G. G.; Yu, J. S.; Fanwick, P. E.; Rothwell, I. P. Organome-

tallics 1991, 10, 321.

(10) (a) Zambrano, C. H.; Fanwick, P. E.; Rothwell, I. P. Organometallics

1994, 13, 1174. (b) Hill, J. E.; Bailich, G.; Fanwick, P. E.; Rothwell, I. P.

Organometallics 1993, 12, 2911. (c) Bailich, G.; Fanwick, P. E.; Rothwell,

I. P. J. Am. Chem. Soc. 1993, 115, 1581. (d) Hill, J. E.; Bailich, G.; Fanwick,

P. E.; Rothwell, I. P. Organometallics 1991, 10, 3428. (e) Floriani, C.;

Corazza, F.; Lesueur, W.; Chiesi-Villa, A.; Guastini, C. Angew. Chem.,

Int. Ed. Engl. 1989, 28, 66. (f) Chisholm, M. H.; Rothwell, I. P. In

ComprehensiVe Coordination Chemistry; Wilkinson, G., Gillard, R. D.,

McCleverty, J. A., Eds.; Pergamon: Oxford, 1988; Vol. 2, Chapter 15.3.

(g) Chamberlain, L. R.; Durfee, L. D.; Fau, P. E.; Fanwick, P. E.; Kobriger,

L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.; Huffman,

J. C.; Streib, W. E., Wang, R. J. Am. Chem. Soc. 1987, 109, 390, 6068 and

references therein. (h) Durfee, L. D.; Fanwick, P. E.; Rothwell, I. P.; Folting,

K.; Huffman, J. C. J. Am. Chem. Soc. 1987, 109, 4720. (i) Lubben, T. V.;

Wolczanski, P. T. J. Am. Chem. Soc. 1987, 109, 424 and references therein.

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Organometallics 1985, 4, 902.

Hydrolysis of 5. 5 (0.074 g, 72.0 mmol) was dissolved in CH₂Cl₂

(10 mL) under an N₂atmosphere and hydrolyzed with diluted

HCl. The organic layer was washed with water (3 × 7 mL) and dried

(Na₂SO₄, then in Vacuo). Clean 8 resulted as determined by ¹H

NMR analysis (CDCl₃). Analogous results were obtained on reacting

4‚(C₆H₆)₂with pyridine; such a treatment, followed by hydrolysis, gave

clean 8.

Synthesis of 6. AgOTf (1.07 g, 4.16 mmol) was added to a benzene

(100 mL) solution of 4‚(C₆H₆)₂(2.1 g, 2.1 mmol). A white, fluffy

solid formed, and the mixture was stirred overnight. Salts were filtered

off, benzene was almost completely removed in Vacuo, and hexane

(80 mL) was added. The white mixture was briefly refluxed and then

extracted for 3 h (some dark solid was left on the frit, filtration in

benzene does not completely remove Ag salts). Keeping the resulting

colorless solution at -25 °C for 12 h gave 6‚C₆H₆as a white

microcrystalline solid, which was collected and dried in Vacuo (1.58

g, 66%). ¹H NMR (C₆D₆, 298 K): δ 7.17 (s, 4H, ArH), 6.76 (s, 4H,

ArH), 4.54 (d, J ) 12.9 Hz, 4H, endo-CH₂), 3.89 (s, 6H, MeO), 3.23

(d, J ) 12.9 Hz, 4H, exo-CH₂), 1.36 (s,18H, Bu^t), 0.65 (s, 18H, Bu^t).

Anal. Calcd for 6‚C₆H₆: C₅₄H₆₄F₆O₁₀S₂Zr: C, 56.77; H, 5.65.

Found: C, 56.72; H, 5.44. Crystals suitable for X-ray analysis were

obtained at room temperature from a supersaturated solution of 6‚C₆H₆

in hexane. The product is thermally stable in C₆D₆(14 h, 65 °C) and

polymerizes THF. 6 reacted with pyridine to give 7, as was observed

in an NMR tube. The hydrolysis of 7 gave clean 8.

Synthesis of 8. 2 (41.0 g, 60.7 mmol) and TiCl₄‚(thf)₂(20.2 g, 60.6

mmol) were dissolved in toluene (500 mL). The dark red solution

was refluxed for 4 days. HCl (10% water solution, 300 mL) was added

and the mixture stirred overnight. The organic layer was extracted,

washed with water until neutrality (3 × 300 mL), dried (Na₂SO₄), and

filtered. The solvent was removed in Vacuo at the diffusive pump (130

°C, 8 h), yielding 8 as a white powder (35.6 g, 89%). ¹H NMR (CDCl₃,

(11) Arduini, A.; Casnati, A. In Macrocycle Synthesis; Parker, O., Ed.;

Oxford University Press: New York, 1996; Chapter 7.

9200 J. Am. Chem. Soc., Vol. 119, No. 39, 1997

Giannini et al.

298 K): δ 10.16 (br s, 1H, Ar-OH), 9.58 (br s, 2H, ArOH), 7.11 (s,

2H, ArH), 7.07 (m, 4H, ArH), 7.00 (m, 2H, ArH), 4.37 (d, J ) 13.7

Hz, 2H, endo-CH₂), 4.32 (d, J ) 13.7 Hz, 2H, endo-CH₂), 4.14 (s, 3H,

MeO), 3.43 (d, J ) 13.7 Hz, 2H, exo-CH₂), overlapping with 3.43 (d,

J ) 13.7 Hz, 2H, exo-CH₂), 1.23 (s, 18H, Bu^t), 1.22 (s, 9H, Bu^t), 1.21

(s, 9H, Bu^t). Anal. Calcd for 8, C₄₅H₅₈O₄: C, 81.53; H, 8.82.

Found: C, 81.20; H, 8.77.

4H, endo-CH₂), 4.22 (s, 6H, MeO), 3.32 (d, J ) 12.5 Hz, 4H, exo-

CH₂), 1.27 (s,18H, Bu^t), 1.07 (s, 18H, Bu^t), 0.62 (s, 6H, Me-Zr). Anal.

Calcd for 12‚C₆H₆, C₅₄H₇₀O₄Zr: C, 74.18; H, 8.07. Found: C, 74.38;

H, 8.18. Crystals suitable for X-ray analysis were obtained by keeping

a pentane solution of 12 saturated at room temperature at 8 °C. The

product is stable to prolonged heating (65 °C, 14 h) in C₆D₆and

CD₂Cl₂, as judged by H NMR; it is not photosensitive in C₆D₆but

gives 4 when photolyzed in CD₂Cl₂. The redistribution reaction

between 12 and 4 is fast; dissolving the two compounds (ca. 20 mg of

each) in ca. equimolar amounts in CD₂Cl₂gives an equilibrium mixture

of the two reagents and a new product in ca. 1:1:2 ratio, as judged by

¹H NMR [for the new species, δ 7.13 (s, 4H, ArH), 7.04 (s, 4H, ArH),

4.43 (d, J ) 12.5 Hz, 4H, endo-CH₂), 4.36 (s, 6H, MeO), 3.37 (d, J )

12.5 Hz, 4H, exo-CH₂), 1.27 (s,18H, Bu^t), 1.13 (s, 18H, Bu^t), 0.82 (s,

3H, Me-Zr)]. Some peaks overlap with those of the two reagents).

Synthesis of 13. Method A. 2 (26.2 g, 39.0 mmol) and ZrCl₄‚

(thf)₂(14.5 g, 38.4 mmol) were suspended in benzene (200 mL), and

the reaction mixture was refluxed for 2 h. The solvent was removed

by distillation and then added again. After a further reflux (10 min),

the solvent was removed by distillation and the residue dried in Vacuo

at 80 °C. The flask was then charged with fresh toluene (200 mL),

and to the stirred mixture, at -30 °C, was added a solution of CH₂-

PhMgCl (118.0 mL, 0.68 M in THF, 80 mmol) dropwise over 45 min.

The mixture, which became bright yellow in seconds, was allowed to

warm to room temperature. Dioxane (20 mL) was added, and the

mixture was stirred over 1 h. Volatiles were removed in Vacuo (heating

to 80 °C over 2 h). The residue was extracted over 3 days with a

mixture of n-hexane (500 mL) and benzene (100 mL), to give a yellow

suspension. The bright yellow microcrystalline 13 was collected

and dried in Vacuo (12.0 g, 33%). A further extraction of the solid

left on the extractor with benzene (250 mL) resulted in the collec-

tion of 13‚(C₆H₆)₂light yellow powder (10.8 g, 25.4%). Anal. Calcd

for 13‚(C₆H₆)₂, C₇₂H₈₄O₄Zr: C, 78.27; H, 7.66. Found: C, 78.25; H,

8.07.

Synthesis of 9. BuLi (20.4 mL, 1.79 M in n-hexane, 36.5 mmol)

was added dropwise over 1 h to a stirred solution of 8 (8.07 g, 12.2

mmol) in toluene (180 mL) kept at 16 °C. The reaction mixture was

refluxed over 2 h. Volatiles were removed in Vacuo, and hexane (150

mL) was added to the residue. 9 was collected as a white powder

(7.24 g, 87%). ¹H NMR (CD₂Cl₂, 298 K): δ 7.10 (d, J ) 2.4 Hz, 2H,

ArH), 7.06 (d, J ) 2.4 Hz, 2H, ArH), 6.85 (s, 2H, ArH), 6.78 (s, 2H,

ArH), 4.31 (d, J ) 13.2 Hz, 2H, endo-CH₂), 3.99 (d, J ) 14.2 Hz, 2H,

endo-CH₂), 3.74 (s, 3H, MeO), 3.29 (d, J ) 14.2 Hz, 2H, exo-CH₂),

overlapping with 3.28 (d, J ) 13.2 Hz, 2H, exo-CH₂), 1.29 (s, 18H,

Bu^t), 1.02 (s, 9H, Bu^t), 0.95 (s, 9H, Bu^t). Anal. Calcd for 9, C₄₅H₅₅O₄-

Li₃: C, 79.40; H, 8.14. Found: C, 79.48; H, 8.23.

Synthesis of 10. 9 (14.0 g, 20.5 mmol) and ZrCl₄‚(thf)₂(7.85 g,

20.8 mmol) were suspended in benzene (180 mL). The reaction mix-

ture was refluxed for 16 h and then extracted for 48 h. Volatiles were

then removed in Vacuo, and hexane (80 mL) was added to the residue.

10‚2(thf)‚2C₆H₆was collected as a white powder (15.76 g, 82%). ¹H

NMR (pyr-d₅, 298 K): δ 7.48 (d, J ) 2.4 Hz, 4H, ArH), 7.37 (d, J )

2.4 Hz, 4H, ArH), 7.34 (s, 12H, C₆H₆), 7.03 (s, 4H, ArH), 6.85 (s, 4H,

ArH), 4.96 (d, J ) 12.2 Hz, 4H, endo-CH₂), 4.66 (d, J ) 12.2 Hz, 4H,

endo-CH₂), 3.91 (s, 6H, MeO), 3.62 (m, 8H, THF), 3.54 (d, J ) 12.2

Hz, 4H, exo-CH₂), 3.19 (d, J ) 12.2 Hz, 4H, exo-CH₂), 1.59 (m, 8H,

THF), 1.46 (s, 36H, Bu^t), 0.85 (s, 18H, Bu^t), 0.78 (s, 18H, Bu^t). Anal.

Calcd for 10‚2(thf)‚2C₆H₆, C₁₁₀H₁₃₈Cl₂O₁₀Zr₂: C, 70.52; H, 7.42.

Found: C, 70.45; H, 7.63.

Synthesis of 11. 10‚2(thf)‚2C₆H₆(3.17 g, 1.69 mmol) was treated

with pyridine to give a turbid solution, which was filtered. The resulting

colorless solution was kept at -24 °C for 2 days to give colorless

crystals of 11‚3(Py) and then dried in Vacuo. ¹H NMR: (pyr-d₅, 298

K): δ 7.60-7.16 (ArH), 4.97 (d, J ) 12.2 Hz, 2H, endo-CH₂), 4.69

(d, J ) 12.7 Hz, 2H, endo-CH₂), 3.93 (s, 3H, MeO), 3.55 (d, J ) 12.2

Hz, 2H, exo-CH₂), 3.21 (d, J ) 12.7 Hz, 2H, exo-CH₂), 1.47 (s, 18H,

Bu^t), 0.86 (s, 9H, Bu^t), 0.79 (s, 9H, Bu^t). Anal. Calcd for C₇₀H₈₀-

ClN₅O₄Zr: C, 71.12; H, 6.82; N, 5.92. Found: C, 71.04; H, 6.67; N,

6.20. Crystals with formula 11‚(Py)_6.5were obtained at -24 °C from

a room temperature saturated solution of 10‚(thf)₂‚(C₆H₆)₂in pyridine.

Synthesis of 12. Method A. 2 (20.8 g, 30.8 mmmol) and ZrCl₄‚

(thf)₂(11.4 g, 30.3 mmol) were suspended in benzene (200 mL), and

the reaction mixture was refluxed for 2 h. The solvent was distilled

off and then added again. After a further 10 min reflux, the solvent

was evaporated to dryness and the residue dried in Vacuo at 80 °C.

The flask was then charged with fresh benzene (300 mL), and to the

stirred mixture was added MeLi (30.3 mL, 2.0 M in Et₂O, 60.6 mmol)

dropwise over 1 h, resulting in a yellow suspension. The mixture was

concentrated to ∼30 mL and n-hexane (250 mL) added to the yellow,

creamy suspension. Extraction over 48 h gave a colorless powder of

12, which was then collected by filtration and finally dried in Vacuo

(10.9 g, 45%). Colorless crystals of 12‚(C₆H₆)₂were collected from

the mothers liquor kept at -18 °C for 2 days (6.48 g, 22.5%). ¹H

NMR (C₆D₆, 298 K): δ 7.23 (s, 4H, ArH), 6.80 (s, 4H, ArH), 4.46 (d,

J ) 12.5 Hz, 4H, endo-CH₂), 3.69 (s, 6H, MeO) 3.18 (d, J ) 12.5 Hz,

4H, exo-CH₂), 1.46 (s, 18H, Bu^t), 1.25 (s, 6H, Me-Zr), 0.77 (s, 18H,

Bu^t). Anal. Calcd for 12, C₄₈H₆₄O₄Zr: C, 72.41; H, 8.10. Found: C,

71.94; H, 8.35.

Method B. PhCH₂MgCl (34 mL, 1.33 M in THF, 45.2 mmol) was

added dropwise to a toluene (300 mL) solution of 4·(C₆H₆)₂(22.75 g,

22.9 mmol) at -35 °C. The mixture, which became bright yellow in

seconds, was allowed to warm to room temperature with stirring.

Dioxane (10 mL) was added, and the mixture was stirred for 1 h.

Volatiles were removed in Vacuo (heating to 50 °C). The residue was

extracted over 3 days with a mixture of hexane (500 mL) and benzene

(60 mL), yielding a yellow suspension. The microcrystalline, bright

yellow 13 was collected and dried in Vacuo (16.8 g, 77%). ¹H NMR

(CD₂Cl₂, 298 K): δ 7.34-7.17 (m, 8H, ArH(CH₂Ph)), 7.12 (s, 4H,

ArH), 7.00 (s, 4H, ArH), 6.85 (m, 2H, ArH(CH₂Ph)), 4.28 (d, J )

12.5 Hz, 4H, endo-CH₂), 3.60 (s, 6H, MeO), 3.27 (d, J ) 12.5 Hz, 4H,

exo-CH₂), 2.69 (s, 4H, CH₂Ph), 1.28 (s,18H, Bu^t), 1.12 (s, 18H, Bu^t).

¹H NMR (C₆D₆, 298 K): δ 7.65 (m, 4H, ArH(CH₂Ph)), 7.31 (s, 4H,

ArH), 7.23 (m, 4H, ArH(CH₂Ph)), 6.86 (m, 2H, ArH(CH₂Ph)), 6.80

(s, 4H, ArH), 4.46 (d, J ) 12.5 Hz, 4H, endo-CH₂), 3.37 (s, 6H, MeO),

3.24 (d, J ) 12.5 Hz, 4H, exo-CH₂), 3.04 (s, 4H, CH₂Ph), 1.45 (s,

18H, Bu^t), 0.70 (s, 18H, Bu^t). Anal. Calcd for 13, C₆₀H₇₂O₄Zr: C,

75.98; H, 7.65. Found: C, 76.21; H, 7.73. Crystals suitable for X-ray

analysis were obtained at room temperature from a supersaturated

solution of 13 in toluene. The product is thermally stable (65 °C, 14

h) in C₆D₆and CD₂Cl₂, as judged by H NMR. It is photosensitive;

exposing C₆D₆solutions of the product to solar light for a few hours

gives quantitatively the PhCH₂-CH₂Ph coupling product (¹H NMR),

together with a lower symmetry calixarene species.

Synthesis of 14. LiCH₂SiMe₃(1.07 g, 11.4 mmol) was added to a

suspension of 4‚(C₆H₆)₂(5.63 g, 5.67 mmol) in toluene (150 mL) kept

at -40 °C. The reaction mixture was allowed to warm to room

temperature under stirring overnight. Volatiles were removed in Vacuo,

and Et₂O (150 mL) was added to the residue, which was extracted for

3 h to yield a white powder of 14 (2.92 g, 55%). ¹H NMR (C₆D₆, 298

K): δ 7.24 (s, 4H, ArH), 6.82 (s, 4H, ArH), 4.58 (d, J ) 12.2 Hz, 4H,

endo-CH₂), 3.81 (s, 6H, MeO), 3.30 (d, J ) 12.2 Hz, 4H, exo-CH₂),

1.40 (s, 18H, Bu^t), 1.23 (s, 4H, CH₂), 0.80 (s, 18H, Bu^t), 0.48 (s, 18H,

SiMe₃). Anal. Calcd for 14, C₅₄H₈₀O₄Si₂Zr: C, 68.95; H, 8.53.

Found: C, 69.10; H, 8.85. The product is stable to prolonged heating

(80 °C, 14 h) in C₆D₆, as judged by NMR. Decomposition of the

product was observed under photolysis (313 nm, 3 h) in C₆D₆.

Method B. MeLi (7.7 mL, 1.71 M in Et₂O, 13.2 mmol) was added

dropwise to a toluene (200 mL) solution of 4‚(C₆H₆)₂(6.6 g, 6.7 mmol)

at -30 °C. The mixture was allowed to warm to room temperature

with stirring, and then volatiles were removed in Vacuo, benzene (150

mL) was added, and the mixture was heated to reflux, filtered while

hot, and concentrated in Vacuo by evaporation to ca. 30 mL. n-Hexane

(200 mL) was added to the resulting white, creamy suspension and the

mixture refluxed to give a colorless solution. Standing at 9 °C for 3

days gave colorless crystals of 12‚C₆H₆, which were collected and dried

in Vacuo (3.66 g, 63%). ¹H NMR (CD₂Cl₂, 298 K): δ 7.36 (s, 6H,

benzene), 7.10 (s, 4H, ArH), 6.96 (s, 4H, ArH), 4.42 (d, J ) 12.5 Hz,

Zr-C Functionalities on a Calix[4]arene Oxo Surface

J. Am. Chem. Soc., Vol. 119, No. 39, 1997 9201

Synthesis of 15. Method A. 2 (14.2 g, 21.0 mmol) and ZrCl₄‚

(thf)₂(7.83 g, 20.7 mmol) were suspended in benzene (200 mL), and

the reaction mixture was refluxed for 2 h. The solvent was removed

by distillation and then readded. After a further reflux of 10 min, the

solvent was removed by distillation, and the residue was dried in Vacuo

at 80 °C. The flask was then charged with fresh toluene (250 mL),

and to the stirred mixture was added p-MeC₆H₄MgBr (41.6 mL, 1 M

in THF, 41.6 mmol) dropwise over 1 h, resulting in a yellow suspension.

The mixture was stirred for 3 h at room temperature, and then dioxane

(10 mL) was added and stirring continued for 1 h. The white salts

were filtered off and washed with toluene (150 mL). Volatiles were

removed in Vacuo. n-Hexane (150 mL) was added to the residue, and

15 was collected as a white powder (15.5 g, 78%). ¹H NMR (C₆D₆,

298 K): δ 8.14 (d, J ) 7.4 Hz, 4H, ArH(p-tolyl)), 7.27 (s, 4H, ArH),

7.12 (d, J ) 7.4 Hz, 4H, ArH(p-tolyl)), 6.79 (s, 4H, ArH), 4.60 (d, J

) 12.5 Hz, 4H, endo-CH₂), 3.35 (s, 6H, MeO), 3.19 (d, J ) 12.5 Hz,

4H, exo-CH₂), 2.22 (s, 6H, CH₃(p-tolyl)), 1.44 (s, 18H, Bu^t), 0.84 (s,

18H, Bu^t). Anal. Calcd for 15, C₆₀H₇₂O₄Zr: C, 75.98; H, 7.65.

Found: C, 75.72; H, 7.73.

ArH), 7.17 (m, 2H, ArH(CH₂Ph)), 7.07 (s, 2H, ArH), 6.97 (m, 1H,

ArH(CH₂Ph)), 6.85 (s, 2H, ArH), 6.75 (m, 2H, ArH(CH₂Ph)), 4.78 (d,

J ) 12.1 Hz, 2H, endo-CH₂), 4.54 (d, J ) 12.5 Hz, 2H, endo-CH₂),

4.14 (s, 3H, MeO), 3.58 (d, J ) 12.1 Hz, 2H, exo-CH₂), 3.25 (d, J )

12.5 Hz, 2H, exo-CH₂), 2.78 (s, 2H, CH₂Ph), 1.45 (s,18H, Bu^t), 0.79

(s, 9H, Bu^t), overlapping with 0.78 (s, 9H, Bu^t). ¹H NMR (C₆D₆, 298

K): δ 8.70 (m, 2H, pyr), 7.30 (d, J ) 2.4 Hz, 2H, ArH), 7.28 (d, J )

2.4 Hz, 2H, ArH), 7.13 (m, 2H, ArH(CH₂Ph)), 6.97-6.80 (m, 8H, ArH,

pyr, CH₂Ph), 6.60 (m, 2H, pyr), 4.63 (d, J ) 12.1 Hz, 2H, endo-CH₂),

overlapping with 4.56 (br d, 2H, endo-CH₂), 3.75 (s, 3H, MeO), 3.40

(d, J ) 12.1 Hz, 2H, exo-CH₂), 3.24 (d, J ) 12.6 Hz, 2H, exo-CH₂),

2.62 (br s, 2H, CH₂Ph), 1.43 (s, 18H, Bu^t), 0.81 (s, 9H, Bu^t), 0.78 (s,

9H, Bu^t). Anal. Calcd for 18, C₅₇H₆₇NO₄Zr: C, 74.30; H, 7.33; N,

1.52. Found: C, 74.48; H, 7.69; N, 1.69. The product is thermally

stable (65 °C, 14 h) in C₆D₆, as judged by ¹H NMR. It is not

photosensitive. When hydrolyzed, clean 8 is obtained. The demeth-

ylation pathway is supported by the following observations: (i) The

reaction was conducted in pyr-d₅, volatiles were removed in Vacuo,

and the residue was dissolved in C₆D₆. ¹H NMR showed clean

18 plus three resonances at δ 2.73 (br d), 2.24 (s), and 2.16 (s). (ii)

(CH₂Ph)₂Mg (1.8 mL, 1.17 N, 2.10 mequiv) was added at -40 °C to

a suspension of PyMe⁺BPh₄^-(0.932 g, 2.25 mmol) in THF (100 mL),

and the mixture was allowed to stir at room temperature. A sample of

the resulting solution was evaporated to dryness, and the residue was

dissolved in C₆D₆. ¹H NMR revealed resonances at δ 5.99 (m), 5.73

(m), 5.45 (m), 4.88 (m), 4.42 (m), 3.82 (m), 3.47 (m), 2.75 (m), 2.24

(s), and 2.16 (s). (iii) A sample of the pyridine reaction mixture, before

workup with n-hexane, was evaporated to dryness and the residue

dissolved in C₆D₆. ¹H NMR showed clean 8, plus resonances at δ

5.99 (m), 5.73 (m), 5.45 (m), 4.88 (m), 4.42 (m), 3.82 (m), 3.47 (m),

overlapping wih one of the CH₂doublets of 18, 2.75 (m), 2.24 (s), and

2.16 (s).

Method B. p-MeC₆H₄MgBr (10 mL, 0.98 M in THF, 9.8 mmol)

was added dropwise to a toluene (50 mL) solution of 4‚(C₆H₆)₂(4.81

g, 4.84 mmol). Dioxane (2 mL) was added to the resulting cloudy

solution, and the mixture was stirred overnight. The salts were filtered

off, and volatiles were removed in Vacuo. n-Hexane (40 mL) was added

to the residue, the flask kept at -24 °C overnight, and the white 15

was finally collected and dried in Vacuo (3.02 g, 65.4%). Anal. Calcd

for 15, C₆₀H₇₂O₄Zr: C, 75.98, H, 7.65. Found: C, 76.23; H, 7.77.

Synthesis of 16. 15 (3.75 g, 3.96 mmol) was dissolved in benzene

(130 mL) and the colorless solution refluxed for 36 h to give an orange-

brown solution. Volatiles were removed in Vacuo, and n-hexane (30

mL) was added to the residue. The resulting 16 was collected as a

white powder (1.55 g, 46%). ¹H NMR (C₆D₆, 298 K): δ 8.05 (d, J )

6.8 Hz, 1H, ArH), 7.91 (s, 1H, ArH), 7.59 (d, J ) 6.8 Hz, 1H, ArH),

7.24 (s, 4H, ArH), 6.87 (s, 4H, ArH), 4.62 (s, 6H, MeO) 4.48 (d, J )

12.2 Hz, 4H, endo-CH₂), 3.23 (d, J ) 12.2 Hz, 4H, exo-CH₂), 2.60 (s,

3H, CH₃), 1.44 (s, 18H, Bu^t), 0.78 (s, 18H, Bu^t). Anal. Calcd for 16,

C₅₃H₆₄O₄Zr: C, 74.34; H, 7.53. Found: C, 74.49; H, 7.95. Crystals

suitable for X-ray analysis were obtained from a saturated toluene

solution of 16 at 8 °C. The product is stable to prolonged heating

Synthesis of 19. [Cp₂Fe]⁺BPh₄^-(1.35 g, 2.40 mmol) was added to

a suspension of 13 (2.06 g, 2.17 mmol) in toluene (100 mL) at -35

°C, and the mixture was warmed to room temperature over 5 h; at this

temperature, all of the [Cp₂Fe]⁺BPh₄had disappeared and a yellow

suspension resulted. It was stirred overnight, and then the bright yellow,

microcrystalline 19‚C₇H₈was collected, washed with hexane (2 × 20

mL), and dried in Vacuo (0.86 g, 31%). ¹H NMR (CD₂Cl₂, 298 K): δ

7.73-6.82 (m, 38H, ArH), 4.18 (d, J ) 12.9 Hz, 4H, endo-CH₂), 3.74

(s, 6H, MeO), 3.45 (d, J ) 12.9 Hz, 4H, exo-CH₂), overlapping with

3.40 (s, 2H, CH₂Ph), 2.34 (s, 3H, C₇H₈) 1.30 (s, 18H, Bu^t), 0.99 (s,

18H, Bu^t). Anal. Calcd for 19·C₇H₈, C₈₄H₉₃BO₄Zr: C, 79.52; H, 7.39.

Found: C, 78.99; H, 7.73. The product is thermally unstable in C₆D₆

(1 h, 90 °C), giving 13 and a dimeric 22 (¹H NMR, X-ray). It is

unstable in CD₂Cl₂(at room temperature, the product disappears in

days). It is photosensitive. It reacts with THF to give the adduct (¹H

NMR, <10 min); coordinated THF is labile, as shown by the fact that,

in the presence of more than 1 THF per Zr, a single set of THF signals

is visible, at chemical shifts strongly dependent on the amount of THF

and falling in between those of free and coordinated THF. 19‚C₇H₈

reacts with pyridine to give PyMe⁺(BPh)₄^-and 18 (¹H NMR). It does

not react with ethylene.

(120 °C, 14 h) in toluene, as determined by H NMR.

Synthesis of 17. (CH₂Ph)₂Mg (4.7 mL, 0.35 M in Et₂O, 1.65 mmol)

was added dropwise over 30 min to a stirred toluene solution (80 mL)

of 10·(thf)₂·(C₆H₆)₂(3.08 g, 1.64 mmol) kept at -30 °C. The mixture,

which became a yellow suspension in seconds, was allowed to warm

to room temperature. Dioxane (2 mL) was added, and the mixture

was refluxed over 2 h and filtered. Volatiles were removed in Vacuo,

n-hexane (30 mL) was added to the residue, and 17 was collected as a

pale yellow powder (1.2 g, 43%). ¹H NMR (C₆D₆, 298 K): δ 7.41

(m, 4H, ArH), 7.28 (m, 4H, ArH), overlapping with 7.26 (d, J ) 2.4

Hz, 4H, ArH), 7.22 (d, J ) 2.4 Hz, 4H, ArH), 6.99 (m, 2H, ArH), 6.87

(s, 4H, ArH), 6.82 (s, 4H, ArH), 4.86 (d, J ) 12.7 Hz, 4H, endo-CH₂),

4.32 (d, J ) 12.2 Hz, 4H, endo-CH₂), 3.49 (s, 6H, MeO), 3.31 (d, J )

12.7 Hz, 4H, exo-CH₂), overlapping with 3.25 (d, J)12.2 Hz, 4H, exo-

CH₂), 2.86 (s, 4H, CH₂Ph), 1.41 (s, 36H, Bu^t), 0.80 (s, 18H, Bu^t), 0.69

(s, 18H, Bu^t). ¹H NMR (pyr-d₅, 298 K): δ 7.51-6.74 (ArH), 4.80 (d,

J ) 12.0 Hz, 2H, endo-CH₂), 4.55 (d, J ) 12.5 Hz, 2H, endo-CH₂),

4.15 (s, 3H, MeO), 3.59 (d, J ) 12.0 Hz, 2H, exo-CH₂), 3.26 (d, J )

12.5 Hz, 2H, exo-CH₂), 2.79 (s, 2H, CH₂Ph), 1.46 (s, 18H, Bu^t), 0.80

(s, 9H, Bu^t), 0.79 (s, 9H, Bu^t). Anal. Calcd for 17, C₁₀₄H₁₂₄O₈Zr₂: C,

74.15; H, 7.42. Found: C, 73.16; H, 7.61. Rather clean 17 (¹H NMR,

C₆D₆) was obtained by refluxing overnight a THF (100 mL) solution

of 13 (2.0 g) and Et₃N (1.0 mL). Gas-mass chromatographical analysis

of the reaction mixture revealed the presence of ethylene, toluene, and

ethylbenzene.

Synthesis of 20. [Cp₂Fe]⁺BPh₄^-(0.82 g, 1.62 mmol) was added to

a solution of 13 (1.44 g, 1.52 mmol) in THF (100 mL) at -35 °C, and

the mixture was warmed to room temperature over 3 h; at this

temperature, all of the [Cp₂Fe]⁺BPh₄had disappeared, and a yellow

solution was obtained. Volatiles were removed in Vacuo, and the

residue was washed with pentane (75 mL), collected, and dried in Vacuo

(1.3 g). ¹H NMR and elemental analyses revealed that the product

was impure due to polymeric THF; analytically pure 20 (1.0 g, 52.7%)

was obtained by recrystallization of the crude product in benzene/hexane

(60/90 mL). ¹H NMR (CD₂Cl₂, 298 K): δ 7.60-6.85 (m, 33H, ArH),

4.31 (m, 4H, THF), 4.14 (d, J ) 12.9 Hz, 4H, endo-CH₂), 3.76 (s, 6H,

MeO), 3.44 (d, J ) 12.9 Hz, 4H, exo-CH₂), 3.02 (s, 2H, CH₂Ph), 2.08

(m, 4H, THF), 1.30 (s,18H, Bu^t), 1.09 (s, 18H, Bu^t). Anal. Calcd for

20, C₈₁H₉₃BO₅Zr: C, 77.91; H, 7.51. Found: C, 77.58; H, 7.49.

Synthesis of 21. A solution of B(C₆F₅)₃(1.03 g, 2.01 mmol) in

toluene (50 mL) was added dropwise to a suspension of 13 (1.93 g,

2.03 mmol) in toluene (150 mL), giving a yellow solution. Volatiles

were removed in Vacuo, and the residue was washed with hexane

(100 mL), collected, and dried in Vacuo (2.65 g, 89.4%). ¹H NMR

Synthesis of 18. 13 (3.12 g, 3.29 mmol) was dissolved at room

temperature in pyridine (60 mL), and the resulting yellow solution was

allowed to stand for 36 h at room temperature in the dark. Volatiles

were then removed in Vacuo, and hexane (60 mL) was added to the

residue. The resulting yellow solution was kept at 9 °C for 24 h,

yielding a pale yellow solid, which was collected, washed with hexane

(2 × 15 mL), and dried in Vacuo (2.24 g, 74%). ¹H NMR (pyr-d₅,

298 K): δ 7.48 (d, J ) 2.3 Hz, 2H, ArH), 7.42 (d, J ) 2.3 Hz, 2H,

9202 J. Am. Chem. Soc., Vol. 119, No. 39, 1997

Giannini et al.

Table 1. Experimental Data for the X-ray Diffraction Studies on Crystalline Complexes 13, 16, 22 and 23

formula

color

a, Å

b, Å

c, Å

R, deg

â, deg

γ, deg

V, Å³

C₆₀H₇₂O₄Zr‚C₇H₈

pale yellow

23.354(1)

20.518(2)

13.238(1)

112.77(1)

5849.0(9)

C₅₃H₆₄O₄Zr‚0.75C₇H₈

colorless

19.925(4)

20.119(4)

14.545(3)

100.82(3)

99.74(3)

63.52(2)

5102(2)

C₁₀₂H₁₂₀O₈Zr2‚C₆H₆

colorless

11.009(2)

12.358(2)

19.990(2)

73.35(1)

87.36(1)

70.17(1)

2447.2(7)

C₅₆H₆₉NO₄Zr‚C₆H₆‚C₆H₁₄

colorless

12.982(3)

28.958(6)

18.424(4)

110.42(3)

6491(3)

formula weight

space group

t, °C

1040.6

C2/c

1.541 78

1.182

18.86

0.711-1.000

0.060

0.166

1.077

925.4

P1h

-140

1.541 78

1.205

21.03

0.427-1.000

0.070

0.215

1.103

1734.6

P1h

1.541 78

1.177

21.63

0.851-1.000

0.052

1075.7

0.710 73

1.101

2.07

0.970-1.000

0.050 [0.051]^d

0.128 [0.133]^d

0.996

λ, Å

_calc, g cm^-3

µ, cm^-1

transm coeff

R^a

wR2^b

0.153

1.036

GOF^c

2 2

^aR ) ∑|∆F|/∑|F_o| calculated on the unique observed data [I > 2 σ(I)]. ^bwR2 ) [∑w|∆F²|²/∑w|F_o| ]^1/2calculated on the unique data having I

> 0. ^cGOF ) [Σw|∆F²|²/(NO - NV)]^{1/2 d}Values in square brackets refer to the “inverted” structure.

(CD₂Cl₂, 298 K): δ 7.79 (m, 2H, ArH(CH₂Ph)), 7.61 (m, 2H, ArH-

(CH₂Ph)), 7.53 (m, 1H, ArH(CH₂Ph)), 7.25 (s, 4H, ArH), 6.89 (s, 4H,

ArH), 6.85 (m, 2H, ArH(CH₂Ph)), 6.77 (m, 1H, ArH(CH₂Ph)), 6.73

(m, 2H, ArH(CH₂Ph)), 4.15 (d, J ) 13.2 Hz, 4H, endo-CH₂), 3.82 (s,

6H, MeO), 3.53 (s, 2H, Zr-CH₂Ph), 3.47 (d, J ) 13.2 Hz, 4H, exo-

CH₂), 2.80 (brs, 2H, B-CH₂Ph), 1.30 (s, 18H, Bu^t), 0.95 (s, 18H, Bu^t).

¹H NMR (C₆D₆, 298 K): δ 7.24-6.80 (m, 14H, ArH), 6.70 (s, 4H,

ArH), 3.89 (d, J ) 12.9 Hz, 4H, endo-CH₂), 3.48 (s, 2H, CH₂Ph), 3.15

(d, 4H, exo-CH₂), overlapping with 3.14 (s, 6H, MeO), 2.97 (s, 2H,

CH₂Ph), 1.34 (s,18H, Bu^t), 0.70 (s, 18H, Bu^t). Anal. Calcd for 21,

C₇₈H₇₂BF₁₅O₄Zr: C, 64.15; H, 4.97. Found: C, 63.88; H, 4.99. Dilute

C₆D₆solutions of the product are thermally stable (3 h, 60 °C). It is

unstable in CD₂Cl₂(at room temperature, the reaction is complete in

hours). It is photosensitive. It reacts with THF to give the adduct; a

small amount of 21 was dissolved in THF, volatiles were removed in

Vacuo, and the residue was dissolved in CD₂Cl₂. ¹H NMR (CD₂Cl₂,

298 K): δ 7.62-6.71 (m, 18H, ArH), 4.16 (d, J ) 12.9 Hz, 4H, endo-

CH₂), 3.90 (m, 12H, THF), overlapping with 3.83 (s, 6H, MeO), 3.45

(d, J ) 12.9 Hz, 4H, exo-CH₂), 3.03 (s, 2H, Zr-CH₂Ph), 2.80 (br s,

2H, B-CH₂Ph), 1.93 (m, 12H, THF), 1.28 (s,18H, Bu^t), 1.08 (s, 18H,

Bu^t). It does not react with ethylene.

2H, endo-CH₂), 4.30 (d, J ) 12.2 Hz, 2H, endo-CH₂), 4.19 (s, 3H,

MeO), 3.30 (d, J ) 12.2 Hz, 2H, exo-CH₂), 3.17 (d, J ) 12.2 Hz, 2H,

exo-CH₂), 2.34 (s, 3H, C₇H₈), 1.62 (s, 9H, Bu^t), 1.31 (m, 8H, CH₂-

hexane), 1.23 (s, 18H, Bu^t), 1.15 (s, 9H, Bu^t), 1.14 (s, 9H, Bu^t), 0.88

(m, 6H, CH₃-hexane). ¹H NMR (C₆D₆, 298 K): δ 7.38 (d, J ) 2.4

Hz, 2H, ArH), 7.26 (d, J ) 2.4 Hz, 2H, ArH), 7.05 (m, 2H, ArH), 6.98

(s, 2H, ArH), 6.93 (s, 2H, ArH), overlapping with 6.92 (m, 1H, ArH),

6.74 (m, 2H, ArH), 5.16 (d, J ) 12.0 Hz, 2H, endo-CH₂), 4.46 (d, J )

12.0 Hz, 2H, endo-CH₂), 3.92 (s, 3H, MeO), 3.58 (d, J ) 12.0 Hz, 2H,

exo-CH₂), 3.31 (d, J ) 12.0 Hz, 2H, exo-CH₂), 2.10 (s, 3H, C₇H₈),

1.57 (s, 9H, Bu^t), 1.46 (s, 18H, Bu^t), 1.23 (m, 8H, hexane), 0.92 (s,

9H, Bu^t), 0.88 (m, 6H, C₆H₁₄), 0.73 (s, 9H, Bu^t). Anal. Calcd for

23‚C₇H₈‚C₆H₁₄, C₆₉H₉₁NO₄Zr: C, 76.05; H, 8.42, N, 1.29. Found: C,

76.30; H, 8.46; N, 1.13. Crystals suitable for X-ray analysis were

obtained from a saturated solution in n-hexane. The product is stable

to prolonged heating (90 °C, 12 h) in C₆D₆, as judged by H NMR.

X-ray Crystallography for Complexes 13, 16, 22, and 23. Crystal

data and details associated with data collection are listed in Tables 1

and S2. The structures were solved by the heavy-atom method starting

from a three-dimensional Patterson map.¹²Refinements were done by

full-matrix least-squares first isotropically and then anisotropically for

all non-H atoms except for some disordered atoms. In the last stage

Synthesis of 22. 10‚(thf)₂‚(C₆H₆)₂(4.49 g, 2.39 mmol) was

suspended in toluene (80 mL). A solution of PhLi (14.1 mL, 0.34 M

in THF, 4.79 mmol) was added dropwise over 20 min at -70 °C. The

reaction mixture was allowed to warm to room temperature under

stirring, and the opalescent suspension was then refluxed over 6 h,

resulting in a brown suspension. Volatiles were removed, and benzene

(130 mL) was then added. The residue was extracted over 36 h to

yield a white precipitate of 22‚(C₆H₆)₂, which was collected and dried

in Vacuo (2.34 g, 54%). ¹H NMR (CD₂Cl₂, 298 K): δ 7.36 (s, 12H,

benzene), 7.31 (m, 4H, ArH), 7.09 (d, J ) 2.4 Hz, 4H, ArH), 7.48 (d,

J ) 2.4 Hz, 4H, ArH), 6.92 (m, 2H, ArH), 6.86 (m, 4H, ArH), 6.80 (s,

4H, ArH), 6.55 (s, 4H, ArH), 4.73 (d, J ) 13.0 Hz, 4H, endo-CH₂),

4.36 (d, J ) 12.3 Hz, 4H, endo-CH₂), 3.18 (d, J ) 12.3 Hz, 4H, exo-

CH₂), 2.84 (s, 6H, MeO), overlapping with 2.84 (d, J ) 13.0 Hz, 4H,

exo-CH₂), 1.28 (s, 36H, Bu^t), 1.02 (s, 18H, Bu^t), 0.97 (s, 18H, Bu^t).

Anal. Calcd for 22·(C₆H₆)₂, C₁₁₄H₁₃₂O₈Zr₂: C, 75.54; H, 7.34.

Found: C, 75.16; H, 7.51.

Synthesis of 23. A solution of Bu^tNC (0.239 g, 2.87 mmol) in

toluene (34 mL) was added dropwise at -50 °C to a suspension of

22‚(C₆H₆)₂(2.54 g, 1.40 mmol) in toluene (90 mL). The resulting

yellow solution was allowed to warm to room temperature with stirring

overnight. The reaction mixture was then refluxed for 12 h, volatiles

were removed in Vacuo, and hexane (30 mL) was added to the resi-

due. The flask was kept 1 day at -24 °C, and then white 23‚C₇H₈‚

C₆H₁₄solid was collected and dried in Vacuo (0.803 g, 26%). ¹H NMR

(CD₂Cl₂, 298 K): δ 7.5-6.97 (m, 18H, ArH), 4.65 (d, J ) 12.2 Hz,

of refinement, the weighting scheme w ) 1/[σ²(F_o) + (aP)²] (with P

) (F_o²+ 2F_c²)/3) was applied, with a resulting in the value of 0.0724,

0.1443, 0.1062, and 0.0922 for 13, 16, 22, and 23, respectively. All

calculations were performed by using SHELX92.¹³Except for those

related to the disordered atoms and to the n-hexane solvent molecule

in 23, which were ignored, the hydrogen atoms for all complexes were

located from difference Fourier maps and introduced in the subsequent

refinements as fixed atom contributions with isotropic U’s fixed at 0.10

Å²for 13 and 22 and at 0.08 Å²for 16 and 23. The hydrogen atoms

associated to the benzene solvent molecules in 22 and 23 were put in

geometrically calculated positions with the isotropic U’s fixed at 0.20

Å². In complex 13, a Bu^tgroup of calixarene was affected by high

thermal parameters, indicating the presence of disorder, which was

solved by splitting the C30, C31, and C32 methyl carbon atoms over

two positions (A and B), isotropically refined with site occupation

factors of 0.7 and 0.3, respectively, applying a constraint to the C-C

bond distances [1.54(1) Å]. In complex 16, a Bu^tgroup of molecule

A was affected by high thermal parameters, indicating the presence of

disorder. The best fit was obtained by splitting the C42, C43, and

C44 methyl carbon atoms over three positions (C, D, E), isotropically

refined with a site occupation factor of 0.3333. In complex 22, troubles

(12) Sheldrick, G. M. SHELX76. Program for crystal structure deter-

mination; University of Cambridge, England, 1976.

(13) Sheldrick, G. M. SHELXL92. Program for Crystal Structure

Refinement; University of Go¨ttingen, Germany, 1992.

Zr-C Functionalities on a Calix[4]arene Oxo Surface

J. Am. Chem. Soc., Vol. 119, No. 39, 1997 9203

Scheme 1

Scheme 2

were encountered in refining the structure because of the rather high

values reached by the U_ijparameters of all the Bu^tgroups, indicating

some disorder, which was solved by splitting the atoms as follows:

C30, C31, and C32 over three positions (A ) 50%, B and C ) 25%);

C34, C35, and C36 over two positions (A ) B ) 50%); C38, C39,

and C40 over three positions (A ) B ) C ) 33%); C42 and C43 over

two positions (A ) B ) 50%); and C44 over three positions (A ) B

) C ) 33%). During the refinement, the C-C bond distances within

the Bu^tgroups were constrained to 1.54(1) Å. In complex 23, all four

Bu^tgroups of calixarene were found to be affected by disorder, which

was solved by splitting all the methyl carbon atoms over two positions

(A and B), isotropically refined with site occupation factors of 0.5,

applying a constraint to the C-C bond distances [1.54(1) Å]. See the

Supporting Information for more details.

bonds was achieved in the reaction of 4 with AgOTf. This

reaction has, among others, the purpose of producing a Lewis

acid, where zirconium is only weakly bound to the OTf^-

anion.^15,16The reaction is carried out in benzene, since the

Lewis acidity of zirconium in 6 promotes THF polymerization.

The X-ray structure of 6 (see the Supporting Information)

revealed the two bonding modes shown for the OTf^-anion.

The use of 6 as a Lewis acid promoter of a variety or organic

reactions is currently under investigation, though 6 suffers from

the limitation of undergoing demethylation in the presence of

strong bases like pyridine. The base-induced demethylation of

6 to 7 has been followed by ¹H NMR spectroscopy. The

hydrolysis of 7 gave, as expected, the free monomethoxycalix-

[4]arene (8).

The demethylation of 4 and 6 led us to develop an appropriate

synthetic approach to the monochlorozirconium(IV) calix[4]-

arene, which can be an attractive parent compound for the

organometallic functionalization. The synthetic procedure is

shown in Scheme 3 and reported in detail in the Experimental

Section, while a detailed discussion on the synthesis of 8 will

be part of a forthcoming paper.¹⁷

Results

The Parent Compounds. The parent compound 4, which

serves as starting material for the organometallic derivatization

of zirconium calix[4]arene, has been prepared according to two

procedures, which are outlined in Scheme 1.

The synthesis avoiding the use of any alkali salt is preferred

in this kind of chemistry because the alkali salt very often

remains complexed by the ensuing calix[4]arene moiety,¹⁴while

that passing through the intermediate 3 gave higher yields when

carried out in situ. Complex 4 crystallizes with two molecules

of benzene, one being hosted in the calix[4]arene cavity. The

¹H NMR spectrum is as expected for a cone conformation

having a C_2Vsymmetry; thus, the methylene groups appear as

one pair of doublets and the Bu^tas two singlets (see the

Experimental Section). The proposed structure has been sup-

ported by an X-ray analysis, which is included in the Supporting

Information. Before showing the organometallic functional-

ization which can be carried out on 4, we should emphasize

that 4 undergoes demethylation reactions in the presence of

relatively strong bases (i.e., NEt₃, Py) (see Scheme 2), with the

formation of the corresponding ammonium or pyridinium salts.

In the reaction with Et₃N, compound 5 was isolated, which

contains the monomethoxycalix[4]arene trianion. The difficulty

in separating the Et₃NMe⁺Cl^-salt from the Zr-calix[4]arene

moiety suggests that the Cl^-is still bonded to the metal, either

outside (see the picture in Scheme 2) or inside the cavity, giving

rise to a trans-dichloro derivative. The same derivatization

reaction was achieved by reacting 4 with pyridine. In both

cases, the reaction of 4 with a base (Et₃N or Py), followed by

hydrolysis, gave clean 8. The Zr-Cl functionality in 4 is very

reactive in metathesis reactions. The ionization of the Zr-Cl

The dimeric structure proposed for 10 in the solid state is

based on the analogous structure found for the corresponding

phenyl derivative (Vide infra, complex 22). As a matter of fact,

a monomeric form can be obtained in the presence of a strongly

binding ligand. The reaction of 10 with an excess of pyridine

gave the monomer 11 (Scheme 3), in which the methoxy group

is also displaced. A preliminary X-ray analysis shows a

Zr‚‚‚OMe distance longer than 2.75 Å in 11.¹⁸

The Synthesis of Zr-C Bonds. The alkylation of 4 (path

b, Scheme 4) has been performed according to conventional

(15) Gennari, C. In ComprehensiVe Organic Synthesis, Heathcock, C.

H., Ed.; Pergamon: Oxford, U.K., 1991; Vol. 1. Beck, W.; Sunkel, K. Chem.

ReV. 1988, 88, 1405.

(16) Cozzi, P. G.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Synlett 1994,

857.

(17) Zanotti-Gerosa, A.; Floriani, C., manuscript in preparation.

(18) Crystal data for 11: C₅₅H₆₅N₂O₄Zr‚C₅H₅N, M ) 1458.96, triclinic,

space group a ) 16.757(3), b ) 19.195(3), and c ) 12.930(2) Å, R )

99.62(2), â ) 100.76(2), γ ) 82.92(2)°, V ) 4010.13(12) Å³, Z ) 2, d_calcd

) 1.2083 g cm^-3, F(000) ) 1542.0, µ ) 18.527 cm^-1, λ ) 1.541 78 Å.

(14) Zanotti-Gerosa, A.; Solari, E.; Giannini, L.; Floriani, C.; Chiesi-

Villa, A.; Rizzoli, C. Chem. Commun. 1997, 183 and references therein.

9204 J. Am. Chem. Soc., Vol. 119, No. 39, 1997

Giannini et al.

Scheme 3

Chart 2

derivatives 12-14 are thermally stable up to 80 °C in C₆D₆.

Further, they are not particularly light-sensitive, though the

photolysis of 12 in CD₂Cl₂gave 4. Under strong solar light

(or UV irradiation), they all undergo reaction/decomposition.

The aryl derivative 15 is more thermally sensitive than the

corresponding alkyl compounds 12-14, and refluxing in

benzene for 36 h gave the corresponding benzyne derivative,

16, Via toluene elimination.^6f,19The analogous R-elimination,

leading to the corresponding alkylidene,²⁰has never been

observed in the case of the attempted thermal decomposition

of 12-14. The reactivity study on 12-15 should take into

account the base-induced demethylation of one of the methoxy

groups when they are treated with a relatively strong base. The

reaction of 13 with pyridine gave the concomitant demethylation

of the methoxy group and the dealkylation at the metal leading

to 18 and to the organic products obtained by reacting (PhCH₂)₂-

Mg and N-methylpyridinium‚BPh₄, as revealed by NMR

analysis. In the case of Et₃N, demethylation led to 17 and a

mixture of toluene, ethylbenzene, and ethylene. The obtention

of 17 rather than the corresponding solvated form depends on

the low affinity of Et₃N for zirconium(IV). Complex 17 has

also been obtained from the alkylation of 10, as shown in

Scheme 6. The key compounds 13 and 16 in Scheme 4 have

been characterized by X-ray analyses.

Scheme 4

The labeling scheme adopted for the calixarene moiety for

all complexes is indicated in Chart 2. Selected bond distances

and angles for complexes 13, 16, 22 and 23 are quoted in Tables

2 and 3. A comparison of relevant conformational parameters

is reported in Table 4. The structure of complex 13, hosting a

toluene molecule in the cavity, is shown in Figure 1.

The complex molecule possesses a crystallographically

imposed C₂symmetry, the two-fold axis running through the

molecular axis. The distorted octahedral coordination around

zirconium is provided by the four oxygen atoms from calixarene

and by the C51 and C51′ methylene carbon atoms from two

symmetry-related benzyl ligands (′ ) -x, y, 0.5 - z). As a

procedures using lithium or Grignard reagents. The preliminary

isolation of 4 is not compulsory; thus, the synthesis of the zir-

conium alkyl or aryl derivatives can be carried out in situ directly

from 2 (path a, Scheme 4), using the sequence specified in the

Experimental Section.

(19) (a) Buchwald, S. L.; Broene, R. D. In ComprehensiVe Organome-

tallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;

Pergamon: Oxford, 1995; Vol. 12, Chapter 7.4 and references therein. (b)

Erker, G.; Albrecht, M.; Kru¨ger, C.; Werner, S. J. Am. Chem. Soc. 1992,

114, 8531. (c) Buchwald, S. L.; Fischer, R. A.; Foxman, B. M. Angew.

Chem., Int. Ed. Engl. 1990, 29, 771. (d) Buchwald, S. L.; Lucas, E. A.;

Davis, W. M. J. Am. Chem. Soc. 1989, 111, 397. (e) Bennett, M. A.;

Schwemlein, H. P. Angew. Chem., Int. Ed. Engl. 1989, 28, 1296. (f) Binger,

P.; Biedebach, B.; Mynott, R.; Regitz, M. Chem. Ber. 1988, 121, 1455. (g)

Buchwald, S. L.; Watson, B. T.; Huffman, J. C. J. Am. Chem. Soc. 1986,

108, 7411.

The H NMR spectra of 12-15 all imply C_2Vsymmetry, as

revealed by the CH₂(one pair of doublets), Bu^t(two singlets),

and MeO (one singlet) patterns. The synthesis of pure

monoalkylchloro derivatives is prevented by the facile redis-

tribution reaction between dichloro and dialkyl derivatives; for

example, mixing equimolar amounts of 4 and 12 in CD₂Cl₂gives

an equilibrium mixture of 4, 12, and [p-Bu^t-calix[4]-(OMe)₂(O)₂-

Zr(Cl)(Me)] (see the Experimental Section). All the alkyl

(20) Fryzuk, M. D.; Mao, S. S. H. J. Am. Chem. Soc. 1993, 115, 5336.

Zr-C Functionalities on a Calix[4]arene Oxo Surface

J. Am. Chem. Soc., Vol. 119, No. 39, 1997 9205

Table 2. Selected Bond Distances (Å) and Angles (deg) for Complexes 13 and 16

Complex 13

Zr1-O1

Zr1-O2

Zr1-C51

1.960(3)

2.298(5)

2.332(5)

C51-Zr1-C51′

83.7(2)

153.9(2)

102.4(2)

175.9(3)

118.2(3)

O2-Zr1-O2′

O1-Zr1-O1′

Zr1-O1-C1

Zr1-O2-C13

Complex 16

mol A

mol B

mol A

mol B

Zr1-O1

1.985(3)

2.322(3)

1.955(4)

2.335(4)

2.172(6)

2.175(7)

1.982(4)

2.346(4)

1.978(3)

2.325(4)

2.185(5)

2.179(6)

C51-C52

1.386(8)

1.407(7)

1.399(10)

1.393(7)

1.402(10)

1.376(10)

1.495(9)

1.383(10)

1.408(7)

1.396(11)

1.354(9)

1.430(14)

1.378(11)

1.489(10)

Zr1-O2

Zr1-O3

Zr1-O4

Zr1-C51

Zr1-C52

C51-C56

C52-C53

C53-C54

C54-C55

C55-C56

C55-C57

O2-Zr1-O4

O1-Zr1-O3

C51-Zr1-C52

154.1(2)

127.9(2)

37.2(2)

1.531(2)

126.7(2)

37.0(2)

Zr1-O1-C1

Zr1-O2-C13

Zr1-O3-C20

Zr1-O4-C27

156.5(3)

161.8(4)

114.7(4)

167.3(4)

114.5(3)

113.6(3)

163.0(4)

116.0(3)

Table 3. Selected Bond Distances (Å) and Angles (deg) for

Complexes 22 and 23

molecule enters the cavity with the aromatic ring perpendic-

ular to the A ring [dihedral angle 92.2(5)°] and nearly parallel

to the B ring [dihedral angle 19.2(5)°]. The minimum

Zr‚‚‚C(toluene) distance [Zr‚‚‚C66, 5.391(12) Å] rules out any

possible interaction involving the metal atom. As a consequence

of the asymmetry of the cavity, the toluene axis is tilted with

respect to the molecular axis, giving rise to a statistical

distribution of the solvent molecule. In spite of the disorder,

host-guest interactions seem to take place involving the C35

methyl group associated to the B ring and the aromatic ring of

toluene, as suggested by the following distances: C35‚‚‚C61,

3.61(2) Å; C61‚‚‚H351, 2.54 Å; C35‚‚‚C62, 3.70(2) Å;

C62‚‚‚H351, 2.62 Å; C35‚‚‚C62′, 3.86(2) Å; C62′‚‚‚H351,

2.78 Å.

Complex 22

Zr1-O1

Zr1-O2

Zr1-O3

1.952(2)

2.662(3)

1.929(2)

Zr1-O4

Zr1-O4′

Zr1-C51

2.197(3)

2.185(2)

2.282(6)

O4-Zr1-O4′

O1-Zr1-O3

O3-Zr1-O4

O2-Zr1-O4

Zr1-O4-C27

64.1(1)

122.3(1)

89.0(1)

151.0(1)

111.6(2)

Zr1-O1-C1

Zr1-O2-C13

Zr1-O3-C20

Zr1-O4-Zr1′

Zr1′-O4-C27

162.4(2)

112.8(2)

161.2(2)

115.9(1)

132.5(2)

Complex 23

Zr1-O1

Zr1-O2

Zr1-O3

Zr1-O4

Zr1-N1

1.954(3)

2.403(3)

1.966(3)

2.037(2)

2.180(3)

Zr1-C51

N1-C51

N1-C58

C51-C52

2.260(3)

1.269(4)

1.482(4)

1.462(4)

The structure of 16, which contains a toluene of crystallization

in the 1:0.75 Zr-toluene ratio, is reported in Figure 2. In the

unit cell, there are two crystallographically independent mol-

ecules (A and B) showing a close geometry. The values

referring to molecule B will be, hereafter, given in square

brackets.

N1-Zr1-C51

O2-Zr1-O4

O1-Zr1-O3

Zr1-O1-C1

Zr1-O2-C13

Zr1-O3-C20

33.1(1)

156.4(1)

129.6(1)

154.7(3)

118.4(2)

155.0(3)

Zr1-O4-C27

Zr1-N1-C58

Zr1-N1-C51

C51-N1-C58

Zr1-C51-N1

122.8(2)

147.1(3)

76.9(2)

136.0(4)

70.0(2)

The calixarene macrocycle assumes an elliptical cross section

conformation, probably as a consequence of the orientation of

the η²-bonded ligand, which forces the B and D rings to bend

toward the cavity of calixarene. With respect to complex 13,

the conformation mainly differs in the orientation of aromatic

rings which are closer to be mutually perpendicular (A and C)

and parallel (B and D) to each other (Table 4). This results in

a more pronounced elliptical nature of the cavity and thus

prevents the inclusion of toluene, which is present in the

structure as a crystallization solvent and not as a guest. The

trend in the Zr-O bond distances (Table 2) is similar to that

observed in 13. The η²-bonded benzyne shows a symmetric

bonding mode to the metal, the Zr-C51 and Zr-C52 bond

distances being very close. Their mean value [2.173(5) Å] is

remarkably shorter than those found for Zr-C σ bonds (see

complexes 13 and 22). The C-C bond distances within the

benzyne ring are very close without alternation of short and

long bond lengths. Such a trend of structural data is quite close

to that observed in [Cp₂Zr(η⁶-C₆H₄)(PMe₃)].^19gThe plane of

the η²-bonded atoms (Zr, C51, C52) is nearly perpendicular to

the mean plane through the O₄core {dihedral angle 84.2(2)

[89.2(2)]°}, and the direction of the C51-C52 bond is parallel

to the O2‚‚‚O4 line {2.7(3) [3.6(3)]°}. The O₄core has some

tetrahedral distortion (displacements ranging from -0.172(4)

consequence of the six-coordination of the metal, the planarity

of the O₄core is completely removed,^5d,14the best coordination

plane being defined by the O1, O2, O2′, and C51 atoms. As is

usually observed for six-coordinated calixarene metal com-

plexes, the macrocycle ligand assumes an elliptical cross sec-

tion conformation, with the A and C rings pushed outward

from and the B and D rings inward to the cavity, as indicated

by the dihedral angles they form with the “reference plane”

(Table 4). The elliptical section of the cavity can be indicated

by the values of the distances between opposite para-carbon

atoms: C4‚‚‚C4′, 9.811(7) Å; C10‚‚‚C10′, 7.081(8) Å. The O₄

core shows tetrahedral distortions ranging from -0.355(4) to

0.355(4) Å, the metal being displaced by 0.873(1) Å from the

mean plane. The C52-C57 aromatic ring of the benzyl ligand

forms a dihedral angle of 57.0(4)° with the O₄mean plane. The

Zr-O1 bond distance [1.960(3) Å] is in agreement with those

in zirconium phenoxo complexes^10g,jand is consistent with some

double bond character supported by the approximate linearity

of the Zr-O1-C1 bond angle (Table 2). The Zr-O2 bond

distance involving the methoxy group is remarkably longer

[2.298(5) Å]. The Zr-C51 bond distance [2.332(5) Å] has the

value expected for a Zr-C(sp³) carbon.⁷The guest toluene

9206 J. Am. Chem. Soc., Vol. 119, No. 39, 1997

Giannini et al.

Table 4. Comparison of Relevant Conformational Parameters within Calixarene for Complexes 13, 16, 22 and 23

(a) Dihedral Angles (deg) between Planar Moieties^b

E ∧ A

E ∧ B

E ∧ C

E ∧ D

A ∧ C

B ∧ D

144.8(2)

109.6(2)

144.8(2)

109.6(2)

109.7(2)

140.8(2)

132.7(1)

98.4(2)

136.8(1)

97.4(2)

90.5(2)

164.2(2)

[133.9(2)]

[96.7(2)]

[135.7(1)]

[100.7(2)]

[90.4(2)]

[162.5(2)]

134.4(1)

100.2(1)

134.5(1)

93.8(1)

91.0(2)

166.0(2)

132.6(1)

110.7(1)

132.0(1)

116.5(1)

95.4(1)

132.9(1)

(b) Contact Distances (Å) between para-Carbon Atoms of Opposite Aromatic Rings^c

C4‚‚‚C17

C10‚‚‚C24

9.811(7)

7.081(8)

9.412(6)

5.884(8)

[9.431(9)]

[5.948(10)]

9.290(6)

5.766(8)

9.101(8)

7.462(5)

^aValues in square brackets refer to molecule B. ^bE (reference plane) refers to the least-squares mean plane defined by the C7, C14, C21, C28

bridging methylenic carbons. A, B, C, and D refer to the least-squares mean planes defined by the aromatic rings bonded to O1, O2, O3, and O4,

respectively. O3, O4, C21, and C28 should be read O1′, O2′, C7′, and C14′, respectively, in complex 13 (′ ) -x, y, 0.5 - z). ^cIn complex 13, C17

and C24 should be read C4′ and C10′ respectively (′ ) -x, y, 0.5 - z).

Figure 1. SCHAKAL view of complex 13, showing the disorder

affecting the guest toluene molecule. Disorder involving the Bu^tgroups

has been omitted for clarity. Prime denotes a transformation of -x, y,

0.5 - z.

Figure 2. SCHAKAL view of molecule A of complex 16. Disorder

has been omitted for clarity.

[-0.175(4)] to 0.173(4) [0.173(4)] Å), zirconium protruding by

0.693(2) [0.715(2)] Å from the mean plane. The most

significant difference between molecules A and B consists in

the orientation of the plane through the C51-C57 atoms with

respect to the O4 mean plane {75.7(2) [89.9(2)]°}.

cationic species 19 and 21 have C_2Vsymmetry, as revealed by

the ¹H NMR spectrum. The Lewis acid activity of such cationic

species is, somehow, not easily defined. Complex 19 reacts

with THF, causing its partial polymerization, as is the case for

20, which can be isolated free of polymeric THF only after

recrystallization. The same behavior has been observed for 21,

like the photolability and the degradation in the presence of

halogenated solvents, i.e., CH₂Cl₂. Both 19 and 21 did not

show, however, any activity toward olefin polymerization. We

believe that, in such compounds, the two methoxy groups

sterically overprotect the metal center. The reaction of 19 with

pyridine emphasizes the action of a strong base in the de-

methylation of one of the methoxy groups. The pyridine

Compounds 12-15 are particularly appropriate precursors for

the corresponding monoalkyl cationic species, which, especially

in the case of [Cp₂Zr] chemistry,²¹are still receiving a lot of

attention as polymerization catalysts. The generation of cationic

species has been achieved Via two major routes: (i) the one-

electron oxidation using [Cp₂Fe]⁺BPh₄to generate 19 in

toluene or 20 in a coordinating solvent like THF^8c,21and (ii)

the reaction with a Lewis acid, like [B(C₆F₅)₃], to give 21

(Scheme 5).^21,22

We should mention that 19 undergoes a thermally induced

(90 °C, 1 h, C₆D₆) disproportionation reaction with simultaneous

arylation of zirconium by BPh₄^-, thus forming 13 and 22. The

functions as the acceptor of the methyl cation and thus forms

18 and PyMe⁺BPh₄

Under basic conditions, the zirconium assists the demeth-

ylation of one of the methoxy groups, especially when it is

particularly acidic. In this context, we have searched for a better

synthetic approach to the organometallic derivatives of the

monomethoxycalix[4]arene-zirconium fragment (Scheme 6).

The reaction of 10 with LiPh gave the phenyl derivative 22,

which behaves as expected in the insertion reaction with

Bu^tNC, i.e., leading to an η²-iminoacyl, 23.²³The reaction

causes the cleavage of the dimer into two monomeric units and

(21) Guram, A. S.; Jordan, R. F. In ComprehensiVe Organometallic

Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;

Pergamon: Oxford, 1995; Vol. 4, Chapter 12. Yang, X.; Stern, C. L.; Marks,

T. J. J. Am. Chem. Soc. 1994, 116, 10015. Guerra, G.; Cavallo, L.; Moscardi,

G.; Vacatello, M.; Corradini, P. J. Am. Chem. Soc. 1994, 116, 2988. Erker,

G.; Aulbach, M.; Knickmeier, M.; Wingbermu¨hle, D.; Kru¨ger, C.; Nolte,

M.; Werner, S. J. Am. Chem. Soc. 1993, 115, 4590. Coates, G. W.;

Waymouth, R. M. J. Am. Chem. Soc. 1993, 115, 91. Jordan, R. F. AdV.

Organomet. Chem. 1991, 32, 325.

(22) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113,

3623.

Zr-C Functionalities on a Calix[4]arene Oxo Surface

J. Am. Chem. Soc., Vol. 119, No. 39, 1997 9207

Scheme 5

Scheme 6

the methoxy group to bind zirconium. For this class of

compounds, the structures of 22 and 23 will illustrate the most

interesting peculiarities, including the role of the methoxy group

as a spectator donor atom.

The structure of 22 consists of centrosymmetric dimers and

benzene molecules of crystallization in the molar ratio 1:1

(Figure 3).

The calixarene macrocycle assumes an elliptical conformation

similar to that observed in 16 (Table 4). Accordingly, the

benzene solvent molecules of crystallization are not included

as guests in the macrocycle. The O₄core is tetrahedrically

distorted [displacements ranging from -0.158(2) to 0.146(2)

Figure 3. SCHAKAL view of complex 22. Disorder has been omitted

for clarity. Prime denotes a transformation of -x, -y, -z.

Å], zirconium protruding by 0.753(1) Å from the mean plane.

The C51-C56 aromatic ring is oriented to form a dihedral angle

of 54.1(2)° with the O₄mean plane. The Zr-O1 and Zr-O3

bond distances compare with the corresponding ones observed

in 13 and 16, while the Zr-O4 bond distances [mean value

2.191(3) Å] are significantly longer as a consequence of the

bridging role of the O4 oxygen atom. The Zr-O2 distance

[2.662(3) Å] involving the methoxy group shows a remarkable

(23) Durfee, L. D.; Rothwell, I. P. Chem. ReV. 1988, 88, 1059 and

references therein.

9208 J. Am. Chem. Soc., Vol. 119, No. 39, 1997

Giannini et al.

Chart 3

and π functionalities in [Zr-aryne]. The O₄macrocycle is a

unique chemical environment for such Zr-C fragments, because

of a number of peculiarities:

(i) The topology of the O₄-Zr moiety is approximately

square-pyramidal, with the metal out of the “O₄” plane.

(ii) The metal orbitals available for binding functionalities

or assisting their transformations are located on the free face of

the [ZrO₄] hemisandwich (Vide infra).

(iii) The partial methylation of the phenoxo groups not only

provides a variable range of charges for an O₄set but allows

one to tune the ratio between strong σ,π donor (the phenoxo)

and weak σ donor oxygens (the methoxy).

(iv) The competition for the same orbitals by the O₄set and

the organometallic functionalities would be an important factor

for their reactivity.

Figure 4. SCHAKAL view of complex 23. Disorder has been omitted

For a better understanding of the basic chemical behavior of

the [ZrO₄]ⁿ⁺[n ) 0, 1, 2] core in binding and assisting the

chemistry of organometallic functionalities, we undertook

extended Hu¨ckel calculations²⁵on the fragments in Chart 3 with

the aim of studying their frontier orbitals and comparing them

with those of other well-known organometallic fragments, such

for clarity.

lengthening with respect to the corresponding distances in 13

and 16, probably reflecting intraligand interactions. In particu-

lar, the H451 hydrogen atom of the C45 methoxy group points

toward the C51-C56 phenyl ring at a distance of 2.54 Å from

its centroid, suggesting a CH₃/π interaction.²⁴The Zr-C bond

distance [2.282(6) Å] (Table 3) is significantly shorter than that

observed in 13 but is in the usual range reported for σ Zr-

C(sp²) bonds.⁷

The structure of 23 contains a guest benzene molecule and

an n-hexane solvent molecule of crystallization in the molar

ratio of 1:1:1 (Figure 4). The η²-bonded N,C fragment shows

a slightly asymmetric bonding mode to the metal, the Zr-N1

and Zr-C51 bond distances being 2.180(3) and 2.260(3) Å,

respectively, as expected for [Zr(η²-imimoacyl)] derivatives.²³

The N1-C51 bond distance [1.269(4) Å] is consistent with a

double bond character.

The calixarene macrocycle assumes an elliptical cross section

conformation similar to that observed in complex 13, allowing

the inclusion of a benzene molecule which enters the cavity

orienting its C71‚‚‚C74 molecular axis nearly parallel to the

calixarene axis, as indicated by the dihedral angle of 9.9(2)°

between the C71‚‚‚C74 line and the normal to the O₄core

and by the value of the Zr‚‚‚C71‚‚‚C74 angle [170.8(6)°].

Disorder affecting the Bu^tgroups of calixarene prevents any

sound discussion on possible host-guest interactions. The O₄

core is tetrahedrically distorted [displacements ranging from

-0.259(3) to 0.154(3) Å], zirconium protruding by 0.601(1) Å

from the mean plane. The plane of the η²-bonded atoms (Zr,

N1, C51) is perpendicular to the O₄mean plane [dihedral angle

91.9(2)°]. The Zr-O1 and Zr-O3 bond distances (Table 3)

are close to those observed in the previous complexes, while

the Zr-O4 bond distance is significantly longer.

as [Cp₂Zr]^{2+ 26}and [Zr(tmtaa)]^{2+ 27}

Further, we wished to

rationalize the conversion of F into E (see reactions in Schemes

2, 4, and 5) in a variety of reactions with nucleophiles.

The ligands have been slightly modified by replacing the Bu^t

groups and the methylene bridges by hydrogens and symmetriz-

ing to C_4V, C_s, and C_2Vgeometries. The simplified models retain

the main features of the whole ligand; in particular, the

geometrical constraints on the O₄set of donor atoms have been

maintained by fixing the geometry of the four phenoxo groups

to the experimental values observed for the mono- or the

dichloro derivatives.

The lowest vacant orbitals of these fragments are depicted

in Figure 5. For all such zirconium(IV) species with a d⁰

electron count, we found four low-lying empty metal-based

orbitals. The d_{x -y}, pointing more closely toward the oxygen

ligands, is pushed higher in energy, while the remaining four d

orbitals are found within 1 eV. For the [calix[4]-(O)₄Zr]

fragment, the LUMO is 1a₁(d_z), with a doubly degenerate 1e

(d_xz, d_yz) ca. 0.5 eV above. Due to a slightly stronger overlap

with the ligands, the 1b₂(d_xy) orbital lies still 0.5 eV higher in

energy. In the [calix[4]-(OMe)₂(O)₂Zr]²⁺fragment, due to the

reduced interaction with the methylated phenoxo ligands in the

xz plane, the (d_xz, d_yz) set splits by ca. 1 eV into the 1b₁(d_xz),

which becomes the LUMO, although it is almost degenerate

with the 1a₁(d_z) and the 1b₂(d_yz), which is pushed higher than

the 1a₂(d_xy). The frontier orbitals of [calix[4]-(OMe)(O)₃Zr]⁺

are similar to those of the latter fragment. However, because

of the lower molecular symmetry (C_s), the two lowest orbitals,

of d_zand d_xzcharacter have the same a′ symmetry and mix

strongly, giving rise to two hybridized 1a′ and 2a′ orbitals, G

Discussion

(25) (a) Hoffmann, R.; Lipscomb, W. N. J. Chem. Phys. 1962, 36, 2179.

(b) Hoffmann, R. J. Chem. Phys. 1963, 39, 1397.

(26) Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.; Hoffmann,

R. J. Am. Chem. Soc. 1985, 107, 4440.

(27) Giannini, L.; Solari, E.; De Angelis, S.; Ward, T. R.; Floriani, C.,

Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem. Soc. 1995, 117, 5801.

The results mentioned in the previous section show the variety

of the Zr-C bonds we can build up over a calix[4]arene oxo

surface, i.e., Zr-C σ functionalities in [ZrR₂], [ZrR], and [ZrR]⁺,

(24) Andreetti, G. D.; Ugozzoli, F. In ref 4b, pp 88-122.

Zr-C Functionalities on a Calix[4]arene Oxo Surface

J. Am. Chem. Soc., Vol. 119, No. 39, 1997 9209

calculations on 12 which give the latter hypothetical structure

ca. 0.5 eV higher than that actually observed, probably because

of a better overlap between the X^-σ orbitals and 1b₂(d_yz) or

of steric interactions with the methyl groups in the xz plane.

A major difference between 4 and 12-15 was observed in

the expected behavior as Lewis acids, and this has been

substantiated by analysis of the frontier orbital energies and of

the charge at the metal in 4 and 12 and by a comparison of

their reactions with bases or nucleophiles. This reactivity is

very important because it is responsible for the conversion of

the organometallic derivatives based on fragment F into those

of fragment E, as reported in Schemes 2, 4, and 5. Such a

reaction can be explained as a Lewis acid-assisted cleavage of

the ether bond, helped by an incoming nucleophile.²⁸The

peculiarity in the present case consists in the fact that the

reaction is concerted due to the template effect of the metal.

The base, Et₃N or pyridine, removes the methyl group from a

methoxy residue as a carbocation (see the reaction of 19 with

Py in Scheme 5, and of 4 with Et₃N in Scheme 2), and then a

further reaction can occur between a nucleophile sitting on the

metal and the CH₃⁺bonded to the base, as shown in the reaction

of 13 with Py and Et₃N (Scheme 4). In the case of pyridine,

the formation of benzyl-N-methyldihydropyridines can be

explained by the nucleophilic attack of a benzyl carbanion from

the metal to the methylpyridinium cation.²⁹The demethylation

of one of the methoxy groups has not only mechanistic but also

has synthetic relevance, since the reaction can be used for

obtaining a variety of organometallic derivatives, including the

starting material of the skeleton E, from the corresponding

derivatives of the skeleton F. We should mention at this stage

that the synthesis of 2 is much easier than that of 8. The

conversion of the derivatives of skeleton F to those of skeleton

E can be accompanied by a dimerization (see structures of 17

and 22). Due to the relevance and generality of the reaction of

bases (nucleophiles) with 4 and all its organometallic derivatives,

we have been engaged in the theoretical analysis of the reaction

of NH₃(mimicking bases and nucleophiles) with 4 and 12,

which represent the limits, in terms of electronic properties, in

the [calix[4]-(OMe)₂(O)₂ZrX₂] class of compounds.

An analysis of the frontier orbitals and of the Mulliken

charges of 4 and 12 shows that, in both cases, the LUMO

orbitals are essentially metal-localized and that the zirconium

atom bears the highest positive charge. Therefore, we expect

the metal to be the most electrophilic center in these compounds

and to undergo direct attack by the base. The spatial extension

of the 1b₁(d_xz) LUMO suggests that the favorable approach of

the NH₃nucleophilic species occurs along a line in the xz plane,

forming an angle of approximately 45° with the z-axis. We

first simulated the initial stages of the NH₃attack by performing

extended Hu¨ckel calculations on the [calix[4]-(OMe)₂(O)₂ZrX₂]‚‚‚

NH₃system (X ) Cl, Me) with (NH₃)-to-metal distances (L)

ranging from 5.0 to 2.5 Å, along the expected most favorable

line. At each point along the attack pathway, we relaxed the

X-Zr-X angle, the dihedral angle between the Zr(X)₂and

Zr(O)₂planes, and also the angular position of NH₃. The two

total energy profiles are reported in Figure 6 and show that the

attack is, by far, energetically more favorable for the bis-methyl

than for the bis-chloro complex. For the bis-methyl complex,

a small activation barrier of ca. 0.4 eV is observed at 3 Å but

is not followed by a significant stabilization at shorter distances,

therefore making the formation of a stable metal-bound inter-

mediate questionable. A dramatically different situation is found

for the bis-chloro complex, for which the energy profile

Figure 5. Frontier orbital energies for [calix[4]-(O)₄Zr]⁰, [calix[4]-

(OMe)(O)₃Zr]⁺, [calix[4]-(OMe)₂(O)₂Zr]²⁺, and [Cp₂Zr]²⁺

Scheme 7

and H, lying in the xz plane and tilted, respectively, toward the

(O-Me) and (O) directions (see Scheme 7).

On the right of Figure 5, we report, for comparison, the

well-known picture of the three low-lying empty orbitals of

[Cp₂Zr]²⁺(1a₁, 1b₁, and 2a₁).²⁶The main difference between

the calix[4]arene-based fragments and [Cp₂Zr]²⁺is that, while

the latter has only three low-lying empty orbitals available for

bonding with additional ligands, all the three former fragments

have four, and this has important consequences on their chemical

behavior. Indeed, these four low-lying d orbitals can accom-

modate up to eight electrons, at variance with [Cp₂Zr]²⁺, which

can accommodate up to a maximum of six electrons without

violating the EAN rule. Moreover, while in [Cp₂Zr]²⁺all the

three low-lying frontier orbitals lie in the symmetry plane

bisecting the Cp-Zr-Cp angle, in the calix[4]arene-based

fragments only two out of the four lowest-lying orbitals are

coplanar.

Most of the structures discussed in this paper can be easily

rationalized on the basis of the frontier orbitals of the above

fragments. Let us first consider the behavior of the fragment

F. With two σ-bonding ligands, like in 4 and 12, the metal

achieves hexacoordination, with the two X^-ligands lying in

the Zr(O)₂plane (yz). Only two of the low-lying d orbitals are

used, notably 1a₁and 1b₂(d_yz), which interact, respectively, with

the in-phase and out-of-phase combinations of the two σ-orbitals

of the X^-groups, leaving as LUMO the 1b₁(d_xz) orbital. Note

that the out-of-phase combination of the two σ-orbitals could,

in principle, interact with the low-lying 1b₁(d_xz) orbital, leading

to a different structure with the two X^-alkyl groups lying in

the xz plane. Moreover, recalling that the energy of 1b₁is lower

than that of 1b₂suggests that this latter structure might be of

lower energy. This is, in fact, not true, as confirmed by explicit

(28) March, J. AdVanced Organic Chemistry, 4^thed., Wiley: New York,

1992; p 433.

(29) Eisner, U.; Kuthani, J. Chem. ReV. 1972, 72, 1.

9210 J. Am. Chem. Soc., Vol. 119, No. 39, 1997

Giannini et al.

Chart 4

core. It is worth noting that the [calix[4]-(OMe)(O)₃ZrX]

complexes still have a low-lying LUMO in the xz plane

(corresponding to a suitable mixing of the 1a′ and 2a′ orbitals

of the metal fragment) and have, therefore, a strong tendency

to bind a Lewis base, giving an adduct in which the X group is

tilted toward the methoxo group. This is supported by the

structure of 22 (see Figure 4) in which the donating electron

pair comes from the phenoxo group of an adjacent [calix[4]-

(OMe)(O)₃ZrX] molecule, thus leading to a dimeric species.

Conclusions

This is the first series of papers on the use of an O₄set of

donor atoms, issued from a calix[4]arene cone conformation,

as an oxo matrix for developing the organometallic chemistry

of a transition metal. The O₄oxo surface can be tuned in its

charge and, by consequence, in its bonding mode to the metal

using a partial methylation of the oxygen donor atoms from

the calix[4]arene. The [calix[4]-(OMe)₂(O)₂Zr]²⁺and [calix-

[4]-(OMe)(O)₃Zr]⁺fragments served to model organometallic

functionalities bonded to a polyoxo surface, like in catalysis,³⁰

and led to the discovery of novel reactivities and bonding modes

of a variety of organic groups bonded to the metal in such an

unusual O₄coordination environment. Extended Hu¨ckel cal-

culations on the above fragments allowed a comparison of their

frontier orbitals with those of the [Cp₂Zr]²⁺fragment. In

addition, using the same approach, we modeled the reaction of

[calix[4]-(OMe)₂(O)₂ZrX₂] [X ) Cl, R] with bases, a quite

general and synthetically useful reaction allowing the conversion

of two coordination environments for the same organometallic

functionality.

Figure 6. Total energy profile for the favored NH₃approach toward

[calix[4]-(OMe)₂(O)₂ZrMe₂] and [calix[4]-(OMe)₂(O)₂ZrCl₂].

continuously increases on decreasing L, reaching a difference

of almost 2 eV at the lowest considered distance of 2.5 Å. This

implies that the bis-chloro complex is less electrophilic than

the bis-methyl analogue, in agreement with the higher energy

of the LUMO orbital (-9.5 Vs -10.5 eV) and the lower charge

on zirconium (+0.9 Vs +1.1). This suggests that, in the bis-

chloro compound, the base will not attack the metal but instead

removes the Me⁺group. [ZrR₂] compounds are much less

reactive because the preferential attack of the nucleophile to

the metal center lowers its Lewis acidity and, hence, its

interaction with the OMe groups. As a consequence, their

tendency to be attacked by a second molecule of nucleophile is

reduced.

We have subsequently considered the monomethylated calix-

[4]arene complexes, the simplest examples being those in which

the zirconium binds only one σ ligand like Cl or Me. The most

symmetrical structure for such a [calix[4]-(OMe)(O)₃ZrX]

molecule is that in which the X^-ligand is located on the z-axis.

However, on the basis of the frontier orbital analysis of [calix-

[4]-(OMe)(O)₃Zr]⁺(Scheme 7) we expect the most stable

structure to be slightly tilted toward the OMe group in the xz

plane, to maximize the overlap of the σ orbital on the X^-ligand

with the lowest vacant metal orbital, 1a′. We have, therefore,

performed a calculation on the [calix[4]-(OMe)(O)₃ZrX] com-

plexes [X ) Cl, R], varying the X-Zr-z angle R (Chart 4).

However, the total energy as a function of the angle R is almost

flat in a wide range around the z-axis ((30°), with a minimum

for X essentially on the z-axis. This is probably due to the

small energy difference between 1a′ and 2a′ (0.2 eV), which

could be compensated by a better overlap of the σ orbital of

X^-with 2a′, which is better directed away from the (O)(OMe)

Acknowledgment. We thank the “Fonds National Suisse de

la Recherche Scientifique” (Grant No. 20-46’590.96), Ciba-

Geigy S.A. (Basel), and Fondation Herbette (N.R.) for financial

support.

Supporting Information Available: X-ray crystallography,

ORTEP or SCHAKAL drawings, tables giving crystal data and

details of the structure determination, fractional atomic coor-

dinates, anisotropic and isotropic thermal parameters, bond

lengths, and bond angles for 4, 6, 13, 16, 22, and 23 (56 pages).

See any current masthead page for ordering and Internet access

instructions.

JA970821C

(30) (a) Corker, J.; Lefebvre, F.; Lecuyer, C.; Dufaud, V.; Quignard, F.;

Choplin, A.; Evans, J.; Basset, J.-M. Science 1996, 271, 966. (b) Niccolai,

G. P.; Basset, J.-M. Appl. Catal., A 1996, 146, 145. (c) Vidal, V.; Theolier,

A.; Thivolle-Cazat, J.; Basset, J.-M.; Corker, J. J. Am. Chem. Soc. 1996,

118, 4595.

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Article abstract of DOI:10.1021/ja970821c

Full text of DOI:10.1021/ja970821c

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