Calix[4]arene stabilized transition metal imido complexes

Forschungsbericht ؊ Research Report

Calix[4]arene stabilized Transition Metal Imido Complexes

U. Radius*

Karlsruhe, Institut für Anorganische Chemie der Universität

Received April 7th, 2004.

Abstract. The usage of calix[n]arenes as ancillary poly(phenolate)

ligands is a rapidly developing area in coordination chemistry. This

article focuses on the synthesis, structure and reactivity of calix[4]-

arene- and calix[4]arene ether-stabilized imido complexes of group

4 Ϫ 6 transition metals as well as on the comparison of calix[4]ar-

ene dialkyl ethers in particular with other widely employed related

ligand systems such as salenes, porphyrins and tetraazaannulenes.

Contrary to these nitrogen containing systems, it is much easier to

control the charge of the ligand system through the degree of alky-

lation of the calixarene’s lower rim without a major change in the

geometry of the resulting metal complex. This could lead to isoelec-

tronic and structurally closely related transition metal complex

fragments for metals in neighboring groups of the periodic table or

for metals in different oxidation states. The “intrinsic” reactivity of

metal imido linkages might therefore be explored using calix[4]ar-

enes and calix[4]arene ethers and first results are summarized in

this research report.

Keywords: Transition metal complexes; Group 4 Ϫ 6 metals;

Calix[4]arene complexes; Imido complexes

Calix[4]aren-stabilisierte Übergangsmetall-Imido-Komplexe

Inhaltsübersicht. Der Einsatz von Calix[n]arenen als Poly(phenolat)-

liganden hat in den letzten Jahren zunehmendes Interesse in der

Koordinationschemie gefunden. Dieser Forschungsbericht be-

schreibt Synthesewege, Strukturen und Reaktivität von Übergangs-

metall-Imidokomplexen der Elemente der vierten bis sechsten

Gruppe, die durch Calix[4]arene bzw. Calix[4]aren-Ether stabilisiert

sind. Ferner werden die Komplexe der Calix[4]aren-Di(alkyl)ether

mit anderen verwandten, vielfach eingesetzten Ligandensystemen

wie den Salenen, Porphyrinen und Tetraazaannulenen verglichen.

Im Gegensatz zu den Stickstoff-haltigen Ligandensystemen ist es

in der Chemie von Calix[4]arenkomplexen durch Variation des Al-

kylierungsgrades am sog. „unteren Kegelrand“ einfach, die Ladung

des Liganden zu kontrollieren, ohne die Koordinationssphäre am

Metallatom des resultierenden Komplexes tiefgreifend zu verän-

dern. Der Einsatz von Calix[4]arenen und Calix[4]aren-Ethern

sollte so zu isoelektronischen und strukturell ähnlichen Übergangs-

metall-Komplexen von benachbarten Metallen im Periodensystem

oder von identischen Metallen in unterschiedlichen Oxidationsstu-

fen führen. Auf diese Weise können „intrinsische“ Reaktivitäten

von Calix[4]aren-stabilisierten Metall-Imidoverbindungen in Ab-

hängigkeit vom Metall bzw. dessen Oxidationsstufe untersucht wer-

den. Erste Ergebnisse sind in diesem Forschungsbericht zusammen-

gefasst.

1 Introduction

metal complexes can produce metal phenolate complexes

with substitution of one to four hydrogen atoms [5]. The

fully deprotonated form of the parent calix[4]arenes act as

tetraanionic ligands and usually assume the cone confor-

mation in metalla-calix[4]arenes, which keeps the set of the

oxygen donor atoms quasi planar. The charge of the O₄set

can be tuned by etherification or esterification of the lower

rim of the calix[4]arene, as pointed out in Scheme 1 for

methylation products of H₄calix.

Calix[n]arenes are macrocyclic molecules made of n phenol

units connected by ortho methylene groups [1, 2]. Calix[4]-

arenes are the simplest and most common members of this

family with four phenolic residues in the macrocyclic ring.

These molecules and their derivatives have been extensively

studied for their interesting properties, e.g. as hosts to cat-

ions, anions and neutral molecules, and for the formation

of supramolecular assemblies [3]. Because of the four

phenoxyl groups in the calix[4]arenes (p-tert-butyl-calix[4]-

arene ϭ H₄calix, see Scheme 1) [4], reactions with transition

* P.D. Dr. habil. U. Radius

Inst. für Anorgan. Chemie der Universität (TH)

Engesserstr., Geb. 30.45

D-76128 Karlsruhe

Tel.: ϩ49(0)721-6088097

Fax: ϩ49(0)721-6087021

Scheme 1 Calix[4]arenes and calix[4]arene ethers as ancillary

E-mail: radius@aoc1.uni-karlsruhe.de

poly(phenolate)ligands.

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U. Radius

Curriculum vitae of the author

Udo Radius was born in Nuremberg, Germany

in 1965 and studied chemistry from 1986 to

1991 at the University of Würzburg. He recei-

ved his doctoral degree in the group of Prof.

Helmut Werner under the guidance of Prof.

Jörg Sundermeyer in 1994. He continued his

scientific education as a postdoctoral fellow

with Prof. Roald Hoffmann (1995 Ϫ 1996) at

the Cornell University, Ithaca, NY, where he

was introduced into theoretical chemistry.

Funded by a Liebig-Stipendium of the Fonds

der Chemischen Industrie, he returned to Ger-

many for his habilitation, which was completed

at the Universität Karlsruhe (TH) in 2001. His

general research interests are in the fields of

coordination chemistry and organometallic

chemistry of the d-block elements including

catalysis, material science, and bioinorganic

chemistry. His group focuses currently on the

usage of macrocyclic ligands in these areas,

especially on calixarenes and thiacalixarenes as

poly(phenolate) ligands.

The degree of functionalization of the metal atom can be

controlled by alkylation or silylation of the oxygen atoms,

which also offers steric protection. The Me₂calix homol-

ogues in particular have received much attention in organo-

transition metal chemistry over the last 10 years, and a

rich chemistry has emerged comprising mainly mononu-

clear group 4 and 5 metals [5]. In these complexes, the

[R₂calix]^2Ϫligands usually provide two negatively charged

phenolate oxygen donor atoms and two neutral anisole oxy-

gen donors to a transition metal atom Ϫ a robust and well-

defined O₄-coordination environment, similar to other

widely used supporting dianionic ligands such as the O₂,N₂-

donor ligands of salene type Schiff bases or N₄-donor li-

gands such as porphyrins and dibenzotetraaza[14]annulenes

[6Ϫ8]. In contrast to these nitrogen containing ligand sys-

tems, the calix[4]arene dialkyl ethers are conformationally

much more flexible (as shown below). Moreover, it is much

easier to change the charge of the ligand system through

the degree of alkylation without a major change in the

structure of the resulting metal complex. Modifying the

above mentioned nitrogen containing ligands in the same

way would require significant synthetic effort, if at all pos-

sible. Therefore, calix[4]arenes seem to be ideal ancillary li-

gands for systematic investigations. Isoelectronic and struc-

turally closely related transition metal complexes fragments,

for example, are available for metals in neighboring groups

of the periodic table. Similar compounds of the complex

fragments [M(R₂calix)], [MЈ(Rcalix)], and [MЉ(calix)], can

be synthesized, if the degree of alkylation of the calix[4]ar-

ene ligand is decreased and the central atom of the complex

is substituted with a metal atom of the next group of the

periodic table (M < MЈ < MЉ) or the same metal atom in

its next higher oxidation state (M < MЈ < MЉ). This is ex-

emplified in Scheme 2 for multiply bonded dianionic li-

gands E such as oxo, sulfido, imido, phosphinidene or car-

bene. In the case that (i) the metal atoms M, MЈ, and MЉ

are of group 4, 5, or 6 and of the same d electron configura-

tion and (ii) that the metal atoms M, MЈ, and MЉ are of

the same group and differ in their formal oxidation states

by one unit, these complexes are isoelectronic and structur-

ally closely related. With these complexes in hand, it should

be possible to isolate and stabilize [MϭE] functionalities

and to study their “intrinsic” reactivity depending on the

metal atom and its oxidation state, provided that the calix-

[4]arene ligand binds in a cone or elliptically distorted cone

conformation and the resulting complexes are monomeric

as illustrated in Scheme 2.

Scheme 2 Similar isoelectronic and structurally closely related

complexes of the type [M(ϭE)(R₂calix)] D, [MЈ(ϭE)(Rcalix)] E,

and [MЉ(ϭE)(calix)] F.

The chemistry of organoimido complexes has experi-

enced a considerable development during the last two dec-

ades [9]. The imido ligand [NR]^2Ϫ(R ϭ alkyl, aryl) usually

coordinates to a transition metal atom through one σ and

up to two π orbital interactions, similar to the ubiquitous

cyclopentadienyl ligand [10] or to phosphorane iminato li-

gands [11]. With respect to the fundamental importance of

group 4 metallocenes as catalysts in olefin polymerizations

and other catalytic transformations, this similarity has be-

come a strategic tool for the development of new classes of

catalytically active imido complexes [12, 13]. Furthermore,

organoimido complexes of the transition metals have been

implicated in catalytic processes such as propylene ammox-

idation [14] and nitrile reduction [15] and have been shown

to function as imido transfer intermediates in aziridination

[16] and amination reactions [17, 18]. The importance of

these fields led to a growing number of imido complexes of

both later [18, 19] and earlier [17, 20] transition metals. The

reactivity of group IV and group V organoimido complexes

include C-H activation, cycloaddition of unsaturated C-C

and C-X bonds, as well as addition of H₂and alkylsilanes

to the metal imido group. Moreover, group IV imido com-

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Calix[4]arene stabilized Transition Metal Imido Complexes

plexes participate in imine metathesis and catalyze the

hydroamination of alkynes to enamines. By contrast, the

metal nitrogen multiple bonds in imido complexes of group

VI and group VII metals rarely display reactivity at the

[MϭNR] bond. Imido groups of diimido molybdenum,

tungsten and rhenium compounds, for example, can act as

spectator ligands in numerous reaction processes including

metathesis reactions [20], whereas mononuclear imido

compounds of more electron rich metals such as [(η⁵-

C₅Me₅)Ir(NR)] [19b Ϫ h] and [(η⁶-arene)Os(NR)] [19a]

show extensive cycloaddition chemistry. Following a con-

ceptual model by Nugent et al. [9, 22], this reactivity follows

largely the relative energy and the composition of the π or

π* orbital of the [MϭNR] linkage, which is mainly influ-

enced by the following factors: (i) the nature of the tran-

sition metal, (ii) the oxidation state of the transition metal,

(iii) the ancillary ligands and (iv) the ligand R of the NR

moiety [9, 22, 23]. However, to date there is no study on

organoimido complexes available, which describes compre-

hensively the reactivity over several groups of transition

metals or the dependence of the particular oxidation state

of the metal atom in complexes, in which the metal atoms

experience a similar ligand environment. Such a comparable

surrounding might be provided by calix[4]arene ligands.

One prerequisite is that the calix[4]arene bind to these com-

plexes while maintaining the cone-like appearance of the

macrocyclic ligand.

higher in energy compared to the trans isomer, and a de-

tailed analysis has shown that this difference in energy is

almost exclusively due to the deformation energy needed to

distort the calix[4]arene ligand. Floriani and coworkers have

demonstrated that the conversion of cis-[WCl₂(calix)] to the

thermodynamically more favorable trans isomer is facili-

tated by reactions with Lewis acids such as AlCl₃[25].

For the Me₂calix ligand system, DFT analyses as well as

experimental results have shown, that the macrocyclic

ligand can bind in an elliptically distorted cone confor-

mation to a metal atom, as adopted in [TiCl₂(Me₂calix)]

(1), but also in a way which is reminiscent of the partial

cone (paco) conformation of calixarenes. In this coordi-

nation mode, the ligand coordinates under loss of its reg-

ular cone-like appearance and its hydrophobic cavity with

one of the anisole methoxy groups located inside the cavity.

This was exemplified by the synthesis of [Mo(O)₂-

(paco-Me₂calix)] (2) and has been proven spectroscopically

as well as crystallographically [26]. The formal change of a

d⁰-[TiCl₂] with a d⁰-[MoO₂] complex fragment completely

changes the coordination form of the calixarene dimethyl

ether dianion. The results of the crystal structure determi-

nations of 1 and 2 are shown in Figure 1.

2 Coordination of calix[4]arene dimethyl ethers in

metallacalix[4]arenes: cone vs. paco coordination mode

As mentioned above, like the successfully applied nitrogen

containing ligand systems such as salenes, porphyrins and

tetraazaannulenes the R₂calix ligands provide a robust and

well-defined O₄-coordination environment, which should be

less rigid compared to TPP and TAA ligands. This raises

the question of what the possible coordination modes of

calix[4]arene ethers in metal complexes are. The calix[4]ar-

ene system [calix]^4Ϫusually binds in a tetradentate fashion

and retains its cone-like appearance in square pyramidal

complexes of the type [ML(calix)] or in octahedral com-

plexes [ML₂(calix)], if both ligands L are oriented trans to

each other. In the latter case, one of the ligands coordinates

endohedrally to the metal atom and is located in the cage

of the calix[4]arene ligand. For group 6 chemistry, imido

compounds [M(NR)L(calix)] (R ϭ tBu, Mes; LЈ ϭ NCMe,

CNtBu, see below) are good examples of this type of coor-

dination. Furthermore, it has been found in mononuclear

complexes, that the calix[4]arene is capable of adopting

alternative conformations when binding to metal centers,

usually in an elliptical cone conformation, in which the ca-

lix[4]arene oxygen atoms adopt cis and trans sites in octa-

hedral [ML₂(calix)] complexes. In these compounds, the li-

gands L are mutually cis oriented, as has been found in the

structurally characterized calixarene molybdenum dichlor-

ide [MoCl₂(calix)] [24]. According to DFT calculations, the

cis isomer of [MoCl₂(calix)] is approximately 18.1 kJ/mol

Figure 1 Schakal plots of the molecular structures of [TiCl₂-

(Me₂calix)] (1, left) and [Mo(O)₂(paco-Me₂calix)] (2, right) [26].

In complex 1 the calix[4]arene ether ligand binds with

two anisole ether and two phenolate groups to the titanium

atom and adopts an elliptically distorted cone confor-

mation. This coordination mode leads to a pseudo C_2vsym-

metric structure with two different sets of Ti-O distances,

178.3(2) pm and 180.6(2) pm to the phenolate oxygen atoms

and 210.1(2) pm and 213.3(2) pm to the ether oxygen

atoms, as well as two sets of different Ti-O-C angles

116.6(1)° and 115.6(1)° (ether moiety) and 153.5(2)° and

163.8(2)° (phenolate moiety). The chlorine ligands trans to

the phenolate units complete the distorted octahedron

around the titanium atom.

In contrast, the Me₂calix ligand in 2 coordinates in a

form which is reminiscent of the paco conformation of the

calix[4]arene. In this complex, the ether groups of the calix-

[4]arene ligand are in trans positions relative to the oxo

[O]^2Ϫligands. As a consequence, one of the methoxy groups

is located inside the cavity of the calix[4]arene ligand leading

to an ’up, up, up, down’ arrangement of the aryloxy units of

the macrocycle. The molybdenum phenolate oxygen bond

lengths (191.6(3) pm and 192.0(3) pm) and molybdenum

oxide ligand distances (169.4(3) pm and 169.0(3) pm) are

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unexceptional. The molybdenum anisole oxygen distances

(Mo-O(1) 239.4(3) pm and Mo-O(3) 255.9(3) pm), are con-

siderably longer. The Mo-O(3) distance is very large, prob-

ably due to structural constraints imposed by the calix[4]ar-

ene ligand, and suggests only weak interaction of O(3) with

the metal atom. The strong trans effect of the multiply

bonded oxo ligand [27] explains the alignment of the li-

gands. The oxo ligands are coordinated cis to each other

with an O(5)-Mo-O(6) angle of 101.5(2)°, increased from

an idealized value of 90° so as to maximize π overlap to the

high valent molybdenum atom.

The dinuclear compounds [{Ti(O-4-C₆H₄R)(Mecalix)}₂]

(5, R ϭ Me; 6, R ϭ tBu) are the result of the elimination

of one equivalent of aryl methyl ether. The products of the

rearrangement reaction are [Ti(O-4-C₆H₄Me)₂(paco-Me₂ca-

lix)] (7) and [Ti(O-4-C₆H₄tBu)₂(paco-Me₂calix)] (8), in

which the calix[4]arene ligand is coordinated in the paco

conformation. This was established by NMR spectroscopy

and X-ray crystallography. The proton NMR spectra of

both isomers of [Ti(O-4-C₆H₄tBu)₂(Me₂calix)] are shown in

Figure 2.

A powerful tool to investigate this behavior in solution

is ¹H NMR spectroscopy, where different signal patterns

depending on the coordination mode of the calix[4]arene

ligand are found, i.e. for the paco form signals which are

typical for the macrocyclic ligand in a local pseudo C_ssym-

metry are detected. More significantly, two signals for the

methyl groups of the calix[4]arene ether of 2 are observed:

one for the exohedrally coordinated anisole unit at 4.18

ppm, which is similar to the chemical shift of 4.19 ppm

found in 1, and the other resonance for the endohedrally

coordinated anisole ether unit at 0.79 ppm, which is shifted

due to ring current effects of the calix[4]arene phenyl rings

within the calix[4]arene cavity.

In compounds of the type [Ti(O-4-C₆H₄R)₂(Me₂calix)]

(R ϭ Me 3, tBu 4), both kinds of coordination mode have

been observed [28b]. These calixarene-stabilized titanium

bis(phenolate) compounds with para-substituted phenolate

ligands have been isolated in good to excellent yields from

the reaction of the titanium imido complex [Ti(NtBu)(Me_2-

calix)] and two equivalents of the corresponding phenol (see

below) to afford complexes in which the calix[4]arene is co-

ordinated in an elliptically distorted cone conformation.

These complexes undergo elimination and/or rearrange-

ment reactions in non polar solvents such as pentane and

hexane (see equation (1)).

Figure 2 Proton NMR spectra of [Ti(O-4-C₆H₄tBu)₂(Me₂calix)]

(4; upper part) and [Ti(O-4-C₆H₄tBu)₂(paco-Me₂calix)] (8; lower

part) in CDCl₃[28b].

For the pseudo C_2vsymmetric cone isomer 4, three sig-

nals arise for the tert.-butyl groups of the calix[4]arene and

the tert.-butyl-phenolate ligand, two doublets for the meth-

ylene protons of the calix[4]arene ligand and a singlet for

the methyl groups of the anisole moiety. In the aryl region

there are, in addition to the resonances of the protons of

the calix[4]arene ligand, the signals of toluene, originally

located in the cavity of the calix[4]arene ligand in the iso-

lated compound 4. In the proton NMR spectrum of C_s

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Calix[4]arene stabilized Transition Metal Imido Complexes

symmetric 8, the tert-butyl groups of the calix[4]arene and

the phenolate ligands appear as signals at 1.33, 1.24, 1.23,

1.14, and 1.07 ppm in an integration ratio of 1:1:2:1:1 and

four doublets can be found for the diastereotopic protons of

the methylene bridges. Most relevant here are two signals for

the methoxide groups of the anisole units, one at 4.30 ppm,

while the other resonance is significantly shifted upfield to

0.82 ppm, as observed for the molybdenum complex 2.

DFT calculations on model compounds [Ti(O-C₆H₅)₂-

(cone-Me₂calix^H)] and [Ti(O-C₆H₅)₂(paco-Me₂calix^H)] re-

veal a slight thermodynamic preference for the paco-isomer,

but the pathway of this isomerization process remains

unclear. The rearrangment reaction is sensitive to changes

in the sterics of the M(OAr)₂fragment. Complexes

[Ti(O-2,6-C₆H₃R₂)₂(Me₂calix)] (9) and [Zr(O-4-C₆H₄Me)₂-

(Me₂calix)] (10) do not rearrange. The rearrangement reac-

tion described here therefore implies a delicate steric

balance. Whereas the complexes with para substituted

phenoxide ligands 4 and 5 rearrange in apolar solvents, the

complexes with the sterically more demanding phenoxides

such as 9 and the zirconium compound 10 do not undergo

analogous rearrangements in benzene, pentane or hexane,

which might be due to a kinetic stabilization of the cone

isomer or different ionic radii of the metal ions. We have

not yet found similar rearrangements in complexes of

calix[4]arene mono(methyl) ether Mecalix, as for example

in compounds of the type [TiX(Mecalix)] [29] and [Mo(N)-

(Mecalix)] [30].

reactions of the dichloro compound [TiCl₂(Me₂calix)] with

two equivalents of alkali metal amides MNHtBu or

MNHAr (Ar ϭ 2,6-C₆H₃Me₂, 2,4,6-C₆H₂Me₃, or 2,6-

C₆H₃iPr₂), proceed cleanly and usually in high yield. On

NMR tube scale, reactions of [TiCl₂(Me₂calix)] and two

equivalents of LiNHRЈ form in >95 % the imido complexes,

and one equivalent of the corresponding RЈNH₂is elimin-

ated during the reaction. There is no evidence for interac-

tion between the ArNH₂and the imido complexes which,

in principle, could form either an adduct with the free am-

ines or significant equilibrium concentrations of bis(amido)

species [Ti(NHRЈ)₂(Me₂calix)]. Alternative pathways are

the reaction of the imido complexes [Ti(NRЈ)Cl₂(py)₃] or

[Ti(NRЈ)Cl₂(NHMe₂)₂] (RЈ ϭ tBu or aryl) with metallated

calix[4]arenes such as [{Na₂(Me₂calix)}₂] [30].

Scheme 3 Feasible routes to calix[4]arene stabilized titanium

These investigations show two major features of the

R₂calix ligand compared to similar nitrogen based ligands:

(i) a more flexible calix[4]arene backbone and (ii) the ease

of dealkylation of the calixarene ether, especially in early

transition metal complexes. Dealkylation reactions have al-

ready been observed in the synthesis of [TiCl₂(Me₂calix)]

starting from H₂Me₂calix and [TiCl₄(thf)₂]. The outcome of

this reaction critically depends upon the reaction con-

ditions. Whereas the reaction of H₂Me₂calix and

[TiCl₄(thf)₂] in toluene for one day at 60 °C affords the di-

methyl ether titanacalix[4]arene [TiCl₂(Me₂calix)], a longer

reaction time in refluxing toluene leads to elimination of

MeCl to give [TiCl(Mecalix)]. The thermal stability of the

calixarene ether dichloride complexes [TiCl₂(R₂calix)] with

respect to RCl elimination to form the [TiCl(Rcalix)] com-

pounds is SiMe₃< Bz << Me, which reflects the stability

of possible radical species R, probable intermediates during

the cleavage reaction, as well as the steric demand of the R

group [29].

imido complexes.

For the synthesis of analogous titanium imido complexes

of other 1,3-disubstituted ether p-tert.-butyl-calix[4]arene

ligands, i.e. Bz₂calix (Bz ϭ CH₂Ph) and (Me₃Si)₂calix, the

synthesis via the dichloro compound [TiCl₂(R₂calix)]

(R ϭ Bz, SiMe₃) is not a practicable way since the dichlor-

ides themselves are not stable and rapidly eliminate RCl.

For the Bz₂calix systems, reaction of one equivalent of

Li₂(Bz₂calix) with [Ti(NR)Cl₂(py)₃] gave complexes

[Ti(NR)(Bz₂calix)] (R ϭ tBu, 2,6-C₆H₃Me₂, C₆H₃iPr₂) in

good yield, whereas the reaction of the disodium salt of

(Me₃Si)₂calix with [Ti(NR)Cl₂(py)₃] gave only a mixture of

products and neither the target complexes nor any other

imido containing compound. All NMR spectra of the com-

plexes 11 Ϫ 17 are consistent with molecular C_2vsymmetry

with the molecular C₂axis passing through the RЈ-NϭTi

bond vector. The result of the X-ray crystal structure deter-

mination of [Ti(NtBu)(Me₂calix)] (11) as determined in

[Ti(NtBu)(Me₂calix)]·2(C₇H₈) 1·2(C₇H₈) is shown in Fig-

ure 3. One of the toluene solvent molecules is included in

the cavity of the calix[4]arene ligand (not shown in Figure

3), the other solvent molecule occupies a general position

in the lattice and gives rise to no significant contacts with

the molecules of 11.

3 Calix[4]arene-supported Group 4 ؊ 6 Imido

Complexes

3.1 Calix[4]arene-supported group 4 imido

complexes

The five-coordinate metal center in 11 possesses a tri-

gonal bipyramidal arrangement with the imido and arylox-

ide donors lying in the equatorial plane as is typically the

Synthesis and Characterization

Feasible routes to complexes of the type [Ti(NtBu)(R₂calix)]

and [Ti(NAr)(R₂calix)] are depicted in Scheme 3 [28]. The

case for Group

4

imido complexes of the type

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Figure 3 Schakal plot of the molecular structure of [Ti(NtBu)-

(Me₂calix)] (11) [28b].

[M(NR)X₂L₂] (X ϭ amide or alkoxide/aryloxide; L ϭ

Lewis base donor) [31]. The TiϭNtBu, Ti-O_aryloxideand

Ti-O_etherdistances are within the usual range for complexes

with fivefold coordinated metal atoms [31, 32]. The Ti-N

bond distance of 170.9(2) pm as well as the TiϭN-tBu bond

angle of 175.7(2)° is consistent with the imido ligand acting

as a 6-electron donor to the titanium atom (heterolytic

cleavage of the Ti-N-bond), while the Ti-O_aryloxide-C angles

of 149.8(2)° and 177.6(2)° suggest that the aryloxide O-do-

nors can act as at least 4-electron donors potentially giving

the titanium atom an 18 valence electron count. The struc-

ture of 1 is similar to that of the mesityl homologue 4 [28a],

but the TiϭNR distance (171.8(3) pm in 14) is slightly

shorter and the Ti-OR slightly longer for the tert.-butyl

species. This is consistent with the general observation that

TiϭNR bonds for arylimido complexes are typically longer

than those in their tert.-butyl homologues, and that tert.-

butylimido ligands are generally more labilising towards

other ligands present than arylimido ligands in homo-

logous complexes.

Ab initio and DFT calculations [33Ϫ36] were performed

on model compounds to gain a better understanding of the

main electronic and structural properties of the titanium

imido complexes supported by the calix[4]arene methyl

ether ligand. Two models have been considered in the calcu-

lations: a detailed model [Ti(NR)(Me₂calix^H)], in which the

ligand has been slightly modified through a replacement of

the tert.-butyl groups with hydrogen atoms, and a second,

more simplified model [Ti(NR)(OMe)₂(OMe₂)₂], in which

the coordination environment at the titanium atom has

been maintained to resemble the main features of the li-

gand, but the aryl groups have been replaced by methyl.

Calculations on different detailed model complexes have

shown that DFT methods (BP86/SV(P)) describe the ge-

ometry very well compared to the structurally obtained

data. The structure of [Ti(NtBu)(Me₂calix^H)] optimizes in

a C_ssymmetric structure with a Ti-N distance of 171.10 pm

and an Ti-N-C- angle of 176.05°. Replacement of the imido

tert.-butyl group with methyl or hydrogen leads to a small

decrease of the Ti-N bond length to 170.34 pm (R ϭ Me)

and 169.52 pm (R ϭ H).

Figure 4 Orbital plots of relevant metal fragment orbitals of the

simplified model [Ti(OMe)₂(OMe₂)₂]^2ϩof the calixarene complexes

(left side) and a schematic FMO diagram of the interaction of an

imido ligand [NR]^2Ϫwith the metallacalixarene fragment

[Ti(Me₂calix)]^2ϩ(right side).

A schematic FMO diagram of the interactions of an im-

ido ligand [NR]^2Ϫwith the metallacalixarene fragment

[Ti(Me₂calix)]^2ϩis depicted on the right side of Figure 4.

The lowest unoccupied, metal-centered orbitals of the

[Ti(Me₂calix)]^2ϩfragment are depicted on the left side of

the FMO scheme in Figure 4, whereas orbital plots of these

relevant orbitals drawn for the simplified model are given

on the left side of Figure 4. For this Ti^IVcomplex fragment

with a d⁰electron count the highest occupied orbitals are

ligand centered, Ti-O non bonding orbitals. There are four

low-lying unoccupied metal-centered orbitals which are

2

higher in energy. The orbital 2a₁, d_{x Ϫy}in character, points

closely towards the oxygen atoms of the ligand and is

pushed up higher in energy while the remaining four d or-

bitals are found within 1.5 eV. Because of a relatively strong

π-overlap of the phenolate oxygen atoms of the ligands with

the titanium atom, the Ti-O π-antibondung orbitals

1a₂(d_xy) and 1b₁(d_yz) lie higher in energy than the LUMO

2

1b₂(mainly titanium d_zin character). Due to the lower

interaction with the anisole oxygen donor atoms in the xz

plane, the orbital 1b₂is approximately 1.00 eV lower in en-

ergy than 1b₁. The [Ti(Me₂calix)]^2ϩfragment is therefore

ideally suited to stabilize good σ,2π donor ligands. In com-

plexes [Ti(NR)(Me₂calix)] with fivefold coordinated ti-

tanium atoms, in which the imido ligand lies along the z

axis, there exists a strong bonding interaction between the

2

la_l(d_z) and the σ-orbital of the imido ligand as shown sche-

matically in the FMO diagram in Figure 4. For π donating

ligands the remaining low-lying metal centered orbitals can

interact with the high lying π-donor orbitals, which leads

to a stabilization of 1b₂and 1b₁to form two titanium imido

π bonds, which are slightly different in energy. For the

model [Ti(NtBu)(Me₂calix^H)] these π bonding orbitals are

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Calix[4]arene stabilized Transition Metal Imido Complexes

LUMO-2 and LUMO-3 and separate fairly well from other

ligand type orbitals, as shown in Figure 5. The importance

of π-contributions to Ti-N-bonding can be substantiated by

population analyses. In a Roby-Davidson analysis [37] of

C_2v-[Ti(NH)(Me₂calix^H)] a total of 1.20 electrons for the

Ti-N-bond is divided into 0.41 electrons emerging from in-

teractions of b₂symmetry, 0.40 electrons from interactions

of b₂symmetry, and only 0.39 electrons due to G interac-

tion of a₁type orbitals. A similar picture arises from an

analysis of C_s-[Ti(NtBu)(Me₂calix^H)], where out of a total

of 1.12 electrons for the Ti-N-bond, 0.74 electrons emerge

from interactions of aЈ symmetry (i. e. σ ϩ π, the π bonding

orbital LUMO-2 itself contributes 0.33 electrons !) and 0.38

electrons from π interactions of aЉ symmetry.

Table 1 ∆δ values of titanium(IV) imido complexes.

Complex

δ(NC(CH₃)₃) δ(NC(CH₃)₃) ∆δ

Lit.

[Ti(NtBu)Cl₂(py)₃]

73.6

68.8

68.3

69.1

30.6

31.7

31.4

32.3

33.4

34.0

31.8

43.0

37.1

36.9

36.8

36.5

36.7

35.2

[20r, t]

[31a]

[32f]

[28]

[32b]

[Ti(NtBu)(ODIP)₂(py)₂]

[Ti(NtBu)(Et₂salene)]

[Ti(NtBu)(tBu₄salene)]

[Ti(NtBu)(Me₂calix)] 11 69.9

[Ti(NtBu)(Bz₂calix)] 15

[Ti(NtBu)(Me₈TAA)]

70.7

67.0

their donor capabilties to salene type ligands but worse than

tetraazaannulene systems.

Floriani et al. have reported the synthesis of a structurally

characterized, binuclear zirconium phenylimido complex

[{Zr(µ₂-NPh)(Me₂calix)}₂] from PhN₃and [Zr(η⁴-C₄H₆)-

(Me₂calix)] [38]. Non-azide routes to zirconium imido com-

plexes based on those discussed for the titanium systems

above are not straight forward. Unlike the titanium set of

synthons [Ti(NR)Cl₂(L)_n], no such convenient set of entry

points to zirconium imido chemistry have yet been estab-

lished, although Wigley and co-worker have reported

[Zr(N-2,6-C₆H₃iPr₂)Cl₂(L)_n] [(L)_nϭ (THF)₂or (py)₃] [39].

While the reaction of [Na₂(Me₂calix)]₂with [Zr(N-2,6-

C₆H₃iPr₂)Cl₂(THF)₂] appeared to form the desired product

[Zr(N-2,6-C₆H₃iPr₂)(Me₂calix)] (18), the reaction does not

proceed cleanly. The salt elimination starting from

[ZrCl₂(Me₂calix)] and two equivalents of LiNH-2,6-

C₆H₃iPr₂is the superior route that gave the imido complex

in the case of the sterically demanding aryl substituent. Like

its titanium congeners [Ti(NR)(Me₂calix)], the compound

Figure 5 Orbital plots of the titanium nitrogen π type orbitals

LUMO-2 (left) and LUMOϪ3 (right) calculated for [Ti(NtBu)-

(Me₂calix^H)].

1

18 affords H and ¹³C{¹H} NMR spectra consistent with

molecular C_2vsymmetry. The usage of other amides

LiNHR (R ϭ tBu, Ph, 2,6-C₆H₃Me₂or 2-C₆H₄tBu) leads

to no isolable zirconium imido products. When these reac-

tions were followed by ¹H NMR spectroscopy the data sug-

gested that in all cases (except where R ϭ Ph) mixtures of

imido and bis(amido) complexes, namely [Zr(NR)(Me₂ca-

lix)] and [Zr(NHR)₂(Me₂calix)], were formed in apparent

equilibrium with each other, the relative amounts de-

pending on the steric demands of the N-substituent. In the

case of R ϭ Ph, the only identifiable carbon-containing

product of the NMR tube scale reaction between

[ZrCl₂(Me₂calix)] and two equivalents of LiNHPh appeared

to be [Zr(NHPh)₂(Me₂calix)] (19) with no evidence for

Floriani’s binuclear phenylimido complex [{Zr(µ₂-NPh)-

(Me₂calix)}₂]. In these calix[4]arene zirconium complexes,

the Me₂calix ligand provides a satisfactory match with the

zirconium atomic radius, but the imido N-substituent still

needs to provide adequate steric bulk to avoid reaction of

[Zr(NR)(Me₂calix)] complexes with amines that may be

present in the reaction mixture.

¹³C-NMR spectroscopy has a prominent role in the

characterization of tert.-butylimido complexes. Nugent and

Haymore [9, 22] proposed the difference in ¹³C-NMR shifts

∆δ of α-(ϭ NC(CH₃)₃) and β-(ϭ NC(CH₃)₃) carbon atoms

of the tert.-butyl group as an approximation of electron

density at the imido nitrogen atom and an experimental

hint on the donor strength of the imido ligand to the metal

center. A decrease of the electron density at the metal atom

leads to an increase of the metal nitrogen bond and therefore

to a decrease of the electron density at the nitrogen atom

of the imido ligand, which can be observed experimentally

by an increase of ∆δ. On the other hand, the donor capa-

bilities of ancillary ligands in complexes of similar coordi-

nation environment as found in complexes of the type

[L_nTi(NtBu)] can be compared. ¹³C-NMR-resonances of

the α- and β- carbon atoms as well as the ∆δ values of some

selected examples of titanium(IV) imido complexes are

given in Table 1 [28].

The ∆δ value of 36.5 ppm (11) and 36.7 ppm (15) found

for the calix[4]arene complexes are similar to those ob-

served for other titanium imido phenolate complexes. They

correspond to values found for salene compounds, but are

larger than those of the TAA system. According to these

∆δ values the calixarene dialkyl ether ligands are similar in

Reactivity of 11

Our investigations on the reactivity of complex 11 are sum-

marized in Schemes 4 and 5. Compound 11 reacts swiftly

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Scheme 4 Reactions of [Ti(NtBu)(Me₂calix)] (11) with heterocumulenes.

and quantitatively with CO₂in benzene at room tempera-

ture. The spectroscopic data are consistent with the

formation of a N,O-bound organocarbamate complex

[Ti{N(tBu)C(O)O}(Me₂calix)] (20) as illustrated in

Scheme 4.

proceed via an intermediate thiocarbamate complex

[Ti{N(tBu)C(S)S}(Me₂calix)] analogous to 20, but this in-

termediate was not observed. In contrast to 21 and 22, the

porphyrin complexes [Ti(O)(OEP)] and tetraaza[14]annu-

lene analogues [Ti(O)(Me_ntaa)] and [Ti(S)(Me_ntaa)] are

monomeric, as are certain heavier chalcogen derivatives

[40Ϫ42], suggesting that the Me₂calix ligand provides a less

sterically protecting environment for stabilising sterically

unprotected metal-ligand multiple bonds.

The reaction of [Ti(NtBu)(Me₂calix)] 11 with p-tolyl iso-

cyanate gave clean conversion to the N,NЈ-bound ureate

complex [Ti{N(tBu)C(O)N(-4-C₆H₄Me)}(Me₂calix)] (23),

which is stable with respect to cycloreversion or extrusion

of tBuNCO to afford a tolylimido complex. The molecular

structure of 23 is shown in Figure 6.

Compound 20 is unstable at room temperature with re-

spect to extrusion of tert.-butylisocyanate and formation of

the dimeric oxo complex [{Ti(µ-O)(Me₂calix)}₂] (21). This

elimination reaction goes quite slowly in the dark, but

under ambient lighting is complete within one hour. The

reaction of 11 with CO₂under ambient light is the most

efficient and clean method for synthesizing the oxo com-

pound 21. The corresponding reaction of 11 with CS₂

proceeds much more slowly. This is attributed to the lower

electrophilicity of the carbon atom in CS₂and the softer

nature of the sulfur atom which would disfavour coordi-

nation to the hard titanium center as compared to CO₂.

The only observed products of this reaction are the bridging

sulfido complex [{Ti(µ-S)(Me₂calix)}₂] (22) and tert.-butyl

isothiocyanate, tBuNCS. The reaction is presumed to

The solid state structure of 23 shows the p-tolylisocyanate

moiety coupled across the former Ti-N(2) imide bond. The

titanium atom has an approximately octahedral coordi-

nation arrangement with the etheral O-donors of Me₂calix

occupying mutually trans coordination sites, and with the

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Calix[4]arene stabilized Transition Metal Imido Complexes

bound ureate intermediates are unstable with respect to

cycloreversion to form cyclopentadienyl-amidinate titanium

oxo complexes and the corresponding carbodiimides

tBuNCNR. The reaction of [Ti(NtBu)(Me₂calix)] (11) with

p-tolyl isocycanate to form the stable, N,NЈ-bound ureate

23 is therefore unusual in the still emerging field of Group

4 imide/heterocumulene reaction chemistry.

Protonolysis reactions of [Ti(NtBu)(Me₂calix)] (11) with

N-H, O-H, S-H and Cl-H bond substrates are summarized

in Scheme 5. Complex 11 easily loses tBuNH₂and new N-

and O- or Cl-donor functional groups are introduced.

The tert.-butyl imide/arylamine exchange reactions are

rather slow requiring prolonged heating to ensure complete

reaction. The reactions to form 12 and 13 proceed quanti-

tatively on an NMR tube scale, but require about three days

at 65 °C to go to completion. The analogous reaction with

H₂N-4-C₆H₄Me to form [Ti(N-4-C₆H₄Me)(Me₂calix)] (24)

is slightly faster, presumably due to formation of a less steri-

cally crowded 6-coordinate titanium atom of the bis(amide)

intermediate. However, this intermediate has not been

detected spectroscopically.

Figure

6

Schakal plot of the molecular structure of

[Ti{N(tBu)C(O)N(-4-C₆H₄Me)}(Me₂calix)] (23) [28b].

four anionic donors [N(1), N(2), O(2) and O(4)] forming

the equatorial plane of the octahedron. The distances and

angles within the structure are as expected [28b].

In recent years the reaction chemistry of Group 4 imido

complexes with CO₂and isocyanates has become better es-

tablished and a diversity of behaviour is starting to emerge,

which depends on the ancilliary ligand(s) and the imide and

isocyanate N-substituents. Reactions of [Ti(NtBu)(Me₄taa)]

with aryl isocyanates failed to give any tractable products.

However, reaction of [Ti(NtBu)(Me₄taa)] with tBuNCO

gives an N,O-bound ureate product as do a number of other

tert.-butylimido titanium complexes. In some cases the N,O-

The reactions of 11 with H₂O, H₂S and HCl afforded the

expected

products

[{Ti(µ-O)(Me₂calix)}₂]

(21),

[{Ti(µ-S)(Me₂calix)}₂] (22), and [TiCl₂(Me₂calix)] (1) in

greater than 90 % yield. The reaction of 11 with H₂S to

form 12 proceeds cleanly and completely within 30 minutes

and is therefore a more convenient synthesis of this com-

pound than that from 1 and CS₂. Phenols react similarly in

Scheme 5 Protonolysis reactions of [Ti(NtBu)(Me₂calix)] (11) with N-H, O-H, S-H and Cl-H bond substrates.

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a smooth reaction to afford the bis(phenolate) complexes,

as exemplified here by the formation of the cone isomers

[Ti(O-4-C₆H₄Me)₂(Me₂calix)] (3) and [Ti(O-4-C₆H₄tBu)₂-

(Me₂calix)] (5) mentioned above.

by Redshaw et al. [48] revealed that mononuclear imido

complexes [M(NR)(calix)] and [M(NR)(calix^H)] (M ϭ Mo,

W) are affordable in good to excellent yields from H₄calix

with compounds of the type [M(NR)₂(NHR)₂],

[M(NR)₂Cl₂L₂] or [M(NR)₂(OSiMe₃)₂], as shown in

Scheme 6.

3.2 Calix[4]arene-supported group 5 imido complexes

Calix[4]arene stabilized imido complexes of group 5 metals

are rare and have not been systematically explored. Calix[4]-

arene complexes with M-N multiple bonds (M ϭ V, Nb,

Ta) have been synthesized from the reaction of [V₂(Meca-

lix)₂] with diphenyldiazomethane to afford the diazoalkane

complex [V(ϭN-NϭCPh₂)(Mecalix)] [43] or prepared in the

stepwise process of N₂activation using [Nb₂(calix)₂]^2Ϫ[44].

During the latter investigations, the synthesis of the phenyl

imido complex [{Nb(NPh)(calix)}₂]^Ϫwas achieved, which

is Ϫ in contrast to the isoelectronic molybdenum complex Ϫ

a dinuclear, calixarene-bridged compound. This complex

and [{Ta(NPh)(Mecalix)}₂], synthesized from the reaction

of [Ta(η⁴-C₄H₆)(Mecalix)] and phenyl azide [45], are the

only examples of calix[4]arene stabilized imido complexes

known in the literature so far. In our group, mononuclear

calix[4]arene vanadium imido complexes, prepared from the

reaction of [{V(NR)Cl₃}] (R ϭ tBu, Ph, 4-C₆H₄Me) and

dinuclear [{Li₃Mecalix}₂], as well as imido complexes of its

higher congener are currently under investigation [46]. The

result of the structural analysis of [V(NtBu)(Mecalix)] (25)

is shown in Figure 7. This complex is less reactive with

respect to cycloaddition reactions and protonolysis reac-

tions compared to the titanium complex [Ti(NtBu)(Me₂ca-

lix)] (11).

Scheme 6 Calix[4]arene-stabilized imido complexes from H₄calix.

These compounds [M(NR)(calix)] can be synthesized in

the fivefold coordinated form as presented in Scheme 6, but

as soon as a sterically non demanding coordinating solvent

is present, adducts of the type [M(NR)(calix)(L)] are ob-

tained. In these compounds an additional donor ligand L

coordinates endohedrally (i.e. within the calix[4]arene cavity)

to form octahedrally coordinated metal atoms, which are

located almost ideally within the O₄plane of the calixarene

ligand. Spectroscopic and analytical data suggest mono-

meric units with local pseudo C_4vsymmetry in solution as

well as in the solid state. Similar chromium complexes

[Cr(NR)(calix)] are unknown so far. [Cr(NtBu)₂(OtBu)₂]

eliminates from the reaction with calix[4]arene two equiva-

lents tert.-butanol and both imido ligands to yield a

mononuclear complex with two calix[4]arene ligands coor-

dinated at the metal atom [49].

Whereas the reaction of calix[4]arene and [WOCl₄]

affords cleanly the oxo complexes [WO(calix)] [25a], the

corresponding reaction of different imidoyl chlorides

[W(NAr)Cl₄] seems to be more sluggish. Jablonski and co-

worker isolated from these reactions the known dichloro

compound [WCl₂(calix)] as well as the HCl adducts

[W(NAr)(Hcalix)]^ϩCl^Ϫ[50] instead of the desired complex

[W(NAr)(calix)]. Elimination of both the imido and the

chloro ligands from the starting material seems to be im-

portant in this case. The complexes [W(NAr)(Hcalix)]^ϩCl^Ϫ

are also available via reaction of aniline derivatives with

[WCl₂(calix)] in refluxing toluene. A possible diamido com-

plex, a likely intermediate in the course of this reaction, has

not been reported. The usage of metallated calix[4]arenes

leads here to isolated imido complexes, as exemplifies the

reaction of [{Na₄calix}₂(thf)₄] with [W(N-4-C₆H₄Me)Cl₄]

to yield [W(N-4-C₆H₄Me)(calix)] (30). This complex is in

Figure 7 Schakal plot of the molecular structure of [V(NtBu)-

(Mecalix)] (25).

3.3 Calix[4]arene-supported group 6 imido

complexes

Synthesis and Characterization

Despite the fact that calix[4]arene complexes of molyb-

denum (VI) and tungsten (VI) have been investigated by a

number of groups there is no unified picture regarding the

structure of these complexes. Studies by ourselves [47] and

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Calix[4]arene stabilized Transition Metal Imido Complexes

equilibrium with its dimeric form [{W(N-4-C₆H₄Me)-

(calix)}₂] in solution [51a].

[{W(calix)(NH)}₂] (34) has been isolated and structurally

characterized. This reaction is supposed to proceed via en-

dohedral HN₃binding to the Lewis-acidic metal atom with

the protonated nitrogen atom inside the cavity and de-

composition under dinitrogen cleavage to give the imido

functionality.

Another important route to calixarene stabilized imido

complexes is the reduction of azides. Floriani et. al. used

[W(η²-C₆H₁₀)(calix)] as a source of calix[4]arene stabilized

W^IVϪ W^VIcomplexes [51], since the olefin is easily dis-

placed by other ligands. The outcome of the reaction with

organic azides RN₃(R ϭ SiMe₃, CPh₃, Ph, H) strongly

depends on the nature of the R substituent, because the

calix[4]arene cavity is able to discriminate between two pos-

sible reaction pathways (see Scheme 7). In the case of R ϭ

SiMe₃or CPh₃the reaction occurs exohedrally at the metal

atom under loss of dinitrogen to yield monomeric alkylim-

ido derivatives [W(NR)(calix)] (R ϭ SiMe₃, 31; R ϭ CPh₃,

32). The reaction with PhN₃, however, occurs inside the ca-

lixarene cavity, leading under two electron reduction of the

phenyl azide to a diazenylimido derivative [{W(calix)-

(ϭN-NϭNPh)}₂] (33). These results were interpreted with

two different reaction pathways that are followed at the me-

tal atom in exo and endo positions. In the case of the steri-

cally demanding azides (R ϭ SiMe₃, CPh₃) the 1,3 dipolar

addition of the azide to the carbenoid metal atom proceeds

for steric reasons with an initial attack from the exohedral

side. In the exo-conformation, the complex provides two

cis-coordination sides which enables a 1,3 addition of the

azide to the metal atom, which according to Bergman et al.

[52] is a prerequisite for dinitrogen loss. The net result of

this sequence is the formation of an alkylimido complex

under loss of N₂.

A dinuclear molybdenum phenyl imido complex was syn-

thesized in Floriani’s group in a one pot reaction starting

from [MoCl₄(thf)₂], the perlithiated calix[4]arene and phe-

nyl azide [51b]. The spectroscopic data of this complex are

typical for a pseudo C_ssymmetrical molecule in solution

and the molecular structure of this complex reveals a di-

nuclear compound with exohedrally bonded imido ligands.

The dimeric form derives from the sharing of one of the

calix[4]arene oxygen atoms, whereas the imido nitrogen

atoms are terminally bound to the metal atoms. This ge-

ometry can be explained with the reduced steric hindrance

at the aryl group (no ortho alkyl groups), but also with the

lack of a donor ligand trans to the imido group, which

makes the metal atom readily available for dimerization. In

our group, four electron reduction of azobenzene was per-

formed starting with two equivalents of the d²complex ion

[MoCl(calix)(NCMe)]^Ϫand azobenzene to afford the

mononuclear complex [Mo(NPh)(calix)(NCMe)] (35) [53].

The molecular structure of this compound is shown as an

example for several X-ray analyses performed on calix[4]ar-

ene imido complexes of molybdenum (VI) and tungsten

(VI) [47] in Figure 8.

Figure 8 Schakal plot of the molecular structure of [Mo(NPh)-

(calix)(NCMe)] (35).

In square pyramidal complexes of the type [M(L)(calix)]

the metal atom is displaced significantly out of the calix[4]-

arene O₄plane towards the ligand in contrast to octahedral

complexes [M(L)(calix)(LЈ)], in which the metal atom lies

more or less exactly within the O₄plane. Thus, similar

monomeric/dimeric complexes [{M(L)(calix)}₂]/[M(L)-

(calix)(LЈ)] are described in the literature, noteworthy ex-

amples being the hydrazido complexes [W(NNR₂)-

(calix^H)(NCMe)] (monomer) and [{W(NNR₂)(calix^H)}₂]

(dimer) published by Redshaw et al. [54].

Scheme 7 Reactivity of [W(η²-C₆H₁₀)(calix)] toward organic

azides RN₃[52].

In the case of PhN₃, the azide adds endohedrally to

[W(η²-C₆H₁₀)(calix)] and the size of the calixarene cavity

prevents 1,3 addition. [51a] The resulting diazenylimido

complex 33 is stable even at elevated temperatures. In the

The calix[4]arene metal fragments of mononuclear imido

compounds [M(NR)(calix)(donor)] investigated by X-ray

crystallography retain pseudo C_4vsymmetry in the solid

state and produce circular calix[4]arene cavities, similar to

case

of

HN₃

the

dinuclear

imido

complex

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the uncoordinated ligand. The molybdenum oxygen and

tungsten oxygen bond distances are in a very narrow range

between 192 pm and 196 pm, the angles N1-M-O are be-

tween 97° and 99°, and the angles M-O-C are approxi-

mately 130°. The short Mo-N1 and W-N1 bonds of 171.6(5)

Ϫ 174.3(4) pm and the almost linear M-N1-C entities with

angles larger than 170° suggest sp hybridized imido nitro-

gen atoms with triple bond character of the metal-imido

linkage, which was confirmed by theoretical calculations.

agreement with addition of Cl₂to 26, which was confirmed

by an X-ray analysis (Figure 9).

Reactivity

Currently there is not very much known about the reactivity

of the calix[4]arene stabilized group 6 imido complexes. In-

vestigations in our group have shown that the molybdenum

and tungsten complexes are far less reactive compared to

the titanium imido compounds. The metal imido linkage

in these complexes is usually not reactive with respect to

cycloaddition reactions and protonations and therefore not

sensitive against hydrolysis. Imido exchange reactions as

observed for the titanium and vanadium compounds are

not viable reactions for the molybdenum and tungsten tert.-

butyl imido complexes. Electron rich, sterically non-

demanding substrates usually do not react with the imido

nitrogen atom but rather add to the acidic metal atom in-

side the calix[4]arene cavity to afford complexes with octa-

hedrally coordinated metal atom (endo coordination), as

observed for example in the structurally characterized com-

Figure 9 Schakal plot of the molecular structure of [Mo(NtBu)-

Cl(calix^{tBu Cl})] (37).

4

The molybdenum atom in 37 is sixfold coordinated with

four oxygen atoms of the calix[4]arene ligand, the imido

nitrogen atom and the chlorine atom Cl(1). The distances

Mo-O(2), Mo-O(3), and Mo-O(4) as well as Mo-Cl(1) are

unexceptional, but the molybdenum nitrogen distance of

170.3(4) pm is approximately 1.5 pm shorter than the

Mo-N distance observed in the starting compound. The N-

Mo-O(1) arrangement is almost linear with an angle of

176.2(2)°. Significantly elongated with respect to the other

molybdenum oxygen bond lengths is the distance Mo-O(1)

of 216.0(3) pm, which correlates with a short O(1)-C(10)

contact of 122.1(5) pm (CϭO double bond). The carbon

atoms C(10) to C(15) of the carbon ring system connected

to O(1) show alternating C-C bond lengths of 145.2(5) pm

on average for C_ipso-C_ortho, 132.8(6) pm and for C_ortho-C_meta

and 150.4(6) pm for C_meta-C_para, which is in accordance

with a description of the previously aromatic unit of the

calix[4]arene as an α,β-unsaturated ring system. The dis-

tance C(15)-Cl(2) of 183.3(5) pm corresponds to a chlorine

bound to a sp³-hybridized carbon atom. As a net result, the

structure of complex 37 in solution and in the solid state is

best described as the 1,6-addition product of chlorine to 26.

To our knowledge, a selective 1,6-addition of chlorine to

an organic or inorganic substrate has never been observed

before. Furthermore, the cyclohexadienone part of the

macrocyclic ligand in 36 is the first example of a structur-

ally characterized 4-halo-4-alkyl-2,5-cyclohexadienone in

the coordination sphere of a transition metal complex. This

moiety is stabilized with the highly Lewis acidic molyb-

denum(VI) complex fragment. After initial chlorine attack

at the negatively charged and therefore activated ring sys-

tem of the calix[4]arene ligand, the molecule does not

recover its aromatic system but remains with an intact

cyclohexadienone system and stabilizes itself with attack of

chlorine at the (positively charged) metal atom.

plexes

[Mo(NtBu)(calix)(NCMe)] (26)(NCMe), [Mo(NMes)(ca-

lix)(NCMe)] (27)(NCMe), [W(NtBu)(calix)(CNtBu)]

[Mo(NtBu)(calix)(CNtBu)]

(26)(CNtBu),

(28)(CNtBu), [W(NtBu)(calix)(OH₂)] (28)(OH₂) and

[W(NMes)(calix)(NCMe)] (29)(NCMe) [47a].

Whereas the imido ligand of [W(NtBu)(calix)] (28) can be

replaced selectively with two chloride ligands via reaction of

the imido complex with HCl, the reactivity of the analogous

molybdenum compound 26 with respect to hydrochlori-

nation is totally different [47b]. The reaction of 28 with one

equivalent of HCl affords a dark violet solution which con-

tains, according to NMR spectroscopy, a compound with

local C_ssymmetry, presumably [Mo(NtBu)Cl(Hcalix)] (36).

A larger amount of HCl during the reaction does not lead

to the scission of the imido group, but results in decompo-

sition of 36. Until now, complex 36 could not be isolated

since it decomposes to the starting material 26, when solu-

tions of this compound are concentrated in vacuo. The ad-

dition of HCl to 26 is totally reversible for some cycles. All

attempts to remove 35 from equilibrium or to crystallize

this complex have failed so far.

Similarly unreactive is the molybdenum imido function

of 26 with respect to chlorine transfer reagents. The ad-

dition of an equimolar amount of PhICl₂to a toluene solu-

tion of yellow 26 causes a spontaneous color change of the

reaction mixture to dark violet and the addition product

Perspectives

[Mo(NtBu)Cl(calix^{tBu Cl})] (37) was isolated in good yield.

Macrocyclic complexes are usually associated with high

thermodynamic and kinetic stability and are therefore used

4

Spectroscopic data of the reaction product were in good

968

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Z. Anorg. Allg. Chem. 2004, 630, 957Ϫ972

Calix[4]arene stabilized Transition Metal Imido Complexes

[2] (a) A. Ikeda, S. Shinkai, Chem. Rev. 1997, 97, 1713; (b) V.

Böhmer, Angew. Chem. 1995, 107, 785; Angew. Chem, Int. Ed.

1995, 34, 713; (c) C. D. Gutsche, Aldrichchim. Acta 1995, 28,

3; (d) S. Shinkai, Tetrahedron 1993, 49, 8933; (e) V. Böhmer,

Liebigs Ann./Recueil 1997, 2019; (f) A. F. D. De Namor, R. M.

Cleverly, M. L. Zapata-Ormachea, Chem. Rev. 1998, 98, 2485.

[3] (a) A. Pochini, R. Ungaro, in: F. Vögtle (Ed.), Comprehensive

Supramolecular Chemistry, Vol. 2, Elsevier, Oxford, 1996, 103;

(b) Y. K. Agrawal, S. Kunji, S. K. Menon, Rev. Anal. Chem.

1998, 17, 69; (c) M. A. McKervey, F. Arnaud-Neu, M.-J.

Schwing-Weill, in: G. Gokel (Ed.), Comprehensive Supra-

molecular Chemistry, Vol. 1, Pergamon, Oxford, 1996,537.

as templates in supramolecular chemistry, in multi compo-

nent assembly processes, as molecular receptors for guest

molecules or as spectator ligands for organometallic trans-

formations at the metal atom. Calix[4]arenes and calix[4]-

arene ethers used as poly(phenolate) ligands in transition

metal chemistry provide the metal atom with a robust and

well-defined O₄-coordination environment, similar to other

widely and successfully used supporting dianionic ligands

such as the O₂,N₂-donor ligands of salene type Schiff bases

or N₄-donor ligands such as porphyrins and dibenzotetra-

aza[14]annulene systems. Results in titanium imido chemis-

try led to the suggestion, that calixarene bis(alkyl)ethers are

in their donor capabilities similar to salene type ligands but

worse compared to the tetraazaannulene system. Further-

more, the Me₂calix ligand seems to provide a less sterically

protecting environment for stabilizing sterically unprotected

metal-ligand multiple bonds. Calix[4]arene dialkyl ethers

are conformationally much more flexible compared to the

nitrogen containing ligand systems, which culminates in a

change of the coordination mode for complexes of the type

[ML₂(Me₂calix)], in which L is a ligand which exhibits a

fairly good trans influence. However, it is much easier to

change the charge of the ligand system, in this case through

the degree of alkylation of the calixarene lower rim, without

a major change of the structure of the resulting metal com-

plex. This concept might be exploited for systematic investi-

gations across oxidation states and rows of transition metals

of different groups (“intrinsic reactivity of MϭE bonds”),

and we started such a model investigation for metal imido

linkages. The first results of this project are given in this

research report. Moreover, transition metal imido precur-

sors have been proven to be convenient entry points into

metallacalixarene chemistry, i. e. to introduce metal com-

plexes into the lower rim of the macrocyclic ligand. This

quite general protocol for group 4 Ϫ 6 metals is currently

being expanded to transition metals beyond group 6.

[4] Abbreviations used: H₄calix

ϭ p-tert.butyl-calix[4]arene;

superscript: substitution pattern of the upper rim of the calix-

arene, [n]: number of monomer units in macrocycle, prefix:

substitution patter at the lower rim. Some examples: H₄calix ϭ

H₄calix[4]^tBuϭ p-tert.butyl-calix[4]arene; H₄calix^Hϭ p-H-ca-

lix[4]arene; H₄calix[8]^tBuϭ p-tert.butyl-calix[8]arene; Alkyl-

ether: R_xH_4-xcalix ϭ R_xH_4-xcalix[4]^tBuϭ p-tert.butyl-calix[4]-

arene mono (x ϭ 1) or di (x ϭ 2) alkyl ether. TPP:Tetra(phenyl)-

porphyrin; TAA: tetraazaannulenes.

[5] (a) C. Floriani, R. Floriani-Moro, Adv. Organomet. Chem.

2001, 47, 167; (b) C. Floriani, Chem. Eur. J. 1999, 5, 19; (c) C.

Wieser, C. B. Dieleman, D. Matt, Coord. Chem. Rev. 1997,

165, 93; (d) D. M. Roundhill, Prog. Inorg. Chem. 1995, 43, 533.

[6] (a) M. Calligiaris, L. Ranaccio: “Schiff Bases as Acyclic Polyd-

entate Ligands” in: G. Wilkinson (Hrsg.), Comprehensive Co-

ordination Chemistry, Vol. 2, Pergamon Press, Exeter 1987; (b)

C. Floriani, Polyhedron 1989, 8, 1717; (c) D. E. Fenton, P. A.

Vigato, Chem. Soc. Rev. 1988, 17, 69; (d) J. Costamagna, J.

Vargas, R. Latorre, A. Alvarado, G. Mena, Coord. Chem. Rev.

1992, 119, 67.

[7] (a) K. M. Smith (Ed.), Porphyrins and Metalloporphyrines,

Elsevier, New York 1975; (b) D. Dolphin (Ed.), The Porphy-

rins, Academic Press, New York 1977-1979; (c) B. D. Berenzin,

Coordination Compounds of Porphyrins and Phtalocyanins,

Wiley, Chichester 1981; (d) T. Mashiko; D. Dolphin: “Porphy-

rins, Hydroporphyrins, Azaporphyrins, Phtalocyanins, Corroles,

Corrines and Related Macrocycles” in: G. Wilkinson (Ed.),

Comprehensive Coordination Chemistry, Vol. 2, Pergamon

Press, Exeter 1987; (e) K. Katylanasundaran, Photochemistry

of Polypyridine and Porphyrine Complexes, Academic Press,

London 1992; (f) R. A. Sheldon (Ed.), Metalloporphyrines in

Catalytic Oxidations, Marcel Dekker, New York 1994; (g) J.

W. Buchler (Ed.), Metal Complexes with Tetrapyrrole Ligands,

Springer Verlag, Berlin 1995, (h) L. R. Milgram (Ed.), The

Colours of Life: An Introduction to the Chemistry of Porphyrine

and Related Compounds, Oxford University Press, Oxford

1997; (i) H. Brand, J. Arnold, Coord. Chem. Rev. 1995, 140, 137.

[8] (a) L. F. Lindoy, The Chemistry of Macrocyclic Ligand

Complexes, Cambridge University Press, Cambridge 1989; (b)

F. A. Cotton, J. Czuchajowski, Polyhedron 1990, 9, 2663; (c)

P. Mountford, Chem. Soc. Rev. 1998, 27, 105.

Acknowledgement. I am deeply grateful to my co-workers who con-

tributed to this project, Dr. Juri Attner, Dr. Andreas Friedrich,

Bettina Bechlars and (last but not least) Simon Dürr. We thank the

Fonds der Chemischen Industrie and the Deutsche Forschungsge-

meinschaft for financial support as well as Fa. H. C. Stark for

gifts of metal halides and Prof. Dr. D. Fenske for his support and

continuing interest in our work.

References

[1] (a) M. Lucinat, R. Ungaro (Ed.), Calixarenes in Action,

Imperial College, London 2000; (b) G. J. Lumetta, R. D. Rog-

ers, A. S. Gopalan, Calixarenes for Separations, American

Chemical Society, Washington D. C. 2000; (c) C. D. Gutsche,

Calixarenes Revisited, Royal Society of Chemistry, Cambridge

1998; (d) J. Vicens, Z. Asfari, J. M. Harrowfield (Ed.), Calixar-

enes 50^thAnniversary: Commemorative Issue, Kluwer Aca-

demic Pub., Dordrecht 1994; (e) J. Vicens, V. Böhmer (Ed.),

Calixarenes: A Versatile Class of Macrocyclic Compounds,

Kluwer Academic Pub., Dordrecht 1991; (f) C. D. Gutsche,

Calixarenes, Royal Society of Chemistry, Cambridge 1989.

[9] (a) W. A. Nugent, B. L. Haymore, Coord. Chem. Rev. 1980,

31, 123; (b) M. H. Chisholm, I. P. Rothwell in Comprehensive

Coordination Chemistry; Vol. 2 (Eds.: G. Wilkinson, R. D. Gil-

lard, J. A. McCleverty), Pergamon Press: Oxford, 1987, p. 161;

(c) W. A. Nugent, J. M. Mayer, Metal-Ligand Multiple Bonds

Ϫ The Chemistry of Transition Metal Complexes Containing

Oxo, Nitrido, Imido, Alkylidene, or Alkylidyne Ligands, Wiley,

New York, 1988; (d) D. E. Wigley, Prog. Inorg. Chem. 1994,

42, 239; (e) P. Mountford, Chem. Commun. 1997, 2127; (f) P.

R. Sharp, Dalton Trans. 2000, 2647; (g) L. H. Gade, P. Mount-

Z. Anorg. Allg. Chem. 2004, 630, 957Ϫ972

zaac.wiley-vch.de

 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim

969

U. Radius

ford, Coord. Chem. Rev., 2001, 216-7, 65; (t) R. A. Eikey,

M. M. Abu-Omar, Coord. Chem. Rev. 2003, 243, 83.

rington, C. T. Kartisek, R. K. Grasselli, J. Catal. 1981, 69,

495; (d) J. D. Burrington, C. T. Kartisek, R. K. Grasselli, J.

Catal. 1984, 87, 363; (e) D. M.-T. Chan, W. A. Nugent, Inorg.

Chem. 1985, 24, 1422; (f) D. M.-T. Chan, W. C. Fultz, W. A.

Nugent, D. C. Roe, T. H. Tulip, J. Am. Chem. Soc. 1985, 107,

251; (g) G. W. Keulks, L. D. Krenzke, T. M. Notermann, Adv.

Catal. 1978, 27, 183; (h) K. Brueckmann, J. Haber, T.

Wiltkowski, J. Catal. 1987, 106, 188; (i) E. A. Maata, Y. Du,

J. Am. Chem. Soc. 1988, 110, 8249; (j) E. A. Maata, Y. Du, A.

L. Rheingold, J. Chem. Soc., Chem. Commun. 1990, 756; (k)

J. Belgacem, J. Kress, J. A. Osborn, J. Chem. Soc., Chem. Com-

mun. 1993, 1125.

[10] This bonding situation reflects

Ϫ from a point of

symmetryϪthe situation found in transition metal cyclo-

pentadienyl complexes and is the origin of the so called “cyclo-

pentadienyl-imido-ligand-analogy” and the basis of isolobal

relationships between, for example, group 4 metallocene frag-

ments [M(η⁵-C₅R₅)₂] and their corresponding imido complex

fragments of group

5

and 6, [MЈ(η⁵-C₅R₅)(NRЈ)] and

[MЉ(NRЈ)₂]. For leading references see for example: (a) D. S.

Williams, M. H. Schofield, J. Anhaus, R. R. Schrock, J. Am.

Chem. Soc. 1990, 112, 6728; (b) D. N. Williams, J. P. Mitchell,

A. D. Poole, U. Siemeling, W. Clegg, D. C. R. Hockless, P. A.

O’Neil, V. C. Gibson, J. Chem. Soc., Dalton Trans. 1992, 739;

(c) D. S. Glueck, J. C. Green, R. I. Michelman, I. N. Wright,

Organometallics 1992, 11, 4221. (d) A. D. Poole, V. C. Gibson,

W. Clegg, J. Chem. Soc., Chem. Commun. 1992, 237; (e) P. W.

Dyer, V. C. Gibson, J. A. K. Howard, B. Whittle, C. Wilson,

J. Chem. Soc., Chem. Commun. 1992, 1666; (f) J. K. Cockcroft,

V. C. Gibson, J. A. K. Howard, A. D. Poole, U. Siemeling,

C. Wilson, J. Chem. Soc., Chem. Commun. 1992, 1668; (g) J.

Sundermeyer, D. Runge, Angew. Chem. 1994, 106, 1328;

Angew. Chem., Int. Ed. 1994, 33, 1255; (h) U. Radius, J.

Sundermeyer, H. Pritzkow, Chem. Ber. 1994, 127, 1827; (i) U.

Radius, A. Schorm, D. Kairies, S. Schmidt, F. Möller, H. Pritz-

kow, J. Sundermeyer, J. Organomet. Chem. 2002, 655, 96;

Although for ease of representation all metal-imide linkages

are drawn “MϭNR”, the formal M-N bond order in the com-

plexes with early trasition metals in their highest oxidation

states described herein is generally best thought of as three

(pseudo-σ²π⁴triple bond) rather than as two. See calculations

below or: (j) T. R. Cundari, Chem. Rev. 2000, 100, 807; (k) T.

R. Cundari, J. Am. Chem. Soc. 1992, 114, 7879.

[15] (a) M. Bakir, P. E. Fanwick, R. A. Walton, lnorg. Chem. 1988,

27, 2016; (b) L. F. Rhodes, L. M. Venanzi, Inorg. Chem. 1987,

26, 2692; (c) S. H. Han, G. Geoffroy, Polyhedron 1988, 7, 2331.

[16] (a) D. Mansuy, J.-P. Mahy, A. Dureault, G. Bedi, P. Battioni,

J. Chem. Soc., Chem. Commun. 1984, 1161; (b) J. T. Groves,

T. Takahashi, J. Am. Chem. Soc. 1983, 105, 2073.

[17] (a) T. E. Müller, M. Beller, Chem. Rev. 1998, 98, 675; (b) T. E.

Müller, M. Beller, in: M. Beller, C. Bolm, (Ed.) Transition Met-

als for Organic Synthesis, Vol. 2 , Wiley-VCH, Weinheim 1998,

316; (c) E. Haak, S. Doye, Chem. Unserer Zeit 1999, 33, 296;

(d) M. Nobis, B. Drießen-Hölscher, Angew. Chem. 2001, 113,

4105; Angew. Chem. Int. Ed. 2001, 40, 3983; (e) P. W. Roesky,

T. E. Müller, Angew. Chem. 2003, 115, 2812; Angew. Chem.

Int. Ed. 2003, 42, 2708; (f) P. J. Walsh, A. M. Baranger, R. G.

Bergman, J. Am. Chem. Soc. 1992, 114, 1708; (g) A. M. Bar-

anger, P. J. Walsh, R. G. Bergman, J. Am. Chem. Soc. 1993,

115, 2753; (h) P. L. McGrane, M. Jensen, T. Livinghouse, J.

Am. Chem. Soc. 1992, 114, 5459; (i) P. L. McGrane, T.

Livinghouse, J. Org. Chem. 1992, 57, 1323; (j) P. L. McGrane,

T. Livinghouse, J. Am. Chem. Soc. 1993, 115, 11485; (k) D.

Fairfax, M. Stein, T. Livinghouse, M. Jensen, Organometallics

1997, 16, 1523; (l) E. Haak, I. Bytschkov, S. Doye, Angew.

Chem. 1999, 111, 3584; Angew. Chem. Int. Ed. 1999, 38, 3389;

(m) F. Pohli, S. Doye, Angew. Chem. 2001, 113, 2361; Angew.

Chem. Int. Ed. 2001, 40, 2305; (n) J. S. Johnson, R. G.

Bergman, J. Am. Chem. Soc. 2001, 123, 2923.

[11] (a) A. Diefenbach, F. M. Bickelhaupt, Z. Anorg. Allg. Chem.

1999, 625, 892; for leading reviews on phosphorane iminato

compounds see: (b) K. Dehnicke, Z. Anorg. Allg. Chem. 2003,

629, 828; (c) K. Dehnicke, A. Greiner, Angew. Chem. 2003,

115, 1378; Angew. Chem., Int. Ed. 2003, 42, 1340; (d) K.

Dehnicke, M. Krieger, W. Massa, Coord. Chem. Rev. 1999,

182, 19; (e) K. Dehnicke, F. Weller, Coord. Chem. Rev. 1997,

158, 103; (f) K. Dehnicke, J. Strähle, Polyhedron 1989, 8, 707.

[12] (a) G. J. P. Britovsek, V. C. Gibson, D. F. Wass, Angew. Chem.

1999, 111, 448; Angew. Chem., Int. Ed. 1999, 38, 439; (b) V. C.

Gibson, S. K. Spitzmesser, Chem. Rev. 2003, 103, 283.

[18] (a) D. W. Patrick, L. K. Truesdale, S. A. Biller, K. B. Sharpless,

J. Org. Chem. 1978, 43, 2628; (b) A. O. Chong, K. Oshima,

K. B. Sharpless, J. Am. Chem. Soc. 1977, 99, 3420; (c) K. B.

Sharpless, D. W. Patrick, L. K. Truesdale, S. A. Biller, J. Am.

Chem. Soc. 1975, 97, 2305; (d) E. W. Harlan, R. H. Holm, J.

Am. Chem. Soc. 1990, 112, 186.

[19] see for example: (a) R. I. Michelman, G. E. Ball, R. G.

Bergman, R. A. Andersen, Organometallics 1994, 13, 869; (b)

D. S. Glueck, F. J. Hollander, R. G. Bergman, J. Am. Chem.

Soc. 1989, 111, 2719; (c) R. I. Michelman, R. A. Andersen,

R. G. Bergman, J. Am. Chem. Soc. 1991, 113, 5100; (d) D. S.

Glueck, J. Wu, F. J. Hollander, R. G. Bergman, J. Am. Chem.

Soc. 1991, 113, 2041; (e) D. A. Dobbs, R. G. Bergman, J. Am.

Chem. Soc. 1993, 115, 3836; (f) A. M. Baranger, F. J. Hollan-

der, R. G. Bergman, J. Am. Chem. Soc. 1993, 115, 7890; (g)

A. M. Baranger, R. G. Bergman, J. Am. Chem. Soc. 1994, 116,

3822; (h) D. A. Dobbs, R. G. Bergman, Organometallics 1994,

13, 4594; (i) A. W. Holland, R. G. Bergman, J. Am. Chem.

Soc. 2002, 124, 9010; (j) A. K. Burrell, A. J. Steedman, J.

Chem. Soc., Chem. Commun. 1995, 2109; (k) T. P. Kee, L. Y.

Park, J. Robbins, R. R. Schrock, J. Chem. Soc., Chem. Com-

mun. 1991, 121; (l) A. A. Danapoulos, G. Wilkinson, B. Hus-

sain-Bates, M. B. Hursthouse, Polyhedron 1992, 11, 2961.

[20] see for example: (a) H. W. Roesky, H. Voelker, M. Witt, M.

Noltemeyer, Angew. Chem. 1990, 102, 712; Angew. Chem. 1nt.

[13] (a) M. C. W. Chan, K. C. Chew, C. I. Dalby, V. C. Gibson, A.

Kohlmann, I. R. Little, W. Reed, Chem. Commun. 1998, 16,

1673; (b) P. T. Witte, A. Meetsma, B. Hessen, P. H. M. Bud-

zelaar, J. Am. Chem. Soc. 1997, 119, 10561; (c) C. Lorber,

B. Donnadieu, R. Choukroun, Dalton 2000, 24, 4497; (d) V.

J. Murphy, H. Turner, Organometallics 1997, 16, 2495; (e) K.

Nomura, A. Sagara, Y. Imanishi, Chem. Lett. 2001, 36; (f) M.

P. Coles, V. C. Gibson, Polym. Bull. 1994, 33, 529; (g) M. P.

Coles, C. I. Dalby, V. C. Gibson, W. Clegg, M. R. J. Elsegood,

J. Chem. Soc., Chem. Commun. 1995, 1709; (h) M. P. Coles,

C. I. Dalby, V. C. Gibson, I. R. Little, E. L. Marshall, M. H.

Ribeiro da Costa, S. Mastroianni, J. Organomet. Chem. 1999,

591, 78; (i) U. Siemeling, L. Kölling, A. Stammler, H.-G.

Stammler, E. Kaminski, G. Fink, J. Chem. Soc., Chem. Com-

mun. 2000, 1177; (j) V. R. Jensen, K. J. Bo’rve, Organometallics

2001, 20, 616;

[14] (a) R. K. Grasselli, J. Chem. Ed. 1986, 63, 216; (b) J. D. Bur-

rington, R. K. Grasselli, J. Catal. 1979, 59, 79; (c) J. D. Bur-

970

 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim

zaac.wiley-vch.de

Z. Anorg. Allg. Chem. 2004, 630, 957Ϫ972

Calix[4]arene stabilized Transition Metal Imido Complexes

Ed. 1990, 29, 669; (b) J. E. HilI, R. D. Profilet, P. E. Fanwick,

I. P. Rothwell, Angew. Chem. 1990, 102, 713; Angew. Chem.

1nt. Ed. 1990, 29, 664; (c) R. D. Profilet, C. H. Zambrano, P.

E. Fanwick, J. J. Nash, I. P. Rothwell, Inorg. Chem. 1990, 29,

4362; (d) J. E. Hill, P. E. Fanwick, I. P. Rothwell, lnorg. Chem.

1991, 30, 1143; (e) P. J. Walsh, F. J. Hollander, R. G. Bergman,

J. Am. Chem. Soc. 1988, 110, 8729; (f) P. J. Walsh, F. J. Hollan-

der, R. G. Bergman. Organometallics 1993, 12, 3705; (g) K. E.

Meyer, P. J. Walsh, R. G. Bergman, J. Am. Chem. Soc. 1994,

116, 2669; (h) K. E. Meyer, P. J. Walsh, R. G. Bergman, J. Am.

Chem. Soc. 1995, 117, 974; (i) C. C. Cummins, S. M. Baxter,

P. T. Wolczanski, J. Am. Chem. Soc. 1988, 110, 8731; (j) C. C.

Cummins, C. P. Schaller, G. D. van Duyne, P. T. Wolczanski,

A. W. E. Chan, R. Hoffmann, J. Am. Chem. Soc. 1991, 113,

2985; (k) J. L. Bennett, P. T. Wolczanski, J. Am. Chem. Soc.

1994, 116, 2179; (l) R. Duchatearu, A. J. Williams, S. Gambar-

otta, M. Y. Chiang, Inorg. Chem. 1991, 30,4863, (m) C. H.

Winter, P. H. Sheridan, T. S. Lewkebandara, M. J. Heeg, J. W.

Proscia, J. Am. Chem. Soc. 1992, 114, 1095; (n) T. S. Lewkeb-

andara, P. H. Sheridan, M. J. Heeg, A. L. Rheingold, C. H.

Winter, 1norg. Chem. 1994, 33, 5879; (o) K. M. Doxsee, J. B.

Farahi, H. Hope, J. Am. Chem. Soc. 1991, 113, 8889; (p) K.

M. Doxsee, L. C. Garner, J. J. Juliette, J. K. M. Mouser, T. J.

R. Weak1ey, H. Hope, Tetrahedron 1995, 51, 4321; (q) D. J.

Arney, M. A. Bruek, S. R. Huber, D. E. Wigley, Inorg. Chem.

1992, 31, 3749; (r) S. C. Dunn, A. S. Batzanov, P. Mountford,

J. Chem. Soc., Chem. Commun. 1994, 2007; (s) S. C. Dunn, P.

Mountford, O. V. Shishkin, 1norg. Chem. 1996, 35, 1006; (t)

A. J. Blake, P. E. Collier, S. C. Dunn, W.-S. Lee, P. Mountford,

O. V. Shishkin, J. Chem. Soc., Dalton Trans. 1997, 1549; (u)

N. Adams, A. R. Cowley, S. R. Dubberley, A. J. Sealey, M. E.

G. Skinner, P. Mountford, J. Chem. Soc., Chem. Commun.,

2001, 2738; (v) L. M. Berreau, V. G. Young, L. K. Woo, 1norg.

Chem. 1995, 34, 527.

J. Chem. Soc., Dalton Trans. 1997, 2911; (b) A. J. Blake, P.

Mountford, G. I. Nikonov, Acta Crystallogr. C. 1996, 52, 1911;

(c) R. D. Profilet, C.H. Zambrano, P. E. Fanwick, J. J. Nash,

I. P. Rothwell, Inorg. Chem. 1990, 29, 4362; (d) C. H. Zam-

brano, R. D. Profilet, J. E. Hill, P. E. Fanwick, I. P. Rothwell,

Polyhedron 1993, 12, 689.

[32] (a) P. Mountford, Chem. Soc. Rev. 1998, 27, 105; (b) D. Swal-

low, J. M. McInnes, P. Mountford, J. Chem. Soc., Dalton

Trans. 1998, 2253; (c) A. J. Blake, J. M. McInnes, P. Mount-

ford, G. I. Nikonov, D. Swallow, D. J. Watkin, J. Chem. Soc.,

Dalton Trans. 1999, 379; (d) M. E. G. Skinner, D. A. Cowhig,

P. Mountford, J. Chem. Soc., Chem. Commun. 2000, 1167; (e)

J. Lloyd, S. Z. Vatsadze, D. A. Robson, A. J. Blake, P. Mount-

ford, J. Organomet. Chem. 1999, 591, 114; (f) J. M. McInnes,

D. Swallow, A. J. Blake, P. Mountford, Inorg. Chem. 1998,

37, 5970.

[33] (a) R. Ahlrichs, TURBOMOLE, in: P. v. R. Schleyer, (ed.)

Enzyclopedia of Computational Chemistry, Wiley, Chichester

1998, Vol. 5, 3123; (b) R. Ahlrichs, M. v. Arnim, TURBO-

MOLE, parallel implementation of SCF, density functional, and

chemical shift modules, in: E. Clementi, G. Corongiu, (ed.)

Methods and Techniques in Computational Chemistry, STEF,

Cagliary 1995.

[34] (a) O. Treutler, R. Ahlrichs J. Chem. Phys. 1995, 102, 346; (b)

K. Eichkorn, O. Treutler, H. Öhm, M. Häser, R. Ahlrichs,

Chem. Phys. Lett. 1995, 242, 652; (c) K. Eichkorn, F. Weigand,

O. Treutler, R. Ahlrichs, Theor. Chim. Acc. 1997, 97, 119; (d)

M. v. Arnim, R. Ahlrichs, J. Comp. Chem. 1998, 97, 331; (e)

F. Weigend, A. Köhn, C. Hättig; J. Chem. Phys. 2002, 116,

3175; (f) P. Deglmann, F. Furche, R. Ahlrichs; Chem. Phys.

Lett. 2002, 362, 511; (g) P. Deglmann, F. Furche; J. Chem.

Phys. 2002, 117, 9535.

[35] (a) F. Haase, R. Ahlrichs, J. Comput. Chem. 1993, 14, 907; (b)

F. Weigand, M. Häser, Theor. Chem. Acc. 1997, 97, 331; (c) F.

Weigand, M. Häser, H. Patzelt, R. Ahlrichs, Chem. Phys. Lett.

1998, 294, 143; (d) A. Schäfer, H. Horn, R. Ahlrichs, J. Chem.

Phys. 1992, 97, 2571.

[36] (a) A.D. Becke, Phys. Rev. A 1988, 38, 3098; (b) S. H. Vosko,

L. Wilk, M. Nusair, Can. J. Phys. 1980, 58, 1200; (c) J. P.

Perdew, Phys. Rev. B 1986, 33, 8822; erratum: J. P. Perdew,

Phys. Rev. B 1986, 34, 7406.

[37] (a) E. R. Davidson, J. Chem. Phys. 1967, 46, 3320; (b) K. R.

Roby, Mol. Phys. 1974, 27, 81; (c) R. Heinzmann, R. Ahlrichs,

Theor. Chim. Acta 1976, 42, 33; (d) especially for main group

elements is the ’shared electron number’ SEN might serve as

a measure for covalent contributions to bonding, see for ex-

ample: R. Ahlrichs, C. Erhardt, Chem. in unserer Zeit 1985,

19, 120.

[38] A. Caselli, L. Giannini, E. Solari, C. Floriani, N. Re, A.

Chiesi-Villa, C. Rizzoli, Organometallics 1997, 16, 5457.

[39] D. J. Arney, M. A. Bruck, S. R. Huber, D. E. Wigley, Inorg.

Chem. 1992, 31, 3749.

[40] (a) C. Lecomte, J. Protas, R. Guilard, C. R. Acad. Sci., Ser.

C (Chim) 1975, 281, 921; (b) P. N. Dwyer, L. Puppe,

J. W. Buchler, W. R. Scheidt, Inorg.Chem. 1975, 14, 1782; (c)

R. Guilard, J.-M. Latour, C. Lecomte, J.-C. Marchon, J. Pro-

tas, D. Ripoll, Inorg.Chem. 1978, 17, 1228.

[21] see for example: (a) R. R. Schrock, Olefin Metathesis by

Well-Defined Complexes of Molybdenum and Tungsten in:

A. Fürstner, (Ed.), Topics in Organometallic Chemistry, Vol. 1:

Metathesis in Organic Synthesis, Springer-Verlag, Berlin,

Germany 1998, 1; (b) C. J. Schaverian, J. C. Dewan, R. R.

Schrock, J. Am. Chem. Soc. 1986, 108, 2771; (c) J. S. Murdzek,

R. R. Schrock, Organometallics 1987, 6, 1373; (d) R. R.

Schrock, R. T. DePue, J. Feldman, K. B. Yap, W. M. Davies,

L. Park, M. DiMare, M. Schofield, J. Anhaus, E. Walborski,

E. Evitt, C. Krüger, P. Betz, Organometallics 1990, 9, 2262.

[22] W. A. Nugent, R. .J. McKinney, R. V. Kasowski, F .W. Van-

Catledge, Inorg. Chim. Acta 65, 1982 L91.

[23] K. Weber, K. Korn, A. Schorm, J. Kipke, M. Lemke, A. Khvo-

rost, K. Harms, J. Sundermeyer, Z. Anorg. Allg. Chem. 2003,

629, 744.

[24] U. Radius, J. Attner, Chem. Eur. J. 2001, 7, 783.

[25] (a) F. Corazza, C. Floriani, A. Chiesi-Villa, C. Rizzoli, Inorg.

Chem. 1991, 30, 4465; (b) L. Giannini, E. Solari, C. Floriani,

N. Re, A. Chiesi-Villa, C. Rizzoli, Inorg. Chem. 1999, 38,

1438.

[26] U. Radius, Inorg. Chem. 2001, 40, 6637.

[27] B. J. Coe, S. J. Glenwright, Coord. Chem. Rev. 2000, 203, 5.

[28] (a) U. Radius, A. Friedrich, Z. Anorg. Allg. Chem. 1999, 625,

2154; (b) S. R. Dubberly, A. Friedrich, D. A. Willman, P.

Mountford, U. Radius, Chem. Eur. J. 2003, 9, 3634.

[41] (a) V. L. Goedken, J. A. Ladd, J. Chem. Soc., Chem. Commun.

1982, 142; (b) C. H. Yang, J. A. Ladd, V. L. Goedken, J. Coord.

Chem. 1988, 19, 235.

[29] A. Friedrich, U. Radius, submitted.

[30] J. Zeller, S. Büschel, B. Reiser, U. Radius, to be published.

[31] See for example: (a) P. E. Collier, A. J. Blake, P. Mountford,

[42] J. L. Kisko, T. Hascall, G. Parkin, J. Am. Chem. Soc. 1997,

119, 7609.

Z. Anorg. Allg. Chem. 2004, 630, 957Ϫ972

zaac.wiley-vch.de

 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim

971

U. Radius

[43] B. Castellano, E. Solari, C. Floriani, R. Scopelliti, N. Re, In-

org. Chem. 1999, 38, 3406.

[48] (a) V. C. Gibson, C. Redshaw, W. Clegg, M. R. J. Elsegood, J.

Chem. Soc., Chem. Commun. 1995, 2371; (b) V. C. Gibson, C.

Redshaw, W. Clegg, M. R. J. Elsegood, J. Chem. Soc., Chem.

Commun. 1998, 1969.

[49] V. C. Gibson, C. Redshaw, W. Clegg, M. R. J. Elsegood, J.

Chem. Soc., Chem. Commun. 1997, 1605.

[50] M. Brown, C. Jablonski, Can. J. Chem. 2001, 79, 463.

[51] (a) G. Guillemot, E. Solari, C. Floriani, C. Rizzoli, Organo-

metallics 2001, 20, 607; (b) G. Guillemot, E. Solari, R. Scopel-

liti, C. Floriani, Organometallics 2001, 20, 2446.

[44] (a) A. Caselli, E. Solari, R. Scopelliti, C. Floriani, N. Re, C.

Rizzoli, A. Chiesi-Villa, J. Am. Chem. Soc. 2000, 122, 3652;

(b) A. Caselli, E. Solari, R. Scopelliti, C. Floriani, J. Am.

Chem. Soc. 1999, 121, 8296; (c) A. Zanotti-Gerosa, E. Solari,

L. Giannini, C. Floriani, A. Chiesi-Villa, C. Rizzoli, J. Am.

Chem. Soc. 1998, 120, 437.

[45] B. Castellano, E. Solari, C. Floriani, N. Re, A. Chiesi-Villa,

C. Rizzoli, Chem. Eur. J. 1999, 5, 722.

[46] B. Bechlars, S. Dürr, U. Radius, unpublished results.

[47] (a) U. Radius, J. Attner, Eur. J. Inorg. Chem. 1999, 2221; (b)

U. Radius, J. Attner, Eur. J. Inorg. Chem. 2002, 161.

[52] G. Proulx, R. G. Bergman, Organometallics 1996, 15, 684.

[53] J. Attner, U. Radius, unpublished.

[54] C. Redshaw, M. R. J. Elsegood, Inorg. Chem. 2000, 39, 5164.

972

 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim

zaac.wiley-vch.de

Z. Anorg. Allg. Chem. 2004, 630, 957Ϫ972

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Calix[4]arene stabilized transition metal imido complexes

DOI: 10.1002/zaac.200400118

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