Organometallic helices: the mechanism of formation of 'metallospiralenes'

5484

Organometallics 2000, 19, 5484-5499

Or ga n om eta llic Helices: Th e Mech a n ism of F or m a tion of

“Meta llosp ir a len es”

J ean-Pierre Djukic,*^,†Aline Maisse-Franc¸ois,^†Michel Pfeffer,*^,†

Karl Heinz Do¨tz,*^,‡Andre´ De Cian,^§and J ean Fischer^§,|

Laboratoire de Synthe`ses Me´tallo-induites, UMR CNRS 7513, Universite´ Louis Pasteur,

4 Rue Blaise Pascal, 67070 Strasbourg, France, Kekule´-Institut fu¨r Biochemie und

Organische Chemie der Universita¨t Bonn, Gerhard-Domagk Strasse 1, 53171 Bonn, Germany,

and Laboratoire de Cristallochimie, UMR CNRS 7513, Universite´ Louis Pasteur,

4 Rue Blaise Pascal, 67070 Strasbourg, France

Received August 9, 2000

A complete investigation of the mechanism of formation of chelated syn-facial heterobi-

metallic benzyl complexes, also referred to as Cr/Mn-spiralenes, is presented. Spectroscopic

evidence for the intermediacy of a metal carbene species was established by ¹³C NMR

spectroscopy. The nature of the substitution pattern at the carbene carbon atom is shown

to play a determining role in the stereoselectivity of spiralene formation. The sequential

addition of alkyllithium reagents and MeOTf to a series of cyclomanganated 2-phenylpyridine

derivatives afforded mixtures of two isomeric spiralenes, of which a pair of examples has

been characterized by X-ray diffraction. The more structurally flexible hetero-bimetallic

isomers display an ability to interconvert with the probable mediation of biradical species

formed upon homolytic disruption of a benzylic C-Mn bond. Investigation of 2-oxazolinyl

derivatives unveiled the origin of the diastereoselective formation of spiralenes. Sequential

addition of PhLi and MeOTf to a cyclomanganated 2-[(η⁶-4-tolyl)Cr(CO)₃]-2-oxazoline

derivative afforded a mixture of two products, both resulting from the insertion of a Ph-

(MeO)C: moiety into the C_Ar-Mn bond. X-ray diffraction analyses reveal that the two

compounds are pseudoconformers which differ from the position of the Mn(CO)₃moiety: in

one compound, the Mn(CO)₃group is located close to the Cr(CO)₃group, while in the other

compound, it is part of a nearly planar six-membered manganacyclic ring coplanar with the

π-coordinated arene. These results indicate that in “spiralenes” the helical and spiral-type

arrangements are stereoselectively produced if at least one substituent of the transient

carbene complex is an aromatic ring capable of electronic interaction with the Mn(I) center

during the cis-migration process.

In tr od u ction

from those classical effects encountered in organic

chemistry as well as from more specific properties of

transition metal complexes.⁴We recently reported on

the formation of a new class of self-arranged helical

chelated (η³-benzyl)Mn(CO)₃and {η¹[(η⁵-cyclohexadienyl)-

Cr(CO)₃]benzylidene}Mn(CO)₃complexes formed via a

putative Fischer-type carbene intermediate.⁵They can

Construction of molecules with controlled geometry

and functional composition is one of the ultimate goals

of modern synthetic chemistry.¹For that purpose cri-

teria such as stereoselectivity and stereospecificity are

of extreme importance in transformations that aim at

geometrically controlled molecular architectures.²Or-

ganometallic chemistry has now well demonstrated its

strong potential in asymmetric synthesis. As a conse-

quence, sophisticated organometallic complexes, such as

some Fischer-type metallacarbenes, increasingly inter-

vene in a stoichiometric fashion, in multistep synthetic

schemes as equals of purely organic synthons.³With

Fischer carbenes, stereoselective transformations arise

(3) (a) Wulf, W. D. Comprehensive Organic Synthesis; Trost, M. M.,

Flemming, I., Paquette, L. A., Eds.; Pergamon Press: Oxford, 1991;

Vol. 5, p 1065. (b) Do¨tz, K. H.; Straub, W.; Ehlenz, R.; Peseke, K.;

Meisel, R. Angew. Chem., Int. Ed. Engl. 1995, 34, 1856. (c) Do¨tz, K.

H.; Ehlenz, R. Chem. Eur. J . 1997, 3, 1751. (d) Do¨tz, K. H.; Klumpe,

M.; Nieger, M. Chem. Eur. J . 1999, 5, 691. (e) Haase, W.-C.; Nieger,

M.; Do¨tz, K. H. Chem. Eur. J . 1999, 5, 2014. (f) J a¨kel, C.; Do¨tz, K. H.

Tetrahedron 2000, 56, 2167. (g) Merlic, C. A.; Aldrich, C. C.; Albanese-

Walker, J .; Saghatelian, A. J . Am. Chem. Soc. 2000, 122, 3224. (h)

Bouaucheau, C.; Parlier, A.; Rudler, H. J . Org. Chem. 1997, 62, 7247.

(i) Su, J .; Wulff, W. D.; Ball, R. G. J . Org. Chem. 1998, 63, 8440. (j)

Quinn, J . F.; Bos, M. E.; Wulff, W. D. Org. Lett. 1999, 1, 161. (k) Bao,

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K. H. Synlett 1999, 231. (r) Zaragoza Do¨rwald, F. Metal Carbenes in

Organic Synthesis; Wiley-VCH: Weinheim, 1999.

^†Laboratoire de Synthe`ses Me´tallo-induites, Universite´ Louis Pas-

teur.

^‡Universita¨t Bonn.

^§Laboratoire de Cristallochimie, Universite´ Louis Pasteur.

^|To whom requests pertaining to X-ray structure determinations

should be addressed.

(1) Nicolaou, K. C.; Sorensen, E. J . Classics in Total Synthesis,

Targets, Strategies, Methods; VCH-Verlag: Weinheim, 1996.

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Ho T.-L. Stereoselectivity in Organic Synthesis; Wiley: New York, 1999.

Publication on Web 11/15/2000

Organometallic Helices

Organometallics, Vol. 19, No. 25, 2000 5485

Sch em e 1

Sch em e 2

point, we demonstrated that the nucleophilic attack of

a carbonyl ligand attached to Mn (or Re) by RLi was

very sensitive to steric hindrance.¹⁰Cyclomanganated

(η⁶-arene)Cr(CO)₃complexes would react selectively

with PhLi to afford a unique benzoylmanganate complex

resulting from the stereoselective addition of the lithi-

ated agent at a Mn (or Re) attached carbonyl ligand

located exo with respect to the sterically demanding

group Cr(CO)₃(Scheme 2, step A). Phenyl-substituted

Cr/Mn-spiralenes derived from 2-phenylpyridine display

a remarkable inertness to photolytic or thermal treat-

ments with phosphines or CO and possess peculiar

structural properties that make them reasonable can-

didates for nonlinear optical and other photophysical

applications.¹¹

At this point of our research, we estimated that two

crucial issues remained to be further addressed in order

to achieve a comprehensive understanding of each of

the elementary steps that lead eventually to the typical

spiralene’s helical arrangements. The first issue was to

bring firm evidence for the transient formation of a

manganese (or rhenium) carbene species that undergoes

the cis-migration of the vicinal aryl group leading to the

final spiralenes. The second issue was to rationalize the

peculiar selectivity with which spiralenes are usually

formed when the PhLi/MeOTf sequence is applied

(Scheme 2, step B). In all cases, including experiments

carried out with mononuclear cyclomanganated aromat-

ics, the phenyl ring originating from PhLi repeatedly

ended in the product above the pyridyl group as a

consequence of a “spirogenic reaction”.^6,12

be synthesized by two methods: (1) the sequential

treatment of cyclomanganated aromatics of the type cis-

(L∧C, κL,κC)Mn(CO)₄(L∧C ) chelating aromatic ligand

with L ) endogenous two-electron ligand and C )

aromatic carbon one-electron ligand) with an aryl-

lithium reagent and MeOTf (the so-called “E. O. Fischer

method”) at subambient temperatures, (2) the ther-

molytic reaction of the cyclomanganated substrate with

a diazoalkane (Scheme 1).⁶

The recurrent helical shape found in either the

monometallic or the bimetallic products motivated us

to establish a trivial, albeit sound, terminology. Hence,

this novel class of organometallic helical complexes

could be accounted for as “spiralenes”, as their struc-

tures are somewhat reminiscent of spiral staircases in

which the metallic core plays the role of a scaffold

sustaining an organic “spiral”.⁷

We showed that it was possible to control the absolute

helicity⁸of the final product by taking advantage of the

metallocenic-like planar chirality⁹existing in ortho-

disubstituted (η⁶-arene)Cr(CO)₃substrates bearing a

chiral arene substituent. From a mechanistic stand-

We decided to deepen our investigations starting with

the hypothesis that such stereoselectivity could arise

from a peculiar behavior of the transient carbene

species. Herein, we bring forth several elements of

answer on the mechanism of formation of spiralenes.

We present spectroscopic evidence for the transient

formation of a rhenium carbene intermediate upon

O-alkylation of a temperature-stable benzoylrhenate

complex. We demonstrate that the stereoselectivity

observed in the formation of metallospiralenes depends

directly upon the nature of the substituents at the

carbene carbon and, when applicable, upon the nature

(4) (a) Do¨tz, K. H.; Tomuschat, P. Chem. Soc. Rev. 1999, 28, 187.

(b) Do¨tz, K. H.; Pfeiffer, J . Transition Metals for Organic Synthesis;

Beller, M., Bolm, C., Eds.; Wiley-VCH: Weinheim, 1998; Vol. 1. (c)

Gleichmann, M. M.; Do¨tz, K. H.; Hess, B. A. J . Am. Chem. Soc. 1996,

118, 10551. (d) Hohmann, F.; Siemoneit, S.; Nieger, M.; Kotila, S.; Do¨tz,

K. H. Chem. Eur. J . 1997, 3, 853. (d) Do¨tz, K. H.; Stinner, C.

Tetrahedron Asym. 1997, 8, 1751. (e) Pfeiffer, J .; Do¨tz, K. H. Angew.

Chem., Int. Ed. Engl. 1997, 36, 2828. (f) Longen, A.; Nieger, M.; Airola,

K.; Do¨tz, K. H. Organometallics 1998, 17, 1538. (g) Tomuschat, P.;

Kro¨ner, L.; Steckhan, E.; Nieger, M.; Do¨tz, K. H. Chem. Eur. J . 1999,

5, 700. (h) Weyershausen, B.; Do¨tz, K. H. Synlett 1999, 231. (i)

Ezquerra, J .; Pedregal, C.; Merino, I.; Florez, J .; Barluenga, J .; Garcia-

Granda, S.; Llorca, M. A. J . Org. Chem. 1999, 64, 6554. (k) Barluenga,

J .; Bernad, P. L.; Concellon, J . M.; Pinera-Nicolas, A.; Garcia-Granda,

S. J . Org. Chem. 1997, 62, 6870.

(5) (a) Djukic, J . P.; Do¨tz, K. H.; Pfeffer, M.; De Cian, A.; Fischer, J .

Organometallics 1997, 16, 5171. (b) Djukic, J . P.; Maisse, A.; Pfeffer,

M.; Do¨tz, K. H.; Nieger, M. Eur. J . Inorg. Chem. 1998, 1781. (c) Djukic,

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Pfeffer, M.; Do¨tz, K. H.; De Cian, A.; Fischer, J . Chem. Eur. J . 2000,

6, 1064.

(10) Djukic, J . P.; Maisse, A.; Pfeffer, M.; Do¨tz, K. H.; Nieger, M.

Organometallics 1999, 18, 2786.

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Angew. Chem. 1995, 107, 37. (b) Dorn, R. D.; Baums, D.; Kersten, P.;

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(7) From the structure of the final product in Scheme 2 the “organic

spiral” consists of the polycyclic organic ligand that is somehow coiled

around the C_benzyl-Mn bond axis.

(8) Eliel, E. L.; Wilen, S. H. In Stereochemistry of Organic Com-

pounds; Wiley: New York, 1994.

(12) A “spirogenic” reaction denotes a transformation that favors

the formation of molecular helical and spiral-like arrangements among

all other possible structures.

(9) Solladie´-Cavallo, A. Adv. Met.-Org. Chem. 1989, 1, 99.

5486 Organometallics, Vol. 19, No. 25, 2000

Djukic et al.

value typical for neutral Re carbene complexes.¹³The

¹³C signal of the Cr(CO)₃moiety appeared at a value of

δ ) 231 ppm, which corresponds to a shielding of 6 ppm

with respect to the value extracted from the spectrum

of PPN-2. This shielding of the ¹³C signals of Cr(CO)₃

is consistent with a decrease of electron density at the

Cr atom¹⁴that is caused by the electron-demanding

alkoxycarbene moiety at the Re atom. It is well estab-

lished that electronic effects of arene’s substituent(s),

i.e., inductive and mesomeric effects, are readily trans-

mitted to the CO ligands via the coordinated aromatic

ring.¹⁵In addition, it may reasonably be proposed that

the shielding of the ¹³C signal of the Cr-bound CO

ligands is caused by a decrease of the d-π* back-

donation from the chromium toward the carbonyls and

an increase of the σ-donation of the latter.¹⁶

F igu r e 1. ¹³C {¹H}NMR spectrum of 3 in CD₂Cl₂(125

MHz). Enlargement of the 310-190 ppm region.

Sch em e 3

Warming the NMR sample tube to room temperature

induced a rapid change in the solution’s content that

was characterized by the disappearance of the signal

at δ ) 308 ppm and the formation of a new major

product that was later identified as Cr/Re-spiralene

complex 4.

of the organolithium reagent used for the formation of

the acylmetalate adduct. Moreover, we propose a mecha-

nistic scheme that rationalizes the formation of spi-

ralenes obtained from cyclomanganated aromatics by

the “E.O. Fischer method”.

Resu lts a n d Discu ssion

1.2. Syn th esis of Cr /Re-Sp ir a len e 4. The synthesis

of complex 4 was carried out on larger scales by starting

from the bimetallic complex 1 (eq 1). The latter was

treated sequentially with PhLi and MeOTf at -50 °C

in DME, and the product, 4, was recovered in 51% yield

after chromatographic purification. Recrystallization of

4 from a mixture of CH₂Cl₂and hexane afforded crystals

suitable for X-ray diffraction analyses.

The ORTEP diagram of the molecular structure of 4

is displayed in Figure 2. Acquisition and refinement

data are listed in Table 1. Selected interatomic distances

and angles are given in Table 2. The structure of 4

1. Sp ectr oscop ic Evid en ce for th e In ter m ed ia cy

of a Rh en iu m (I)-Ca r ben e Sp ecies in th e Syn th e-

sis of a Cr (0)/Re(I)-Sp ir a len e. 1.1. Sp ectr oscop ic

Detection of th e [(Meth oxy)(p h en yl)m eth ylid en e]-

r h en iu m (I) Sp ecies 3. We recently underlined the

synthetic versatility of the acylmanganate salts obtained

from a reaction of RLi with a cyclomanganated (η⁶-

arene)Cr(CO)₃complex, as they could be valuable

intermediates for the synthesis of ortho acyl-substituted

(η⁶-arene)Cr(CO)₃complexes.¹⁰We described the X-ray

diffraction structure of the rhenium analogue 2 that

confirmed the stereoselectivity of the nucleophilic attack

of PhLi at the Re(CO)₄fragment of 1 (Scheme 3). Hence,

we undertook to monitor by ¹³C NMR spectroscopy the

reaction between an excess amount of MeOTf and the

PPN salt of the benzoylrhenate 2, e.g., PPN-2 (Scheme

3). The reaction was carried out by injecting MeOTf in

an NMR sample tube containing a CD₂Cl₂solution of

PPN-2 at -50 °C. Complete conversion of PPN-2 into

the neutral carbene complex 3 took place in approxi-

mately 1 h (Scheme 3).

(13) (a) Darst, K. P.; Lenhert, P. G.; Lukehart, C. M.; Warfield, L.

T. J . Organomet. Chem. 1980, 195, 317. (b) Singh, M. M.; Angelici, R.

J . Inorg. Chem. 1984, 23, 2699. (c) Alvarez-Toledano, C.; Parlier, A.;

Rudler, M.; Daran, J . C.; Knobler, C.; J eannin, Y. J . Organomet. Chem.

1987, 328, 357. (d) Miessler, G. L.; Kim, S.; J acobson, R. A.; Angelici,

R. J . Inorg. Chem. 1987, 26, 1690. (e) Casey, C. P.; Nagashima, H. J .

Am. Chem. Soc. 1989, 111, 2352. (f) Casey, C. P.; Sakoba, H.;

Underiner, T. L. J . Am. Chem. Soc. 1991, 113, 6673. (g) Mashima, K.;

J yodol, K.; Ohyoshi, A.; Takaya, H. Bull. Chem. Soc. J pn. 1991, 64,

2065.

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1979, 182, 499.

(15) (a) Neuse, E. W. J . Organomet. Chem. 1975, 99, 287. (b) Hunter,

A. D.; Shilliday, L.; Furey, W. S.; Zaworotko, M. J . Organometallics

1992, 11, 1550. (c) Hunter, A. D.; Mozol, V.; Tsai, S. D. Organometallics

1992, 11, 2251. (d) Djukic, J . P.; Rose-Munch, F.; Rose, E.; Vaisser-

mann, J . Eur. J . Inorg. Chem. 2000, 1295.

A large series of scans were then acquired at -50 °C

in order to obtain a ¹³C NMR spectrum of the carbene

intermediate with an acceptable signal-to-noise ratio.

The latter spectrum displayed a series of typical signals

in the carbonyl ligand resonance region (Figure 1). The

carbene carbon signal showed up at δ ) 308 ppm, a

(16) Ruiz-Morales, Y.; Schreckenbach, G.; Ziegler, T. J . Phys. Chem.

1996, 100, 3359.

Organometallic Helices

Organometallics, Vol. 19, No. 25, 2000 5487

F igu r e 2. ORTEP diagram of the structure of 4. Thermal

ellipsoids are drawn at the 30% probability level. Solvent

and hydrogen atoms have been omitted for clarity.

w ith n -Bu Li a n d MeOTf. Addition of a stoichiometric

amount of n-BuLi to complex 5 in DME at -50 °C

afforded a dark brown solution that was subsequently

treated with a slight excess of MeOTf and warmed at

room temperature. The resulting mixture of products

(76% conversion) was separated by chromatographic

means to yield two dark red compounds, 6a and 6b, in

a ratio of 38:62 (eq 2, R ) Me). Both complexes afforded

crystals that allowed X-ray diffraction analyses. Com-

pounds 6a and 6b were subsequently identified as two

new Cr/Mn-spiralene complexes in which, for 6a , a n-Bu

group was located above the heterocyclic ring at the

endo position (Figure 3) and, for 6b, the methoxy group

was located above the pyridyl fragment while the n-Bu

group stood at the exo position (Figure 4).

presents several similarities to those of previously

described bimetallic Cr/Mn-spiralenes. The phenyl ring

originating from PhLi is typically located above the

pyridyl group, thus generating π-π contacts in the area

where interplanar distances are inferior to 3.6 ( 0.1 Å

(Table 2).¹⁷Noteworthy, the Cr-Re distance of 3.080-

(3) Å in 4 is slightly longer than in the Mn analogue

although remaining in the range of values reported by

us in several previous cases. The main difference

between Mn and Re analogues arises from the confor-

mational behavior of the Cr(CO)₃tripod.¹⁸In complex

4 studied at 283 K, the ¹³C (125 MHz) nuclei of the

slowly rotating Cr(CO)₃group resonate as three distinct

and sharp signals, while in the Mn isomer complete

decoalescence may be observed only starting from 253

K.¹⁹This suggests that a tiny variation of ca. 0.1 Å of

the atomic radius of the atom M (M ) Mn or Re)

connected to the benzylic position in a Cr/M-spiralene

complex induces changes of the conformational behavior

of the Cr(CO)₃tripod. According to our previous inves-

tigations on the conformational behavior of the Cr(CO)₃

rotor in Cr/Mn-spiralenes,¹⁹we may reasonably ascribe

the relative slackening in 4 essentially to an increased

steric interaction of the Cr-centered rotor with the

vicinal M(CO)₃(M ) Re) group generated by a decreased

molecular flexibility.

Acquisition and refinement parameters for structures

of 6a and 6b are provided in Table 1. Selected inter-

atomic distances and angles are given in Table 3. The

two ORTEP diagrams of compounds 6a and 6b indicate

that these syn-facial bimetallic isomers possess very

close structural features. The stereochemical differences

existing between these two diastereoisomers at the

benzylic carbon position can also be revealed by ¹H NMR

spectroscopy. Indeed, the chemical shift of the methoxy

group protons singlet may be used as a probe for

determining the spatial position of the latter group

relative to the heterocyclic ring; in 6a as well as in other

phenyl-substituted Cr/Mn-spiralene complexes the exo-

methoxy group protons resonate as a singlet around 3.6

ppm, while in 6b the same protons which are now

located directly in the shielding cone of the pyridyl group

resonate at about 3.0 ppm. Complexes 6a and 6b are

both formed following a process that includes the cis-

migration of the π-coordinated arene to a R-methoxy-

n-pentylidene moiety. In view of these results, the

absence of unsaturation at R and â positions from the

The intriguing stereoselectivity observed in the for-

mation of spiralenes from the reactions carried out by

the “E.O. Fischer method” prompted us to investigate

the outlet of sequential reactions that would involve

alkyllithium nucleophiles such as n-BuLi and MeLi

knowing that the latter are either efficient bases capable

of removing aryl protons from (η⁶-arene)Cr(CO)₃com-

plexes²⁰or capable of attacking unsaturated N-hetero-

cycles.²¹

(20) (a) Semmelhack, M. F. Comprehensive Organometallic Chem-

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

Oxford, 1995; Vol. 9, p 1117. (b) Nesmeyanov, A. N.; Kolobova, N. E.;

Anisimov, K. N.; Markarov, Yu. V. Izv. Akad. Nauk. SSSR, Ser. Khim.

1969, 2665. (c) Fraser, R. R.; Mansour, T. S. J . Organomet. Chem. 1986,

310, C60. (d) Ghavshou, M.; Widdowson, D. A. J . Chem. Soc., Perkin

Trans. 1 1983, 3065. (e) Semmelhack, M. F.; Bisaha, J .; Czarny, M. J .

Am. Chem. Soc. 1979, 101, 768. (f) Card, R. J .; Trahanovski, W. S. J .

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48, 2349. (h) Rose-Munch, F.; Rose, E. Current Org. Chem. 1999, 3,

445.

2. Alk yl-Su bstitu ted Cr (0)/Mn (I)-Sp ir a len es. 2.1.

Sequ en tia l Rea ction of Cyclom a n ga n a ted 3-Meth -

yl,2-[tr ica r bon yl(η⁶-p h en yl)ch r om iu m ]p yr id in e, 5,

(17) For leading references please see: (a) Dahl, T. Acta Chem.

Scand. 1994, 48, 95. (b) Hunter, C. A. Chem. Soc. Rev. 1994, 101. (c)

Mu¨ller-Dethlefs, K.; Hobza, P. Chem. Rev. 2000, 100, 143.

(18) McGlinchey M. J . Adv. Organomet. Chem. 1992, 34, 285, and

references therein.

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Ser. IIc 1999, 403.

(21) Oae, S.; Furukawa, N. Adv. Heterocycl. Chem. 1990, 48, 35.

5488 Organometallics, Vol. 19, No. 25, 2000

Ta ble 1. Acqu isition a n d Refin em en t Da ta for Com p lexes 4, 6a , 6b, 9, 18, a n d 19

Djukic et al.

4

6a

6b

formula

mol wt

cryst syst

space group

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

C

₂₆H₁₈CrNO₇Re‚CH₂C_l2

C₂₄H₂₂NO₇CrMn

543.38

monoclinic

P2₁/n

10.1444(3)

14.3587(3)

16.4887(6)

2(C₂₄H₂₂NO₇CrMn)‚H₂O‚CH₂Cl₂

779.57

monoclinic

P2₁/n

9.5566(2)

13.7631(3)

20.9170(5)

1189.71

triclinic

P1h

9.1890(2)

12.9030(4)

13.0610(4)

62.701(7)

76.915(7)

76.943(7)

1327(7)

101.106(2)

92.744(9)

2699.7(2)

4

2399.0(2)

4

Z

1

color

orange

cryst dimens (mm)

0.20 × 0.18 × 0.14

0.20 × 0.15 × 0.11

0.20 × 0.12 × 0.10

F_calcd(g‚cm^-3

)

1.92

1.50

1.49

µ (mm^-1

)

5.127

173

0.71073

Mo KR graphite

monochromated

KappaCCD

0,13/0,18/-29,29

2.5/30.53

19 975

0.989

294

0.71073

Mo KR graphite

monochromated

KappaCCD

0,12/0,17/-20,20

2.5/26.37

18 113

1.001

173

0.71073

Mo KR graphite

monochromated

KappaCCD

0,12/-15,17/-16,16

2.5/29.55

11 668

temp (K)

λ (Å)

radiation

diffractometer

hkl limits

θ limits (deg)

number of data measd

number of data

with I > 3σ(I)

weighting scheme

no. of variables

R

6892

3108

4279

4F_o²/(σ²(F_o²) + 0.0064F_o

352

0.035

0.051

1.015

0.703

)

4F_o²/(σ²(F_o²) + 0.0064F_o

307

0.034

0.049

1.020

0.389

)

4F_o²/(σ²(F_o²) + 0.0064F_o

343

0.047

0.075

1.525

0.464

)

4

R_w

GOF

largest peak in

final diff (e‚Å^-3

)

9

18

19

formula

mol wt

cryst syst.

space group

a (Å)

C

₂₈H₃₂CrMnNO₇

C₂₆H₂₂CrMnNO₈

583.40

monoclinic

P2₁/c

20.2330(7)

16.5760(3)

16.9120(5)

C₂₆H₂₂CrMnNO₈

583.40

monoclinic

P2₁/c

15.3920(7)

10.8910(5)

14.8720(5)

601.50

orthorhombic

P2₁2₁2₁

10.4149(3)

16.1127(3)

16.8256(5)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

Z

114.618(4)

91.030(2)

2823.5(2)

4

5156.4(6)

8

2492.7(3)

4

color

dark red

red

orange

cryst. dimens (mm)

F_calcd(g‚cm^-3

µ (mm^-1

temp (K)

λ (Å)

radiation

0.18 × 0.16 × 0.12

0.20 × 0.20 × 0.08

0.16 × 0.14 × 0.10

)

1.41

1.50

1.55

)

0.877

173

0.71073

Mo KR graphite

monochromated

KappaCCD

-10,14/-20,17/-23,16

2.5/30.54

0.961

294

0.71073

Mo KR graphite

monochromated

KappaCCD

0,23/0,21/-28,26

2.5/30.52

34 497

0.994

173

0.71073

Mo KR graphite

monochromated

KappaCCD

0,19/-13,14/-19,19

2.5/27.55

17 357

diffractometer

hkl limits

θ limits (deg)

no. of data meas.

number of data with I > 3σ(I)

weighting scheme

no. of variables

R

18 579

3163

7921

7294

4F_o²/(σ²(F_o²) + 0.0001F_o

343

)

4F_o²/(σ²(F_o²) + 0.0064F_o

667

)

4F_o²/(σ²(F_o²) + 0.0064F_o

334

)

4

0.034

0.040

0.044

R_w

0.041

0.059

0.083

GOF

0.924

1.108

1.509

largest peak in

0.330

0.307

0.801

final diff (e‚Å^-3

)

carbene carbon atom clearly affects the stereoselectivity

of the process leading to alkyl-substituted bimetallic

spiralenes.

2.2. Sequ en tia l Rea ction of Cyclom a n ga n a ted

2-[Tr ica r b on yl(η⁶-p h en yl)ch r om iu m ]p yr id in e, 7,

w ith RLi (R ) n -Bu , Me) a n d MeOTf. Sequential

treatment of the bimetallic chelate 7 with stoichiometric

amounts of n-BuLi and MeOTf at -50 °C afforded a new

mixture of two compounds that were identified accord-

ing to ¹H NMR investigations as being Cr/Mn-spiralene

complexes 8a and 8b in a ratio of 48:52 (eq 2, R ) H).

The latter two compounds displayed spectroscopic fea-

tures similar to those of 6a and 6b. The stoichiometry

of the first step of the preparation, e.g., the nucleophilic

Organometallic Helices

Organometallics, Vol. 19, No. 25, 2000 5489

F igu r e 4. ORTEP diagram of the structure of 6b. Thermal

ellipsoids are drawn at the 40% probability level. Solvent

and hydrogen atoms have been omitted for clarity.

Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d

An gles (d eg) for Com p lexes 6a a n d 6b

6a

6b

Distances (Å)

Mn-Cr

3.035(4)

3.018(4)

2.132(3)

2.416(4)

2.939(4)

2.388(4)

2.251(3)

2.212(3)

2.192(3)

2.215(3)

2.238(3)

1.457(4)

Mn-C10

Mn-C16

Mn-C17

Cr-C16

Cr-C17

Cr-C18

Cr-C19

Cr-C20

Cr-C21

C10-C16

2.157(3)

2.396(4)

2.922(4)

2.413(3)

2.246(2)

2.196(3)

2.190(3)

2.211(3)

2.239(3)

1.446(4)

F igu r e 3. ORTEP diagram of the structure of 6a . Thermal

ellipsoids are drawn at the 40% probability level. Hydrogen

atoms have been omitted for clarity.

Ta ble 2. Selected In ter a tom ic Dista n ces (Å),

An gles (d eg), a n d Tor sion An gles (d eg) for

Com p lex 4

Angles (deg)

Distances (Å)

C22-Cr-C23

C23-Cr-C24

C12-C10-O4

82.4(2)

93.4(1)

85.2(1)

110.7(2)

82.5(2)

94.2(1)

82.6(2)

Re-Cr

3.080(3)

2.269(3)

3.090(3)

2.601(3)

2.237(3)

2.345(4)

2.228(3)

2.214(4)

2.197(3)

2.222(3)

1.459(4)

Re-C4

Re-C18

Re-C19

Cr-C18

Cr-C19

Cr-C20

Cr-C21

Cr-C22

Cr-C23

C4-C19

Torsion Angles (deg)

46.6

C16-C17-C8-N

45.8

Sch em e 4

Angles (deg)

C24-Cr-C25

C24-Cr-C26

C25-Cr-C26

81.8(2)

97.7(2)

83.7(2)

Torsion Angle (deg)

C19-C18-C12-N

47.6

Inter-ring Distances (Å)

C6-N

C6-C13

C11-C12

3.054

3.553

3.334

attack of RLi, was found to be crucial. We found that

reaction of 7 with 2 equiv of n-BuLi followed by a

treatment with excess MeOTf would yield a unique new

product (55% yield) having nothing in common with 8a

and 8b according to the spectroscopic data (Scheme 4).

This new complex, 9, was successfully crystallized and

characterized by X-ray diffraction analysis. Acquisition

and refinement data are listed in Table 1. Complex 9

crystallized spontaneously in the noncentrosymmetric

space group P2₁2₁2₁(the Flack parameter is given in

the Experimental Section). Selected interatomic dis-

tances and angles are given in Table 4. The structure

of 9 (Figure 5) reveals that substrate 7 underwent two

successive nucleophilic attacks of n-BuLi, the first one

occurring at a Mn-bound CO ligand and the second one

at the 6 position of the pyridyl group, i.e., atom C20 in

Figure 5 (Scheme 4). The methyl group connected to C17

originates from MeOTf as a result of the C-alkylation

of a putative dianionic intermediate. Strikingly, the two

alkyl groups, n-Bu and Me, selectively attacked the

5490 Organometallics, Vol. 19, No. 25, 2000

Djukic et al.

Ta ble 5. Equ ilibr a tion of 8a a n d 8b: Com p osition

of th e Rea ction Med iu m (m ol %) ver su s Tim e (h )

experiment 1

experiment 2

t (h)

8a (mol %)

8b (mol %)

8a (mol %)

8b (mol %)

0

24

48

93

56

7

44

15

51

85

49

substituents of the benzylic carbon, which is chemically

possible, in our opinion, only after homolytic cleavage

of the C_benzyl-Mn bond²²and a subsequent 180° rotation

of the (n-Bu)(MeO)C- fragment around the C_benzyl

-

C_ipso/ArCraxis. This would imply the transient formation

of a dissymmetric biradical species in which the un-

paired electrons are formally located at the Mn atom

and at the benzylic position and more probably delo-

calized over all the surrounding ligands.²³An ESR

experiment that was carried out with a frozen solution

of 8a in degassed CDCl₃supports the hypothesis of a

mediation by a biradical species as relatively weak,

broad, and complex ESR signals were recorded at ca. g

) 2.02 and 2.77 (see Supporting Information). The lack

of resolution in the latter spectrum may be ascribed to

the inherent complexity of the system, i.e., short ESR

T₁and T₂relaxation times and complex superimposition

of signals resulting from classical hyperfine couplings

and spin-orbit interaction(s) between the two intramo-

lecularly unpaired electrons. A priori, the strongest

signal at g ) 2.02 may be related to either carbon or a

Mn(0)-centered radicals.²⁴Further investigations are

currently in progress to understand the origin of the

second signal.

F igu r e 5. ORTEP diagram of the structure of 9. Thermal

ellipsoids are drawn at the 40% probability level. Hydrogen

atoms have been omitted for clarity.

Ta ble 4. Selected In ter a tom ic Dista n ces (Å) a n d

An gles (d eg) for Com p lex 9

Distances (Å)

Angles (deg)

Mn-Cr

3.060(4)

2.338(4)

2.881(4)

2.148(4)

2.422(4)

1.443(5)

1.290(5)

1.327(7)

C1-Cr-C2

C1-Cr-C3

C2-Cr-C3

95.0(2)

87.1(2)

81.6(2)

Mn-C4

Mn-C5

Mn-C10

Cr-C4

C4-C10

N-C16

C18-C19

pyridyl ring from the side opposite the Cr(CO)₃tripod.

A rough analysis of the molecular geometry of 9 reveals

a “boat”-type conformation for the 1,4-dihydropyridyl

group. Further applications of this new reaction are

under investigation.

Complexes 8a and 8b in solution displayed a peculiar

ability to interconvert within a few hours period (eq 3).

We never observed this behavior with the relatively

rigid phenyl-substituted Cr/Mn-spiralenes. The study

of the equilibration between 8a and 8b could be followed

by monitoring the ¹H NMR signal of the relevant

methoxy groups of the two latter complexes. Two

parallel experiments were carried out by dissolving

mixtures enriched in either 8a or 8b in CDCl₃at room

temperature; three spectra were measured at t ) 0, 24,

48 h. Table 5 gives the composition of the corresponding

solutions at each time interval; experiment 1 corre-

sponds to the isomerization of 8a into 8b + 8a and

experiment 2 to the isomerization of 8b into 8a + 8b.

Within experimental errors, the two experiments led

after 24 h to a rough 50:50 mixture of 8a and 8b.

Aiming at molecules that would possess a higher

fluxionality, we decided to attempt the preparation of

complexes 10a and 10b by treatment of 7 with a

stoichiometric amount of MeLi and a slight excess of

(22) (a) Tyler, D. R. Prog. Inorg. Chem. 1988, 36, 125. (b) Brown, T.

L. Organometallic Radical Processes, J ournal of Organometallic

Chemistry Library 32; Trogler, W. C., Ed.; Elsevier: Amsterdam, 1990;

p 67.

(23) For reviews on organometallic radicals see: (a) Connelly, N. G.;

Geiger, W. E. Adv. Organomet. Chem. 1984, 23, 1. (b) Sun, S.; Sweigart,

D. Adv. Organomet. Chem. 1996, 40, 171.

(24) (a) Ran, S.; Cheng, C. P. J . Chem. Soc., Dalton Trans. 1988,

2695. (b) Milukov, V. A.; Sinyashin, O. G.; Ginzburg, A. G.; Kon-

dratenko, M. A.; Loim, N. M.; Gubskaya, V. P.; Musin, R. Z.; Morozov,

V. I.; Batyeva, E. S.; Sokolov, V. I. J . Organomet. Chem. 1995, 493,

221. (c) Mach, K.; Novakova, J .; Raynor, J . B. J . Organomet. Chem.

1992, 439, 341. (d) Symons, M. C. R.; Sweany, R. L. Organometallics

1982, 1, 834. (d) Rattinger, G. B.; Belford, R. L.; Walker, H.; Brown,

T. L. Inorg. Chem. 1989, 28, 1059. (e) Myers, R. J . Molecular

Magnetism and Magnetic Resonance Spectroscopy; Prentice Hall:

London, 1973.

It is worth noting that such a fluxional behavior was

not observed with 6a and 6b. The isomerization of 8a

into 8b corresponds to a formal permutation of the

Organometallic Helices

Organometallics, Vol. 19, No. 25, 2000 5491

MeOTf. The latter reactions carried out from -50 to -10

°C afforded a crude mixture of the two expected com-

pounds in which 10b was the minor component (less

than 7%) (eq 4). The moderate conversion obtained for

this reaction (33%) suggests either that the products

displayed some sensitivity to air or that the acylman-

ganate intermediate did not completely O-alkylate. The

major product, 10a , was carefully purified by flash

column chromatography at -5 °C and was firmly

1

identified on the basis of the H chemical shifts of the

MeO and Me groups, which showed up respectively at

δ ) 3.69 and 1.75 ppm. Although complex 10b could be

formed by allowing 10a to isomerize at room tempera-

ture in CH₂Cl₂, it could not be isolated in a pure form.

1

A qualitative H NOESY two-dimensional NMR experi-

F igu r e 6. Conversion of 10a into 10b; plot of the concen-

tration of 10b (mmol‚L^-1) versus time (min). The inset

displays the evolution of the ¹H NMR signal of the benzylic

carbon bound Me group in 10b versus time.

ment revealed a set of cross-peaks between the ¹H NMR

signals of 10a and 10b, thus confirming that the two

latter compounds were undergoing interconversion in

solution (eq 5).

The ¹H NMR spectrum of 10b displayed two reso-

nances at δ ) 2.91 and 2.03 ppm ascribed to the endo-

MeO and exo-Me groups, respectively. Compounds 10a ,b

were found more reactive and air sensitive than 8a ,b.

From a practical point of view, we noticed that the isom-

erization of 10a into 10b was more convenient to moni-

tor by NMR spectroscopy than that of a 8a + 8b mixture

1

since the complexity of the H NMR spectrum was very

much reduced for the former in the 0-4 ppm region.

2.3. F lu xion a l Beh a vior of th e Alk yl-Su bstitu ted

Cr /Mn -Sp ir a len e 10a . Complex 10a and an exact

amount of internal standard, e.g., tris-1,3,5-tert-butyl-

benzene, were dissolved in dry and degassed C₆D₆. The

resulting dark brown solution was injected in a NMR

sample tube that was introduced in the probe of the

NMR spectrometer and kept at 293 K. The isomeriza-

tion of 10a into 10b was monitored by ¹H NMR

spectroscopy. The relative concentrations of 10a and

10b were calculated from the integrations of the signals

of MeO and Me groups of the two complexes relative to

those of the internal standard (c_standard) 0.0124 M). The

concentrations of 10a and 10b were summed and

compared with the initial concentration of 10a in order

to evaluate the extent of the competing decomposition

process that could involve both 10a and 10b. The values

of (c_10a+ c_10b) plotted versus time (not shown herein)

indicated that the process could be followed over 5 h

without noticeable decomposition taking place.

e

F igu r e 7. Conversion of 10a into 10b; plot of ln[(c_10b

c

-

e

_10b)(c_10b)

^-1] versus time (min).

which allowed the determination of the direct and

reverse apparent rate constants: k₁) 3.6 × 10^-5s^-1

,

k_-1) 8.60 × 10^-5s^-1(R ) 0.99944). However, the first-

order kinetic law that is used here to extract the

apparent rate constants does not reflect the actual

mechanism of the conversion of 10a into 10b. It seems

likely that this reversible process involves a three-step

mechanism that includes (i) the slow homolytic cleavage

of the C_benzyl-Mn bond and the subsequent formation

of radicals at the (η⁶-benzyl)Cr(CO)₃and Mn(CO)₃L

26

fragments (Scheme 5, step A), (ii) the slow rotation of

the Me(MeO)C- fragment around the C_benzyl-C_Araxis,

which is expected to occur with a relatively high energy

barrier since a part of the spin density is expected to

be transferred to the “hermaphroditic” Cr(CO)₃moiety,²⁷

thus increasing the double-bond character (Scheme 5,

Figure 6 displays the plot of the concentration in 10b,

c_10b(mmol‚L^-1), versus time (min). The data could be

satisfactorily fitted (R ) 0.99951) with a first-order

kinetic law corresponding to the relaxation of an out-

e

of-equilibrium two-component system: c_10b) c_10b× (1

e

- exp[-t/(k₁+ k_-1)]) with c_10b) 6.18 × 10^-3M. By

extrapolation, the value of the concentration in 10a at

equilibrium, c_10a^e, could be determined as equal to 20.88

× 10^-3M. The value of the equilibrium constant K ) k₁

(25) A similar study carried out at +40 °C indicated that the

equilibrium was reached in ca. 6 min and that significant decomposi-

tion was starting after 15 min; the two complexes 10a and 10b were

estimated to be in a respective ratio of 4:1 at t ) 6 min (K ) 0.25).

(26) (a) Schmaltz, H. G.; Siegel, S.; Bats, J . W. Angew. Chem., Int.

Ed. Engl. 1995, 34, 2383. (b) Taniguchi, N.; Kaneta, N.; Uemura, M.

J . Org. Chem. 1996, 61, 6088. (c) Taniguchi, N.; Uemura, M. Synlett

1997, 51. (d) Taniguchi, N.; Uemura, M. Tetrahedron Lett. 1997, 38,

7199. (e) Merlic, C. A.; Walsh, J . C. Tetrahedron Lett. 1998, 39, 2083.

(f) Schmaltz, H. G.; Siegel, S.; Bernicke, D. Tetrahedron Lett. 1998,

39, 6683. (g) Schmaltz, H. G.; de Koning, C. B.; Bernicke, D.; Siegel,

S.; Pfletschinger, A. Angew. Chem., Int. Ed. Engl. 1999, 38, 1620.

-1

e

e -1

× (k_-1

)

) c_10b× (c_10a

)

determined to be 0.42

indicates that the interconverting system favors the

isomer in which steric interactions with the pyridyl

group are minimized, e.g., 10a .²⁵Figure 7 displays the

)

^{e -1}] versus time (min).

e

plot of ln[(c_10b- c_10b) × (c_10b

The curve was fitted to a least-squares linear equation,

5492 Organometallics, Vol. 19, No. 25, 2000

Djukic et al.

Sch em e 5

benzylamine analogues.¹⁰Reaction of 13 with a slight

excess of MeLi in DME at -50 °C afforded a dark brown

solution, which yielded the aromatic ketone 15 in 86%

yield upon warming the medium to room temperature

and exposing it to air (eq 6).

Sch em e 6

step B), (iii) the fast recombination of the biradical to

form a new C_benzyl-Mn bond (Scheme 5, step C).

For such a system that implies successive reversible

steps there exists unfortunately no straightforward

formulation of the complete kinetic law. Nevertheless,

it can be easily demonstrated that, at equilibrium, the

value of the equilibrium constant K directly depends on

the conformational equilibrium constant K_rotinvolving

the two biradical species I and II (Scheme 5). This is

further verified if one assumes that the cleavage (k_a,

k_-c) and recombination (k_-a, k_c) rate constants have

similar magnitudes. The equilibrium constant K can

then be assimilated to K_rot(Scheme 5).

In other cases where such conformational exchange

and homolytic C_benzyl-Mn bond cleavage do not proceed

either for steric or electronic reasons, like with 6a ,b and

with other Cr/Mn(Re)-spiralene complexes having a Ph

group attached to the benzylic position, the observed

high stereoselectivity of the cis-migration step that

precedes spiralene formation very likely stems from a

late transition state and/or a transient intermediate

that prefigures the structure of the final product. The

study of bimetallic chelates derived from 2-aryl-2-

oxazoline brought us decisive elements for the estab-

lishment of the main factors that control the stereose-

lectivity.

3. 2-Oxa zolin e-Der ived Su bstr a tes a n d Cr (0)/

Mn (I) Heter obim eta llic Com p lexes. 3.1. Rea ctivity

of 13 a n d 14 ver su s Or ga n olith iu m a n d Dia zoa l-

k a n e Rea gen ts. Chromium complexes 11 and 12

afforded in satisfactory yields complexes 13 and 14

respectively upon treatment with [Mn(CO)₅(CH₂Ph)] in

refluxing heptane (Scheme 6).

Complex 13 reacted readily with PPh₃in refluxing

heptane to yield 16, a new complex resulting from the

displacement of the exo axial CO ligand of the Mn(CO)₄

moiety (eq 7).⁶The relative lability of 13 prompted us

to treat it with N₂dCPh₂, which was expected to yield

a new syn-facial heterobimetallic Cr/Mn-spiralene with

an oxazoline chelating arm (eq 8). The product of the

reaction, i.e., 17, afforded at 263 K a ¹³C NMR spectrum

that suggested that the Cr(CO)₃tripod was not under-

going restricted rotation since its ¹³C nuclei generated

a unique sharp singlet. The ¹³C signals of the carbonyl

ligands connected to the manganese(I) atom were

detected at values of chemical shift that suggested that

the chelated Mn(CO)₃moiety was not located in the

vicinity of the Cr(CO)₃group but was rather engaged

in the η²coordination of one of the two phenyl groups

attached to the benzylic carbon. Indeed, in syn-facial

bimetallic complexessor Cr/Mn-spiralenessthe Mn-

(CO)₃fragment generates three distinct ¹³C NMR

signals at approximately δ ) 230, 229, and 220 ppm,^5b

while in chelated η³-benzylic complexessor Mn-spi-

ralenessthe resonances related to Mn(CO)₃appear at

δ ) 230, 221, and 220 ppm.^5aOur hypothesis for a non-

syn-facial bimetallic structure was further supported by

the IR spectrum of 17 that displayed a fac-Mn(CO)₃-

Complex 13 displayed a reactivity versus MeLi simi-

lar to that of the 2-phenylpyridine and N,N-dimethyl-

(27) (a) Pfletschinger, A.; Dargel, T. K.; Schmaltz, H. G.; Koch, W.

Chem. Eur. J . 1999, 5, 537. (b) Merlic, C. A.; Walsh, J . C.; Tantillo, D.

J .; Houk, K. N. J . Am. Chem. Soc. 1999, 121, 3596.

Organometallic Helices

Organometallics, Vol. 19, No. 25, 2000 5493

Ta ble 6. Selected In ter a tom ic Dista n ces (Å) a n d

An gles (d eg) for Com p lexes 18 a n d 19

18

19

Distances (Å)

3.137(5)

Mn-Cr

4.887(4)

Mn-C8

Mn-C16

Mn-C18

Mn-C19

Cr-C4

2.474(5)

2.133(3)

2.130(3)

2.242(3)

2.355(3)

2.246(3)

2.229(3)

2.193(3)

2.214(2)

2.277(3)

2.228(3)

1.510(4)

1.489(4)

1.428(4)

1.414(4)

1.374(4)

1.406(5)

1.375(5)

1.434(4)

2.232(3)

2.205(3)

2.227(3)

2.219(3)

2.377(5)

2.215(3)

1.459(4)

1.508(4)

1.385(4)

1.391(5)

1.368(5)

1.381(5)

1.368(5)

1.404(4)

Cr-C5

Cr-C6

Cr-C7

Cr-C8

Cr-C9

C8-C16

C16-C18

C18-C19

C19-C20

C20-C21

C21-C22

C22-C23

C23-C18

F igu r e 8. ORTEP diagram of the structure of 18. Thermal

ellipsoids are drawn at the 40% probability level. Hydrogen

atoms have been omitted for clarity.

Angles (deg)

116.4(2)

120.2(2)

111.4(2)

111.0(2)

83.1(1)

Mn-C16-C18

C8-C16-C18

C8-C16-O5

C18-C16-O5

C1-Cr-C2

122.6(3)

115.9(2)

110.4(2)

106.7(2)

88.6(1)

89.7(1)

84.3(1)

84.9(1)

85.7(1)

97.4(1)

90.56(9)

related stretching A-mode vibration band at 2004 cm^-1

,

while it usually appears in syn-facial heterobimetallic

C1-Cr-C3

84.8(1)

90.2(1)

89.4(1)

90.3(2)

85.9(2)

85.79(9)

complexes 5-10 cm^-1higher at around 2010-2015

C2-Cr-C3

cm^{-1 5b}

.

C24-Mn-C25

C25-Mn-C26

C24-Mn-C26

C16-Mn-N

longer than in Cr/Mn-spiralenes derived from 2-phenylpy-

ridine^5binvalidates the existence of an efficient metal-

metal bonding interaction. The phenyl ring introduced

by PhLi eclipses the bulky 4,4-dimethyl,2-oxazoline

heterocycle. One of the two methyl groups of the latter

ring (C15) points toward the centroid of the phenyl

group, leading us to suspect the existence of a stabilizing

intramolecular C-H‚‚‚π interaction.²⁸Observation of

the molecular structure of 18 suggests at first glance

that this complex is a geometrically locked conformer

of 19 resulting from the rocking of the Mn(CO)₃group

toward the Cr(CO)₃moiety. The molecular structure of

19 (Figure 9) differs from that of 18 by the position of

the Mn center with respect to the π-coordinated aro-

matic ligand. In 19, the Mn atom is ideally positioned

in the mean plane formed by C16, C8, C7, C11, and N,

which is nearly coplanar with the vicinal π-coordinated

arene and the oxazoline rings. The interatomic distances

C16-Mn, C18-Mn, and C19-Mn reveal that the man-

ganese atom is bonded to C16 and C18-C19 respec-

tively in η¹and η²coordination modes. The molecular

structure of 19 displays an example of a nearly planar

six-membered metalacycle from which the planarity is

ensured by three fused rings, namely, the chromium-

complexed arene ring at C7-C8, the 2-oxazolinyl group

at N-C11, and the four-membered manganacycle formed

by Mn, C16, C18, C19 at Mn-C16.

3.2. Seq u en t ia l R ea ct ion of 14 w it h P h Li a n d

MeOTf. Our procedure for the synthesis of 2-phenylpy-

ridine-derived Cr/Mn-spiralenes was applied to complex

14 with PhLi as nucleophile and MeOTf as alkylating

agent. The experiment afforded a mixture of two new

compounds of brown and bright orange color, respec-

tively, that could be separated only by recrystallization

and hand sorting of the crystals (eq 9). Recrystallization

of the crude mixture indicated that the orange complex

was the minor component of the solid mixture. A rough

ratio of 15:1 could be established by comparison of the

respective weights of the brown and orange crystals.

Crystals of acceptable quality of both 18 and 19 were

submitted to X-ray diffraction analyses.

Complexes 18 and 19 were thus undoubtedly identi-

fied as products both resulting from the insertion of a

(phenyl)(methoxy)methylidene unit in the C_Ar-Mn

bond of 14. Acquisition and refinement parameters for

18 and 19 are listed in Table 1. Selected interatomic

distances and angles are given in Table 6. The ORTEP

diagram representing complex 18 (Figure 8) clearly

shows the syn-facial relationship between the two metal

centers. The intermetallic distance of 3.137(5) Å that is

Surprisingly, solution ¹H NMR investigations of a

mixture of 18 and 19 did not afford satisfactory results.

(28) (a) Nishio, M.; Hirota, M.; Umezawa, Y. The CH/π Interaction,

Evidence, Nature and Consequences, Methods in Stereochemical Analy-

sis; Marchand, A. P., Ed.; Wiley-VCH: New York, 1998. (b) Umezawa,

Y.; Tsuboyama, S.; Takahashi, H.; Uzawa, J .; Nishio, M. Tetrahedron

1999, 55, 10047.

5494 Organometallics, Vol. 19, No. 25, 2000

Djukic et al.

Ta ble 7. Devia tion s (Å) fr om th e Lea st-Squ a r es

Mea n -P la n e F or m ed by Atom s C13, O4, C11, N,

a n d C12 in Molecu la r Str u ctu r es of Com p lexes 18

a n d 19

atom

18

19

C13

O4

-0.0069

0.045

-0.097

0.082

C11

N

C12

0.001

-0.034

0.058

-0.22

-0.55

0.091

and 19 and the existence of radical species was further

verified by submitting a mixture of the latter two to a

treatment with n-Bu₃SnH in the presence of 2 equiv of

PPh₃in refluxing DME (eq 12). It is well established

that n-Bu₃SnH possesses an affinity for radicals such

•

as Mn(CO)₃L₂(L ) PR₃).²⁹According to analytical data,

this experiment afforded one major product, 20, which

plausibly resulted from the coordination of PPh₃to the

Mn atom of either 18 or 19, small amounts of fac-n-

Bu₃Sn-Mn(CO)₃(PPh₃)₂21, and 22, which presumably

arose from the quenching with n-Bu₃SnH of a biradical

F igu r e 9. ORTEP diagram of the structure of 19. Thermal

ellipsoids are drawn at the 40% probability level. Hydrogen

atoms have been omitted for clarity.

species formed upon homolytical cleavage of the C_benzyl

-

Mn bond in 18 or 19 (eq 11). At this stage of our

investigations the involvement of radical species in the

interconversion process between 18 and 19 is still

unclear.

We first assumed that some molecular fluxionality was

responsible for the low resolution of the measurements

at room temperature. As low-temperature investigations

did not improve at all the quality of the ¹H NMR

spectra, we started to suspect the occurrence of radical

species. ESR investigations of a frozen solution of 18

containing some amount of 19 in degassed CDCl₃

confirmed the presence of paramagnetic species, but the

low resolution of the spectrum precluded any detailed

interpretations. Nonetheless the signal observed at g

) 1.99 suggests that the radical species is likely located

at a carbon or/and a Mn(0) atom.²⁴Difficulties arose

when we attempted the ¹³C NMR characterization of

either 18 or 19. With both complexes, taken as pure as

possible, the resulting ¹³C NMR spectra revealed the

presence in solution of two different species, assumed

to be 18 and 19, in equal proportions and likely in

equilibrium (eq 10).

We nevertheless may state that the ready conversion

of 18 into 19 and vice versa in solution is at least

facilitated by the relative conformational flexibility of

the 2-oxazolinyl heterocycle. To accommodate a η¹:η²

coordination mode involving the Mn atom and the endo-

phenyl group bonded to C16, the chelate must be able

to absorb a part of the strains generated during the

conversion of 18 into 19. This is achieved mainly by

slight distortions of the 2-oxazolinyl ring and a widening

of the C16-Mn-N angle from 85.79(9)° in 18 to 90.56-

(9)° in 19 (Table 6). The distortions of the oxazolinyl

ring are revealed by the deviations of atoms C13, O4,

C11, N, and C12 from the corresponding least-squares

mean planes, which are slightly larger in 19 as com-

pared with 18 (Table 7).

Two sets of poorly resolved ¹³C signals produced by

the Cr(CO)₃and Mn(CO)₃moieties of 18 and 19 could

be detected in addition to the broad signals produced

by the other parts of the molecules. Solution IR inves-

tigations of 18 and 19 afforded identical spectra, whereas

KBr pellet samples afforded different patterns for each

compounds. Thus in the solid state 18 produced a

spectrum composed of two intense A bands at 2009 and

1958 cm^-1and two sets of E-bands with lifted degen-

eracy at 1936 and 1915 cm^-1(Mn(CO)₃) and at 1899

and 1880 cm^-1(Cr(CO)₃); complex 19 afforded a spec-

trum composed of two sets of CO stretching-mode bands

at 2004 (A₁), 1933, 1900 cm^-1(Mn(CO)₃) and at 1957

(A₁), 1887 and 1877 cm^-1(Cr(CO)₃). The lability of 18

Con clu sion

The above-mentioned results establish the interme-

diacy of metal-carbene species and provide new infor-

mation on the process of formation of spiralenes in the

experimental conditions of the sequential reaction of RLi

(29) McCullen, S. B.; Brown, T. L. J . Am. Chem. Soc. 1982, 104,

7496.

Organometallic Helices

Organometallics, Vol. 19, No. 25, 2000 5495

Sch em e 7

expected to be greatly favored with derivatives of

2-phenylpyridine, as the aromatic pyridyl ring is less

flexible than an oxazolinyl. From these considerations,

it appears that the putative intermetallic interactions

between the Cr and Mn (Re) atoms as well as the

intramolecular π-π and CH/π interactions are not

essential in the process of formation of syn-facial het-

erobimetallic complexes. The helicity coding³⁰or direct-

ing effect³¹involved in the process leading to the

organometallic spiralenes mainly arises from the con-

straints brought by the coordination modes of the

chelated-Mn(0) center as well as from the nature of the

chelating organic fragment.

The nature of the incidental intermetallic Cr-Mn

interaction in Cr/Mn-spiralenes is currently being theo-

retically investigated and will be addressed in a future

report. A reasonable part of the above discussion on the

mechanism may likely be extrapolated to the Mn-

spiralene case.

and MeOTf. The stereoselectivity of the cis-migration

step that follows the formation of the metal-carbene

intermediate is seemingly determined by two main

factors. The first one is the relative flexibility of the

organic chelating ligand that will determine the extent

of the subsequent intramolecular structural rearrange-

ments. The second one is the existence of an unsatura-

tion at R,â positions with respect to the carbene carbon

that will condition the degree of stereoselectivity of the

cis-migration step. Notwithstanding the speculative

intermetallic Cr-Mn (Re) interaction in the final bime-

tallic products, the cis-migration step should cause the

Mn (Re) atom to formally “lose” two electrons in its

valence shell and to adopt a formal 16-electron config-

uration upon conversion of the carbene intermediate

into a Cr/Mn-spiralene.

Before the aryl ring moves from one of the equatorial

positions of the Mn-centered octahedron to the carbene

carbon, the carbene moiety may adopt only two confor-

mations that are efficient for the optimal interaction

between the vacant p-orbital of the carbene and the

σ-orbital of the migrating arene carbon (Scheme 7).

Given the octahedral geometry at the manganese atom

and the obvious absence of steric strain for the free

rotation of the carbene moiety around the Mn-C_carbene

axis, it is unlikely that the observed stereoselectivity

of spiralene formation stems from the existence of a

favored conformer of the transient carbene complex.

Therefore, we may rely on Winstein-Holness and

Curtin-Hammett considerations⁸to address the present

mechanistic issues. Hence, a reasonable explanation for

the observed stereoselectivity more probably lies in the

intervention of a late transition state that prefigures

an intermediate with a structure similar to that of 19

(Scheme 7). In such a case the Mn atom would circum-

vent the “loss” of two valence electrons formed during

the cis-migration step by a stabilizing interaction with

an adjacent two-electron ligand such as the Ph group

attached to the former carbene carbon. This would allow

a discrimination between the two carbene conformers

by favoring the one in which the two-electron ligand,

e.g., the phenyl group, is at an accessible position for

the Mn center to interact with it. The formation of the

C_Ar-C_benzylbond thus affords a strained and tense

planar six-membered manganacyclic product which

conformationally may stabilize itself by tilting the Mn-

(CO)₃group toward the Cr(CO)₃tripod. The structural

change from a planar to a boatlike manganacycle is

In conclusion we have further confirmed the inter-

mediacy of metal carbene species in the process leading

to heterobimetallic spiralenes (Scheme 8). We have

found mechanistic evidence that rationalizes the pecu-

liar selectivity observed in the formation of helical

phenyl-substituted spiralenes (Scheme 8). The unprec-

edented fluxionality of the structurally flexible alkyl-

substituted spiralenes has also attracted our attention

(Scheme 8). The intermediacy of biradicals formed upon

homolytic cleavage of the C_benzyl-Mn bond has been

partly evidenced and should be confirmed by further

studies that will be carried out to clarify the influence

of the benzylic carbon substituents over the homolytic

C_benzyl-Mn bond cleavage. In the future, we will con-

centrate our efforts in the development of the “spirogenic

reaction” concept to the construction of elaborated

polynuclear molecules having further applications in

material sciences.

Exp er im en ta l Section

All experiments were carried out under a dry atmosphere

of argon with dry and degassed solvents. The acylrhenate

anion PPN-2 was synthesized by applying a published proce-

dure.¹⁰Solutions of phenyllithium (1.8 M), n-butyllithium (1.8

M), and methyllithium (1.6 M) were purchased from Aldrich

and Fluka companies. NMR spectra were acquired on Bruker

DRX 500 and AC 300 spectrometers at room temperature

unless otherwise stated. Chemical shifts were reported in parts

per million downfield of Me₄Si. IR spectra were measured on

a Perkin-Elmer FT spectrometer. Mass spectra were performed

at the Service of Mass Spectrometry of University Louis

Pasteur and at the Analytical Center of the Chemistry

Institute of the University of Bonn. Elemental analyses

(reported in % mass) were performed at the “Service Central

d’Analyses du CNRS” and at the analytical center of the

Charles Sadron Institute in Strasbourg. ESR experiments were

carried out with a Bruker ESP 300 spectrometer at the Charles

Sadron Institute in Strasbourg.

Exp er im en ta l P r oced u r e for th e X-r a y Diffr a ction

An a lysis of Com p ou n d s 4, 6a , 6b, 9, 18, a n d 19. Acquisition

and processing parameters are displayed in Table 1. Reflec-

tions were collected on a KappaCCD diffractometer using Mo

KR graphite-monochromated radiation (λ ) 0.71073 Å). The

structure was solved using direct methods and refined against

(30) Ohkita, M.; Lehn, J . M.; Baum, G.; Fenske, D. Chem. Eur. J .

1999, 5, 3471.

(31) Katz, T. J . Angew. Chem. Int. Ed. 2000, 39, 1921.

5496 Organometallics, Vol. 19, No. 25, 2000

Djukic et al.

Sch em e 8

|F|. Hydrogen atoms were introduced as fixed contributors. For

9, the absolute structure was determined by refining Flack’s

x parameter (x ) 0.03(3)). For all computations the Nonius

OpenMoleN package was used.³²

150.0, 148.0, 146.0, 141.1, 138.0, 137.0, 129.4, 122.7, 120.1,

117.6, 115.1, 97.9, 94.1, 94.0, 92.0, 60.6 (MeO-C_carbene), 20.3

(Me_py).

Syn th esis of 4. A solution of complex 1 (200 mg, 0.33 mmol)

in 1,2-dimethoxyethane (15 mL) was cooled to -50 °C and

added to a slight excess of PhLi (0.23 mL, 0.41 mmol, 1.8 M

in hexane). The resulting greenish solution was stirred for 30

min and added to an excess of MeOTf (0.1 mL, 0.90 mmol),

which caused the color of the mixture to turn to dark red. The

mixture was warmed to room temperature in 6 h. The solvent

was removed in vacuo and the oily residue dissolved in CH₂-

Cl₂. The solution was added to SiO₂and evaporated to dryness

under reduced pressure. The coated silica gel was loaded on

top of a refrigerated column of SiO₂packed in dry hexane. The

separation was carried out by cooling the column at ca. 10 °C.

Complex 4 was eluted with a mixture of hexane/CH₂Cl₂(20:

80) and the bright orange solution evaporated to dryness. The

resulting solid (117.2 mg, 0.15 mmol, 51% yield) was hence

recrystallized from a mixture of hexane and CH₂Cl₂to afford

yellow-orange crystals. Complex 4: Anal. Calcd for C₂₆H₁₈NO₇-

CrRe‚CH₂Cl₂: C, 41.60; H, 2.59; N, 2.02. Found: C, 42.05; H,

2.45; N, 2.08. IR (CH₂Cl₂) ν(CO): 2015 (s), 1970(s), 1926 (vs),

Sp ectr oscop ic Detection of 3³³by Low -Tem p er a tu r e

¹³C NMR a fter O-Alk yla tion of P P N-2. To a solution of

complex PPN-2 in a NMR sample tube was added an excess

of MeOTf at 203 K. The sample tube was then introduced in

the NMR spectrometer and brought to 223 K. A total number

of 8120 scans were acquired, and the ¹³C NMR spectrum

showed clearly after 78 min the signals of a unique reaction

product, which was identified as carbene complex 3. Warming

the NMR sample tube to room temperature induced the

formation of a new species identified as 4. Complex 3: ¹³C-

{¹H}NMR (CD₂Cl₂, 223 K, 125 MHz): δ 308.0 ((Ph)(MeO)Cd

Re), 231.4 (Cr(CO)₃), 197.3 (1C, Re-CO), 194.7 (2C, Re-CO),

(32) Open Mole N. Interactive Structure Solution; Nonius, B. V.:

Delft, The Netherlands, 1997.

(33) Proposed systematic names for the compounds studied herein

according to IUPAC recommendations for inorganic compounds: 3,

(OC-6-33) exo-(R-methoxybenzylidene)(tricarbonyl){3-methyl,2-[tri-

carbonyl(η⁶-phenyl-κC^2′)chromium], pyridine-κN}rhenium(I); 4, [2-

{2′,3′,4′,5′,6′-η⁵-[1′(R-methoxybenzylidene-κC^R)cyclohexadienyl-κC^1′]-

tricarbonylchromium},3-methylpyridine-κN] tricarbonylrhenium (Cr-

Re); 6a , [2-{2′,3′,4′,5′,6′-η⁵-[1′((exo-R-methoxy)-n-pentylidene-κC^R)-

cyclohexadienyl-κC^1′]tricarbonylchromium},3-methylpyridine-κN] tri-

carbonylmanganese (Cr-Mn); 8a , [2-{2′,3′,4′,5′,6′-η⁵-[1′((exo-R-meth-

oxy)-n-pentylidene-κC^R)cyclohexadienyl-κC^1′]tricarbonylchromium},-

pyridine-κN] tricarbonylmanganese (Cr-Mn); 9, tricarbonyl[6-n-butyl,-

{t r ica r bon yl{η⁶-2′-[(n -bu t yl)(exo-m et h oxy)m et h ylen e-κC^R]ph en -

yl}chromium},3-methyl,3,6-dihydropyridine-κN]manganese(I); 10a ,

[2-{2′,3′,4′,5′,6′-η⁵-{1′[(exo-R-methoxy)-n-ethylidene-κC^R]cyclohexadienyl-

κC^1′}tricarbonylchromium},pyridine-κN]tricarbonylmanganese (Cr-

Mn); 11, 4,4-dimethyl-2-[tricarbonyl(η⁶-phenyl)chromium]-2-oxazoline;

12, 4,4-dimethyl-2-[tricarbonyl(η⁶-para-tolyl)chromium]-2-oxazoline;

13, tetracarbonyl[4,4-dimethyl-2-{tricarbonyl(η⁶-phenyl-κC^2′)chromium}-

2-oxazoline-κN]manganese(I); 14, tetracarbonyl[4,4-dimethyl-2-{tri-

carbonyl(η⁶-para-tolyl-κC^2′)chromium}-2-oxazoline-κN]manganese(I); 15,

4,4-dimethyl-2-[tricarbonyl(η⁶-2′-acetylphenyl)chromium]-2-oxazo-

line; 16, fac-tricarbonyl[4,4-dimethyl-2-{tricarbonyl(η⁶-phenyl-κC^2′)chro-

mium}-2-oxazoline-κN](exo-triphenylphosphine)manganese(I); 17, tri-

carbonyl[2-{tricarbonyl{η⁶-2[(phenyl-κ²C^1′C^2′)phenylmethylene-κC^R]-

phenyl}chromium}pyridine-κN]manganese(I); 18, tricarbonyl[4,4-di-

methyl-2{tricarbonyl{1′,2′,3′,4′,5′,6′-η⁶-4′-methyl, 2′-[(R-exo-methoxy)-

phenylmethylene-κC^R]phenyl}chromium},2-oxazoline]manganese(I); 19,

tricarbonyl[4,4-dimethyl-2{tricarbonyl{1′,2′,3′,4′,5′,6′-η⁶-4′-methyl,2′-

[(R-exo-methoxy)(phenyl-κ²C^1′′C^2′′)methylene-κC^R]phenyl}chromium}-

2-oxazoline]manganese(I).

1

3

1879 (vs) cm^-1. H NMR (CDCl₃): δ 8.25 (d, 1H, H_py, J ) 5.2

Hz), 7.33 (d, 1H, H_orthoPh-endo

³J ) 7.4 Hz), 7.21 (d, 1H,

_orthoPh-endo, ³J ) 7.2 Hz), 7.14 (t, 1H, H_metaPh-endo, ³J ) 7.2 Hz),

6.97 (m, 2H, H_py, H_paraPh-endo), 6.89 (t, 1H, H_metaPh-endo

³J )

7.5 Hz), 6.69 (dd, 1H, H_py, J ) 5.5 Hz, J ) 8.0 Hz), 6.04 (t,

,

H

,

3

1H, H_metaArCr, J ) 6.1 Hz), 5.38 (t, 1H, H_metaArCr, J ) 6.7 Hz),

3

4.88 (d, 1H, H_orthoArCr, J ) 7.1 Hz), 4.45 (dd, 1H, H_orthoArCr, J

4

) 6.3 Hz, J ) 1.0 Hz), 3.21 (s, 3H, MeO-C_benzyl), 1.81 (s, 3H,

Me_py). ¹³C{¹H} NMR (CDCl₃, 258 K): δ 233.9 (Cr-CO), 233.0

(Cr-CO), 227.8 (Cr-CO), 202.0 (Re-CO), 198.1 (Re-CO),

195.0 (Re-CO), 155.8, 151.4, 142.8, 140.5, 133.4, 132.7, 131.9,

129.1, 127.6, 126.8, 123.8, 98.8, 93.3, 92.4, 90.2, 89.7, 83.6, 78.4

(C_benzyl), 55.7 (MeO-C_benzyl), 20.2 (Me_py).

Syn th esis of 6a a n d 6b. 5 (0.20 g, 0.42 mmol), n-BuLi (0.25

mL, 0.40 mmol), and MeOTf (0.10 mL, 0.90 mmol) were used,

with 76% overall conversion (0.17 g). The crude mixture of 6a

and 6b was separated by flash chromatography on SiO₂.

Complex 6a (64 mg, 37%) was eluted with a hexane/CH₂Cl₂

mixture (4:6). Complex 6b (105 mg, 62%) was eluted with a

hexane/CH₂Cl₂mixture (3:7). Complex 6a : Anal. Calcd for

C

₂₄H₂₂NO₇CrMn: C, 53.05; H, 4.08; N, 2.58. Found: C, 53.65;

Organometallic Helices

Organometallics, Vol. 19, No. 25, 2000 5497

H, 4.31; N, 2.48. HRMS (EI) Calcd for C₂₄H₂₂CrMnNO₇:

543.0182. Found (deviation): 543.0175 (0.6 ppm). IR (CH₂Cl₂):

Syn th esis of 9. To a solution of complex 7 (200 mg, 0.44

mmol) in DME (10 mL) at -50 °C was added a solution of

n-BuLi (0.55 mL, 0.88 mmol) in hexane. The resulting mixture

was stirred 30 min and then added to MeOTf (0.19 mL, 1.76

mmol). The solution was slowly brought to room temperature

within 5 h. The resulting solution was evaporated to dryness

under reduced pressure, the residue redissolved in dry CH₂-

Cl₂, and SiO₂added. The solvent was removed in vacuo and

the coated silica gel loaded on top of a column packed with

SiO₂(60 µm) in dry distilled hexane. Complex 9 was eluted

with a mixture of hexane and CH₂Cl₂(3:7) and recovered as a

black microcrystaline powder after removal of the solvents

1

ν(CO) 2005, 1955, 1921, 1888 cm^-1. H NMR (CDCl₃): δ 7.78

(d, J ) 5.4 Hz, 1H, H_py), 7.20 (d, J ) 7.8 Hz, 1H, H_py), 6.69

(dd, ³J ) 7.8 Hz,³J ) 5.4 Hz, 1H, H_py), 6.16 (t, J ) 6.0 Hz, 1H,

H_ArCr), 4.91 (t, J ) 7.6 Hz, 1H, H_ArCr), 4.18 (d, J ) 6.2 Hz, 1H,

H

_ArCr), 4.11 (d, J ) 7.8 Hz, 1H, H_ArCr), 3.67 (s, 3H, OMe), 3.15

(m, 1H, n-Bu), 2.19 (s, 3H, Me), 1.73 (m, 1H, n-Bu), 1.14 (m,

3H, n-Bu), 0.77 (t, J ) 7.3 Hz, 3H, n-Bu), 0.52 (m, 1H, n-Bu)

ppm. ¹³C{¹H} NMR (CDCl₃, 258 K): δ 235.0 (3C, Cr-CO), 231.3

(1C, Mn-CO), 231.2 (1C, Mn-CO), 220.4 (1C, Mn-CO), 157.0,

151.0, 140.7, 129.5, 122.6, 94.4, 90.7, 88.2, 86.3, 84.6, 83.9, 78.0,

54.3 (OMe), 30.7 (1C, n-Bu), 30.0 (1C, n-Bu), 23.1 (1C, n-Bu),

19.8 (Me), 13.9 (1C, n-Bu) ppm. MS (EI): m/e 543.1 [M]⁺, 487.1

[M - 2CO]⁺, 459.1 [M - 3CO]⁺, 375.1 [M - 6CO]⁺, 320.1 [M

- 6CO - Mn]⁺, 286.1, 260.1, 248.0, 220.1, 194.1. Complex 6b:

Anal. Calcd for C₂₄H₂₂NO₇CrMn: C, 53.05; H, 4.08; N, 2.58.

Found: C, 53.21; H, 4.37; N, 2.66. IR (CH₂Cl₂): ν(CO) 2005,

under reduced pressure (146 mg, 55%). Anal. Calcd for C₂₈H₃₂

-

NO₇CrMn: C, 55.91; H, 5.32; N, 2.33. Found: C, 56.07; H, 5.14;

N, 2.30. HRMS (FAB⁺) Calcd for C₂₈H₃₂NO₇CrMn: 601.09643.

Found (deviation): 601.09574 (1 ppm). IR (CH₂Cl₂) ν(CO):

1

2006, 1955, 1932, 1883 cm^-1. H NMR (CDCl₃): δ 6.13 (t, 1H,

H

_ArCr), 5.66 (dd, 1H, H_Hpy), 5.39 (dd, 1H, H_Hpy), 4.94 (ddd, 1H,

1954, 1921, 1894 cm^-1

.

¹H NMR (CDCl₃): δ 7.74 (d, J ) 5.3

H

_ArCr), 4.16 (dd, 1H, H_ArCr), 4.09 (dd, 1H, H_ArCr), 3.69 (s, 3H,

3

MeO-), 3.47 (m, 1H), 2.35 (m, 2H), 1.93 (m, 2H), 1.5-0.8 (m,

18H). ¹³C{¹H} NMR (CD₂Cl₂): δ 234.9 (Cr(CO)₃), 232.0 (Mn-

CO), 230.5 (Mn-CO), 220.2 (Mn-CO), 177.2 (CdN), 128.5

(C_Hpy), 123.1 (C_Hpy), 90.4, 89.9, 88.5, 83.7, 83.0, 82.5, 79.3, 66.1

(C₆), 54.0 (MeO-), 36.3, 33.1, 30.5, 30.2, 28.5, 23.2, 22.4, 18.1,

14.3, 13.9. MS (FAB⁺) m/e: 602.1 [MH]⁺, 517.1 [M - 3CO]⁺,

433.1 [M - 6CO]⁺, 381.2 [M - 6CO - Cr]⁺, 326.3 [M - 6CO

- Cr - Mn]⁺.

Syn th esis of 10a a n d 10b. 7 (0.23 g, 0.50 mmol), MeLi

(0.38 mL, 0.61 mmol), and MeOTf (0.10 mL, 0.90 mmol) were

used, with 33% overall yield (72 mg). Flash chromatography

on SiO₂with a mixture of hexane/CH₂Cl₂(4:6) at - 5 °C yielded

10a (67 mg). Complex 10b could be formed by allowing a

solution of 10a in CH₂Cl₂to equilibrate at room temperature.

Both complexes displayed sensitivity to air and a propensity

to decompose after several hours spent in solution. Complex

10a : Anal. Calcd for C₂₀H₁₄CrMnNO₇: C, 49.30; H, 2.90; N,

2.87. Found: C, 49.42; H, 3.08; N, 3.06. HRMS (EI) Calcd for

Hz, 1H, H_py), 7.17 (d, J ) 7.7 Hz, 1H, H_py), 6.60 (dd, J ) 7.9

3

Hz, J ) 5.4 Hz, 1H, H_py), 6.17 (t, J ) 5.9 Hz, 1H, H_ArCr), 4.75

(t, J ) 7.5 Hz, 1H, H_ArCr), 4.34 (d, J ) 6.2 Hz, 1H, H_ArCr), 3.12

(d, J ) 7.7 Hz, 1H, H_ArCr), 3.06 (s, 3H, OMe), 2.89 (m, 1H,

n-Bu), 2.21 (s, 3H, Me), 1.82 (m, 1H, n-Bu), 1.66 (m, 1H, n-Bu),

1.40 (m, 2H, n-Bu), 0.96 (t, J ) 7.3 Hz, 3H, n-Bu), 0.87 (m,

1H, n-Bu) ppm. ¹³C{¹H} NMR (CDCl₃): δ 234.9 (3C, Cr-CO),

231.1 (1C, Mn-CO), 229.1 (1C, Mn-CO), 220.6 (1C, Mn-CO),

158.9, 150.2, 140.1, 127.6, 121.1, 98.5, 89.5, 87.7, 87.5, 87.1,

81.5, 75.4, 54.0 (OMe), 35.7 (1C, n-Bu), 28.6 (1C, n-Bu), 23.1

(1C, n-Bu), 20.0 (Me), 14.2 (1C, n-Bu) ppm.

Syn th esis of 8a , a n d 8b. 7 (0.30 g, 0.66 mmol), n-BuLi

(0.41 mL, 0.66 mmol), and MeOTf (0.15 mL, 1.36 mmol) were

used, with 68% overall conversion (0.21 g). The mixture of two

products was separated by flash chromatography on SiO₂.

Complex 8a (0.10 g) was eluted with a mixture of hexane/CH₂-

Cl₂(4:6). Further elution with a hexane/CH₂Cl₂mixture (4:6)

yielded 8b (0.11 g). Complex 8a : Anal. Calcd for C₂₃H₂₀

-

C

₂₀H₁₄CrMnNO₇: 486.9556. Found (deviation): 486.9561 (0.5

CrMnNO₇: C, 52.19; H, 3.81; N, 2.65. Found: C, 52.17; H, 4.23;

N, 2.36. HRMS (EI) Calcd for C₂₀H₂₀CrMnNO₄((M - 3CO)⁺):

445.0178. Found (deviation): 445.0173 (0.5 ppm). IR (CH₂Cl₂):

ppm). IR (CH₂Cl₂): ν(CO) 2008, 1958, 1925, 1890 cm^-^{1 1}H

.

NMR (C₆D₆): δ 7.39 (d, J ) 5.5 Hz, 1H, H_py), 6.17 (td, ³J ) 7.8

Hz, J ) 1.4 Hz, 1H, H_py), 5.63 (t, J ) 6.7 Hz, 1H, H_py), 5.44

4

1

ν(CO) 2006, 1957, 1923, 1888 cm^-1. H NMR (CDCl₃): δ 7.89

(d, J ) 7.7 Hz, 1H, H_py), 5.08 (t, J ) 6.2 Hz, 1H, H_ArCr), 4.07

(d, J ) 7.6 Hz, 1H, H_ArCr), 3.96 (t, J ) 6.9 Hz, 1H, H_ArCr), 3.69

(d, J ) 5.4 Hz, 1H, H_py), 7.37 (t, J ) 7.7 Hz, 1H, H_py), 6.83 (t,

J ) 6.6 Hz, 1H, H_py), 6.72 (d, J ) 7.7 Hz, 1H, H_py), 6.23 (t, J

3

4

) 6.0 Hz, 1H, H_ArCr), 5.01 (ddd,³J ) 7.5 Hz, J ) 6.1 Hz, J )

(s, 3H, OMe), 2.94 (dd, J ) 6.1 Hz, 4J ) 1.2 Hz, 1H, H_ArCr),

1.75 (s, 3H, Me) ppm. Complex 10b: ¹H NMR (C₆D₆): δ 7.33

(d, 1H, H_py), 6.28 (td, 1H, H_py), 5.68 (m, 2H, H_py), 5.10 (t, 1H,),

3.80 (t, 1H, H_ArCr), 3.11 (dd, 1H, H_ArCr), 2.91 (s, 3H, -OMe),

2.59 (d, 1H, H_ArCr), 2.03 (s, 3H, Me) ppm. MS (EI): m/e 487.0

[M]⁺, 431.1 [M - 2CO]⁺, 403.1 [M - 3CO]⁺, 347.1 [M - 5CO]⁺,

319.1 [M - 6CO]⁺, 264.1 [M - 6CO - Mn]⁺, 234.1, 206.0,

180.1. Due to equilibration between the two complexes, the

¹³C NMR spectra could not be measured separately for 10a

and 10b even at a lower temperatures. The following data are

those obtained with the corresponding mixture. ¹³C{¹H} NMR

(CDCl₃, 258 K): δ 234.7 (Cr-CO), 231.8 (Mn-CO), 230.6 (Mn-

CO), 230.5 (Mn-CO), 229.6 (Mn-CO), 221.2 (Mn-CO), 220.9

(Mn-CO), 160.6, 159.8, 153.5, 152.7, 138.9, 138.3, 124.0, 122.9,

118.1, 116.3, 98.0, 93.7, 91.6, 91.2, 91.0, 90.4, 87.3, 86.5, 85.8,

83.7, 83.3, 79.9, 79.0, 76.6, 54.9, 54.5, 23.0, 20.6 ppm.

1.2 Hz, 1H, H_ArCr), 4.23 (dd, ³J ) 6.1 Hz, ⁴J ) 1.2 Hz, 1H,

_ArCr), 4.16 (d, J ) 7.5 Hz, 1H, H_ArCr), 3.68 (s, 3H, OMe), 3.19

H

(m, 1H, n-Bu), 1.69 (m, 1H, n-Bu), 1.15-0.8 (m, 3H, n-Bu),

0.75 (t, 3H, n-Bu), 0.70 (m, 1H, n-Bu) ppm. ¹³C{¹H} NMR

(CDCl₃, 258 K): δ 236.1 (3C, Cr-CO), 231.8 (1C, Mn-CO),

230.6 (1C, Mn-CO), 220.4 (1C, Mn-CO), 159.3, 153.1, 138.3,

123.7, 117.3, 92.9, 91.1, 90.3, 85.5, 83.7, 83.5, 77.9, 54.4 (OMe),

31.0 (1C, n-Bu), 29.9 (1C, n-Bu), 22.8 (1C, n-Bu), 14.3 (1C,

n-Bu) ppm. MS (EI): m/e 529.0 [M]⁺, 473.0 [M - 2CO]⁺, 445.0

[M - 3CO]⁺, 361.0 [M - 6CO]⁺, 306.1 [M - 6CO - Mn]⁺,

275.0, 234.0, 206.0, 180.1. Complex 8b: HRMS (EI) Calcd for

C

₂₃H₂₀CrMnNO₇: 529.0025. Found (deviation): 529.0023 (0.2

ppm). IR (CH₂Cl₂): ν(CO) 2006, 1956, 1923, 1896 cm^-^{1 1}H

.

NMR (CDCl₃): δ 7.88 (d, J ) 4.8 Hz, 1H, H_py), 7.35 (t, J ) 7.7

Hz, 1H, H_py), 6.76 (t, J ) 6.6 Hz, 1H, H_py), 6.70 (d, J ) 7.7 Hz,

1H, H_py), 6.24 (t, J ) 5.9 Hz, 1H, H_ArCr), 4.86 (t, J ) 6.7 Hz,

1H, H_ArCr), 4.37 (d, J ) 6.2 Hz, 1H, H_ArCr), 3.21 (d, J ) 7.5 Hz,

1H, H_ArCr), 3.14 (s, 3H, OMe), 3.09 (m, 1H, n-Bu), 1.79 (m, 1H,

n-Bu), 1.68 (m, 1H, n-Bu), 1.59 (m, 1H, n-Bu), 1.37 (m, 2H,

n-Bu), 0.93 (t, J ) 7.3 Hz, 3H, n-Bu) ppm. ¹³C{¹H} NMR

(CDCl₃, 258 K): δ 236.4 (1C, Cr-CO), 234.4 (1C, Cr-CO), 231.8

(1C, Cr-CO), 230.5 (1C, Mn-CO), 229.4 (1C, Mn-CO), 220.5

(1C, Mn-CO), 160.8, 152.5, 137.8, 122.3, 115.7, 96.4, 90.0, 89.4,

86.8, 86.6, 80.2, 75.6, 54.0 (1C, OMe), 36.0 (1C, n-Bu), 28.4

(1C, n-Bu), 23.1 (1C, n-Bu), 14.4 (1C, n-Bu) ppm. MS (EI): m/e

529.0 [M]⁺, 473.0 [M - 2CO]⁺, 445.0 [M - 3CO]⁺, 361.0 [M -

6CO]⁺, 306.1 [M - 6CO - Mn]⁺, 274.0, 234.0, 206.0, 180.0.

Isom er iza tion of Com p lex 8a in Com p lex 8b. A solution

of complex 8a in CDCl₃was prepared in an NMR tube under

an atmosphere of argon and degassed. The evolution of the

composition of the solution was followed by acquiring a series

of three free induction decays at t ) 0, t ) 24 h, and t ) 48 h

at 20 °C. Proportions in complexes 8a and 8b were calculated

by comparison of the intensity of the methoxy group signal in

8a (δ ) 3.68 ppm) and the intensity of the methoxy group

signal in 8b (3.14 ppm). The same experiment was carried out

by starting from a solution enriched in 8b.

¹H NMR Mon itor in g of th e Isom er iza tion of 10a in to

10b. A solution of complex 10a (8.6 mg) and reference (1,3,5-

5498 Organometallics, Vol. 19, No. 25, 2000

Djukic et al.

tris(terbutyl)benzene, 2.3 mg) in 0.75 mL of C₆D₆was prepared

in an NMR tube under a dry atmosphere of argon, degassed,

and frozen. Scans were acquired on a Bruker AC300 spec-

trometer at 20 °C by using Bruker’s software KINETICS.

Chosen delays between recordings were the following: 20

spectra recorded with a 2 min delay, 10 spectra recorded with

a 5 min delay, 6 spectra recorded with a 10 min delay, 9

spectra recorded with a 30 min delay, 9 spectra recorded with

a 60 min delay. Calibration of the temperature was ac-

complished with a sample of ethylene glycol. The concentration

in complex 10a was calculated by comparison of the intensity

of the methyl group signal (δ ) 1.75 ppm) with that of the

reference signal. For reaction times longer than 5 h, decom-

position in the NMR sample tube precluded further investiga-

tions.

raised to room temperature during 3 h. The color of the

mixture changed from bright orange to deep red-brown. The

reaction mixture was stirred overnight and the vessel opened

to air. The brownish suspension that formed was filtered

through a plug of Celite. The resulting solution was mixed with

silica gel and the solvent removed under reduced pressure.

The resulting coated silica gel was loaded on top of a silica gel

column that was packed in hexane. Flash chromatography on

SiO₂and elution with a CH₂Cl₂/MeOH (98:2) mixture yielded

an orange solution of complex 15 (80 mg, 54%). Anal. Calcd

for C₁₆H₁₅NO₅Cr: C, 54.39; H, 4.28; N, 3.96. Found: C, 54.22;

H, 4.33; N, 4.00. IR (CH₂Cl₂) ν(CO): 1983 (s), 1914 (s), 1654

1

3

(m) cm^-1. H NMR (CDCl₃): δ 5.73 (d, 1H, J ) 6.4 Hz, H_ArCr),

5.47 (m, 2H, H_ArCr), 5.30 (t, 1H, ³J ) 6.1 Hz, H_ArCr), 4.10 (d,

3

1H, J ) 8.3 Hz, O-CH₂-), 4.05 (d, 1H, J ) 8.3 Hz, O-CH₂-

), 2.51 (s, 3H, -C(O)Me), 1.36 (s, 3H, -Me), 1.33 (s, 3H, -Me).

¹³C{¹H} NMR (CDCl₃): δ 230.6 (Cr-CO), 198.5 (-C(O)Me),

159.7 (CdN), 107.9 (C_ArCr), 92.1 (C_ArCr), 91.6 (C_ArCr), 90.3 (C_ArCr),

89.2 (C_ArCr), 80.0 (O-CH₂), 79.7 (C_ArCr), 68.6 (-N-CMe₂), 30.2

(-C(O)Me), 28.1 (-N-CMe₂), 27.9 (-N-CMe₂).

P r ep a r a tion of 11.³⁴Cr(CO)₆(3.2 g, 14.5 mmol), 4,4-

dimethyl-2-phenyl-2-oxazoline (2.5 g, 14.3 mmol), THF (15

mL), and DBE (150 mL) were refluxed for 36 h. Chromatog-

raphy was performed on SiO₂/CH₂Cl₂; 77% yield (3.42 g). IR

1

(CH₂Cl₂) ν(CO): 1975, 1898 cm^-1. H NMR (CDCl₃): δ 5.96 (d,

2H, J ) 5.6 Hz, H_ArCr), 5.36 (m, 3H, H_ArCr), 4.08 (s, 2H, -O-

CH₂), 1.35 (s, 6H, Me). ¹³C{¹H} NMR (CDCl₃): δ 231.5 (Cr-

CO), 159.9 (CdN), 92.5 (C_ArCr), 92.1 (2C_ArCr), 91.5 (C_ArCr), 90.9

(2C_ArCr), 79.5, 67.9, 28.1 (2CH₃).

Syn th esis of 16. Complex 13 (0.15 g, 0.31 mmol) and an

excess of triphenylphosphine (0.25 g, 0.94 mmol) were dis-

solved in dry degassed heptane (10 mL) and brought to reflux

during 5 h. The resulting red solution was stripped of solvent,

the resulting residue dissolved in CH₂Cl₂, and silica gel added.

The solvent was evaporated under reduced pressure and the

coated silica gel loaded on top of a SiO₂column packed in

hexane. Chromatography on SiO₂/hexane:CH₂Cl₂(6:4) yielded

P r ep a r a tion of 12. Cr(CO)₆(2.4 g, 10.9 mmol), 4,4-

dimethyl-2-p-tolyl-2-oxazoline (2-p-tolyl,4,4-dimethyl,3-aza,1-

oxa,cyclopent-2-ene) (2.0 g, 10.6 mmol), THF (8 mL), and DBE

(80 mL) were refluxed for 36 h. Chromatography was done

on SiO₂/CH₂Cl₂:acetone (8:2); 44% yield (1.52 g). HRMS

(FAB) Calcd for C₁₅H₁₅NO₄Cr: 325.040618. Found (devia-

tion): 325.040920 (0.9 ppm). IR (CH₂Cl₂) ν(CO): 1972, 1894

an orange-red complex (77%, 0.17 g). Anal. Calcd for C₃₅H₂₇

-

NO₇CrMnP‚CH₂Cl₂: C, 54.29; H, 3.67; N, 1.76. Found: C, 54.18;

H, 3.85; N, 1.86. IR (CH₂Cl₂): ν(CO) 2015, 1955, 1896 cm^-1

.

1

cm^-1. H NMR (CDCl₃): δ 6.02 (d, 2H, J ) 6.0 Hz, H_ArCr), 5.15

¹H NMR (CDCl₃): δ 7.31-7.26 (m, 15H, PPh₃), 5.85 (d, 1H, J

(d, 2H, J ) 6.0 Hz, H_ArCr), 4.04 (s, 2H, -O-CH₂), 2.20 (s, 3H,

Me_Ar), 1.31 (s, 6H, Me_oxazoline) ppm. ¹³C{¹H} NMR (CDCl₃): δ

231.0 (Cr(CO)₃), 159.7 (CdN), 109.5 (C_ArCr), 93.6 (2C_ArCr), 91.1

(2C_ArCr), 88.8 (C_ArCr), 79.4, 67.7, 28.1 (2CH₃), 20.5 (CH₃) ppm.

MS (FAB⁺): m/e 326.1 [M + H]⁺, 269.2 [M - 2CO]⁺, 241.2 [M

- 3CO]⁺, 190.2 [MH - 3CO - Cr]⁺.

Syn th esis of 13. Complex 11 (1.06 g, 3.4 mmol), [Mn(CO)₅-

(PhCH₂)] (1.17 g, 4.1 mmol), and heptane (25 mL) were

refluxed for 8 h. Chromatography was performed on SiO₂/

3

) 6.3 Hz, H_ArCr), 5.25-5.18 (m, 2H, H_ArCr), 4.66 (td, 1H, J )

6.0 Hz, ⁴J ) 1.5 Hz, H_ArCr), 4.34 (d, 1H, J ) 8.3 Hz, -O-CH₂),

3.73 (d, 1H, J ) 8.3 Hz, -O-CH₂), 1.41 (s, 3H, Me), 0.44 (s,

3H, Me). ³¹P NMR (CDCl₃): δ 49.32 (s, 1P, PPh₃). ¹³C{¹H} NMR

(CDCl₃): δ 235.4 (Cr-CO), 223.7 (d, 1C, J ) 21.4 Hz, Mn-

CO), 219.4 (d, 1C, J ) 16.3 Hz, Mn-CO), 216.9 (d, 1C, J )

24.4 Hz, Mn-CO), 172.4 (CdN), 151.2 (d, 1C, J ) 20.6 Hz,

C

_ArCr-ipso), 133.6-133.3 (m, 9C, PPh₃), 129.9 (s, 3C, PPh₃), 128.3

(d, 6C, J ) 8.1 Hz, PPh₃), 107.8, 101.8, 93.6, 90.1, 87.1, 81.8,

67.7, 29.2 (Me), 24.0 (Me).

hexane:CH₂Cl₂(5:5); 96% yield (1.56 g). Anal. Calcd for C₁₈H₁₂

-

NO₈CrMn: C, 45.30; H, 2.53; N, 2.93. Found: C, 44.95; H, 2.49;

N, 2.84. IR (CH₂Cl₂) ν(CO): 2086, 2005, 1988, 1958, 1945, 1886

cm^-1. ¹H NMR (CDCl₃): δ 6.10 (d, 1H, J ) 6.4 Hz, H_ArCr), 5.52-

5.45 (m, 2H, H_ArCr), 5.24 (t, 1H, J ) 6.1 Hz, H_ArCr), 4.52 (d,

1H, J ) 8.5 Hz, -O-CH₂), 4.47 (d, 1H, J ) 8.5 Hz, -O-CH₂),

1.47 (s, 3H, Me), 1.43 (s, 3H, Me). ¹³C{¹H} NMR (CDCl₃): δ

234.6 (Cr-CO), 218.5 (Mn-CO), 213.7 (Mn-CO), 210.8 (Mn-

CO), 209.4 (Mn-CO), 172.8 (CdN), 137.1, 106.8, 100.5, 93.7,

91.8, 88.7, 82.6, 66.8, 27.6 (Me), 27.2 (Me).

Syn th esis of 17. Compound 13 (97 mg, 0.20 mmol) and N₂d

CPh₂(120 mg, 0.60 mmol) were dissolved in dry and degassed

heptane. The mixture was then brought to reflux for 1 h until

a reddish precipitate appeared. An additional amount of N₂d

CPh₂(120 mg, 0.60 mmol) was added to the medium, and the

suspension was refluxed for additional 30 min. The reaction

mixture was then cooled to room temperature and the solvent

evaporated under reduced pressure to afford a solid. The latter

was dissolved in CH₂Cl₂, and SiO₂was added. The solvent was

evaporated in vacuo and the coated silica gel loaded on top of

a SiO₂column packed in hexane. Chromatography on SiO₂and

elution with a hexane/CH₂Cl₂mixture (5:5) yielded an orange-

red complex (69%, 85 mg). Anal. Calcd for C₃₀H₂₂NO₇CrMn‚

1/4CH₂Cl₂: C, 57.07; H, 3.56; N, 2.20. Found: C, 56.91; H, 3.60;

N, 2.20. HRMS (FAB⁺) Calcd for C₂₇H₂₂CrMnNO₄([M -

3CO]⁺): 531.033439. Found (deviation): 531.033147 (0.3 ppm).

Syn th esis of 14. Complex 12 (0.5 g, 1.5 mmol), [Mn(CO)₅-

(PhCH₂)] (0.66 g, 2.3 mmol), and heptane (15 mL) were

refluxed for 8 h. Chromatography was performed on SiO₂/

hexane:CH₂Cl₂(6:4); 86% yield (0.65 g). Anal. Calcd for C₁₉H₁₄

-

NO₈CrMn: C, 46.45; H, 2.87; N, 2.85. Found: C, 46.49; H, 2.92;

N, 2.82. IR (CH₂Cl₂): ν(CO) 2086.3, 2002.8, 1987.2, 1953.2,

1

4

1942.3, 1882.2 cm^-1. H NMR (CDCl₃): δ 5.98 (d, 1H, J ) 1.0

3

Hz, H_ArCr), 5.54 (d, 1H, J ) 6.6 Hz, H_ArCr), 5.33 (dd, 1H, J )

6.6 Hz, ⁴J ) 1.1 Hz, H_ArCr), 4.48 (d, 1H, ³J ) 8.5 Hz, -O-

CH₂-), 4.43 (d, 1H, ³J ) 8.5 Hz, -O-CH₂-), 2.22 (s, 3H, Me),

1.45 (s, 3H, Me), 1.41 (s, 3H, Me). ¹³C{¹H} NMR (CDCl₃): δ

234.5 (Cr-CO), 218.5 (Mn-CO), 213.6 (Mn-CO), 210.8 (Mn-

CO), 209.3 (Mn-CO), 172.5 (CdN), 139.3, 108.3, 107.6, 98.4,

93.8, 89.6, 82.5, 66.7, 27.5 (Me), 27.3 (Me), 21.1 (Me).

IR (CH₂Cl₂) ν(CO): 2004, 1985, 1903 (broad) cm^-^{1 1}H NMR

.

(CDCl₃): δ 8.18 (br, 1H), 7.73 (d, 1H, J ) 7.6 Hz), 7.62 (br,

2H), 7.41 (t, 1H, J ) 6.8 Hz), 7.29 (t, 1H, J ) 7.3 Hz), 7.21-

7.08 (m, 2H), 6.61 (d, 1H, J ) 7.6 Hz), 5.97 (d, 1H, J ) 6.6 Hz,

H

_Ar), 5.79 (br, 1H), 5.43 (t, 1H, J ) 6.5 Hz, H_Ar), 5.30 (t, 1H, J

) 6.2 Hz, H_Ar), 5.20 (d, 1H, J ) 7.1 Hz, H_Ar), 4.22 (d, 1H, J )

8.3 Hz, -O-CH₂-), 3.72 (d, 1H, J ) 8.3 Hz, -O-CH₂-), 1.13

(s, 3H), 0.54 (s, 3H). ¹³C{¹H} NMR (CDCl₃, T ) 263 K): δ 232.5

(Cr-CO), 229.5 (Mn-CO), 220.4 (Mn-CO), 220.2 (Mn-CO),

163.8 (CdN), 147.7, 137.4, 135.7, 132.1, 130.6, 129.4, 128.7,

128.2, 126.8, 126.0, 123.5, 116.7, 94.9, 94.4, 93.9, 93.5, 88.1,

87.8, 79.5, 71.3, 61.4, 26.8 (N-CMe₂), 25.1 (N-CMe₂). MS

Syn th esis of 15. To a solution of 13 (0.20 g, 0.42 mmol) in

dry DME (10 mL) was added MeLi (0.34 mL, 0.54 mmol) at

-50 °C. The temperature of the reaction mixture was slowly

(34) Ku¨ndig, E. P.; Ripa, A.; Liu, R.; Amurrio, D.; Bernardinelli, G.

Organometallics 1993, 12, 3724.

Organometallic Helices

Organometallics, Vol. 19, No. 25, 2000 5499

2

(FAB⁺): m/e 615.1 [M]⁺, 531.1 [M - 3CO]⁺, 504.1[M - 4CO +

H]⁺, 395.1 [M - 6CO - Cr]⁺, 341.2 [M - 6CO - Cr - Mn]⁺.

P r ep a r a tion of 18, a n d 19. 14 (0.20 g, 0.41 mmol), PhLi

(0.25 mL, 0.45 mmol), MeOTf (0.07 mL, 0.63 mmol) were used.

Chromatography of the crude mixture on silica gel afforded

after elution with a hexane/CH₂Cl₂mixture (4:6) a 10:1

mixture of the two complexes 18 and 19, respectively (0.16 g,

67% overall conversion). Careful recrystallization in a mixture

of CH₂Cl₂/hexane at -18 °C allowed the isolation of pure

samples of complexes 18 (dark brown crystals) and 19 (orange

crystals). Complex 18: Anal. Calcd for C₂₆H₂₂CrMnNO₈: C,

53.33; H, 3.80; N, 2.40. Found: C, 53.46; H, 3.82; N, 2.34.

HRMS (FAB⁺) Calcd for C₂₆H₂₂CrMnNO₈: 583.013098. Found

(deviation): 583.012911 (0.3 ppm). IR (CH₂Cl₂): ν(CO) 2011,

1963, 1926, 1892 cm^-1. IR (KBr) ν(CO): 2009, 1958, 1936, 1915,

1899, 1880 cm^-1. MS (FAB⁺): m/e 583.2 [M]⁺, 499.2 [M -

3CO]⁺, 415.2 [M - 6CO]⁺, 361.2 [MH - 6CO - Mn]⁺. Complex

19: HRMS (FAB⁺) Calcd for C₂₆H₂₂CrMnNO₈: 583.013098.

Found (deviation): 583.012466 (1.1 ppm). IR (CH₂Cl₂) ν(CO):

2010, 1964, 1926, 1893 cm^-1. IR (KBr) ν(CO): 2004, 1957, 1933,

1900 (sh), 1887, 1877 cm^-1. MS (FAB⁺): m/e 583.2 [M]⁺, 499.2

[M - 3CO]⁺, 415.2 [M - 6CO]⁺, 364.5 [M - 6CO - Cr + H]⁺,

308.3 [M - 6CO - Cr - Mn]⁺.

Rea ction of 18 a n d 19 w ith n -Bu ₃Sn H a n d P P h ₃. A

mixture of 18 and 19 (82 mg, 0.14 mmol) was dissolved in DME

(20 mL) and added with n-Bu₃SnH (0.08 mL, 0.28 mmol) and

PPh₃(120 mg, 0.46 mmol). The solution was then brought to

reflux during 10 min, allowed to cool to room temperature,

and stirred overnight. The color of the solution changed from

dark brown to bright red. The mixture was then stripped of

solvents and the solid residue redissolved in CH₂Cl₂. The

solution was added with SiO₂and evaporated to dryness under

reduced pressure. The resulting coated silica gel was loaded

on top of a SiO₂column packed in hexane under argon and

cooled to 5 °C. Complex 21 was eluted with a mixture of 10%

CH₂Cl₂in hexane and recovered after removal of the solvents

as a pale yellow solid (10 mg, 7.5% yield). Complex 20 was

eluted with a mixture of 50% CH₂Cl₂in hexane and recovered

as an orange powder after removal of the solvents (64 mg,

54%). Complex 22 was eluted with a mixture of 80% CH₂Cl₂

in hexane and recovered as a yellow oily residue after removal

of the solvents (less than 10 mg). Complex 20: Anal. Calcd

for C₄₄H₃₇NO₈PCrMn‚1/2CH₂Cl₂: C, 60.21; H, 4.26; N, 1.66.

Found: C, 60.74; H, 4.37; N, 1.52. HRMS (FAB⁺) Calcd for

8.0 Hz, -CH₂-O-), 3.57 (d, 1H, J ) 8 Hz, -CH₂-O-), 3.42

(s, 3H, MeO-), 1.92 (s, 3H, p-Me-Ar_Cr), 1.34 (s, 3H, -(Me)₂C-

O-), -0.04 (s, 3H, -(Me)₂C-O-). ³¹P NMR (CDCl₃): δ 50.7.

¹³C{¹H} NMR (CDCl₃, 283 K): δ 235.3 (Cr(CO)₃), 224.3 (d, J _C-P

) 14.4 Hz, Mn-CO), 219.2 (d, J _C-P) 11.4 Hz, Mn-CO), 216.3

(d, J _C-P) 15.1 Hz, Mn-CO), 172.7, 156.0, 155.9, 141.7, 133.9,

133.7, 133.4 (d, 6C, J _C-P) 5.3 Hz, PPh₃), 129.9 (3C, PPh₃),

128.8, 128.7 (d, 3C, J _C-P) 23.5 Hz, PPh₃), 128.2 (d, 6C, J _C-P

) 4.5 Hz, PPh₃), 109.4, 108.3, 106.5, 95.3, 91.1, 81.3, 79.9, 67.2,

57.6, 29.1, 22.3, 21.3. MS (FAB⁺): m/e 845.0 [M]⁺, 761.0, 677.1,

625.1, 611.0, 527.0, 499.0, 415.0. Complex 21: HRMS (FAB⁺)

Calcd for C₅₁H₅₇P₂O₃Mn¹²⁰Sn: 954.21854. Found (deviation):

954.21845 (0.1 ppm). IR (CH₂Cl₂) ν(CO): 1958 (m), 1877 (s)

cm^-1. H NMR (C₆D₆): δ 7.85 (m, 12H, PPh₃), 7.11-6.95 (m,

1

18H, PPh₃), 1.61 (m, 6H, PPh₃), 1.39 (m, 6H, n-Bu), 1.07-0.93

(m, 30H, n-Bu). ³¹P NMR (C₆D₆): δ 75.5. MS (FAB⁺): m/e 954.1

[M]⁺, 897.0 [M - n-Bu]⁺, 663 [M - n-Bu₃Sn - H]⁺, 579 [M -

n-Bu₃Sn - H - 3CO]⁺, 374 [M - n-Bu₃Sn - CO - PPh₃]⁺,

318 [M - n-Bu₃Sn - 3CO - PPh₃]⁺. Complex 22: IR (KBr)

ν(CO): 1956, 1883 cm^-1

.

¹H NMR (CD₂Cl₂): δ 7.50-6.90 (m,

2

5H, Ph), 6.37 (m, 1H, Ar_Cr), 5.98 (s, 1H, Ar_Cr), 5.86 (d, 1H, J

) 6.6 Hz, -CH₂-O-), 5.71 (m, 1H, Ar_Cr), 5.02 (d, 1H, ²J ) 6.6

Hz, -CH₂-O-), 3.89 (s, 1H, -CH(Ph)(OMe)), 3.28 (s, 3H,

MeO-), 2.18 (s, 3H, p-Me-Ar_Cr), 1.47 (s, 3H, -(Me)₂C-), 1.06

(s, 3H, -(Me)₂C-). ¹³C{¹H} NMR (278 K, CDCl₃): δ 232.3 (s,

Cr(CO)₃), 160.1, 140.4, 128.2, 115.7, 115.3, 114.1, 109.9, 95.8,

89.9, 88.3, 86.9, 79.0, 78.9, 67.4 (MeO-), 57.0 (-CH₂O-), 28.1

(Me₂C), 20.9 (Me₂C). MS (FAB⁺): m/e 446.2 [MH]⁺, 414.1 [MH

- CH₃OH]⁺, 391.3 [MH - 2CO]⁺, 361.2 [M - 3CO]⁺, 310.2

[MH - 3CO - Cr]⁺.

Ack n ow led gm en t. We thank the Deutscher Aka-

demischer Austauschdienst (DAAD), the Deutsche

Forchung Gemeinschaft (DFG), the Alexander von

Humboldt Foundation (AvH Stiftung), and the Centre

National de la Recherche Scientifique (CNRS) for sup-

porting this work. We gratefully acknowledge the as-

sistance provided by Ulrike Weynand (Kekule´ Institut-

Bonn) for the ¹³C NMR low-temperature experiments

and thank Rouben Allagapen (Strasbourg) for his

contribution to this work.

Su p p or tin g In for m a tion Ava ila ble: ESR spectra of

compounds 8a and 18, tables of crystal data, and complete lists

of structural information for compounds 4, 6a , 6b, 9, 18, and

19 (refined atomic coordinates, anisotropic thermal param-

eters, interatomic distances and angles). This material is

available free of charge via the Internet at http://pubs.acs.org.

C

₄₄H₃₇NO₈PCrMn: 845.10424. Found (deviation): 845.10436

(0.1 ppm). IR (CH₂Cl₂) ν(CO): 2012, 1947, 1894, 1876 cm^-1

.

¹H NMR (CDCl₃): δ 7.54 (t, 2H, J ) 7.3 Hz, Ph), 7.47 (t, 1H,

3

³J ) 7.4 Hz, Ph), 7.29 (m, 5H, Ph + PPh₃), 7.13 (t, 6H, J )

3

7.5 Hz, PPh₃), 6.96 (t, 6H, ³J ) 8.8 Hz, PPh₃), 5.73 (m, 1H,

2

Ar_Cr), 5.68 (m, 1H, Ar_Cr), 5.58 (s, 1H, Ar_Cr), 4.35 (d, 1H, J )

OM0006920

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Organometallic helices: the mechanism of formation of 'metallospiralenes'

DOI: 10.1021/om0006920

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