Controlled nucleophilic activation of different sites in [Mo 2Cp2L2(μ-SMe)2(μ-L′)] + cations (L = ButNC, xylNC, CO; L′ = SMe or PPh2)

Journal of Organometallic Chemistry 690 (2005) 4583–4601

www.elsevier.com/locate/jorganchem

Controlled nucleophilic activation of diﬀerent sites

in [Mo₂Cp₂L₂(l-SMe)₂(l-L⁰)]⁺cations

(L = Bu^tNC, xylNC, CO; L⁰= SMe or PPh₂)

a

a,

a

,a

Nolwenn Cabon , Franc¸ois Y. Petillon ^*, Pierre-Yves Orain , Philippe Schollhammer ^*

,

´

a

,b

*

Jean Talarmin , Kenneth W. Muir

a

UMR CNRS 6521 ‘‘Chimie, Electrochimie Mole´culaires et Chimie Analytique’’, UFR Sciences et Techniques,

Universite´ de Bretagne Occidentale, CS 93837, 29238 Brest-cedex 3, France

b

Chemistry Department, University of Glasgow, Glasgow G12 8QQ, UK

Received 24 May 2005; accepted 4 July 2005

Available online 19 August 2005

Abstract

The thiolato-bridged binuclear molybdenum complexes [Mo₂Cp₂L₂(l-SMe)₂(l-L⁰)]Y (Cp = g⁵-C₅H₅; L⁰= SMe, L = Bu^tNC

(1a), xylNC (1b) or CO (3); L⁰= PPh₂, L = Bu^tNC (16); Y = BF₄, Cl) react with the anionic reagents NaBH₄, NaBD₄, LiR

(R = Me, Buⁿ), R⁰MgCl (R⁰= Me, Prⁱ, Buⁿor Ph). The products are unsubstituted (5, 7) or substituted (8–12) g⁴-cyclopentadiene

derivatives, [Mo₂(g⁵-C₅H₅)(g⁴-C₅H₅R)L₂(l-SMe)₃] (L = xylNC, CO), or l-formimidoyl dinuclear products, [Mo₂Cp₂L₂(l-

SMe)₂(l-L⁰)(l-CHNR)] (L⁰= SMe, L = Bu^tNC (4) or xylNC (6); L⁰= PPh₂, L = Bu^tNC (17)). Since the reduced dinuclear species

[Mo₂Cp₂(CO)₂(l-SMe)₂] and the related oxo-compound [Mo₂Cp₂(CO)(O)(l-SMe)₂] are sometimes isolated as minor products, the

anionic reagent can play a secondary role as a reductant in these reactions in addition to its main role as a nucleophile. The elec-

tronic properties of the donor carbon atoms of the cyclopentadienyl rings and of the terminal ligands L, together with the nature of

the anionic reagent, are the dominant factors controlling selective formation of 4–12 and 17. Tetraﬂuoroboric acid reacts with the

substituted cyclopentadiene derivatives 9, 11 and 12 to form new functionalised cyclopentadienyl derivatives, [Mo₂(g⁵-C₅H₅)(g⁵-

C₅H₄R)(CO)₂(l-SMe)₃](BF₄) (R = Me (13), Buⁿ(14) or Ph (15)). New complexes have been characterised by spectroscopic and

chemical methods, supplemented for 5, 6 and 12 by X-ray diﬀraction studies at 100 K.

Keywords: Dimolybdenum complexes; Cyclopentadienyl; Cyclopentadiene; Thiolato-bridged complexes; Crystal structure; Isocyanide liagand; C-

arbonyl ligand; Formyl ligand; Nucleophilic activation

1. Introduction

Y = anion) can lead to scission of the M–M bond.

Alternatively, the unsaturated ligands oﬀer several sites

at which reaction can occur. In addition, with poly(l-

thiolato) complexes, where L⁰= SMe for example, there

is the further possibility of C–S bond cleavage promoted

by nucleophilic attack [1]. The extent to which these

reactions are selective depends to a large extent on the

relative Lewis acidities of the metal and ligand sites.

These comments are prompted in part by our earlier

study of the action of various nucleophiles on the

cations [Mo₂Cp₂L₂(l-SMe)₃]⁺(L = RNC (1), MeCN

Nucleophilic addition to the coordinatively saturated

metal ions in [M₂Cp₂L₂L⁰_n]Y complexes (M = transition

metal; Cp = g⁵-C₅H₅; L = terminal two electron-donor

ligand; L⁰= bridging three electron-donor ligand;

*

Corresponding author.

´

E-mail addresses: francois.petillon@univ-brest.fr (F.Y. Petillon),

schollhal@uni-brest.fr (P. Schollhammer), ken@chem.gla.ac.uk (K.W.

Muir).

doi:10.1016/j.jorganchem.2005.07.034

4584

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

(2) or CO (3)). Thus, we have shown that 2 reacts with

NaBH₄to yield two products: substitution of both ter-

minal MeCN ligands leads to the l-borohydride deriva-

tive [Mo₂Cp₂(l-BH₄)(l-SMe)₃], whereas nucleophilic

addition of hydride to one of the nitrile ligands gives

the l-azavinylidene compound [Mo₂Cp₂(l-N@CHMe)-

(l-SMe)₃] [2]. In addition, nucleophilic attack on 1a

(R = Bu^t) by LiBuⁿis directed at an isocyanide ligand,

subsequent dealkylation giving rise to the terminal cya-

nide ligand in the product complex [Mo₂Cp₂(CN)-

(Bu^tNC)(l-SMe)₃] [3].

Formation of 4 requires addition of hydride to an

isocyanide carbon atom, thereby generating a formimi-

doyl ligand which then displaces the second isocyanide.

This reaction is driven by the ability of the formimi-

doyl ligand to participate in a Mo₂CN ring. We

previously described the formation of a related l-

formimidoyl dimolybdenum compound [Mo₂Cp₂-

(l-SMe)₂(l-PPh₂)(l-CH@NBu^t)] by the reaction of

[Mo₂Cp₂(l-SMe)₂(l-H)(l-PPh₂)] with Bu^tNC via the

insertion of isonitrile into an Mo–H bond [2]. In Sec-

tion 2.3, we will show that [Mo₂Cp₂(l-SMe)₃-

(l-CH@Nxyl)] (6) is obtained in a way similar to its

close analogue 4 by reaction of [Mo₂Cp₂(l-SMe)₃-

(xylNC)₂](BF₄) (1b) with NaBH₄. Although crystals

of 4 proved unsuitable for a diﬀraction study, the com-

plex was successfully characterised from analytical and

NMR data. The latter show obvious parallels

with those of [Mo₂Cp₂(l-SMe)₂(l-PPh₂)(l-CH@NBu^t)]

and the related dimanganese species [Mn₂(CO)₆(l-H)-

We now report an extension of these studies on the

reactivity of ½M₂Cp₂L⁰ðl-SMeÞ ðl-L⁰Þꢀ^þcations. Reac-

2

tions of [Mo₂Cp₂L₂(l-SMe)₃]Y (L = Bu^tNC (1a) [3],

xylNC (1b) or CO (3) [4]; Y = BF₄,Cl) with NaBH₄, Li-

Buⁿ, R⁰MgCl (R⁰= Me, Prⁱ, Buⁿ, Ph) are ﬁrst described.

Selectivity in these reactions is controlled by varying

both the ligands L attached terminally to the Mo(III)

centres and the strength of the nucleophile. A rough

aﬃnity order is established by determining whether a

Cp ring atom or terminal L ligand is the site for nucle-

ophilic addition. The inﬂuence of the three-electron-do-

nor l-L⁰ligand on the reactivity of nucleophiles towards

[M₂Cp₂L₂L⁰_n]⁺cations has also been assessed by exam-

ining the chemistry of the species obtained when one of

the l-thiolate groups in 1a is replaced by a l-phosphido

ligand. Finally, we have tested the reaction of electro-

philes with the g⁴-cyclopentadiene derivatives previ-

ously obtained by nucleophilic addition.

(l-Ph₂PCH₂PPh₂)(l-CH@N–C₆H₄-Me-4)] [2,5].

The

¹H NMR spectra indicate that the solution contains

two isomeric forms of the complex, 4a and 4b, in 3:1

ratio. The isomers appear to diﬀer only in the orien-

tation (syn or anti) of the two in-plane ‘‘Mo₂S₂’’

bridging SMe groups. They were inseparable by con-

ventional chromatographic techniques. The presence

of

a three electron-donor, bridging formimidoyl

ligand (HC@NBu^t) in 4 is mainly supported by the

observation of one resonance (d ꢁ 230), at low ﬁeld

in the carbene range, corresponding to a carbon atom

attached to an H nucleus. This was established by an

1

2. Results

HMQC H–¹³C experiment which showed clearly that

carbon atoms at d ꢁ 230 correlate with hydrogen

atoms detected at low ﬁeld (d ꢁ 10.6) in the region typ-

ical for formimidoyl protons [5,6]. The results of

¹H–¹⁵N correlation NMR experiments are in accord

with these assignments. Moreover, both ¹H and ¹³C

NMR spectra exhibit peaks which can be attributed

to two inequivalent cyclopentadienyl ligands in agree-

ment with the unsymmetrical geometry proposed for

4. Finally, NMR spectra show the sets of resonances

expected for the {Mo₂Cp₂(l-SMe)₃} core and for the

Bu^tgroup.

2.1. Reaction of 1a with NaBH₄: synthesis and

characterisation of 4

Treatment of a red solution of 1a under reﬂux in ace-

tonitrile with 4.0 equivalents of sodium borohydride

over 3 h led to a maroon solution in which only two

organometallic products were detected by ¹H NMR

analysis. Substantial quantities (70%) of starting com-

pound 1a were recovered. However, chromatography

of the diethyl ether extract produced a new derivative

4 in low yield (ꢁ15%) as an orange, analytically pure so-

lid (Reaction (1)). The yield was not improved when the

reaction was carried out either for a prolonged time in

acetonitrile or under reﬂux in tetrahydrofuran.

2.2. Reaction of 1b with LiBuⁿ: synthesis and molecular

structure of 5

Me

Treatment of

a

dichloromethane solution of

-

Me

S

Cp

Mo

+,BF₄

Cp

Mo

S

Me

[Mo₂Cp₂(MeCN)₂(l-SMe)₃](BF₄) [7] with excess xylNC

at room temperature aﬀorded [Mo₂Cp₂(xylNC)₂-

(l-SMe)₃](BF₄) (1b) as a brown solid in 81% yield.

The formulation of 1b was deduced from the analytical

and NMR data (see Section 5). Addition of LiBuⁿto 1b

led to the formation of a new compound 5 (Reaction

(2)).

S

C

Me

H

- BH₃

- CNBu^t

- NaBF₄

+ NaBH₄

C

S

t

N

S

Mo

Cp

Bu

Mo

Cp

Me

N

Bu^t

C

t

N

Bu

4

1a

ð1Þ

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

4585

assigned to the geminal hydrogen atoms. The ¹³C{¹H}

NMR spectrum accords with the formulation proposed

according to the ¹H NMR data. A second NMR pattern

of similar but less intense resonances is assigned to the

minor isomer 5b.

Me

S

Me

-

+,BF₄

S

Cp

Mo

Me

S

Me

S

+ LiBuⁿ

S

Me

S

Me

Mo

Cp

Mo

- C₂H₅-CH=CH₂

- LiBF₄

Cp

C

N

xyl

C

This formulation of 5 as a g⁴-cyclopentadiene com-

plex is consistent with X-ray analysis of single crystals

obtained from a cooled pentane solution (see Section

5 and Tables 1 and 3). The molecular skeleton

(Fig. 1) contains similar (g⁴-C₅H₆)Mo(xylNC) and

(g⁵-C₅H₅)Mo(xylNC) units linked directly by an

C

N

xyl

1b

5

ð2Þ

n-Butene is a product of this reaction but no eﬀort

1

was made to detect this volatile species. The H NMR

spectra of CDCl₃solutions of product taken after reac-

tion was complete indicated that there had been essen-

tially quantitative conversion of 1b into 5. Complex 5

was isolated in analytically pure form with a recovered

˚

Mo–Mo bond of 2.797(1) A and indirectly by three

l-SMe groups. The coordination geometry around

each Mo atom is that of a distorted square pyramid,

with three sulfur atoms and one isocyanide carbon

atom in the basal plane and the centroid of either

the g⁴-cyclopentadiene or g⁵-cyclopentadienyl ring at

the apical position. The S(2) and S(3) methyl groups

adopt an anti orientation relative to the Mo₂S(2)S(3)

plane. The aromatic rings of the xylNC ligands are

nearly parallel [dihedral angle 8.1(5)ꢁ]. Departures

from linear coordination at C(4) and C(5) and more

especially at N(1) and N(2) [C–N–C = 162(1)ꢁ and

168(1)ꢁ] ensure that there are no short intramolecular

contacts between these rings and give support to the

yield of 65%. On the basis of H and ¹³C{¹H} NMR

1

data 5 was identiﬁed as a cyclopentadiene complex aris-

ing from hydride addition to a cyclopentadienyl ligand.

The ¹H NMR spectrum shows evidence for two isomers

in the 6.5/1 ratio. These may correspond to syn and anti

orientations of the two in-plane thiolate methyl groups.

The ¹H NMR spectrum of the major isomer 5a shows

a singlet for the unchanged cyclopentadienyl ligand

(5.17 ppm) and four multiplets for the four vinyl hydro-

gen atoms of the cyclopentadiene ring (4.91, 4.62, 3.31

and 3.25 ppm). An AB pattern centered at 3.45 ppm is

Table 1

4

˚

Selected distances and angles (A and ꢁ) in the g -C₅H₄R complexes 5 (R = H) and 12 (R = Ph)

5 – Mo(1)

5 – Mo(2)

12A

12B

(a) Bond lengths in the (g⁴-C₅H₄R)-MoL(l-SMe)₃units, L = CNPh (5), CO (12)

Mo–L

2.005(7)

2.240(10)

2.229(9)

2.364(11)

2.340(9)

2.712(10)

2.456(2)

2.450(2)

2.516(2)

2.797(1)

1.442(13)

1.438(13)

1.445(12)

1.426(13)

1.389(13)

2.043(7)

2.265(10)

2.259(9)

2.316(10)

2.330(11)

2.520(9)

2.474(2)

2.479(2)

2.489(2)

1.951(4)

2.262(3)

2.273(3)

2.308(4)

2.844(4)

2.493(1)

2.454(1)

2.561(1)

2.773(1)

1.516(5)

1.534(5)

1.402(5)

1.444(5)

1.404(5)

1.519(5)

1.966(3)

2.205(3)

2.231(3)

2.362(4)

2.405(4)

2.926(4)

2.440(1)

2.464(1)

2.546(1)

2.755(1)

1.518(5)

1.528(5)

1.403(5)

1.456(5)

1.410(5)

1.530(5)

Mo–C(9)

Mo–C(8)

Mo–C(10)

Mo–C(7)

Mo–C(6)

Mo–S(2)

Mo–S(3)

Mo–S(1)

Mo–Mo

C(6)–C(10)

C(6)–C(7)

C(7)–C(8)

C(8)–C(9)

C(9)–C(10)

C(6)–C(Ph)

1.409(12)

1.442(13)

1.414(13)

1.436(12)

1.423(12)

(b) Other bond lengths in 12

Mo(2)–CO

C(Cp)–C(Cp)

1.984(4)–1.994(4)

1.403(5)–1.433(5)

Mo(2)–S

Mo(2)–C(Cp)

2.460(1)–2.488(1)

2.260(4)–2.379(3)

5 – Ring A

5 – Ring B

12A

12B

(c) Endocyclic g⁴-C₅H₄R ring torsion angles: s(i,j) is the C–C(i)–C(j)–C torsion angle

s(6,7)

s(7,8)

s(8,9)

s(9,10)

s(6,10)

22.8(10)

ꢂ15.0(11)

0.8(12)

13.9(13)

ꢂ22.8(12)

ꢂ10.9(12)

33.7(3)

ꢂ23.2(4)

0.7(4)

22.4(4)

ꢂ33.3(3)

32.4(4)

ꢂ21.5(4)

ꢂ0.6(4)

22.6(4)

6.0(12)

1.2(11)

ꢂ8.3(11)

11.7(12)

ꢂ32.6(3)

4586

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

Fig. 1. A view of the structure of 5. Here and elsewhere 20% probability ellipsoids are shown. There is a ca. 2:1 disorder of the p-rings: Ring A (C6a–

C10a) is predominantly g⁴-C₅H₆whereas Ring B (C6b–C10b) is mainly g⁵-C₅H₅. Note that a consistent atom numbering scheme is used for 5 and for

both rotamers of 12.

Me

unexpected very low C–N stretches in IR spectrum

(see Section 5).

S

Mo

In Section 2.5, the g⁴-cyclopentadiene–Mo interac-

tions in 5 and in the related complex 12 will be

compared both with each other and with previously

characterised [8,9] g⁴-C₅R₆complexes. Here, we antici-

pate this discussion to note that in 5 there is a roughly

2:1 disorder of the g⁴-C₅H₆and g⁵-C₅H₅rings: Ring

A bonded to Mo(1) is predominantly but not exclusively

g⁴-C₅H₆and Ring B attached to Mo(2) is mainly

g⁵-C₅H₅.

Me

S

Me

Mo

Cp

C

N

xyl

Me

S

-

C

+,BF₄

N

xyl

Cp

Mo

Me

S

- BH₃

5

+

S

Me + NaBH₄

Mo

Cp

- CNxyl

- NaBF₄

C

Me

S

N

Cp

Mo

xyl

S

C

Me

H

C

N

xyl

S

Mo

Cp

Me

N

1b

2.3. Reaction of 1b with NaBH₄and BuⁿMgCl: synthesis

of 5 and 6; structure of 6

xyl

6

ð3Þ

When the reagents 1b and NaBH₄were heated in tet-

rahydrofuran at 120 ꢁC in a sealed tube dipped into an

oil-bath, complexes 5, 6 and the known compound

[Mo₂Cp₂(l-SMe)₄] [10] were formed; they were detected

Complex 5 was also prepared by reacting 1b with so-

dium borohydride in tetrahydrofuran under reﬂux.

Though 5 was the major product of the reaction,

approximately 12% of the material was converted into

the neutral formimidoyl compound 6. It is presumed

that displaced xylNC is a by-product in the formation

of complex 6 (Reaction (3)). Although the neutral deriv-

atives 5 and 6 were diﬃcult to separate, 6 was obtained

in pure form, as shown below. Compound 5 was identi-

1

in about 1:4:1.75 ratio by H NMR spectroscopy of the

crude products. Work-up of these products gave, after

chromatography on silica gel, a mixture of compounds

6 and [Mo₂Cp₂(l-SMe)₄] in about equimolar amounts.

Complex 6 was then isolated in pure form as red crystals

by recrystallization from a cooled CH₂Cl₂/pentane (1:1)

solution of the above mixture.

1

ﬁed by comparing the H NMR spectrum of a solution

of the two products 5 and 6 of Reaction (3) with that of

a pure sample of 5 obtained by the method described in

Section 2.2.

¹H NMR spectroscopy showed that in solution 6 is

present in only one isomeric form. The spectrum of 6

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

4587

Table 2

exhibits the sets of resonances expected for the

˚

Selected distances (A) and angles (ꢁ) for compound 6

˚

Bonds lengths (A)

{Mo₂Cp₂(l-SMe)₃} core and for the xyl group (see Sec-

tion 5). A singlet detected at low ﬁeld (d 10.40) is typical

of a formimidoyl proton [5,6]. The presence of two res-

onances at 5.29 and 5.02 ppm assigned to the two cyclo-

pentadienyl ligands accords with the unsymmetrical

geometry proposed for 6. These conclusions were con-

ﬁrmed by an X-ray analysis of a single crystal of 6

(see Fig. 2 and Tables 2 and 3). The molecule contains

two CpMo fragments which are bridged by three thio-

lates and by a formimidoyl ligand derived by proton-

ation of an isocyanide ligand. As expected, the

Mo(1)–Mo(2)

Mo(1)–S(1)

Mo(1)–S(2)

Mo(1)–S(3)

Mo(1)–C(4)

N(1)–C(4)

Mo–C(Cp)

Mo(2)–S(1)

Mo(2)–S(2)

Mo(2)–S(3)

Mo(2)–N(1)

N(1)–C(31)

2.681(1)

2.451(1)

2.445(1)

2.474(1)

2.088(5)

1.312(7)

2.224(5)–2.384(5)

2.449(1)

2.482(1)

2.469(1)

2.223(4)

1.434(6)

˚

Mo–Mo distance [2.681(1) A] in the quadruply-bridged

complex 6 is somewhat shorter than that in the triply-

bridged derivative 5 [2.797(1) A]. The Mo–C(Cp) and

Bonds angles (ꢁ)

C(4)–N(1)–Mo(2)

C(4)–N(1)–Mo(31)

C(4)–Mo(1)–Mo(2)

C(31)–N(1)–Mo(2)

Mo(1)–C(4)–N(1)

N(1)–Mo(2)–Mo(1)

˚

100.7(3)

122.7(4)

70.2(1)

135.7(3)

116.6(4)

72.5(1)

Mo–S distances [respective ranges 2.224(5)–2.384(5)

˚

and 2.449(1)–2.482(1) A] show no unusual features. As

in 5, there is an anti orientation of the S(1) and S(2)

methyl groups relative to the Mo₂S(1)S(2) plane. The

four-membered Mo(2)–N(1)–C(4)–Mo(1) ring system

is essentially planar, with an internal torsion angle

across N(1)–C(4) of 0.9(4)ꢁ. The formimidoyl unit thus

displays the l-g²coordination mode typical of formimi-

doyl, imino and diazenido ligands in transition metal

complexes [11]. It is, therefore, a 3e donor. This con-

trasts strongly with its mode of coordination in the only

other structurally characterised formimidoyl dimolybde-

num derivative, [Mo₂Cp₂(CO)₂(l-Pcy₂)(l-CHNBu^t)]

[12], where the C–N axis is perpendicular to the Mo–

Mo vector. These diﬀerent orientations may be a result

of orbital requirements but a steric interpretation ap-

pears more likely. Steric factors may also explain the

Torsion angles (ꢁ)

C(4)–Mo(1)–Mo(2)–S(1)

C(4)–Mo(1)–Mo(2)–S(2)

C(4)–N(1)–C(31)–C(32)

C(4)–Mo(1)–Mo(2)–S(3)

Mo(2)–N(1)–C(4)–Mo(1)

ꢂ83.9(2)

91.3(2)

ꢂ51.8(7)

ꢂ177.8(2)

0.9(4)

weakness of the Mo(2)–N(1) bond in 6: its length is

appreciably greater [cf. 2.223(4) and 2.096(4) A] than

˚

that of the corresponding bond in the isoelectronic dia-

zenido species [Mo₂Cp₂(l-SMe)₃(l-g²-N@NMe)] which

has otherwise, apart from syn-SMe groups,

a

Fig. 2. A view of the structure of 6.

4588

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

Table 3

Crystallographic data at 100 K for compounds 5, 6, and 12

5

6

12

Empirical formula

Formula weight

Crystal system

Space group

C₃₁H₃₈Mo₂N₂S₃

726.69

C₂₂H₂₉Mo₂NS₃

595.52

Triclinic

C₂₁H₂₄Mo₂O₂S₃

596.46

Triclinic

Monoclinic

C2/c

33.2989(3)

8.2747(1)

23.0429(2)

ꢀ

P1

˚

a (A)

8.0034(3)

8.4263(3)

17.4782(6)

80.375(3)

77.039(2)

77.608(2)

1113.1(1)

2

13.2107(4)

13.2740(4)

13.9111(5)

103.318(2)

104.903(2)

102.334(2)

2195.3(1)

4

˚

b (A)

˚

c (A)

a (ꢁ)

b (ꢁ)

c (ꢁ)

108.764(1)

3

˚

V (A )

6011.8(1)

8

1.606

Z

q_calc(Mg mm^ꢂ3

)

1.777

1.417

1.805

1.443

l (mm^ꢂ1

)

1.067

Crystal size (mm)

Range of h (ꢁ)

Reﬂections measured

R_int

0.35 · 0.32 · 0.08

1.9–27.5

34906

0.25 · 0.10 · 0.10

2.7–30.0

11422

0.43 · 0.10 · 0.09

1.7–28.6

30713

0.049

0.035

0.054

Unique data/parameters

R(F), wR(F²) (all data)

Goodness-of-ﬁt on F²

6799/343

0.091, 0.190

1.36

6011/258

0.056, 0.134

1.16

10531/523

0.057, 0.099

1.04

3

˚

|Dq| maximum (e/A )

1.96

2.62

1.31

{Mo₂Cp₂(l-SMe)₃(l-g²-L)} core strikingly similar to

that of 6 [11g]. The formimidoyl function in 6 also shows

an interesting diﬀerence from other structurally charac-

terised imino complexes [11–13]: it displays extensive

delocalization of electrons along the Mo–C(4)–N(1)

chain, as is evident from the sequence of distances

tolyl)] (d 241.2) [5], none of which have been structurally

characterised by X-ray analysis.

Thus, reaction of 1b with borohydride brings about

addition of hydride to either a Cp (5) or isocyanide (6)

carbon atom (Reaction (3)). We were interested to see

how the stronger nucleophile n-butylmagnesium chlo-

ride would react with 1b. However, no reaction (Reac-

tion (4)) was observed under conditions similar to

those employed for the corresponding reaction of 1b

with NaBH₄.

˚

2.088(5) and 1.312(7) A. The former distance is in the

range for typical of Mo–C(carbenes) [14], while the lat-

ter indicates a C–N bond order of ꢁ1.5 [15]. These re-

sults suggest that C(4) has a signiﬁcant amount of

carbene-like character, so that 6 is best represented as

a hybrid based on the canonical forms I and II (Chart

Me

-

+,BF₄

S

1

1). Finally, H and ¹³C{¹H} NMR data for 6 are in ac-

Cp

Mo

thf

Me

S

+ BuⁿMgCl

cord with this formulation. In particular, the Mo-bound

C(4) atom of the formimidoyl moiety appears at low

ﬁeld in the ¹³C NMR spectrum, as it does in the spectra

of closely related bimetallic compounds [Mo₂Cp₂(l-

SMe)₃(l-CH@NBu^t)] (4) (d 233.3 and 230.0) [see Section

2.1], [Mo₂Cp₂(l-SMe)₂(l-PPh₂)(l-CH@NBu^t)] (17) (d

232.5) [2] and [Mn₂(CO)₆(l-H)(l-dppm)(l-CH@Np-

S

Me

Mo

Cp

C

ð4Þ

N

xyl

C

N

xyl

1b

2.4. Reaction of 3 with NaBH₄and NaBD₄: synthesis and

characterisation of 7 and 8

Reaction of the dicarbonyl derivative [Mo₂Cp₂-

(CO)₂(l-SMe)₃](BF₄) (3) with sodium borohydride in

tetrahydrofuran at room temperature for 1 h aﬀorded

the new g⁴-cyclopentadiene compound [Mo₂Cp-

(g⁴-C₅H₆)(CO)₂(l-SMe)₃] (7) as the sole organometallic

product in good yield (71%) (Reaction (5)). Similar

Me

Cp

Mo

Me

S

Cp

Mo

S

C

Me

H

S

C

Me

H

S

Mo

Cp

S

Me

N

Mo

Cp

Me

N

xyl

II

I

treatment of

3

with NaBD₄gave [Mo₂Cp-

Chart 1.

(g⁴-C₅H₅D)(CO)₂(l-SMe)₃] (8), also in good overall

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

4589

yield. Complexes 7 and 8 have been characterised by ¹H,

¹³C NMR and IR spectroscopy and by microanalysis

(Section 5). The ¹H NMR spectrum of 7 shows evidence

for two isomers 7a and 7b in 4:1 ratio. These are thought

to have diﬀerent orientations, syn and anti, of the thio-

late methyl groups relative to the Mo₂S₂plane. NMR

analysis indicates that the corresponding derivative 8 ex-

ists in solution as a mixture of four isomers 8a, 8b, 8c

and 8d in the ratio 70/17/6/1. These may be syn and anti

isomers of two rotamers (see Section 3).

formed, together with the corresponding g⁴-cyclopent-

adiene derivative 9, 10 or 12. It was noted that reaction

of 3 with phenylmagnesium chloride in cooled tetrahy-

drofuran (ꢂ60 ꢁC) aﬀorded 12 as the sole product in

very high yield (98%).

H

R

Me

S

+,Cl^-

Me

S

Cp

Mo

Me

S

Me

S

- MgCl₂

S

Me + RMgCl

S

Me

Mo

Cp

Mo

Cp

C

H

X

O

C

Me

+,Cl^-

C

Me

S

O

S

O

Cp

Mo

X = Me (9), Prⁱ(10), Buⁿ(11), Ph (12)

3

Mo

Me

S

Me

S

- BX₃

S

+ NaBX₄

Me

S

Me

ð6Þ

NMR analyses reveal that all the products 9–12 exist

Mo

Cp

Mo

Cp

-Na Cl

C

O

C

O

in solution as mixtures of four isomers a, b, c and d in

variable ratios 20–8:5.5–2.5:3–2:1. These are probably

due to syn and anti isomers of two rotamers (see Section

3). Complexes 9–12 show similar patterns of bands

which resemble those for the corresponding compound

8, indicating that all these derivatives have in common

a substituted g⁴-cyclopentadiene ligand. Accordingly,

only complex 9 will be discussed here since it exempliﬁes

the entire series. Its ¹H NMR spectrum displays the typ-

ical pattern of substituted cyclopentadiene ligands, con-

sisting of four multiplets between 4.90 and 3.94 ppm

attributed to the four vinyl hydrogen atoms, and a quar-

tet (d 3.52) due to the endo hydrogen atom of the cyclo-

pentadiene ring which couples with the vicinal methyl

O

X = H (7), D (8)

3

ð5Þ

The NMR spectroscopic characteristics of bis-car-

bonyl derivatives 7 and 8 closely match those of the

bis(isocyanide) analogue 5. In particular, the H NMR

1

spectra of 7 show for each isomer the typical pattern

of a {(g⁵-C₅H₅)M–M(g⁴-C₅H₆)} moiety with a singlet

at about 5.4 ppm attributed to the unchanged cyclopen-

tadienyl, and an AB system due to the geminal hydrogen

atoms and four multiplets between 5.63 and 3.25 ppm

assigned to the four vinyl hydrogen atoms of the cyclo-

pentadiene ring. In the ¹³C NMR spectrum of 7a at

room temperature, peaks are seen for the four diene

carbon atoms (between 82.0 and 70.0 ppm) and for

the carbon atom (d 46.6) of the CH₂entity of the cyclo-

pentadiene ligand. In addition, resonances for the

carbonyl, cyclopentadienyl and thiolate groups are

group (³J_H–H= 6.0 Hz). Three other H NMR patterns

of similar but much less intense resonances in the cyclo-

pentadiene region are assigned to minor isomers 9b, 9c

and 9d. However, in the H NMR spectra a few of the

1

expected peaks are so weak that they are either not de-

tected or obscured. It should be pointed out that the ob-

served chemical shifts of the endo H atoms are in the

order Ph > Me > Buⁿ> Prⁱ(i.e., d 4.62, 3.52, 3.38 and

3.01, respectively, for major isomers a). This parallels

closely the electron donating ability of these substituents

which increases in the order Ph < Me < Buⁿ< Prⁱ. The

C₅H₅R ring carbons, being diastereotopic, give rise to

ﬁve distinct signals in the ¹³C NMR spectra: e.g., for

9a four vinylic carbon resonances of approximatively

equal intensity are observed at 79.4, 78.9, 77.9 and

76.3 ppm, and a methylenic carbon signal appears at

52.5 ppm. In addition, intense resonances due to two

carbonyl (d 243.0, 230.7), one cyclopentadienyl (d

90.7), one alkyl (R = Me; d 30.7) and three thiolate (d

25.4, 25.2 and 6.4) groups are detected in the ¹³C

NMR spectra. Further less intense resonances are also

discernible and may be conﬁdently attributed to the

three minor isomers 9b, 9c and 9d.

1

observed. The H NMR patterns of each isomer of the

corresponding deuterated compound 8 diﬀer from those

of the hydrogenated derivative 7 by the absence of an

AB resonance due to geminal hydrogen atoms and by

the expected presence of ﬁve multiplets between 5.63

and 3.17 ppm instead of the four observed for 7.

2.5. Reaction of 3 with RMgCl (R = Me, Prⁱ, Buⁿ, Ph):

synthesis and characterisation of 9–12. Molecular

structure of 12

When a tetrahydrofuran solution of 3 with Grignard

reagents, RMgCl, was stirred at room temperature

for 15–60 min, the new products [Mo₂(g⁵-C₅H₅)-

(g⁴-C₅H₅R)(CO)₂(l-(SMe)₃] [R = Me (9), Prⁱ(10), Buⁿ

(11), Ph (12)] were obtained in moderate-to-high yields

(68–90%) (Reaction (6)). When R is methyl, isopropyl

or phenyl group small amounts of known by-products,

[Mo₂Cp₂(l-SMe)₄] [10], trans–syn/anti-[Mo₂Cp₂(CO)₂-

(l-SMe)₂] [16] and [Mo₂Cp₂(CO)(O)(l-SMe)₂] [17] were

The formulation of 9, 10, 11 and 12 as g⁴-C₅H₄R

cyclopentadiene complexes was conﬁrmed by X-ray

4590

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

Fig. 3. Views of the two independent molecules of 12 present in the crystal. (a) Rotamer A. (b) Rotamer B.

analysis of a single crystal of 12 obtained from cold

diethyl ether (see Section 5, Fig. 3 and Table 1). Two

independent molecules, 12A and 12B, are present in

the crystal of 12. As can be seen from Fig. 3, these mol-

ecules are rotamers: Ph-substituted C(6) is on the same

side of the Mo₂S(2)S(3) plane from S(1) in 12A but on

the opposite side in 12B. Both rotamers have (g⁵-

C₅H₅)(CO)Mo–Mo(CO)(g⁴-C₅H₅Ph) skeletons bridged

by three thiolate groups, with an syn orientation of the

S(2) and S(3) methyl groups, both of which lie on the

opposite side of the Mo₂S(2)S(3) plane from S(1). All

four independent molybdenum atoms in the crystal of

12 adopt a similar distorted square pyramidal coordina-

tion, with a basal S₃C donor set and the centroid of

either a g⁵-C₅H₅or g⁴-C₅H₅Ph ring occupying the api-

cal site. In both rotamers the g⁴-cyclopentadiene ring

adopts a symmetrical envelope conformation; C(6) at

the ﬂap carries an exo Ph substituent. This is consistent

with the absence of a C–H stretching frequency near

2780 cm^ꢂ1, believed to be characteristic of an exo C–H

group [18,21c], in the IR spectra of 9–12, whereas this

peak is present in the spectrum of the related but unsub-

stituted compound 7.

The Mo–g⁴-C₅H₅Ph bond lengths in 12A and 12B

show interesting diﬀerences: in both the inner Mo–

C(8) and –C(9) bonds are shorter than the outer Mo–

C(7) and –C(10) bonds but the mean shortening is much

˚

more marked in 12B (0.17 A) than it is in 12A (0.04 A).

In other structurally characterised Mo–g⁴-C₅R₆species

individual Mo–C distances are quite variable [8] but

˚

the mean values (outer 2.297 A, inner 2.265 A) agree

with those in 12A. The non-bonded Moꢃ ꢃ ꢃC(6) distances

˚

[2.844(4) and 2.926(4) A] in 12 fall in the range of 2.747–

4

˚

2.930 A observed in other Mo–g -C₅R₆species [8]. De-

spite the diﬀerences in Mo(1)–C bond lengths the Mo–S

distances in 12A and 12B show the same pattern, with

˚

Mo(1)–S(1) [2.561(1) and 2.546(1) A] longer than the

˚

other Mo–S bonds [2.440(1)–2.493(1) A]. The Mo–Mo

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

4591

˚

H

R

distances [2.773(1) and 2.755(1) A] are also in

Me

S

agreement.

+,Cl^-

Me

S

Like other Mo–g⁴-C₅R₆species [8], the C(6)–C(7)

Cp

Mo

Me

S

Me

S

- LiCl

and C(6)–C(10) single bonds in 12 are longer than the

other cyclopentadiene ring C–C bonds; however, in 12

the sequence C(7)–C(8)–C(9)–C10 shows signiﬁcant

S

Me + LiR

S

Me

Mo

Cp

Mo

Cp

C

O

C

˚

C

bond alternation [means 1.403(4), 1.450(4), 1.408(4) A]

O

not typical of other Mo–g⁴-C₅R₆species [8] where the

R = Me (9), Buⁿ(11)

3

corresponding bonds are more nearly equal in length

(means 1.423, 1.406 and 1.415 A), though again individ-

ð7Þ

˚

ual values show much variation. Finally, we note that

symmetrical envelope conformations of the g⁴-C₅R₆

rings, with C(6) at the ﬂap, are evident from the endocy-

clic torsion angles in Table 1(c), which agree well with

the means for other Mo–g⁴-C₅R₆species; for example

the magnitudes of the endocyclic torsion angles across

C(6)–C(7) and C(6)–C(10), 32–34ꢁ in 12, compare with

a range of 26–39ꢁ in related molybdenum complexes [8].

The results for the ordered structure 12 clarify those

for the disordered structure 5, in which xylNC takes

the place of CO and g⁴-C₅H₆replaces g⁴-C₅H₅Ph. Ring

A in 5 diﬀers from the g⁴-C₅H₅Ph rings in 12 in several

ways: it is less puckered, with smaller torsion angles

across the C(6)–C(7) and C(6)–C(10) bonds, the ring

C–C bonds do not vary so much and C(6) is only

2.7. Reaction of 16 with NaBH₄: formation of 17

To evaluate the inﬂuence of the bridging 3e-donor li-

gand L⁰upon the reactivity of nu_þcleophiles towards cat-

ionic derivatives ½Mo₂Cp₂L₂L⁰_nꢀ , we synthesised an

analogue of 1a in which one l-SMe group is replaced

by the better electron-donor ligand l-PPh₂. For this

purpose we treated an acetonitrile solution of

[Mo₂Cp₂(l-SMe)₂(l-Cl)(l-PPh₂)] [2] with excess Bu^tNC

at room temperature to obtain the desired product

[Mo₂Cp₂(Bu^tNC)₂(l-SMe)₂(l-PPh₂)]Cl (16) as an ochre

solid in good yield (79%). The formulation of 16 was de-

1

duced from its analytical, H and ¹³C{¹H} NMR data

(see Section 5). Stirring a tetrahydrofuran solution of

16 with excess NaBH₄at ambient temperature aﬀorded

17 in good yield (ca. 80%) (Reaction (8)).

˚

2.712(10) A from Mo(1). Ring B, bonded to Mo(2), de-

ﬁnes an even ﬂatter envelope, again with C(6) at the ﬂap.

The longest Mo–S bonds again involve S(1) but the

lengthening is not so obvious as in 12. Disorder of the

g⁴-C₅H₅Ph and g⁵-C₅H₅rings seems the most probable

explanation for these results. This disorder may involve

diﬀerent rotamers, since C(6a) lies on the opposite side

of the Mo₂S(2)S(3) plane from S(1), while C(6b) lies

on the same side.

Ph

+,Cl^-

Cp

Mo

P

Mo

S

Me

Ph

S

C

Me

H

- BH₃

+ NaBH₄

C

S

t

N

S

Mo

Cp

Bu

Mo

Cp

Me

- NaCl

Me

N

Bu^t

- Bu^tNC

C

t

N

Bu

16

17

2.6. Reaction of 3 with alkyllithium LiR (R = Me, Buⁿ):

synthesis of 9 and 11

ð8Þ

The NMR spectra of 17 were identical to those of the

l-formimidoyl derivative [Mo₂Cp₂(l-SMe)₂(l-PPh₂)(l-

CH@NBu^t)] previously obtained in good yield from

the reaction of [Mo₂Cp₂(l-H)(l-SMe)₂(l-PPh₂)] with

Bu^tNC in tetrahydrofuran [2]. Reaction (8) required

addition of hydride onto isocyanide to give a formimi-

doyl ligand which then displaced the other isocyanide.

Complexes 9 and 11, obtained by reacting 3 with the

appropriate alkylmagnesium chloride (see Section 2.5)

may also be synthesised by action of the corresponding

alkyllithium on the dicarbonyl derivative 3. Indeed,

treatment of a tetrahydrofuran solution of 3 with

excess alkyllithium LiR (R = Me, Buⁿ) at room tem-

perature for 20 min aﬀorded the g⁴-substituted cyclo-

pentadiene derivatives 9 and 11 with improved yields

(76% and 82%, respectively) (Reaction (7)). In both

cases small amounts of known by-products, trans-

syn/anti-[Mo₂Cp₂(CO)₂(l-SMe)₂] [16] (in about 13%

yield) and trans-syn/anti-[Mo₂Cp₂(CO)(O)(l-SMe)₂]

[17] (yield: R = Me, 10.5%; R = Buⁿ, 5.5%), were

formed in addition to the main products 9 or 11.

All the products of these reaction were characterised

by comparing their ¹H NMR spectra with those of

authentic samples obtained by methods already

described.

2.8. Reaction of 9, 11, and 12 with HBF₄: synthesis and

characterisation of 13, 14 and 15

For metal-bound cyclopentadienyl rings most func-

tionalization reactions involve either Friedel–Crafts

electrophilic alkylation or proton abstraction by base,

followed by reaction of the resulting anion with an alkyl

halide [19]. Hydrogen abstraction from the substituted

cyclopentadiene rings present in complexes 9, 11 and

12 oﬀered us an alternative route to functionalised

cyclopentadienyls. Thus, addition of one equivalent of

4592

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

HBF₄ꢃOEt₂to dichloromethane solutions of compounds

9, 11 or 12 caused their rapid transformation into the

corresponding cationic bis(cyclopentadienyl) derivatives

13, 14 or 15 as sole product with respective yields of

49%, 51.5% and 33% (Reaction (9)).

pair of spectroscopically indistinguishable enantiomers

[Mo₂(g⁵-C₅H₅){g⁴-C₅H₅R)}(CO)₂(l-SMe)₃] (7–12). Only

four isomers characterisable by NMR spectrometry

seem stereochemically possible: they result from syn or

anti orientations of the two in plane ‘‘Mo₂S₂’’ bridging

SMe groups and two possible rotamer arrangements

(A and B) of the g⁴-cyclopentadiene ligand (Scheme 1).

R

H

R

-

Me

S

+,BF₄

Me

S

1

As expected, each H NMR spectrum of a g⁴-cyclo-

Mo

pentadiene derivative showed the presence in solution

of four isomers (a–d), except in the case of compound

7 for which only two isomers were detected. It should

be noted that 7 and the formally oxidised bis(cyclopen-

tadienyl) derivatives 13–15 displayed very similar ¹H

NMR patterns in the SMe region, suggesting strongly

similar patterns of isomerism. Moreover, ¹H NMR spec-

troscopy revealed that each of the compounds 13–15

was present in solution as a mixture of two isomers:

these may diﬀer either in the orientations (syn or anti)

of the two in-plane ‘‘Mo₂S₂’’ bridging SMe groups or

in relative positions (cis or trans) of the two carbonyl

ligands relative to the Mo–Mo axis. However, separate

experiments showed that electrochemical oxidation

of the cis-bis(carbonyl)-g⁴-cyclopentadiene derivative

[Mo₂(g⁵-C₅H₅)(g⁴-C₅H₆)(CO)₂(l-SMe)₃] (7), formed

by addition of H^ꢂto the cis-bis(carbonyl) complex

[Mo₂(g⁵-C₅H₅)₂(CO)₂(l-SMe)₃]Cl (3), gave back the

starting compound. This observation appears to elimi-

nate the possibility that two isomers are formed by a

cis-trans rearrangement of the two CO groups in

13–15. Therefore, from the similarity of the SCH₃

NMR patterns of 7 and 13–15, we attribute the isomer-

ism observed for 7 to syn and anti orientations of the

SMe groups. Such an assignment is also in accordance

Me

S

Mo

Me

S

Me

S

+ HBF₄

Me

Mo

Cp

Mo

Cp

- 2H

C

O

C

O

R = Me (9), Buⁿ(11), Ph (12)

R = Me (13), Buⁿ(14), Ph (15)

ð9Þ

The new compounds 13, 14 and 15 were identiﬁed

from their analytical and spectroscopic data. Since the

NMR and IR spectra suggest a close structural similar-

ity between these three species, only one of them, namely

13, will be discussed here as an example. A typical broad

band between 1100 and 1000 cm^ꢂ1, attributable to a

m(B–F) absorption, is observed in the IR spectrum of

13 and is indicative of the presence of a tetraﬂuorobo-

rate anion, suggesting a cationic molybdenum dimer as

counter-ion. NMR suggests that two isomeric forms of

the cation are present. Since the patterns of resonances

of both isomers are similar and the spectra diﬀer only

in the chemical shifts of two of the SMe groups, it is

likely that syn and anti isomers 13a and 13b are present

in solution. These cations exhibit a deshielded ¹H NMR

singlet at ca. 6.03 ppm which is assigned to one cyclo-

pentadienyl ligand. Furthermore, both isomers show

in the expected region the typical pattern of a mono-

substituted cyclopentadienyl ring, consisting of two

multiplets of equal intensity at ca 5.95 and 5.84 ppm.

Additional resonances due to three thiolates, between

2.65 and 1.75 ppm, and to one ring methyl substituent

are observed in the ¹H NMR spectra. The C₅H₅Me ring

carbons, being diastereotopic, display ﬁve distinct sig-

nals in the ¹³C{¹H} NMR spectra of 13a and 13b, at

ca. 97.2, 94.1, 93.3, 90.8 and 89.9 ppm; other resonances

due to two carbonyls, one cyclopentadienyl, one methyl

and three thiolate groups are also detected.

H

Me

S

Me

S

R

S

Me

Mo

R

Me

H

S

Me

Mo

Cp

C

O

C

O

B-anti

A-anti

3. Discussion

H

Me

S

Me

3.1. Isomerism in g⁴-cyclopentadiene molybdenum

derivatives (7–12) and in mono-substituted g⁵-

cyclopentadienyl molybdenum compounds (13–15)

R

S

Mo

R

S

H

S

Me

Mo

Cp

Mo

Cp

Me

C

Me

O

Reaction of the symmetrical bis(cyclopentadienyl)

derivative [Mo₂Cp₂(CO)₂(l-SMe)₃]Cl (3) with either

NaBR₄(R = H, D), LiR (R = Me, Buⁿ) or RMgCl

(R = Me, Prⁱ, Buⁿ, Ph) formally proceeds by nucleo-

philic attack at a Cp carbon atom by R^ꢂto give a

O

C

O

A-syn

B-syn

Scheme 1. Possible g⁴-cyclopentadiene molybdenum isomers 7–12.

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

4593

1

with the diﬀerence in H NMR chemical shifts for the

cyclopentadienyl ring, (ii) attack at the metal with for-

mation of a transient metal–nucleophile bond, and (iii)

attack at a terminal ligand L with possible displacement

of a second ligand L (Scheme 2).

SMe resonances in the two isomers (2.53, 2.52 and

1.31 ppm for 7a, and 2.28, 2.23 and 1.59 ppm for 7b),

which may reﬂect diﬀerent methyl orientations in the

two derivatives. Interestingly, when a CH(D/R) frag-

ment is present in the g⁴-cyclopentadiene group, the

two more abundant isomers a and b of compounds 8–

12, and those of bis(g⁵-cyclopentadienyl) derivatives

13–15 displayed very similar patterns in both cyclopen-

tadienyl and SMe regions in all seven complexes. We,

therefore, conﬁdently assign the corresponding reso-

nances to syn and anti orientations of the two SMe

groups of one rotamer in 8–12. The remaining reso-

Investigation of the reactivity of binuclear cyclopen-

tadienyl transition metal complexes with anionic re-

agents, such as hydride, alkyl- or aryl anions or

Grignard reagents, described either here or in previous

reports [23] reveals that the regioselectivity of the reac-

tion depends on: (i) the nature of the terminal (L) or/

and bridging (L⁰) ligands, (ii) the strength of the nucle-

ophile, (iii) the oxidation state of the metal, (iv) the ste-

ric inﬂuence of substituents of terminal or bridging

ligands, and (v) the temperature. Further complications

arise because the anionic reagent can behave as a base or

as a reducing agent as well as a nucleophile. In order to

appreciate how these factors determine the site of the re-

agent attack in dinuclear cyclopentadienyl carbonyl and

carbonyl-like molybdenum cations, we have summa-

rized in Scheme 3, the set of addition reactions of anio-

nic reagents with [Mo₂Cp₂L₂(l-SMe)₂(l-L⁰)]⁺.

1

nances observed in the H NMR spectra of 8–12 were

attributed to the two less abundant isomers c and d,

which accordingly were identiﬁed with the other syn

and anti rotamer. While the rotamer isomerization rates

are slow in substituted cyclopentadiene dimolybdenum

derivatives (8–12), allowing the characterisation of each

of the two rotamers, they are rapid in the unsubstituted

cyclopentadiene compounds 7 and 5, for which only one

1

form has been detected in solution by H NMR spec-

Examination of the reactions gathered in Scheme 3

suggests that the dominant factor governing regioselec-

tivity is the nature of the terminal ligand L. Indeed,

when L has adequate p-acceptor power, e.g., CO or

xylNC, irrespective of the anionic reagent the cyclopen-

tadienyl carbon atoms are activated to nucleophilic at-

tack, thus aﬀording cyclopentadiene derivatives. The

failure of BuⁿMgCl to give any reaction when

L = xylNC is the single exception to this rule. However,

it must be emphasized that, with BH^ꢂ₄as reagent, the

selectivity of these nucleophilic additions is higher if

the terminal ligands are CO rather than xylNC. Forma-

tion of small amounts of the l-formimidoyl product 6

together with the unsubstituted cyclopentadiene deriva-

tive 5 when BH^ꢂ₄reacts with 1b (Scheme 3) supports this

statement. Consistently, the higher p-acceptor power of

CO relative to xylNC disfavours attack at the CO car-

bon: thus H^ꢂaddition occurs exclusively at the cyclo-

pentadienyl carbon atom when BH^ꢂ₄reacts with 3,

whereas some H^ꢂaddition also occurs at the iminium

carbon in the related reaction of BH^ꢂ₄with 1b.

troscopy. Similar trends have been previously observed

in Mo(II) and Mo(III) diene derivatives [MoCp(g⁴-

C₄H₄)(g³-C₃H₅)]ⁿ⁺(n = 0, 1) [20]. It should be noted

that syn-anti isomerization rates are slow for all the

cyclopentadiene complexes of this study (5, 7–12),

allowing the detection of the expected two

conformations.

The existence of a pair of endo–exo isomers, resulting

from attack of the nucleophile onto the metal followed

by its migration to the cyclopentadienyl ligand, has been

also considered, but on the basis of the X-ray character-

isation of a pair of rotamers for complex 12 this hypoth-

esis has been rejected.

It is worth noting that, until now, there was no evi-

dence from NMR spectra or from diﬀraction studies

for the existence of rotamers for substituted or unsubsti-

tuted g⁴-cyclopentadiene binuclear complexes [9c,21],

whereas a few examples of prone and supine isomers of

mononuclear substituted g⁴-cyclopentadiene derivatives

1

have been detected in solution by H NMR spectros-

copy [22]. Thus, as far as we know, isomers 8–12 are

the ﬁrst well-established examples of rotamers of binu-

clear g⁴-cyclopentadiene species.

3.2. Factors inﬂuencing the regiochemical control in the

reactions of anionic reagents with metal carbonyl and

metal carbonyl-like complexes

L'

Mo

L'

Mo

L

L = RNC, CO;

L' = 3e donor ligand

Reactions of nucleophilic reagents, such as sodium

borohydride, alkyl- or aryllithium compounds, or al-

kyl-or arylmagnesium halides, with binuclear cyclopen-

tadienyl transition metal complexes bearing a positive

charge proceed by three general pathways determined

by the nature of the metal and ligands: (i) attack on a

L

(i)

(ii)

(iii)

Nu

Scheme 2. Potential electrophilic sites in cationic metal carbonyl-like

dinuclear complexes.

4594

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

Me

S

Me

Cp

S

Mo

Me

S

C

Me

H

S

Me

+

S

Mo

Cp

C

Mo

Cp

Me

N

xyl

Me

S

C

xyl

N

5 (68 %)

6 (12 %)

xyl

Mo

Me

S

Me

S

Cp

Mo

Cp

C

S

C

Me

H

NaBH₄

N

xyl

C

S

Mo

Cp

N

Me

N

Bu^t

xyl

5 (65 %)

LiBuⁿ

4 (15 %)

NaBH₄

Buⁿ

H

Ph

P

+

Cp

Mo

Cp

Me

S

L'

SMe

Ph

Mo

S

C

Me

H

LiBuⁿ

NaBH₄

Mo

L

Me

S

MeS

S

Mo

Cp

Mo

Cp

S

Me

N

Bu^t

Mo

Cp

C

L

O

17 (80 %)

L' = SMe: L = Bu^tNC (1a), XylNC(1b), CO (3)

L' = PPh₂: L =Bu^tNC (16)

C

O

11 (82 %)

NaBH₄

BuⁿMgCl

LiCH₃

Me

S

RMgCl

L = XylNC

(L' = SMe)

Mo

Me

S

Me

Mo

H

Me

Cp

C

O

Me

S

H

R

C

no reaction

O

Me

S

Mo

Me

S

7 (71 %)

S

Mo

Cp

Mo

Me

S

C

S

Me

O

Mo

Cp

C

O

C

9 (76%)

O

9-12 (70-90 %)

Scheme 3. Summary of the reactivity of complexes [Mo₂Cp₂L₂(l-SMe)₂(l-L⁰)]⁺towards anionic reagents.

Now, it is well known that increased back-donation

from the metal to the p-acidic L = CO or CNR terminal

ligands increases the polarization of both the C–X

(X = O or N) bonds of the terminal ligand and of the

Cp C–H bonds. The relative electrophilicity of the donor

carbon atoms of the Cp and L ligands depends on the

metal, its oxidation state and the charge of the complex.

These factors govern the regiochemical control in

reactions of nucleophiles with metal carbonyl or car-

bonyl-like complexes. Previous studies on reactions of

nucleophiles with cationic dinuclear carbonyl iron com-

plexes, [Fe₂Cp₂(CO)₂(l-CO/S)(l-CSMe)]⁺and [Fe₂Cp₂-

(CO)₂(l-CO)(l-CNRMe)]⁺[9c,21b,21c,23e], oﬀer some

parallels with our systems, although they involve iro-

n(II) rather than molybdenum(III). This electronic

diﬀerence may be responsible for the diﬀerent trends

observed in the two series. Thus, the exclusive addition

of nucleophile to the C₅H₅ring of the dicarbonyl complex

3 contrasts with the vulnerability of dinuclear car-

bonyl iron compounds to nucleophilic attack at the

terminal carbonyl group as well as on the Cp ring

[9c,21b,21c,23e]. It is also pertinent to note here that

Rakowski Dubois et al. [21a] have shown that the dicar-

bonyl molybdenum cation, [Mo₂Cp₂(CO)₂(l-SMe)-

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

4595

(l-SCH₂S)]⁺, reacts with LiEt₃BH to give a single cyclo-

pentadiene product resulting from direct addition of H^ꢂ

to the cyclopentadienyl ring. The reactions between

anionic reagents and dimolybdenum complexes with

L = CO or xylNC as terminal ligands contrast with

those where L = Bu^tNC, a poorer p-acceptor group

than CO and xylNC but a valuable r-donor, in which

no nucleophilic attack at a Cp carbon atom is observed.

This diﬀerence in electronic behaviour between Bu^tNC

and xylNC upon coordination to the {CpMo(l-SMe)₃-

MoCp} core is illustrated by the eﬀect of coordination

cally favoured l-formimidoyl complex 17 by loss of

isonitrile from the second molybdenum atom which then

accepts N-co-ordination from the modiﬁed isocyanide.

Thus, 16 and 1a show similar reactivity with NaBH₄.

Both aﬀord l-formimidoyl products, respectively, 17

and 4. However, 17 is formed in signiﬁcantly higher

yield than 4, possibly owing to the higher lability of

the isonitrile in 16 compared with 1a.

3.3. Reactivity of the cyclopentadiene derivatives towards

electrophiles: mechanistic considerations

on the m(CN) bands: for Bu^tNC the drop is 18 cm^ꢂ1

,

from 2130 cm^ꢂ1in the free ligand [24] to 2112 cm^ꢂ1in

1a, whereas xylNC displays a more substantial drop of

31 cm^ꢂ1, from 2120 to 2089 cm^ꢂ1in 1b.

The addition of tetraﬂuoroboric acid to substituted

cyclopentadiene complexes reverses the nucleophile

addition. The products are hydrogen and an analogue

of the starting complex with diﬀerent functionality (see

Reaction (9)).

The nature of the ancillary ligands in [Mo₂Cp₂L₂-

(l-SMe)₂(l-L⁰)]⁺determine also the character of the

anionic reagent acting either as reducing agent or nucle-

ophile. For example, when the anion reacting with 1b

(L = xylNC) is derived from n-butyllithium, it acts as

a reducing agent rather than a nucleophile, since the

g⁴-cyclopentadiene C₅H₆ligand is formed rather than

the substituted cyclopentadiene C₅H₅Buⁿ. This contrasts

with alkyllithium LiR (R = Buⁿ) which reacts with the

bis-carbonyl derivative 3 mainly as a nucleophile, giving

substituted cyclopentadiene complexes as the major

products. Nevertheless, small quantities of reduced

dimolybdenum derivatives, [Mo₂Cp₂(CO)₂(l-SMe)₂]

and related oxo-complexes, are also formed, indicating

that lithium compounds may also reduce bis(cyclopenta-

dienyl) derivatives. Similar trends are observed when 3

reacts with Grignard reagents at room temperature.

However, at low temperature, PhMgCl, for example,

acts exclusively as nucleophile, aﬀording quantitatively

the Ph-substituted derivative. Evidently, arylmagnesium

compounds are less likely to act as reducing agents at

low temperature.

In coordinated isonitriles, RNC, the electronic prop-

erties of the substituent R gives rise to diﬀerent modes of

activation but the outcome also depends on the anionic

reagent. When R is a good electron-donor, such as Bu^t,

no activation of the cyclopentadienyl carbon atoms oc-

curs and thus no cyclopentadiene derivative is formed.

However, when the anionic compound reacting with

1a is LiBuⁿ, a dealkylation reaction, involving ejection

of the Bu^tgroup, is observed (Scheme 3) [3]; this requires

that LiBuⁿshould act as a base. On the other hand,

when the anionic reagent is BH^ꢂ₄, hydride attack occurs

at the isonitrile carbon in 1a (L = Bu^tNC), aﬀording the

l-formimidoyl derivative 4.

The formation of 13, 14 and 15 implies the oxidation

of 9, 11 and 12 by H⁺, promoting a g⁴! g⁵rearrange-

ment of the C₅ring, with concomitant elimination of a

radical (H^Å). It is noteworthy that electrochemical oxida-

tion of the g⁴-cyclopentadiene compounds 9 and 11 in

the absence of protons aﬀords the g⁵-cyclopentadienyl

derivatives 13 and14, respectively. This supports the

proposed reaction path. Nevertheless, a second route

to the g⁵-cyclopentadienyl compounds 13, 14 and 15

from the reaction of g⁴-cyclopentadiene derivatives 9,

11 and 12 with HBF₄may also be considered. This in-

volves b-elimination in the initial step, then electrophilic

attack by H⁺at one Mo atom (second step) and a ﬁnal

loss of dihydrogen via a reductive elimination (third

step). However, two observations make this unlikely.

First, we have already shown that addition of HBF₄

to related dimolybdenum complexes gave rise to a

face-addition of the proton to a Mo–C bond, with for-

mation of a a-agostic structure rather than an Mo–H

bond [14]. Second, the second step requires a higher

coordination number for the molybdenum atom than

is usual in these compounds. The radical mechanism

for formation of functionalized cyclopentadienyl prod-

ucts thus seems more likely.

4. Conclusions

We have shown that the reactivity of dinuclear

molybdenum cationic complexes, [Mo₂Cp₂L₂(l-

SMe)₂(l-L⁰)]⁺(L = Bu^tNC, xylNC, CO; L⁰= SMe,

PPh₂), towards anionic reagents aﬀords g⁴-cyclopent-

adiene, l-formimidoyl and reduced dinuclear dimolyb-

denum, neutral products, according to the relative

inﬂuences of the terminal (L) and bridging (L⁰) ligands,

the nature and oxidation state of the metal, the nature of

the anionic reagent and the temperature. Attack of the

anion, acting mainly as nucleophile but also as reduc-

tant, at the carbon atoms of the C₅H₅ring is favoured

Finally, when the bis(t-BuNC) derivative 16, derived

from 1a by replacement of one l-SMe ligand by the bet-

ter r-donor l-PPh₂, reacts with NaBH₄, one isonitrile

undergoes selective hydride addition at an iminium-like

carbon. This reaction does not stop at the imino com-

plex but proceeds ultimately to form the more geometri-

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N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

when good p-acceptor terminal ligands L are present in

the cationic derivatives, aﬀording new monocyclopent-

adiene dinuclear molybdenum complexes. When the ter-

minal ligand L is a poor p-acceptor unit, e.g., Bu^tNC,

the nucleophile adds at the iminium carbon atom, lead-

ing to the formation of new l-formimidoyl molybdenum

complexes. Nucleophilic addition at the C₅H₅ring, giv-

ing cyclopentadiene complexes, is well known in mono-

nuclear derivatives [25] but has been less often seen in

dinuclear species [9a,21].

showed that 70% of the starting material was recovered.

The organometallic derivatives were extracted from the

residue with diethylether (2 · 20 ml). Evaporation of

the volatiles gave a solid, which was dissolved in CH₂Cl₂

(20 ml) and chromatographed on silica gel. Elution with

hexane–CH₂Cl₂(1:1) removed an orange band which

aﬀorded, after evaporation of solvents, complex 4 as

an orange powder (26 mg, 15% yield). Complex 4 was

obtained as a mixture of two inseparable syn and anti

isomers by chromatography. Several attempts to im-

prove the yields of 4 by increasing the time of reaction

were unsuccessful.

5. Experimental

Complex 4: Anal. Calc. for C₁₈H₂₉Mo₂NS₃, CH₂Cl₂:

C, 36.1; H, 4.9; N, 2.2. Found: C, 36.2; H, 5.1; N, 2.2%.

¹H NMR d/ppm (toluene-d₈; 253 K), 4a (major isomer):

10.60 (s, 1H, CHN), 5.15, 5.07 (s, 5H, C₅H₅), 1.81, 1.57,

1.55 (s, 3H, SCH₃), 0.81 (s, 9H, Bu^t); 4b (minor isomer):

10.63 (s, 1H, CHN), 5.23, 5.05 (s, 5H, C₅H₅), 1.64, 1.51,

1.50 (s, 3H, SCH₃), 0.76 (s, 9H, Bu^t). ¹³C{¹H} NMR d/

ppm (toluene-d₈; 253 K), 4a: 230.0 (CHN), 91.5, 84.0

(C₅H₅), 29.7 (C(CH₃)₃), 18.6, 12.7, 11.5 (SCH₃); 4b:

233.3 (CHN), 92.3, 89.3 (C₅H₅), 29.2 (C(CH₃)₃), 17.2,

12.4 (SCH₃). ¹⁵N NMR d/ppm (toluene-d₈; 253 K),

4a: ꢂ129.3 (NBu^t); 4b: ꢂ136.2 (NBu^t).

5.1. General procedures and materials

All reactions were performed under an atmosphere of

argon or dinitrogen using conventional Schlenk tech-

niques. Solvents were deoxygenated and dried by

standard methods. Some of the starting materials

[Mo₂Cp₂(Bu^tNC)₂(l-SMe)₃](BF₄) (1a) [3], [Mo₂Cp₂-

(MeCN)₂(l-SMe)₃](BF₄) [7], [Mo₂Cp₂(CO)₂(l-SMe)₃]Cl

(3) [4] and [Mo₂Cp₂(l-SMe)₂(l-Cl)(l-PPh₂)] [26] were

prepared as described previously. All other reagents

were purchased commercially: Bu^tNC (98%), CH₃MgCl

(3.0 M solution in tetrahydrofuran), (CH₃)₂CHMgCl

and CH₃(CH₂)₃MgCl (2.0 M solution in diethyl ether),

(C₆H₅)MgCl (2.0 M solution in tetrahydrofuran),

CH₃(CH₂)₃Li (2.5 M solution in hexanes) and HBF₄

(54 wt% solution in Et₂O) from Aldrich, CH₃Li (1.6

M solution in diethyl ether) and CH₃(CH₂)₃Li (2.5 M

solution in hexanes) from Acros Organics, and xylNC

(98%) from Fluka Chemica. Yields of all products are

relative to the starting dimolybdenum complexes. Col-

umn chromatography was carried out with either silica

gel or Florisil purchased from SDS. Chemical analyses

were performed either by the Service de Microanalyse

I.C.S.N., Gif sur Yvette (France), or by the Centre de

Microanalyses du CNRS, Vernaison (France). IR spec-

tra were recorded on a Nicolet-Nexus FT-IR spectrom-

eter from either KBr pellets or dichloromethane

solution. The NMR spectra (¹H, ¹³C, ¹⁵N) were

recorded either at room temperature or at 253 K in

CDCl₃, C₆D₆, toluene-d₈or (CD₃)₂CO solutions with

a Bruker AMX 400 spectrometer and were referenced

to SiMe₄(¹H, ¹³C) and CH₃NO₂(¹⁵N). ¹H–¹³C and

¹H–¹⁵N 2D experiments were carried out on a Bruker

DRX 500 spectrometer.

5.3. Synthesis of 1b

A solution of [Mo₂Cp₂(l-SMe)₃(MeCN)₂](BF₄) (500

mg, 0.79 mmol) in dichloromethane (50 ml) was stirred

in the presence of 2 equiv. of xylNC (206 mg) for 1 h at

room temperature. The solution turned readily from red

to brown. After evaporation of the solvent, the residue

was washed with diethyl ether (2 · 20 ml) and pentane

(2 · 20 ml), aﬀording complex 1b as a brown solid

(520 mg, 81% yield).

Complex 1b: Anal. Calc. for C₃₁H₃₇BF₄Mo₂N₂S₃, 0.5

CH₂Cl₂: C, 44,2; H, 4.5; N, 3.3. Found: C, 44.2; H, 4.5;

N, 3.2%. IR (CH₂Cl₂, cm^ꢂ1): 2089 s (m CN), 1100–1000

1

s, br (m BF). H NMR d/ppm ((CD₃)₂CO; 298 K): 6.95

3

(t, J_H–H= 7.6 Hz, 2H, C₆H₃Me₂), 6.82 (d, J_H–H

=

7.6 Hz, 4H, C₆H₃Me₂), 5.66 (s, 10H, C₅H₅), 2.65 (s,

3H, SCH₃), 2.22 (s, 12H, CH₃), 1.85 (s, 3H, SCH₃),

1.65 (s, 3H, SCH₃).

5.4. Reaction of 1b with LiBuⁿ

The complex 1b (200 mg, 0.246 mmol) and 4 equiv.

of n-butyllithium (V = 390 ll) were heated in tetrahy-

drofuran (30 ml) at reﬂux for 12h. The solvent was

then removed under vacuum and only one organome-

tallic product was extracted with diethylether (2 · 20

ml). Evaporation of the volatiles aﬀorded complex 5

as an analytically pure, red solid (116 mg, 65% yield).

Complex 5 was obtained as a mixture of two insepara-

ble isomers 5a and 5b in the 87:13 ratio by

chromatography.

5.2. Reaction of 1a with NaBH₄

The complex 1a (200 mg, 0.28 mmol) and 4 equiv. of

NaBH₄(42mg) were heated in acetonitrile (50 ml) at re-

ﬂux for 3h. The colour of the solution turned from red

to maroon. The solvent was then removed under vac-

1

uum, and the H NMR analysis of the crude products

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

4597

Complex 5: Anal. Calc. for C₃₁H₃₈Mo₂N₂S₃: C, 51.2;

5.6. Reaction of 1b with BuⁿMgCl

H, 5.3; N, 3.8. Found: C, 51.3; H, 5.4; N, 3.7%. IR (KBr

pellet, cm^ꢂ1), 5a: 2052 s and 1933 s (m CN); 5b: 1995 m

and 1857 m (m CN). H NMR d/ppm (CDCl₃; 298 K),

Several attempts to react complex 1b (110 mg, 0.135

mmol) with 3.8 equiv. of BuⁿMgCl (V = 250 ll) either

by stirring at room temperature or by heating in tetrahy-

drofuran (30 ml) at reﬂux for 1 h failed. The starting

material was fully recovered in each experiment.

1

5a: 6.83–6.66 (m, 6H, CHar(xyl)), 5.17 (s, 5H, C₅H₅),

2

4.91, 4.62 (m,1H,C₅H₆), 3.70 (AB, J_H–H= 10.4 Hz,

2

1H, C₅H₆), 3.31, 3.25 (m,1H, C₅H₆), 3.20 (AB, J_H–

_H= 10.4 Hz, 1H, C₅H₆), 2.56 (s, 3H, SCH₃), 2.22, 2.11

(s, 6H, CH₃), 1.54, 1.31 (s, 3H, SCH₃); 5b: 6.80–6.61

(m, 6H, CHar(xyl)), 5.36 (m, 1H, C₅H₆), 5.32 (s, 5H,

5.7. Reaction of 3 with NaBH₄and NaBD₄

2

C₅H₅), 5.14 (m, 1H, C₅H₆), 3.93 (AB, J_H–H= 10.8

A mixture of 3 (300 mg, 0.54 mmol) and NaBH₄(82

mg, 2.16 mmol) was stirred in thf (15 ml) until a clear

red solution was obtained (about 1 h). The solvent

was then removed under vacuum and the organometal-

lic product was extracted from the residue with diethyl

ether (20 ml). Evaporation of the volatiles gave a solid,

which was washed with pentane (10 ml) to aﬀord com-

plex 7 as an analytically pure red powder (200 mg,71%

yield). Complex 7 was obtained as a mixture of two

inseparable isomers 7a and 7b in 4:1 ratio by

chromatography.

Hz, 1H, C₅H₆), 3.24, 3.12 (m, 1H, C₅H₆), 2.27 (s, 3H,

SCH₃), 2.06, 2.03 (s, 6H, CH₃), 1.86, 1.64 (s, 3H,

SCH₃). ¹³C{¹H} NMR d/ppm (C₆D₆; 298 K), 5a:

211.7, 199.5 (xylNC), 135–125 (Car(xyl)), 89.4 (C₅H₅),

78.5, 77.8, 62.8, 59.8, 46.0 (C₅H₆), 26.0, 19.2, 10.2

(SCH₃).

5.5. Reaction of 1b with NaBH₄

Method (a) – In a Schlenk tube: The complex 1b (100

mg, 0.123 mmol) and 4 equiv. of NaBH₄(18 mg) were

heated in tetrahydrofuran (30 ml) at reﬂux for 4h. The

solvent was then removed under vacuum and the crude

Complex 7: Anal. Calc. for C₁₅H₂₀Mo₂O₂S₃: C, 34.6;

H, 3.9. Found: C, 34.7; H, 3.9%. IR (CH₂Cl₂, cm^ꢂ1), 7a:

2850 w (m C–Hendo), 2780 m (m C–Hexo), 1938 s and

1

products were characterised in (CD₃)₂CO by H NMR

1859 s (m CO). H NMR d/ppm (CDCl₃; 298 K), 7a:

spectroscopy. A valuable amount of the starting mate-

rial (20%) was recovered. The compounds 5 and 6 were

formed in the 85:15 ratio. Attempts to separate the three

complexes by chromatography failed.

5.37 (s, 5H, C₅H₅), 5.09, 5.02, 3.95, 3.86 (m, 1H, CH

(C₅H₆)), 3.67 and 3.54 (AB, J_H–H= 12.3 Hz, 2H,

2

CH₂(C₅H₆)), 2.53, 2.52, 1.31 (s, 3H, SCH₃), 7b: 5.63,

5.55 (m, 1H, CH (C₅H₆)), 5.51 (s, 5H, C₅H₅), 3.31,

3.25 (m, 1H, CH(C₅H₆)), obscured peaks and 3.16

1

Complex 6: H NMR d/ppm (CDCl₃; 298 K): 10.40

2

(s, 1H, CH), 7.0–6.6 (m, 3H, CHar.), 5.29, 5.02 (s, 5H,

C₅H₅), 2.13, 2.04 (s, 3H, CH₃), 1.83, 1.57, 1.55 (s, 3H,

SCH₃).

(AB, J_H–H= 13.6 Hz, 2H, CH₂(C₅H₆)), 2.28, 2.23,

1.59 (s, 3H, SCH₃). ¹³C NMR d/ppm (CDCl₃; 298 K),

1

7a: 242.9, 231.5 (s, CO), 90.7 (dm, J_C–H= 179.0 Hz,

1

Method (b) – In a sealed tube: The reaction was car-

ried out as above, but the reagents were heated at 120 ꢁC

in a sealed tube dipped into an oil-bath. After complete

consumption of the starting material (about 4h), the sol-

vent was removed under vacuum and the crude products

C₅H₅), 81.9 (dm, J_C–H= 178.5 Hz, C₅H₆), 81.3 (dm,

1

¹J_C–H= 176.5 Hz, C₅H₆), 71.7 (dm, J_C–H= 170.5 Hz,

1

C₅H₆), 70.0 (dm, J_C–H= 174.0 Hz, C₅H₆), 46.6 (ddm,

¹J_C–H= 141.5 Hz, CH₂(C₅H₆)), 25.5, 25.2, 6.3 (q,

¹J_C–H= 139.0 Hz, SCH₃); 7b: 242.1, 233.6 (CO), 90.4

(C₅H₅), 82.7, 81.0, 66.0, 65.0 (CH(C₅H₆)), 41.0

(CH₂(C₅H₆)), 26.2, 25.9, 8.4 (SCH₃).

1

were analysed in (CD₃)₂CO by H NMR spectroscopy.

Three complexes, 5, 6 and [Mo₂Cp₂(l-SMe)₄], were

detected in the 13:55:23 ratio. The organometallic com-

pounds were then extracted with diethyl ether (20 ml).

Evaporation of the volatiles gave a solid, which was dis-

solved in CH₂Cl₂(3 ml) and chromatographed on silica

gel. Elution with hexane–CH₂Cl₂(4:1) removed only one

red band, which gave, after evaporation of solvents, a

mixture (44 mg) of compounds 6 (yield: 30%) and

[Mo₂Cp₂(l-SMe)₄] (yield: 35%) (¹H NMR analysis) as

a red-brown powder in 1:1 ratio. The complex 5 decom-

posed onto the silica gel column.

No elemental analysis is available for 6 as a pure sam-

ple of this compound was not obtained after chromatog-

raphy. However, 6 has been fully characterised by X-ray

analysis of red crystals picked from a diethyl ether solu-

tion of an equimolar (¹H NMR analysis) mixture of 6

and [Mo₂Cp₂(l-SMe)₄] at 8 ꢁC.

Using a similar procedure, a solution of 3 (300 mg,

0.54 mmol) and NaBD₄(91 mg, 2.16 mmol) in thf (15

ml) was stirred at room temperature for 1 h. Work up

of the product as described above aﬀorded 8 in good

yield. Complex 8 was obtained as a mixture of four

inseparable isomers 8a–8d in the ratio 70:17:6:1 by

chromatography.

¹H NMR d/ppm (CDCl₃; 298 K), 8a: 5.36 (s, 5H,

C₅H₅), 5.08, 5.01, 3.94, 3.83, 3.51 (m, 1H, C₅H₅D),

2.53, 2.51, 1.31 (s, 3H, SCH₃); 8b: 5.63 (m, 1H,

C₅H₅D), 5.51 (s, 5H, C₅H₅), 3.65, 3.55, 3.32, 3.26 (m,

1H, C₅H₅D), 2.28, 2.23, 1.58 (s, 3H, SCH₃); 8c: 5.40

(s, 5H, C₅H₅), 5.23, 4.93, 3.67, 3.17 (m, 1H, C₅H₅D),

2.36, 1.44, 1.33 (s, 3H, SCH₃); 8d: 5.58 (m, 1H,

C₅H₅D), 5.55 (s, 5H, C₅H₅), 5.18, 5.13, 3.21 (m, 1H,

C₅H₅D), 2.10, 1.78, 1.63 (1, 3H, SCH₃).

4598

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

5.8. Reaction of 3 with alkyl-arylmagnesium chloride

RMgCl

(9.5%) and the oxo-derivatives trans–syn/anti-[Mo₂Cp₂-

(CO)(O)(l-SMe)₂] (2.5%). The residue was dissolved in

n-hexane (3 ml) and chromatographed on silica gel. Elu-

tion with hexane-diethyl ether (95:5) removed a red

band, which gave, after evaporation of the solvents,

compound 10 as a pure sticky solid (ꢁ95 mg, 85% yield).

For the reasons which applied for complex 9 an elemen-

tal analysis cannot be provided for 10. It was obtained

as mixture of four inseparable isomers 10a, 10b, 10c

and 10d in the 20:5.5:2.5:1 ratio by chromatography.

Complex 10: IR (CH₂Cl₂, cm^ꢂ1): 1939 vs and 1863 s

(a) – R = CH₃: In a typical procedure ca. 3 equiv. of

methylmagnesium chloride (V = 200 ll) were added to a

suspension of 3 (100 mg, 0.18 mmol) in tetrahydrofuran

(30 ml). The solution was stirred at room temperature

for 15 min and then was ﬁltered to remove insoluble

material. The ﬁltrate was evaporated to yield an oily res-

1

idue (96.4 mg), which was shown by H NMR analysis

to contain three compounds: 9 (70%), trans–syn/anti-

[Mo₂Cp₂(CO)₂(l-SMe)₂] (24%) and [Mo₂Cp₂(l-SMe)₄]

(6%). The residue was dissolved in n-hexane (3ml) and

chromatographed on silica gel. Elution with hexane-

diethyl ether (95:5) removed an orange band, which

aﬀorded, after evaporation of the solvents, compound

9 as a pure sticky orange solid (65.5 mg, 68% yield).

Complex 11 was obtained as a mixture of four insepara-

ble isomers 9a, 9b, 9c and 9d in 10:2.5:2:1 ratio by

chromatography.

1

(m CO). H NMR d/ppm (CDCl₃; 298 K), 10a: 5.37 (s,

5H, C₅H₅), 4.90, 4.82, 4.09, 4.00 (m, 1H, C₅H₅CHMe₂),

3.01 (dm, ³J_H–H= 8.2 Hz, 1H, C₅H₅CHMe₂), 2.52, 2.50,

1.30 (s, 3H, SCH₃), 1.08 (m, 1H, C₅H₅CHMe₂), 0.86 (m,

6H, C₅H₅CHMe₂); 10b: 5.50 (s, 5H, C₅H₅), 5.43, 3.40,

3.35, 2.78 (m, 1H, C₅H₅CHMe₂), 2.29, 2.24, 1.54 (s,

3H, SCH₃), 0.94 (m, 1H, C₅H₅CHMe₂), 0.73 (dm,

³J_H–H= 6.6 Hz, 6H, C₅H₅CHMe₂); 10c: 5.40 (s, 5H,

C₅H₅), 5.05, 4.75, 4.02, 3.87, 2.66 (m, 1H,

C₅H₅CHMe₂), 2.36, 1.44, 1.32 (s, 3H, SCH₃); 10d: 5.53

(s, 5H, C₅H₅), 5.08, 5.02, 3.96, 2.88 (m, 1H,

C₅H₅CHMe₂), 2.10, 1.75, 1.58 (s, 3H, SCH₃).

Complex 9: IR (CH₂Cl₂, cm^ꢂ1): 1939 vs and 1862 s (m

CO). Complex 9 was only obtained as a sticky solid in

spite of several attempts to get it as a powder by crystal-

lization from various solvents. For this reason, no ele-

mental analysis is available for 9. ¹H NMR d/ppm

(CDCl₃; 298 K), 9a: 5.37 (s, 5H, C₅H₆), 4.90, 4.83,

Trans-syn-[Mo₂Cp₂(CO)(O)(l-SMe)₂]: ¹H NMR

d/ppm (CDCl₃; 298 K): 5.96 (s,5H, C₅H₅), 5.42 (s, 5H,

C₅H₅), 2.32 (s, 6H, SCH₃).

3

4.03, 3.94 (m, 1H, C₅H₅Me), 3.52 (q, J_H–H= 6.0 Hz,

Trans-anti-[Mo₂Cp₂(CO)(O)(l-SMe)₂]: ¹H NMR

d/ppm (CDCl₃; 298 K): 6.03 (s, 5H, C₅H₅), 5.40 (s,

5H, C₅H₅), 2.68 (s, 3H, SCH₃), 2.17 (s, 3H, SCH₃).

(c) – R = (CH₂)₃CH₃: When a red suspension of 3

(200 mg, 0.36 mmol) in 30 ml of tetrahydrofuran was

treated with butylmagnesium chloride (2.5 equiv.,

V = 460 ll), a rapid colour change to dark-red occurred.

After stirring for 1 h, the solvents were removed to dry-

ness and the residue was dissolved in hexane (5 ml) and

chromatographed on silica gel. Elution with CH₂Cl₂–

hexane (1:1) aﬀorded a red band, which gave 11 as a

red sticky solid (m = 170 mg, 82% yield). Complex 11

was obtained as a mixture of four inseparable isomers

11a, 11b, 11c and 11d in 19.5:4.5:3:1 ratio by

chromatography.

1H, C₅H₅Me), 2.52, 2.50, 1.30 (s, 3H, SCH₃), 0.84 (d,

³J_H–H= 6.0 Hz, 3H, CH₃); 9b: 5.51 (s, 1H, C₅H₅),

5.45, 3.38, 3.31, 3.17 (m, 1H, C₅H₅Me), 2.29, 2.24,

3

1.56 (s, 3H, SCH₃), 0.74 (d, J_H–H= 6.1 Hz, 3H,

CH₃); 9c: 5.40 (s, 5H, C₅H₅), 5.05, 4.76, 3.97, 3.82,

3.04 (m, 1H, C₅H₅Me), 2.36, 1.44, 1.32 (s, 3H, SCH₃),

3

0.96 (d, J_H–H= 6.6 Hz, 3H, CH₃); 9d: 5.54 (s, 5H,

C₅H₅), 5.11, 4.97, 4.15, 3.26 (m, 1H, C₅H₅Me), 2.10,

3

1.75, 1.59 (s, 3H, SCH₃), 0.78 (d, J_H–H= 6.5 Hz, 3H,

CH₃). ¹³C {¹H} NMR d/ppm (CDCl₃; 298 K), 9a:

243.0, 230.7 (CO), 90.7 (C₅H₅), 79.4, 78.9, 77.9, 76.3

(C₅H₅Me), 52.5 (C₄H₄CHMe), 30.7 (CH₃), 25.4, 25.2,

6.4 (SCH₃); 9b: 242.4, 233.1 (CO), 90.5 (C₅H₅), 78.9,

72.2, 71.3 (C₅H₅Me), 46.8 (C₄H₄CHMe), 29.7 (CH₃),

26.3, 26.0, 8.4 (SCH₃); 9c: 242.4, 231.1 (CO), 90.5

(C₅H₅), 79.6, 76.0, 74.4 (C₅H₅Me), 52.3 (C₄H₄CHMe),

31.9 (CH₃), 8.9, 7.2 (SCH₃); 9d: 242.0, 232.0 (CO),

71.0, 69.0, 65.8, (C₅H₅Me), 47.5 (C₄H₄CHMe), 27.0

(CH₃), 15.3, 11.0, 9.0 (SCH₃).

Complex 11: IR (CH₂Cl₂, cm^ꢂ1): 1939 vs and 1862 s

1

(m CO). H NMR d/ppm (CDCl₃; 298 K), 11a: 5.37 (s,

5H, C₅H₅), 4.91, 4.83, 4.07, 3.97, 3.38 (m, 1H,

C₅H₅Buⁿ), 2.52, 2.50, 1.30 (s, 3H, SCH₃), 1.28 (m, 6H,

(CH₂)₃CH₃), 0.88 (m, 3H, (CH₂)₃CH₃); 11b: 5.51 (s,

5H, C₅H₅), 5.46, 3.42, 3.38, 3.06 (m, 1H, C₅H₅Buⁿ),

2.29, 2.24, 1.55 (s, 3H, SCH₃), 1.10 (m, 6H, (CH₂)₃CH₃),

0.82 (m, 3H, (CH₂)₃CH₃); 11c: 5.40 (s, 5H, C₅H₅), 5.06,

4.77, 4.01, 3.85 (m, 1H, C₅H₅Buⁿ), 2.36, 1.44, 1.32 (s,

3H, SCH₃), 1.10 (m, 6H, (CH₂)₃CH₃), 0.82 (m, 3H,

(CH₂)₃CH₃); 11d: 5.54 (s, 5H, C₅H₅), 5.28, 5.14, 3.60,

3.17 (m, 1H, C₅H₅Buⁿ), 2.09, 1.75, 1.58 (s, 3H, SCH₃),

1.21 (m, 6H, (CH₂)₃CH₃), 0.98 (m, 3H, (CH₂)₃CH₃).

¹³C {¹H} NMR d/ppm (CDCl₃; 298 K), 11a: 243.1,

230.6 (CO), 90.8 (C₅H₅), 79.9, 79.3, 76.5, 74.9

(b) – R = CH(CH₃)₂: A mixture of 3 (110 mg, 0.180

mmol) and 2 equiv. of isopropylmagnesium chloride

(V = 200 ll) was stirred in tetrahydrofuran (20 ml) until

a clear red solution was obtained (about 15 min). The

solvent was then removed under vacuum and the orga-

nometallic products were extracted from the residue

with diethyl ether (2 · 20 ml). Evaporation of the vola-

tiles gave an oily product (105 mg), which was shown

1

by H NMR (CDCl₃) analysis to contain three com-

pounds: 10 (88%), trans–syn-[Mo₂Cp₂(CO)₂(l-SMe)₂]

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

4599

1

(C₅H₅Buⁿ), 58.1 (C₄H₄CHBuⁿ), 45.6, 29.0 ((CH₂)₃CH₃),

25.4, 25.2 (SCH₃), 23.0 ((CH₂)₃CH₃), 14.2 ((CH₂)₃CH₃),

6.4 (SCH₃); 11b: 242.6, 233.4 (CO), 90.5 (C₅H₅), 81.0,

79.2, 71.0, 70.0 (C₅H₅Buⁿ), 52.2 (C₄H₄CHBuⁿ), 46.6,

28.9 ((CH₂)₃CH₃), 26.4, 26.3 (SCH₃), 22.8 ((CH₂)₃CH₃),

14.2 ((CH₂)₃CH₃), 8.2 (SCH₃); 11c: 242.6 (CO), 90.7

(C₅H₅), 79.5, 78.0, 74.7, 73.1 (C₅H₅Buⁿ), 57.7

(C₄H₄CHBuⁿ), 29.8 ((CH₂)₃CH₃), 26.0 (SCH₃), 14.2

((CH₂)₃CH₃), 8.9, 7.2 (SCH₃).

(d) – R = C₆H₅: A large excess of phenylmagnesium

(4 equiv., V = 720 ll) was added to a suspension of 3

(200 mg, 0.36 mmol) in tetrahydrofuran (30 ml) at

ꢂ60 ꢁC. The mixture was stirred until the temperature

reached 20 ꢁC, aﬀording a clear red solution. The sol-

vents were then removed under vacuum and the organo-

metallic products were extracted from the residue with

diethyl ether (3 · 20 ml). Evaporation of the volatiles

gave an oily product (211 mg), which was shown by

¹H NMR (CDCl₃) analysis to contain only one com-

pound 12 (98% yield). Complex 12 was formed as a mix-

ture of four isomers 12a, 12b, 12c and 12d in 21:9:2:1

ratio. Red analytically pure crystals of 12 of X-ray qual-

ity were obtained from cold diethyl ether by fractional

crystallization of the complex. When the above reaction

was conducted at ambient temperature trans–syn bis

(carbonylthiolato) and oxo-derivatives, [Mo₂Cp₂(CO)₂-

(l-SMe)₂] (8.5%) and [Mo₂Cp₂(CO)(O)(l-SMe)₂]

(1.5%), were recovered together with compound 12

(90%), which was obtained as a mixture of four isomers

12a, 12b, 12c and 12d in the 8:3:2:1 ratio.

shown by H NMR analyses to be a mixture of the g⁴-

cyclopentadiene compound [R = CH₃:

9

(76%);

R = Buⁿ: 11 (82%)], trans–syn/anti-[Mo₂Cp₂(CO)₂(l-

SMe)₂] (R = CH₃: 13.5%; R = Buⁿ: 12.5%) and trans–

syn/anti oxo-derivatives [Mo₂Cp₂(CO)(O)(l-SMe)₂]

(R = CH₃: 10.5%; R = Buⁿ: 5.5%). This mixture was

dissolved in n-hexane (5 ml) and chromatographed on

silica gel. Elution with n-hexane-diethyl ether (95:5) re-

moved either an orange (R = CH₃) or red (R = Buⁿ)

band, which gave, after evaporation of the solvents,

the g⁴-cyclopentadiene complex as a pure sticky orange

or red solid [9 (R = CH₃): 95 mg, 49% yield; 11

(R = Buⁿ): 109 mg, 52.5% yield].

5.10. Preparation of 16

A solution of [Mo₂Cp₂(l-SMe)₂(l-Cl)(l-PPh₂)] (300

mg, 0.47 mmol) in acetonitrile (60 ml) was stirred in

the presence of 2.5 equiv. of Bu^tNC (V = 130 ll) for 1

h at room temperature. The colour of the solution turned

from violet to orange. Evaporation of the volatiles gave a

solid, which was washed with diethyl ether (2 · 20 ml)

and pentane (2 · 20 ml) to aﬀord complex 16 as an ana-

lytically pure ochre powder (315 mg, 79% yield).

Complex 16: Anal. Calc. for C₃₄H₄₄ClMo₂N₂PS₂, 0.5

CH₂Cl₂: C, 49.0; H, 5.4, N, 3.3; P, 3.7. Found: C, 48.8;

H, 5.4; N, 3.4; P, 4.2%. IR (KBr pellet, cm^ꢂ1): 2127 s (m

1

CN). H NMR d/ppm ((CD₃)₂CO; 298 K): 7.4–6.8 (m,

3

10H, C₆H₅), 5.37 (d, J_P–H= 0.7 Hz, 10H, C₅H₅), 2.45

(s, 6H, SCH₃), 1.66 (s, 18H, C(CH₃)₃). ¹³C{¹H} NMR

2

Complex 12: Anal. Calc. for C₂₁H₂₄Mo₂O₂S₃. C, 42.3;

H, 4.05. Found: C, 42.1; H, 4.06%. IR(CH₂Cl₂, cm^ꢂ1):

d/ppm ((CD₃)₂CO_;298 K): 162.0 (d, J_P–C= 9.3 Hz,

Bu^tNC), 135.2 (d, J_P–C= 40.4 Hz, Cipso(C₆H₅)),

1

1939 s and 1862 s (m CO). H NMR d/ppm (CDCl₃;

134.0 (d, J_P–C= 7.4 Hz, C₆H₅), 129.0 (s, Cpara(C₆H₅)),

127.8 (d, J_P–C= 9.9 Hz, C₆H₅), 89.7 (s, C₅H₅), 59.6 (s,

CMe₃), 30.3 (s, C(CH₃)₃), 27.6 (d, J_P–C= 18 Hz,

298 K), 12a: 7.58–7.15 (m, 5H, C₆H₅), 5.37 (m, 5H,

C₅H₅), 5.01, 4.94, 4.62, 4.17, 4.08 (m, 1H, C₅H₅Ph),

2.54, 2.52, 1.30 (s, 3H, SCH₃); 12b: 7.58–7.15 (m, 5H,

C₆H₅), 5.52 (s, C₅H₅), 5.43, 4.39, 3.52 (m, 1H,

C₅H₅Ph), 2.30, 2.26, 1.62 (s, 3H, SCH₃); 12c: 7.58–7.15

(m, 5H, C₆H₅), 5.40 (s, 5H, C₅H₅), 5.17, 4.84, 4.11,

3.97 (m, 1H, C₅H₅Ph), 2.38, 1.43, 1.32 (s, 3H, SCH₃);

12d: 7.58–7.15 (m, 5H, C₆H₅), 5.54 (s, 5H, C₅H₅) 4.48,

3.68, (m, 1H, C₅H₅Ph), 2.11, 1.77, 1.66 (s, 3H, SCH₃).

3

SCH₃).

5.11. Reaction of 16 with NaBH₄

The complex 16 (200 mg, 0.236 mmol) and 4 equiv. of

NaBH₄(35 mg) were stirred in tetrahydrofuran (50 ml)

at room temperature for 1 h. The solvent was then re-

moved under vacuum and the organometallic product

was extracted with diethyl ether (2 · 20 ml). Evapora-

tion of the volatiles gave a solid, which was dissolved

in CH₂Cl₂(5 ml) and chromatographed on ﬂorisil. Elu-

tion with dichloromethane removed an orange band,

which gave, after evaporation of the solvents, com-

pound 17 as an analytically pure, orange powder (134

mg, 80% yield).

5.9. Reaction of 3 with alkyllithium LiR (R = CH₃, Buⁿ)

A suspension of the red complex 3 (200 mg, 0.36

mmol) in 40 ml of tetrahydrofuran was stirred at room

temperature in presence of n equiv. of alkyllithium

(R = CH₃: n = 2, V = 45 ll; R = Buⁿ: n = 4, V = 576

ll) until a clear orange (R = CH₃) or red (R = Buⁿ)

solution was obtained (about 20 min). Filtration of the

mixture and removal of the solvents gave an oily resi-

due. Organometallic products were extracted from the

residue with either dichloromethane or diethyl ether

(2 · 30 ml). Evaporation of the volatiles aﬀorded sticky

solids (R = CH₃: 125 mg; R = Buⁿ: 133 mg), which were

5.12. Reactions of g⁴-cyclopentadiene compounds 9, 11

and 12 with HBF₄

A dichloromethane (20 ml) solution of 9 (150 mg,

0.28 mmol) or 11 (150 mg, 0.26 mmol) or 12 (210 mg,

4600

N. Cabon et al. / Journal of Organometallic Chemistry 690 (2005) 4583–4601

0.35 mmol) was treated at room temperature with 1

equiv. of tetraﬂuoroboric acid (9: V = 38 ll; 11:

V = 35 ll; 12: V = 47 ll). The mixture was stirred for

a few minutes, and the solution changed from either or-

ange (9) or red (11, 12) to dark-red. The volume of the

solution was then reduced under vacuum and diethyl

ether was added to precipitate powders that were

washed twice with pentane (2 · 10 ml), aﬀording mar-

oon products 13 (86 mg, 49% yield), 14 (100 mg,

51.5% yield) and 15 (80 mg, 33% yield). Complexes

13–15 were each obtained as mixtures of two isomers

13a and 13b, 14a and 14b, and 15a and 15b in 4:1, 3:1

and 7:1 ratios, respectively.

5.13. X-ray crystallographic studies of 5, 6 and 12

All measurements were made at 100 K on a Nonius

KappaCCD diﬀractometer with Mo Ka radiation,

˚

k = 0.71073 A. Standard procedures were used to solve

and reﬁne each structure [2,27] In general, non-hydro-

gen atoms were reﬁned with anisotropic displacement

tensors. H-atoms were located using stereochemical con-

siderations or from diﬀerence maps and subsequently

rode on their parent C atoms. Only the H-atoms bonded

to C(7) and C(10) in 12 were freely reﬁned. Further de-

tails for each structure are given in Table 3. For 5 and 6

the crystals were of poor quality for diﬀraction analysis;

the results presented here are in each case the better of

two separate (and consistent) analyses performed with

diﬀerent crystals. For 5 there was the further complica-

tion, discussed above, that the C₅H₅and C₅H₆rings are

disordered. Attempts to model this disorder explicitly

were unsuccessful. Apart from systematic errors in bond

lengths discussed above, the disorder manifests itself

through some physically unreasonable vibration tensors,

particularly for the ring carbon atoms.

Complex 13: Anal. Calc. for C₁₆H₂₁BF₄Mo₂O₂S₃: C,

30.9; H, 3.4. Found: C, 30.5; H, 3.4%. IR (CH₂Cl₂,

cm^ꢂ1), 13a: 1999 vs and 1967 sh (m CO), 1100–1000 s,

br (m B–F); 13b: masked peak and 1941 m (m CO),

1

1100–1000 s, br (m B–F). H NMR d/ppm ((CD₃)₂CO;

298 K), 13a: 6.02 (s, 5H, C₅H₅), 5.93, 5.86 (m, 2H,

C₅H₄Me), 2.65, 2.61 (s, 3H, SCH₃), 2.16 (s, 3H, CH₃),

1.75 (s, 3H, SCH₃); 13b: 6.05 (s, 5H, C₅H₅), 5.98, 5.82

(m, 2H, C₅H₄Me), 2.47, 2.24 (s, 3H, SCH₃), 1.81 (s,

3H, CH₃), 1.75 (s, 3H, SCH₃). ¹³C{¹H} NMR d/ppm

((CD₃)₂CO; 298 K), 13a: 233.7, 233.0 (CO), 94.1

(C₅H₅), 97.1, 94.7, 93.9, 90.5, 90.4 (C₅H₄Me), 27.3,

26.5 (SCH₃), 15.4 (CH₃), 8.5 (SCH₃); 13b: 234.0,

233.4 (CO), 94.1 (C₅H₅), 97.3 93.5, 92.8, 91.0, 89.4

(C₅H₄Me).

Acknowledgements

We are grateful to N. Kervarec and Dr. R. Pichon for

the recording of two dimensional NMR on a Bruker

CRX 500 (500 MHz) spectrometer. We thank the

CNRS, the EPSRC, Glasgow University and the Uni-

versity of Brest for ﬁnancial support.

Complex 14: Anal. Calc.for C₁₉H₂₇BF₄Mo₂O₂S₂,

CH₂Cl₂: C, 32.1; H, 3.9. Found: C, 32.0; H, 3.8%.

IR (CH₂Cl₂, cm^ꢂ1) 1999vs and 1972 sh (m CO). ¹H

NMR d/ppm ((CD₃)₂CO; 298 K), 14a:6.01 (s, 5H,

C₅H₅), 5.99, 5.87 (m, 2H, C₅H₄Me), 2.65, 2.60 (s,

3

Appendix A. Deposited material

3H, SCH₃), 2.35(t, J_H–H= 7.6 Hz, 2H, CH₂-(CH)₂–

CH₃), 1.74 (s, 3H, SCH₃), 1.65, 1.45 (m, 2H, CH₂-

(CH)₂–CH₃), 0.92 (t, J_H–H= 7.2 Hz, 3H, (CH₂)₃CH₃);

3

Crystallographic data for the structures reported in

this paper have been deposited with the Cambridge

Crystallographic Data Centre as CCDC Nos. 268261–

268263. Copies can be obtained free of charge on

application to CCDC, 12 Union Road, Cambridge

CB2 1EZ, UK [fax: (international) +44 1223 336 033;

e-mail: deposit@ccdc.com.ac.uk]. Also deposited as

supplementary data are tables of crystallographic data

atomic parameters and bond lengths and angles.

Supplementary data associated with this article can

be found, in the online version, at doi:10.1016/

j.jorganchem.2005.07.034.

14b: 6.04 (s, 5H, C₅H₅), 5.92, 5.83 (m, 2H, C₅H₄Buⁿ),

2.69, 2.62 (s, 3H, SCH₃), 2.41 (t, 2H, (CH₂)₃CH₃),

1.79 (s, 3H, SCH₃), 1.72, 1.27 (m, 2H, (CH₂)₃CH₃),

0.87 (t, 3H, (CH₂)₃CH₃). ¹³C{¹H} NMR d/ppm

((CD₃)₂CO_;298 K), 14a: 233.9, 233.2 (CO), 97.3, 95.2

(C₅H₄Buⁿ), 94.3 (C₅H₅), 93.6, 91.1, 90.7 (C₅H₄Buⁿ),

33.8 (CH₂–CH₂–CH₂CH₃), 27.5, 26.7 (SCH₃), 22.9,

15.6 (CH₂–CH₂–CH₂–CH₃), 14.0 ((CH₂)₃CH₃), 8.6

(SCH₃); 14b: 234.4, 233.6 (CO), 96.4, 94.4 (C₅H₄Buⁿ),

94.1 (C₅H₅), 92.7, 91.8, 90.6 (C₅H₄Buⁿ), 34.3 (CH₂–

CH₂–CH₂–CH₃), 28.3 (SCH₃), 9.4 ((CH₂)₃CH₃), 8.7

(SCH₃).

Complex 15: IR (CH₂Cl₂, cm^ꢂ1): 1999 s and 1951 mw

(m CO), 1075–1053 s, br (m B–F). ¹H NMR d/ppm

((CD₃)₂CO; 298 K), 15a: 7.68–7.65 and 7.39–7.37 (m,

5H, C₆H₅), 6.56 (m, 2H, C₅H₄Ph), 6.11 (m, 2H,

C₅H₄Ph), 5.96 (s, 5H, C₅H₅), 2.51, 2.49, 1.49 (s, 3H,

SCH₃); 15b: 7.90 and 7.42–7.41 (m, 5H, C₆H₅), 6.67

(m, 2H, C₅H₄Ph), 5.97 (m, 5H, C₅H₅), 2.48, 2.47, 1.44

(s, 3H, SCH₃).

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Article Doi

Controlled nucleophilic activation of different sites in [Mo 2Cp2L2(μ-SMe)2(μ-L′)] + cations (L = ButNC, xylNC, CO; L′ = SMe or PPh2)

DOI: 10.1016/j.jorganchem.2005.07.034

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