Fischer-type alkyl(hydrazino)carbene complexes: New synthetic potential in comparison with aminocarbene complexes

www.elsevier.nl/locate/jorganchem

Journal of Organometallic Chemistry 617–618 (2001) 399–411

Fischer-type alkyl(hydrazino)carbene complexes: new synthetic

potential in comparison with aminocarbene complexes

Emanuela Licandro ^a,*, Stefano Maiorana ^a, Dario Perdicchia ^a, Clara Baldoli ^a,

Claudia Graiff ^b, Antonio Tiripicchio ^b

^aDipartimento di Chimica Organica e Industriale, Uni6ersita` degli Studi di Milano, Via C. Golgi 19, I-20133 Milan, Italy

^bDipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Uni6ersita` di Parma,

Centro di Studio per la Strutturistica Diffrattometrica del C.N.R., Parco Area delle Scienze 17A, I-43100 Parma, Italy

Received 25 July 2000; accepted 6 September 2000

Abstract

A general picture is given of the reactivity of the two Fischer-type alkyl(hydrazino)carbene complexes (CO)₅CrꢀC(CH₃)-

N(Bn)N(CH₃)₂(1) and (CO)₄^¸C^¹rꢀ^¹C^¹(C^¹H^¹₃^¹)N^¹¹(B^¹n^º)N(CH₃)₂(3). Unlike their organic isolobal hydrazide analogues, they easily yield

the corresponding a-anions at −78°C, which react with various electrophiles. Furthermore, the tetracarbonyl chelate 3 (easily

generated from 1) has greater synthetic potential than aminocarbenes: for example, it can be alkylated stepwise twice in the

reserved.

Keywords: Hydrazino carbenes; Hydrazides; Alkylation; Chelate Fischer carbenes

1. Introduction

bases at low temperature. The resulting anions easily

react with electrophilic reagents, such as alkyl halides [3],

epoxides [4], aldehydes [5] and Michael acceptors [6], and

so the complexes have been widely (and also stereoselec-

tively) functionalised, thus allowing the synthesis of a

large number of interesting organic compounds.

The synthesis of alkyl(hydrazino)carbene complex 1

(Chart 2) made it possible to compare its reactivity with

that of aminocarbenes; a further interesting point is that

alkyl(hydrazino)carbenes can be used as synthetic hydra-

zide equivalents because hydrazides are the organic

isolobal analogues of hydrazinocarbenes. We here show

that the formal substitution of the pentacarbonyl-

chromium moiety for the oxygen atom in the hydrazide

leads to a fundamental differentiation in chemical reac-

tivity. In this study, we chose to use the pentacarbonyl

methyl(hydrazino)carbene of chromium(0) 1 as a model

compound.

We have recently [1] published two complementary

methodologies for the synthesis of alkyl(hy-

drazino)carbene complexes, a new class of nitrogen-sta-

bilised Fischer-type carbenes (Chart 1).

Chart 1.

As a result, we have been able to synthesise a large

number of complexes, and this has opened up the

possibility of systematically studying this new class of

organometallics about which very little has so far been

reported in the literature [2].

It is well known that the hydrogen atoms of aminocar-

bene complexes located in the a position with respect to

the carbene carbon atom are acidic, and that these

complexes can be efﬁciently deprotonated using strong

* Corresponding author. Tel.: +39-02-2663978; fax: +39-02-

70636857.

E-mail address: emanuela.licandro@unimi.it (E. Licandro).

Chart 2.

PII: S0022-328X(00)00633-1

400

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

2. Results and discussion

2.1. Crystal structures and spectroscopic data of the

complexes (Z)-1 and (E)-1

Compound 1 was synthesised as previously reported

[1a]¹. The two rotational isomers (Z)-1 and (E)-1 can

be easily separated by ﬂash column chromatography

and are conﬁgurationally stable (Chart 2).

The crystal structures of both isomers have been

determined by X-ray diffraction methods. Views of the

structures of (Z)-1 and (E)-1 are shown in Figs. 1 and

2, selected bond distances and angles in them in Tables

1 and 2, respectively. The structural features are typical

of the Fischer-type pentacarbonylchromium aminocar-

bene complexes [7]. The structural parameters in the

isomers are very similar, the only difference being in the

carbenic Cr(1)–C(6) bond, which is slightly longer in

,

(E)-1, 2.132(3) A, than in (Z)-1, 2.108(2) A. In both

structures the N1N2C6C10 moiety is strictly planar,

with the Cr and C7 atoms deviating on opposite sides

,

by 0.206(1) and 0.095(4) A in (E)-1 and 0.265(1) and

,

0.169(3) A in (Z)-1, respectively.

Fig. 2. ORTEP view of the structure of complex (Z)-1 together with

the atomic numbering scheme. The ellipsoids for the atoms are drawn

at 30% probability level.

Comparison of the spectroscopic data of hydrazi-

nocarbene complex (E)-1 and aminocarbene complex

(Z)-2 (Chart 3) [7] reveals that the chemical shift values

1

of the H- and ¹³C-NMR are very similar, thus indicat-

ing their qualitative analogy in terms of charge distribu-

tion. The structural parameters are also quite similar,

,

including the carbenic CrꢁC bond which is 2.134(3) A

in (Z)-2.

Chart 3.

However, the isomers 1 have some steric peculiarities

due to the presence of the second nitrogen atom. (i) The

b-nitrogen lone pair in both the (E)- and (Z)-1 isomers

forms a dihedral angle of about 90° with the lone pair

of the a-nitrogen, thus making it almost coplanar with

the Cr–C–N(a) moiety. The same conformation is also

found in trialkyl substituted hydrazides, and makes it

possible to minimise the interaction between the two

lone pairs [8]. Moreover, in contrast to hydrazinocarbe-

nes, trialkyl substituted hydrazides only exist as (E)-iso-

Fig. 1. ^ORTEPview of the structure of the complex (E)-1 together

with the atomic numbering scheme. The ellipsoids for the atoms are

drawn at 30% probability level.

¹The trisubstitued hydrazide necessary to the synthesis of com-

pound 1 has been prepared following a general and efﬁcient protocol

we have set up. A patent application has been presented for this

procedure.

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

401

Table 2

mers, due to the steric repulsion between the oxygen

,

Selected bond lengths (A) and angles (°) for (Z)-1

and b-nitrogen lone pairs present in (Z)-isomers. (ii) In

the (Z)-1 isomer the b-nitrogen N2 is rather close to the

chromium atom, the N2···Cr separation being 3.316(2)

Bond distances

Cr(1)–C(1)

Cr(1)–C(2)

Cr(1)–C(3)

Cr(1)–C(4)

Cr(1)–C(5)

Cr(1)–C(6)

O(1)–C(1)

O(2)–C(2)

O(3)–C(3)

O(4)–C(4)

O(5)–C(5)

N(1)–C(6)

N(1)–C(10)

N(1)–N(2)

C(6)–C(7)

C(10)–C(11)

1.863(3)

1.875(3)

1.885(3)

1.887(3)

1.881(3)

2.108(2)

1.149(3)

1.147(3)

1.142(3)

1.139(3)

1.317(3)

1.485(3)

1.422(2)

1.511(3)

1.520(3)

,

A, with the lone pair pointing towards the metal atom.

This fact could facilitate the elimination of a CO ligand

and the chelation of the nitrogen atom. (iii) Some

intramolecular interaction of the type CO···p_arenecould

be envisaged in the (E)-1 isomer between the oxygen

atom O5 of a carbonyl and the p electron cloud of the

aromatic ring of the benzyl substituent. The structural

parameters indicated by Gambaro et al. [9] to empha-

sise this type of interaction are: the C5–O5 line is

almost parallel to the arene plane (deviation angle:

13.0(2)°), the distance between the O5 atom and the

,

mean plane of the arene is 3.176(2) A, the minimum

Bond angles

Table 1

C(1)–Cr(1)–C(2)

C(1)–Cr(1)–C(5)

C(2)–Cr(1)–C(5)

C(1)–Cr(1)–C(4)

C(5)–Cr(1)–C(4)

C(1)–Cr(1)–C(3)

C(2)–Cr(1)–C(3)

C(4)–Cr(1)–C(3)

C(2)–Cr(1)–C(6)

C(5)–Cr(1)–C(6)

C(4)–Cr(1)–C(6)

C(3)–Cr(1)–C(6)

C(6)–N(1)–N(2)

C(6)–N(1)–C(10)

N(2)–N(1)–C(10)

O(1)–C(1)–Cr(1)

O(2)–C(2)–Cr(1)

O(3)–C(3)–Cr(1)

O(4)–C(4)–Cr(1)

O(5)–C(5)–Cr(1)

N(1)–C(6)–C(7)

N(1)–C(6)–Cr(1)

C(7)–C(6)–Cr(1)

N(1)–C(10)–C(11)

91.92(11)

87.82(12)

89.97(16)

90.70(11)

90.37(15)

87.57(11)

89.81(14)

90.06(14)

86.07(10)

91.22(10)

91.32(9)

93.38(10)

118.07(16)

125.65(18)

116.28(16)

179.5(3)

178.1(3)

174.3(2)

179.0(3)

176.1(3)

113.71(18)

127.96(16)

118.30(15)

114.20(17)

,

Selected bond lengths (A) and angles (°) for (E)-1

Bond distances

Cr(1)–C(3)

Cr(1)–C(4)

Cr(1)–C(2)

Cr(1)–C(1)

Cr(1)–C(5)

Cr(1)–C(6)

O(1)–C(1)

O(2)–C(2)

O(3)–C(3)

O(4)–C(4)

O(5)–C(5)

N(1)–C(6)

N(1)–N(2)

N(1)–C(10)

C(6)–C(7)

C(10)–C(11)

1.863(3)

1.880(3)

1.878(4)

1.885(3)

1.890(3)

2.132(3)

1.147(3)

1.153(3)

1.147(4)

1.139(3)

1.144(3)

1.313(3)

1.449(3)

1.470(3)

1.508(4)

1.504(4)

Bond angles

C(3)–Cr(1)–C(4)

C(3)–Cr(1)–C(2)

C(4)–Cr(1)–C(2)

C(3)–Cr(1)–C(1)

C(2)–Cr(1)–C(1)

C(3)–Cr(1)–C(5)

C(4)–Cr(1)–C(5)

C(1)–Cr(1)–C(5)

C(4)–Cr(1)–C(6)

C(2)–Cr(1)–C(6)

C(1)–Cr(1)–C(6)

C(5)–Cr(1)–C(6)

C(6)–N(1)–N(2)

C(6)–N(1)–C(10)

N(2)–N(1)–C(10)

O(1)–C(1)–Cr(1)

O(2)–C(2)–Cr(1)

O(3)–C(3)–Cr(1)

O(4)–C(4)–Cr(1)

O(5)–C(5)–Cr(1)

N(1)–C(6)–C(7)

N(1)–C(6)–Cr(1)

C(7)–C(6)–Cr(1)

N(1)–C(10)–C(11)

91.19(14)

85.24(14)

91.96(13)

95.65(13)

88.69(14)

81.38(14)

89.94(13)

91.01(13)

85.97(12)

91.85(13)

87.20(12)

101.60(12)

120.0(2)

124.2(2)

115.8(2)

178.0(3)

174.3(3)

176.4(3)

178.9(3)

170.6(3)

114.0(3)

128.9(2)

117.1(2)

114.7(3)

and maximum distances from O5 to the carbon atoms

of the six-membered of the arene ring (3.202(3) and

,

4.373(5) A) and the distance from C5 to the nearest

,

carbon atom of the arene ring (3.111(4) A).

2.2. General reacti6ity of complex 1

The structural features of the two isomers 1 revealed

by the X-ray studies described above suggested that

they may have interesting and important a priori effects

on reactivity: ﬁrst of all, the lone pair of the b-nitrogen

atom in the (Z)-rotamer is directed towards the metal

atom, and therefore may be suitably oriented to coordi-

nate to the metal by displacing a carbonyl ligand;

furthermore, the lithium enolates of both the (E) and

(Z) rotamers may have the same structure 4, which

402

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

methyl iodide, allyl bromide and t-butylbromoacetate,

and gives quantitative yields of a mixture of the ex-

pected alkylated pentacarbonyl complexes 5–7 as Z

rotamers, as well as the tetracarbonyl derivatives 8–10

(Scheme 3). The crystal structure of complex 8 has been

previously reported by us [1a]. As shown in Scheme 3,

the amount of tetracarbonyl derivatives 8–10 in the

reaction mixtures increases with the bulkiness of the R

group, probably because of a steric repulsion between

the benzyl substituent on the nitrogen atom and the

alkyl substituent on the a carbon atom (the alkyl

substituent pushes the b-nitrogen close to the chromium

atom, thus facilitating the elimination of a CO ligand

and the chelation of the nitrogen atom).

Scheme 1. Transformation of the (Z)-1 complex into the chelate 3.

would be stabilised by the chelation of the lithium

cation by the nitrogen and chromium atoms. The reac-

tivity of the isomers 1 completely conﬁrmed both ex-

pectations: when heated in dichloromethane at reﬂux

for 3.5 hours, compound (Z)-1 is quantitatively trans-

formed into the solid, red chelate complex 3 (Scheme 1)

[1a].

The mixtures of penta- and tetracarbonyl complexes

can be converted into tetracarbonyl derivatives 8–10 by

means of heating in dichloromethane at 39°C (Scheme

3) and, once again, the chelate complex is more easily

obtained as the bulkiness of the a substituent increases.

We observed the transformation of t-butoxycarbonyl-

methyl derivative 7 into tetracarbonyl complex 10 at

room temperature during puriﬁcation over column

chromatography of the mixture of the two complexes.

Starting from complex 1, the overall yields in com-

pounds 8–10 are very high (see Scheme 3).

Despite the presence of the strained four member

ring, this new complex is much more stable to air than

the starting compound 1 in solution and also in the

solid state (see below for the oxidation conditions). On

the contrary, (E)-1 is thermally stable.

Treatment of the (E) and (Z) rotamers (alone or

together) with n-BuLi in THF solution at −78°C,

followed by quenching with water, quantitatively gives

the (Z)-1 isomer (Scheme 2).

This result is fully explained by the conformation of

intermediate 4², in which a ﬁve-member ring is formed

as a result of the coordination of the lithium cation to

both of the chromium and nitrogen atoms³.

2.4. Reacti6ity of the complex 3 anion with electrophiles

It is worth noting that, when treated with lithium

bases, aminocarbenes lead to a mixture of the two

rotamers, which in some cases reduces their usefulness

in stereoselective synthesis.

The chelate complex 3 can be deprotonated using

n-BuLi at −78°C, and the anion easily reacts with

iodomethane at the same temperature to give com-

pound 8 in quantitative yield (Scheme 4).

An explorative study using other electrophiles

showed that the anion of 3 also reacts with ethylene

and propylene oxides, cyclohexenone and benzalde-

hyde, respectively providing functionalised carbene

complexes 11, 12, 13 and 14 in good yields (Scheme 5).

The reactions with epoxides were run in the presence

of one equivalent of BF₃·Et₂O as a Lewis acid, follow-

ing a protocol previously set up for aminocarbenes [4].

In these reactions, a new stereocentre is formed in the

g or b position with respect to the carbene carbon

atom. The high chemical yields of the reactions and the

stability of compounds 11–14 make the anion of

chelate complex 3 a very interesting and useful d²-syn-

thon in the formation of new carbon–carbon bonds.

2.3. Reacti6ity of complex 1 anion with electrophiles

The anion of complex 1,⁴generated by treatment

with n-BuLi as described above, is easily alkylated with

²The chelation of Li⁺to a CO ligand seems less probable because

of the more constrained geometry of the resulting seven-membered

ring.

³To support this hypothesis, we performed an experiment in which

we added 12-crown-4 ether to the reaction mixture in order to

disassociate the lithium chelate and, after quenching with water,

recovered a mixture of the two (E) and (Z) rotamers.

⁴The pK_aof some of the synthesised hydrazino complexes was

measured in collaboration with Professor Claude F. Bernasconi of the

University of California (results to be published).

Scheme 2. Transformation of a (Z/E) mixture of complex 1 into the (Z)-1.

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

403

Scheme 3. Alkylation reactions of complex 1.

2.5. Dialkylation reactions

One particularly interesting behaviour concerning the

reactivity of chelate complex 8 is the fact that it can

react further with electrophiles: the anion generated by

using n-BuLi at −78°C can be alkylated with

iodomethane or benzyl bromide to give the correspond-

ing dialkylated complexes 15 and 16 in high yields

(Scheme 6).

Chart 4.

The a-difunctionalised complexes 15 and 16 are very

stable to air, as is shown by the time required for their

oxidation to the corresponding hydrazides (Scheme 7):

exposure to air and sunlight for 7 days transforms

complex (E)-1 into the organic isolobal hydrazide 18 in

90% yield, but it takes 78 days to transform chelate

complex 15 into organic product 19 under the same

conditions (Scheme 7).

In chelate and dialkylated complexes, there is proba-

bly great steric hindrance around the chromium atom

and, furthermore, the presence of the two alkyl sub-

stituents in the a-position pushes the chelate b-nitrogen

atom closer to the metal and thus stabilises the four-

member ring. The qualitative order of increasing stabil-

ity of hydrazinocarbene complexes to air and sunlight

is: a-methyl pentacarbonylBa-methyl tetracarbonylB

monoalkyl tetracarbonylBdialkyl tetracarbonyl.

The most important consequence of this reactivity is

the formation of a new stereogenic centre on the a

carbon atom, as in compound 16. This behaviour dif-

ferentiates chelate complex 8 from the aminocarbenes

bearing an alkyl group on the carbene carbon atom,

which makes alkylation almost impossible [3]. The par-

ticular reactivity shown in Scheme 6 opens up the

possibility of using type 8 chelate complexes in a new

strategy for developing the stereoselective carbon-car-

bon bond forming reactions that are still impossible to

develop using Fischer aminocarbene chemistry⁵.

The different reactivity of the a-alkylation reactions

between the amino- and chelate hydrazinocarbene can

be attributed to the rigid structure of the latter, because

the presence of the four-member ring in complex 8

forces the hydrazino moiety towards the metal atom.

Unlike in the case of aminocarbenes, the a-carbon

atom in ‘enolate’ 17 (Chart 4) is less sterically hindered

and more accessible to electrophile attack, an explana-

tion that is also supported by the fact that the pentacar-

bonyl ethyl(hydrazino)carbene 5 cannot be further

alkylated on the a-carbon.

2.6. Reaction of nitrogen–nitrogen bond breaking

In an attempt to obtain further functionalisation at

the a-position, the a-dimethyl complex 15 was made to

react with n-BuLi at −78°C, and then quenched with

iodomethane. This unexpectedly led to the quantitative

⁵In this regard, diastereoselective aldol and Michael additions are

currently in progress in our laboratory; and very high d.e. values are

obtained (results to be published).

Scheme 4. Alkylation reaction of the chelate complex 3.

404

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

Scheme 7. Oxidation reactions of complexes 1 and 15.

Scheme 5. Reactions of the chelate complex 3 with electrophiles.

Scheme 8. Rearrangment of complex 15 into aminocarbene 20.

Finally, although hydrazinocarbenes are isolobal or-

ganic analogues of hydrazides, trialkyl hydrazide eno-

lates have only been used for carbon–carbon bond

forming reactions in rare and speciﬁc cases [10] because

hydrazides do not react to or are unstable towards bases

[8]. This means that they are not useful for synthetic

purposes in reactions with bases, but hydrazinocarbenes

can act as efﬁcient synthetic equivalents.

Scheme 6. Alkylation reactions of complex 8.

formation of the new complex 20 (Scheme 8), an

aminocarbene arising from a nitrogen–nitrogen bond

breaking and rearrangment that introduces a stereocen-

tre between the two nitrogen atoms⁶.

The structural parameters inferred from the X-ray

structures of both isomers anticipated and justiﬁed some

of the behaviours we found for complexes 1 and 3.

3. Conclusions

We here report the reactivity of the pentacarbonyl

methyl(hydrazino)carbene 1 and tetracarbonyl deriva-

tive 3, which were chosen as model compounds of the

new class of hydrazinocarbene complexes. Both com-

pounds have a high synthetic potential in carbon–

carbon bond forming reactions. The most interesting

characteristic, which is due to the presence of the b-ni-

trogen atom in complex 1, is the possibility of generat-

ing rigid structures, such as the ‘enolate’ 4 or the chelate

3. In particular, as a consequence of the decreased con-

formational freedom and easier accessibility to the a-

carbon atom in chelate complexes, it is possible to

alkylate the ethyl(hydrazino)carbene 8 and therefore

generate a new stereogenic centre on the a-carbon atom.

Furthermore, both the penta- and tetracarbonyl

derivatives proved to be very stable and easy to handle,

thus making them simple and practical to use in

synthesis.

4. Experimental

4.1. General experimental considerations

All reactions were carried out under an atmosphere of

dry argon or nitrogen; glasswares were ﬂame-dried be-

fore use. THF was dried by distillation over sodium

wires/benzophenone prior to use; butyllithium solutions

were titrated prior to use. Flash and vacuum chro-

matography were performed with Merck silica gel 60,

230–400 mesh. Melting points (m.p.s) were determined

with a Bu¨chi 510 apparatus and are uncorrected. All

samples were ﬁltered over a celite pad before NMR

spectroscopic registration. ¹H-NMR (300 MHz, CDCl₃)

and ¹³C-NMR (75 MHz, CDCl₃) spectra were recorded

on Bruker AC 300 and Bruker AMX 300. IR spectra

were recorded on Perkin–Elmer FTIR 1725X. Mass

spectra (EI, FAB) were recorded on Vg Analytical 7070

EQ.

⁶Further work is in progress in our laboratory concerning the

study of the mechanism of this rearrangement and the synthetic

potential.

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

405

4.2. Preparation of Na₂Cr(CO)₅solution

(M⁺–3CO); 256 (M⁺–4CO); 228 (M⁺–5CO); 207

(M⁺–3CO -C₆H₅); 184 (M⁺–5CO–NMe₂); 176 (M⁺–

Cr(CO)₅); 132 (M⁺–Cr(CO)₅–NMe₂).

To a mixture of naphtalene (21.08 g, 164 mmol) and

ﬁnely cut metallic sodium (3.13 g, 136 mmol), 98 ml of

THF was added. The mixture, deep green, was stirred

at room temperature (r.t.) for 2.5 h. Using a double-

tipped needle, the naphtalenide solution was dropped

into a slurry of Cr(CO)₆(14.06 g, 61.3 mmol) in 130 ml

of THF at −78°C, during 2 h. The mixture was

allowed to warm to r.t. and stirred overnight. The

brown dianion solution (0.268 M) can be kept at

−20°C for several weeks.

4.4. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)methyl carbene]chromium(0) (3)

Complex (Z)-1 (1.346 g, 3.658 mmol) was dissolved

in 100 ml of dichloromethane and the solution degassed

by ultrasound for 30 min. The mixture was then heated

at reﬂux for 3 h. After cooling to r.t., the solvent was

removed in vacuo. The residue (1.1761 g) was pure

complex 3. Yield 95%. Yellow–orange solid; m.p.

124°C (CH₂Cl₂–pentane). Anal. Found: C, 53.14; H,

5.05; N, 8.33. Calc. for C₁₅H₁₆O₄N₂Cr: C, 52.94; H,

4.74; N, 8.23%. ¹³C-NMR (CDCl₃) l (ppm) 289.5

(C_carbene), 232.2 (trans CO), 229.6 (cis CO), 218.4 (cis

CO), 133.8 (C_qPh), 129.5, 128.5, 126.1 (C Ph), 52.2

(NMe₂) 48.9 (CH₂Ph); 28.9 (CrCCH₃); IR/FT (nujol) w

(cm⁻¹) 1997 (trans CO), 1888, 1868, 1830 (cis CO); MS

(FAB⁺), m/z 340 (M⁺); 312 (M⁺–CO); 284 (M⁺–

2CO); 256 (M⁺–3CO); 228 (M⁺–4CO); 91 (C₇H⁺₇).

4.3. Synthesis of complex 1

To 35.8 ml of the Na₂Cr(CO)₅solution in THF (9.6

mmol, 1.5 equivalents) cooled to −78°C, a solution of

the hydrazide 18 (6.4 mmol, one equivalent) in 4 ml of

THF was added. The mixture was allowed to react at

−78°C for 30 min and then at 0°C for 6.5 h. After

cooling to −78°C, trimethylsilyl chloride (19.2 mmol, 3

equivalent) was added and the mixture allowed to react

at −78°C for 30 min and then to r.t. for 30 min.

Neutral alumina (16 g), degassed under vacuum, was

then added to the reaction mixture and the solvent

removed under reduced pressure. The residue was

puriﬁed by column chromatography over silica gel;

eluent light petroleum for the elution of naphtalene and

then light petroleum–diethyl ether 8:2), thus recovering

rotamer (E)-1, 0.713 g and rotamer (Z)-1, 0.715 g.

Yield of the two rotamers 60.6%⁷.

4.5. Isomerisation of complex (E)-1 into (Z)-1

n-BuLi (0.3 mmol, 0.18 ml of a 1.6 M solution in

hexane) was added dropwise to a −78°C cooled solu-

tion of complex (E)-1 (0.1 g, 0.27 mmol) in 4 ml of

THF. After 30 min, 4 ml of water was added to the

reaction mixture at the same temperature. The organic

solvent was removed in vacuo and the residue extracted

with dichloromethane. The organic layer was separated,

dried over Na₂SO₄and the solvent removed in vacuo,

to give 0.099 g of pure complex (Z)-1. Yield \98%.

4.3.1. (E)-Pentacarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)methyl carbene]chromium(0) (1)

Yellow solid; m.p. 57°C (Et₂O–pentane). X-ray qual-

ity crystals were grown by slow diffusion of pentane

into a saturated solution of the complex in diethyl

ether.

4.6. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)ethyl carbene]chromium(0) (8)

MS (EI), m/z 368 (M⁺); 340 (M⁺–CO); 204 (M⁺–

3CO); 256 (M⁺–4CO); 228 (M⁺–5CO); 207 (M⁺–

3CO–C₆H₅); 184 (M⁺–5CO–NMe₂); 176 (M⁺–

Cr(CO)₅); 132 (M⁺–Cr(CO)₅–NMe₂).

4.6.1. Starting from complex 1

n-BuLi (6.4 mmol, 4.2 ml of a 1.53 M solution in

hexane) was added dropwise to a −78°C cooled solu-

tion of complex (E)-1 (2.32 g, 6.3 mmol) in 20 ml of

THF. After 30 min, iodomethane (0.79 ml, 12.69 mmol)

was added by a syringe. The mixture was let to react at

−78°C for 5 min and then at r.t. for 25 min. After that

time, 15 ml of water was added to the reaction mixture.

The organic solvent was removed in vacuo and the

residue extracted with dichloromethane (3×50 ml).

The organic layer was separated, dried over Na₂SO₄

and the solvent removed in vacuo to give the reaction

product as a mixture of (Z)-5 and 8 complexes. From

4.3.2. (Z)-Pentacarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)methyl carbene]chromium(0) (1)

Yellow solid; m.p. 85°C (CH₂Cl₂–pentane). X-ray

quality crystals were grown by slow diffusion of pen-

tane into a saturated solution of the complex in

CH₂Cl₂.

IR/FT (nujol) w (cm⁻¹) 2050 (CO trans), 1926, 1882

(CO cis); MS (EI), m/z 368 (M⁺); 340 (M⁺–CO); 204

1

the H-NMR analysis of the crude, the ratio of (Z)-5/8

was 79.3: 20.7. The mixture of the complexes was

directly dissolved in 100 ml of CH₂Cl₂and the solution

was degassed under nitrogen by ultrasound for 30 min.

⁷For both (E) and (Z) rotamers of complex 1, ¹H- and ¹³C-NMR

spectroscopic data have already been reported [1a].

406

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

The mixture was heated at reﬂux for 40 min, then

cooled to r.t. and ﬁltered over a celite pad. The solvent

was removed in vacuo to give complex 8 (2.238 g, 6.32

mmol) as pure compound. Yield \98%.

CH₂Cl₂and heating at reﬂux for 30 min. Overall yield

from 1, 95.6%.

4.7.1. Z-Pentacarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)1-but-3-enyl carbene]chromium(0)

(Z)-6

4.6.1.1. Z-Pentacarbonyl[(N-benzyl-N%,N%-dimethylhy-

drazinyl)ethyl carbene]chromium(0) (5-Z). ¹H-NMR

(CDCl₃, 300 MHz) l (ppm) 7.50–7.00 (5H, m, H_arom.),

4.85 (2H, s, CH₂Ph), 3.01 (2H, q, J=7.6 Hz, CrCCH₂),

2.59 (6H, s, NMe₂), 1.03 (3H, t, J=7.6 Hz, CH₂CH₃);

¹³C-NMR (CDCl₃) l (ppm) 280.2 (C_carbene), 225.1 (trans

CO), 218.6 (cis CO), 134.6 (C_qPh), 129.3, 127.9, 125.2

(C Ph), 48.1 (CH₂Ph), 43.8 (NMe₂); 43.0 (CrCCH₂),

10.7 (CH₂CH₃); IR/FT (nujol) w (cm⁻¹) 2043 (trans

CO), 1900–1800 (cis CO).

¹H-NMR (CDCl₃, 300 MHz) l (ppm) 7.45–7.00 (5H,

m, H_arom.), 5.75 (1H, ddt, CH₂CHꢀCH₂, J_trans=16.9;

J_cis=10.17; J_HC–CH2=6.6), 5.06 (1H, dd, CH₂CHꢀCH₂

cis,

J_tran=16.9;

J_gem=1.36), 5.00 (1H, dd,

CH₂CHꢀCH₂trans, J_cis=10.17, J_gem=1.36), 4.89 (2H,

s, CH₂Ph), 3.15–3.00 (2H, m, CrCCH₂), 2.60 (6H, s,

NMe₂), 2.35–2.2 (2H, m, CH₂–CHꢀ); IR/FT (neat) w

(cm⁻¹) 2049 (trans CO), 1800–1970 (cis CO).

4.6.1.2.

Tetracarbonyl[(N-benzyl-N%,N%-dimethylhy-

4.7.2. Tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)1-but-3-enyl carbene]chromium(0)

(9)

drazinyl)ethyl carbene]chromium(0) (8). Orange solid;

m.p. 119°C (CH₂Cl₂–pentane). X-ray quality crystals

were grown by slow diffusion of pentane into a satu-

rated solution of the complex in toluene. IR/FT (nujol)

w (cm⁻¹); 1997 (trans CO), 1865, 1829 (cis CO), 727,

685 (g CH_arom); MS (FAB⁺), m/z 354 (M⁺); 326 (M⁺–

CO); 298 (M⁺–2CO); 270 (M⁺–3CO); 242 (M⁺–

4CO); 206 (M⁺–2CO–C₇H₈); 198 (M⁺–4CO–NMe₂);

190 (M⁺–Cr(CO)₄); 146 (M⁺–Cr(CO)₄–NMe₂); 107

(M⁺–4CO-NMe₂–PhCH₂); 91 (C₇H⁺₇).

Orange solid; m.p. 90–95°C (CH₂Cl₂–pentane).

Anal. Found: C, 57.02; H, 5.16; N, 7.55. Calc. for

1

C₁₈H₂₀O₄N₂Cr: C, 56.84; H, 5.26; N, 7.36%. H-NMR

(CDCl₃, 300 MHz) l (ppm) 7.45–7.00 (5H, m, H_arom),

6.0–5.8 (1H, m, CH₂CHꢀCH₂), 5.12 (1H, dd,

CH₂CHꢀCH₂cis, J_trans=16.9; J_gem=1.25), 5.05 (1H,

dd, CH₂CHꢀCH₂trans, J_cis=10.05, J_gem=1.25), 4.69

(2H, s, CH₂Ph), 2.80 (6H, s, NMe₂), 2.8–2.75 (4H, m,

CH₂–CH₂); ¹³C-NMR (CDCl₃)

l

(ppm) 292.6

4.6.2. Starting from complex 3

(C_carbene), 231.9 (trans CO), 229.8 (cis CO), 218.4 (cis

CO), 137.1 (CHꢀ), 133.4 (Cq Ph), 129.5, 128.5, 126.5 (C

Ph), 116.1 (ꢀCH₂), 52.4 (NMe₂) 49.2 (CH₂Ph); 40.8

n-BuLi (0.64 mmol, 0.41 ml of a 1.55 M solution in

hexane) was added dropwise to a −78°C cooled solu-

tion of complex 3 (0.214 g, 0.63 mmol) in 5 ml of THF.

After 30 min, iodomethane (0.08 ml, 1.28 mmol) was

added by a syringe. The mixture was let to react at

−78°C for 5 min and then at r.t. for 20 min. After that

time, 4 ml of water was added to the reaction mixture.

The organic solvent was removed in vacuo and the

residue extracted with dichloromethane (3×15 ml).

The organic layer was separated, dried over Na₂SO₄

and the solvent removed in vacuo to give the complex

8 (0.223 g, 0.63 mmol). Yield \98%.

(CrCCH₂), 32.5 (CH₂CHꢀ); IR/FT (neat) w (cm⁻¹

)

1998 (trans CO), 1865, 1828 (cis CO); 1641 (CꢀC); 916

(ꢀCH); MS (FAB⁺), m/z 380 (M⁺); 352 (M⁺–CO);

324 (M⁺–2CO); 296 (M⁺–3CO); 268 (M⁺–4CO).

4.8. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)2-terbutoxycarbonylethyl carbene]-

chromium(0) (10)

The same procedure as reported for complex 8 was

used. The following amounts of reagents and solvent

used: (E)-1, 0.207 g, 0.562 mmol, 5 ml THF, 0.38 ml

(0.56 mmol) of 1.48 M BuLi–hexane solution, tert-bu-

tyl bromoacetate 0.165 ml, 1.1 mmol. After work-up, a

crude of 0.2948 g was obtained, as a 22:78 mixture of

the two (Z)-7 and 10 complexes and the unreacted

tert-butyl bromoacetate. This crude was puriﬁed by

column chromatography over silica gel (30 g),

eluent light petroleum–diethyl ether (1:1). The fraction

of the (Z)-7 complex was completely transformed into

complex 10 within 1 h at r.t. Yield in complex 10,

83.7%.

4.7. Synthesis of (Z)-pentacarbonyl

[(N-benzyl-N%,N%-dimethylhydrazinyl)1-but-3-enyl

carbene]chromium(0) (Z)-6

The same procedure as reported for complex 8 was

used. In this case we started from the (Z)-1 rotamer

and the following amounts of reagents and solvent

used: (Z)-1 0.1367 g, 0.371 mmol, 5 ml THF, 0.255 ml

(0.41 mmol) of 1.6 M BuLi hexane solution, allyl

bromide 0.047 ml, 0.56 mmol. After work-up, a crude

of 0.1476 g was obtained, as a 56: 44 mixture of the two

(Z)-6 and 9 complexes. This mixture was quantitatively

converted into complex 9 by dissolving in 50 ml of

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

407

4.8.1. Z-Pentacarbonyl[(N-benzyl-N%,N%-dimethyl-

4.10. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

hydrazinyl)2-terbutoxycarbonylethyl carbene]

chromium(0) (7-Z)

dimethylhydrazinyl)-1-(butyl-3-hydroxy)

carbene]chromium(0) (12)

¹H-NMR (CDCl₃, 300 MHz) l (ppm) 7.5–7.00 (5H,

m, H_aromat), 5.08 (2H, s, CH₂Ph), 3.12 (2H, t, J=7.6

Hz, CrCCH₂), 2.60 (2H, t, J=7.6 Hz, CH₂COO), 2.60

(6H, s, NMe₂), 1.39 (9H, s, OC(CH₃)₃).

The reaction was run as reported for complex 11,

using the following amounts of reagents and solvent:

complex 3, 0.1014 g, 0.298 mmol; BuLi, 0.21 ml, 0.33

mmol of a 1.58 M solution in hexane; BF₃·OEt₂, 0.045

ml, 0.35 mmol; propylene oxide, 0.045 ml, 0.35 mmol.

After 4 h at −78°C, 0.4 ml of NaHCO₃saturated

aqueous solution was added at the same temperature.

The solvent was then evaporated at reduced pressure

and the crude mixture puriﬁed by column chromatogra-

phy over silica gel; eluent CH₂Cl₂for recovering unre-

acted complex 3 (0.0153 g) and then CH₂Cl₂–MeOH

(9.5:0.5) for complex 12 (0.1008 g); yield 85%.

4.8.2. Tetracarbonyl[(N-benzyl-N%,N%-dimethyl-

hydrazinyl)2-terbutoxycarbonyletyl carbene]chromium(0)

(10)

1

Red oil; H-NMR (CDCl₃, 300 MHz) l (ppm) 7.5–

7.1 (5H, m, H_aromat), 4.87 (2H, s, CH₂Ph), 3.1–3.0 (2H,

m, CrCCH₂), 2.9–2.8 (2H, m, CH₂COO), 2.80 (6H, s,

NMe₂), 1.45 (9H, s, OC(CH₃)₃); ¹³C-NMR (CDCl₃) l

(ppm) 290.2 (C_carbene), 231.7 (trans CO), 229.5 (cis CO),

218.0 (cis CO), 172.0 (COO), 133.8 (Cq Ph), 129.3,

128.1, 126.9 (C Ph), 80.8 (C(Me)₃), 52.0 (NMe₂) 49.2

(CH₂Ph); 36.1 (CrCCH₂), 33.8 (CH₂COO), 27.9

(C(CH₃)₃); IR/FT (neat) w (cm⁻¹) 2000 (trans CO),

1871, 1833, (cis CO), 1723 (COO^tBu); 731, 686 (g

CH_arom).

4.10.1. Complex 12

Orange oil; ¹H-NMR (CDCl₃, 300 MHz) l (ppm)

7.45–7.1 (5H, m, H_arom), 4.79, 4.69 (2H, AB sistem,

J=17.2 Hz, CH₂Ph), 4–3.8 (1H, m, CHOH), 2.9–2.7

(2H, m, CrCCH₂), 2.81, 2.79 (6H, s, NMe₂), 2.35–2.2

(1H, m, CH₂CHOH), 2.1–1.5 (1H, m, CH₂CHOH), 1.3

(1H, s br., OH), 1.27 (3H, d, J=6.2 Hz, CH₃); ¹³C-

NMR (CDCl₃) l (ppm) 292.5 (C_carbene), 232.1 (trans

CO), 229.6 (cis CO), 218.3 (cis CO), 133.6 (Cq Ph),

129.4, 128.4, 126.0 (C Ph), 67.5 (CHOH), 52.2 (NMe₂),

49.2 (CH₂Ph), 37.6 (CrCCH₂), 37.4 (CH₂), 23.7 (CH₃);

IR/FT (neat) w (cm⁻¹) 3397 (w OH), 1997 (w trans CO),

1870, 1828 (w cis CO), 729, 686 (g CH_aromat); MS

(FAB⁺), m/z 398 (M⁺); 370 (M⁺–CO); 342(M⁺–

2CO); 314 (M⁺–3CO); 286(M⁺–4CO).

4.9. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)-1-(propyl-3-hydroxy) carbene]-

chromium(0) (11)

n-BuLi (0.34 mmol, 0.215 ml of a 1.58 M solution in

hexane) was added dropwise to a −78°C cooled solu-

tion of complex 3 (0.1045 g, 0.307 mmol) in 5 ml of

THF. After 30 min, BF₃·Et₂O (0.045 ml, 0.35 mmol)

was added by a syringe and gaseous ethylene oxide was

bubbled for 5 min. After stirring for 5 h at −78°C, 0.5

ml of NaHCO₃saturated aqueous solution was added

at the same temperature. The solvent was then evapo-

rated at reduced pressure and the crude mixture

puriﬁed by column chromatography over silica gel;

eluent CH₂Cl₂for recovering unreacted complex 3

(0.0415 g) and then CH₂Cl₂–MeOH (9.5:0.5) for com-

plex 11 (0.0602 g); yield 51%.

4.11. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)metylene-(3-cycloesanone)

carbene]chromium(0) (13)

n-BuLi (0.327 mmol, 0.2 ml of a 1.645 M solution in

hexane, 1.1 equivalents) was added dropwise to a

−78°C cooled solution of complex 3 (0.101 g, 0.297

mmol, one equivalent) in 5 ml of THF and the mixture

allowed to react at the same temperature for 30 min;

cyclohexenone (0.035 ml, 0.363 mmol, 1.22 equivalents)

was then added by a syringe. After stirring for 3 h at

−78°C, 0.25 ml of water was added at the same

temperature. The organic solvent was removed in vacuo

and the residue taken up with CH₂Cl₂and dried over

Na₂SO₄. The solvent was then evaporated at reduced

pressure giving a crude, as a red oil, of 0.126 g which

was puriﬁed by column chromatography over silica gel

(15 g); eluent: Et₂O thus recovering a ﬁrst fraction of

unreacted complex 3, 0.01 g, and a second fraction of

complex 13, 0.1099 g; yield 84%.

4.9.1. Complex 11

Yellow–orange oil; H-NMR (CDCl₃, 300 MHz) l

1

(ppm) 7.5–7.1 (5H, m, H_arom), 4.74 (2H, s, CH₂Ph),

3.9–3.7 (2H, m, CH₂OH), 2.9–2.7 (2H, m, CrCCH₂),

2.80 (6H, s, NMe₂), 2.4–2.1 (2H, m, CH₂); ¹³C-NMR

(CDCl₃) l (ppm) 292.8 (C_carbene), 232.2 (trans CO),

229.6 (cis CO), 218.6 (cis CO), 218.4 (cis CO), 133.5

(Cq Ph), 129.4, 128.4, 126.0 (C Ph), 62.1 (CH₂OH),

52.3 (NMe₂), 49.2 (CH₂Ph), 37.8 (CrCCH₂), 31.4

(CH₂); IR/FT (neat) w (cm⁻¹) 3369 (w OH), 1997 (w

trans CO), 1865, 1828 (w cis CO), 728, 686 (g CH_arom);

MS (FAB⁺), m/z 384 (M⁺); 356 (M⁺–CO); 328 (M⁺–

2CO); 300 (M⁺–3CO); 272 (M⁺–4CO); 248 (M⁺–Cr–

3CO).

408

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

4.11.1. Complex 13

Orange solid; m.p. 143°C (CH₂Cl₂–pentane). Anal.

Found: C, 57.40; H, 5.90; N, 6.21. Calc. for

C₂₁H₂₄O₅N₂Cr: C, 57.79; H, 5.54; N, 6.42%. H-NMR

(C_carbene), 231.9 (trans CO), 229.3 (cis CO), 218.5 (cis

CO), 218.2 (cis CO), 143.5 (Cq CHOHPh), 133.4 (Cq

NCH₂Ph), 129.4, 128.4, 125.5 (C Ph), 73.2 (CHOH),

52.6, 52.2 (NMe₂), 50.8 (CrCCH₂), 49.3 (NCH₂Ph);

IR/FT (neat) w (cm⁻¹) 3402 (OH), 2000 (trans CO),

1865, (cis CO), 728, 701, 685.7 (g CH_aromat); MS (EI),

m/z 446 (M⁺); 429 (M⁺–OH); 334 (M⁺–4CO); 289

(M⁺–4CO–HNMe₂); 107 (PhCHꢀOH⁺); 91 (C₇H⁺₇);

79 (C₆H⁺₇); 69 (C₅H⁺₉).

1

(CDCl₃, 300 MHz) l (ppm) 7.5–7.1 (5H, m, H_arom),

4.71 (2H, s, CH₂Ph), 2.9–2.8 (1H, m, CrCCH₂), 2.80

(3H, s, NMe₂), 2.81 (3H, s, NMe₂), 2.65–2.50 (1H, m,

CrCCH₂, 2H, m, CHCH₂CO), 2.45–2.30 (1H, m,

COCH₂CH₂CH₂ax.), 2.30–2.15 (1H, m, COCH₂-

CH₂CH₂eq., 1H, m, COCH₂CH₂CH₂ax.), 2.15–2.00

(CHCH₂CO), 2.00–1.90 (1H, m, COCH₂CH₂CH₂eq.),

1.90–1.70 (1H, m, COCH₂CH₂CH₂ax.), 1.50–1.30

(1H, m, COCH₂CH₂CH₂eq.); ¹³C-NMR (CDCl₃) l

(ppm) 291.0 (C_carbene), 231.4 (trans CO), 229.5 (cis CO),

218.5 (cis CO), 218.1 (cis CO), 210.4 (CO ketone), 133.1

(Cq Ph), 129.4, 128.5, 125.9 (C Ph), 52.3 (NMe₂), 49.4

(CH₂Ph), 48.0 (CH₂CO), 47.3 (CrCCH₂), 41.1

(CH₂CO), 38.5 (CH), 31.4 (CH₂CH₂CO), 24.4

(CHCH₂CH₂); IR/FT (nujol) w (cm⁻¹) 1996 (trans

CO); 1891, 1869, 1819 (cis CO); 1708 (CO ketone); 726,

686 (g CH_aromat); MS (FAB⁺), m/z 436 (M⁺); 380

(M⁺–2CO); 364 (M⁺–1CO–NMe₂); 352 (M⁺–3CO);

324 (M⁺–4CO); 307 (M⁺–3CO–HNMe₂); 279 (M⁺–

4CO–HNMe₂); 233 (M⁺–4CO–PhCH₂); 91 (C₇H⁺₇).

4.13. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)isopropyl carbene] chromium(0) (15)

n-BuLi (0.6 mmol, 0.4 ml of a 1.5 M solution in

hexane) was added dropwise to a −78°C cooled solu-

tion of complex 8 (0.2106 g, 0.595 mmol) in 5 ml of

THF. After stirring for 1 h at the same temperature,

iodomethane (0.075 ml 1.2 mmol) was added by a

syringe and the mixture allowed to react at −78°C for

1 h and then at r.t. for 30 min. The reaction was

quenched by adding 0.2 ml of water and the organic

solvent removed in vacuo. The residue was taken-up

with CH₂Cl₂and dried over Na₂SO₄. The solvent was

evaporated giving pure complex 15, 0.2188 g; yield

\98%.

4.12. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)-1-(ethyl-2-phenyl-2-hydroxy)

carbene]chromium (0) (14)

4.13.1. Complex 15

Orange solid; m.p. 122–123°C (CH₂Cl₂–pentane).

n-BuLi (0.347 mmol, 0.23 ml of a 1.51 M solution in

hexane, 1.1 equivalents) was added dropwise to a

−78°C cooled solution of complex 3 (0.115 g, 0.313

mmol, one equivalent) in 6 ml of THF and the mixture

allowed to react at the same temperature for 30 min.

Benzaldehyde (0.49 mmol, 1.58 eq) was then added by

a syringe; the mixture was stirred for 4.5 h and during

this time the temperature was slowly allowed to reach

−30°C. A total of 0.25 ml of a NH₄Cl saturated

aqueous solution was then added at −30°C. The or-

ganic solvent was then evaporated at reduced pressure

and the residue taken up with CH₂Cl₂and dried over

Na₂SO₄. The solvent was then evaporated at reduced

pressure and the residue, 0.163 g, was puriﬁed by

column chromatography over silica gel (15 g); eluent:

light petroleum–CH₂Cl₂(1:1) thus recovering a ﬁrst

fraction of unreacted complex 3, 0.01 g, and CH₂Cl₂for

the second fraction of complex 14, 0.127 g; yield 89.2%.

Anal. Found: C, 55.26; H, 5.35; N, 7.33. Calc. for

1

C₁₇H₂₀O₄N₂Cr: C, 55.43; H, 5.47; N, 7.61%. H-NMR

(CDCl₃, 300 MHz) l (ppm) 7.5–7.1 (5H, m, H_arom),

4.68 (2H, s, CH₂Ph), 2.80 (6H, s, NMe₂), 2.75 (1H,

J=6.45 Hz, CrCCH), 1.35 (6H, d, J=6.45 Hz,

CH(CH₃)₂); ¹³C-NMR (CDCl₃)

l

(ppm) 296.5

(C_carbene), 232.2 (trans CO), 229.9 (cis CO), 218.6 (cis

CO), 133.6 (Cq Ph), 129.4, 128.5, 126.0 (C Ph), 52.3

(NMe₂) 48.7 (CH₂Ph); 38.0 (CrCCH), 21.2

(CH(CH₃)₂); IR/FT (neat) w (cm⁻¹) 1996 (trans CO),

1888, 1834, 1820 (cis CO), 734, 685 (g CH_arom); MS

(EI), m/z 368 (M⁺); 340 (M⁺–CO); 312 (M⁺–2CO);

295 (M⁺–CO–NMe₂); 284 (M⁺–3CO); 267 (M⁺–

2CO–NMe₂); 256 (M⁺–4CO); 239 (M⁺–3CO–NMe₂);

232 (M⁺–Cr–3CO); 211 (M⁺–4CO–NMe₂); 204 (M⁺

–Cr–4CO); 160 (M⁺–Cr–4CO–MeNꢀCH₂).

4.14. Alkylation of the mixture of (Z)-5 and 8

4.12.1. Complex 14

complexes

Red viscous oil; ¹H-NMR (CDCl₃, 300 MHz) l

(ppm) 7.5–7.1 (10H, m, H_aromat), 5.72 (1H, dd, J₁=

9.45 Hz, J₂=3.16 Hz, OHCHPh), 4.87, 4.60 (2H, AB

system, J=17.2 Hz, CH₂Ph), 3.17 (1H, dd, J_gem=14.9

Hz, J_6ic=3.16 Hz, CrCCH₂), 3.02 (1H, dd, J_gem=14.9

Hz, J_6ic=9.45 Hz, CrCCH₂), 2.86, 2.76 (6H, s, NMe₂),

2.55 (1H, s br., OH); ¹³C-NMR (CDCl₃) l (ppm) 288.4

The reaction was run as reported for complex 5,

using the following amounts of reagents and solvent:

mixture of (Z)-5 and 8, 0.244 g, 5-Z:8=58%: 42%,

0.622 mmol; THF, 5 ml; BuLi, 1.578 M, 0.66 mmol;

0.08 ml of MeI, 1.28 mmol; after work-up 0.230 g of

crude was obtained.

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

409

Ratio of compounds (from the ¹H-NMR of the

crude) (Z)-5:8:15=47.5:22.2:30.3; overall yield 99.3%.

1.58 (3H, d, J=6.6 Hz, CrCCH(CH₃)₂), 1.34 (3H, d,

J=6.6 Hz, CrCCH(CH₃)₂). A NMR NOESY experi-

ment was also performed; ¹³C-NMR (CDCl₃) l (ppm)

305.5 (C_carrbene), 230.1 (trans CO), 229.0 (cis CO), 218.9

(cis CO), 130.2, 128.6, (C Ph), 129.3 (Cq Ph), 55.8

(NNMe anti to Ph), 50.4 (NNMe syn to Ph), 42.1

(CrCCH), 38.9 (CrCNMe), 22.9, 20.4 (CH(CH₃)₂). The

assignment of the peaks was done by two-dimensional

heteronuclear (H,C)-correlated NMR Spectroscopy. IR/

FT (neat) w (cm⁻¹) 1993 (trans CO); 1860, 1816 (cis

CO); 739, 688 (g CH_aromat); MS (EI), m/z 382 (M⁺); 354

(M⁺–CO); 326 (M⁺–2CO); 298 (M⁺–3CO); 270 (M⁺

–4CO); 225 (M⁺–4CO–HNMe₂); 174 (M⁺–4CO–Cr–

4.15. Synthesis of tetracarbonyl[(N-benzyl-N%,N%-

dimethylhydrazinyl)ethyl-1-benzyl carbene]chromium(0)

(16)

The reaction was run as reported for complex 15

using the following amounts of reagents and solvent;

complex 8, 0.2096 g, 0.59 mmol; THF, 5 ml; n-BuLi,

0.598 mmol, 0.42 ml of a 1.425 M solution in hexane);

benzylbromide, 0.145 ml. The reaction mixture was

stirred at −78°C for 2 h, and then at 0°C for 40 min;

after the work-up, the crude was puriﬁed by under

vacuum column chromatography over silica gel (20 g);

eluent: light petroleum for benzylbromide, then light

petroleum/diethyl ether 1: 1 to give complex 16, 0.2417

g; yield 92%.

NMe₂);

158

(M⁺–4CO–Cr–NMe₂–CH₄);

134

(PhCHꢀNMe⁺₂); 132 (M⁺–4CO–Cr–NMe₂–C₃H₆); 91

(C₇H⁺₇).

4.17. Oxidation of complex (E)-1 into hydrazide 18

4.15.1. Complex 16

Orange solid; m.p. 117°C (CH₂Cl₂–pentane). Anal.

Found: C, 62.33; H, 5.27; N, 6.44. Calc. for

C₂₃H₂₄O₄N₂Cr: C, 62.12; H, 5.44; N, 6.30. H-NMR

(CDCl₃, 300 MHz) l (ppm) 7.4–7.1 (10H, m, H_aromat),

4.20 (2H, s, NCH₂Ph), 3.15 (1H, dd, J_gem=13.4 Hz,

A solution of complex (E)-1 (0.213 g, 0.579 mmol) in

30 ml of ethyl acetate was exposed to air and sunlight

for 7 days at r.t. The precipitate was eliminated by

ﬁltration over a celite pad and the solvent removed in

vacuo. The residue, colourless oil, was pure hydrazide

18 [11], 0.0998 g; yield 89.7%.

1

J

_6ic=7.9 Hz, CHCH₂Ph), 3.02 (1H, dd, J_gem=13.4 Hz,

_6ic=5.8 Hz, CHCH₂Ph), 2.9–2.8 (1H, m, CrCCH),

2.74, (3H, s, NMe₂), 2.69 (3H, s, NMe₂), 1.44 (3H, d,

J

4.18. Oxidation of complex 15 into hydrazide 19

_6ic=6.4 Hz, CH₃CH); ¹³C-NMR (CDCl₃) l (ppm)

294.3 (C_carbene), 232.2 (trans CO), 229.6 (cis CO), 219.5

(cis CO), 218.5 (cis CO) 139.1 (Cq CHCH₂Ph), 133.7

(Cq NCH₂Ph), 129.3, 128.5, 128.4, 126.6, 125.7 (C Ph),

52.3, 52.1 (NMe₂), 48.8 (NCH₂Ph); 46.0 (CrCCH), 41.9

A solution of complex 15 (0.1532 g, 0.417 mmol) in 40

ml of ethyl acetate was exposed to air and sunlight for

78 days at r.t. The precipitate was eliminated by ﬁltra-

tion over a celite pad and the solvent removed in vacuo.

The residue, colourless oil, was pure hydrazide 19,

0.0771 g; yield 84.3%.

(CHCH₂Ph), 19.9 (CH₃CH); IR/FT (neat) w (cm⁻¹

)

1997 (trans CO), 1865, 1829 (cis CO), 738, 680 (g

CH_aromat).

4.16. Synthesis of tetracarbonyl[(N-benzyl-

(1-dimethylamino)-N-methylamino)isopropyl

carbene]chromium(0) (20)

4.18.1. 1-Benzyl-1-isopropionyl-2,2-dimethyl hydrazine

19

Colorless oil; HRMS (EI) for C₁₃H₂₀ON₂: M⁺

Calc.=220.15756, Found=220.1629; M⁺+1 Calc.=

221.16538, Found=221.1691; ¹H-NMR (CDCl₃, 300

MHz) l (ppm) 7.4–7.1 (5H, m, H_aromat), 4.60 (2H, s,

CH₂Ph), 3.41 (1H, ept, J=6.86 Hz, COCH), 2.48 (6H,

s, NMe₂), 1.14 (6H, d, J=6.86 Hz, CH(CH₃)₂; ¹³C-

NMR (CDCl₃) l (ppm) 179.9 (CO), 139.4 (Cq Ph),

128,4, 127.1, 126.6 (C Ph), 44.7 (NMe₂), 41.2 (CH₂Ph),

29.9 (CH(Me)₂), 19.5 (CH(CH₃)₂); IR/FT (neat) w

(cm⁻¹) 1656 (w CO), 1605, 1497, (ArC–C), 1352 (d sy

CH₃of the CHMe₂), 1151 (g CH₃of the CHMe₂), 911,

698 (d e g CH_aromat); MS (EI), m/z 221 (M⁺+1); 220

(M⁺); 178 (M⁺–C₃H₆); 177 (M⁺+1–NMe₂); 176 (M⁺

–NMe₂); 149 (M⁺–CO–C₃H₆); 129 (M⁺–PhCH₂); 92

(C₇H⁺₈); 91 (C₇H₇⁺); 79 (C₆H₇⁺); 65 (C⁵H⁺₅).

The reaction was run as reported for the synthesis of

complex 8 using the following amounts of reagents and

solvent; idrazino carbene 15, 0.1427 g, 0.388 mmol;

THF, 5 ml; BuLi, 1.48 M, 0.3 ml, 0.44 mmol; MeI,

0.027 ml, 0.43 mmol; after the work-up, 0.1504 g of the

complex 20 were obtained. Yield \98%.

4.16.1. Complex 20

Yellow–orange solid; m.p. 136–140°C (Et₂O–pen-

1

tane); H-NMR (CDCl₃, 300 MHz) l (ppm) 7.5–7.2

(5H, m, H_aromat), 4.99 (1H, s, CHPh), 3.02 (1H, ept.,

J=6.6 Hz, CrCCH), 3.02 (3H, s, CrCNCH₃), 2.70 (3H,

s, NNMe anti to Ph), 2.20 (3H, s, NNMe syn to Ph),

410

E. Licandro et al. / Journal of Organometallic Chemistry 617–618 (2001) 399–411

Table 3

thermal parameters in the last cycles of reﬁnement for

all the non-hydrogen atoms.

Crystal data and structure reﬁnement for (E)-1 and (Z)-1.

(E)-1

(Z)-1

In both structures the hydrogen atoms were intro-

duced into the geometrically calculated positions and

reﬁned riding on the corresponding parent atoms. In

the ﬁnal cycles of reﬁnement a weighting scheme w=

1/[|²F²_o+(0.0523 P)²] ((E)-1) and w=1/[|²F²_o+

(0.0619P)²+0.2221P] ((Z)-1) where P=(F_o²+2F²_c)/3

was used.

Formula

Formula weight

C₁₆H₁₆CrN₂O₅

368.31

Temperature (K) 293(2)

C

₁₆H₁₆CrN₂O₅

368.31

293(2)

0.71069

Monoclinic

C2/c

,

Wavelength (A)

0.71069

Monoclinic

P2₁/c

Crystal system

Space group

Unit cell

All calculations were carried out on the DIGITAL

AlphaStation 255 computers of the ‘Centro di Studio

per la Strutturistica Diffrattometrica’ del CNR,

Parma, using the ^SHELX-97 crystallographic computer

program systems [12].

dimensions

,

a (A)

9.214(5)

15.990(5)

12.401(5)

103.47(5)

1777(1)

4

25.746(5)

10.281(3)

16.391(4)

125.19(2)

3546(1)

8

,

b (A)

,

c (A)

i (°)

Volume

Z

D_calc(Mg m⁻³

Absorption

coefﬁcient

)

1.377

6.70

1.380

6.71

5. Supplementary material

(cm⁻¹

F(000)

)

The supplementary material for the structures in-

clude lists of atomic coordinates for the non-H

atoms, calculated coordinates for the hydrogen atoms,

anisotropic thermal parameters and complete lists of

bond lengths and angles. Crystallographic data for

the structures reported in this paper have been de-

posited with the Cambridge Crystallographic Data

Centre, CCDC no. 151799 for (E)-1 and CCDC no.

151800 for (Z)-1. Copies of this information may be

obtained free of charge from the Director, CCDC, 12

Union Road, Cambridge, CB2 1EZ, UK (fax: +44-

1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or

http://www.ccdc.cam.ac.uk).

760

1520

Crystal size (mm) 0.23×0.33×0.41

q range (°)

Index ranges

0.32×0.26×0.18

1.94–28.23

−335h528,

−135k513,

−135l521

10494

3.06–24.95

−105h510,

−55k518,

−145l514

3236

Reﬂections

collected

Independent

reﬂections

Observed

reﬂections

[I\2|(I)]

Data/restraints/

parameters

Goodness-of-ﬁt

on F²

3093 [R_int=0.0176]

3966 [R_int=0.0249]

1669

2762

3093/0/282

3966/0/221

0.821

1.017

Final R indices

[I\2|(I)]

R indices

^aR₁=0.0346,

^bwR₂=0.0792

R₁=0.0803,

wR₂=0.0898

R₁=0.0401,

wR₂=0.1051

R₁=0.0643,

wR₂=0.1156

Acknowledgements

(all data)

The authors gratefully acknowledge joint ﬁnancial

support from MURST (Rome), the University of Mi-

lan (National Project ‘Stereoselezione in Sintesi Or-

ganica, Metodologie e Applicazioni’) and the CNR of

Rome.

^aR₁=ꢀꢁꢁF_o−F_cꢁꢁ/ꢁꢁꢀꢁF_oꢁ.

^bwR₂=[ꢀ[w(F_o²−F_c²)²]/ꢀ[w(F²_o)²]]^1/2

.

4.19. X-ray structure determination of (E)-1 and (Z)-1

References

The intensity data of both complexes were collected

at r.t. on a Philips PW 1100 ((E)-1) and on an

Bruker AMX SMART 1000, equipped with an area

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a

graphite-

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The structures were solved by Patterson and

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squares procedures (based on F²_o) with anisotropic

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.

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Fischer-type alkyl(hydrazino)carbene complexes: New synthetic potential in comparison with aminocarbene complexes

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