Carbon monoxide-isocyanide coupling promoted by acetylide addition to a diiron complex

Article abstract of DOI:10.1039/c5cc01958c

C-N bond formation involving carbon monoxide and isocyanide ligands is promoted by addition of a series of lithium acetylides to a diiron μ-aminocarbyne complex, i.e. [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO)(CNXyl)(Cp)₂][SO₃CF_3<

Full text of DOI:10.1039/c5cc01958c

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Carbon monoxide–isocyanide coupling promoted
by acetylide addition to a diiron complex†
Cite this:DOI: 10.1039/c5cc01958c
a
b
b
Fabio Marchetti,* Stefano Zacchini and Valerio Zanotti
Received 8th March 2015,
Accepted 7th April 2015
DOI: 10.1039/c5cc01958c
www.rsc.org/chemcomm
C–N bond formation involving carbon monoxide and isocyanide LiCRCR (R = Ph, Tol, SiMe ; Tol = 4-C H Me) in THF solution
3
6
4
ligands is promoted by addition of a series of lithium acetylides to a required prolonged heating at reflux temperature in order to
diiron l-aminocarbyne complex, i.e. [Fe {l-CN(Me)(Xyl)}(l-CO)(CO)- effectively obtain the final products. The complexes [Fe {m-CN-
CNXyl)(Cp) ][SO CF ] (Xyl = 2,6-C Me
three steps, i.e. (a) acetylide addition to the CO ligand, (b) acetylide R = Tol, 1b; R = SiMe
migration to the isocyanide ligand, and (c) C–N coupling. The X-ray alumina chromatography (Scheme 1).
2
2
(
2
3
3
H
6 3
2
). The reaction proceeds in (Me)(Xyl)}(m-CO){m-C(O)N(Xyl)C(CRCR)}(Cp)
2
] (R = Ph, 1a;
3
, 1c) were isolated in ca. 70% yields after
molecular structures of 1a and 1b comprise the first example of a
X-ray crystals of 1aꢀCH
a CH Cl –pentane mixture and a diethyl ether solution, respec-
tively, and their molecular structures are shown in Fig. 1 and 2
One of the most attractive goals of modern synthetic chemistry together with the relevant bonding parameters.
2
Cl
2
and 1bꢀ0.5Et
2
O were grown from
0
j(C,C )-N-carbonyl-aminocarbene ligand.
2
2
consists of the assembly of small organic components through
The molecular structures of 1a and 1b share a Fe {m-CN(Me)-
2
simple and efficient procedures. Over the past few decades, (Xyl)}(m-CO)(Cp)
2
core to which a bridging N-carbonyl-alkynyl-
considerable progress has been made in fulfilling this demand aminocarbene ligand [C(O)N(Xyl)C(CRCR), with R = Ph or Tol]
0
by taking advantage of transition metal chemistry. In particular, is k(C,C ) coordinated through the carbonyl C(22) and the
multimetallic complexes have offered the opportunity for metal aminocarbene C(23) carbons, respectively. Being adjacent to
1
centers to work together in the activation of small molecules;
in this respect, dinuclear systems often operate effectively by
nitrogen, C(22) may also be viewed as part of a carbamoyl moiety.
2
,3
exploiting the cooperating ability of the two metal centers.
Carbon monoxide and isocyanides are two extremely valuable
classes of C1 synthons for the construction of molecular archi-
tectures: while use of the former represents the traditional
4
cornerstone of important industrial processes, isocyanides have
recently been known to constitute an irreplaceable, versatile role
5
in synthetic chemistry. Herein we show that CO and CNXyl (Xyl =
2
,6-C H Me ), bound to two distinct metal centers in a diiron
6 3 2
complex, undergo unprecedented combination which is initiated
by addition of lithium acetylides.
The reaction of [Fe
2
{m-CN(Me)(Xyl)}(m-CO)(CO)(CNXyl)(Cp)
2
]-
6
[
SO CF ], containing a bridging aminocarbyne ligand, with
3 3
a
Dipartimento di Chimica e Chimica Industriale, University of Pisa,
Via Moruzzi 3, I-56124 Pisa, Italy. E-mail: fabio.marchetti1974@unipi.it;
Web: http://www.dcci.unipi.it/fabio-marchetti.html; Tel: +39 050 2219245
Dipartimento di Chimica Industriale ‘‘Toso Montanari’’, University of Bologna,
Viale Risorgimento 4, I-40136 Bologna, Italy
b
†
Electronic supplementary information (ESI) available: Experimental details,
1
13
X-ray crystallography, full characterization of the products, and H and C NMR
spectra. CCDC 1036806(1a) and 1036807(1b). For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c5cc01958c
Scheme 1 Three-step reaction involving carbon monoxide, 2,6-dimethyl-
phenyl isocyanide and lithium acetylides at a diiron m-aminocarbyne
complex (R = Ph, Tol, SiMe ).
3
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electron densities on Fe(1) and Fe(2). Fe(1) displays the strongest
interaction with m-CO because it is bound to
a good
s-donor (carbamoyl), whereas Fe(2) interacts with the more
acidic aminocarbene C(23) (see above). Even the bridging amino-
carbyne ligand shows asymmetry, albeit with a minor degree
[Fe(1)–C(12) 1.830(4) in 1a and 1.841(7) Å in 1b; Fe(2)–C(12)
1.870(4) in 1a and 1.851(8) Å in 1b]. The aminocarbyne N-sub-
stituents are oriented with the bulkier Xyl on the opposite side with
respect to the alkynyl group, in order to minimize steric repulsions;
this configuration suggests that the stereochemistry of the starting
+
complex [Fe {m-CN(Me)(Xyl)}(m-CO)(CO)(CNXyl)(Cp) ] is retained
2
2
during the reaction.
Compounds 1a–c were characterized in solution by spectro-
Fig. 1 ORTEP drawing of 1a, with key atoms labeled (all H atoms have been
omitted for clarity). Displacement ellipsoids are at the 30% probability level. scopic techniques, showing substantial accordance with the
Only the main image of the disordered Cp ligand bonded to Fe(1) is reported.
solid-state features determined for 1a and 1b by X-ray diffracto-
Selected bond lengths (Å) and angles (deg): Fe(1)–Fe(2) 2.4815(11); Fe(1)–C(11)
2 2
metry. Thus, the IR spectra of 1a–c (in CH Cl ) display diagnostic
1
.867(4); Fe(2)–C(11) 1.943(4); Fe(1)–C(12) 1.830(4); Fe(2)–C(12) 1.870(4);
Fe(1)–C(22) 1.912(4); Fe(2)–C(23) 1.863(4); C(11)–O(11) 1.181(5); C(12)–N(1)
.320(5); C(22)–N(2) 1.463(4); C(22)–O(2) 1.242(4); N(2)–C(23) 1.366(5);
N(2)–C(32) 1.451(5); C(23)–C(24) 1.396(6); C(24)–C(25) 1.236(6); (e.g., for 1a, at 1769, 1606, 2167 and 1510 cm , respectively).
absorptions due to the bridging carbon monoxide ligand and
7
8
the carbamoyl, alkynyl and bridging aminocarbyne moieties
1
ꢁ1
1
3
C(25)–C(26) 1.445(6); Fe(1)–C(22)–N(2) 118.8(2); N(2)–C(23)–Fe(2) 122.6(3);
N(2)–C(23)–C(24) 113.1(3); C(22)–N(2)–C(23) 119.5(3); C(23)–C(24)–C(25)
The C NMR resonances of the carbons belonging to the
five-membered dimetallacycle occur at ca. 240 and 225 ppm
171.4(5); C(24)–C(25)–C(26) 177.1(5).
9
(
CDCl
3
solutions), in agreement with their aminocarbene and
1
0
carbamoyl nature, respectively.
To the best of our knowledge, 1a–c represent the first example of
0
a k(C,C )-coordinated N-carbonyl aminocarbene ligand ever reported.
This may be alternatively described as a mixed carbamoyl–
aminocarbene bridging ligand. Another key point regards the
synthetic route: it consists of C–N bond forming combination
between carbon monoxide and imidoyl units, the latter being
previously generated by acetylide addition to 2,6-dimethylphenyl
isocyanide (see Scheme 1). Although nucleophilic attack at the
carbon monoxide ligand in transition-metal complexes is a well-
1
1
known feature and includes a variety of addition reactions
1
2
by nitrogen donors, the C–N coupling described herein has
no precedent, to the best of our knowledge. As a matter of fact,
very few coupling reactions between carbon monoxide and
isocyanide molecules have been reported up to now and all of
Fig. 2 ORTEP drawing of 1b, with key atoms labeled (all H atoms have
1
3
been omitted for clarity). Displacement ellipsoids are at the 30% probability these proceed with C–C bond formation.
level. Selected bond lengths (Å) and angles (deg): Fe(1)–Fe(2) 2.4823(15);
In order to shed light on the mechanism of the reaction leading
Fe(1)–C(11) 1.867(9); Fe(2)–C(11) 1.939(8); Fe(1)–C(12) 1.841(7); Fe(2)–C(12)
.851(8); Fe(1)–C(22) 1.919(8); Fe(2)–C(23) 1.854(8); C(11)–O(11) 1.189(9);
C(12)–N(1) 1.314(10); C(22)–N(2) 1.486(9); C(22)–O(2) 1.207(9); N(2)–C(23)
.362(9); N(2)–C(32) 1.458(10); C(23)–C(24) 1.424(11); C(24)–C(25)
.181(11); C(25)–C(26) 1.420(13); Fe(1)–C(22)–N(2) 116.9(5); N(2)–C(23)–Fe(2) these conditions, the alkynyl–acyl complexes [Fe {m-CN(Me)-
to 1a–c, [Fe
was allowed to react with lithium acetylide in THF solution at
20 1C to room temperature (see the ESI† for details). Under
2 2 3 3
{m-CN(Me)(Xyl)}(m-CO)(CO)(CNXyl)(Cp) ][SO CF ]
1
ꢁ
1
1
2
1
23.5(5); N(2)–C(23)–C(24) 114.8(7); C(22)–N(2)–C(23) 122.0(6); C(23)–
(
Xyl)}(m-CO){C(O)CRCR}(CNXyl)(Cp) ] (R = Ph, 2a; R = Tol, 2b;
2
C(24)–C(25) 172.3(10); C(24)–C(25)–C(26) 174.9(12).
and R = SiMe , 2c) were isolated in 61–74% yields after work-up
3
(Scheme 1). The formation of 2a–c has been unambiguously
indicated by IR and NMR evidence (ESI†), showing that the
1
4
The Fe(2)–C(23) distance [1.863(4) in 1a and 1.854(8) Å in 1b] is acetylide attack selectively occurs at the CO ligand. The IR
considerably shorter than a pure s Fe–C bond, thus suggesting spectra of 2a–c clearly exhibit absorptions ascribable to the
the presence of a strong p-interaction. Conversely the Fe(1)– bridging carbonyl, the acyl group and the intact isocyanide
ꢁ1
C(22) distance [1.912(4) in 1a and 1.919(8) Å in 1b] manifests a ligand (e.g., in the case of 2a, at 1598, 1766 and 2082 cm
weak p-interaction; accordingly, C(22)–O(2) [1.242(4) in 1a and respectively). Accordingly, no bands in the terminal-carbonyl
.207(9) Å in 1b] is an almost pure double bond. The bridging region have been recognized.
carbon monoxide ligand shows a marked asymmetry [Fe(1)– Heating 2a–c in boiling THF resulted in the direct conver-
C(11) 1.867(4) in 1a and 1.867(9) Å in 1b; Fe(2)–C(11) 1.943(4) in sion into 1a–c. Therefore, we investigated the thermal reaction
a and 1.939(8) in 1b], as a consequence of the different of 2a–c in a lower boiling point solvent (dichloromethane), with
,
1
1
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Notes and reference
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Scheme 2 Three-step reaction involving m-aminocarbyne, CNXyl and
hydride at a diiron m-aminocarbyne complex.
Chem., 2001, 73, 315.
2
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2
(
m-CO)(CO){C(CRCR )Q NXyl}(Cp) ] (R = Ph, 3a; R = Tol, 3b;
2
P. L. Holland, Chem. Sci., 2014, 5, 267; (e) A. R. Kennedy, J. Klett,
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1
1
31, 10358; (g) V. Ritleng and M. J. Chetcuti, Chem. Rev., 2007,
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ꢁ
1
13
1
775 cm (CH
ca. 270 and 210 ppm (CDCl
20 ppm accounts for the imidoyl ligand. According to the NOE
2 2
Cl solutions), and C NMR resonances at
1
3
3
). Instead, C resonance at around
3 Examples regarding homobimetallic systems include: (a) C. T. Saouma,
P. M u¨ ller and J. C. Peters, J. Am. Chem. Soc., 2009, 131, 10358;
2
(b) A. J. Esswein, A. S. Veige, P. M. B. Piccoli, A. J. Schultz and
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D. G. Nocera, Organometallics, 2008, 27, 1073; (c) K. Severin,
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2
D. Garcı
a-Viv ´o , M. A. Ruiz and M. F. Vega, Organometallics, 2013, 32,
´
1
5
complexes (L = encumbered C or N donor).
4543–4555.
The thermal treatment of 3a–c (in THF) afforded 1a–c in
high yields (Scheme 1). The final formation of 1a–c from 3a–c
seems to be the result of nucleophilic migration of the imidoyl
fragment to the carbonyl ligand. This rearrangement generates
the aminocarbene ligand, which is found to be functionalized
with C-bound alkynyl and N-bound carbonyl units. It should be
noted that alkynylaminocarbene species are typically accessible
4 (a) X.-F. Wu, X. Fang, L. Wu, R. Jackstell, H. Neumann and M. Beller,
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(
b) M. A. Mironov, General Aspects of Isocyanide Reactivity in
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16
from isocyanide ligands, although the aminolysis of appropriate
alkoxycarbene precursors may represent a viable, alternative
2
006, 106, 17.
6
7
F. Marchetti, S. Zacchini and V. Zanotti, Organometallics, 2014,
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9
a,c,17
synthetic strategy.
On the other hand, the N-acylation of
aminocarbene ligands has been achieved using a variety of acyl-
1
8
19
transfer agents, resulting in acylaminocarbene derivatives.
The present situation is different, in which N-carbonylation
involves a CO ligand which remains bound to the metal atom.
Concerning the overall three-step process leading to 1a–c
8 L. Busetto, F. Marchetti, S. Zacchini and V. Zanotti, Eur. J. Inorg.
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9
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´
rearrangements do not affect the aminocarbyne ligand, despite the
11a,20
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ii) we have recently reported that the imidoyl obtained by the
reaction of [Fe {m-CN(Me)(Xyl)}(m-CO)(CO)(CNXyl)(Cp) ][SO CF
with NaBH undergoes, in turn, selective C–C coupling with the
(
2
(
2
2
3
3
]
(
4
J. Organomet. Chem., 2005, 690, 348.
6
aminocarbyne frame (Scheme 2). These considerations point
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reaction pathways.
1
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1
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21
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2
{m-CN(Me)(R)}(m-CO)(CO)
R = Me, CH Ph) selectively occurs at the carbonyl ligand [see J. Chem.
2 2
(Cp) ]
(
2
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