Hydrolysis of coordinated diazoalkanes to yield side-on 1,2-diazene derivatives

Article abstract of DOI:10.1021/ic502963n

Diazoalkane complexes [Ru(η⁵-C₅Me₅)(N₂CAr1Ar2)(PPh₃){P(OR)₃}]BPh₄ [R = Me (1), Et (2); Ar1 = Ar2 = Ph (a); Ar1 = Ph, Ar2 = p-tolyl (b); Ar1Ar2 = C₁₂H₈ (c)] were prepared by allowing chloro complexes RuCl(η⁵-C₅Me₅)(PPh₃)[P(OR)₃] to react with diazoalkane Ar1Ar2CN₂ in ethanol. The treatment of compounds 1 and 2 with H₂O afforded 1,2-diazene derivatives [Ru(η⁵-C₅Me₅)(η²-NH=NH)(PPh₃){P(OR)₃}]BPh₄ (3 and 4) and ketone Ar1Ar2CO. A reaction path involving nucleophilic attack by H₂O on the coordinated diazoalkane is proposed. The complexes were characterized spectroscopically (IR and NMR) and by X-ray crystal structure determination of [Ru(η⁵-C₅Me₅)(η²-NH=NH)(PPh₃){P(OMe)₃}]BPh₄ (3).

Full text of DOI:10.1021/ic502963n

Communication
pubs.acs.org/IC
Hydrolysis of Coordinated Diazoalkanes To Yield Side-On 1,2-
Diazene Derivatives
Gabriele Albertin,* Stefano Antoniutti, Alessandra Botter, and Jesus
,†
†
†
Castro‡
́
†
Dipartimento di Scienze Molecolari e Nanosistemi, Universita
̀
Ca’ Foscari Venezia, Dorsoduro 2137, 30123 Venezia, Italy
‡
́
Facultade de Química, Edificio de Ciencias Experimentais, Departamento de Química Inorganica, Universidade de Vigo, 36310 Vigo,
Galicia, Spain
*
S Supporting Information
a
Scheme 1
5
ABSTRACT: Diazoalkane complexes [Ru(η -C Me )-
5
5
(
(
N CAr1Ar2)(PPh ){P(OR) }]BPh [R = Me (1), Et
2); Ar1 = Ar2 = Ph (a); Ar1 = Ph, Ar2 = p-tolyl (b);
2 3 3 4
Ar1Ar2 = C H (c)] were prepared by allowing chloro
12
8
5
complexes RuCl(η -C Me )(PPh )[P(OR) ] to react with
5
5
3
3
diazoalkane Ar1Ar2CN in ethanol. The treatment of
2
compounds 1 and 2 with H O afforded 1,2-diazene
2
5
2
derivatives [Ru(η -C Me )(η -NHNH)(PPh ){P-
5
5
3
(
OR) }]BPh (3 and 4) and ketone Ar1Ar2CO. A
3 4
reaction path involving nucleophilic attack by H O on
2
a
R = Me (1), Et (2); Ar1 = Ar2 = Ph (a); Ar1 = Ph, Ar2 = p-tolyl (b);
Ar1Ar2 = C H (c).
the coordinated diazoalkane is proposed. The complexes
were characterized spectroscopically (IR and NMR) and
12
8
5
by X-ray crystal structure determination of [Ru(η -
2
C Me )(η -NHNH)(PPh ){P(OMe) }]BPh (3).
5
5
3
3
4
1
anion, the H NMR spectra of compounds 1 and 2 show the
characteristic resonances of the substituents 4-CH C H and
3
6
4
he chemistry of transition-metal complexes containing
31
C H of the diazoalkane, whereas the P NMR spectra are AB
12
8
T
diazoalkanes Ar1Ar2CN as ligands is of long-standing
2
multiplets, fitting the proposed formulation for the complexes.
At room temperature, diazoalkane complexes 1 and 2 react
1
−3
interest
because of not only the close relationship with N2
coordination and fixation processes but also the various
4
5
2
with H O to afford 1,2-diazene derivatives [Ru(η -C Me )(η -
2
5
5
coordination modes and reactivity of metal-bonded diazo-
NHNH)(PPh ){P(OR) }]BPh (3 and 4), which were
1
−3,5
1,2a,f,5
3
3
4
alkane.
Carbene complexes can be obtained
from
isolated in about quantitative yield and characterized (Scheme
2). The ketone Ar1Ar2CO was also separated from the reaction
mixture in about quantitative yield, indicating the stoichiometry
shown in Scheme 2 for the hydrolysis reaction.
Ar1Ar2CN derivatives after extrusion of N , but in some cases,
2
2
2
f,h,i
2d
dinitrogen M−N complexes form.
reduction of a coordinated N CAr1Ar2 ligand,
dipolar cycloaddition
observed.
N−N bond cleavage,
2
2f,h
and 1,3-
2
3a,b
with alkene and alkyne were also
The formation of diazene complexes 3 and 4 is rather
surprising but may be explained as due to the nucleophilic
As part of our study of diazoalkane complexes, we now
attack of H O on the carbon atom of the coordinated
2
report a novel reaction of coordinated Ar1Ar2CN , which
2
diazoalkane, according to the reaction path shown in Scheme 3.
undergoes an unprecedented hydrolysis reaction, yielding 1,2-
2
diazene complexes [M](η -NHNH) and ketone Ar1Ar2CO.
a
Scheme 2
Pentamethylcyclopentadienyl half-sandwich complexes RuCl-
5
(
η -C Me )(PPh )[P(OR) ] react with an excess of diazo-
5
5
3
3
alkane Ar1Ar2CN , in the presence of NaBPh , to give the
2
4
5
diazoalkane derivatives [Ru(η -C Me )(N CAr1Ar2)(PPh ){P-
5
5
2
3
(
OR) }]BPh (1 and 2) in good yield (Scheme 1).
3 4
The complexes are reddish-brown solids stable in air and in a
solution of polar organic solvents, where they behave as 1:1
6
electrolytes. The IR spectra show a medium-intensity band at
−
1
1
950−1919 cm , attributed to ν
of the coordinated
CNN
1
diazoalkane. This value also suggests an end-on η -coordination
mode for the Ar1Ar2CN group, like that found in the
comparable cyclopentadienyl derivatives [Ru(η -C H )-
N CAr1Ar2)(PPh ){P(OR) }]BPh . Besides the signals of
a
1
R = Me (3), Et (4).
2
5
5
5
3a
(
Received: December 11, 2014
Published: February 19, 2015
2
3
3
4
−
the ancillary ligands C Me , PPh , and P(OR) and the BPh
4
5
5
3
3
©
2015 American Chemical Society
2091
DOI: 10.1021/ic502963n
Inorg. Chem. 2015, 54, 2091−2093

Inorganic Chemistry
Communication
a
Scheme 3
a
5
+
[
Ru] = [Ru(η -C Me )(PPh ){P(OR) }] .
5 5 3 3
H O attack, with C−O bond formation, is followed by the
2
shift of one hydrogen atom, giving hydrazido intermediate [A].
This species is probably unstable and may give rise to
intramolecular hydrogen transfer from the acidic OH group
to the hydrazido Nα group with concurrent cleavage of the C
1
5
Figure 1. ORTEP view of the cation of 3. P1 represents a PPh3
ligand, and P2 represents a P(OMe) ligand. Selected bond lengths
[
3
3
Å] and angles [deg]: Ru−CT1, 1.9212(3); Ru−CT2, 1.9160(3); Ru−
sp −Nβ bond, affording free ketone Ar1Ar2CO and the 1,2-
C1, 2.257(4); Ru−C2, 2.304(3); Ru−C3, 2.295(4); Ru−C4, 2.243(5);
diazene molecule, which acts as a π-bonded ligand. The
Ru−C5, 2.216(4); Ru−C , 2.263; Ru−N1, 2.030(3); Ru−N2,
av
progress of the reaction between complex 1 and H O was
2
2
1
.039(3); Ru−P1, 2.3720(9); Ru−P2, 2.2964(11); N1−N2,
.367(5); CT1−Ru−N1, 115.77(9); CT1−Ru−N2, 121.95(9); N1−
followed by NMR in an attempt to detect any intermediate
such as [A]. Unfortunately, as the reaction proceeded, no new
species were observed in the spectra, apart from the reagents
and the final diazene 3 and ketone Ar1Ar2CO. However,
nucleophilic attack at the carbon atom of coordinated
Ru−P2, 116.86(10); N2−Ru−P2, 85.58(12); CT1−Ru−P1,
1
29.07(2); CT1−Ru−P2, 119.76(3); N1−Ru−P1, 81.14(10); N2−
Ru−P1, 101.98(10); P1−Ru−P2, 85.80(4); CT2−Ru−CT1,
120.783(15); CT2−Ru−P1, 91.67(2); CT2−Ru−P2, 101.45(3).
CT1 represents the centroid of the Cp ligand and CT2 the middle
of the N1−N2 bond.
7
diazoalkanes has previously been reported, and this precedent
supports the path we propose in Scheme 3.
Free diazomethane and substituted ones are reported to
8
,9
undergo hydrolysis, yielding alcohol and N . Coordination at
2
5
+
our [Ru(η -C Me )(PPh ){P(OR) }] fragment entails a novel
5
5
3
3
Compound 3 consists of the tetraphenylborate salt of a
reactivity toward hydrolysis, affording diazene NHNH and
ketone.
ruthenium complex, which crystallizes with a CH Cl solvent
2 2
10
1
,2-Diazene is a very unstable species that can be stabilized
molecule. Only the cation is shown in Figure 1. The cation
complex contains a ruthenium atom in a pseudooctahedral half-
11−13
by coordination on a metal center.
It is a molecule of
5
possible importance to the inorganic and bioinorganic N
sandwich piano-stool structure, coordinated by a η -pentam-
2
14
2
reduction process and was prepared from oxidation of
ethylcyclopentadienyl ligand (Cp*) having one side-on η -
1
1−13
2
hydrazine complexes.
Hydrolysis of a coordinated
diazene (η -HNNH) and two phosphine ligands [one PPh and
3
diazoalkane highlights a new method of synthesizing this
important nitrogen dihydride species.
one P(OMe) ] as legs. The Ru−N bond lengths, 2.030(3) and
3
2
2.038(3) Å, are shorter than those found in [Ru(η -NH
13a
Good analytical data were obtained for diazene complexes
NH)(depe) ], being 2.123(4) and 2.134(3) Å, and this was
2
5
2
[
4
Ru(η -C Me )(η -NHNH)(PPh ){P(OR) }]BPh (3 and
attributed to the different trans behavior of Cp* and depe
ligands. It is worth noting that, to the best of our knowledge,
only two nonbridging side-on diazene ruthenium complexes
have been crystallographically described, the aforementioned
5
5
3
3
4
), which were isolated as stable yellow solids and characterized
by conductivity measurements and IR and NMR spectra.
1
At room temperature, the H NMR spectra of diazene
complexes 3 and 4 show only the characteristic signals of the
2
2
[
Ru(η -NHNH)(depe) ] and the closely related [Ru(η -
2
1
5
13a
ancillary ligands C Me , PPh , and P(OR) . However, the N-
5
5
3
3
NHNH)(dmpe) ] complex. In those compounds, the N−
2
5
2 15
labeled complexes [Ru(η -C Me )(η - NHNH)(PPh ){P-
5
5
3
N bond lengths were reported to be 1.414(5) and 1.427(3) Å,
respectively; in 3, this value is now 1.366(5) Å. Both values are
shorter than those found in other ruthenium end-on-bound
hydrazine complexes (between 1.38 and 1.48 Å), so that they
can be considered as multiple bonds. However, these values are
longer than those found in other ruthenium diazene complexes
(
OR) }]BPh (3a and 4a) were synthesized, and their proton-
3 4
1
5
coupled N NMR spectra show a doublet of multiplets at
210.9 (3a) and −211.1 (4a) ppm, which can be simulated
with an NXYAB model (N = N; X, Y = H; A, B = P; see
−
1
5
1
31
1
1
5
NH
the Supporting Information, Figure S1) with J = 92.4 Hz
2
13a
1
5
NH
and J = 2.7 Hz. The spectra collapsed to a single multiplet
reported in the literature (about 1.28 Å), especially those in
1
2
upon H decoupling, confirming the presence of the NHNH
the [Ru(η -NHNH)(depe)
2
] complex. Their authors
3
1
moiety in the complexes. The P NMR spectra are AB
attributed the lengthening of the N−N bond to back-bonding
from filled d orbitals of ruthenium to the antibonding π*
orbitals of the diazene ligand.
1
5
multiplets (ABN in the N-labeled complex), fitting the
proposed formulation for the complexes, and this was further
supported by X-ray crystal structure determination of 3, the
ORTEP of which is shown in Figure 1.
Further studies on both hydrolysis and other reactions of
metal-bonded diazoalkane derivatives are in progress.
2
092
DOI: 10.1021/ic502963n
Inorg. Chem. 2015, 54, 2091−2093

Inorganic Chemistry
Communication
(
12) (a) Cheng, T.-Y.; Ponce, A.; Rheingold, A. L.; Hillhouse, G. L.
ASSOCIATED CONTENT
Supporting Information
Experimental and spectroscopic details and crystallographic
data in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
E-mail: albertin@unive.it.
■
(
*
2
Notes
(
The authors declare no competing financial interest.
5
(
ACKNOWLEDGMENTS
■
We thank Daniela Baldan, from the Universita
Venezia (Italy), for technical assistance.
̀
Ca’ Foscari
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DOI: 10.1021/ic502963n
Inorg. Chem. 2015, 54, 2091−2093