Reactions of a ruthenium(VI) nitride with rhodium(III) and iridium(III) aryl complexes. Insertion of the Ru≡N group into the Rh-C bonds of trimesitylrhodium(III)

Article abstract of DOI:10.1021/om301114p

The reaction of the Ru^VI nitride L_OEtRu ^VI(N)Cl₂ (1; L_OEt^- = [Co(η⁵-C₅H₅){P(O)(OEt)₂} ₃]^-) with Rh^III(mes)₃ (mes = mesityl) results in insertion of the Ru≡N group into the Rh-C bonds and formation of trinuclear (L_OEt)ClRu^IV(μ-Cl)(μ-2- CH₂-4,6-Me₂C₆H₂N)Rh ^III(μ-Nmes)(μ-Cl)₂Ru^IV(L_OEt) (2), containing a cyclometalated μ-mesitylimido ligand, whereas that with Ir^III(dtbpy)R₃ gives the μ-nitrido complexes (dtbpy)R₃Ir^III(μ-N)Ru^IVCl₂(L _OEt) (dtbpy = 4,4′-di-tert-butyl-2,2′-bipyridyl; R = 2,5-dimethylphenyl (3), 4-methoxy-2-methylphenyl (4)). The crystal structures of 2 and 4 have been determined.

Full text of DOI:10.1021/om301114p

Communication
pubs.acs.org/Organometallics
Reactions of a Ruthenium(VI) Nitride with Rhodium(III) and
Iridium(III) Aryl Complexes. Insertion of the RuN Group into the
Rh−C Bonds of Trimesitylrhodium(III)
Enrique Kwan Huang, Wai-Man Cheung, Herman H. Y. Sung, Ian D. Williams, and Wa-Hung Leung*
Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, People’s
Republic of China
S
* Supporting Information
ABSTRACT: The reaction of the RuVI nitride LOEtRuVI(N)Cl2 (1; LOEt
−
= [Co(η5-C5H5){P(O)(OEt)2}3]−) with RhIII(mes)3 (mes = mesityl)
results in insertion of the RuN group into the Rh−C bonds and
formation of trinuclear (LOEt)ClRuIV(μ-Cl)(μ-2-CH2-4,6-Me2C6H2N)-
RhIII(μ-Nmes)(μ-Cl)2RuIV(LOEt) (2), containing a cyclometalated μ-
mesitylimido ligand, whereas that with IrIII(dtbpy)R3 gives the μ-nitrido
complexes (dtbpy)R3IrIII(μ-N)RuIVCl2(LOEt) (dtbpy = 4,4′-di-tert-butyl-
2,2′-bipyridyl; R = 2,5-dimethylphenyl (3), 4-methoxy-2-methylphenyl
(4)). The crystal structures of 2 and 4 have been determined.
ransition-metal nitrido complexes have attracted much
Tattention because of their involvement as reactive
intermediates in metal-catalyzed nitrogen fixation and their
applications in nitrogen atom transfer.1−3 Of special interest are
nitrido complexes of late transition metals that have been
shown to exhibit electrophilic behavior.4 In particular, reactions
of OsVI nitrido complexes with nucleophiles resulting in N−X
(X = C, N, O, S, P, etc.) bond formation have been studied
extensively.5 Lau and co-workers reported that, in the presence
of pyridine, [RuVI(N)(salen)(MeOH)]+ is capable of aziridi-
nation of alkenes and amination of alkanes.2a,c This prompted
us to explore the C−N bond forming reactions of RuVI nitrido
complexes with facially coordinating ligands.
can act as π acid ligands like CO due to the presence of low-
lying M−N π* orbitals.8 This led to us explore the possibility of
insertion of 1 into metal−carbon σ bonds. In this work, we
studied the reactions of 1 with the RhIII and IrIII triaryl
complexes RhIII(mes)3 (mes = mesityl)9 and IrIII(dtbpy)R3
(dtbpy = 4,4′-di-tert-butyl-2,2′-bipyridyl; R = 2,5-dimethyl-
phenyl (R1),10 4-methoxy-2-methylphenyl (R2)11). The former
led to insertion of RuN into the Rh−C bonds to give a
trinuclear RuIV−RhIII−RuIV μ-imido complex, whereas the latter
yielded dinuclear RuVI−IrIII μ-nitrido complexes. The character-
ization and crystal structures of the heterometallic imido and
nitrido complexes will be presented.
Reactions of 1 with the homoleptic aryl complexes MIV(o-
tol)4 (M = Ru, Os; o-tol = 2-methylphenyl)12 and RhIII(mes)3
have been examined. Whereas no reactions were found between
1 and MIV(o-tol)4, the reaction of 1 with 1 equiv of RhIII(mes)3
at room temperature led to the isolation of orange crystals
characterized as the μ-imido complex (LOEt)ClRu(μ-Cl)(μ-2-
CH2-4,6-Me2CH2C6H2N)Rh(μ-Nmes)(μ-Cl)2RuLOEt (2) in
low yield (<10%) (Scheme 1) along with unreacted
RhIII(mes)3. 2 could be obtained in better yield (38%) from
the reaction of RhIII(mes)3 with 2 equiv of 1.13
To our knowledge, this is the first report of insertion of the
nitrido ligand into a transition-metal−carbon σ bond, although
the insertion of OsN into B−C bonds of organoboranes has
been observed previously.14 The 1H NMR spectrum of 2
(Figure S2, Supporting Information) displayed sharp signals
Recently, we found that the RuVI nitride LOEtRuVI(N)Cl2
(1)6 containing Klaui’s tripodal ligand L
([Co(η5-C5H5)-
−
̈
OEt
{P(O)(OEt)2}3]−) (Chart 1) underwent migratory insertion
with the RuII hydride LOEtRuII(H)(CO)(PPh3) to afford a μ-
7
imido complex, LOEtCl2RuIV(μ-NH)RuII(CO)(PPh3)LOEt
.
The insertion of RuN into the Ru−H bond is reminiscent
of migratory insertion of metal hydrides with CO, lending
support to Mayer’s suggestion that late-transition-metal nitrides
−
Chart 1. Structure of Klaui’s Tripodal Ligand L
̈
OEt
Received: November 23, 2012
Published: January 24, 2013
© 2013 American Chemical Society
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that 1 reacted rapidly with RhIII(dtbpy)(R1)3 in C6D6 to give a
mixture of products. Recrystallization from hexane led to
isolation of RhIII(dtbpy)(R1)3 along with a minor unknown
species. On the other hand, treatment of 1 with IrIII(dtbpy)-
(R1)3 afforded the μ-nitrido complex (dtbpy)(R1)3IrIII(μ-
N)RuVICl2(LOEt) (3) (Scheme 1). Complex 3 is remarkably
stable and could be purified by silica column chromatography
Scheme 1. Reactions of 1 with RhIII and IrIII Triaryl
Complexes
1
in air without decomposition. The H NMR spectrum of 3
(Figure S4, Supporting Information) showed sharp signals
assignable to the IrIII(dtbpy)(R1)3 and LOEtRu moieties in the
normal regions, indicative of the diamagnetic nature of the
complex. Similarly, 1 reacted with IrIII(dtbpy)(R2)3 to give
(dtbpy)(R2)3IrIII(μ-N)RuVICl2(LOEt) (4), which has been
characterized by X-ray crystallography (Figure 2). The Ir−C
distances (2.070(6)−2.167(6) Å) are slightly longer than those
in IrIII(dtbpy)(R1)3 (1.988(6)−2.041(5) Å).10 The Ru−N and
Ir−N(nitride) distances are 1.679(5) and 1.872(5) Å,
respectively, and the Ru−N−Ir linkage is slightly bent with
an angle of 163.7(3)°. The Ru−N distance in 4 is intermediate
between those of Ru−N triple (e.g., 1.573(6) Å in 16) and
double bonds (e.g., 1.718(3) Å in [Ru2(μ-N)Cl10]3−16) bonds,
whereas the IrIII−N distance is significantly shorter than a
typical Ir−N single bond as a result of a dπ(Ir)−π*(Ru−N)
interaction. Therefore, the bonding in 4 can be described by
two resonance forms, RuVIN−IrIII ↔ RuIVNIrV. The
latter is isoelectronic with the antiferromagnetically coupled
RuIVNRuIV system, e.g. [{LOEtRuCl2}2(μ-N)]−,17 which is
−
assignable to the LOEt and mesityl ligands in the normal
regions, indicative of the diamagnetic nature of the complex. 2
is tentatively formulated as a RuIV−RhIII−RuIV complex. It
should be noted that the related RuIV−RuII μ-imido complex
(LOEt)Cl2RuIV(μ-NH)RuII(CO)(PPh3)(LOEt) is also diamag-
netic.8 Figure 1 shows the molecular structure of 2. The RuIV−
N bond distances (1.821(5) and 1.859(5) Å) are short and
comparable to that in (LOEt)Cl2RuIV(μ-NH)RuII(CO)(PPh3)-
(LOEt) (1.818(4) Å),8 whereas the RhIII−N distances (1.966(6)
and 1.963(5) Å) are quite long (cf. 1.8946(18) and 1.8969(19)
Å in (η5-C5Me5)2Rh2(μ-NAr), where Ar = 2,6-diisopropyl-
phenyl15), suggesting that the bonding in 2 is best described as
RuIVN(R)−RhIII−N(R)RuIV featuring unsymmetrical
imido bridges. The Rh−Ru separations are 2.9026(6) and
3.1228(6) Å, and the RuIV−N−RhIII angles are 101.5(3) and
109.7(3)°.
diamagnetic. Unlike IrIII(dtbpy)(R1)3, which exhibits a
10
reversible IrIV−IrIII couple of +0.18 V versus Cp2Fe+/0
,
no
oxidation events were found in the cyclic voltammogram of 3 in
CH2Cl2 (up to +1.5 V). This result can be explained by the fact
that the Ir center in 3 is strongly stabilized by the π-accepting
RuVI nitride, rendering the IrIII−IrIV oxidation unfavorable.
A plausible mechanism for the formation of 2 is shown in
Scheme 2. It seems reasonable to assume that the first step
involves the coordination of the RuN group to Rh, because
similar μ-nitrido complexes were formed from 1 and
Reactions of 1 with dtbpy-stabilized IrIII and RhIII triaryl
complexes have also been studied. NMR spectroscopy indicated
Figure 1. Molecular structure of 2. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at the 30% probability level. Selected bond
lengths (Å): Rh(2)−N(3) = 1.966(6), Rh(2)−N(4) = 1.963(5), Rh(2)−C(137) = 2.038(7), Ru(3)−N(3) = 1.821(5), Ru(4)−N(4) = 1.859(5),
Rh(1)−Ru(1) = 2.9026(6), Rh(1)−Ru(2) = 3.1228(6).
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Figure 2. Molecular structure of 4. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at the 30% probability level. Selected bond
lengths (Å) and angles (deg): Ir(1)−N(1) = 1.872(5), Ir(1)−N(2) = 2.154(5), Ir(1)−N(3) = 2.194(5), Ir(1)−C(51) = 2.167(6), Ir(1)−C(61) =
2.070(6), Ir(1)−C(71) = 2.100(7), Ru(1)−Cl(1) = 2.3445(16), Ru(1)−Cl(2) = 2.3582(17), Ru(1)−N(1) = 1.679(5); Ru(1)−N(1)−Ir(1) =
163.7(3).
migratory insertion was found between IrIII(dtbpy)R3 and 1,
Scheme 2. Plausible Mechanism for Formation of 2
possibly due to the high metal−carbon bond strength and/or
the chelate effect of dtbpy. Additional work is needed to
elucidate the mechanism of the insertion of nitride into the
metal−carbon bond.
ASSOCIATED CONTENT
* Supporting Information
■
S
Text, tables, figures, and CIF files giving experimental details
and characterization data of the complexes reported and
crystallographic data for 2 and 4. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: chleung@ust.hk.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the Hong Kong Research Grants Council (projects
603111 and 602310) and the Hong Kong University of Science
and Technology for support.
■
IrIII(dtbpy)R3. Insertion of the RuN group into a Rh−C
bond affords a μ-imido intermediate, A. It may be noted that
the migratory insertion of RhIII(mes)3 with CO has been
reported previously.9 Addition of a second RuVI nitride
followed by migratory insertion gives a di-μ-imido species, B.
Finally, intramolecular C−H activation of a mesitylimido ligand
in B and reductive elimination of mesitylene yields the
cyclometalated product 2.
In summary, we have demonstrated that, analogous to CO,
the RuVI nitride 1 can insert into the Rh−C bonds in Rh(mes)3
to give a heterometallic μ-imido complex. This is a new reaction
for transition-metal nitrides that may provide a new strategy for
the synthesis of dinuclear imido complexes. On the other hand,
reaction of 1 with IrIII(dtbpy)R3 afforded dinuclear RuVI−IrIII
nitrido complexes that show Ir−N multiple-bond character. No
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