Communication
Dalton Transactions
to give corresponding alkenes in good yields (Table 2). In both tions. Di- and trinuclear Ir complexes were active toward cata-
reactions, light irradiation accelerated the reactions. However, lytic hydrogenation of alkynes under atmospheric pressure,
in the case of 1-phenyl-1-propyne, the product ratio of alkane and the catalytic activities were accelerated under
(n-propylbenzene) was relatively high at about 30%. The photoirradiation.
precise kinetics of the hydrogenation reactions as well as the
scope of the substrates are now under investigation.
Density functional theory (DFT) calculation of the trinuc- Conflicts of interest
lear Ir complex 3 was conducted by using Gaussian 16
There are no conflicts to declare.
program packages.13 Although optimization of the structure
was completed successfully, the position of the six hydrogen
atoms was different from the structure obtained from the crys-
tallographic study. As mentioned in the previous section,
Acknowledgements
complex
3 possessed two terminal and four μ-bridging
This work was supported by the Cooperative Research Program
of “Network Joint Research Center for Materials and Devices”
and JSPS KAKENHI (B) Grant Number 16H0412100. Part of
this work was supported by a JSPS Grant-in-Aid for Scientific
Research on Innovative Areas (“3D Active-Site Science”: Grant
No. 26105003) from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan. We thank Dr Masaki
Mishima for the 13C NMR measurement.
hydrides. However, in the theoretical calculation, the final
optimized structure had three terminal and three μ-bridging
hydrides (Fig. S16†) although initial optimization was started
from the same hydride position as the crystallographic data.
The probable reason for the deviation between the theoretical
and experimental results could be that the energy differences
between these isomers are very small. The difference in the
hydride position affected the bond lengths of the Ir3 core, in
which the optimized structure possessed a slightly lengthened
Ir2–Ir3 bond (Table 1).
Notes and references
Frontier molecular orbitals are depicted in Fig. S17.† The
highest occupied molecular orbital (HOMO) and the nearby
orbitals possessed Ir d-orbital and Ir-hydride bonding orbital
characters. In contrast, the lowest occupied molecular orbital
(LUMO) and the nearby orbitals (LUMO+1 and LUMO+2) pos-
sessed Ir d-character with contribution from an Ir–H anti-
bonding orbital. The results indicated that the low-energy tran-
sition of the molecule will result in the release of the hydrides.
One of the effects of visible-light irradiation is the dissociation
of hydride ligands to provide unsaturated coordination sites
on the Ir centers. We will continue to elucidate the transition
structures of the starting complex as well as the intermediate
complexes in the catalytic cycle.
In summary, we have succeeded in synthesizing di- and tri-
nuclear Ir hydride complexes ligated with diphosphine con-
taining a light-absorbing fluorenyl moiety. The molecular
structure of the trinuclear complex possessed a monocationic
Ir3 core with two terminal and four bridging hydride ligands.
The VT-1H NMR spectra of the di- and trinuclear hydride com-
plexes showed dynamic behavior of the hydride ligands which
gives several structural isomers with different hydride posi-
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Reaction
time/h
Conversion/%,
ON (OFF)
Product ratio,
Z : E : alkane
Substrate
diphenylacetylene
1-phenyl-1-propyne
phenylacetylene
9
6
5
88 (33)
98 (9.8)
97 (50)
81 : 16 : 3
47 : 21 : 32
90 (alkene) : 10
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a Atmospheric pressure of H2, using a CD2Cl2 solution of 3 in a
J-YOUNG NMR tube at ambient temperature (λirr = 430 nm, ε(3)430 nm
=
1594).
Dalton Trans.
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