Arylimido complexes of ruthenium(IV) porphyrins
Abstract
Treatment of [Ru(tbpp)O
2
]
[H
2
tbpp = 5,10,15,20-tetrakis(p-tert
-butylphenyl)porphyrin] with SiMe
3
Cl gave
[Ru(tbpp)Cl
2
] in good yield. Reaction of
[Ru(tbpp)Cl
2
] with para-substituted anilines
NRH
2
(R = p-XC
6
H
4
where X = Me, H, Cl or I) afforded the first
arylimidoruthenium(IV) complexes [Ru(tbpp)(NR)]. These are
paramagnetic with µ
eff
ca. 2.8 µ
B
and
display
1
H NMR spectra that are typical for paramagnetic
ruthenium(IV) porphyrins. The cyclic voltammograms of
[Ru(tbpp)(NR)] exhibit reversible Ru
V
–Ru
IV
and
Ru
IV
–Ru
III
couples. Treatment of
[Ru(tbpp)(NR)] with Ag
I
or Ce
IV
afforded the
imidoruthenium(V) complex [Ru(tbpp)(NR)]
+
. The
complexes [Ru(tbpp)(NR)] underwent imido-group transfer reactions with
tertiary phosphines to give
[Ru(tbpp)(PR′
3
)
2
] and
RN![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
PR
3
′. The reduction of [Ru(tbpp)(NR)] by
PMe
2
Ph shows saturation kinetics, in which the rate is first
order in [Ru
IV
]. The mechanism proposed for the Ru-mediated
imido transfer involves reversible binding of phosphine to Ru
IV
and rate-limiting intramolecular imido-group transfer. The first-order rate
constant (k
1
) and phosphine binding constant
(K) and for the reduction of
[Ru(tbpp)(NC
6
H
4
Me-p)] by PMe
2
Ph
at 25.0 °C in toluene solution were determined to be
(6.86 ± 0.19) × 10
-4
s
-1
and
(23.6 ± 6.5) × 10
3
mol
dm
-3
, respectively. The activation enthalpy
(ΔH
‡
) and entropy
(ΔS
‡
) for the above
reaction are 125 ± 1 kJ mol
-1
and
113 ± 21 J K
-1
mol
-1
, respectively. For the reduction of
para-X-substituted arylimido complexes
[Ru(tbpp)(NC
6
H
4
X-p)] by tertiary
PMe
2
Ph the rate decreases in the order
X = I > H ≈ Cl >
Me. The imido transfer from
[Ru
V
(tbpp)(NC
6
H
4
Me-p)]
to PMe
2
Ph is about 60 times faster than that from
[Ru
IV
(tbpp)(NC
6
H
4
Me-p)].
]
[H
2
tbpp = 5,10,15,20-tetrakis(p-tert
-butylphenyl)porphyrin] with SiMe
3
Cl gave
[Ru(tbpp)Cl
2
] in good yield. Reaction of
[Ru(tbpp)Cl
2
] with para-substituted anilines
NRH
2
(R = p-XC
6
H
4
where X = Me, H, Cl or I) afforded the first
arylimidoruthenium(IV) complexes [Ru(tbpp)(NR)]. These are
paramagnetic with µ
eff
ca. 2.8 µ
B
and
display
1
H NMR spectra that are typical for paramagnetic
ruthenium(IV) porphyrins. The cyclic voltammograms of
[Ru(tbpp)(NR)] exhibit reversible Ru
V
–Ru
IV
and
Ru
IV
–Ru
III
couples. Treatment of
[Ru(tbpp)(NR)] with Ag
I
or Ce
IV
afforded the
imidoruthenium(V) complex [Ru(tbpp)(NR)]
+
. The
complexes [Ru(tbpp)(NR)] underwent imido-group transfer reactions with
tertiary phosphines to give
[Ru(tbpp)(PR′
3
)
2
] and
RNPR
3
′. The reduction of [Ru(tbpp)(NR)] by
PMe
2
Ph shows saturation kinetics, in which the rate is first
order in [Ru
IV
]. The mechanism proposed for the Ru-mediated
imido transfer involves reversible binding of phosphine to Ru
IV
and rate-limiting intramolecular imido-group transfer. The first-order rate
constant (k
1
) and phosphine binding constant
(K) and for the reduction of
[Ru(tbpp)(NC
6
H
4
Me-p)] by PMe
2
Ph
at 25.0 °C in toluene solution were determined to be
(6.86 ± 0.19) × 10
-4
s
-1
and
(23.6 ± 6.5) × 10
3
mol
dm
-3
, respectively. The activation enthalpy
(ΔH
‡
) and entropy
(ΔS
‡
) for the above
reaction are 125 ± 1 kJ mol
-1
and
113 ± 21 J K
-1
mol
-1
, respectively. For the reduction of
para-X-substituted arylimido complexes
[Ru(tbpp)(NC
6
H
4
X-p)] by tertiary
PMe
2
Ph the rate decreases in the order
X = I > H ≈ Cl >
Me. The imido transfer from
[Ru
V
(tbpp)(NC
6
H
4
Me-p)]
to PMe
2
Ph is about 60 times faster than that from
[Ru
IV
(tbpp)(NC
6
H
4
Me-p)].
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