Rhodium(III) 21-(μ-ethylidene)-21-carbaporphyrin 85-Rh is reactive in solution
and in solids. After a few hours, it converts into the corresponding green-brown
compound 90-Rh [25].
The protonation of the internal C(25) atom in 85-Rh leads to a transient form –
rhodium(III) 21-ethyl-21-carbaporphyrin 88-Rh. The oxidation of 88-Rh generates
21-ethylidene-21-carbaporphyrin 89-Rh, which formally contains an embedded
6-methylfulvene motif. The isomerization of 89-Rh produces rhodium(III)
N
N
N
Ph
Ph
Tol
Tol
Rh
CH 3
Cl
N
N
N
Ph
Ph
Tol
Tol
Rh
CH 3
N
N
N
Ph
Ph
Tol
Tol
Rh
CH 3
N
N
N
Ph
Ph
Tol
Tol
Rh
OHC
CH 3
CHO
H
H
H
Al 2 O 3
H
73-Rh
85-Rh
86-Rh
87-Rh
+
+
Scheme 47 Formation of 21-(μ-ethylidene)-21-carbaporphyrins 85-Rh, 86-Rh, and 87-Rh
81-Rh
82-Rh
N
N
N
Ar
Ar
Ar
Ar
Rh
CHO
HO H
C
HO H
HCHO
N
N
N
Ar
Ar
Ar
Ar
Rh
CHO
N
N
N
Ar
Ar
Ar
Ar
Rh
CHO
OH
H
H
H
N
N
N
Ar
Ar
Ar
Ar
Rh
CHO
N
N
N
Ar
Ar
Ar
Ar
Rh
CHO
CHO
N
N
N
Ar
Ar
Ar
Ar
Rh
CHO
OH
H
H
H
Al 2 O 3
- [H2]
74-Rh
(74-OH)-Rh
84-t 1
84-t 2
-
+
Scheme 46 Postulated mechanism of the contraction of m-phenylene to cyclopentadiene
216
K. Hurej and L. Latos-Grażyński