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Journal of Organometallic Chemistry 596 (2000) 77 – 83
The metal–metal bond in the
dibenzotetramethyltetraaza[14]annulene – ruthenium dinuclear
complex: a structural, magnetic, and theoretical analysis
Joe ¨lle Hesschenbrouck
a
, Euro Solari
a
, Rosario Scopelliti
a
, Carlo Floriani
a,
*,
Nazzareno Re
b
a
Institut de Chimie Mine ´rale et Analytique, BCH, Uniersite ´ de Lausanne, CH-1015 Lausanne, Switzerland
b
Facolta ` di Farmacia, Uniersita ` degli Studi ‘G. D’Annunzio’, I -66100 Chieti, Italy
Received 23 June 1999
Dedicated to Professor F. Albert Cotton in the occasion of his 70th birthday. We thank him for being the academic mentor of our science
Abstract
The thermal decomposition of [{Ru(tmtaa)}
2
(1,5-cyclooctadiene)] (1) in boiling toluene has led to the formation of the
metal – metal bonded dinuclear complex [{Ru(tmtaa)}
2
](2), (RuRu, 2.3829(4) A ). Upon oxidation using Cp
2
FeBPh
4
, the
corresponding monocation [{Ru(tmtaa)}
2
]BPh
4
(3) is synthesized with an RuRu bond distance of 2.2782(4) A . The magnetic
measurements of 2 and 3 are in agreement with a ground state s =1 and s =
1
2
, respectively. Calculations indicate an RuRu
2
4
2
*
2
*
2
electron configuration and suggest an RuRu double bond character for 2, while the significant shortening by 0.105
A of the RuRu distance in 3 is in agreement with a
2
4
2
*
2
*
1
electron configuration and an RuRu bond order of 2.5.
Complex 2 serves as a source of the [Ru(tmtaa)] fragment in a variety of reactions, one of which is the reaction with ethylene in
THF leading to the quite rare ethylene diamagnetic complex [Ru(tmtaa)(THF)(
2
-C
2
H
4
)] (4), (Ru···(
2
-C
2
H
4
), 2.009(2); CC,
1.384(5) A ). © 2000 Elsevier Science S.A. All rights reserved.
Keywords: RuRu bonds; Ru – macrocycle; Ru – ethylene; Tetramethyltetraaza[14]annulene
1. Introduction
The chemistry of the [RuRu] functionality has been
intensely investigated in the context of Ru – porphyrin
derivatization [1 – 3]. However, such functionalities have
not received the appropriate attention when ruthenium
was bonded to other macrocycles or polydentate lig-
ands. More than 20 years ago, Goedken et al. published
a very short communication on the metal – metal
bonded dinuclear complex [Ru
2
(tmtaa)
2
]
0/+
(tmtaa =
dibenzotetramethyltetraaza[14]annulene dianion) [4,5],
without providing details of the structure and the mag-
netic behavior [6]. Such a metal – metal bonded dinu-
clear complex can be considered as the appropriate
source of the [Ru(tmtaa)] monomer, which has been
recently found to display a quite rich Ru – carbene
chemistry [7]. A high-yield synthetic methodology for
[Ru
2
(tmtaa)
2
] has been developed for the synthesis of
quantities suitable for reactivity studies. Its oxidation to
the corresponding cationic species [Ru
2
(tmtaa)
2
]
+
BPh
4
-
has been performed as well as its transformation into
the monomeric Ru – ethylene complex. A detailed struc-
tural, magnetic, and theoretical analysis is reported for
the three complexes.
2. Results and discussion
2.1. Synthesis, structure, and magnetism
The synthesis of the metal – metal bonded dinuclear
complex 2 has been performed via a thermal displace-
* Corresponding author. Tel.: +41-21-6923902; fax: +41-21-
6923905.
E-mail address: carlo.floriani@icma.unil.ch (C. Floriani)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII:S0022-328X(99)00542-2