Inorg. Chem. 1996, 35, 7845-7849
7845
Syntheses, Structures, and Reactivity of Diruthenium Phosphine Carbonyl Complexes of
Nitrites and Nitrates
Kom-Bei Shiu,*,† Luh-Tin Yang,† Shih-Wei Jean,† Chien-Hsing Li,† Ru-Rong Wu,†
Ju-Chun Wang,‡ Lin-Shu Liou,‡ and Michael Y. Chiang§
Departments of Chemistry, National Cheng Kung University, Tainan 701, Taiwan, Republic of China,
Soochow University, Taipei 111, Taiwan, Republic of China, and National Sun Yat-Sen University,
Kaohsiung 804, Taiwan, Republic of China
ReceiVed May 16, 1996X
A series of diruthenium phosphine carbonyl complexes containing bridging nitro and nitrato groups, [Ru2(CO)4-
(µ-NO2)2L2] (1-4) and [Ru2(CO)4(µ-NO3)2L2] (5-9), were cleanly prepared from the reactions of [Ru2(CO)4-
(NCMe)4L2][BF4]2 (L ) PPh3, PPh2(allyl), PPh2Me, PPhMe2, or PMe3) with excess NaNO2 or NaNO3 in MeOH.
Complexes 1-4 are present in two isomeric forms, A and B, with a head-to-head orientation of two bridging
η2-(N,O)-NO2 groups for form A and a head-to-tail arrangement of the groups for form B, in an approximate 3:1
ratio, but complexes 5-9 are present in only one isomeric form with an η2-(O,O)-NO3 attachment. Crystal data:
1A, a ) 12.452(2) Å, b ) 23.520(3) Å, c ) 13.441(2) Å, â ) 98.280(1)°, monoclinic P21/n, Z ) 4; 5, a )
11.737(3) Å, b ) 23.496(5) Å, c ) 14.629(3) Å, â ) 100.34(2)°, monoclinic P21/n, Z ) 4. The five-membered
metallacycle {Ru2(ONO)} in 5-9 is more reactive than the four-membered metallacycle {Ru2(NO)} in 1-4,
reflected by the different reactivity of [Ru2(CO)4(µ-NO2)2(PPh3)2] (1) and [Ru2(CO)4(µ-NO3)2(PPh3)2] (5) with
various reagents to give [Ru2(CO)4(µ-I)2(PPh3)2] (10), [Ru2(CO)4(µ-N3)2(PPh3)2] (11), and [Ru2(CO)4(η1-NO3)2-
(µ-X)2(PPh3)2] (X ) Br (12), I (13)). Crystal data of 13: a ) 31.394(3) Å, b ) 9.761(1) Å, c ) 18.200(2) Å,
â ) 118.420(1)°, monoclinic C2/c, Z ) 4. The intermolecular oxygen transfer from the ligated NO2 groups in
1 to exogenous PMe3 is readily observed in MeCN at ambient temperature, apparently forming nitrosyl groups
and free OPMe3.
Introduction
Results and Discussion
The cation [Ru2(CO)4(NCMe)6]2+ has recently been reported
to be very versatile, leading to various substitution products such
as [Ru2(CO)4(NCMe)4L2]2+ via replacement of two acetonitrile
ligands at the axial sites of the complex by phosphines (L).4a
The low-valent metal-metal-bonded transition-metal com-
plexes of nitro and nitrato groups, especially those containing
reducing phosphine and carbonyl ligands, are of fundamental
importance, because the related chemistry can, in principle, help
to provide or design suitable metal reagents or catalytic systems
to destroy NOx (x ) 1, 2),1 which are produced in all high-
temperature combustion processes by the oxidation of N2 and
fuel-bound nitrogen. However, finding a suitable entry to the
complexes remains a great challenge to coordination chemists,
in view of the weak coordination ability of nitrate2 and the facile
oxygen transfer from the groups to phosphine and CO.3 From
a serendipitous discovery, we offer here a convenient synthetic
approach, leading to a clean and high-yield preparation of a
series of such complexes without any accompanying oxygen-
transfer product. However, related studies on the transfer and
other chemical reactivity are reported. Importantly, the evidence
described below indicate that exogenous rather than coordinated
phosphines enable the removal of oxygen atoms from coordi-
nated nitro groups.
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† National Cheng Kung University.
‡ Soochow University.
§ National Sun Yat-Sen University.
X Abstract published in AdVance ACS Abstracts, November 15, 1996.
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S0020-1669(96)00530-7 CCC: $12.00 © 1996 American Chemical Society