The ruthenium hydrido bis(dihydrogen) complex [Cn*RuH(H2)2][PF6] (2-PF
6
; Cn* = 1,4,7-trimethyl-1,4,7-triazacyclononane) was synthesized by treatment of Cn*RuCl3 with NaBH4. Complex 2-PF
6
undergoes a H/D exchange between its hydrido ligands and CD3OD, D2, or THF-d
8. Treatment of 2-PF
6
with Cp*IrH4 or Cp*OsH5 (Cp* = C5Me5) affords the heterometallic dinuclear polyhydrido complexes [Cn*Ru(μ-H)3IrCp*][PF6] (3-PF
6
) and [Cn*Ru(μ-H)3OsHCp*][PF6] (4-PF
6
), respectively. Treatment of 3-PF
6
with triphenylphosphine affords the complex [Ru(PPh3)(μ-η3:η1-Cn*CH2)(μ-H)2IrCp*][PF6] (5-PF
6
), in which the triphenylphosphine is coordinated to the Ru atom as a terminal ligand and the C−H bond of the methyl group in the Cn* ligand is cleaved by the Ir atom. Reaction of 3-PF
6
with acetylene gives a bis(μ-vinyl) complex, [Cn*Ru(μ-σ,π-CHCH2)IrH(μ-σ,π-CHCH2)Cp*][PF6] (6-PF
6
), in which one vinyl ligand is σ-bonded to the Ru atom and the other is σ-bonded to the Ir atom. The molecular structures of 2-PF
6
, [Cn*Ru(μ-H)3Ir(C5Me4Et)][BPh4] (3′-BPh
4
), 4-BPh
4
, 5-BPh
4
, and 6-PF
6
were confirmed by X-ray analyses, and the coordination modes of the hydrido ligands in 2-PF
6
were confirmed by density functional theory calculations.
Trinuclear heterometallic mono(μ 3 -oxo)-and bis(μ 3 -oxo)hydrido clusters, (Cp*Ru) n (Cp*Os) 3−n (μ 3 -O)(μ-H) 3 (8: n = 2; 10: n = 1; 12: n = 0) and (Cp*Ru) n (Cp*Os) 3−n (μ 3 -O) 2 (μ-H) (Cp* = η 5 -C 5 Me 5 ; n = 2, 1, and 0), were synthesized by the reaction of the corresponding trinuclear metal pentahydrido complexes, (Cp*Ru) n (Cp*Os) 3−n (μ-H) 5 , with the appropriate oxidizing agents. The mono(μ 3 -oxo) complex is proven to be highly active toward nitrogen−hydrogen bond cleavage of ammonia. While the reaction of (Cp*Ru) 3 (μ-H) 3 (μ 3 -H) 2 with ammonia proceeded slowly and reached a plateau in its conversion, the mono(μ 3 -oxo) complex reacted smoothly with ammonia to generate a μ 3 -imido complex and an equivalent of water. A notable heterometallic effect, namely, the acceleration of the formation rate of the μ 3 -imido complex, was observed in the reactions of 8 and 10 with ammonia. The relative ratios of the pseudo-first-order rate constants k obs for (Cp*Ru) 3 (μ 3 -O)(μ-H) 3 (3), 8, and 10 are 1:8:11, and polarization of the metal−metal bond induced in the metal core of the cluster is responsible for the acceleration of the reaction rate.
The novel mixed-ligand diruthenium trihydrido complex
Cn*Ru(μ-H)3RuCp* (2; Cn* = 1,4,7-trimethyl-1,4,7-triazacyclononane,
Cp* = η5-C5Me5) was synthesized,
and its structure was determined
by an X-ray diffraction study. Density functional theory (DFT) calculations
for 2 revealed that the electron density at the Cn*-ligated
ruthenium atom is higher than that at the Cp*-ligated ruthenium atom.
Whereas the unmixed Cp*,Cp*-ligated Cp*Ru(μ-H)4RuCp*
(5) exhibited no reactivity toward CO2 at
20 atm, the mixed-ligand complex 2 reacted with CO2 smoothly at atmospheric pressure and afforded the bis(μ-formato)
complex Cn*Ru(μ-η1:η1-O2CH)2(μ-H)RuCp* (4) quantitatively.
A ruthenium bis(η 2 -dihydrogen)-hydrido complex with 1,4,7-triazacyclononane (Cn), [CnRuH(H 2 ) 2 ]-(BPh 4 ) (2a-BPh 4 ), was prepared. The infrared spectra, longitudinal relaxation time (T 1 ) measurements, and density functional theory calculations reveal that the electron density at the metal center of complex 2a is higher than that of the 1,4,7-trimethyl-1,4,7-triazacyclononane (Cn*) analogue [Cn*RuH(H 2 ) 2 ] þ (2b). Complex 2a-BF 4 is converted into the tetranuclear octahydrido cluster complex [(CnRu) 4 (μ-H) 6 -(μ 3 -H) 2 ](BF 4 ) 4 (3-BF 4 ) via spontaneous dehydrogenation, whereas the dehydrogenation of 2b-PF 6 exclusively affords the diruthenium trihydrido complex [(Cn*Ru) 2 (μ-H) 3 ](PF 6 ) 2 (4-PF 6 ).
To construct electronically and sterically anisotropic reaction sites of dinuclear cluster, mixed-ligand diruthenium pentahydrido complexes [Cn*Ru(μ-H) 3 Ru-(H) 2 (PR 3 ) 2 ] + (Cn* = 1,4,7-trimethyl-1,4,7-triazacyclononane; R = Cy (3a), i Pr (3b), cyclopentyl (Cyp, 3c)) were synthesized by the reaction of [Cn*RuH(H 2 ) 2 ] + (1) with Ru-(H) 2 (H 2 ) 2 (PR 3 ) 2 (R = Cy (2a) i Pr (2b), Cyp (2c)). The treatment of 3a−c with KH afforded the corresponding neutral tetrahydrido complexes Cn*Ru(μ-H) 3 RuH(PR 3 ) 2 (R = Cy (4a), i Pr (4b), Cyp (4c)). The structures of 3 and 4 were confirmed by X-ray diffraction studies. Introduction of the Cn* ligand into the cluster increased the electron density at the Cn*ligated metal center and significantly stimulated reactivitiy toward molecular nitrogen and carbon dioxide. Complexes 3a−c reacted with molecular nitrogen to produce the terminal dinitrogen complexes [Cn*Ru(N 2 )(μ-H) 2 RuH(PR 3 ) 2 ] + (R = Cy (5a), i Pr (5b), Cyp (5c)), which readily underwent dimerization to form the bridging dinitrogen complexes [(μ-N 2 ){RuCn*(μ-H) 2 RuH(PR 3 ) 2 } 2 ] 2+ (R = i Pr (6b), Cyp (6c)), through the liberation of N 2 . Cationic complexes 3a−c reacted with CO 2 to produce the bridging formato complexes [Cn*Ru(μη 1 :η 1 -O 2 CH)(μ-H) 2 Ru(H 2 )(PR 3 ) 2 ] + (R = Cy (7a), i Pr (7b), Cyp (7c)), whereas neutral 4a−c reacted with CO 2 to form the carbonyl complexes [Cn*Ru(CO)(μ-H) 2 RuH(PR 3 ) 2 ] + (R = Cy (9a), i Pr (9b), Cyp (9c)), via cleavage of the CO bond.
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