Piano‐stool dinuclear ruthenium (II) complexes of pyrazine‐carboxylate/carboxamide ligands: Structural studies and catalytic transfer hydrogenation of ketones

• Published in: Applied organometallic chemistry Vol. 37; no. 11
• Main Authors: Kumah, Robert T., Ojwach, Stephen O.
• Format: Journal Article
• Language: English
• Published: Chichester Wiley Subscription Services, Inc 01-11-2023
• Subjects: Carboxylic acids; Chemistry; Coordination; Crystallography; Hydrogenation; Ketones; Ligands; Mass spectrometry; Molecular structure; NMR; Nuclear magnetic resonance; Pianos; Pyridines; Ruthenium; Substrates
• ISSN: 0268-2605; 1099-0739
• DOI: 10.1002/aoc.7269

Reactions of ligand pyrazine‐2‐carboxylic acid (
HL1
) with [Ru(η
6
‐
p
‐cymene)Cl
2
]
2
precursor gave the dinuclear piano‐stool ruthenium (II) complex [{Ru(η
6
‐
p
‐cymene)Cl
2
}‐μ‐(
L1
)‐{Ru(
p
‐cymene)Cl}] (
Ru1
). Separately, reactions of
N‐
(quinolin‐8‐yl) pyrazine‐2‐carboxamide (
HL2
), 5‐methyl‐
N
‐(−(quinolin‐8‐yl) pyridine‐2‐carboxamide (
HL3
) and 5‐chloro‐
N
‐(quinolin‐8‐yl) pyridine‐2‐carboxamide (
HL4
) with [Ru(η
6
‐
p
‐cymene)Cl
2
]
2
dimer in the presence of KPF
6
afforded the cationic dinuclear complexes [{Ru(η
6
‐
p
‐cymene)Cl}
2
‐μ‐(
L2
)][PF
6
] (
Ru2
), [{Ru(η
6
‐
p
‐cymene)Cl}
2
‐μ‐(
L3
)][Ru(
L3
)Cl
3
] (
Ru3
) and [{Ru(η
6
‐
p
‐cymene)Cl}
2
‐μ‐(
L4
)][PF
6
] (
Ru4
). The Ru (II) complexes were analysed using FT‐IR,
1
H,
13
C{
1
H},
31
P{
1
H} (
Ru2
and
Ru4
) and
19
F (
Ru2
and
Ru4
) NMR spectroscopic techniques, micro‐analyses and mass spectrometry. Molecular structures of complexes
Ru1
and
Ru3
were confirmed to display piano‐stool coordination nature using single‐crystal X‐ray crystallography analyses. All the complexes (
Ru1–Ru4
) mediated the transfer hydrogenation (TH) of a broad spectrum of ketones in isopropanol in the presence of a base and demonstrated high catalytic activities (TON of 24,000) at catalyst concentrations of 0.002 mol%. In general, the catalytic performance of these Ru (II) complexes depended on the identity of the ligands, coordination chemistry and ketone substrates.