Metal–metal multiple bonded intermediates in catalysis

Overview of Rh2-catalysed C–H functionalization and C–H anination chemistries

Rh2 carbene chemistry
The key electronic feature of this intermediate is delocalized Rh–Rh–C three-centre bonding with appropriate three-centre orbitals of σ and π symmetry

Trends in reactivity for the different classes of organic diazo compounds

Preparation of the first Rh2 D/A carbene complex

Rh2 nitrene chemistry
Rh2-catalysed nitrenoid chemistry is mechanistically more complex than the corresponding carbenoid chemistry

Reactions using pre-formed iminoiodinane compounds
(a) – intramolecular cyclization
(b) – intermolecular reaction

Proposed mechanism for intermolecular C–H amination
Organic groups on the catalyst are removed for clarity

Ru2 nitrido chemistry
Rh–Rh=E ? M–M=E ? Ru–Ru≡N
structures
structures
structure
(E = CR2/NR)
The first Ru2 nitrido compound –Ru2(DPhF)4N
(DPhF = N,N′-diphenylformamidinate) – was found to be thermally unstable
In an effort to understand the nature of this instability,
the related Ru2(D(3,5-Cl2)PhF)4N3 azide complex was investigated

Crystal structure of Ru2[(D(3,5-Cl2)PhF)3(D(3,5-Cl2-2-NH)PhF)]

Synthetic cycle for N-atom transfer using the Ru2(chp)4 core

Summary
Efforts to identify reactive metal–metal bonded complexes having a linear M–M=E structure have led to the observation of important intermediates in Rh2-catalysed carbenoid and nitrenoid transformations. Inspired by the structures of these intermediates, chemists have been able to explore novel reactivity of the Ru–Ru≡N core including intramolecular C–H amination as well as intermolecular N atom transfer.