The activation of CO2, CS2 as well as of PhNCO at [Rh(Bpin)(PEt3)3] led to C=X bond cleavage and the formation of {RhXBpin} species (X = O, S, N). Treatment of the boryl complex [Rh(Bpin)(PEt3)3] with 0.5 equivalents of CS2 resulted in the fragmentation of CS2 and the formation of the remarkable μ-carbido complex trans-[Rh2(μ-C)(SBpin)2(PEt3)4].
The rhodium(I) boryl complex [Rh(Bpin)(PEt3)3] (1) reacts with the ketones α,α,α-trifluoroacetophenone and 9-fluorenone by insertion of the C=O bond to give [Rh{η(3)-C(CF3)(OBpin)C6H5}(PEt3)2] (4) and [Rh{η(5)-C13H8(OBpin)}(PEt3)2] (6), whereas the reaction with acetophenone leads to the formation of [Rh(H)(PEt3)3] (2), [Rh(OBpin)(PEt3)3] (3) and (E)-(Ph)CH=CHBpin. Treatment 1 of with ketimines generates [Rh{η(3)-C6H5=C(Ph)N(Ph)(Bpin)}(PEt3)2] (7), [Rh{(η(3)-C12H8)N(Ph)(Bpin)}(PEt3)2] (8) or [Rh{CPh2N(H)(Bpin)}(PEt3)2] (9). The insertion of aldimines into the Rh-B bond gives access to [Rh[η(3)-CH{N(C6H13)Bpin}C6H5](PEt3)2] (11) or [Rh[η(3)-CH{N(Ph)Bpin}C6H5](PEt3)2] (12). The latter is converted into the C-H activation product [Rh{(C6H4)-o-N(Bpin)(CH2Ph)}(PEt3)3] (13). Complex 13 reacts with B2pin2 to yield the boryl complex 1 and the amine PhCH2N(Bpin)(C6H4-o-Bpin).
An unprecedented reaction pathway for the borylation of SCF3-containing arenes using [Rh(Bpin)(PEt3)3] (pin=pinacolato) is reported. Catalytic processes were developed and the functionalizations proceed under mild reaction conditions. The C-H activations occur with a unique regioselectivity for the position ortho to the SCF3 group, which apparently serves as directing group. Borylated SCF3 compounds can serve as versatile building blocks.
In this work, a benzene-1,2-dithiolate
(bdt) pentamethylcyclopentadienyl di-iron complex [Cp*Fe(μ–η2:η4-bdt)FeCp*] and its [Cp*Fe(bdt)(X)FeCp*]
analogues (where X = N2H2, N2H3
–, H–, NH2
–, NHCH3
–, or NO+) were investigated through spectroscopic and computational studies.
These complexes are of relevance as model systems for dinitrogen activation
in nitrogenase and share with its active site the presence of iron,
sulfur ligands, and a very flexible electronic structure. On the basis
of a combination of X-ray emission spectroscopy (XES), X-ray crystallography,
Mössbauer, NMR, and EPR spectroscopy, the geometric and electronic
structure of the series has been experimentally elucidated. All iron
atoms were found to be in a local low-spin configuration. When no
additional X ligand is bound, the bdt ligand is tilted and features
a stabilizing π-interaction with one of the iron atoms. The
number of lone-pair orbitals provided by the nitrogen-containing species
is crucial to the overall electronic structure. When only one lone-pair
is present and the iron atoms are bridged by one atom, a three-center
bond occurs, and a direct Fe–Fe bond is absent. If the bridging
atom provides two lone-pairs, then an Fe–Fe bond is formed.
A recurring theme for all ligands is σ-donation into the unoccupied
eg manifolds of both iron atoms and back-donation from
the t2g manifolds into the ligand π* orbitals. The
latter results in a weakening of the double bond of the bound ligand,
and in the case of NO+, it results in a weakening of all
bonds that comprise triple bond. The electron-rich thiolates further
amplify this effect and can also serve as bases for proton binding.
While the above observations have been made for the studied di-iron
complexes, they may be of relevance for the active site in nitrogenase,
where a similar N2 binding mode may occur allowing for
the simultaneous weakening of the N2 σ bond and π
bonds.
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