Reversible, heterolytic addition of H2 across an iron-boron bond in a ferraboratrane with formal hydride transfer to the boron gives iron-borohydrido-hydride complexes. These compounds catalyze the hydrogenation of alkenes and alkynes to the respective alkanes. Notably, the boron is capable of acting as a shuttle for hydride transfer to substrates. The results are interesting in the context of heterolytic substrate addition across metal-boron bonds in metallaboratranes and related systems, as well as metal-ligand bifunctional catalysis.
The reactivity of the anionic dinitrogen complex [(TPB)Fe(N2)]− (2, TPB = tris-[2-(diisopropylphosphino)phenyl]borane) towards silicon electrophiles has been examined. Compound 2 reacts with trimethylsilyl chloride (TMSCl) to yield the silyldiazenido complex (TPB)Fe(NNSiMe3) (3), which is reduced by Na/Hg in THF to yield the corresponding sodium-bound anion [(TPB)Fe(NNSiMe3)]Na(THF) (4). The use of 1,2-bis(chlorodimethylsilyl)ethane in the presence of excess Na/Hg results in the disilylation of the bound N2 molecule to yield the disilylhydrazido(2−) complex (TPB)Fe≡NR (5, R = 2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentyl). One of the phosphine arms of TPB in 5 can be substituted by CO or tBuNC to yield crystalline adducts (TPB)(L)Fe≡NR (6: L = CO; 7: L = tBuNC). The N-N bond in 7 is cleaved upon standing at room temperature to yield a phosphoraniminato/disilylamido iron(II) complex (8). The flexibility of the Fe–B linkage is thought to play a key role in these transformations of Fe-bound dinitrogen.
On-surface
synthesis with molecular precursors has emerged as the
de facto route to atomically well-defined graphene nanoribbons (GNRs)
with controlled zigzag and armchair edges. On Au(111) and Ag(111)
surfaces, the prototypical precursor 10,10′-dibromo-9,9′-bianthryl
(DBBA) polymerizes through an Ullmann reaction to form straight GNRs
with armchair edges. However, on Cu(111), irrespective of the bianthryl
precursor (dibromo-, dichloro-, or halogen-free bianthryl), the Ullmann
route is inactive, and instead, identical chiral GNRs are formed.
Using atomically resolved noncontact atomic force microscopy (nc-AFM),
we studied the growth mechanism in detail. In contrast to the nonplanar
BA-derived precursors, planar dibromoperylene (DBP) molecules do form
armchair GNRs by Ullmann coupling on Cu(111), as they do on Au(111).
These results highlight the role of the substrate, precursor shape,
and molecule–molecule interactions as decisive factors in determining
the reaction pathway. Our findings establish a new design paradigm
for molecular precursors and opens a route to the realization of previously
unattainable covalently bonded nanostructures.
Tris(phosphine)borane ligated Fe(I) centers featuring N2H4, NH3, NH2, and OH ligands are described. Conversion of Fe-NH2 to Fe-NH3+ by addition of acid, and subsequent reductive release of NH3 to generate Fe-N2, is demonstrated. This sequence models the final steps of proposed Fe-mediated nitrogen fixation pathways. The five-coordinate trigonal bipyramidal complexes described are unusual in that they adopt S = 3/2 ground states and are prepared from a four-coordinate, S = 3/2 trigonal pyramidal precursor.
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