Ambireactive (R₃P)₂BH₂ Groups Facilitating Temperature‐Switchable Bond Activation by an Iron Complex

Abstract

An iron pincer complex containing a hemi-labile (R P) BH group exhibits temperature-switchable reactivity patterns: a reversible B-H activation concomitant with a P-B bond cleavage is observed at room temperature. Below 4 °C, intra- and intermolecular C-H activation pathways are becoming faster and more dominant. Mechanistic investigations reveal that the lability of the (R P) BH group in combination with the exothermic formation of σ-bonded complexes are responsible for the switchable bond activation. Finally, a protocol for an iron-catalyzed H/D-exchange of organic solvents in the absence of oxidants has been developed.

Umpolung at Boron: Ancillary‐Ligand‐Induced Formation of Boron‐Based Donor Ligands from Phosphine‐Boranes

“…Complexes of type 4 have previously been obtained via a different route with CO and H 2 as ligands trans to the hydrido ligand . Slow conversion of complex 4‐H 2 back to I shows the accessibility of this reaction path.…”

“…[47,48] Complexes of type 4 have previously been obtained via a different route with CO and H 2 as ligands trans to the hydrido ligand. [39] Slow conversion of complex 4-H 2 backt oI shows the accessibility of this reaction path. Formal loss of H 2 from 1-tBuNC anda ddition of another equivalent of tBuNC leads to the formation of 1-(tBuNC) 2 .L eavingasolution of 1-(tBuNC) 2 and 4-tBuNC under CO atmosphere for up to 24 hd id not result in anyreaction.…”

Redox-Active, Boron-Based Ligands in Iron Complexes with Inverted Hydride Reactivity in Dehydrogenation Catalysis

“…In the case of the amine-bridged ligand in 3a the deprotonation of the second P-NH-P group led to the stabilization of the iron(0) intermediate 46 and the coordination of the resulting diphosphinoborate has been observed for iron(II) complexes, too. 72 In the current case the available spectroscopic data gives rise to the assumption that a bisphosphino-borate iron(0) complex [({Ph 2 P-CH-PPh 2 }BH 2 )Fe(CO) 2 ] − (7b) is formed. However, this complex immediately disappears upon addition of DMAB and is not observed during or after the catalytic dehydrogenation reaction.…”

Small Chains of Main Group Elements by BH3 Adduct Formation of tBu2E‐N(H)‐EtBu2 (E = P, As)

“…These phosphine boranes can be used as bench‐stable pre‐ligands or to facilitate substitution at the phosphorus, which can even lead to the introduction of chirality at the phosphorus atom . In connection with a suitable transition metal fragment, the reactivity of such phosphine boranes can result in novel boron‐containing species . In this context, we recently discovered the re‐arrangement of an iron phosphine borane to a novel type of boron‐based pincer complex and became therefore interested in BH 3 adducts of diphosphines with a small bite angle such as bis (diphenylphosphanyl)amine [dppa = Ph 2 P‐N(H)‐PPh 2 ].…”

“…[5] In connection with a suitable transition metal fragment, the reactivity of such phosphine boranes can result in novel boron-containing species. [6][7][8] In this context, we recently discovered the re-arrangement of an iron phosphine borane to a novel type of boron-based pincer complex and became therefore interested in BH 3 adducts of diphosphines with a small bite angle such as bis(diphenylphosphanyl)amine [dppa = Ph 2 P-N(H)-PPh 2 ]. Depending on the substituents at the phosphorus center, very different reactivities can be observed in combination with metal precursors.…”