Cooperative activation of O–H and S–H bonds across the Co–P bond of an N-heterocyclic phosphido complex

Abstract

A cobalt N-heterocyclic phosphido complex is shown to cleave element–hydrogen bonds via a metal–phosphorus ligand cooperative pathway.

N‐Heterocyclic Phosphido Complexes of Rhodium Supported by a Rigid Pincer Ligand

“…[23] In contrast, the reaction between (PPP)Co(PMe 3 ) and thiophenol was found to be much more complex, featuring an intermolecular ligand exchange process, where the (PP H P)Co(SPh)(PMe 3 ) complex was initially formed, but ultimately converted into the more thermodynamically stable (PP SPh P)Co(H)(PMe 3 ) product in solution. [24] Both the kinetic and thermodynamic product in the cobalt case remained five-coordinate with no evidence for dissociation of the PMe 3 ligand. Although 4 could not be broken into two monomeric species either through the addition of an exogenous ligand or via reaction with thiophenol, we were hopeful that 5 would be a reactive complex due to its differing structure, such that no large reorganization of the binding in the phosphine side arms would be required for it to form two monomeric complexes.…”

“…[23] In contrast, the reaction between (PPP)Co(PMe3) and thiophenol was found to be much more complex, featuring an intermolecular ligand exchange process, where the (PP H P)Co(SPh)(PMe3) complex was initially formed, but ultimately converted to the more thermodynamically stable (PP SPh P)Co(H)(PMe3) product in solution. [24] Both the kinetic and thermodynamic product in the cobalt case remained fivecoordinate with no evidence for dissociation of the PMe3 ligand.…”

“…In the case of the cobalt complex (PPP)Co(PMe 3 ), there was always a Berry pseudorotation observed after substrate addition that moved the substrate to a position trans to the central phosphorus. [18,24] For 7, it is likely that the lower steric demand of the tert-butyl isocyanide ligand compared to trimethylphosphine stabilizes the syn addition product without the need for subsequent isomerization. The Rh-P NHP bond length of 2.1755(9) Å is very similar to that of 3.…”

“…For example, the monodentate NHP + complex (NHP Dipp )Mn(CO) 4 (NHP Dipp = 1,3-bis(2,6-diisopropylphenyl)-1,3,2-diazaphospholium) synthesized by Gudat and co-workers was shown to be an active catalyst for ammonia borane dehydrogenation, [21] and was also shown to undergo backbone C-H deprotonation, yielding an anionic carbene phosphenium complex. [22] Our group has shown that NHPcomplexes of platinum(II) and cobalt(I) activate E-H (E = O, S) bonds across the metal-P NHP bond, [23,24] showcasing the potential for metal-ligand cooperativity. [25] Moreover, (PPP)Co(PMe 3 ) was shown to cleave H 2 across its cobalt-phosphorus bond to yield (PP H P)Co(H)(PMe 3 ).…”

Highly Selective Hydroboration of Terminal Alkenes Catalyzed by a Cobalt Pincer Complex Featuring a Central Reactive N-Heterocyclic Phosphido Fragment

“…Many of the most successful cobalt hydroboration catalysts take advantage of the stability and rigidity imparted by tridentate pincer ligands. , We turn our attention herein to a (PPP) − pincer ligand that incorporates an N-heterocyclic phosphido (NHP – ) moiety in the central donor position flanked by two diarylphosphine side arms . We have previously demonstrated that the tridentate (PPP) − pincer ligand can engage in metal–ligand cooperativity, through either bifunctional substrate activation across the metal-P bond or ligand-assisted redox processes. − …”