Hydroboration of CO₂ catalyzed by bis(phosphinite) pincer ligated nickel thiolate complexes

Abstract

We report the hydroboration of CO with catecholborane catalyzed by a series of bis(phosphinite) pincer ligated nickel thiolate complexes. Turnover frequencies (TOFs) up to 2400 h were achieved at room temperature under an atmospheric pressure of CO. This represents the highest TOF value known to date for the reduction of CO to the methoxide level under mild conditions.

The Reactivity of Mercapto Groups against Boron Hydrides in Pincer Ligated Nickel Mercapto Complexes

“…The resulting RSBcat species catalyzes the degradation of HBcat to form B 2 (cat) 3 and the Lewis base adduct of BH 3 . The latter further reacts with the nickel hydride species to produce the corresponding nickel borohydride complexes . Clearly, the present POCOP nickel mercapto complexes react similarly towards HBcat, resulting in the formation of the nickel borohydride complexes and the degradation of HBcat, rather than the mercapto groups being deprotonated by HBcat .…”

“…However, the POCOP pincer backbones survived the present basic condition of NaSH salt at room temperature. Similar to the related thiolate complexes,, these nickel pincer mercapto complexes are orange to red crystalline solids and air stable in solid state. No significant decomposition was observed when the solid samples were exposed to air for a few hours as confirmed by 31 P{ 1 H} NMR spectroscopy.…”

“…This indicates that the Ni‐S bond strength is not significantly influenced by the POCOP or PCP pincer backbones. The Ni‐S bond lengths in all of these complexes are comparable to those of the corresponding POCOP‐pincer ligated nickel aliphatic thiolate complexes (2.16–2.21 Å), but slightly shorter than those of the corresponding nickel aromatic thiolate complexes (2.22–2.26 Å),, implying a stronger Ni−S bond in the nickel mercapto and nickel aliphatic thiolate complexes.…”

Syntheses and Structures of Group 10 Metal POCOP Pincer Complexes Bearing A Mercapto‐o–carborane Auxiliary Ligand

“…The bond lengths and angles of the POCOP pincer backbone are also similar to the previous observations for this ligand. [2b,g,i,k,m, ° ,p,q,7] In the structure of complex 1 , the Ni‐C ipso bond length (1.896(3) Å) is comparable with those of the corresponding POCOP−Ni phenylthiolate/benzylthiolate (SPh/SCH 2 Ph) complexes (1.880(2)‐1.910(3) Å); however, the Ni−S bond length (2.2438(11) Å) is longer than those of the most POCOP−Ni‐SPh/SCH 2 Ph complexes (2.1734(6)‐2.2556(9) Å) ,. For complex 2 , the Pd‐C ipso bond length (1.995(3) Å) is similar to those of the correlated POCOP−Pd‐SPh/SCH 2 Ph complexes (2.000(4)‐2.015(2) Å); nevertheless, the Pd−S bond length (2.3974(10) Å) is slightly longer than those of the POCOP−Pd‐SPh/SCH 2 Ph complexes (2.3635(8)‐2.3745(12) Å) and noticeably longer than those of several Pd(II) complexes with square‐planar configuration bearing 1‐mercapto‐2‐phenyl‐ o ‐carborane ligands (2.302(1)‐2.3595(4) Å) .…”

“…Especially, we explored the structures, reactivities and catalytic applications of nickel and palladium complexes with bis(phosphinite) (POCOP) pincer ligands. Recently, we applied a series of POCOP pincer Ni/Pd phenylthiolate, benzylthiolate, mercapto, azide and isothiosyanate complexes in the catalytic reduction of CO 2 with a borane and excellent catalytic activities of these complexes were observed under very mild conditions ,,. Encouraged by the catalytic activities of these pincer Ni/Pd complexes and the unusual properties of the carborane cluster, we initiated a study on the structures and reactivities of group 10 metal POCOP pincer complexes bearing a carboranylthiolate auxiliary ligand.…”