Catalyst‐Free Hydroboration of CO₂ With a Nucleophilic Diborane(4)

Abstract

Hydroboration generally requires the presence of a catalyst to lower the barrier for hydride transfer. This work reports on the first catalyst-free CO hydroboration with a neutral boron compound, the nucleophilic diborane [HB(hpp)] , 1 (hpp=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate). Further hydroboration reactions to bis(boryl)acetals are possible. In acetonitrile, but not in dichloromethane solutions, hydroboration of a first CO is followed by hydroboration of a second CO molecule. Detailed kinetic measurements for both hydroboration steps were carried out and the influence of the solvent and the addition of a Lewis base on the rate constants analyzed. In contrast to catalyst-free hydroboration of CO , hydroboration of the less electrophilic acetone requires the presence of an activating Lewis acid.

B–B vs. B–H Bond Activation in a (μ‐Hydrido)diborane(4) Anion upon Cycloaddition with CO2, Isocyanates, or Carbodiimides

“…[31] The 1 Ha nd 13 [22] which points toward as ignificantly altered electronic situation within the B(m-H)B core.Alow-field resonance at d( 13 C) = 195.5 ppm is consistent with the presence of aB-O-C(O)-B fragment. [29,32] In line with that, two 11 BNMR resonances are found in the region of tetracoordinated boron nuclei (d( 11 B) = À1.6, À5.1 ppm). [33] X-ray crystallography on the centrosymmetric dimer {[K(pmdta)][2H]} 2 •THF finally confirmed the molecular structure of the cycloaddition product (Figure 2 3) ,r espectively.W en ote that the BÀO bond of K[2H],which is inert toward excess CO 2 over hours, is shorter by 0.065 than the B À Ob ond of ac omparable cycloadduct Na 2 [A](Scheme 2b), which readily inserts asecond molecule of CO 2 .…”

Study of the Reactivity of the [(PE1CE2P)Ni(II)] (E1, E2 = O, S) Pincer System with Acetonitrile and Base: Formation of Cyanomethyl and Amidocrotononitrile Complexes versus Ligand Decomposition by P–S Bond Activation

“…To evaluate this, we have reacted LiCH 2 CN with [( i Pr POCOP i Pr )­Ni­(NCMe)]­OTf but did not observe formation of 1-ACN (Figure S13). From these experiments, it remains unclear why the second equivalent of base is needed to generate the Ni amidocrotononitrile complexes as Himmel’s Zn complex is formed with only 1 equiv of base, supporting the insertion mechanism depicted in Scheme …”

“…3-Amidocrotononitrile is a rather unusual ligand for transition metal complexes; however, examples are known in which two of these ligands bind to two metal centers via the amide and nitrile nitrogen atom. − Apart from that, only one Zn complex exists, where 3-amidocrotononitrile does not act as a bridging ligand, only coordinating via the amido nitrogen to the metal center . The complexes presented herein are, to the best of our knowledge, the first examples of fully characterized metal pincer complexes, where 3-amidocrotononitrile coordinates as a monodentate ligand to a single metal center.…”

A Highly Effective Route to Si−O−Si Moieties through O‐Silylation of Silanols and Polyhedral Oligomeric Silsesquioxane Silanols with Disilazanes

“…[59] Therefore, it is highly desirable to reduce the amount of catalyst (or avoid its use), and to minimize waste generatedd uring the reaction. [63][64][65][66][67][68][69][70][71][72] Important advantages of many of thesem ethods are their simplicity and efficiency.I np articular,r oom-temperature (RT) reactions are very attractive for potential further application.G iven all this, we focusedo nd eveloping the synthesis of organosilicon compoundsi nagreen chemistry manner. [63][64][65][66][67][68][69][70][71][72] Important advantages of many of thesem ethods are their simplicity and efficiency.I np articular,r oom-temperature (RT) reactions are very attractive for potential further application.G iven all this, we focusedo nd eveloping the synthesis of organosilicon compoundsi nagreen chemistry manner.…”

“…[60][61][62] Consequently,t he development of catalyst-free synthetic procedures has received significant interesti nr ecent times. [63][64][65][66][67][68][69][70][71][72] Important advantages of many of thesem ethods are their simplicity and efficiency.I np articular,r oom-temperature (RT) reactions are very attractive for potential further application.G iven all this, we focusedo nd eveloping the synthesis of organosilicon compoundsi nagreen chemistry manner.…”