Diamidocarbene Induced B–H Activation: A New Class of Initiator-Free Olefin Hydroboration Reagents

Abstract

Enabled by its enhanced electrophilicity and attenuated nucleophilicity, an N,N′-diamidocarbene (DAC) was found to promote the B–H bond activation of various BH3 complexes and the B–B bond of bis­(pinacolato)­diboron, constituting the first such examples for an isolable carbene. The resultant DAC-BH3 adducts datively coordinated to Lewis bases (i.e., dimethyl sulfide, trimethylamine, or pyridine) and facilitated the hydroboration of various olefins under mild conditions and in the absence of exogenous initiators.

P–N Cooperative Borane Activation and Catalytic Hydroboration by a Distorted Phosphorous Triamide Platform

“…26 Main group B–H activation is also precedented, for instance 1,1-oxidative addition by carbenes. 27 More common, though, are formally heterolytic reactivity modes, either FLP-type activation 28 in the presence of Lewis bases or formally metathetical transformations across polarized σ-bonds, 29 where catalytic applications are known. 30 Also, although not rigorously involving B–H activation, the Corey-Bakshi-Shibata protocol warrants mention in conjunction with a discussion of bifunctional main group catalyzed hydroboration.…”

Electronic and Ligand Properties of Skeletally Substituted Cyclic (Alkyl)(Amino)Carbenes (CAACs) and Their Reactivity towards Small Molecule Activation: A Theoretical Study

“…[10] Further,there are reports which demonstrate that stable singlet carbene can mimic the behaviour of transition-metal complexes as evidentf rom the activation of CÀO, SiÀH, BÀHa nd PÀHb onds. [9,11,28] However, use of diaminocarbenes towards activation of small molecules such as H 2 ,NH 3 were found to be unlikely which may be attributed to the large singlet-triplet gap as well as the presence of the comparatively lower lying s-symmetric donor orbital and higher lying p-symmetric acceptoro rbitalc oncentrated at the carbenic carbon. [10,29] This indicates that the carbenes used for small molecule activation should be ambiphilic in nature.…”

Olefin Hydroborations with Diamidocarbene–BH3 Adducts at Room Temperature

“…In a separate experiment, a stoichiometric mixture of cyclohexene and 1-octene was added in excess to a benzene solution of 1a. The product of this reaction was determined by 1 H NMR spectroscopy and mass spectrometry to contain a nearly equimolar mixture of the mixed product 11, the ring-expanded product 6, and 12 [29] (Scheme 8). We surmise that after the initial hydroboration of cyclohexene, the respective product did not enable the hydroboration of 1-octene, but instead underwent intramolecular ring-expansion to yield 6.…”

“…Unless otherwise specified, reagents were purchased from commercial sources and used without further purification. N,N'-dimesityl-4,6-diketo-5,5-dimethylpyrimidin-2-ylidene, as well as adducts 1a and 1b, were synthesized according to previously-reported procedures [29,30]. The hydroboration reactions described herein are unoptimized.…”

“…As shown in Scheme 2, we previously demonstrated that the N,N'-diamidocarbenes (DACs), a unique class of stable carbenes [28], afford 1 upon exposure to either BH 3 -pyridine or BH 3 -SMe 2 [29].…”