Unprecedented Borylene Insertion into a C–N Bond

Abstract

Keywords: Donor-acceptor systems / Boron / Nitrogen heterocycles / Bond activation / Structure elucidation Carbenes are well established reactive intermediates and play an important role in organic synthesis, whereas the scope of borylenes is rather limited. Selective borylene insertion into a C-N bond to yield boryl-functionalized N-heterocyclic olefins (NHOs), [{N(Dipp)N(DippBH)CHCH}CCH 2 ] 2 (6) and [{N(Dipp)N(DippBPh)CHCH}CCH 2 ][{N(Dipp)N-(2-iPr-6-CHMeCH 2 BC 6 H 3 )CHCH}CCH 2 ] (8) (Dipp = 2,6-iPr 2 C 6 H 3 ) is reported for the first time. KC 8 reduction of [a]

N‐Heterocyclic Vinylidene‐Stabilized Phosphorus Biradicaloid

“…All the P−C bond lengths (av 1.79 Å) are equal within three standard deviations, which are shorter than a P−C single bond but considerably longer than a P=C double bond length . The exocyclic C−C bond lengths (av 1.38 Å) are longer than the C=C bond length of 1 (1.332(4) Å) but shorter than the corresponding C−C bond length of 1 in donor–acceptor compounds (av 1.46 Å) . This indicates that a significant π‐electron density from the NHC has been transferred onto the C 2 P 2 ring, therefore 3 may also be regarded as a 6π‐electron aromate.…”

A Modular Access to Divinyldiphosphenes with a Strikingly Small HOMO–LUMO Energy Gap

“…We began our study with the synthesis of two new NHOs, (NHC)CHPh (NHC=IPr: C{(NAr)CH} 2 1 ; NHC=SIPr: C{(NAr)CH 2 } 2 2 ; Ar=2,6‐ i Pr 2 C 6 H 3 ) derived from the classical N‐heterocyclic carbenes (NHCs) IPr and SIPr, respectively (Scheme , see the Supporting Information for further details). The new NHOs 1 and 2 were prepared by employing a method previously reported by this laboratory using air stable 1,3‐imidazoli(ni)um salts, benzyl bromide, and a deprotonating base . Dehydrochlorination of 1 and 2 with PCl 3 gave the dichlorovinylphosphanes {(NHC)C(Ph)}PCl 2 (NHC=IPr, 3 ; SIPr, 4 ) as colorless crystalline solids.…”

“…The new NHOs 1 and 2 were prepared by employing am ethod previously reported by this laboratory using air stable 1,3-imidazoli(ni)um salts, benzyl bromide, and ad eprotonating base. [14] Dehydrochlorination of 1 and 2 with PCl 3 gave the dichlorovinylphosphanes {(NHC)C(Ph)}PCl 2 (NHC = IPr, 3;S IPr, 4)a sc olorless crystalline solids. The 1 Ha nd 13 C{ 1 H} NMR spectrao f3 and 4 exhibit expected resonances for the N-heterocyclic vinyl (NHV) moiety.T he 31 P{ 1 H} NMR spectrum of each of 3 and 4 shows a sharp signal at d =+ +170 AE 2ppm, which is consistent with dichlorophosphane derivatives.…”

“…The NHO 1 was prepared by employing a similar protocol previously reported by this laboratory . To a Schlenk flask containing (IPr)HCl (51.2 g, 120.4 mmol) and KO t Bu (27.9 g, 248.6 mmol) was added THF (300 mL) at room temperature (rt).…”

The Resurgence of the Highly Ylidic N‐Heterocyclic Olefins as a New Class of Organocatalysts

“…They can also be used as dienophiles in inverse‐electron‐demand Diels–Alder and other cycloaddition reactions . Due to the strong nucleophilicity of the α‐carbon, NHOs are often stronger Lewis bases than their parent NHCs, leading to several applications of NHOs as end‐on ligands in transition metal coordination and catalysis,– as well as stabilization of the metalloid boron and silicon in borenium ions, and silylenes . Very recently, NHOs have elicited great interest among synthetic chemists for their intriguing new roles as organocatalysts in important chemical transformations, such as CO 2 sequestration and polymerization reactions (Figure ) .…”