Phosphaborenes: Accessible Reagents for the Synthesis of C−C/P−B Isosteres

Abstract

Formal exchange of C=C units with isoelectronic B=N or B=P units can provide access to molecules with unique electronic or chemical properties. Herein, we report the simple solution-phase generation of highly reactive phosphaborenes, RP=BR, and demonstrate their use for the introduction of P=B units into organic systems. Ring opening of a P-B-containing cyclobutene isostere provided access to unique 1,4-boraphosphabutadiene systems with conjugated main-group multiple bonds.

Preparation and Characterization of P2BCh Ring Systems (Ch=S, Se) and Their Reactivity with N‐Heterocyclic Carbenes

“…The NHC-stabilizedp hosphaborene 5 has been reported as the product from the reaction of 2 with NHC Me and was therefore easily identified. [20] Similarly,aderivative of an NHC-stabilized phosphinidene sulfide has also been reported, [18] with 31 P{ 1 H} NMR chemical shifts similar to that observed for 4S Me . [18] While 4S Me is stable andc an be observed by NMR spectroscopy in crude reaction mixtures, there is no direct evidence of the analogous selenide 4Se Me ( Figure 5).…”

“…Heating a solution of NHC Me and 3Ch at 80 °C for 16 hours resulted in consumption of the starting material and appearance of two phosphorus‐containing products in the 31 P{ 1 H} NMR spectra: two singlets at δ P =32 and 151 for Ch=S, corresponding to 4S Me and 5 , and two singlets at δ P =−77 and 151 for Ch=Se, corresponding to 6 Me and 5 (Figure ). The NHC‐stabilized phosphaborene 5 has been reported as the product from the reaction of 2 with NHC Me and was therefore easily identified . Similarly, a derivative of an NHC‐stabilized phosphinidene sulfide has also been reported, with 31 P{ 1 H} NMR chemical shifts similar to that observed for 4S Me .…”

“…In agreement with these notions, density functional theory (DFT) calculations showed that the reaction begins with a P→B attack after which the resulting intermediate can follow multiple pathways with the most favourable ones lead to the formation of a P−P bond. The synthesized P 2 BCh main group rings can be monomerized at elevated temperatures in the presence of NHCs, reforming Ar*P = Ch and Mes*P = BNR 2 as well as giving access to NHC‐stabilized phosphinidenes …”

“…The synthesized P 2 BCh main group rings can be monomerized at elevated temperatures in the presence of NHCs, reforming Ar*P=Ch and Mes*P=BNR 2 as well as giving access to NHC-stabilized phosphinidenes. [20]…”

Self‐Assembly and C−H⋅⋅⋅Anion Hydrogen Bonding of Palladium(II)‐based Metallacalixarenes Using Pyridyl‐ or Phenyl‐Bridged Di‐Naphthoimidazoles

“…[15] To further elucidate the nature of the CÀH…anion hydrogen bonding interaction within this kind of metal-assembled receptors, we present here that self-assembly, crystal structures and solution anion complexation processes of the two novel boat-shaped metallomacrocyclic complexes using pyridyl or phenyl bridgedd i-naphthoimidazoles as ligands as shown in Scheme1.M osti nterestingly, the anions can subtly regulate the supramolecular architectures in solid statest hroughm ultiple hydrogen bondingi nteractions and other weak interactions. To the best of our knowledge,t he metal-assembled anion receptors through CÀH…anion hydrogen bonding interactions are still rare, [16] although various organic imidazolium and triazole ring derivatives have been synthesized and used as anion receptors. [17] The dinuclear palladium(II) macrocyclic complexes, [(tmeda) 2 Pd 2 L 1 2 ](NO 3 ) 4 (1a )a nd [(tmeda) 2 Pd 2 L 2 2 ](NO 3 ) 4 (2a)( tmeda = N, N, N',N '-tetramethylethylenediamine) were synthesized exclusively through coordination-driven self-assembly of a cis-coordinated palladium(II) nitrate precursor with ad itopic ligand 2,6-bis(1H-naphtho[2,3] imidazol-1-yl)pyridine (L 1 )o r1 ,3bis(1H-naphtho[2,3]imidazol-1-yl)benzene (L 2 )r espectively, which con-tains two naphthoimidazole moieties linked with a rigid bridge (benzene or pyridine ring) as shown in Scheme1.…”