Three‐Coordinate Boron(III) and Diboron(II) Dications

Abstract

The enhanced electron-donor properties of the bulky bisimino ligand 1,2-(L N) -C H (1; L =1,3-bis(mesityl)-imidazolin-2-ylidene), mesityl=2,4,6-trimethylphenyl) were exploited for the stabilization of elusive electron-deficient and low-coordinate boron dication species. The reaction of 1 with PhBBr or (B(Cl)NMe ) afforded a dicationic mononuclear boron(III) complex or a dicationic dinuclear boron(II) complex, respectively (4 , 6 ). The bonding situations of 4 and 6 were examined by means of single crystal X-ray diffraction analysis, as well as theoretical methods. Significant allocation of positive charge density into the ligand system was diagnosed for both dications. However, the metalloid-centered Lewis acidity of the dications was confirmed via hydride transfer reactions.

Chemistry of Dicationic Diboranes

“…[30] Two years later Inoue et al reported a higher yield synthesis of another representative 10 with a strongly πelectron donating bisguanidine ligand stabilizing the electron deficient boron centers ( Figure 2). [31] However, considerable allocation of positive charge into the bisimino substituent as well as the NMe 2 groups lower the boron-centered electrophilicity thus mitigating its Lewis acidity.…”

Electron‐Deficient Triborane and Tetraborane Ring Compounds: Synthesis, Structure, and Bonding

“…[6,97,102] Theb icyclic guanidinate substituent hpp efficiently delocalizes the positive charge,t hereby enabling the stabilization of highly positively charged cationic boranes (enriching the field of cationic boron compounds currently being intensively studied [90,91,[106][107][108][109][110][111] ). [6,97,102] Theb icyclic guanidinate substituent hpp efficiently delocalizes the positive charge,t hereby enabling the stabilization of highly positively charged cationic boranes (enriching the field of cationic boron compounds currently being intensively studied [90,91,[106][107][108][109][110][111] ).…”

Cationic Complexes of Boron and Aluminum: An Early 21st Century Viewpoint

“…As econd example for at hree-coordinateb oron dication complex salt was presentedb yo ur group in 2018 (45[A n ] 2 ; with A n = Br,A lBr 4 ;F igure 13). [68] Theb is(imino) group that constitutest he ligand in 30 + ,a sw ell as 31 + was implementedt o stabilizet he cationic boronc enter.I nterestingly, 45[Br] 2 was converted to am onocation with af our-coordinate metalloid center (i.e.,b oronium ion 46 + )u pon reaction with Li[BH 4 ] (note: 46 + was also independently synthesized by conversion of bis(iminiumtosylate) with Li[PhBH 3 ], Figure 13). This sug- Figure 13.…”

“…Ah ighery ield synthesis of at hree-coordinate diboron(II) dication complex salt (60[SbCl 6 ] 2 )w as described by ourg roup and we implementedastrongly p-electron donating bis(imino) system for thermodynamic stabilizationo ft he p-acidic boron centers (Figure17). [68] Substantiala llocationo fpositivec harge density intot he ligand was diagnosed by theoretical,a sw ella s structurala nalysis.T he mean CÀN imino bond length of 1.37 correspondst ot he dication complex 45 2 + (vide supra) andt he MBO for each of theset wo bondsa mounts to 1.17( MBO = Mayer BondI ndex). This accounts for considerables ingle-bond character of thei mino nitrogen-carbonb onds as illustratedb y ther esonance structure 60 A 2 + (i.e., ligand-centeredb oron cation, Figure 17).…”

“…[115] Recently,o ur group has discovered that the conversion of the bis(imino) diboron(II) dications alt 60[SbCl 6 ] 2 with an excess of Li[AlH 4 ]r esults in ligand transfer between the two Group 13 metals to produce the bis(imino) aluminum dihydride cation salt 61[AlB 2 H 8 ] ( Figure 17 and Figure 28). [68] With regard to the structural parameters of the ligand scaffold, the XRD study of the complex cation revealed CÀN imino bond lengths of 1.330(2) and 1.329(2) ,w hich is slightly longer than in the lighter boron homologue 30 + (Figure 10, 1.317(5), 1.318(4) ). This accounts for marginally increaseds ingle-bond character of the imino nitrogen-carbon bond for 61 + ,w hich is an indicator of charge allocation into the N-heterocyclic imino ligands (an increaseds ingle bond character often marks higherc harge allocation into the ligand).…”