Stable Boron Dithiolene Radicals

Abstract

Whereas low‐temperature (−78 °C) reaction of the lithium dithiolene radical 1. with boron bromide gives the dibromoboron dithiolene radical 2., the parallel reaction of 1. with (C6H11)2BCl (0 °C) affords the dicyclohexylboron dithiolene radical 3.. Radicals 2. and 3. were characterized by single‐crystal X‐ray diffraction, UV/Vis, and EPR spectroscopy. The nature of these radicals was also probed computationally. Under mild conditions, 3. undergoes unexpected thiourea‐mediated B−C bond activation to give zwitterion 4, which may be regarded as an anionic dithiolene‐modified carbene complex of the sulfenyl cation RS+ (R=cyclohexyl).

Diradical Character of Neutral Heteroleptic Bis(1,2-dithiolene) Metal Complexes: Case Study of [Pd(Me2timdt)(mnt)] (Me2timdt = 1,3-Dimethyl-2,4,5-trithioxoimidazolidine; mnt2– = 1,2-Dicyano-1,2-ethylenedithiolate)

“…In Figure 3 , the optimized C–C distances and the corresponding Wiberg bond indices (WBIs) 97 are compared for a variety of R′ 2 timdt derivatives showing a C=C double bond, as in 4,5,9,10-tetrathiocino[1,2- b :5,6- b ′]diimidazolyl-1,3,6,8-tetramethyl-2,7-dithione (Me 2 timdt) 2 and compound 7 , 74 or a single bond, as in the neutral complex 2 and in compound 5 ( Chart S2 ). 72 , 73 For these compounds, a clear correlation ( R 2 = 0.99) holds between the optimized C–C bond distance d C–C within the R 2 timdt ring and the corresponding WBI C–C values. This clearly shows that WBIs calculated at the optimized distances represent a reliable parameter for evaluating the charge distribution and hence the oxidation state of noninnocent 1,2-dithiolene ligands.…”

“…The C–C distance in the Me 2 timdt ligand of 3 (1.454(16) Å) is intermediate between the corresponding distance in [Pd(Et 2 timdt)Br 2 ] (1.474(10) Å; Chart S2 ), 48 featuring an authentic neutral Et 2 timdt ligand, and that of Li( 5 , R″ = 2,6-diisopropylphenyl, Chart S2 ; 1.417(4) Å), featuring the R″ 2 timdt •– radical monoanion. 72 , 73 Analogously, the C(4)–C(4) i distance in 3 (1.364(16) Å) is shorter than that found in [Pd(mnt) 2 ] ( 4 ; 1.39(2) Å; Chart S2 ) 116 and the average value for 4 – monoanions (1.377(24) Å) 117 but slightly larger than the average value found in salts of the complex 4 2– (1.359(19) Å). 118 This suggests that the Me 2 timdt ligand in 3 should be considered to carry a partial negative charge and that the GS of 3 should include a partial DC.…”

“…Quantum-chemical calculations were carried out on [Pd(Me 2 timdt) 2 ] q − ( 1 q – ; Chart S2 for q = 0), [Pd(Me 2 timdt)Br 2 ] ( 2 ; Chart S2 ), [Pd(Me 2 timdt)(mnt)] q − ( 3 q – ; q = 0, 1, 2; Chart S2 for q = 0), [Pd(mnt) 2 ] q − ( 4 q – ; q = 0, 1, 2; Chart S2 for q = 0), [Pt(phen)(tdt)] (phen = 1,10-phenanthroline; tdt 2– = 3,4-toluenedithiolate; Chart S2 ), 71 and [Ni(bdt) 2 ] (bdt 2– = benzene-1,2-dithiolate) 33 , 37 and the compounds (Me 2 timdt) 2 ( Chart S2 ), Li(R′′ 2 timdt)·2THF (R′′ = 2,6-diisopropylphenyl; 5 ; Chart S2 ), 72 , 73 and Me 2 timdt(SPh) 2 ( 7 ; Chart S2 ) 74 at the density functional theory (DFT) 75 level with the commercial suite Gaussian 16. 76 The computational setup was validated as previously described for the strictly related [Ni(Me 2 timdt) 2 ] complex and derivatives, 52 and it took into account three hybrid functionals (B3LYP, 77 mPW1PW, 78 and PBE0 79 ) and six basis sets with relativistic effective core potentials (RECPs) 80 , 81 for the central metal ion (LANL08(f), 82 SBKJC, 83 Stuttgart 1997 RC, 84 CRENBL, 85 LANL2DZ, 86 and LANL2TZ 82 ).…”

Reactivity of a Hexaaryldiboron(6) Dianion as Boryl Radical Anions

“…In 1924, the Krause group reported that the reaction of triphenylborane and sodium in diethyl ether resulted in a product with the chemical composition of NaBPh 3 , which was later confirmed to be a radical anion. − Since then, the study of boron-containing radical species has received tremendous research interest, which might be ascribed to their applications in chemical sensors, organic synthesis, polymer chemistry, and material science. − In the past decades, many boron-containing radical compounds have been successfully designed and synthesized. − The synthesis of these radical species has mainly relied on the reduction of organoboron compounds by strong reducing agents, such as Li, Na, K, etc . Generally, stable boron-centered radical compounds can be obtained through the steric effect of the substituents or spin delocalization through π conjugation.…”

Labile Imidazolium Cyclopentadienides

“…The anionic diisopropylphenyl-substituted N-heterocyclic dicarbene NHDC Dipp (Scheme 2), reported by this laboratory, 27 has proven to be a versatile synthetic platform from which a variety of abnormal carbene-based complexes, poly-NHCs, NHDC-based binuclear complexes, main-group dithiolene radicals, 28,29 and C4-functionalized NHCs may be accessed. 30−34 Notably, our synthetic efforts regarding the lowtemperature reaction of NHDC Dipp with Cp 2 Ti IV Cl 2 in THF and subsequent workup in toluene did not afford the expected C4-titanocenyl-substituted N-heterocyclic carbene.…”