The Reactions of Diboron Tetrachloride with Some Hydrogen Compounds of Non-metallic Elements and with Dimethyl Sulfide¹

Stable Lewis Base Adducts of Tetrahalodiboranes: Synthetic Methods and Structural Diversity

“…Ac omparison of the 11 BNMR resonanceso fa nalogous tetrachloro, tetrabromo, and tetraiodo B 2 X 4 L 2 derivatives, both new and literature-known, shows increasing highfields hifts down the group (Table 1). The adduct B 2 I 4 (CNtBu) 2 ,f or example, displays an 11 BNMR resonance at d11 B = À43.1 ppm, shifteda pproximately 27 ppm to higher field compared with the resonance of B 2 Br 4 (CNtBu) 2 at À16.5 ppm. [25c] Ac omparably large shift difference of 20-24 ppm is observed for B 2 I 4 (SMe 2 ) 2 and B 2 Br 4 (SMe 2 ) 2 (d11 B = À20.0 and À0.3 ppm, respectively), [10] as well as B 2 I 4 (PCy 3 ) 2 and B 2 Br 4 (PCy 3 ) 2 (d11 B = À28.0 ppm and À4.3 ppm, respectively).…”

“…Furthermore, the reaction of IMes (1,3-bis(2,4,6-trimethylphenyl)-imidazole-2-ylidene) or IDip with one equivalent of B 2 Cl 4 at À78 8Cl ed to the formationo ft he mono-adductsB 2 Cl 4 (IMes) and B 2 Cl 4 (IDip), respectively,a sw ell as small amounts of the corresponding B 2 Cl 4 (NHC) 2 bis-adducts (Scheme 5). These highly unstable compounds were identified by low-temperature 11 BNMR spectroscopy by their two major broad resonances around À69 and À5ppm, alongside severalm inor side products.T hese resonancesa re similar to those observed for the only other reported B 2 Cl 4 mono-adduct, B 2 Cl 4 {P(SiMe 3 ) 3 }, at 69.5 (sp 2 -B) and À0.9 (sp 3 -B) ppm. [13] An X-ray crystallographic experiment on single crystals of B 2 Cl 4 (IMes) obtainedb ydiffusion of pentane into as aturated o-difluorobenzene solution at À30 8Cc onfirmed the formation of the 1:1a dduct (see below).…”

“…Warming of these reactionmixtures to room temperature resulted in decompositioni nto the ionic, chloride-bridged compounds [B 2 Cl 3 (IMes) 2 ][BCl 4 ]a nd [B 2 Cl 3 (IDip) 2 ][BCl 4 ], respectively, both structurally confirmed by X-ray crystallographic analysis (see Figure 7). Both compounds displayasharp 11 BNMR singlet at 6.9 ppm for the BCl 4 À counteranion, which is likely formed by the addition of the eliminated chloride anion to free BCl 3 , resultingf rom the inevitable disproportionation of excess B 2 Cl 4 upon warming the reaction mixture to room temperature. The broad 11 BNMR B 2 resonanceso ft he [B 2 Cl 3 (NHC) 2 ]c ations (13.6 and 36.6 ppm for NHC = IMes and IDip, respectively) are lowfield-shifted from those of their B 2 Cl 4 (NHC) 2 counterparts (2.7 and 1.5 ppm, respectively).…”

“…[5,6] With SH 2 and PH 3 ,B 2 Cl 4 forms bis-adducts at À78 8C, which decompose upon warming, liberating H 2 and PH 4 Cl, respectively (Scheme 1b,c). [11] With weaker phosphine donors, such as PCl 3 and PBr 3 ,a dduct formation with B 2 Cl 4 and B 2 Br 4 was found to be reversible in solution (Scheme 1d). [12,13] In contrast, the mono-adduct B 2 Cl 4 (P 2 Me 4 )p roved surprisingly stable, and upon addition of NMe 3 yieldedthe first mixed-base diborane (4) bis-adduct, B 2 Cl 4 (P 2 Me 4 )(NMe 3 ).…”

Spectra and structure of phosphorus-boron compounds. IX. Vibrational analysis and molecular symmetry of solid diboron tetrachloride-bis(phosphine) and diboron tetrachloride-bis(phosphine-d3)

“…(24) C. D. Cornwell and R. S . (26) Ail incorrect value was given in rei' 10. ( 2 4 ) R. J. Oillespie and M. 1. Phys., 27, 1060 (1957).…”