Diverse Bonding Activations in the Reactivity of a Pentaphenylborole toward Sodium Phosphaethynolate: Heterocycle Synthesis and Mechanistic Studies

The reaction of the pentaphenylborole [(PhC)4BPh] (1) with sodium phosphaethynolate·1,4-dioxane (NaOCP­(1,4-dioxane)1.7) afforded the novel sodium salt of phosphaboraheterocycle 2. It comprises anionic fused tetracyclic P/B-heterocycles that arise from multiple bond activation between the borole backbone and [OCP]−anion. Density functional theory calculations indicate that the [OCP]− anion prefers the form of phosphaethynolate –O–CP over phosphaketenide OCP– to interact with two molecules of 1, along with various B–C, C–P, and C–C bond activations to form 2. The calculations were verified by experimental studies: (i) the reaction of 1 with NaOCP­(1,4-dioxane)1.7 and a Lewis base such as the N-heterocyclic carbene IAr [:C­{N­(Ar)­CH}2] (Ar = 2,6-iPr2C6H3) and amidinato amidosilylene [{PhC­(NtBu)2}­(Me2N)­Si:] afforded the Lewis base-pentaphenylborole adducts [(PhC)4B­(Ph)­(LB)] (LB = IAr (3), :Si­(NMe2)­{(NtBu)2CPh} (4)), respectively; (ii) the reaction of 1 with the carbodiimide ArNCNAr afforded the seven-membered B/N heterocycle [B­(Ph) (CPh)4C­(NAr)­N­(Ar)] (5). Compounds 2–5 were fully characterized by NMR spectroscopy and X-ray crystallography.五苯基硼咯[(PhC)₄BPh]（1，pentaphenylborole）与磷乙炔氧基钠·1,4-二氧六环（sodium phosphaethynolate·1,4-dioxane，NaOCP·1,4-dioxane₁.₇）反应，得到新型磷硼杂环钠盐2。该产物包含阴离子稠合四环P/B杂环，其结构源于硼咯骨架与[OCP]⁻阴离子之间的多重键活化。密度泛函理论（density functional theory，DFT）计算表明，[OCP]⁻阴离子更倾向于以磷乙炔氧基形式（–O–C≡P）而非磷烯酮基形式（O=C=P–）与两分子1发生作用，同时伴随多种B–C、C–P及C–C键活化过程，最终生成2。该计算结果得到实验研究的佐证：（i）1分别与NaOCP·1,4-二氧六环₁.₇以及两类路易斯碱——氮杂环卡宾IAr[:C{N(Ar)CH}₂]（Ar=2,6-ⁱPr₂C₆H₃）和脒基氨基硅烯[{PhC(NᵗBu)₂}(Me₂N)Si:]反应，分别得到路易斯碱-五苯基硼咯加合物[(PhC)₄B(Ph)(LB)]（其中LB=IAr（3）、:Si(NMe₂){(NᵗBu)₂CPh}（4））；（ii）1与碳二亚胺ArN=C=NAr反应，生成七元B/N杂环[B(Ph)(CPh)₄C(=NAr)N(Ar)]（5）。化合物2至5均通过核磁共振波谱法（NMR spectroscopy）与X射线晶体衍射（X-ray crystallography）完成了全面表征。