The reaction of 5-diphenoxyphosphanyl-6-diisopropylphosphinoacenaphthene 12 with chlorotrimethylsilane unexpectedly gave a phosphonium-phosphine compound 13, containing the structural motif of four phosphorus atoms connected in a chain. To explain the mechanism of this complex transformation, a proposed intermediate 5-dichlorophosphino-6-diisopropylphosphinoacenaphthene 14 was synthesized by an alternative method. The two (formally) phosphine environments in 14 form an intramolecular donor-acceptor (phosphonium-phosphoranide) complex, stable at room temperature in the solid state and as a solution in certain solvents. A (31)P NMR mechanistic study showed that, despite the presence of a rigid acenaphthene backbone, 14 is unstable in the presence of nucleophiles and disproportionates into 13 and other phosphorus containing products. Both 13 and 14 have been crystallographically characterized.

Synthetic and bonding aspects of heavier Group 15 (P, As, Sb, Bi) and 16 (S, Se, Te) peri-substituted naphthalenes, are discussed in this review. An important and unifying feature of the chemistry of these systems is the lively discussion about the nature of the interaction between peri-atoms. Are atoms bonded when they are closer than the sum of their van der Waals radii? Is there any (weak) bonding, or just a strained repulsive interaction? Positioning atoms of Group 15 and 16 at the naphthalene 1,8-positions provides leading systems with which to study these bonding issues.

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'P' undressed: A stable phosphanylidene phosphorane with a sterically accessible (naked) two‐coordinate P is reported (see structure). Coordination to Pd0 reveals its phosphine donor/phosphinidene acceptor (R3P→PR′) nature by exposing its phosphinidene‐like reactivity.

A proximate Lewis basic group facilitates the mild dehydrogenative P-As intramolecular coupling in the phosphine-arsine peri-substituted acenaphthene 3, affording thermally and hydrolytically stable arsanylidine-phosphorane 4 with a sterically accessible two-coordinate arsenic atom. The formation of 4 is thermoneutral due to the dehydrogenation being concerted with the donor coordination. Reaction of 4 with a limited amount of oxygen reveals arsinidene-like reactivity via formation of cyclooligoarsines, supporting the formulation of the bonding in 4 as base-stabilized arsinidene R3P→AsR.