New Adventures in the Molecular Chemistry of Phosphorus

Dearomatization [4+2] Cycloaddition of Nonactivated Benzene Derivatives

Dearomatization reactions have recently emerged as a powerful tool for the rapid buildup of molecular complexity. Here, an unparalleled thermal dearomatization [4+2] cycloaddition reaction between benzene derivatives and a 2H-phosphindole tungsten complex was reported. The unique reactivity of the in situ-generated 2H-phosphindole complex toward benzene was revealed by density functional theory calculations. We thus provide new insights into the dearomatization of nonactivated arenes and pave the way for the manipulation of the dearomatization for further applications.

1,3-Diphosphacyclobutene Cobalt Complexes

The synthesis and characterization of rare 1,3-diphosphacyclobutene transition-metal complexes is described. Reactions of the cobalt-hydride complex [Co(P₂ C₂ tBu₂ )₂ H] (G) with nBuLi, tBuLi, or PhLi afforded [Li(solv)_x {Co(η³ -P₂ C₂ tBu₂ HR)(η⁴ -P₂ C₂ tBu₂ )}] (1: R=nBu, (solv)_x =(Et₂ O)₂ ; 2: R=tBu, (solv)_x =(thf)₂ ; 3: R=Ph, (solv)_x =(Et₂ O)(thf)₂ ), with an η³ -coordinated 1,3-diphosphacyclobutene ligand as a result of organyl-anion attack at one of the phosphorus atoms of the bis(1,3-diphosphacyclobutadiene) backbone. In contrast to the reactions with PhLi, the aryl-magnesium compounds p-tolyl magnesium chloride and p-fluorophenyl magnesium bromide deprotonate [Co(P₂ C₂ tBu₂ )₂ H] to give the magnesium salt [Mg(MeCN)₆ ][Co(η⁴ -P₂ C₂ tBu₂ )₂ ]₂ (4), which contains a bis(1,3-diphosphacyclobutadiene)-cobaltate anion. The [Co(η⁴ -P₂ C₂ tBu₂ )₂ ]^- anions are well separated from the octahedral [Mg(MeCN)₆ ]²⁺ cation in the molecular structure of 4. Compound 1 reacts with Me₃ SiCl to give neutral [Co(η³ -P₂ C₂ tBu₂ HnBu)(η⁴ -P₂ C₂ tBu₂ SiMe₃ )] (5, 52 % yield) with an SiMe₃ group attached to one of the P atoms of the previously unfunctionalized backbone.