Contents Introduction 429 I. Synthetic Problems 430 A. Building the 1W-Phosphole Ring 430 B. 2Hand 3H-Phospholes and the 1H-432 2H-Phosphoie Equilibrium C. Synthesis of the Phospholyl Anions 434 II. Physicochemical Data and Theoretical 435 Problems A. 1H-Phospholes 435 1. Structural Data 435 2. Spectroscopic Data 435 3. The Aromaticity Problem 437 B. Phospholyl Anions 438 NMR Data and Theoretical Calculations 438 III. Chemical Properties 439 A. 1H-Phospholes 439 1. Nucleophilic Properties of Phosphorus 439 2. Electrophilic Properties of Phosphorus 440 3. Heatand UV-Induced Transformations 440 4. Diels-Alder Reactivity of the Dienic 441 System 5. Other Reactions of the Dienic System 444 6. Ring Opening 445 7. Ring Expansions 446 B. 2H-Phospholes 447 Dimerization and Reactivity toward A-H 447 Compounds, Dienes, and Dienophiles C. Phospholyl Anions 448 Nucleophilic Properties of Phosphorus 448 IV. Phospholes as Synthons 449 A. Synthesis of Other Phosphorus 449 Heterocycles B. Uses In Synthetic Organic Chemistry and in 450 Homogeneous Catalysis

Reaction of U( BH4)4 with K[tmp] (tmp = 2,3,4,5-tetramethylphospholyl) afforded the uranium(tv) complexes [U(tmp)(BH,),] and [U(tmp),(BH,),]. Sodium amalgam reduction of these complexes in tetrahydrofuran gave the uranate(ri1) anions [U(tmp)(BH,),] -and [U(tmp),(BH,),] -which were alternatively obtained by treating [U(C,H,Me,-1,3,5) (BH,),] with K[tmp]. Similar reactions in toluene led to the formation of the neutral compound [{U(tmp),(BH,)},].The fluxionality and the stability of the complexes are described.

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The title compounds 2 obtainable from the dihydrodiphosphetes 1 are analogues of the tetrathiafulvalenes, which are of interest as components of organic metals and superconductors. An X‐ray structure analysis of the tetrasulfide of 2, R = Et, revealed a planar five‐membered ring with a dihedral angle of 4.22° and completely localized CC double bonds (R = Me, Et, Ph).