We report the synthesis and properties of the much sought-after tris(1,1,3,3-tetramethylguanidinyl) phosphine P(tmg) 3 , a crystalline, superbasic phosphine accessible through a short and scalable procedure from the cheap and commercially available bulk chemicals 1,1,3,3-tetramethylguanidine, tris(dimethylamino)-phosphine and phosphorus trichloride. The new phosphine exhibits exceptional electron donor properties and readily forms transition metal complexes with gold(I), palladium(II) and rhodium(I) precursors. The formation of zwitterionic Lewis base adducts with carbon dioxide and sulfur dioxide was explored. In addition, the complete series of phosphine chalcogenides was prepared from the reaction of P(tmg) 3 with N 2 O and the elemental chalcogens.

Phosphoniumylidyl and phosphazenyl groups are effective substituents to increase the electron‐donating ability of tertiary phosphines. However, the influence of structural variations among those substituents on the electronic properties of the phosphines is little explored. Herein, we show that protonation of the ylidic carbon atom of phosphoniumylidyl phosphines increases the Tolman electronic parameter (TEP) by ΔTEP = 16.0–18.8 cm–1. Furthermore, phosphazenyl phosphines were synthesized with isopropyl groups (NP{iPr}3) and tetramethylguanidino groups (NP{tmg}3) at the phosphonium center. Determination of their TEP values reveals a remarkable low substituent parameter of χ = –18.5 cm–1 for the NP(tmg)3 group. In addition, we prepared the corresponding gold(I) complexes and determined their solid‐state structures using single‐crystal X‐ray diffraction studies to analyze the steric profile of the new phosphine ligands.

While the metathesis reaction between alkynes and carbonyl compounds is an important tool in organic synthesis, the reactivity of alkynes with isoelectronic main-group R 2 EO compounds is unexplored. Herein, we show that oxophosphonium ions, which are the isoelectronic phosphorus congeners to carbonyl compounds, undergo [2 + 2] cycloaddition reactions with different alkynes to generate 1,2-oxaphosphete ions, which were isolated and structurally characterized. The strained phosphorus−oxygen heterocycles open to the corresponding heterodiene structure at elevated temperature, which was used to generate six-membered phosphorus heterocycles via hetero Diels−Alder reactions. Insights into the influence of the substituents at the phosphorus center on the energy profile of the oxygen atom transfer reaction were obtained by quantum-chemical calculations.

Arylphosphines are among the most important ligands in coordination chemistry and catalysis but are generally inferior to alkylphosphines when strong electron donor properties are required. Herein, we report the synthesis and properties of 1,2,5-trimethylpyrrolyl phosphines and show that their electrondonating ability can exceed that of alkylphosphines. The new phosphines can be prepared on a multi-gram scale in one-pot procedures starting from commercially available reagents. Tris-(1,2,5-trimethyl)pyrrolylphosphine P(tmp) 3 is a crystalline solid, displays a Tolman electronic parameter (TEP) of 2055.0 cm −1 and can be handled in air. Nickel(0), palladium(II), gold(I), and ruthenium(II) complexes with 1,2,5-trimethylpyrrolyl-based phosphines are reported in addition to preliminary investigations on the use of P(tmp) 3 in ruthenium-catalyzed olefin metathesis.

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