Reactivity Studies on a Diazadiphosphapentalene

Abstract

The reactivity of diazadiphosphapentalene 1 towards various substrates was investigated. Reaction of 1 with ammonia-borane resulted in transfer hydrogenolysis concomitantly with the cleavage of a P-N bond. By treatment of 1 with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), oxidation took place at one of the phosphorus atoms of 1, and a P(V) /P(III) mixed-valence derivative was isolated. At the same time, it was demonstrated that only one of the phosphorus atoms in 1 behaves as an electron donor for electrophiles and Lewis acids. The former afforded an intramolecularly coordinated phosphine-phosphenium species, whereas the latter demonstrates the ligand property of 1. UV irradiation induced rearrangement of 1 into another example of another diazadiphosphapentalene.

Sterically Constrained Bicyclic Phosphines: A Class of Fascinating Compounds Suitable for Application in Small Molecule Activation and Coordination Chemistry

“…That phosphorus atom, which is bound to two carbon atoms, seems to be more basic than the central atom of the PN 2 group (see above) and is coordinated to the metal atom. A better accessibility due to a lower steric shielding of this position may further help to understand the preference of this coordination mode . It is interesting to note that a similar behavior was observed upon treatment of 4 with the sulfane–borane adduct H 3 B←SMe 2 which resulted in the formation of the simple borane adduct 38 with a BH 3 molecule coordinated to the PC 2 phosphorus atom .…”

“…A better accessibility due to a lower steric shielding of this position may further help to understand the preference of this coordination mode . It is interesting to note that a similar behavior was observed upon treatment of 4 with the sulfane–borane adduct H 3 B←SMe 2 which resulted in the formation of the simple borane adduct 38 with a BH 3 molecule coordinated to the PC 2 phosphorus atom . Both phosphorus atoms may be able to act as bases for the coordination of electron pair acceptors, but 38 did not react with an additional equivalent of the borane to form the corresponding diborane adduct.…”

“…A coordination compound similar to 35 was obtained upon treatment of the diphosphine 4 with [PtCl 2 (COD)] ( 37 , Figures and ) . Crystal structure determination revealed a square‐planer coordination sphere of the platinum atom with a cis ‐arrangement of the ligands.…”

“…Two mechanisms were suggested by quantum‐chemical calculations, which both identify ring cleavage similar to Scheme b as the key step at the beginning of the reaction, but differ with respect to the mechanism of ring closure for completion of the hydrogenation process (H 3 B←NH 3 versus ammonia contribution). Ring opening as an essential reaction pathway has been confirmed experimentally by treatment of the diphosphorus compound 4 with H 3 B←NH 3 . Hydrogen transfer was observed once again, but the hydrogen molecule was not added to the phosphorus atom to yield a PH 2 group similar to 29 .…”

“…TEMPO (2,2,6,6‐tetramethylpiperidinyloxyl) reacted with the diphosphorus compound 4 as an oxygenation reagent. The transferred oxygen atom in the product 19 is not bonded to the PN 2 phosphorus atom, but to the second one bound to two carbon atoms (Figure ; δ ( 31 P)=113.4 and 62.1 ppm] . The regioselectivity of this oxygen transfer reaction may be correlated to the different donor strengths of the phosphorus atoms in 4 .…”