Phosphino ureas

Fig. 5.5 Comparison of phosphorus chemical shifts between phosphino amines, phosphino amides, and phosphino ureas...

Of particular interest in the latter case is the use of N-NMR spectroscopy for the determination of J( P, N) data, of which there are few examples for systems having two coordinate sp -hybridised nitrogen linked to phosphorus. " Various acyclic bis(aminophosphines) have also been reported, including the imino-functional system (96), the bis(phosphino)-hydrazines (97) and -ureas (98), and the l,8-bis[bis(dialkylamino)phosphino]naphthalenes (99). There has also been significant activity in the synthesis of cyclic aminophosphines. An improved route to the four-membered ring system (100) is afforded by the reaction of phosphorus trichloride with t-butylamine in a 1 3 mole ratio in THF. Treatment of this with ammonia in THF/triethylamine at — 78°C gives (101),... 

Note In the urea/thiourea system, phosphoramidinato groups can withdraw electron density from the phosphino substituted side. As a result, the phosphoramidinato signal is relatively upfield shifted, and the phosphino signal is relatively downfield shifted. 

Figure 2.14 Some chiral phosphino(thio)ureas.

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