The Reaction of Triphenylmethyl-substituted Primary and Secondary Phosphines with Phosgene

The nature of the products from the reaction of TrtPH₂ ( 1 ) with an equimolar amount of phosgene strongly depends on the solvent. The initial intermediate 2 was isolated from toluene, but lost CO in dichloromethane, and HCl in diethyl ether, yielding TrtP(H)Cl ( 3 ), and (TrtPCO)₂ ( 4 b ), respectively. TrtP(H)Cl ( 3 ) was found to be a halophosphine of amazing stability. Treatment of 3 with excess phosgene led to partial substitution of the P-bonded proton for C(:O)Cl with formation of 5 , which did not eliminate CO to give TrtPCl₂. Substitution of chlorine in TrtP(H)Cl ( 3 ) for fluorine or bromine furnished the halophosphines, 6 and 7 . Minute quantities of the diphosphene 8 were formed upon treatment of 3 with NEt₃ or DBU. The course of the reaction between the secondary phosphines Trt(R)PH and phosgene depends on the group R. If R was t-Bu, formation of a mixture of Trt(t-Bu)PCl ( 10 ), and t-BuPCl₂ (resulting from partial cleavage of the P–C-bond) was observed. Although in the case of R = Ph, the intermediate 12 could be isolated, at elevated temperature HCl was eliminated from 12 , giving Trt(Ph)PCl ( 13 ). The diphosphine (TrtPH)₂ ( 14 ) is inert towards HCl-free phosgene. In the presence of HCl the P–P-bond in 14 was cleaved, and upon chlorination of the resulting TrtPH₂ ( 1 ) by phosgene, TrtP(H)Cl ( 3 ) was obtained as the only phosphorus-containing product.