The nature of the products from the reaction of TrtPH 2 (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 TrtPCl 2 . 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 NEt 3 or DBU. The course of the reac-tion 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 ( ), and t-BuPCl 2 (resulting from partial cleavage of the PΒ±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 ( ). The diphosphine (TrtPH) 2 ( ) is inert towards HCl-free phosgene. In the presence of HCl the PΒ±Pbond in 14 was cleaved, and upon chlorination of the resulting TrtPH 2 (1) by phosgene, TrtP(H)Cl (3) was obtained as the only phosphorus-containing product.