Coordination chemistry of alkali metal dimesityl-thio- and dimesityl-selenophosphinites [(L) 2 A-EPMes 2 ] 2 (A = Li, Na, K; E = S, Se; L = THF, THP) and [(18C6)K-SPMes 2 ].

The reactions of dimesitylphosphane oxide Mes 2 P(O)H with Lawessons reagent and dimesitylphoshane with selenium yield Mes 2 P(E)H with E = S (1a) and E = Se (1b), respectively, with moderate yields. Metalation of dimesitylphosphane sulfide 1a with n -butyllithium, sodium hydride or potassium hydride in THF allows the isolation of dinuclear dimesityl-thiophosphinites of the type [(thf) 2 A-S-PMes 2 ] 2 [A = Li (4), Na (5), K (2a)] with central four-membered A 2 S 2 rings. The weaker base THP leads to the very similar aggregate [(thp) 2 K-S-PMes 2 ] 2 (3a) as has also been observed for the homologous potassium dimesityl-selenophosphinites of the type [(L) 2 K-Se-PMes 2 ] 2 [L = thf (2b), thp (3b)]. Addition of 18-crown-6 ether leads to deaggregation and expectedly to formation of mononuclear [(18C6)K-S-PMes 2 ] (6). Moderate yields have been obtained due to dismutation reactions that yield the corresponding phosphinates AE 2 PMes 2 and phosphanides APMes 2 , a degradation process which has been observed earlier also for Li-O-PMes 2 . This side reaction hampers the application of these thio- and selenophosphinites as catalysts in the addition of phosphane sulfides and selenides across alkynes.