1,3,2-DIAZAPHOSPHININES AND 1,3,2-DIAZAARSININES AS PRECURSORS FOR POLYFUNCTIONAL PHOSPHININES AND ARSININES

Thermal reactions of 4,6-di-tert-butyl-1,3,2-diazaphosphinine la, obta ined from the reaction of the corresponding diazatitanacycle with PCl3 in the presence of NEt3, with various functional alkynes are dicussed . Phosphinines are produced in good yields (from 55 to 75%) via two [4 + 2] cycloaddition-cycloreversion sequences with extrusion of two mol ecules of pivalonitrile from la. Two 2-diethoxymethyl-substituted, 3 a nd 4, one 3-propynyl-substituted, 6, and two examples of 3-monosubstit uted and 3,5-disubstituted ferrocenylphosphinines, 8 and 9, have been synthesized, The X-ray structure of the -bis(trimethylsilyl)3,5-bis(fe rrocenyl)phosphinine 9 has been determined. Due to a strong steric cro wding between the silyl and ferrocenyl groups, the ring adopts a twist ed geometry with a dihedral angle of 11.65 degrees. Upon reaction of l a with bis(diphenylphosphino)acetylene, a 2,3-bis(diphenylphosphino)-s ubstituted, 11, and the 2,3,5,6-tetrakis(diphenylphosphino)-substitute d, 12, phosphinines have been obtained. Reactions of la with 1,n-diyne s (n > 3) also provides easy access to Ph-P-, (CH2)(3-), and SiMe2-, l inked bis(phosphinines) 14, 16, and 18, respectively. A SiMe2 linked t ris(phosphinine) has also been prepared using a two step sequence whic h involves the preliminary synthesis of a 2,6-bis(phenylethynyl)dimeth ylsilylphosphinine 20. Reaction of 2 equiv of la with 1 equiv of 20 an d then with 2 equiv of (trimethylsilyl)acetylene gave the tris(phosphi nine) 22. This methodology has also been extended to the synthesis of arsinine derivatives. In a similar way, the first example (4,6-di-tert -butyl) of a 1,3,2-diazaarsinine Ib has been prepared (yield 20-25% re lative to Cp-2-TiMe2) from the reaction of the corresponding diazatita nacycle with AsCl3 in the presence of Et3N. Similar to its phosphorus counterpart la, Ih reacts with alkynes by the same cycloaddition-cyclo reversion sequence to give tetrafunctional arsinines (yields from 40 t o 50%). The 2,6-bis- and 2,3,5,6-tetrakis(trimethylsilyl), 23 and 24, respectively, derivatives have been obtained from reaction of Ib with phenyl(trimethylsilyl)acetylene and bis(trimethylsilyl)acetylene ,resp ectively. The reaction of Ib with bis(diphenylphosphino)acetylene gave a 2,6-bis(diphenylphosphino)arsinine 25, which has also been characte rized by an X-ray diffraction study.