Phosphaborane chemistry. Syntheses and calculated molecular structures of mono-and di-chloro derivatives of 1,2-diphospha-closo-dodecarborane(10)

摘要

The reaction between nido-B_(10)H_(14) and PCl_3 in the presence of proton sponge (PS = 1,8-bis(dimethylamino)naphthalene) in CH_2Cl_2 yielded a mixture of icosahedral diphosphaboranes from which 1,2-closo-P_2B_(10)H_(10) (1a) and its mono- and di-chloro derivatives 3-Cl-1,2-closo-P_2B_(10)H_9 (2a), 4-Cl-1,2-closo-P_2B_(10)H_9 (2b), 3,6-Cl_2-1,2-closo-P_2B_(10)H_8 (3a), and 3,4-Cl_2-1,2-closo-P_2B_(10)H_8 (3b) were isolated together with 4-Cl(CH_2)_4O-1,2-closo-P_2B_(10)H_(10) 4 via preparative HPLC. Individual compounds were characterized by NMR (~1H, ~(11)B, ~(31)P) spectroscopy, and except for 4, geometry optimised at the (RMP2(fc)) level with a 6-31G basis set. The optimisation disclosed considerable distortions of the icosahedral cage as documented by the narrowing of the pentagonal B-P-B angles (ca. 93 deg) and the longer P-P separations (> 2.31 A). In this context, the RMP2(fc)/6-31G geometries of 1,7-closo-P_2B_(10)H_(10) (1b) and that of the non-isolated 4,5-Cl_2-1,2-closo-P_2B_(10)H_8 isomer (3c) were also derived. The geometries were used as a basis for GIAO-SCF/II calculations of the ~(11)B NMR chemical shifts which were in good agreement with experimental delta (~(11)B) values. Moreover, the molecular structure of 3a was determined by an X-ray diffraction analysis to demonstrate satisfactory agreement with the theoretical geometry.