SYNTHESIS AND STRUCTURES OF P2(BNR2)3 CAGES

The reaction of (i-Pr2N)B(Cl)P(SiMe3)2 with (i-Pr2N)BCl2 in a 2:1 ratio results in the formation of a trigonal-bipyramidal compound, P2(i-Pr2NB)3. A more controlled, predictable synthesis of related P2B3 cages is available from reactions of 1,3,2,4-diphosphadiboretanes (HPBNR2)2 with n-BuLi, followed by addition of R2NBCl2 and then t-BuLi. In this fashion, compounds with the formulas P2(i-Pr2NB)2(Btmp), P2(i-Pr2NB)2[(Me3Si)2NB], P2(tmpB)3, P2(tmpB)2(i-Pr2NB), and P2(tmpB)2[(Me3Si)2NB] have been prepared in good yield. Coordination complexes P2(i-Pr2NB)2(tmpB).Cr(CO)5, P2(i-Pr2NB)2[(Me3Si)2NB].Fe(CO)4, and P2(tmpB)2(i-Pr2NB).Fe(CO)4 have been synthesized; however, attempts to obtain bismetal carbonyl complexes of these ligands or monometal carbonyl complexes of P2(Btmp)3 were unsuccessful. Molecular structure determinations for two ligands and one complex have been completed by single-crystal X-ray diffraction techniques: P2(i-Pr2NB)2[Me3Si)2NB](C18H46B3N3P2Si2) crystallizes in the monoclinic space group P2(1)/c with a = 17.782 (5) angstrom, b = 10.098 (2) angstrom, c = 16.826 (4) angstrom, beta = 90.58 (2)-degrees, and Z = 4; P2(tmpB)3 (C27H54B3N3P2) crystallizes in the hexagonal space group P6(3)/m with a = 10.9085 (15) angstrom, c 14.948 (3) angstrom, and Z = 2; P2(i-Pr2NB)2(tmpB).Cr(CO)5 (C26H46B3N3O5P2Cr) crystallizes in the triclinic space group P1BAR with a = 11.548 (5) angstrom, b = 16.525 (5) angstrom, c = 19.911 (8) angstrom, alpha = 104.85 (3)-degrees, beta = 105.87 (3)-degrees, gamma = 92.57 (3) angstrom, and Z = 4. The structural parameters for these ligands and the metal complex are compared with parametric data from several diphosphadiboretane ligands and complexes.