MACROCYCLES CONTAINING TIN - CRYSTAL-STRUCTURES AND MOLECULAR MECHANICS CALCULATED STRUCTURES OF MACROBICYCLIC LEWIS ACIDIC HOSTS

MM2 molecular modeling was employed in an analysis of the structures of several symmetrical macrobicycles containing tin atoms at the bridgehead positions. Compounds studied were 1,7-dichloro-1,7-distannabicyclo[5.5.5]heptadecane (1a) and the corresponding 1,7-diphenyl analogue (2a), 1,8-dichloro-1,8-distannabicyclo[6.6.6]eicosane (1b), 1,9-dichloro-1,9-distannabicyclo[7.7.7]tricosane (1c), 1,10-dichloro-1,10-distannabicyclo[8.8.8]hexacosane and the corresponding 1,10-diphenyl analogue (2d), 1,11-dichloro-1,11-distannabicyclo[9.9.9]nonacosane (1e), and 1,12-dichloro-1,12-distannabicyclo[10.10.10]dotriacontane (1f) and the corresponding 1,12-diphenyl analogue (2f). MM2 minimized structures generally closely reproduced the observed crystal structures when the crystal structure coordinates were used as the initial structures for minimizations. Alternative structures were also modeled, and the total energies of several possible structures were compared. The macrobicycles fall into one of two homologous series of structures, depending upon whether the connecting polymethylene chains have an odd or even number of carbon atoms. The odd-chain-length series typically have a low-energy structure of C3 symmetry with the axis passing through the two tin atoms and the three chains in parallel conformations. For the even-chain-length series, an analogous series of structures with C3 symmetry was found to be higher in energy than the typically observed C2 symmetry containing two chains with antiparallel conformations and an axis passing through the center of the third chain. Crystal structures are reported for compounds 1a,c,e,f and 2a,d,f. Compound 1a (C15H30Sn2Cl2) crystallized in the hexagonal space group P6(3)/m with a = 8.348 (2) angstrom, c = 16.672 (2) angstrom, V = 1006.1 (4) angstrom 3, and Z = 2. Compound 1c (C21H42Sn2Cl2) crystallized in the monoclinic space group P2(1)/n with a = 12.482 (5) angstrom, b = 22.738 (2) angstrom, c = 9.196 (2) angstrom, beta = 90.59 (2)degrees, V = 2610 (1) angstrom 3, and Z = 4. Compound 1e (C27H54Sn2Cl2) crystallized in the monoclinic space group C2/c with a = 24.476 (3) angstrom, b = 9.127 (2) angstrom, c = 14.283 (2), beta = 90.80 (2)degrees, V = 3189 (3) angstrom 3, and Z = 4. Compound 1f (C30H60Sn2Cl2) crystallized in the monoclinic space group P2(1)/c with a = 14.391 (3) angstrom, b = 17.080 (7) angstrom, c = 15.130 (3) angstrom, beta = 106.76 (1)degrees, V = 3561 (2) angstrom 3, and Z = 4. Compound 2a (C27H40Sn2) crystallized in the monoclinic space group P2(1)/c with a = 16.645 (3) angstrom, b = 8.210 (4) angstrom, c = 19.331 (4) angstrom, beta = 91.84 (2)degrees, V = 2640 (1) angstrom 3, and Z = 4. Compound 2d (C36H58Sn2) crystallized in the monoclinic space group C2/c with a = 25.504 (7) angstrom, b = 9.112 (2) angstrom, c = 18.502 (4) angstrom, beta = 124.14 (2)degrees, V = 3558.7 (15) angstrom 3, and Z = 4. Compound 2f (C42H70Sn2) crystallized in the monoclinic space group C2/c with a = 25.947 (9) angstrom, b = 9.189 (3) angstrom, c = 21.256 (7) angstrom, beta = 122.33 (2)degrees, V = 4262 (2) angstrom 3, and Z = 4.