CHEMISTRY OF C-TRIMETHYLSILYL-SUBSTITUTED HETEROCARBORANES .15. SYNTHETIC, SPECTROSCOPIC, REACTIVITY, AND BONDING STUDIES ON THE CARBONS APART CLOSO-1-SN-2-(SIME3)-4-(R)-2,4-C2B4H4 - CRYSTAL-STRUCTURES OF THE DONOR-ACCEPTOR COMPLEXES 1-SN(L)-2,4-(SIME3)2-2,4-C2B4H4 [R=SIME3, ME, L=2,2'-C10H8N2, 2,2'-C8H6N4, OR (ETA(5)-C5H5)FE(ETA(5)-C5H4CH2(ME)2N)]

The reactions of the THF-solvated ''carbons apart'' disodium compounds, closo-exo-5,6-Na(THF)2-1-Na(THF)2-2-(SiMe3)-4-(R)-2,4-C2B4H4 (R = SiMe3, Me), with anhydrous SnCl2 in THF in molar ratios of 1:1 at 0-degrees-C produced the corresponding closo-stannacarboranes, 1-Sn-2,4-(SiMe3)2-2,4-C2B4H4 (I) and 1-Sn-2-(SiMe3)-4-(Me)-2,4-C2B4H4 (11), as colorless liquids in 86 and 51 % yields, respectively. The closo-stannacarboranes react with 2,2'-bipyridine, 2,2'-bipyrimidine, (ferrocenylmethyl)-N,N-dimethylamine, and 2,2':6',2''-terpyridine in benzene at room temperature to form the corresponding donor-acceptor complexes, 1-Sn(C10H8N2)-2,4-SiMe3)2-2,4-C2B4H4 (III), 1-Sn(C8H6N4)-2,4-(SiMe3)2-2,4-C2B4H4 (IV), 1-Sn(C8H6N4)-2-(SiMe3)-4-Me)-2,4-C2B4H4 (V), 1-Sn[(eta5-C5H5)Fe(eta5-C5H4CH2(Me)2N)]-2,4-(SiMe3)2-2,4-C2B4H4 (VI), 1-Sn[(eta-C5H5)Fe(eta5-C5H4CH2(Me)2N)]-2-(SiMe3)-4-(Me)-2,4-C2B4H3 (VII), and 1-Sn(C15H11N3)-2,4-(SiMe3)2-2,4-C2B4H4(VIII) in 62-95% yields. The complexes I-VIII were all characterized on the basis of H-1, B-11, C-13, and Sn-119 NMR spectra and IR and mass spectra. The mass spectra of donor-acceptor complexes show only groupings corresponding to their stannacarborane and base fragments rather than the molecular ions. The complexes II, IV, and VI were also characterized by single crystal X-ray analyses. The crystal structures show that each complex has a distorted pentagonal bipyramidal geometry with the capping tin metal coordinating to the nitrogen atom(s) of the respective Lewis base, in a manner similar to that found in the corresponding ''carbons adjacent'' isomers. However, the geometries of the donor-acceptor complexes in the two carborane systems are quite different. The structures of I and III were analyzed using MNDO and Fenske-Hall molecular orbital calculations. The donor-acceptor complexes III, IV, and VI all crystallized in the monoclinic space group P2(1)/c with a = 6.807(l), 10.887(2), and 6.518(2) angstrom, b = 18.841(5),19.472(5), and 39.56(1) angstrom, c = 19.513(4), 11.661(3), and 11.192(4) angstrom, beta = 96.82(2), 97.89(2), and 93.81(3)degrees, V = 2484.8(9), 2449(1), and 2879(2) angstrom3 and Z = 4, 4, and 4, respectively. The final refinements of III, IV, and VI converged at R = 0.028, 0.031, and 0.033 and R(w) = 0.038, 0.046, and 0.039, respectively.