Internally versus externally solvated derivatives of doubly bridged 1,4-dilithio-2-butene: structures and dynamic behavior. A "T" shaped dimeric cluster in the solid state.

X-ray crystallographic NMR and calculational modeling studies using B3LYP/6-311G* of selected dilithium derivatives of the 1,3-butadiene dianion including cis-dilithio-1,4-bis(TMS)-2-butene center dot(TMEDA)(2) 2, internally solvated cis-dilithio-1,4-bis[bis(2-methoxyethyl)aminomethyldimethylsilyl]-2-butene 5, and using only modeling, 1,4-dilithio-2-butene center dot(TMEDA)(2) 9 reveal remarkably similar structural and NMR parameters. In the solid, 5 consists of unusual "T" shaped dynamic clusters. In all three bridging lithiums are sited between 1.8 and 1.9 angstrom normal to the centroids of opposite faces of the near coplanar of the 2-butene component. Typical bond lengths of the latter are 1.458 +/- 0.004, 1.385 +/- 0.006, and 1.459 +/- 0.003 angstrom, for C1-C2, C2-C3, and C3-C4, respectively. The C-13 chemical shifts lie within the ranges delta 21 +/- 0.5, 99 +/- 0.7, 99 +/- 0.7 and 21 +/- 0.5 for C1, C2 and C3 together, and C4, respectively. Dynamic C-13 NMR provides activation parameters for nitrogen inversion in 2 and 5, overall molecular inversion of 5, and conformational interconversion of 2.