Preparation, crystal structures, and isomerization of the tellurium diimide dimers RNTe(mu-NR')(2)TeNR (R=R'=(t)Bu; R=PPh(2)NSiMe(3), R'=(t)Bu, (t)Oct): X-ray structure of the telluradiazole dimer [(t)Bu(2)C(6)H(2)N(2)Te](2)

The reaction of R'NHLi (R = (t)Bu, (t)Oct) with Ph(2)P(NSiMe(3))(2)Te(Cl)NPPh(2)NSiMe(3) in toluene at -78 degrees C, followed by warming to 23 degrees C, produces the tellurium diimide dimers RNTe(mu-NR')(2)TeNR (2a, R' = (t)Bu, R = NPPh(2)NSiMe(3); 2b, R' = (t)Oct, R = NPPh(2)NSiMe(3)) and Ph(2)P(NHSiMe(3))(NSiMe(3)). X-ray analyses revealed that 2a and 2b have centrosymmetric structures containing a planar four-membered Te2N2 ring and short exocyclic tellurium-nitrogen bond lengths (d(Te-N) = 1.900(5) and 1.897(4) or 1.905(4) Angstrom for 2a and 2b, respectively). The exocyclic imido substituents adopt a trans arrangement with respect to the Te2N2 ring. By contrast, the reaction of 2,4,6-(t)Bu(3)C(6)H(2)NHLi with Ph(2)P(NSiMe(3))(2)Te(Cl)NPPh(2)NSiMe(3) in toluene under similar conditions produces the telluradiazole ((t)Bu(2)C(6)H(2)N(2)Te)(2) (3), which exists as a weakly associated dimer in the solid state with intramolecular Te-N distances of 2.628(4) Angstrom. The tellurium diimide dimer (t)BuNTe9(mu-N(t)Bu)(2)Te(t)Bu (2c'), prepared by the reaction of TeCl4 with (t)BuNHLi in a 1:4 molar ratio, consists of a folded Te2N2 ring with exocyclic N(t)Bu groups in a cis orientation. The H-1, P-31, and Te-125 NMR spectra of 2a and 2b indicate that the trans isomers slowly transform into the corresponding cis isomers in solution. Crystals of 2b are triclinic, space group P (1) over bar (No. 2), with a = 13.304(3) Angstrom, b = 16.927(3) Angstrom, c = 13.292(5) Angstrom, alpha = 98.94(2), beta = 109.27(2), gamma = 69.04(2)degrees, V = 2636(1) Angstrom(3), and Z = 4. The final R and R(w) values were 0.034 and 0.033, respectively. Crystals of 2c' are orthorhombic, space group Pnma (No. 62), with a = 9.535(3) Angstrom, b = 14.264(3) Angstrom, c = 16.963(4) Angstrom, V = 2307.1(9) Angstrom(3), and Z = 4. The final R and R(w) values were 0.040 and 0.040, respectively. Crystals of 3 are monoclinic, space group P2(1)/n (No. 14), with a = 9.117(3) Angstrom, b = 11.481(4) Angstrom, c = 16.550(4) Angstrom, beta = 97.76(2)degrees, V = 1716.5(8) Angstrom(3), and Z = 4. The final R and R(w) values were 0.031 and 0.034, respectively.