Synthetic, structural, and theoretical studies of diphenyltetrazene complexes of silicon and germanium

Article abstract of DOI:10.1021/om00105a025

The reaction between dilithium 1,4-diphenyltetrazenide (1) and SiCl(CH₃)₃ or GeCl(CH₃)₃ in toluene yields trans-(Ph)(Me₃Si)NN=NN(Ph)(SiMe₃) (3) and trans-(Ph)(Me₃Ge)NN=NN(Ph)(GeMe₃) (5). Bis(trimethylsilyl)aniline and bis(trimethylgermyl)aniline are formed as by products of fragmentation of (Ph)(Me₃E)N₄(Ph)^- to Ph(Me₃E)N^- and phenyl azide, where E = Si or Ge. Crystals of 3 belong to the triclinic space group P1 with a = 6.337 (2) ?, b = 7.986 (2) ?, c = 10.713 (2) ?, α = 76.52 (2)°, β = 89.59 (2)°, γ = 86.02 (2)°, V = 529.9 (2) ?³, and Z = 1. Refinement of 153 least-squares variables for 1431 unique reflections of I > 2σ(I) led to R = 0.032 and R_w = 0.050. Crystals of 5 belong to the monoclinic space group P2₁/n with a = 9.363 (2) ?, b = 9.011 (3) ?, c = 12.595 (3) ?, β = 106.96 (2)°, V = 1016.3 (4) ?³, and Z = 2. Refinement of 138 least-squares variables on 2202 unique reflections of I > 3σ(I) led to R = 0.034 and R_w = 0.038. Both 3 and 5 adopt a planar trans structure with a planar bent N(1)-N(2)-N(2a)-N(1a) chain. For 3 N(1)-N(2) = 1.394 (2) ? and N(2)-N(2a) = 1.254 (3) ?. For 5 N(1)-N(2) = 1.377 (3) ? and N(2)-N(2a) = 1.260 (4) ?. The chief difference between the structures is that the phenyl rings in 3 are 54.7° out of conjugation with the N₄ π system, whereas in 5 the phenyl rings are in partial resonance (27.9° out of plane) with the N₄ π system. This is consistent with the longer Ge-N(1) bond of 1.912 (3) ? in 5 (Si-N(1) = 1.781 (1) ? in 3) reducing repulsions between the GeMe₃ and Ph substituents. Addition of 1 to SiCl₂Me₂ produced the cyclic species Me₂SiN(Ph)N=NN(Ph) (6) and (PhNSiMe₂)₂ (7). Compound 6 crystallizes in the monoclinic space group C2/c with a = 19.408 (3) ?, b = 6.704 (1) ?, c = 11.815 (2) ?, β = 111.77 (2)°, V = 1427.5 (4) ?³, and Z = 4. Refinement of 120 least-squares variables converged to R = 0.032 and R_w = 0.049 for 1417 unique reflections with I > 3σ(I). The structure contains a planar SiN(1)-N(2)-N(2a)-N(1a) ring with Si-N(1) = 1.755 (1) ?, N(1)-N(2) = 1.392 (1) ?, and N(2)-N(2a) = 1.267 (2) ?. SCF-DV-Xα calculations for the model complexes trans-(H₃Si)HNN=NNH(SiMe₃) and H₂SiN(H)N=NN(H) are presented to compare the bonding in the planar acyclic and cyclic tetrazenes. Good agreement was observed between the observed electronic absorption spectra of 3 and 6 and that calculated for the model complexes. In 3 and 6 the lowest electronic transition arises from a π₃ → π₄ transition of the N₄ π system at 3.97 eV in 3 (3.95 eV, calculated) and 4.11 eV in 6 (4.35 eV calculated).