Triple bonds of niobium with silicon, germaniun and tin: the tetrylidyne complexes [(κ3-tmps)(CO)2NbE-R] (E = Si, Ge, Sn; tmps = MeSi(CH2PMe2)3; R = aryl)

A systematic, efficient approach to first complexes containing a triple bond between niobium and the elements silicon, germanium or tin is reported. The approach involves a metathetical exchange of the niobium-centered nucleophile (NMe4)[Nb(CO)(4)(kappa(2)-tmps)] (1) (tmps = MeSi(CH2PMe2)\(3)) with a suitable organotetrel(II) halide. Compound 1 was obtained from (NMe4)[Nb(CO)(6)] and the triphosphane tmps by photodecarbonylation. Reaction of 1 with the disilene E-Tbb(Br) Si] Si(Br) Tbb in the presence of 4-dimethylaminopyridine afforded selectively the red-brown silylidyne complex [(kappa(3)-tmps)(CO)(2)Nb SiTbb] (2-Si, Tbb = 4-tert-butyl-2,6-bis(bis(trimethylsilyl) methyl) phenyl). Similarly, treatment of 1 with E(Ar-Mes) Cl (E = Ge, Sn; Ar-Mes = 2,6-mesitylphenyl) afforded after elimination of (NMe4)Cl and two CO ligands the deep magenta colored germylidyne complex [(kappa(3)-tmps)(CO)(2)Nb Ge-Ar-Mes] (3-Ge), and the deep violet, light-sensitive stannylidyne complex [(kappa(3)-tmps)(CO)(2)Nb Sn-Ar-Mes] (3-Sn), respectively. Formation of 3-Sn proceeds via the niobiastannylene [(kappa(3)-tmps)(CO)(3)Nb-SnArMes] (4-Sn), which was detected by IR and NMR spectroscopy. The niobium tetrylidyne complexes 2-Si, 3-Ge and 3-Sn were fully characterized and their solid-state structures determined by single-crystal X-ray diffraction studies. All complexes feature an almost linear tetrel coordination and the shortest Nb-E bond lengths (d(Nb-Si) = 232.7(2) pm; d(Nb-Ge) = 235.79(4) pm; d(Nb-Sn) = 253.3(1) pm) reported to date. Reaction of 3-Ge with a large excess of H2O afforded upon cleavage of the Nb-Ge triple bond the hydridogermanediol Ge(Ar-Mes) H(OH)(2). Photodecarbonylation of [CpNb(CO) 4] (Cp =eta(5)-C5H5) in the presence of Ge(Ar-Mes) Cl afforded the red-orange chlorogermylidene complex [Cp(CO) 3Nb] Ge(Ar-Mes) Cl] (5-Ge). The molecular structure of 5-Ge features an upright conformation of the germylidene ligand, a trigonal-planar coordinated Ge atom, and a Nb-Ge double bond length of 251.78(6) pm, which lies in-between the Nb-Ge triple bond length of 3-Ge (235.79(4) pm) and a Nb-Ge single bond length (267.3 pm). Cyclic voltammetric studies of 2-Si, 3-Ge, and 3-Sn reveal several electron-transfer steps. One-electron oxidation and reduction of the germylidyne complex of 3-Ge in THF are electrochemically reversible suggesting that both the radical cation and radical anion of 3-Ge are accessible species in solution.