Triple bonds of niobium with silicon, germaniun and tin: the tetrylidyne complexes [(κ 3 -tmps)(CO) 2 Nb[triple bond, length as m-dash]E-R] (E = Si, Ge, Sn; tmps = MeSi(CH 2 PMe 2 ) 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 (NMe ₄ )[Nb(CO) ₄ (κ ² -tmps)] ( 1 ) (tmps = MeSi(CH ₂ PMe ₂ ) ₃ ) with a suitable organotetrel(ii)halide. Compound 1 was obtained from (NMe ₄ )[Nb(CO) ₆ ] and the triphosphane tmps by photodecarbonylation. Reaction of 1 with the disilene E -Tbb(Br)Si[double bond, length as m-dash]Si(Br)Tbb in the presence of 4-dimethylaminopyridine afforded selectively the red-brown silylidyne complex [(κ ³ -tmps)(CO) ₂ Nb[triple bond, length as m-dash]Si-Tbb] ( 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 (NMe ₄ )Cl and two CO ligands the deep magenta colored germylidyne complex [(κ ³ -tmps)(CO) ₂ Nb[triple bond, length as m-dash]Ge-Ar ^Mes ] ( 3-Ge ), and the deep violet, light-sensitive stannylidyne complex [(κ ³ -tmps)(CO) ₂ Nb[triple bond, length as m-dash]Sn-Ar ^Mes ] ( 3-Sn ), respectively. Formation of 3-Sn proceeds via the niobiastannylene [(κ ³ -tmps)(CO) ₃ Nb-SnAr ^Mes ] ( 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 H ₂ O afforded upon cleavage of the Nb-Ge triple bond the hydridogermanediol Ge(Ar ^Mes )H(OH) ₂ . Photodecarbonylation of [CpNb(CO) ₄ ] (Cp = η ⁵ -C ₅ H ₅ ) in the presence of Ge(Ar ^Mes )Cl afforded the red-orange chlorogermylidene complex [Cp(CO) ₃ Nb[double bond, length as m-dash]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.
(This journal is © The Royal Society of Chemistry 2017.)