Softer Is Better for Titanium: Molecular Titanium Arsenido Anions Featuring Ti≡As Bonding and a Terminal Parent Arsinidene.

We introduce the arsenido ligand onto the Ti IV ion, yielding a remarkably covalent Ti≡As bond and the parent arsinidene Ti═AsH moiety. An anionic arsenido ligand is assembled via reductive decarbonylation involving the discrete Ti II salt [K(cryptand)][(PN) 2 TiCl] ( 1 ) (cryptand = 222-Kryptofix) and Na(OCAs)(dioxane) 1.5 in thf/toluene to produce the mixed alkali ate-complex [(PN) 2 Ti(As)] 2 (μ 2 -KNa(thf) 2 ) ( 2 ) and the discrete salt [K(cryptand)][(PN) 2 Ti≡As] ( 3 ) featuring a terminal Ti≡As ligand. Protonation of 2 or 3 with various weak acids cleanly forms the parent arsinidene [(PN) 2 Ti═AsH] ( 4 ), which upon deprotonation with KCH 2 Ph in thf generates the more symmetric anionic arsenido [(PN) 2 Ti(As){μ 2 -K(thf) 2 }] 2 ( 5 ). Experimental and computational studies suggest the p K a of 4 to be ∼23, and the bond orders in 2 , 3 , and 5 are all in the range of a Ti≡As triple bond, with decreasing bond order in 4 .