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 TiIV 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 TiII salt [K(cryptand)][(PN)2TiCl] (1) (cryptand = 222-Kryptofix) and Na(OCAs)(dioxane)1.5 in thf/toluene to produce the mixed alkali ate-complex [(PN)2Ti(As)]2(µ2-KNa(thf)2) (2) and the discrete salt [K(cryptand)][(PN)2Ti≡As] (3) featuring a terminal Ti≡As ligand. Protonation of 2 or 3 with various weak acids cleanly forms the parent arsinidene [(PN)2Ti═AsH] (4), which upon deprotonation with KCH2Ph in thf generates the more symmetric anionic arsenido [(PN)2Ti(As){µ2-K(thf)2}]2 (5). Experimental and computational studies suggest the pKa 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.

A mononuclear, terminal titanium(III) imido.

We report the first mononuclear TiIII complex possessing a terminal imido ligand. Complex [TptBu,MeTi{NSi(CH3)3}(THF)] (2) (TptBu,Me = hydridotris(3-tert-butyl-5-methylpyrazol-1-yl)borate) is prepared by reduction of [TptBu,MeTi{NSi(CH3)3}(Cl)] (1) with KC8 in high yield. The connectivity and metalloradical nature of 2 were confirmed by single crystal X-ray diffraction studies, Q- and X-band EPR, UV-Vis and 1H NMR spectroscopies. The d1 complex [(TptBu,Me)TiCl(OEt2)][B(C6F5)4] (3), was prepared to spectroscopically compare it to 2. Electrochemical studies of 1 and 2 reveal a reversible 1e- process, and chemical oxidants ClCPh3 or 1/2 eq. XeF2 react cleanly with 2 yielding 1 or the fluoride derivative [TptBu,MeTi{NSi(CH3)3}(F)] (4), respectively.

Nuclearity effects in supported, single-site Fe(ii) hydrogenation pre-catalysts.

Dimeric and monomeric supported single-site Fe(ii) pre-catalysts on SiO2 have been prepared via organometallic grafting and characterized with advanced spectroscopic techniques. Manipulation of the surface hydroxyl concentration on the support influences monomer/dimer formation. While both pre-catalysts are highly active in liquid-phase hydrogenation, the dimeric pre-catalyst is ∼3× faster than the monomer. Preliminary XAS experiments on the H2-activated samples suggest the active species are isolated Fe(ii) sites.