A homoleptic triamidoamine zirconium complex featuring a metalated trimethylsilyl substituent, [κ 5 -(Me 3 SiNCH 2 CH 2 ) 2 NCH 2 CH 2 NSiMe 2 CH 2 ]Zr (1), was synthesized by reaction of Zr(CH 2 Ph) 4 with N(CH 2 CH 2 NHSiMe 3 ) 3 followed by sublimation. Complex 1 is a general precursor to a family of complexes with the formulation (N 3 N)ZrX (N 3 N ) N(CH 2 CH 2 NSiMe 3 ) 3 3-, X ) anionic ligand) by reactions that parallel expected reactivity of a hydride derivative. Treatment of 1 with phosphines, amines, thiols, alkynes, and phenol resulted in the formation of new, pseudo-C 3V -symmetric (N 3 N)ZrX complexes (X ) phosphido, amido, alkynyl, thiolate, or phenoxide) via element-H bond activation. Thus, the reactivity of complex 1 is that best described as a hydride surrogate. For example, complex 1 reacted with PhPH 2 at ambient temperature to provide (N 3 N)ZrPHPh (2) in 86% yield. Density functional theory studies and X-ray crystal structures provide a general overview of the bonding in these complexes, which appears to be highly ionic. In general, there is little evidence for ligand-to-metal π-bonding for the pseudoaxial X ligand in these complexes except for strongly π-basic terminal amido ligands. The limited π-bonding appears to be the result of competitive π-donation by the pseudoequatorial amido arms of the triamidoamine ancillary ligand. Thus, the relative Zr-X bond energies are governed by the basicity of the anionic ligand X. Solid-state structures of phosphido (3, 4, 5), amido (10), and thiolate (15) complexes support the computational results.

The reduction of nitrate (NO) to nitrite (NO) is of significant biological and environmental importance. While Mo(O) and Mo(O) complexes that mimic the active site structure of nitrate reducing enzymes are prevalent, few of these model complexes can reduce nitrate to nitrite through oxygen atom transfer (OAT) chemistry. We present a novel strategy to induce nitrate reduction chemistry of a previously known catalyst Mo(O)(SN) (2), where SN = bis(4- tert-butylphenyl)-2-pyridylmethanethiolate, that is otherwise incapable of achieving OAT with nitrate. Addition of nitrate with the Lewis acid Sc(OTf) (OTf = trifluoromethanesulfonate) to 2 results in an immediate and clean conversion of 2 to Mo(O)(SN) (1). The Lewis acid additive further reacts with the OAT product, nitrite, to form NO and O. This work highlights the ability of Sc additives to expand the reactivity scope of an existing Mo(O) complex together with which Sc can convert nitrate to stable gaseous molecules.