Triamidoamine-supported zirconium phosphido complexes, (N 3 N)ZrPRR 0 (N 3 N=N(CH 2 CH 2 -NSiMe 3 ) 3 3-; R = alkyl, aryl; R 0 = R, H), have been shown to catalyze the hydrophosphination of terminal alkynes as well as that of symmetric aryl and alkyl carbodiimides. A mechanism based on insertion of the substrate into the Zr-P bond is proposed on the basis of competition experiments and model examples of stoichiometric insertion reactions of polar, small-molecule substrates possessing CdO, CdN, CtN, and CdS functionalities into the Zr-P bond. Molecular structures of the insertion products (N 3 N)ZrNdC(PHCy)Ph (4), (N 3 N)ZrNdC(PPh 2 )Ph (5), and (N 3 N)ZrPhNC-(O)PPh 2 (11), as well as (N 3 N)Zr[η 2 (N,N)-( i PrN) 2 C(PPh 2 )] (9), a key intermediate in the catalytic hydrophosphination of carbodiimides, have been determined.

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.

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