Reactions of Group 4 Amide Guanidinates with Dioxygen or Water. Studies of the Formation of Oxo Products

Abstract

Reactions of the zirconium amide guanidinates (R2N)2M[(i)PrNC(NR2)N(i)Pr]2 (R = Me, M = Zr, 1; M = Hf, 2; R = Et, M = Zr, 3) with O2 or H2O give products that are consistent with the oxo dimers {M(μ-O)[(i)PrNC(NR2)N(i)Pr]2}2 (R = Me, M = Zr, 4; M = Hf, 5; R = Et, M = Zr, 6) and polymers {M(μ-O)[(i)PrNC(NR2)N(i)Pr]2}n (R = Me, M = Zr, 7; M = Hf, 8; R = Et, M = Zr, 9). Mass spectrometric (MS) analyses of the reactions of water in air with 1 and 2 show formation of the Zr monomer Zr(═O)[(i)PrNC(NMe2)N(i)Pr]2 (10), oxo dimers 4 and 5, and dihydroxyl complexes M(OH)2[(i)PrNC(NMe2)N(i)Pr]2 (M = Zr, 11; Hf, 12). Similar MS analyses of the reaction of diethylamide guanidinate 3 with water in air show the formation of Zr(═O)[(i)PrNC(NEt2)N(i)Pr]2 (13), Zr(OH)2[(i)PrNC(NEt2)N(i)Pr]2 (14), 6, and {(Et2N)Zr[(i)PrNC(NEt2)N(i)Pr]2}(+) (15). Kinetic studies of the reaction between 1 and a continuous flow of 1.0 atm of O2 at 80-105 °C indicate that it follows pseudo-first-order kinetics with ΔH(‡) = 8.7(1.1) kcal/mol, ΔS(‡) = -54(3) eu, ΔG(‡)(358 K) = 28(2) kcal/mol, and a half-life of 213(1) min at 85 °C.

1,1′-Dicarbodiimidoferrocenes: Synthesis, Characterization, and Group IV 1,1′-Bisguanidinateferrocene Complexes

“…These data are consistent with a Bailar twist rearrangement through a trigonal prismatic intermediate being the source of the peak broadening. This behavior is known for other group IV amidate and amidinate transition metal compounds and a recently reported zirconium ferrocene azomethine. − …”

Hydrolysis of organometallic and metal–amide precursors: synthesis routes to oxo-bridged heterometallic complexes, metal-oxo clusters and metal oxide nanoparticles

“…50 Studies have suggested that the lone pair of electrons on the NR2 unit may accelerate the rate of hydrolysis, through facilitating proton transfer from H2O to the NR2 unit, to form a hydroxide species. 51,52 Once formed, M−OH units may undergo subsequent condensation to form M−O−M bonds, within metaloxo clusters 53 or molecular (mixed-)metal-oxo compounds. 25 54 Despite this lower basicity, the hydrolysis of metal-alkoxides may be driven by an entropically favoured condensation process.…”

“…Alternatively, the reactivity observed with Ti(NMe)4 or Zr/Hf(NEt)4 may be attributed to the enhanced kinetic basicity of organoamide units 50 and the ability of the lone pair of electrons on N to facilitate proton transfer. 51,52 Comparison of the 1 H NMR spectra of these Ga-OH precursors suggests that the galloxane precursor [{LMesNacNacGa(OH)}2(μ-O)] will display weaker Brønsted acidity than [LdippNacNacGa(Me)(OH)], as the Ga-OH 1 H NMR resonance is further upfield (−1.38 ppm and 0.08 ppm respectively, both in C6D6). 143,152 The experimental data provides support for these relative Brønsted acidities, as while [LdippNacNacGa(Me)(OH)] dealkylates Cp2ZrMe2, 143 the bis-Ga precursor [{LMesNacNacGa(OH)}2(μ-O)] does not.…”

Density Functional Theory Study of the Reaction between d0 Tungsten Alkylidyne Complexes and H2O: Addition versus Hydrolysis

“…The reactions of early-transition-metal complexes with H 2 O have been studied intensely. − The reactions of d 0 complexes with H 2 O have been used to prepare highly uniform, conformal films of metal oxides in the microelectronic industry. , An understanding of the elementary steps in the reactions may facilitate the design of organometallic precursors for such surface growth or modification. Metal complexes have also been grafted onto a support material, such as silica or alumina, to develop supported heterogeneous catalysts. , Protonolysis of ligands on the metal complexes by surface hydroxyl groups is a strategy commonly used to immobilize a metal complex on a support medium. − Investigation of the hydrolysis of metal precursors may therefore shed light on the formation of a catalytically active site of the heterogeneous catalysts .…”