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

Reactions of the zirconium amide guanidinates (R2N)2M[iPrNC(NR2)NiPr]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)[iPrNC(NR2)NiPr]2}2 (R = Me, M = Zr, 4; M = Hf, 5; R = Et, M = Zr, 6) and polymers {M(μ-O)[iPrNC(NR2)NiPr]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)[iPrNC(NMe2)NiPr]2 (10), oxo dimers 4 and 5, and dihydroxyl complexes M(OH)2[iPrNC(NMe2)NiPr]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)[iPrNC(NEt2)NiPr]2 (13), Zr(OH)2[iPrNC(NEt2)NiPr]2 (14), 6, and {(Et2N)Zr[iPrNC(NEt2)NiPr]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...