Novel μ3-Coordination of Urea at a Nickel(II) Site: Structure, Reactivity and Ferromagnetic Superexchange

Synthetic Models for the Active Sites of Nickel‐Containing Enzymes

“…In 94, the presence of two terminal four-coordinate low-spin Ni II and two central six-coordinate high-spin Ni II leads to a mixed-spin situation, while results from UV/Visspectroscopy and magnetic measurements in solution suggest the coordination of additional solvent ligands to the outer metal ions at low temperature [168]. It is generally believed that the hydrolytic stability of the urea molecule is due to its high resonance stabilization energy (estimated to be 30-40 kcal/mol), which presumably is reduced upon coordination to metal ions, activating it for nucleophilic attack.…”

Synthetic Models for the Active Sites of Nickel‐Containing Enzymes

“…In 94, the presence of two terminal four-coordinate low-spin Ni II and two central six-coordinate high-spin Ni II leads to a mixed-spin situation, while results from UV/Visspectroscopy and magnetic measurements in solution suggest the coordination of additional solvent ligands to the outer metal ions at low temperature [168]. It is generally believed that the hydrolytic stability of the urea molecule is due to its high resonance stabilization energy (estimated to be 30-40 kcal/mol), which presumably is reduced upon coordination to metal ions, activating it for nucleophilic attack.…”

Cu 2+ and Pt 2+ complexes of pyrazole and triazole based dinucleating ligands

“…The highest value clearly corresponds to the deprotonation of the heterocycle. In fact there is as expected a distinct difference between the pyrazole derivatives (16)(17)(18)(19) with higher and the a Functional group at the end of the side chain with n carbon atoms.…”

Reactivity of a (μ-Oxo)(μ-hydroxo)diiron(III) Diamond Core with Water, Urea, Substituted Ureas, and Acetamide

“…The simple ureate anion CO(NH 2 )-NHpresent in 3 was only recently structurally characterized, in the µ 2 -N,O coordination mode in two dinickel(II) complexes 70,71 and one diiron(III) complex 20 and in the µ 3 -N,N′,O mode in a tetranuclear nickel(II) complex. 72 In all those complexes, and also in complex 3 from this work, the ureate CO(NH 2 )NHanion has similar structural parameters, d(C-O) ) 1.24-1.29 Å, d(C-NH) ) 1.29-1.31 Å, d(C-NH 2 ) ) 1.37-1.44 Å, and a nearly planar arrangement of all atoms. Although the distinction between the bound oxygen and nitrogen atoms of the ureate molecule is difficult, there is a significant elongation of the distal C-NH 2 bond in the N,O-coordinated ureate compared to the neutral urea [d(C-NH 2 ) ) 1.35 Å], 62 which indicates a partial loss of resonance upon N,O-coordination.…”

“…To the best of our knowledge, complex 4 is the first structurally characterized compound with the 1-methylureate anion CO(NHCH 3 )NH - . The simple ureate anion CO(NH 2 )NH - present in 3 was only recently structurally characterized, in the μ 2 -N,O coordination mode in two dinickel(II) complexes 70,71 and one diiron(III) complex 20 and in the μ 3 -N,N‘,O mode in a tetranuclear nickel(II) complex . In all those complexes, and also in complex 3 from this work, the ureate CO(NH 2 )NH - anion has similar structural parameters, d (C−O) = 1.24−1.29 Å, d (C−NH) = 1.29−1.31 Å, d (C−NH 2 ) = 1.37−1.44 Å, and a nearly planar arrangement of all atoms.…”

Synthetic Models for the Active Sites of Nickel‐Containing Enzymes

“…In 94, the presence of two terminal four-coordinate low-spin Ni II and two central six-coordinate high-spin Ni II leads to a mixed-spin situation, while results from UV/Visspectroscopy and magnetic measurements in solution suggest the coordination of additional solvent ligands to the outer metal ions at low temperature [168]. It is generally believed that the hydrolytic stability of the urea molecule is due to its high resonance stabilization energy (estimated to be 30-40 kcal/mol), which presumably is reduced upon coordination to metal ions, activating it for nucleophilic attack.…”

Cu 2+ and Pt 2+ complexes of pyrazole and triazole based dinucleating ligands

“…The highest value clearly corresponds to the deprotonation of the heterocycle. In fact there is as expected a distinct difference between the pyrazole derivatives (16)(17)(18)(19) with higher and the a Functional group at the end of the side chain with n carbon atoms.…”

Reactivity of a (μ-Oxo)(μ-hydroxo)diiron(III) Diamond Core with Water, Urea, Substituted Ureas, and Acetamide

“…The simple ureate anion CO(NH 2 )-NHpresent in 3 was only recently structurally characterized, in the µ 2 -N,O coordination mode in two dinickel(II) complexes 70,71 and one diiron(III) complex 20 and in the µ 3 -N,N′,O mode in a tetranuclear nickel(II) complex. 72 In all those complexes, and also in complex 3 from this work, the ureate CO(NH 2 )NHanion has similar structural parameters, d(C-O) ) 1.24-1.29 Å, d(C-NH) ) 1.29-1.31 Å, d(C-NH 2 ) ) 1.37-1.44 Å, and a nearly planar arrangement of all atoms. Although the distinction between the bound oxygen and nitrogen atoms of the ureate molecule is difficult, there is a significant elongation of the distal C-NH 2 bond in the N,O-coordinated ureate compared to the neutral urea [d(C-NH 2 ) ) 1.35 Å], 62 which indicates a partial loss of resonance upon N,O-coordination.…”

“…To the best of our knowledge, complex 4 is the first structurally characterized compound with the 1-methylureate anion CO(NHCH 3 )NH - . The simple ureate anion CO(NH 2 )NH - present in 3 was only recently structurally characterized, in the μ 2 -N,O coordination mode in two dinickel(II) complexes 70,71 and one diiron(III) complex 20 and in the μ 3 -N,N‘,O mode in a tetranuclear nickel(II) complex . In all those complexes, and also in complex 3 from this work, the ureate CO(NH 2 )NH - anion has similar structural parameters, d (C−O) = 1.24−1.29 Å, d (C−NH) = 1.29−1.31 Å, d (C−NH 2 ) = 1.37−1.44 Å, and a nearly planar arrangement of all atoms.…”

Synthetic Models for the Active Sites of Nickel‐Containing Enzymes

“…In 94, the presence of two terminal four-coordinate low-spin Ni II and two central six-coordinate high-spin Ni II leads to a mixed-spin situation, while results from UV/Visspectroscopy and magnetic measurements in solution suggest the coordination of additional solvent ligands to the outer metal ions at low temperature [168]. It is generally believed that the hydrolytic stability of the urea molecule is due to its high resonance stabilization energy (estimated to be 30-40 kcal/mol), which presumably is reduced upon coordination to metal ions, activating it for nucleophilic attack.…”

Cu 2+ and Pt 2+ complexes of pyrazole and triazole based dinucleating ligands

“…The highest value clearly corresponds to the deprotonation of the heterocycle. In fact there is as expected a distinct difference between the pyrazole derivatives (16)(17)(18)(19) with higher and the a Functional group at the end of the side chain with n carbon atoms.…”

Reactivity of a (μ-Oxo)(μ-hydroxo)diiron(III) Diamond Core with Water, Urea, Substituted Ureas, and Acetamide

“…The simple ureate anion CO(NH 2 )-NHpresent in 3 was only recently structurally characterized, in the µ 2 -N,O coordination mode in two dinickel(II) complexes 70,71 and one diiron(III) complex 20 and in the µ 3 -N,N′,O mode in a tetranuclear nickel(II) complex. 72 In all those complexes, and also in complex 3 from this work, the ureate CO(NH 2 )NHanion has similar structural parameters, d(C-O) ) 1.24-1.29 Å, d(C-NH) ) 1.29-1.31 Å, d(C-NH 2 ) ) 1.37-1.44 Å, and a nearly planar arrangement of all atoms. Although the distinction between the bound oxygen and nitrogen atoms of the ureate molecule is difficult, there is a significant elongation of the distal C-NH 2 bond in the N,O-coordinated ureate compared to the neutral urea [d(C-NH 2 ) ) 1.35 Å], 62 which indicates a partial loss of resonance upon N,O-coordination.…”

“…To the best of our knowledge, complex 4 is the first structurally characterized compound with the 1-methylureate anion CO(NHCH 3 )NH - . The simple ureate anion CO(NH 2 )NH - present in 3 was only recently structurally characterized, in the μ 2 -N,O coordination mode in two dinickel(II) complexes 70,71 and one diiron(III) complex 20 and in the μ 3 -N,N‘,O mode in a tetranuclear nickel(II) complex . In all those complexes, and also in complex 3 from this work, the ureate CO(NH 2 )NH - anion has similar structural parameters, d (C−O) = 1.24−1.29 Å, d (C−NH) = 1.29−1.31 Å, d (C−NH 2 ) = 1.37−1.44 Å, and a nearly planar arrangement of all atoms.…”