Coordination versus Coupling of Dicyanamide in Molybdenum and Manganese Pyrazole Complexes

Abstract

The reactions of cis-[MoCl(η(3)-methallyl)(CO)(2)(NCMe)(2)] (methallyl = CH(2)C(CH(3))CH(2)) with Na(NCNCN) and pz*H (pzH, pyrazole, or dmpzH, 3,5-dimethylpyrazole) lead to cis-[Mo(η(3)-methallyl)(CO)(2)(pz*H)(μ-NCNCN-κ(2)N,N)](2) (pzH, 1a; dmpzH, 1b), where dicyanamide is coordinated as bridging ligand. Similar reactions with fac-[MnBr(CO)(3)(NCMe)(2)] lead to the pyrazolylamidino complexes fac-[Mn(pz*H)(CO)(3)(NH═C(pz*)NCN-κ(2)N,N)] (pzH, 2a; dmpzH, 2b), resulting from the coupling of pyrazol with one of the CN bonds of dicyanamide. The second CN bond of dicyanamide in 2a undergoes a second coupling with pyrazole after addition of 1 equiv of fac-[MnBr(CO)(3)(pzH)(2)], yielding the dinuclear doubly coupled complex [{fac-Mn(pzH)(CO)(3)}(2)(μ-NH═C(pz)NC(pz)=NH-κ(4)N,N,N,N)]Br (3). The crystal structure of 3 reveals the presence of two isomers, cis or trans, depending on whether the terminal pyrazoles are coordinated at the same or at different sides of the approximate plane defined by the bridging bis-amidine ligand. Only the cis isomer is detected in the crystal structure of the perchlorate salt of the same bimetallic cation (4), obtained by metathesis with AgClO(4). All the N-bound hydrogen atoms of the cations in 3 or 4 are involved in hydrogen bonds. Some of the C-N bonds of the pyrazolylamidino ligand have a character intermediate between single and double, and theoretical studies were carried out on 2a and 3 to confirm its electronic origin and discard packing effects. Calculations also show the essential role of bromide in the planarity of the tetradentate ligand in the bimetallic complex 3.

1,2-Azolylamidino ruthenium(ii) complexes with DMSO ligands: electro- and photocatalysts for CO2 reduction

“…13 A second exponent, this time on Mn(I), emerges from the use of a somehow uncommon nitrile, such as dicyanamide, which allowed a bimetallic Mn(I) complex containing a bridging tetradentate bis( pyrazolylamidino) ligand to be obtained, where the bromide anion plays a crucial role in its planarity, as demonstrated by DFT calculations. 14 Herein, we report the synthesis and characterization of new 1,2-azolylamidino Ru(II) complexes. Their chlorido(1,2-azole) precursors are also described.…”

Complejos de Reniotricarbonilo con Amidinos: síntesis, mecanismo y propiedades

“…En los últimos años en nuestro grupo de investigación se ha estudiado el comportamiento de un tipo especial de ligandos quelato nitrógeno dadores en los que cada átomo de nitrógeno forma parte de un grupo dador diferente. [57][58][59][60][61][62][63][64][65][66][67][68][69] Estos ligandos se suelen denominar "mixtos" y presentan un atractivo especial, debido a la diferente estabilidad y reactividad de cada uno de los fragmentos. Tras estos precedentes y lo expuesto anteriormente sobre el ligando amidino, decidimos centrar nuestros estudios en el ligando pirazolilamidino (Figura 4, B).…”