The Effect of One Valence Electron: Contrasting (PNP)Ni(CO) with (PNP)Ni(NO) to Understand the Half-Bent NiNO Unit

Abstract

Reaction of a (PNP)Ni radical with NO finishes in the time of mixing to form a 1:1 adduct with a NO stretching frequency of 1654 cm (-1). NMR data of this diamagnetic product indicate C 2 v symmetry, which is contradicted by the X-ray structure, which shows it to be nonplanar at Ni, with a geometry intermediate between planar and tetrahedral; the planar geometry is thus the transition state for fluxionality giving time-averaged C 2 v symmetry. The X-ray structure, together with DFT calculations, reveals that the "half-bent" NiNO unit and the intermediate coordination geometry result from a Ni --> NO charge transfer, which has a nonintegral value, resulting in a continuum between NO (+) (hence Ni (0)) and NO (-) (hence Ni (II)). This is related to the nonaxially symmetric character of the Ni --> NO back-donation caused by the (PNP) environment on Ni. Steric effects of ( t )Bu and even chelate constraints are ruled out as the cause of the unusual electronic and structural features.

One metal is enough: a nickel complex reduces nitrate anions to nitrogen gas

“…Thus, the crystal structure suggests that complex 3 may contain a Ni( i )-center. The metrical parameters with d Ni1–N2 = 1.694(4) Å and d N2–O1 = 1.174(6) Å and the aforementioned vibrational frequency compare well with a previous reported four-coordinate nickel nitrosyl complex, (PNP*)Ni(NO) (PNP* = ( t Bu 2 PCH 2 SiMe 2 ) 2 N) by Caulton and coworkers ( ν NO = 1654 cm –1 , d Ni–N = 1.692(4) Å, d N–O = 1.185(5) Å, ∠Ni–N–O = 149.3(4)°) 18. The nickel in this complex was assigned to be a Ni( i )-center 18…”

Azanone (HNO): generation, stabilization and detection

“…126 NOstabilization by complexes with pincer scaffolds is far better known. Several structural analyses of this kind of species exist in bibliography, 124,[127][128][129][130][131][132][133] along with reports of their catalytic activity. [134][135][136] Within our group, several rhodium-based pincer ligand systems have been studied (the most relevant are highlighted in Figure 3b).…”

Structure and Reactivity of NO/NO+/NO−Pincer and Porphyrin Complexes

“…DFT calculations of half-bent systems showed large spin densities to be located on the nitrosyl ligand, which could be more reasonably thought of as radical NO * coordinating via a lone pair in the N atom. [26,27] Interestingly, this {MNO} 10 system should have a "full" bent nitrosyl in a square planar conformation (Ni II NO À ) or a linear nitrosyl in a a tetrahedral geometry (Ni 0 NO + ). Since the PNP ligand prohibits reaching a tetrahedral coordination geometry, the system stays at an intermediate point with the NiNO bend at an intermediate value.…”

“…Most used is the direct method of nitrosylation by injection of gaseous nitric oxide into a solution of the pincer precursor complex. [22,26,27,30,[33][34][35] This route was first employed by Milstein's group, who proved Rh(PNP)(NO)(Cl) (1 + ) obtention could be achieved both by reaction of a Rh(II) precursor and NO * and by reaction of Rh(I) and NO + , as is depicted in Scheme 1. [33] This last alternative has been scarcely reported thereafter.…”

“…[28] Up to that moment, very few pincer nitrosyls had been reported, none with a PCP scaffold. [26,27,33,36] Synthesis consisted of reaction of Rh(PCP)(N 2 ) with a nitrosonium salt yielding [Rh(PCP)(NO)] + (6 + ). This linear nitrosyl complex (vide infra) was found to bend by reaction with LiCl.…”