Synthesis, Characterization, and Catalytic Reactivity of {CoNO}⁸ PCP Pincer Complexes

Abstract

The reaction of coordinatively unsaturated Co(II) PCP pincer complexes with nitric oxide leads to the formation of new, air-stable, diamagnetic mono nitrosyl compounds. The synthesis and characterization of five- and four-coordinate Co(III) and Co(I) nitrosyl pincer complexes based on three different ligand scaffolds is described. Passing NO through a solution of [Co(PCP NMe - i Pr)Cl], [Co(PCP O - i Pr)Cl] or [Co(PCP CH2 - i Pr)Br] led to the formation of the low-spin complex [Co(PCP- i Pr)(NO)X] with a strongly bent NO ligand. Treatment of the latter species with (X = Cl, Br) AgBF 4 led to chloride abstraction and formation of cationic square-planar Co(I) complexes of the type [Co(PCP- i Pr)(NO)] + featuring a linear NO group. This reaction could be viewed as a formal two electron reduction of the metal center by the NO radical from Co(III) to Co(I), if NO is counted as NO + . Hence, these systems can be described as {CoNO} 8 according to the Enemark–Feltham convention. X-ray structures, spectroscopic and electrochemical data of all nitrosyl complexes are presented. Preliminary studies show that [Co(PCP NMe - i Pr)(NO)] + catalyzes efficiently the reductive hydroboration of nitriles with pinacolborane (HBpin) forming an intermediate {CoNO} 8 hydride species.

Synthesis and Characterization of Cobalt NCN Pincer Complexes

“…The NCN ligand is coordinated to the metal center in a tridentate meridional fashion. The C1À Co1À Br1 angle is essentially linearly being 179.35 (8)°and the N1À Co1À N2 angle is 167.76(9)°. The Co1À C1 distance of 1.850(3) Å is significantly shorter than in corresponding PCP CH2 and PCP O (cf 1.955 and 1.914 Å) complexes.…”

Synthesis and Catalytic Reactivity of Cobalt Pincer Nitrosyl Hydride Complexes

“…Co–N–O 140.1°) could suggest a different electronic behavior, no evidence was found to support a Co(II) character. 8 An unequivocal assignment is hindered by orbital mixing, but the d -splitting calculated for complex 2a indicates a d 6 species (see Figure 2 ) and, thus, a Co(III) metal center. Moreover, a clear negative charge on the NO ligand, C NO = −0.24, calculated by a NPA analysis (see Computational Details ) as well as a Co–N NO Wiberg index typical of a single bong (WI = 0.96) strongly support the same conclusion.…”

“… 7 Very recently, our group reported on a set of new {CoNO} 8 PCP pincer complexes and an initial study on their catalytic reactivity. 8 In this contribution, we describe the synthesis, characterization, and catalytic application of new cobalt {CoNO} 8 hydride complexes in anti-Markovnikov alkene hydroboration. Two different synthetic approaches, X-ray structures and a DFT-modeled mechanism, are presented.…”

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).…”