Triply Carbonyl-Bridged Ni₂(CO)₅Featuring Triple Three-Center Two-Electron Ni—C–Ni Bonds Instead of Ni≡Ni Triple Bond

Abstract

Motivated by the predicted unusual short NiNi bond length that is comparable to the intermetallic distance anticipated for the triple bond, the nature of Ni Ni bonding interaction in the triply carbonyl-bridged geometry of the neutral Ni 2 (CO) 5 complex has been investigated using a range of state-of-the-art quantum chemistry methods. The elaborate analyses manifest that the tribridged Ni 2 (CO) 5 features triple three-center two-electron NiCNi bonds instead of NiNi triple bond. The electron pair donated by the bridging carbonyl ligand should be shared by both nickel centers to achieve the favored (18, 18) configuration.

Metal–Metal Bonding in Late Transition-Metal [M2L5] Complexes: Exploring the Limits of the Isolobal Analogy between the CO and AlCp* Ligands

“…In particular, substantial bonding is induced by the occupation of the diffuse σ(sp) (a′ 1 ) and π(4p) 3) is indicative of a weak bonding interaction. As already shown by Liu et al 28 in their QTAIM analysis of the electron density, the indicators associated with the Ni−Ni bond critical point (bcp) are also in line with a weak Ni−Ni bonding character (Table 4).…”

“…Single crystal X-ray measurement unambiguously verifies the isolation of [Ni 2 (AlCp*) 5 ]. Indeed, 1 is isostructural to the already known [TM 2 (ECp*) 5 ] (TM = Pd, Pt; E = Al, Ga) compounds and the predicted structure of the hypothetical [Ni 2 (CO) 5 ], , having three bridging and two terminal ligands at the central Ni-dimer (Figure ). The Ni–Ni distance of 2.2702 Å is considerably shorter (about 8%) than twice the covalent radius of Ni (2.48 Å) and only slightly longer than the predicted Ni–Ni distance in [Ni 2 (CO) 5 ] (2.18 Å), hinting to the presence of significant Ni–Ni interactions.…”

“…27 However, accessing the neutral Ni 2 (CO) x (x = 5, 6, 7) on a macroscopic scale still remains elusive. 28 This delocalized representation allows the Ni centers to attain the 18-electron configuration without assuming any direct metal−metal bond (Scheme 1). 22 TMcontaining compounds and especially multiple TM−TM bonds are of fundamental interest and may be viewed as building blocks for larger clusters or even surfaces.…”

“…56 Especially, the structural motif TM 2 (μ 2 -ER) 3 , in which two TMs are bridged by three ER ligands frequently occurs in such compounds. 44,56−58 28 and Using the Half-Arrow Representation of Green et al, 22 in which each μ-CO Lone Pair is Represented by a Pair of Half-Arrows. In this Representation, Each Bridging Carbonyl may be Regarded as Effectively Contributing two Electrons to the Electron Count of Both Nickel Atoms Figure 1.…”

“…Scheme 1. Lewis Representation of [Ni 2 (CO) 5 ] Proposed by Liu et al28 and Using the Half-Arrow Representation of Green et al,22 in which each μ-CO Lone Pair is Represented by a Pair of Half-Arrows. In this Representation, Each Bridging Carbonyl may be Regarded as Effectively Contributing two Electrons to the Electron Count of Both Nickel Atoms…”