Polyhedral [M2B5] Metallaborane Clusters and Derivatives: An Overview of Their Structural Features and Chemical Bonding

Abstract

A large number of metallaborane clusters and their derivatives with various structural arrangements are known. Among them, M2B5 clusters and derivatives constitute a significant class. Transition metals present in these species span from group 4 to group 7. Their structure can vary from oblatonido, oblatoarachno, to arachno type open structures. Many of these clusters appear to be hypoelectronic and are often considered as ‘rule breakers’ with respect to the classical Wade–Mingos electron counting rules. This is due to their unique highly oblate (flattened) deltahedral structures featuring a cross-cluster M−M interaction. Many theoretical calculations were performed to elucidate their electronic structure and chemical bonding properties. In this review, the synthesis, structure, and electronic aspects of the transition metal M2B5 clusters known in the literature are discussed. The chosen examples illustrate how, in synergy with experiments, computational results can provide additional valuable information to better understand the electronic properties and electronic requirements which govern their architecture and thermodynamic stability.

Degradation Chemistry of Dimetallaboranes, [(Cp*M)2B5H9+x] with [Ph2Se2] (x = 2 or 0, M = V or Cr)

“…This interpretation implies the presence of a V–V single bond, and the bond length 2.748 Ȧ is consistent with this. All the structural parameters of 2 were found to be well in accordance with similar {M 2 B 5 } clusters …”

“…But this metathesis reaction lacks control over product formation, which renders our stepwise degradation method more favorable. It has been well established that {M 2 B 4 } clusters undergo cluster expansion reactions with boranes to form corresponding {M 2 B 5 } clusters . In the presence of Lewis bases, metallaborane clusters are known to undergo degradation reaction, forming a cluster of smaller size.…”

“…All the structural parameters of 2 were found to be well in accordance with similar {M 2 B 5 } clusters. 26 Cluster 2 also shows a fast scrambling between the protons connected to apical and equatorial borons. This was established by a variable-temperature 1 H NMR study.…”

“…At clusters. 26 In the presence of Lewis bases, metallaborane clusters are known to undergo degradation reaction, forming a cluster of smaller size.…”

“…The electronic structure and bonding in {M 2 B 5 } type clusters have been extensively studied by our group, 26 however, those aspects of {M 2 B 4 } type of clusters have been sparsely explored. Hence the study of the electronic structure and bonding of 3 became of interest.…”