Polyhedral Trimetallaboranes of the Group 9 Metals: Isocloso versus Capped and Uncapped Closo Deltahedra

Abstract

The structures and energetics of the trimetallaboranes Cp 3 M 3 B n−3 H n−3 (Cp = η 5 -C 5 H 5 ; M = Co, Rh, Ir; n = 5−12) have been investigated by density functional theory. The capped-octahedral structures of the experimentally known 7-vertex trimetallaboranes (η 5 -R 5 C 5 ) 3 M 3 B 4 H 4 (R = H, M = Co; R = Me, M = Co, Rh, Ir) with the three degree 5 vertices occupied by metal atoms correspond to the lowest-energy structures by substantial margins. The lowest-energy structures for the 8-and 9-vertex Cp 3 M 3 B n−3 H n−3 (M = Co, Rh, Ir) systems have central closo deltahedra despite their 2n rather than the 2n + 2 skeletal electrons suggested by the Wade−Mingos rules for closo deltahedra. The lowest-energy structures for the 10-vertex Cp 3 M 3 B 7 H 7 as well as the experimentally known Cp* 3 Rh 3 B 7 H 7 have a central M 3 B 7 isocloso deltahedron with one of the metal atoms located at the unique degree 6 vertex. All of the low-energy 11-vertex Cp 3 M 3 B 8 H 8 (M = Co, Rh, Ir) structures, including the experimentally known Cp* 3 Co 3 B 8 H 8 , have a central M 3 B 8 closo/isocloso deltahedron with one of the metal atoms located at the unique degree 6 vertex. The central M 3 B 9 polyhedra in the lowest energy structures for the 12-vertex systems Cp 3 M 3 B 9 H 9 (M = Co, Rh, Ir) are not regular icosahedra but instead 12vertex deltahedra with two degree 6 vertices for two of the three metal atoms balanced by two degree 4 vertices. This deltahedron is derived from the regular icosahedron by a diamond−square−diamond transformation.

Reversible Transformation of a μ3-η3-C3 Ring into μ3-η2-Ethyne and μ-Vinylidene Ligands at a Triruthenium Site upon Deprotonation and Protonation

“…This is similar to the isostructural trinuclear complexes of group 9 metals, [{(η 5 -C 5 R 5 )­M} 3 (μ 3 -BH)­(μ 3 -η 3 -B 3 H 3 −)] (R = H, M = Co: R = Me, M = Co, Rh, Ir). Since the capping vertex adds skeletal electrons but does not add bonding molecular orbitals in these 7-vertex capped octahedrons, these types of clusters require 2 n skeletal electrons . Thus, the transformation of 1 to 2 can be rationalized as a skeletal rearrangement to compensate for the 2 removed electrons upon oxidation.…”

“…Since the capping vertex adds skeletal electrons but does not add bonding molecular orbitals in these 7-vertex capped octahedrons, these types of clusters require 2n skeletal electrons. 15 Thus, the transformation of 1 to 2 can be rationalized as a skeletal rearrangement to compensate for the 2 removed electrons upon oxidation. Recently, we reported another route to the μ 3 -η 3 -C 3 skeleton, which involves the coupling of two hydrocarbyl moieties at a neutral Ru 3 site; thermolysis of a μ 3 -ethylidyne-μethylidyne complex, [(Cp*Ru) 3 (μ 3 -CMe)(μ-CMe)(μ-H)(μ-CO)], resulted in the formation of a triruthenium complex containing a face-capping μ 3 -η 3 -C 3 ring, [(Cp*Ru) 3 (μ 3 -η 3 -C 3 MeH 2 −)(μ 3 -CO)] (Scheme 2a).…”

Structure and Electronic Properties of Metalloboranes with General Formula Cp*3(μ‐H)M3B8H8 (M=Cr, Mo and W): The Effect of the Size of the Metal

“…These systems possess rich structures that range from metal lattices containing interstitial boron atoms at one compositional extreme to boron cage networks containing metal atoms in voids at the other, being very versatile [12] . In this sense, metallaboranes are an interesting research topic, because these derivatives exhibit molecular cluster structures with interstitial boron atoms for metal‐rich compounds and boron cages with one or more vertexes subrogated by metal fragments for boron‐rich compounds [8,13–15] …”

“…[12] In this sense, metallaboranes are an interesting research topic, because these derivatives exhibit molecular cluster structures with interstitial boron atoms for metal-rich compounds and boron cages with one or more vertexes subrogated by metal fragments for boron-rich compounds. [8,[13][14][15] To gain insight into the cage structures that metalloboranes adopt, Thomas P. Fehlner et al [2] synthesized and characterized the compound Cp* 3 (μ-H)W 3 B 8 H 8 (see Figure 1). Atoms are denoted with white (carbon), light gray (hydrogen), dark gray (wolframium), and gray (boron) spheres (Edited imagen).…”