Bis(borylene) Complexes of Cobalt, Rhodium, and Iridium [(η⁵-C₅H₅)M(BNX₂)₂] (X = Me, SiH₃, SiMe₃): A Bonding Analysis

Abstract

Geometry, electronic structure, and bonding analysis of the terminal neutral bis­(borylene) complexes of cobalt, rhodium, and iridium [(η5-C5H5)­M­(BNX2)2] (M = Co, Rh, Ir; X = Me, SiH3, SiMe3) were investigated at the DFT/BP86/TZ2P/ZORA level of theory. The calculated geometry of iridium complex [(η5-C5H5)­Ir­{BN­(SiMe3)2}2] is in excellent agreement with structurally characterized iridium complex [(η5-C5Me5)­Ir­{BN­(SiMe3)2}2]. Pauling, Mayer, and Nalewajski-Mrozek bond multiplicities of the optimized structures of bis­(borylene) complexes show that the M–B bonds in these complexes are nearly MB double bonds. On substitution of the BNX2 ligand by the more π-acidic CO ligand, the calculated M–B bond distances increase, while substitution of the BNX2 ligand by the less π-acidic PMe3 ligand results in a decrease of the calculated M–B bond distances. The acute B–M–B bond angle and short B–B bond distance, in particular in cobalt bis­(borylene) complexes, reveal the presence of a MB2 interaction consistent with some degree of weak B–B bonding. The π-bonding contribution is, in all complexes, smaller (28.4–32.6% of total orbital contributions) than the σ-bonding contribution. The BNX2 ligands are relatively poor π acceptors compared with the CO ligand, but better π acceptors than the PMe3 ligand. The contribution of M ← BNX2 ΔE σ is clearly the dominant term of the orbital interaction. The σ-donor ability of borylene ligands BNX2 is greater in bis­(borylene) complexes [(η5-C5H5)­M­(BNX2)2] than in carbonyl borylene complexes [(η5-C5H5)­(CO)­M­(BNX2)] and phosphine borylene complexes [(η5-C5H5)­(PM3)­M­(BNX2)2]. The absolute value of various energy terms for the MB bond decreases upon going from X = Me to SiH3 and SiMe3.

Formation and Reactivity of Electron‐Precise B−B Single and Multiple Bonds

“…[28] Borylene transfer from [(OC) 5 [29] DFT calculations by Pandey later showed that the degree of BÀBb onding in Group 9 cisbis(aminoborylenes) increases from Ir to Co, [30] yet without ever reaching the degree observed in 4.U nder photolytic conditions,the iron bis(borylene) complex 4,first underwent dimerization to diiron species 5 by loss of one CO ligand. Themost notable example remains the iron-templated catenation of four boron atoms presented in Scheme 3b.…”

B–B Coupling and B–B Catenation: Computational Study of the Structure and Reactions of Metal–Bis(borylene) Complexes

“…The structure of [Cp*Ir(NSiMe 3 ) 2 ] ( 1 d ) (Cp*=1,2,3,4,5‐pentamethylcyclopentadiene) is very different from 1 a where the diffuse metal orbitals of Ir push two borylene units far apart, 2.353 Å . A detailed bonding analysis of 1 d has been reported previously . The electronic structure of 1 d is shown in Figure e.…”

“…[3a] Ad etailed bonding analysis of 1d has been reported previously. [14] The electronic structure of 1d is shown in Figure 1e.…”

Einfach‐, Doppel‐, Dreifachbindungen und Ketten: Knüpfung elektronenpräziser B‐B‐Bindungen

“…[20] Der Tabelle 1). [22] Wir gingen jedoch davon aus, dass die starke p-Donierung der Bor-gebundenen Aminogruppen das grçßte Hindernis für eine B-B-Kupplung darstellt und somit der Einsatz von Borylenliganden ohne p-basische Substituenten grçßeren Erfolg versprechen sollte.…”