A Homoleptic Beryllium Carbonyl Complex with an End‐On and Side‐On Bridging Carbonyl Ligand

Abstract

Homoleptic dinuclear beryllium carbonyl cation complexes have been produced and characterized in the gas phase. Infrared photodissociation spectroscopic and theoretical results confirm that Be 2 (CO) 5 + is a coordination saturated complex that can be assigned to a mixture of two almost isoenergetic structural isomers. Besides a beryllium-beryllium single-bonded (OC) 2 Be-Be(CO) 3 + isomer, another structure involving an unusual end-on and side-on bridging carbonyl ligand with very low carbonyl stretching frequency is identified. Carbonmonoxidecanbindtomanytransition-metalcentersin forming diverse transition-metal carbonyl complexes, which are not only of close relevance to many industrial processes in synthesis [1] and catalysis, [2] but also served as prototypical models in understanding the metal-ligand and metal-metal bonding. [3] The carbon monoxide ligands engage in a range of bonding modes in the transition metal carbonyl complexes. [4] Besides the ubiquitous terminal end-on type, the symmetrical and unsymmetrical end-on bridging, [5] the sideon bridging [6,7] as well as the linear M-C-O-M bridging [8] coordination modes are also known in bi-and multinuclear transition metal carbonyl complexes.Compared to the countless transition-metal carbonyl complexes, only very few stable main-group metal carbonyl complexes have been synthesized and crystallographically characterized owing to the lack of accessible valence d orbitals for bonding with carbon monoxide. [9][10][11] Most of homoleptic carbonyl complexes of main group elements are not stable at ambient conditions, and they can usually only be observed in low-temperature matrices [12][13][14][15][16] or in the gas phase. [17][18][19] In these main-group element carbonyl complexes, the carbon monoxide ligand binds predominantly in terminal end-on mode. The other coordination modes that are quite common in transition-metal carbonyl complexes are rarely observed in the main-group element carbonyl complexes. Only very few dinuclear Group 13 metal carbonyl complexes were reported to involve the end-on bridging carbonyl ligands, [20] and a high-lying BeCOBe species has been characterized to involve a linear bridging CO unit. [21]