Organometallic Cluster Complexes with Face-Capping Arene Ligands. 8. Nucleophilic Reactivity of Cluster Complexes with Face-Capping Arene Ligands:  Metal vs Ligand Protonation

Abstract

Protonation of some cluster complexes with face-capping arene ligands has been studied. The complexes [(CpCo) 3 (µ 3 -η 2 :η 2 :η 2 -arene)] [arene ) isopropylbenzene (1a), 1,4-diethylbenzene (1b), 1,2-diphenylethane (1c), 1,1-diphenylethane (1d)] are protonated at the metal clusters to afford the hydrido cluster cations [(µ 3 -H)(CpCo) 3 (µ 3 -η 2 :η 2 :η 2 -arene)] + (3a-d). The crystal structure of 3d[CF 3 COO] -‚H 2 O has been determined. In marked contrast, derivatives with µ 3 -arenes bearing unsaturated substituents [arene ) R-methylstyrene (2a), β-methylstyrene (2b), p-methoxystyrene (2c)] take up a proton at the β-carbon atom of the side chain to give the novel metal cluster stabilized benzyl cations [(CpCo -c). On attempted crystallization as a tetrafluoroborate, the derivative 4a with a protonated R-methylstyrene ligand is converted to the paramagnetic [(CpCo) 3 {µ 3 -η 2 :η 2 :η 2 -(R-methylstyrene)}] + (2a + ), the crystal structure of which is reported. The different sites of protonation for 1 and 2 are explained by an extended Hu ¨ckel (EH) MO study, using both charge and overlap control arguments. The paramagnetic cation was studied, and its geometry found to agree very well with the experimentally determined structure described for 2a + , suggesting that it is indeed this the species being observed. A detailed analysis of the geometrical preferences of the protonation products 4 was carried out, using EH and density functional methods. A slipped eclipsed arrangement of a nonplanar η 7 -benzyl ligand on top of the Co 3 cluster with the side chain bent away appears to be energetically favored over a staggered substituted benzene.

Reductive Degradation of Tetracobalt Cluster Complexes with a Facial C8H8 Ligand – Synthesis of [Co3(CO)3(μ3-CO)3(μ3-C8H8)]– and [Ru(C5Me5)Co3(CO)3(μ3-CO)3(μ3-C8H8)]

“…A similar situation was encountered previously involving part of the µ 3 -η 2 :η 3 :η 3 -cycloheptatrienyl ligand in the related complex [Co 4 (CO) 3 (µ 3 -CO) 3 (η 5 -C 7 H 9 )(µ 3 -C 7 H 7 )] (11) (Scheme 3), [7] and the µη 3 :η 3 -coordinated cyclohexadienyl part of the benzyl ligand in the cations [{(C 5 H 5 )Co} 3 (µ 3 -benzyl)] ϩ (12) (Scheme 3). [14] It should be stressed, however, that we do not wish to attach much significance to the variations in the actual orientation of the facial C 8 H 8 ring relative to the bonding M 3 plane, as observed in the crystals. Topologically, there is little difference between these coordination modes; they can be converted into one another by a rather small (less than 8°) rotation of one ring.…”

Trinuclear Nickel Complexes with Metal–Arene Interactions Supported by Tris- and Bis(phosphinoaryl)benzene Frameworks

“…Beyond nickel, trimetallic complexes supported by μ 3 -arene donors are known for Os, 17 Co, 18 Rh, 19 Ru, 11 and Pd. 20 Given the unusual binding mode for Ni in the trimetallic complex 4 , the versatility of such coordination mode was investigated with fewer phosphine donors linked by a central arene.…”

“…Typically, the Ni 3 core is coordinated by two μ 3 -ligands such as alkyne, CO, alkylidyne, benzyne, halide, chalcogenide, or hydride moieties. Beyond nickel, trimetallic complexes supported by μ 3 -arene donors are known for Os, Co, Rh, Ru, and Pd . Given the unusual binding mode for Ni in the trimetallic complex 4 , the versatility of such coordination mode was investigated with fewer phosphine donors linked by a central arene.…”

Aromaticity of Benzene in the Facial Coordination Mode: A Structural and Theoretical Study

“…An explanation of these effects has been given previously,21 based on simple frontier orbital arguments and approximate (Fenske–Hall) MO calculations, and need not be reiterated here. Differences of the electronic structures between derivatives with saturated and unsaturated side‐chains, respectively, on the μ 3 ‐arene have also been examined and discussed earlier 22. They do not affect the bonding between the facial arene and the Co 3 cluster.…”