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Four-co-ordinate rhodium(I) complexes [{Rh(CO)2Cl}n(α-diimine)] (n = 1, 2) with σ,σ-N,N′ chelate or σ-N, σ-N′ bridge bonded RNC(R′)C(R″)NR ligands. Influence of the branching at Cα of R on the RhIα-diimine interaction

1981; Elsevier BV; Volume: 51; Linguagem: Inglês

10.1016/s0020-1693(00)88345-0

1873-3255

Henk G. van der Poel, Gerard van Koten, Kees Vrieze,

Coordination Chemistry and Organometallics

RNC(R′)C(R″)NR ligands (R-dim{R′,R″}) react quantitatively with [(CO)2Rh(μ-Cl)2Rh(CO)2] via a bridge splitting reaction to form complexes with [Rh2Cl2(CO)4(R-dim{R′,R″})] stoichiometry. An extensive infrared, 1H and 13C NMR study revealed that the nature of [Rh2Cl2(CO)4(R-dim{R′,R″})] depends on the substituents R,R′ and R″ connected to the NCCN skeleton. Complexes with R-dim{R′,R″} ligands having R′R″H, Ri-Pr-, i-Pr2C(H)-2,6-Me2Ph; R′H, R″Me, Ri-Pr; R′R″Me, R4-MePh- have ionic structures [Rh(CO)2(R-dim{R′,R″})][RhCl2(CO)2] both in polar (acetone) and less polar (CHCl3, C6H6) solvents. The cation contains a σ,σ-N,N′ chelate bonded R-dim{R′,R″} ligand. In contrast, when for R-dim{H,H} the R group is t-bu or EtMe2C the complex in solution at low temperature exists as an equilibrium mixture of the dinuclear species [(CO)2ClRh(μ-(σ-N,σ-N′)-R-dim{R′,R″})RhCl(CO)2] (as the major component) and the ionic species [Rh(CO)2(R-dim{R′,R″})][RhCl2(CO)2] (in minor amounts). The dinuclear species is most probably present as two stereoisomers. At room temperature the exchange between these species becomes fast on the NMR time scale. The different structures are explained in terms of the branching at Cα in R. For R substituents which are triply branched at Cα the interaction with the fcis-CO ligands in a σ,σ-N,N′ chelate bonded R-dim{R′,R″} ligand is larger than in a complex with a σ-N bonded R-dim{R′,R″} ligand. Comparison of the 13CO chemical shifts of the ionic and dinuclear species with those of Bu4N[RhCl2(CO)2] as well as the 1H and 13C resonance patterns of complexes in which the R substituent contained prochiral groupings (e.g. EtMe2C-) were particularly helpful for the structural assignment of the species in solution.