Effects of the conformational rearrangement of the (np3)M fragment in the course of the reaction between (np3)MH hydrides [M = Co, Rh; np3 = N(CH2CH2PPh2)3] and carbon disulfide

Article abstract of DOI:10.1021/om00125a009

The reactivity of the complex (np₃)RhH toward CS₂ has been investigated. Depending on the presence or absence of NaBPh₄ in the reaction mixture, two different compounds are obtained: [(np₃)Rh(η²-CS₂)]BPh ₄·0.5C₂H₅OH and (np₃)Rh(S₂CH). In contrast to the rhodium hydride, the cobalt analogue is reported to yield [(np₃)Co(CS)]BPh₄ and (np₃)Co(η²-CS₂). An indirect way of obtaining a stable rhodium analogue of the cobalt thiocarbonyl complex is presented. The structure of the Rh(I)-η²-CS₂ complex has been determined by X-ray diffraction analysis in order to compare its stereochemical features with those of the Co(O) analogue: a = 19.134 (3) A?, b = 17.061 (3) A?, c = 9.111 (1) A?, α = 83.95 (2)°, β = 79.70 (1)°, γ = 84.46 (1)°, triclinic, P1, Z = 2. In the complex cation the (np₃)M fragment distorts from the common C_3v, symmetry by accommodating two phosphorus atoms in trans axial positions of an octahedron; the nitrogen and the third phosphorus atoms lie cis to each other in the equatorial plane. This arrangement corresponds to the shape of typical L₄M fragments with C_2v symmetry where d⁸ metal fragments of this type are supportive of η²-CS₂ coordination. Although the four different products obtainable from the reaction of the cobalt and rhodium hydrides with CS₂ indicate multiple-reaction pathways, there is enough evidence that these may be caused by the ease of the rearrangement of the (np₃)M fragment and by the amphoteric nature of the (np₃)MH hydrides. This paper, by referring to a series of experimental and theoretical observations for complexes containing the (np₃)M fragment, offers suggestions as to how one can interpret major, different trends of the reactivity. Qualitative MO arguments, supported in some cases by EHMO calculations, are used to check whether the existence of the proposed key intermediates is allowed or not.