The sandwich type product CpCoL (1c) and the carbonyl species (OC)3FeL (2c), (OC)4CrL (3e), (OC)4MOL (4b), and (OC)4WL (5b) were prepared with diazadiboretidines (RBNR′) : (L) as tetra-hapto ligands (a-d: R = Me, Et, Pr. Bu; R′ = tBu; e: R = R′ = iPr). The ligand (iPrBNiPr)2 , prepared by a novel catalytic cyclodimerisation of iPrB≡NiPr, undergoes subsequent cyclodimerisation to the eight-membered ring (iPrBNiPr)4 at ambient temperature, where-as the corresponding cycloreversion occurs at 100 °C. The structure of the complexes (OC)xML is discussed by means of IR and NMR data and the structures of crystalline 2c and 5d were determined by X-ray crystallography.
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Paetzold et al. (1988) studied this question.