Electronic versus steric control in palladium complexes of carboranyl phosphine-iminophosphorane ligands.

A new family of carboranyl phosphine-iminophosphorane ligands was prepared and characterized. The new ligands present a carboranyl group directly attached to the iminophosphorane nitrogen atom through a cage carbon atom (C-carboranyl derivatives L1-L3) or through the B3 boron atom (B-carboranyl derivatives L4 and L5), and the phosphine group on a side chain derived from the diphosphine dppm, i.e.

Deactivation of the coordinating ability of the iminophosphorane group by the effect of ortho-carborane.

The C-carboranyl iminophosphorane compounds derived from triphenylphosphine (I1) and o-(methylthiophenyl)-diphenylphosphine (I2) were obtained and structurally characterized. Functionalization with sulfur on the other cage carbon atom gave the corresponding disulfides (L1L1 and L2L2). In the case of I1 it was also possible to isolate the trisulfide (L1SL1) and the thiol (L1H), which is not in the expected zwitterionic form, showing that the carborane group reduces the basicity of the nitrogen atom.