Lithium and Potassium Complexes with dbn- and dbu-Based Enamido Phosphine Ligands: Syntheses and Applications

The phosphines 6-diphenylphosphino-1,8-diazabicyclo[5.4.0]undec-7-ene (dbuPH) and 7-diphenylposphino-1,5-diazabicyclo[4.3.0]non-5-ene (dbnPH), containing amidine subunits, were successfully deprotonated by n-butyllithium or benzylpotassium. In the presence of Et2O or THF, the well-defined complexes [{Li(dbnP)(Et2O)}(2)] (1), [{Li(dbuP)(Et2O)}(2)] (2), [{K(dbnP)(THF)}8] (3b) and [{K(dbuP)(THF)(2)}(2)] (4) were obtained, while in the absence of such donors, polymeric [{K(dbnP)}(infinity)] (3a) was formed. These alkali-metal derivatives are useful precursors for salt-metathesis reactions, and they allow the transfer of the enamido phosphine ligands to appropriate transition metals, as demonstrated by the syntheses of the new rhodium complexes [Rh(dbnP)(cod)] (5) and [Rh(dbuP)(cod)] (6). The reaction of 1 and 2 with Ph2PCl underlined the ambident character of dbnP- and dbuP(-) as nucleophiles and led to the new diphosphines dbn(PPh2)(2) (two isomers C-7 and N-7) and dbu(PPh2)(2) (N-8), in which either the carbon or the nitrogen atom of the former enamido moiety was substituted.