Variable coordination of a chiral diphosphine containing an amidinium/NHC group within its backbone: μ-P,P', κ2-P,P' and κ3-P,C,P' coordination modes.

A diphosphine ligand (1·HPF(6)), which is a potential precursor to a PC(NHC)P pincer, with a backbone containing two phenylene groups and a central bicyclic 4-aza-2-azoniabicyclo[3.2.1]oct-2-ene unit has been synthesised and coordinated to Pd(II) and Pt(II) to give trans-[M(κ(2)-P,P'-)Cl(2)]PF(6) where M = Pd (2) or Pt (3a). Single-crystal structure determinations of 2 and 3a show the complexes to be isostructural with the diphosphine coordinated in a trans-spanning fashion and the amidinium unit being protonated and non-coordinated. 2 and 3a react with CH(3)I to give the dimers trans-[Pd(2)(μ-1·H)(2)I(4)](PF(6))(2), 6, and trans-[Pt(2)(μ-1·H)(2)I(4)](PF(6))(2), 7, as the major products. This bridging mode of coordination of [1·H](+) is also seen in trans-[Rh(2)(μ-1·H)(1,5-COD)(2)Cl(2)]PF(6), 4, and [Pt(2)(μ-κ(2)-1·H)(dvdms)]PF(6), 5. Upon treatment with KO(t)Bu complexes and undergo deprotonation at the amidinium carbon to give trans-[M(κ(3)-P,C,P'-1)Cl]PF(6) where M = Pd (8), and Pt (9). The related trans-[Rh(κ(3)-P,C,P'-1)(CO)]PF(6) (10) is prepared directly from 1·HPF(6) and Rh(acac)(CO)(2): this and the palladium and platinum complexes 8 and 9 are isolated as isomeric mixtures as a consequence of a conformational isomerism. In situ deprotonation of 1·HPF(6) followed by addition of Ag(CF(3)SO(3)) gave S(Ag)-[Ag(κ(3)-P,C,P'-1)(CF(3)SO(3))], 11. Some preliminary studies of the reactivity of 2 and 8 in Suzuki-type reactions are reported and the Pt(0) system has been shown to be an active hydrosilylation catalyst.