A diphosphine ligand (1·HPF66666), which is a potential precursor to a PCNHCP 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(κ2-P,P′-1·H)Cl2]PF6 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 CH3I to give the dimers trans-[Pd2(μ-1·H)2I4](PF6)2, 6, and trans-[Pt2(μ-1·H)2I4](PF6)2, 7, as the major products. This bridging mode of coordination of [1·H]+ is also seen in trans-[Rh2(μ-1·H)(1,5-COD)2Cl2]PF6, 4, and [Pt2(μ-κ2-1·H)(dvdms)]PF6, 5. Upon treatment with KOtBu complexes 2 and 3a undergo deprotonation at the amidinium carbon to give trans-[M(κ3-P,C,P′-1)Cl]PF6 where M = Pd (8), and Pt (9). The related trans-[Rh(κ3-P,C,P′-1)(CO)]PF6 (10) is prepared directly from 1·HPF66666 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·HPF66666 followed by addition of Ag(CF3SO3) gave SAg-[Ag(κ3-P,C,P′-1)(CF3SO3)], 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.