Variable coordination of a chiral diphosphine containing an amidinium/NHC group within its backbone: μ-P,P′, κ 2-P,P′ and κ 3-P,C,P′ coordination modes

Abstract

A diphosphine ligand (1·HPF 6), which is a potential precursor to a PC NHCP 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′-1·H)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 3I to give the dimers trans-[Pd 2(μ-1·H) 2I 4](PF 6) 2, 6, and trans-[Pt 2(μ-1·H) 2I 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) 2Cl 2]PF 6, 4, and [Pt 2(μ-κ 2- 1·H)(dvdms)]PF 6, 5. Upon treatment with KO tBu complexes 2 and 3a 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 3SO 3) gave S Ag- [Ag(κ 3-P,C,P′-1)(CF 3SO 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. © 2012 The Royal Society of Chemistry.