Synthesis of Transition Metal Complexes Supported by Mixed Donor PSiP' Bis-Phosphino Silyl Pincer Ligands

Abstract

In an effort to explore new metal mediated reactivity and further the versatility of metal pincer chemistry, research in the Turculet group has targeted the synthesis of novel bis(phosphino)silyl PSiP pincer complexes. Given the profound influence that ligand design can have on the reactivity of the ensuing metal complexes, pincer ligands that feature a mixed neutral donor set have emerged as an intriguing ligand class that offers enhanced control over the steric and electronic features of a metal pincer complex. In this context the synthesis and reactivity of metal complexes supported by unsymmetrical PSiP’ ligation was pursued. In this work three novel PSiP’ ligands were synthesized: (Cy-PSiP’-Ph)H, (Ph-PSiP*-iPr)H and (Cy-PSiP*-iPr)H. Group 10 complexes of the type (Cy-PSiP’-Ph)MX (M = Pt, Pd, Ni; X = Cl, Me, Ph) were prepared. The Pd and Ni chloride complexes were structurally characterized and found to exhibit approximate square planar coordination geometry in the solid state, with the silyl donor coordinated trans to the chloride ligand. The Me derivatives proved to be surprisingly unreactive with hydrosilanes, which is unlike the related Cy-PSiP analogues previously reported by the Turculet group. Amido complexes of the type (Cy-PSiP’-Ph)M(NHR) (M = Pt, Ni; R = H, Ph) and (Cy-PSiP’-Ph)Pd(NH2) were also synthesized. While the latter complexes proved to be quite stable, related complexes of the type (Cy-PSiP’-Ph)Pd(NHR) (R = Ph, tBu) underwent facile rearrangement processes involving Si-C (sp2) bond cleavage in the ligand backbone. Such processes have previously been reported for related (Cy-PSiP)MX (M = Ni, Pd; X = alkyl, amido) species. Group 10 complexes supported by alternative PSiP’ ligands including (Ph-PSiP*-iPr)PtCl and (Cy-PSiP*-iPr)MCl (M = Pt, Ni) were also synthesized. The complex (Cy-PSiP*-iPr)PdCl was structurally characterized and found to exist as a dimeric species in the solid state, with the CH2PiPr2 ligand arms bridging between Pd centers. Solution NMR data suggests that in some cases, κ3-coordination of Ph-PSiP*-iPr and Cy-PSiP*-iPr is achieved. Finally preliminary studies revealed that Group 8 and 9 complexes supported by such PSiP’ ligands are synthetically viable.