Synthesis and Reactivity of Group 10 Silyl Pincer Complexes

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. In this context, the synthesis and reactivity of Group 10 complexes featuring [Cy-PSiP] ([Cy-PSiP] = [?3-(2-Cy2PC6H4)2SiMe]⁻) ligation is described herein. The central silyl donor is anticipated to promote the formation of electron rich metal species capable of diverse and challenging reactivity. In the course of this work, it was found that [Cy-PSiP] ligation supports the synthesis of square planar PtII alkyl complexes that can mediate Si-H and Si-Cl bond cleavage chemistry. A cationic PtII species was accessed by treatment of [Cy-PSiP]PtMe with B(C6F5)3. The latter complex underwent B-C bond cleavage in the [MeB(C6F5)3]⁻ counteranion to produce [Cy-PSiP]Pt(C6F5). Examples of Si-C bond cleavage reactions at Pt0 and PtII centers were also observed. Related alkyl complexes of Ni and Pd were observed to undergo rearrangement processes involving net Si-C(sp2) and Si-C(sp3) bond cleavage. In the case of Ni these Si-C bond cleavage steps are reversible on the NMR timescale. Attempts to prepare a terminal hydride complex of the type [Cy-PSiP]MH (M = Pd, Pt) resulted in the isolation of ?2-Si-H coordination complexes of the type [Cy-PSi(µ-H)P]M, which were shown to undergo insertion of CO2 to form the corresponding formate species. In the presence of B(C6F5)3, these ?2-Si-H complexes were capable of mediating the catalytic reduction of CO2 to CH4 using hydrosilanes as the reducing agent. The synthesis and characterization of terminal, monomeric Pt hydroxide and alkoxide complexes of the type [Cy-PSiP]Pt(OR) (R= H, Ph, tBu) was achieved, and these complexes were shown to readily deprotonate relatively acidic C-H bonds in phenylacetylene and acetonitrile. A rare example of hydrogenolysis of the Pt-OR linkage with H2 was documented, as was an unusual example of Si-H addition across the Pt-OR bond to form Pt silyl species. While terminal anilido Pt complexes of the type [Cy-PSiP]Pt(NHAr) (Ar = Ph, 2,6-Me2C6H3, 2,6-iPr2C6H3) proved readily isolable, related Ni and Pd anilido species underwent rearrangement processes similar to those observed in their alkyl analogues. Terminal phosphido complexes supported by [Cy-PSiP] ligation were successfully isolated and characterized for all Group 10 metals. Lastly, the Pt and Pd coordination chemistry of a new PSiN pincer derivative was explored, and the amino donor arm of this pincer ligand was demonstrated to exhibit hemilabile coordination to the metal center.