Silanol-based pincer Pt(II) complexes: Synthesis, structure, and unusual reactivity

Aiming at the generation of a silanone intramolecularly bound to platinum, we prepared pincer-type PSiP silanol Pt(II) complexes. While a stable silanone complex was not isolated, unusual reactivity modes, involving its possible intermediacy, were observed. Treatment of the new PSiH₂P-type ligand (o-iPr₂PC₆H₄)₂SiH₂ (7) with (Me₂S)₂Pt(Me)Cl yields the pincer-type hydrosilane complex [{(o- iPr₂PC₆H₄)₂SiH}PtCl] (8), which upon Ir(I)-catalyzed hydrolytic oxidation gives the structurally characterized silanol complex [{(o- iPr₂PC₆H ₄)₂SiOH}PtCl] (3). Complex 3, comprising in its structure the nucleophilic silanol fragment and electrophilic Pt(II)-Cl moiety, exhibits dual reactivity. Its reaction with the non-nucleophilic KB(C₆F ₅)₄ in fluorobenzene leads to the ionic complex [{(o- iPr₂PC₆H₄)₂SiOH}Pt]⁺ [(C₆F₅)₄B]^- (9), which reacts with CO to yield the structurally characterized [{(o- iPr₂PC ₆H₄)₂SiOH}PtCO]⁺ [(C ₆F₅)₄B]^- (10). Treatment of 3 with non-nucleophilic bases leads to unprecedented rearrangement and coupling, resulting in the structurally characterized, unusual binuclear complex 11. The structure of 11 comprises two different fragments: the original O-Si-Pt(II)-Cl pattern, and the newly formed silanolate Pt(II)-H pattern, which are connected via a disiloxane bridge. Complex 9 undergoes a similar hydrolytic rearrangement in the presence of iPr₂NEt to give the mononuclear silanolate Pt(II)-H complex 17. Both these rearrangement-coupling reactions probably involve the inner-sphere generation of an intermediate silanone 14, which undergoes nucleophilic attack by the starting silanol 3 to yield complex 11, or adds a water molecule to yield complex 17. X-ray diffraction studies of 3, 10, and 11 exhibit a very short Si-Pt bond length (2.27-2.28 Å) in the neutral complexes 3 and 11 that elongates to 2.365 Å in the carbonyl complex 10. A significantly compressed geometry of the silanolate platinum(II)-hydride fragment B of the binuclear complex 11 features a Pt(2)-O(2)-Si(2) angle of 100.4 (3)° and a remarkably short Pt(2)⋯Si(2) [2.884 (3) Å] distance.