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-/Pr2PC6H4)(2)SiH2 (7) with (Me2S)(2)Pt(Me)Cl yields the pincer-type hydrosilane complex [{(o- iPr(2)PC(6)H(4))(2)SiH)PtCl] (8), which upon lr(l)-catalyzed hydrolytic oxidation gives the structurally characterized silanol complex [{(o- iPr(2)PC(6)H(4))(2)SiOH]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(C6F5)(4) in fluorobenzene leads to the ionic complex [{(o- iPr(2)PC(6)H(4))(2)SiOH)Pt](+) [(C6F5)(4)B](-)(9), which reacts with CO to yield the structurally characterized [{(o- iPr(2)PC(6)H(4))(2)SiOH)PtCO](+) [(C6F5)(4)B](-) (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 iPr(2)NEt 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 angstrom) in the neutral complexes 3 and 11 that elongates to 2.365 angstrom 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)degrees and a remarkably short Pt(2)...Si(2) (2.884 (3) angstrom] distance.