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 PSiH 2P-type ligand ( o-IPr 2PC 6H 4) 2SiH 2 ( 7) with (Me 2S) 2Pt(Me)Cl yields the pincer-type hydrosilane complex [{( o- iPr 2PC 6H 4) 2SiH}PtCl] ( 8), which upon Ir(I)-catalyzed hydrolytic oxidation gives the structurally characterized silanol complex [{( o- iPr 2PC 6H 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(C 6F 5) 4 in fluorobenzene leads to the ionic complex [{( o- iPr 2PC 6H 4) 2SiOH}Pt] (+) [(C 6F 5) 4B] (-) ( 9), which reacts with CO to yield the structurally characterized [{( o- iPr 2PC 6H 4) 2SiOH}PtCO] (+) [(C 6F 5) 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 iPr 2NEt 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 A) in the neutral complexes 3 and 11 that elongates to 2.365 A 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) A] distance.