Silanol-Based Pincer Pt(II) Complexes: Synthesis, Structure, and Unusual Reactivity

Abstract

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.

Activation of Molecular Hydrogen and Oxygen by PSiP Complexes of Cobalt

“…Related reactivity involving oxidation at Si exclusively has also been reported (Figure , H – L ). Milstein and co‐workers observed that exposure of a Pt II ‐chloride precursor supported by a bis(diisopropylphosphanyl)silyl ligand featuring an Si‐H unit to air in benzene solution over the course of a month afforded a Pt II ‐metallosilanol species (Figure , H ). This reactivity was accelerated by addition of an Ir catalyst that had previously been shown to facilitate the hydrolytic oxidation of organosilanes to silanols .…”

Synthesis and Characterization of α,α-Dimethyl-4-[1-Hydroxy-4-[4-(Hydroxyldiphenyl- Methyl)-1-Piperidinyl]Butyl] Benzeneacetic Acid Metal Complexes of Biological Interest

“…Fexofenadine showed C=O stretching at 1700 cm -1 due to carboxylic group which shifted to 1680 cm -1 as doublet strong band in magnesium complex whereas in cadmium, calcium, chromium, manganese, iron chloride, iron sulfate, iron ammonium citrate, cobalt, nickel, copper and zinc complexes this band appeared in the region 1715-1720 cm -1 [24,25] complexes indicating the coordination of this moiety to the metal ions [26] (Figure 7).…”

Late Transition‐Metal Complexes of 2‐Ph2PC6H4NHC(O)CH2NHCO2Bz: Observation of Three Distinct Ligation Modes (κ1‐P,κ2‐P/N and κ3‐P/N/N′)

“…[17] Pincer ligands based on P/C/P [18] or P/Si/P [19] donor sets afford interesting complexes, display unusual reactivity and find applications in catalysis. Furthermore, P/O/O and P/O/P ligands have been employed in self-assembly reactions.…”