Stabilization of Trans Disilyl Coordination at Square-Planar Platinum Complexes

Abstract

By using two different multidentate phosphinosilyl ligands, we prepared the two platinum complexes [Pt{PhP((o-C 6 H 4 )CH 2 SiMe 2 ) 2 }PPh 3 ] (3) and [Pt{P((o-C 6 H 4 )CH 2 SiMe 2 ) 2 (o-C 6 H 4 )CHSiMe 2 )}PPh 3 ] (4) exhibiting a trans configuration of the silicon atoms in a typical square-planar geometry around a Pt(II) center. Complex 4 results from intramolecular C− H activation of a methylene moiety by the third silicon atom of the original ligand and displays an anagostic C−H•••Pt interaction, as supported by solution NMR data and solid-state X-ray diffraction analysis. The reactivity of 3 toward small molecules is also discussed. In the case of H 2 and CO, the corresponding dihydride [PtH 2 {PhP((o-C 6 H 4 )CH 2 SiMe 2 ) 2 }PPh 3 ] (5) and dicarbonyl [Pt{PhP((o-C 6 H 4 )CH 2 SiMe 2 ) 2 }(CO) 2 ] (6) complexes were characterized, whereas reduction to Pt(0) and release of PPh 3 and HSiMe 3 were observed upon thermolysis in the presence of HBpin.

Modulation of an Anagostic Interaction in SiPSi-Type Pincer Platinum Complexes

“…Previously, we had reported the reaction of the related complex [Pt{PhP(o-C 6 H 4 -CH 2 SiMe 2 ) 2 }PPh 3 ] with CO leading to the dicarbonyl [Pt{PhP(o-C 6 H 4 -CH 2 SiMe 2 ) 2 }-(CO) 2 ] (A). 15 However, in our case, the experimental and theoretical evidence is not consistent with the formation of a saturated species, and we propose the monocarbonyl formulation 5) (Scheme 2). As in the case of complex A, removal of the solvent upon vacuum or changing the CO atmosphere to argon resulted in the recovery of 2, which prevented the isolation of complex 5.…”

“…10−14 As part of our program for studying the chemistry of coordination of silylphosphine ligands to transition metals, we recently reported the quantitative reaction of tris- created from the third Si atom (Scheme 1). 15 We pointed out a C−H−Pt anagostic interaction at the apical position from one hydrogen of the methylene attached to the noncoordinated Si.…”

“…The downfield shift of the Scheme 1. Reactions of [Pt(PPh 3 ) 3 ] with Tribenzylsilylphosphines 1 15 anagostic hydrogen is well within the range proposed by several authors. 1,3,16,17 As for complex 2, the 31 P{ 1 H} NMR spectra of 3 or 4 display two signals exhibiting large 2 J P−P coupling constants indicative of a trans disposition of the two P ligands (357 and 552 Hz for 3 and 4, respectively).…”

“…19−23 Crystals of 4 suitable for single-crystal X-ray diffraction analysis were grown from evaporation of a toluene/pentane solution at room temperature. As expected, the molecular structure (Figure 2, ESI) greatly resembles that of complex 2, 15 with bond distances and angles very similar for the "PSi 3 " ligand, the main difference being the substitution of PPh 3 with P(OPh) 3 . The close to ideal square planar geometry around the platinum center is confirmed as well as the trans disposition of the Si atoms characterized by a Si1−Pt−Si2 angle of 174.04(2)°, even larger than the corresponding angle in 2 [169.43(4)°], to the best of our knowledge the largest experimentally measured in a Pt(II) system.…”

Versatile Silylphosphine Ligands for Transition Metal Complexation

“…There are various reasons for this behaviour including an excellent sigma orbital overlap as well as a favourable electronic release of the Si [4,5]. This is in agreement with only a few compounds exhibiting a trans coordination of the Si atoms in many cases as kinetic products in equilibria with their cis isomers [6,7] even when employing chelating silylphosphines (vide supra) [8][9][10][11] (Section 8).…”