Synthesis and Characterization of Neutral and Cationic Platinum(II) Complexes Featuring Pincer-like Bis(phosphino)silyl Ligands: Si−H and Si−Cl Bond Activation Chemistry

The synthesis and characterization of a new series of Pt(II) complexes bearing the tridentate bis(phosphino)silyl ligands [κ 3 -(2-R 2 P C 6 H 4 ) 2 Si Me] − ([R-PSiP], R = Ph, Cy) are reported. The tertiary silane [Ph-PSiP]H reacted with PtCl 2 (SEt 2 ) 2 to afford [Ph-PSiP]PtCl ( 1 ), which was structurally characterized. Alkyl derivatives of 1 were prepared in high yields by the reaction of 1 with either PhCH 2 K to afford [Ph-PSiP]PtCH 2 Ph ( 2 ) or MeLi to afford [Ph-PSiP]PtMe ( 3 ). The X-ray crystal structure of 2·CH 2 Cl 2 was obtained and confirmed a square-planar geometry about Pt, with the benzyl ligand positioned trans to Si. Treatment of either 2 or 3 with 1 equiv of B(C 6 F 5 ) 3 in benzene solution led to the formation of the corresponding cationic species {[Ph-PSiP]Pt} + [RB(C 6 F 5 ) 3 ] − (R = CH 2 Ph, 4; R = Me, 5 ). X-ray quality crystals of 4(OEt 2 )·OEt 2 were grown from an Et 2 O solution of 4; the crystal structure of 4(OEt 2 )·OEt 2 features an Et 2 O molecule coordinated to the cationic Pt center, resulting in square-planar coordination geometry at Pt. Both 4 and 5 underwent a subsequent reaction to generate [Ph-PSiP]Pt(C 6 F 5 ) ( 6 ). Treatment of 1 with 1 equiv of Li[B(C 6 F 5 ) 4 ](OEt 2 ) 2.5 in fluorobenzene afforded {[Ph-PSiP]Pt(OEt 2 )} + [B(C 6 F 5 ) 4 ] − ( 7(OEt 2 ) ). Although the reaction of 1 with AlCl 3 led to a mixture of products, crystallization attempts enabled the isolation of a minute quantity of fluorobenzene-solvated [Ph-PSiP]PtCl·AlCl 3 ( 1(AlCl 3 )·(C 6 H 5 F) 2 ), which was crystallographically characterized and features a chloride ligand bridging the Pt and Al centers. The dicyclohexylphosphino derivative [Cy-PSiP]H reacted with PtCl 2 (SEt 2 ) 2 in the presence of Et 3 N to afford [Cy-PSiP]PtCl ( 8 ), which reacted with AgOTf to form [Cy-PSiP]PtOTf ( 9 ). Heating of either 8 or 9 for extended periods in benzene solution in the presence of amine bases did not result in benzene activation. Treatment of 8 with RLi reagents (R = Me, Ph) afforded the corresponding methyl ([Cy-PSiP]PtMe, 10 ) and phenyl ([Cy-PSiP]PtPh, 11 ) complexes, the latter of which was crystallographically characterized. As was observed for 3, compound 10 reacted with 1 equiv of B(C 6 F 5 ) 3 to form {[Cy-PSiP]Pt} + [MeB(C 6 F 5 ) 3 ] − ( 12 ), which upon heating in benzene afforded [Cy-PSiP]Pt(C 6 F 5 ) ( 13 ) with loss of MeB(C 6 F 5 ) 2 . Treatment of 8 with LiEt 3 BH led to the formation of [Cy-P Si (μ-H)P] Pt ( 14 ), which was identified on the basis of NMR and IR spectroscopic data as a bis(phosphino) Pt derivative of [Cy-PSiP]H that features η 2 -Si-H coordination involving the tethered silicon fragment. Although complexes 2, 3, and 10 did not react with an atmosphere of H 2, these compounds reacted readily with 1 equiv of PhSiH 3 to form the corresponding silyl complexes ([Ph-PSiP]PtSiH 2 Ph, 15; [Cy-PSiP]PtSiH 2 Ph, 16 ) upon loss of toluene or methane, respectively. While 2 and 3 also reacted with 1 equiv of Ph 2 SiHCl to form the silyl complex [Ph-PSiP]PtSiPh 2 Cl ( 17 ), 10 reacted with either Ph 2 SiHCl or i Pr 2 SiHCl to form [Cy-PSiP]PtCl ( 8 ). Complex 10 also reacted with 1 equiv of Me 3 SiCl to form 8 and Me 4 Si upon heating. Although complex 11 also reacted with hydridochlorosilanes to form 8, these reactions were significantly slower relative to 10 . In contrast to 10 and 11, the η 2 -Si-H complex 14 reacted with 1 equiv of either PhSiH 3 or Ph 2 SiHCl to form the corresponding Pt silyl complexes 16 and [Cy-PSiP]PtSiPh 2 Cl ( 18 ), with loss of H 2 .