Reversible Cyclometalation of Silyl Ligands. First X-ray Structure of an Iridium(I) Silyl That Is Not Stabilized by Chelation

The iridasilacycle fac -(PMe 3 ) 3 Ir( o -C 6 H 4 SiMe 2 )(H) ( 1 ) results from the ortho metalation of the transient (PMe 3 ) 3 Ir(SiMe 2 Ph) ( 7 ), generated from Ir(PMe 3 ) 4 Cl and PhMe 2 SiLi at ambient temperature. Complex 1 can also be obtained from fac -(PMe 3 ) 3 Ir(CH 3 )(H)(SiMe 2 Ph) ( 6 ), which, when heated, reductively eliminates methane. 1 and its analog fac -(PMe 3 ) 3 Ir( o -C 6 H 4 SiPh 2 )(H) ( 2 ), react with hydrogen at 80 °C to yield the dihydridosilyliridium(III) complexes fac -(PMe 3 ) 3 Ir(SiR 2 Ph)(H) 2 ( 3, R = Me; 4, R = Ph). The reaction of 1 with deuterium demonstrates that initial opening of the iridasilacycle takes place, followed by D−D oxidative addition to 7 . The reaction of 1 with CO allows us to trap the iridium(I) species and provides a synthetic route to Ir(PMe 3 ) 2 (CO) 2 (SiMe 2 Ph) ( 5 ). Complex 5 was identified by spectroscopy and by X-ray crystallography and was synthesized independently from 3 and CO. The chemistry presented shows that metalation of silyl ligands can be a facile reversible process that takes place under mild conditions. It also indicates that iridasilacycles can be used as a masked form of electron-rich Ir(I) silyl complexes, which are not readily accessible species.