Synthesis and reactivity of an iridium complex based on a tridentate aminophosphano ligand.

The iridium(III) hydride compound [IrH{κ 3 C , P , P '-(SiNP-H)}(CN t Bu) 2 ][PF 6 ] (1PF 6 ) was obtained by reaction of [Ir(SiNP)(cod)][PF 6 ] with CN t Bu as the result of the intramolecular oxidative addition of the SiCH 2 -H bond to iridium(I) [SiNP = Si(CH 3 ) 2 {N(4-tolyl)PPh 2 } 2 , SiNP-H = CH 2 Si(CH 3 ){N(4-tolyl)PPh 2 } 2 ]. The mechanism of the reaction was investigated by NMR spectroscopy and DFT calculations showing that the pentacoordinated intermediate [Ir(SiNP)(cod)(CN t Bu)][PF 6 ] (2PF 6 ) forms in the first place and that further reacts with CN t Bu, affording the square planar intermediate [Ir(SiNP)(CN t Bu) 2 ][PF 6 ] (3PF 6 ) that finally undergoes the intramolecular oxidative addition of the SiCH 2 -H bond. The reactivity of 1PF 6 was investigated. On one hand, the reaction of 1PF 6 with N -chlorosuccinimide or N -bromosuccinimide provides the haloderivatives [IrX{κ 3 C , P , P '-(SiNP-H)}(CN t Bu) 2 ][PF 6 ] (X = Cl, 4PF 6 ; Br, 5PF 6 ), and the reaction of 5PF 6 with AgPF 6 in the presence of acetonitrile affords the solvato species [Ir{κ 3 C , P , P '-(SiNP-H)}(CH 3 CN)(CN t Bu) 2 ] 2+ (6 2+ ) isolated as the hexafluorophosphate salt. On the other hand, the reaction of 1PF 6 with HBF 4 gives the iridium(III) compound [IrH(CH 2 SiF 2 CH 3 )(HNP) 2 (CN t Bu) 2 ][BF 4 ] (7BF 4 ) as the result of the formal addition of hydrogen fluoride to the Si-N bonds of 1 + [HNP = HN(4-tolyl)PPh 2 ]. A similar outcome was observed in the reaction of 1PF 6 with CF 3 COOH rendering 7PO 2 F 2 . In this case the intermediate [IrH{κ 2 C , P -CH 2 SiMeFN(4-tolyl)PPh 2 }(HNP)(CN t Bu) 2 ] + (8 + ) was observed and characterised in situ by NMR spectroscopy. DFT calculations suggests that the reaction goes through the sequential protonation of the nitrogen atom of the Si-N-P moiety followed by the formal addition of fluoride ion to silicon. Also, the crystal structures of SiNP, 1PF 6 , 4PF 6 and 7BF 4 have been determined by X-ray diffraction measurements.