613673-01-1Relevant articles and documents
Iridium- and rhodium-silanol complexes: Synthesis and reactivity
Goikhman, Roman,Aizenberg, Michael,Shimon, Linda J.W.,Milstein, David
, p. 4020 - 4024 (2008/10/08)
Methods of metallo-silanol synthesis have been developed. The Ir(I) complex (Et3P)2Ir(C2H4)Cl (1) oxidatively adds secondary silanols R2SiHOH (R = iPr, tBu) to yield the iridium-silanol complexes [(Et3P)2Ir(H)(Cl)(SiR2OH)] (R = iPr, 2; R = tBu, 3). The crystal structure of 2 exhibits a trigonal-bipyramidal geometry, and intermolecular Si-O-H- - -Cl hydrogen bonding is present. Deprotonation of 2 results in the highly thermodynamically stable metallo-silanolate [(Et3P)2Ir(H)(Cl) (SiiPr2OLi)]2 (4). Compound 4 has an almost planar core, consisting of two atoms each of iridium, silicon, chlorine, oxygen, and lithium. Upon treatment of (Et3P)3RhCl with HSiiPr2OH, the first Rh-silanol complex, trans-[(Et3P)2Rh(H)(Cl)(iPrSi2OH)], is formed in an equilibrium with the starting complex (Keq = 4 × 10-3); hence, the reaction is dependent on the concentration of the silanol and Et3P, an excess of the latter shifting the equilibrium to the starting compounds. Reaction of the bis-phosphine complex [(Et3P)2RhCl]2 with the silanol, which does not generate free phosphine, results in 96% conversion to the adduct. On the other hand, the chelating bis-phosphine complex [(bis-(diisopropylphosphino)propane)RhCl]2 does not add the silanol even in the presence of a 10-fold excess of the silanol, indicating that the cis-phosphine configuration in the adduct is unfavorable. In contrast to the Et3P-containing Ir complex, and similarly to the Rh complex, (PPh3)3Ir(CO)H reacts with iPr2SiHOH reversibly, leading to 60% conversion to the metallosilanol (PPh3)2Ir(CO)(H)2(SiiPr2O H) (6). A stable PPh3-containing Ir-silanol was prepared by starting from (PPh3)2Ir(CO)(H)2(Si(SEt)3). Following reaction with Et3SiOSO2CF3 to exchange one SEt substituent with OSO2CF3, reaction with NaOH generates the stable silanol complex (PPh3)2Ir(CO)(H)2(Si(SEt)2OH) (14).
