Alkyl- und arylkomplexe des iridiums und rhodiums: XIII. Modellhafte intermediate der phosphitinduzierten co-insertions- und benzyl-CH-additionsreaktion ortho-alkylsubstituierter iridiumaryle

Abstract

Infrared spectroscopic evidence is presented to show that formation of the metallacyclic iridaindanone compound IrH[C(O)C 6H 2Me 2-(4,6)C H 2-(2)][P(OPh) 3] 3 from Ir(CO)[C 6H 2Me 3-(2,4,6)](PPh 3) 2 (I) and triphenyl phosphite proceeds via mono and disubstituted iridium(I) aryls of type trans-Ir(CO)[C 6H 2Me 3-(2,4,6)](L)[P(OPh) 3] with L  PPh 3 (II) or P(OPh) 3 (III). Complexes II and III have been prepared on an independent route from Ir(CO)(Cl)(L)[P(OPh) 3] and mesityl lithium. Since III has been found unreactive with respect to intramolecular ortho-methyl CH addition, the ring-closure step Ir(CO)[C 6H 2Me 3-(2,4,6)]-[P(OPh) 3] 2/P(OPh) 3 → IrH [C(O)C 6H 2Me 2(4,6)-CH 2(2)][P(OPh) 3] 3 does not appear to involve an intermediate species IrH[C(O)C 6H 2Me 2(4,6)-C H 2(2)](CO)[P(OPh) 3] 2 capable of phosphite-assisted CO insertion into its four-membered chelate system. A reaction scheme considering spontaneously cyclometallating acyls such as Ir(C(O)C 6H 2Me 3-(2,4,6)][P(OPh) 3] 3 as possible iridaindanone precursors is therefore suggested. Although the 16 e insertion products themselves could not be exemplified, coordinatively saturated model compounds Ir[C(O)R](CO) m (PPh 3) n ( m  n  2: R  CH 2CMe 3 (IV), CH 2SiMe 3 (V), C 6H 4Me-(2) (VI), C 6H 3Me 2-(2,4) (VII); m  3, n  1: R  C 6H 3Me 2-(2,6)_(VIII)) have readily been obtained by carbonylation of the respective alkyls and aryls Ir(CO)(R)(PPh 3) 2. Based on IR and low-temperature 31P NMR data, a trigonal-bipyramidal ground-state with equatorial CO and axial acyl ligands is assigned to complexes IV–VIII which, in solution, exhibit fluxional behaviour at room temperature.