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Type: Artigo de periódico
Title: Synthesis and structural characterisation of [Ir-4(Co)(8)(CH3)(mu(4)-eta(3)-Ph2PCCPh)(mu-PPh2) and of the carbonylation product [Ir-4(CO)8{C(O)CH3}(mu(4)-eta(3)-Ph2PCCPh)(mu-PPh2)]; First evidence for the formation of a CO cluster adduct before CO insertion
Author: Braga, D
Fujiwara, FY
Grepioni, F
Pereira, RMS
Vargas, MD
Abstract: Deprotonation of [(mu-H)Ir-4(CO)(10)(mu-PPh2)], 1, gives [Ir-4(CO)(10)(mu-PPh2)](-) that reacts with Ph2PCCPh and CH3I to afford [Ir-4(CO)(8)(CH3)(mu(4)-eta(3)-Ph2PCCPh)(mu-PPh2)], 2 (34%), besides [Ir-4(Co)(9)(mu(3)-eta(3)-Ph2PC(H)CPh)(mu-PPh2)] and [(mu-H)Ir-4(CO)(9)(Ph2PC=CPh)(mu-PPh2)]. Compound 2 was characterised by a single crystal X-ray diffraction analysis and exhibits a flat butterfly of metal atoms, with the Ph2PCCPh ligand interacting with all four Ir atoms and the methyl group bonded terminally to a wingtip Tr atom. Carbonylation of 2 yields initially (25 degrees C, 20 min) a CO addition product that, according to VT P-31{H-1} and C-13{H-1} studies, exists in solution in the form of two isomers 4A and 4B (8:1), and then (40 degrees C, 7 h), the CO insertion product [Ir-4(CO)(8){C(O)CH3}-(mu(4)-eta(3)-Ph2PCCPh)(mu-PPh2)], 5. The molecular structure of 5, established by an X-ray analysis, is similar to that of 2, except for the acyl group that remains bound to the same Ir atom. The process is reversible at both stages. Treatment of 2 with PPh3 and P(OMe)(3) affords the CO substitution products [Ir-4(CO)(7)L(CH3)(mu(4)-eta(3)-Ph2PCCPh)(mu-PPh2)] (L = PPh3, 6 and P(OMe)(3), 7), instead of the expected CO inserted products. According to the H-1 and P-31{H-1} NMR studies, the PPh3 derivative 6 exists in the form of two isomers (1:1) that differ with respect to the position of this ligand.
Subject: migratory insertion
iridium carbonyl clusters
alkyl clusters
Country: Brasil
Editor: Soc Brasileira Quimica
Rights: aberto
Date Issue: 1999
Appears in Collections:Artigos e Materiais de Revistas Científicas - Unicamp

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