Synthesis, characterization and reactions of [RhCl(CO){(Ph2P(CH2CH2O)m CH2CH2Ph2-P,P′)}]n (m=3, 4, 5 n=1, 2...) metallacrown crown ethers

The reactions of [RhCl(cod)](2) and Ph2P(CH2CH2O)(n)CH2CH2PPh2P (n = 3, 4, 5) under a CO atmosphere yield [RhCl(CO){(Ph2P(CH2CH2O)(n) CH2CH2Ph2 P,P')}](m) monocarbonyl metallacrown ethers. These complexes are mixtures of cyclic n-mers and monomers with trans coordination geometries at the rhodium. The monocarbonyl rhodium metallacrown ethers reversibly react with CO at atmospheric pressure to form [RhCl(CO)(2){(Ph2P(CH2CH2O)(n)CH2CH2Ph2-P,P')}](m) dicarbonyl metallacrown ethers. These complexes are only stable under a CO atmosphere as demonstrated by P-31{H-1} NMR spectroscopy. Upon prolonged exposure to the atmosphere, all the monocarbonyl metallacrown ethers lose CO and undergo phosphine ligand oxidation to form [RhCl(H2O){Ph2P(O)(CH2CH2O)(n)CH2CH2P(O)Ph-2-O,O'}] metallacrown ethers. These are the first examples of metallacrown ethers in which the transition metal is coordinated via phosphine oxide donors. (C) 2018 Elsevier B.V. All rights reserved.