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Reversible addition of ethylene to a pincer-based boryl-iridium unit with the formation of a bridging ethylidene.

ABSTRACT: This report examines reactions of a series of Ir complexes supported by the diarylboryl/bis(phosphine) PBP pincer ligand with ethylene: (PBP)IrH₄ (1), (PBP)IrH₂(CO) (2), and (PBP)Ir(CO)₂ (3). The outcomes of these reactions differ from those typical for Ir complexes supported by other pincer ligands and do not give rise to simple ethylene adducts or products of insertion of Ir into the C-H bond of ethylene. Instead, the elements of ethylene are incorporated into the molecules to result in B-C bonds. In the case of 2 and 3, ethylene addition results in the formation of B/Ir bridging ethylidene complexes 5 and 6. For 6, the addition of ethylene (and the analogous addition of 1-hexene) is shown to be partially reversible. Addition of ethylene to 2 and 3 is remarkable because they are saturated at Ir and yet the net outcome is such that ethylene binds without replacing any ligands already present. A mechanistic inquiry suggests that dissociation of CO from 3 or 6 is necessary in order for the addition or loss of ethylene to proceed.

SUBMITTER: Cao Y

PROVIDER: S-EPMC8162418 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The structure of [Ir{(4-Cl-C6H4N3)C(dppm)-κ3 P,C,N}(dppm-κ2 P,P')]Cl·1.5CH2Cl2·0.5C7H8 (C57H48Cl2IrN3P4·1.5CH2Cl2·0.5C7H8) (2), dppm = bis-(di-phenyl-phosphino)methane {systematic name: [7-(4-chloro-phen-yl)-1,1,3,3-tetra-phenyl-5,6,7-tri-aza-κN 7-1,3λ4-diphospha-κP 1-hepta-4,6-dien-4-yl][methyl-ene-bis(di-phenyl-phosphine)-κ2 P,P']iridium(I) chloride-di-chloro-methane-toluene (2/3/1)}, resulting from the reaction of [IrClH{C(dppm)2-κ3 P,C,P)(MeCN)]Cl (1a) with 1-azido-4-chloro-benzene, shows a monocationic five-coordinate IrI complex with a distorted trigonal-bipyramidal geometry. In 2, the iridium centre is coordinated by the neutral triazeneyl-idene-phospho-rane (4-Cl-C6H4N3)C(dppm) acting as a PCN pincer ligand, and a chelating dppm unit. The structure of the coordination compound [IrCl(CN)H(C(dppm)2-κ3 P,C,P)]·CH3CN, (C52H45ClIrNP4·CH3CN) (1b) [systematic name: chlorido-cyanidohydrido(1,1,3,3,5,5,7,7-octa-phenyl-1,3λ5,5λ4,7-tetra-phospha-κ2 P 1,P 7-hept-3-en-4-yl)iridium(III) aceto-nitrile monosolvate], prepared from 1a and KCN, reveals an octa-hedral IrIII central atom with a meridional PCP pincer carbodi-phospho-rane (CDP) ligand; the chloride ligand is located trans to the central carbon of the CDP functionality while the hydrido and cyanido ligands are situated trans to each other. The chiral coordination compound [Ir(CN)((4-Cl-C6H4N3)CH(CH(P(Ph)2)2)-κ3 P,C,N)(dppm-κ2 P,P')]·2CH3OH, (C58H48ClIrN4P4·2CH3OH) (3) (systematic name: {4-[3-(4-chloro-phen-yl)triazenido-κN 3]-1,1,3,3-tetra-phenyl-1,3λ5-diphospha-κP 1-but-2-en-4-yl}cyanido[methyl-enebis(di-phenyl-phosphine)-κ2 P,P']iridium(III) methanol disolvate), formed via prolonged reaction of 1-azido-4-chloro-benzene with 1b, features a six-coordinate IrIII central atom. The iridium centre is coordinated by the dianionic facial PCN pincer ligand [(4-Cl-C6H4N3)CH(CH(P(Ph2)2)2)], a cyanido ligand trans to the central carbon of the PCN pincer ligand and a chelating dppm unit. Complex 2 exhibits a 2:1 positional disorder of the Cl- anion. The CH2Cl2 and C7H8 solvent mol-ecules show occupational disorder, with the toluene mol-ecule exhibiting additional 1:1 positional disorder with some nearly overlying carbon atoms.

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Reversible addition of ethylene to a pincer-based boryl-iridium unit with the formation of a bridging ethylidene.

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