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A heterobimetallic complex featuring a Ti-Co multiple bond and its application to the reductive coupling of ketones to alkenes.

ABSTRACT: To explore metal-metal multiple bonds between first row transition metals, Ti/Co complexes supported by two phosphinoamide ligands have been synthesized and characterized. The Ti metalloligand Cl₂Ti(XylNPⁱPr₂)₂ (1) was treated with CoI₂ under reducing conditions, permitting isolation of the Ti/Co complex [(μ-Cl)Ti(XylNPⁱPr₂)₂CoI]₂ (2). One electron reduction of complex 2 affords ClTi(XylNPⁱPr₂)₂CoPMe₃ (3), which features a metal-metal triple bond and an unprecedentedly short Ti-Co distance of 2.0236(9) Å. This complex is shown to promote the McMurry coupling reaction of aryl ketones into alkenes, with concomitant formation of the tetranuclear complex [Ti(μ₃-O)(NXylPⁱPr₂)₂CoI]₂ (4). A cooperative mechanism involving bimetallic C[double bond, length as m-dash]O bond activation and a cobalt carbene intermediate is proposed.

SUBMITTER: Wu B

PROVIDER: S-EPMC5654242 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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A heterobimetallic complex featuring a Ti-Co multiple bond and its application to the reductive coupling of ketones to alkenes.

Wu Bing B Bezpalko Mark W MW Foxman Bruce M BM Thomas Christine M CM

Chemical science 20150119 3

To explore metal-metal multiple bonds between first row transition metals, Ti/Co complexes supported by two phosphinoamide ligands have been synthesized and characterized. The Ti metalloligand Cl2Ti(XylNPiPr2)2 (1) was treated with CoI2 under reducing conditions, permitting isolation of the Ti/Co complex [(μ-Cl)Ti(XylNPiPr2)2CoI]2 (2). One electron reduction of complex 2 afford ...[more]

PMID: 29142672

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Project description:The reactivity of the bis(pentalene)dititanium double-sandwich compound Ti2Pn†2 (1) (Pn† = 1,4-{SiiPr3}2C8H4) with CO2 is investigated in detail using spectroscopic, X-ray crystallographic, and computational studies. When the CO2 reaction is performed at -78 °C, the 1:1 adduct 4 is formed, and low-temperature spectroscopic measurements are consistent with a CO2 molecule bound symmetrically to the two Ti centers in a μ:η2,η2 binding mode, a structure also indicated by theory. Upon warming to room temperature the coordinated CO2 is quantitatively reduced over a period of minutes to give the bis(oxo)-bridged dimer 2 and the dicarbonyl complex 3. In situ NMR studies indicated that this decomposition proceeds in a stepwise process via monooxo (5) and monocarbonyl (7) double-sandwich complexes, which have been independently synthesized and structurally characterized. 5 is thermally unstable with respect to a μ-O dimer in which the Ti-Ti bond has been cleaved and one pentalene ligand binds in an η8 fashion to each of the formally TiIII centers. The molecular structure of 7 shows a "side-on" bound carbonyl ligand. Bonding of the double-sandwich species Ti2Pn2 (Pn = C8H6) to other fragments has been investigated by density functional theory calculations and fragment analysis, providing insight into the CO2 reaction pathway consistent with the experimentally observed intermediates. A key step in the proposed mechanism is disproportionation of a mono(oxo) di-TiIII species to yield di-TiII and di-TiIV products. 1 forms a structurally characterized, thermally stable CS2 adduct 8 that shows symmetrical binding to the Ti2 unit and supports the formulation of 4. The reaction of 1 with COS forms a thermally unstable complex 9 that undergoes scission to give mono(μ-S) mono(CO) species 10. Ph3PS is an effective sulfur transfer agent for 1, enabling the synthesis of mono(μ-S) complex 11 with a double-sandwich structure and bis(μ-S) dimer 12 in which the Ti-Ti bond has been cleaved.

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A heterobimetallic complex featuring a Ti-Co multiple bond and its application to the reductive coupling of ketones to alkenes.

Publications

A heterobimetallic complex featuring a Ti-Co multiple bond and its application to the reductive coupling of ketones to alkenes.

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