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Issue 18, 2000
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Deprotonation of [Mo(COMe)(CO)2(PPh2H)(η-C5H5)] and reaction with activated alkynes: controllable formation of vinylphosphine and η3-acryloyl ligands

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Abstract

Deprotonation of the secondary phosphine ligand in the complex [Mo(COMe)(CO)2(PPh2H)(η-C5H5)] 1 with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) at −78 °C followed by reaction with DMAD (dimethyl acetylenedicarboxylate, MeO2CC[triple bond, length as m-dash]CCO2Me) afforded the vinylphosphine complex trans-[Mo(COMe)(CO)2{PPh2C(CO2Me)[double bond, length half m-dash]CHCO2Me}(η-C5H5)] 2a after protonation. The crystal structure of this compound confirms that the phosphine ligand is formed exclusively as the Z isomer. A similar reaction employing methyl propiolate afforded an analogous product [Mo(COMe)(CO)2(PPh2CH[double bond, length half m-dash]CHCO2Me)(η-C5H5)] 2b with complete regioselectivity but less stereoselectivity in that three isomers (trans-E, trans-Z and cis-E) are formed in a ratio of 9.4∶2.8∶1. Deprotonation of 1 at room temperature, which has previously been shown to form the anion [Mo(CO)2(PPh2COMe)Cp] by migration of the acetyl group to phosphorus, followed by treatment with DMAD and rapid addition of acid produces the acryloyl complex [Mo{COC(CO2Me)[double bond, length half m-dash]CHCO2Me}(CO)(PPh2COMe)(η-C5H5)] 3a, accompanied by the chelating vinyl species [Mo{C(CO2Me)[double bond, length half m-dash]CHCOOMe}(CO)2(η-C5H5)] 4. A similar reaction with methyl propiolate gave [Mo(η3-COCH[double bond, length half m-dash]CHCO2Me)(CO)(PPh2COMe)(η-C5H5)] 3b but in this case the isomeric vinyl complex trans-[Mo(CH[double bond, length half m-dash]CHCO2Me)(CO)2(PPh2COMe)(η-C5H5)] 5 was formed as the minor product. Finally, deprotonation of 1 at room temperature followed by treatment with DMAD without subsequent addition of acid gives the metallacycle [Mo{PPh2COCH[double bond, length half m-dash]C(CO2Me)}(CO)2(η-C5H5)] 6.

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Publication details

The article was received on 10 May 2000, accepted on 27 Jul 2000 and first published on 18 Aug 2000


Article type: Paper
DOI: 10.1039/B003739G
Citation: J. Chem. Soc., Dalton Trans., 2000, 3074-3081
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    Deprotonation of [Mo(COMe)(CO)2(PPh2H)(η-C5H5)] and reaction with activated alkynes: controllable formation of vinylphosphine and η3-acryloyl ligands

    H. Adams, N. A. Bailey, P. Blenkiron and M. J. Morris, J. Chem. Soc., Dalton Trans., 2000, 3074
    DOI: 10.1039/B003739G

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