Deprotonation of [Mo(COMe)(CO)(2)(PPh2H)(eta-C5H5)] and reaction with activated alkynes: controllable formation of vinylphosphine and eta(3)-acryloylligands

Deprotonation of the secondary phosphine ligand in the complex [Mo(COMe)(CO )(2)(PPh2H)(eta-C5H5)] 1 with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) at - 78 degrees C followed by reaction with DMAD (dimethyl acetylenedicarboxylat e, MeO2CC=CCO2Me) afforded the vinylphosphine complex trans-[Mo(COMe)(CO)(2 ){PPh2C(CO2Me)=CHCO2Me}(eta-C5H5)] 2a after protonation. The crystal struct ure of this compound confirms that the phosphine ligand is formed exclusive ly as the Z isomer. A similar reaction employing methyl propiolate afforded an analogous product [Mo(COMe)(CO)(2)(PPh2CH=CHCO2Me)(eta-C5H5)] 2b with c omplete 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. Deprotonati on of 1 at room temperature, which has previously been shown to form the an ion [Mo(CO)(2)(PPh2COMe)Cp](-) by migration of the acetyl group to phosphor us, followed by treatment with DMAD and rapid addition of acid produces the acryloyl complex [Mo{COC(CO2Me)=CHCO2Me}(CO)(PPh2COMe)(eta-C5H5)] 3a, acco mpanied by the chelating vinyl species [Mo{C(CO2Me)=CHCOOMe}(CO)(2)(eta-C5H 5)] 4. A similar reaction with methyl propiolate gave [Mo(eta(3)-COCH=CHCO2 Me)(CO)(PPh2COMe)(eta-C5H5)] 3b but in this case the isomeric vinyl complex trans-[Mo(CH=CHCO2Me)(CO)(2)(PPh2COMe)(eta-C5H5)] 5 was formed as the mino r product. Finally, deprotonation of 1 at room temperature followed by trea tment with DMAD without subsequent addition of acid gives the metallacycle [Mo{PPh2COCH=C(CO2Me)}(CO)(2)(eta-C5H5)] 6.