Deprotonation of [Mo(COMe)(CO)_2(PPh_2H)(#eta#-C_5H_5)] and reaction with activated alkynes: controllable formation of vinylphosphine and #eta#~3-acryloyl ligands

摘要

Deprotonation of the secondary phosphine ligand in the complex [Mo(COMe)(CO)_2(PPh_2H)(#eta#-C_5H_5)] 1 with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) at -78 deg C followed by reaction with DMAD (dimethyl acetylenedicarboxylate, MeO_2CC (ident to) CCO_2Me) afforded the vinylphosphine complex trans- [Mo(COMe)(CO)_2{PPh_2C(CO_Me)=CHCO_2Me}(#eta#-C_5H_5)] 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(PPh_2CH=CHCO_2Me)(#eta#-C_5H_5)] 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)(PPh_2COMe)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(CO_2Me)=CHCO_2Me}(CO)(PPh_2COMe)(#eta#-C_5H_5)] 3a, accompanied by the chelating vinyl species [Mo{C(CO_2Me)=CHCOOMe}(CO)_2(#eta#-C_5H_5)] 4. A similar reaction with methyl propiolate gave [Mo(#eta#~3-COCH=CHCO_2Me)(CO)(PPh_2COMe)(#eta#-C_5H_5)] 3b but in this case the isomeric vinyl complex trans-[Mo(CH=CHCO_2Me}(CO)_2(PPh_2COMe)(#eta#-C_5H_5)] 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{PPh_2COCH=C(CO_2Me)}(#eta#-C_5H_5)] 6.