P[sbnd]C coupling reactions of pyramidal phosphinidene-bridged dimolybdenum complexes with alkynes

Abstract

The new pyramidal phosphinidene-bridged complex [Mo2Cp(μ-κ1: κ1,η5-PC5H4)(η6-HMes*)(CO)2{P(OMe)3}] (2b) was prepared in situ upon reaction of the trigonal phosphinidene complex [Mo2Cp(μ – κ1: κ1, η5-PC5H4)(η6-HMes*)(CO)2] (1) with P(OMe)3. This complex underwent an unexpected Michaelis-Arbuzov-like rearrangement when dissolved in tetrahydrofuran, to give the phosphanyl-phosphonate isomer [Mo2Cp{μ – κ1: κ1, η5-P(Me)C5H4}(η6-HMes*)(CO)2{P(O)(OMe)2}] in a quantitative way. The reactions of complex 2b, and also its PMe3 analogue [Mo2Cp(μ – κ1: κ1, η5-PC5H4)(η6-HMes*)(CO)2(PMe3)] (2a), with different internal alkynes (EtCCC(O)Me and MeCCCO2Me) and terminal alkynes (HCCR; R = 4-C6H4Me, C(O)Me, CO2Me) were then investigated. These reactions proceeded in all cases rapidly at room temperature (less than 1 min) with very high regioselectivity, to give the corresponding metallacyclic products [Mo2Cp{ μ – κ2P,C: κ1P, η5-P(C5H4)CR1CR2C(O)}(η6-HMes*)(CO)(PX3)] in high yield (X = Me, OMe; R1 = Et, Me, H; R2 = C(O)Me, CO2Me, 4-C6H4Me). Spectroscopic data for these complexes indicate that they all share the same structure, further confirmed through an X-ray single crystal study on the EtCCC(O)Me derivative of compound 2b.