Chemistry of phosphide-bridged dimolybdenum complexes. Part 6. The insertion of allene into co-ordinated µ-vinyl and η3-allyl ligands; X-ray crystal structures of [Mo2(η-C5H5)2(µ-PMe2){η3-CH2C(CH2)C(Me)CH2}(CO)3] and [Mo2(η-C5H5)2{µ-η5-CH2C(CH2)C(Me)CH2}(µ-PMe2)(CO)2]

Abstract

Prolonged photolysis of [Mo₂(η-C₅H₅)₂(µ-H)(µ-PMe₂)(CO)₄] in the presence of allene gives the new complexes [Mo₂(η-C₅H₅)₂{µ-η⁵-CH₂C(CH₂)C(Me)CH₂}(µ-PMe₂)(CO)₂] and [Mo₂(η-C₅H₅)₂(µ-PMe₂){η³-CH₂C(CH₂)C(Me)CH₂}(CO)₃] the structures of which in the solid state have been determined by single-crystal X-ray analyses. The former of these new complexes is also obtained in the reaction of the µ-vinyl complex [Mo₂(η-C₅H₅)₂{µ-σ:η²-C(Me)CH₂}(µ-PMe₂)(CO)₃] with allene but not in the reaction of the isomeric η³-allyl complex [Mo₂(η-C₅H₅)₂(µ-PMe₂)-(η³-C₃H₅)(CO)₃] with allene. On the other hand the syn-methylallyl complex [Mo(η-C₅H₅)₂(µ-PMe₂)(η³-syn-MeCHCH₂CH₂)(CO)₃] does react with allene to give a ca. 1:2 inseparable mixture of [Mo₂(η-C₅H₅)₂{µ-η⁵-CH₂C(CH₂)C(Me)CHMe}(µ-PMe₂)(CO)₂] and [Mo₂(η-C₅H₆)₂{µσ:η⁵-CH₂C(CH₂)C(Et)CH₂}(µ-PMe₂)(CO)₂]. These complexes may be obtained separately from reactions of the appropriate µ-vinyl complexes with allene. The mechanism of formation of the new complexes is discussed in the light of the above experimental results.