Synthesis and reactivity of μ-butadienyl diruthenium cations

Abstract

Propargyl alcohols HCCCR 2OH (R=H, Me or Ph) react with [Ru 2(CO)(MeCN)(μ-CO)(μ-CH 2)(η-C 5H 5) 2] ( 2) to form the allylidene complexes [Ru 2(CO)(μ-CO){μ-η 1,η 3-C(CR 2OH)CHCH 2}(η-C 5H 5) 2] ( 4a, R=H; 4b, R=Me; 4c, R=Ph). Treatment of complexes 4a– c with HBF 4 removes the hydroxide group as water, giving the 2-butadienyl complexes [Ru 2(CO)(μ-CO)(μ-η 2,η 3-CR 2CCHCH 2)(η-C 5H 5) 2][BF 4] ( 5a, R=H; 5b, R=Me; 5c, R=Ph). The reactivity of 5a– c towards nucleophiles and bases is described. With hydride, 5a– c undergo nucleophilic attack at the C(R 2) carbon to give the allylidene complexes [Ru 2(CO)(μ-CO){μ-η 1,η 3-C(CR 2H)CHCH 2}(η-C 5H 5) 2] ( 6a, R=H; 7, R=Me; 11, R=Ph) and, in the case of 5c, the butadiene complex [Ru 2(CO) 2(μ-η 2,η 2-CPh 2CHCHCH 2)(η-C 5H 5) 2] ( 12) and the allene complex [Ru 2(CO) 2(μ-η 2,η 2-CPh 2CCHMe)(η-C 5H 5) 2] ( 13), formally due to attack at the μ-C and CH 2 carbons, respectively. The complexes 5a– c react with methyl lithium to undergo nucleophilic attack predominantly at the C(R 2) carbon, giving methylated allylidene complexes [Ru 2(CO)(μ-CO){μ-η 1,η 3-C(CR 2Me)CHCH 2}(η-C 5H 5) 2] ( 6b, R=Me; 9, R=Me; 14, R=Ph). With 5b and 5c methyl lithium also acts as a base, abstracting protons to give the novel divinylcarbene complex [Ru 2(CO)(μ-CO){μ-η 1,η 3-C(CMeCH 2)CHCH 2}(η-C 5H 5) 2] ( 8) and the μ-butatriene complex [Ru 2(CO) 2(μ-η 2,η 2-CPh 2CCCH 2)(η-C 5H 5) 2] ( 15), respectively. Complexes 8 and 15 are formed exclusively by treating 5b and 5c, respectively, with diazabicyclo[5.4.0]undec-7-ene (DBU). Complexes 8 and 9 were also prepared in good yield by reaction of complex 2 with 2-methyl-1-buten-3-yne {CH 2C(Me)CCH} and t-butylacetylene, respectively. Treatment of complex 8 with HBF 4 resulted in protonation at each of the methylene groups, affording 5b and isomeric [Ru 2(CO)(μ-CO){μ-η 2,η 3-CH(Me)CC(Me)CH 2}(η-C 5H 5) 2][BF 4] ( 10). The structures of 5b, 5c and 8 were established by X-ray diffraction.