Synthesis and reactivity of (mu)-butadienyl diruthenium cations

Propargyl alcohols HC6-point triple bond; length half of m-dashCCR2OH (R=H, Me or Ph) react with [Ru2(CO)(MeCN)((mu)-CO)((mu)-CH2)((eta)C5H5)2] (2) to form the allylidene complexes [Ru2(CO)((mu)-CO){(mu)(eta)^1,(eta)^3-C(CR2OH)CH=CH2}((eta)-C5H5)2] (4a, R=H; 4b, R=Me; 4c, R=Ph). Treatment of complexes 4a–c with HBF4 removes the hydroxide group as water, giving the 2-butadienyl complexes [Ru2(CO)((mu)-CO) ((mu)-(eta)^2,(eta)^3-CR2=CCH=CH2)((eta)-C5H5)2][BF4] (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 (R2) carbon to give the allylidene complexes [Ru2(CO)((mu)-CO){(mu)(eta)^1,(eta)^3-C(CR2H)CH=CH2}((eta)-C5H5)2] (6a, R=H; 7, R=Me; 11, R=Ph) and, in the case of 5c, the butadiene complex [Ru2(CO)2((mu)(eta)^2,(eta)^2-CPh2=CHCH=CH2)((eta)-C5H5)2] (12) and the allene complex [Ru2(CO)2((mu)-(eta)^2,(eta)^2-CPh2=C=CHMe)((eta)-C5H5)2] (13), formally due to attack at the (mu)-C and CH2 carbons, respectively. The complexes 5a–c react with methyl lithium to undergo nucleophilic attack predominantly at the C(R2) carbon, giving methylated allylidene complexes [Ru2(CO)((mu)-CO){(mu)-(eta)1,(eta)^3 -C(CR2Me)CH=CH2}((eta)-C5H5)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 [Ru2(CO)((mu)-CO){(mu)-(eta)^1,(eta) ^3-C(CMe=CH2)CH=CH2}((eta)-C5H5)2] (8) and the (mu)-butatriene complex [Ru2(CO)2((mu)-(eta)^2,(eta)^2-CPh2=C=C=CH2)((eta)-C5H5)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 {CH2=C(Me)C6-point triple bond; length half of m-dashCH} and t-butylacetylene, respectively. Treatment of complex 8 with HBF4 resulted in protonation at each of the methylene groups, affording 5b and isomeric [Ru2(CO)((mu)-CO){(mu)(eta)^2,(eta)^3-CH(Me)=CC(Me)=CH2}((eta)-C5H5)2][BF4] (10). The structures of 5b, 5c and 8 were established by X-ray diffraction.