de Montigny Frédéric, Macias Ramón, Noll Bruce C, Fehlner Thomas P, Costuas Karine, Saillard Jean-Yves, Halet Jean-François
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
J Am Chem Soc. 2007 Mar 21;129(11):3392-401. doi: 10.1021/ja068999z. Epub 2007 Feb 24.
Building on earlier work that showed the formation of [1-Cp*-2,2,2-(CO)3-2-THF-nido-1,2-IrMoB(4)H(8)], 2, from the reaction of [1-Cp*-arachno-1-IrB(4)H(10)], 1, with (arene)Mo(CO)3, the stoichiometric mechanism for the generation of [1-Cp*-5,6,7,8-(R)4-nido-1,5,6,7,8-IrC(4)B(3)H(3)], 8, from the reaction of 2 with RCCR, R = Me, Ph, has been identified. For R = Me, the major product in solution is [1-Cp*-5,6,7,8-(CH3)4-closo-1,5,6,7,8-IrC(4)B(3)H(3)Mo(CO)3], 7, which is in equilibrium with 8. The equilibrium 8 + Mo(THF)3(CO)3 <==> 7 + 3THF is characterized by DeltaH = 8 kcal/mol and DeltaS = 34 cal/mol K. Density functional theory calculations carried out on 7 indicate that the Mo(CO)3 moiety is weakly bound to the cluster mainly through Mo-C rather than Mo-B interactions. Under alkyne deficient conditions, the product [1-Cp*-2,2,2-(CO)3(mu-CO)-3,4-(CH3)2-closo-1,2,3,4-IrMoC(2)B(3)H(3)], 6, can be isolated. Solid-state structures of 1 and 2 have been reported previously, and those of 6, 7, and 8, R = Me, Ph, are reported here. The evolution of products with time was monitored by 1H and 11B NMR and showed the formation and decay of two additional species which have been identified as the structural isomers [1-Cp*-7,7,7-(CO)3-7-THF-2,3-(CH3)2-nido-1,7,2,3-IrMoC(2)B(3)H(5)], 4, and [5-Cp*-7,7,7-(CO)3-7-THF-2,3-(CH3)2-nido-5,7,2,3-IrMoC(2)B(3)H(5)], 5, with the metals nonadjacent in 4 and adjacent in 5. Circumstantial evidence suggests that 4 is the precursor to 5 and 5 is the precursor to both 6 and 7. Cluster 2 also is a catalyst or catalyst precursor for the isomerization of olefins, namely, hex-1-ene to cis-hex-2-ene and tetramethyl allene to 2,4-dimethylpenta-1,3-diene. These novel results also establish that [1-Cp*-2,2,2-(CO)3-2-(alkyne)-nido-1,2-IrMoB(4)H(8)], 3, forms from 2 and constitutes a logical precursor to 4. The entire process, 1 + 2alkyne = 8 + BH3 + 2H2, which is promoted by (arene)Mo(CO)3, constitutes an explicit example of a transition-metal-facilitated process analogous to metal-facilitated organic transformations observed in organometallic chemistry.
基于早期的研究工作，该研究表明通过[1-Cp*-蛛网状-1-IrB₄H₁₀]（1）与(芳烃)Mo(CO)₃反应生成了[1-Cp*-2,2,2-(CO)₃-2-THF-巢式-1,2-IrMoB₄H₈]（2），现已确定了2与RCCR（R = 甲基、苯基）反应生成[1-Cp*-5,6,7,8-(R)₄-巢式-1,5,6,7,8-IrC₄B₃H₃]（8）的化学计量反应机理。对于R = 甲基，溶液中的主要产物是[1-Cp*-5,6,7,8-(CH₃)₄-闭式-1,5,6,7,8-IrC₄B₃H₃Mo(CO)₃]（7），它与8处于平衡状态。平衡8 + Mo(THF)₃(CO)₃ ⇌ 7 + 3THF的特征为ΔH = 8千卡/摩尔，ΔS = 34卡/摩尔·开尔文。对7进行的密度泛函理论计算表明，Mo(CO)₃部分主要通过Mo-C而非Mo-B相互作用与簇合物弱结合。在炔烃不足的条件下，可以分离出产物[1-Cp*-2,2,2-(CO)₃(μ-CO)-3,4-(CH₃)₂-闭式-1,2,3,4-IrMoC₂B₃H₃]（6）。1和2的固态结构先前已有报道，此处报道了6、7和8（R = 甲基、苯基）的固态结构。通过¹H和¹¹B NMR监测产物随时间的演变，结果表明还形成并衰减了另外两种物质，它们被鉴定为结构异构体[1-Cp*-7,7,7-(CO)₃-7-THF-2,3-(CH₃)₂-巢式-1,7,2,3-IrMoC₂B₃H₅]（4）和[5-Cp*-7,7,7-(CO)₃-7-THF-2,3-(CH₃)₂-巢式-5,7,2,3-IrMoC₂B₃H₅]（5），其中4中的金属不相邻，5中的金属相邻。间接证据表明4是5的前体，5是6和7的前体。簇合物2也是烯烃异构化反应的催化剂或催化剂前体，即己-1-烯异构化为顺-己-2-烯以及四甲基丙二烯异构化为2,4-二甲基戊-1,3-二烯。这些新结果还表明[1-Cp*-2,2,2-(CO)₃-2-(炔烃)-巢式-1,2-IrMoB₄H₈]（3）由2形成，并且是4的合理前体。由(芳烃)Mo(CO)₃促进的整个过程1 + 2炔烃 = 8 + BH₃ + 2H₂，构成了一个类似于有机金属化学中观察到的金属促进的有机转化的过渡金属促进过程的明确例子。
