C−C, C−S, and C−N Coupling versus Dealkylation Processes in the Cationic Tris(thiolato)dimolybdenum(III) Complexes [Mo₂Cp₂(μ-SMe)₃L₂]⁺ (L = xylNC, <i>t</i>-BuNC, CO, MeCN)

Reductive coupling between isocyanide ligands attached to adjacent molybdenum atoms in the bis(aryl isocyanide) complex [Mo2Cp2(μ-SMe)3(xylNC)2](BF4) (1) was initiated by addition of the hydrosulfide anion (HS−) to 1 under reflux in tetrahydrofuran, affording, in nearly quantitative yields, the dimetallaimidoyl(amino)carbene derivative [Mo2Cp2(μ-SMe)3{μ-η1(C):η1(C)-C(NHxyl)C(Nxyl)}] (7), in which both isocyanide groups of 1 are now linked by a new C−C bond. When the previous reaction was conducted in the presence of a large excess of hydrosulfide (20 equiv), under similar experimental conditions, the dithiocarbonimidate compound [Mo2Cp2(μ-SMe)2(μ-S2CNxyl)] (8) was obtained in quantitative yields. This product results from subsequent thiolate exchange and substitution reactions to afford a quadruply sulfur bridged intermediate, followed by free isonitrile addition to sulfido S atoms. Treatment of the coupled isocyanide derivative 7 with HBF4 led exclusively to the formation of the starting complex 1 by reversible isocyanide ligand decoupling. The heating of a tetrahydrofuran solution of 1 with the base NaCCH gave, in high yields, the μ-alkylidyne and μ-acetylide product [Mo2Cp(μ-SMe)2{μ-(η5-C5H4)(xylN)CN(xyl)C}(μ-CCH)] (9), in which a deprotonated Cp and both isocyanide ligands of 1 are now linked by new C−C and C−N bonds, and in addition an acetylide has replaced a thiolate ligand of 5. Reaction of the μ-alkylidyne complex [Mo2Cp(μ-SMe)3{μ-(η5-C5H4)(xylN)CN(xyl)C}] (5) with NaCCH under reflux in tetrahydrofuran produced, in high yields, the μ-alkylidyne and bis(μ-acetylide) cationic compound [Mo2Cp(μ-SMe)2{μ-(η5-C5H4)(xylN)CN(xyl)C}(μ-CCH)2]Br (10), in which two xylNC ligands have replaced a thiolate group of 5. Further reactions of the bis(μ-isocyanide) complex 10 with NaOH (suspension), on the one hand, and HBF4, on the other hand, under reflux in tetrahydrofuran or at room temperature in dichloromethane, respectively, led to the formation in high yields of the known mixed μ-alkylidyne and μ-amino-oxycarbene species [Mo2Cp(μ-SMe)2{μ-(η5-C5H4)(xylN)CN(xyl)C}{μ-η1(O):η1(C)-OCNHxyl}] (12) and the new tetrakis(isocyanide) dicationic derivative [Mo2Cp2(μ-SMe)2(xylNC)4](BF4)2 (11), respectively. The latter complex results from successive protonation at one carbon atom of the cyclopentadienyl ligand linked with isocyanides of 10 and decoupling between deprotonated Cp and isocyanide ligands. The heating of a tetrahydrofuran solution of a mixture of the bis(alkyl isocyanide) complex [Mo2Cp2(μ-SMe)3(t-BuNC)2](BF4) (2) and NaSH proceeded exclusively through the dealkylation of one tert-butyl isocyanide ligand to afford the known product [Mo2Cp2(μ-SMe)3(t-BuNC)](CN)] (13). Similar reaction of the dicarbonyl derivative [Mo2Cp2(μ-SMe)3(CO)2]Cl (3) with NaSH proceeded through dealkylation of one thiolate group to yield the new neutral sulfido species [Mo2Cp2(μ-SMe)2(μ-S)(CO)2] (14). Further heating of 14 in dichloromethane led to the formation of the chloromethanethiolate derivative [Mo2Cp2(μ-SMe)2(μ-SCH2Cl)(CO)2]Cl (15). Treatment of the bis(nitrile) species [Mo2Cp2(μ-SMe)3(MeCN)2]BF4 (4) under reflux in tetrahydrofuran with NaSH afforded, in valuable yields, the thio-amidato derivative [Mo2Cp2(μ-SMe)3(μ-MeCSNH)] (18). All new complexes have been characterized by elemental analyses and spectroscopic methods, supplemented for 7−10, 11′, 14, and 15 by X-ray diffraction studies.双(芳基异氰)配合物[Mo₂Cp₂(μ-甲硫基(μ-methylthio, μ-SMe))₃(xylNC)₂](BF₄)（1）中，相邻钼原子上连接的异氰配体发生还原偶联反应：将硫氢根阴离子(HS⁻)加入至四氢呋喃(tetrahydrofuran, THF)回流的配合物1体系中，以近乎定量的收率得到双金属亚胺酰(氨基)卡宾衍生物[Mo₂Cp₂(μ-SMe)₃{μ-η¹(C):η¹(C)-C(NHxyl)C(Nxyl)}]（7），该产物中配合物1的两个异氰基团已通过新形成的碳-碳键相连。 当在20当量过量硫氢根存在下，于相同实验条件下进行上述反应时，以定量收率得到二硫代碳亚胺酸酯类配合物[Mo₂Cp₂(μ-SMe)₂(μ-S₂CNxyl)]（8）。该产物源自后续的硫醇盐交换与取代反应，先生成四重硫桥联中间体，随后游离异氰与硫代S原子发生加成反应。 将偶联异氰衍生物7与四氟硼酸(HBF₄)反应，仅通过可逆的异氰配体解离，即可得到起始配合物1。 将配合物1的四氢呋喃溶液与强碱乙炔钠(NaC≡CH)加热反应，以较高收率得到μ-烷基卡拜与μ-乙炔基配合物[Mo₂Cp(μ-SMe)₂{μ-(η⁵-C₅H₄)(xylN)CN(xyl)C}(μ-CCH)]（9），其中配合物1中一个去质子化的环戊二烯基(Cyclopentadienyl, Cp)与两个异氰配体通过新形成的碳-碳与碳-氮键相连，且一个乙炔基配体取代了配合物5中的一个硫醇盐配体。 将μ-烷基卡拜配合物[Mo₂Cp(μ-SMe)₃{μ-(η⁵-C₅H₄)(xylN)CN(xyl)C}]（5）与乙炔钠在四氢呋喃中回流反应，以较高收率得到μ-烷基卡拜与双(μ-乙炔基)阳离子配合物[Mo₂Cp(μ-SMe)₂{μ-(η⁵-C₅H₄)(xylN)CN(xyl)C}(μ-CCH)₂]Br（10），其中两个二甲苯基异氰(xylyl isocyanide, xylNC)配体取代了配合物5中的一个硫醇盐配体。 分别将双(μ-异氰)配合物10与悬浮态氢氧化钠(NaOH)在四氢呋喃中回流、与四氟硼酸在二氯甲烷(dichloromethane)中室温反应，均以较高收率分别得到已知的混合型μ-烷基卡拜与μ-氨基氧卡宾物种[Mo₂Cp(μ-SMe)₂{μ-(η⁵-C₅H₄)(xylN)CN(xyl)C}{μ-η¹(O):η¹(C)-OCNHxyl}]（12），以及新型四(异氰)二阳离子衍生物[Mo₂Cp₂(μ-SMe)₂(xylNC)₄](BF₄)₂（11）。 后者即配合物11，源自10中与异氰配体相连的环戊二烯基配体的一个碳原子的连续质子化，以及去质子化环戊二烯基与异氰配体之间的解离过程。 将双(烷基异氰)配合物[Mo₂Cp₂(μ-SMe)₃(tert-butyl isocyanide, t-BuNC)₂](BF₄)（2）与硫氢化钠(NaSH)的混合四氢呋喃溶液加热反应，仅通过一个叔丁基异氰配体的脱烷基化过程，即可得到已知产物[Mo₂Cp₂(μ-SMe)₃(t-BuNC)(CN)]（13）。 二羰基衍生物[Mo₂Cp₂(μ-SMe)₃(CO)₂]Cl（3）与硫氢化钠的类似反应，则通过一个硫醇盐配体的脱烷基化过程，得到新型中性硫代物种[Mo₂Cp₂(μ-SMe)₂(μ-S)(CO)₂]（14）。 将配合物14在二氯甲烷中进一步加热，可得到氯甲硫醇盐衍生物[Mo₂Cp₂(μ-SMe)₂(μ-SCH₂Cl)(CO)₂]Cl（15）。 将双(腈)类物种[Mo₂Cp₂(μ-SMe)₃(acetonitrile, MeCN)₂]BF₄（4）与硫氢化钠在四氢呋喃中回流反应，以可观收率得到硫代酰胺基衍生物[Mo₂Cp₂(μ-SMe)₃(μ-MeCSNH)]（18）。 所有新型配合物均通过元素分析与光谱手段进行了表征，其中配合物7~10、11'、14与15还通过X射线衍射(X-ray diffraction)分析进行了补充结构确认。