Dipartimento di Chimica, Università di Venezia, Dorsoduro 2137, 30123 Venezia, Italy.
Inorg Chem. 2010 Apr 19;49(8):3721-9. doi: 10.1021/ic901569w.
cis-[Pd(ONO(2))(2)(PPh(3))(2)] (1) reacts under mild conditions with CO in methanol (MeOH) in the presence of pyridine (py), yielding trans-[Pd(COOMe)(ONO(2))(PPh(3))(2)] (1a). The use of NEt(3) instead of py leads to a mixture of 1a, trans-[Pd(COOMe)(2)(PPh(3))(2)] (2), and [Pd(CO)(PPh(3))(3)]. Pure 2 was prepared by reacting cis-[Pd(OTs)(2)(PPh(3))(2)] with CO in MeOH and subsequently adding NEt(3). The nitro complex trans-[Pd(COOMe)(NO(2))(PPh(3))(2)] (3a) was prepared by reacting trans-[Pd(COOMe)Cl(PPh(3))(2)] with AgNO(2) or with AgOTs and NaNO(2). New syntheses for 1 and trans-[Pd(NO(2))(2)(PPh(3))(2)] (3) are also reported. All complexes have been characterized by IR and (1)H and (31)P{(1)H} NMR spectroscopies. Complexes 1 and 2 exchange irreversibly and quantitatively one nitrato with one carbomethoxy ligand, yielding 1a. 2 in CD(2)Cl(2) at 40 degrees C decomposes with the formation of dimethyl carbonate (DMC), whereas under 4 atm of CO, DMC and dimethyl oxalate (DMO) are formed, ca. 12% each; in the presence of PPh(3) and in the absence of CO, decomposition occurs at 60 degrees C with the formation of DMC only, suggesting that decarbonylation involves a five-coordinate intermediate or predissociation of a PPh(3) ligand. The oxidative carbonylation of MeOH does not occur when using NaNO(2) or NaNO(3) as the oxidant and 1, 1a, 3, or 3a as the catalyst precursor. On the contrary, when using benzoquinone (BQ) as the oxidant, these complexes, 2, or [Pd(COOMe)(2-n)X(n)(PPh(3))(2)] (X = Cl, OAc, OTs; n = 1, 2) promote selective catalysis to DMO. After catalysis the precursors are transformed into Pd(BQ)(PPh(3))(2).H(2)BQ, Pd(CO)(PPh(3)) and [Pd(CO)(PPh(3))(3)]. Also the last with BQ gives selective catalysis to DMO. The solid-state structures of 1.CH(2)Cl(2) and 1a have been determined by means of single-crystal X-ray diffraction.
cis-[Pd(ONO(2))(2)(PPh(3))(2)]（1）在温和条件下与 CO 在甲醇（MeOH）中反应，在吡啶（py）存在下生成 trans-[Pd(COOMe)(ONO(2))(PPh(3))(2)]（1a）。使用 NEt(3)代替 py 会导致 1a、trans-[Pd(COOMe)(2)(PPh(3))(2)]（2）和[Pd(CO)(PPh(3))(3)]的混合物。纯 2 通过 cis-[Pd(OTs)(2)(PPh(3))(2)]与 CO 在 MeOH 中反应并随后添加 NEt(3)制备。硝基配合物 trans-[Pd(COOMe)(NO(2))(PPh(3))(2)]（3a）通过 trans-[Pd(COOMe)Cl(PPh(3))(2)]与 AgNO(2)或 AgOTs 和 NaNO(2)反应制备。还报告了 1 和 trans-[Pd(NO(2))(2)(PPh(3))(2)]（3）的新合成方法。所有配合物均通过 IR 和 (1)H 和 (31)P{(1)H}NMR 光谱学进行了表征。配合物 1 和 2 不可逆地定量交换一个硝酸盐和一个甲氧基羰基配体，生成 1a。2 在 40°C 的 CD(2)Cl(2)中分解，形成碳酸二甲酯（DMC），而在 4 个大气压的 CO 下，形成约 12%的 DMC 和草酸二甲酯（DMO）；在 PPh(3)存在下且无 CO 时，在 60°C 下分解，仅形成 DMC，表明脱羰涉及五配位中间体或 PPh(3)配体的预解离。当使用 NaNO(2)或 NaNO(3)作为氧化剂和 1、1a、3 或 3a 作为催化剂前体时，甲醇的氧化羰基化不会发生。相反，当使用苯醌 (BQ) 作为氧化剂时，这些配合物、2 或 [Pd(COOMe)(2-n)X(n)(PPh(3))(2)]（X = Cl、OAc、OTs；n = 1、2）促进 DMO 的选择性催化。催化后，前体转化为Pd(BQ)(PPh(3))(2).H(2)BQ、Pd(CO)(PPh(3))和[Pd(CO)(PPh(3))(3)]。BQ 与最后一个也可以选择性地催化 DMO。通过单晶 X 射线衍射确定了 1.CH(2)Cl(2)和 1a 的固体结构。
