Glucopyranoside-incorporated silver(I) bis(carbene) complexes have been prepared through the reactions of silver oxide with related imidazolium salts. The palladium(II) bis(carbene) complexes were synthesized from their corresponding silver(I) complexes via the technique of transmetalation. In solution, both trans-anti and trans-syn rotamers are observed for these square-planar Pd(II) complexes. In the solid state, the complex [1-methyl-3-(methyl 2,3,4-tri-O-benzoyl-6-deoxy-R-Dglucopyrano-6-yl)imidazol-2-ylidene] 2 PdBr 2 adopts a trans-anti conformation, while the complexesPdBr 2 adopt a trans-syn conformation. The steric congestion between the two glucopyranoside groups in the last two trans-syn compounds are perhaps relaxed through tilting of the imidazole rings and rotation of the flexible CH 2 spacer, which connects the imidazole ring and the glucopyranoside group. The palladium(II) complexes were further hydrolyzed to produce water-soluble hydrolysates. Preliminary catalytic studies show that these hydrolyzed palladium precatalysts are efficient in the Suzuki-Miyaura coupling reaction between phenylboronic acid and a hydrophilic substrate, 2-chlorobenzoic acid, in aqua medium. In the presence of tetra-n-butylammonium bromide (TBAB), these precatalysts also display efficient catalytic properties in the reaction of phenylboronic acid with both the hydrophilic substrate 1-chloro-3-nitrobenzene and the hydrophobic substrate 2-chlorophenol. In all cases, the catalytic systems are stable, which allow them to be reused for at least three cycles. This catalytic system also facilitates the separation of products from the catalyst and, therefore, is environmentally benign.
Compound Cp*ZrCl(BH4)2, 1, was isolated from a reaction of Cp*ZrCl3 with two equivalents of Cp*Zr(BH4)3. The tetranuclear Zr(IV) polyhydride [(μ2-H)(μ3-H)(Cp*ZrCl)]4, 2, was prepared by the reaction of 1 with excess N(C2H5)3, whereas the related Zr(IV) polyhydrides [(μ2-H)3(μ2-η2-BH4){Cp*Zr(BH4)}2]2, 3, and [(μ2-H)3(μ2-H){Cp*Zr(BH4)}2]2, 4, were isolated from the reaction of Cp*Zr(BH4)3 with excess N(C2H5)3. Compound 4 can be also prepared from the reaction of Cp*Zr(BH4)3 with excess N(CH3)3. Single-crystal X-ray structures of 1, 2, 3, and 4 were determined. In compound 1 two tetrahydroborate ligands coordinate to a zirconium atom in a tridentate bonding mode. Compounds 2, 3, and 4 are tetranuclear polyhydrides. Compound 2 features a butterfly arrangement of zirconium atoms surrounded by eight bridging hydrides. Each triangular face is capped by a μ3-bridging hydride, and the other four hydrides are μ2-bridging to the zirconium atoms in the perimeter. Compounds 3 and 4 are rectangular planar polyhydrides where the adjacent Zr atoms in 3 are linked by a bridging tetrahydroborate ligand and three μ2-bridging hydrides, and the adjacent Zr atoms in 4 are linked by a μ2-bridging hydride and three μ2-bridging hydrides. The proton NMR spectrum and the solid-state structure of 4·(toluene) suggested that the tetramer dissociates to [Cp*Zr(BH4)H(μ-H)]2 in solution.
From the reactions of Cp*ZrCl(3) with 3 equiv. of LiBH(3)R (R = CH(3), Ph), the organotrihydroborate complexes, Cp*Zr(BH(3)CH(3))(3), 1, and Cp*Zr(BH(3)Ph)(3), 2, were isolated. One of the Zr-H-B bonding interactions in 2 could be described as an intermediate case between the bidentate and tridentate modes. Reactions of and Cp*Zr(BH(4))(3), 3, with Lewis acid B(C(6)F(5))(3) in diethyl ether produced the novel 14-electron ionic compounds [(micro(3)-O)(micro(2)-OC(2)H(5))(3){(Cp*Zr(OC(2)H(5)))(2)(BCH(3))}][HB(C(6)F(5))(3)], 4, and [(micro(3)-O)(micro(2)-OC(2)H(5))(3){(Cp*Zr(OC(2)H(5)))(2)(BOC(2)H(5))}][HB(C(6)F(5))(3)], 5, respectively. These two unique compounds resulted from a sequential cleavage of Zr-H-B bonds of 1 and 3 and C-O bonds of ether followed by the formation of O-B bonds. The solid state single crystal X-ray analyses revealed that both compounds have similar structures. A micro(3)-oxygen bridges two zirconiums and a boron atom. The latter three atoms are further connected by three micro(2)-bridging ethoxy groups giving rise to three four-membered metallacycles within the structure of each cation.
The reduction of [(μ(2)-H)( μ(3)-H)(Cp*ZrCl)](4) by excess Na/Hg led to the isolation of the mixed-valence Zr(III)/Zr(IV) Zr(4) cluster [(μ(2)-H)(8)(μ(2)-Cl)(2)(Cp*Zr)(4)], 1, and the Zr(II)/Zr(III) Zr(4) cluster [(μ(2)-H)(6)(Cp*Zr)(4)], 2. The proton NMR data supports the diamagnetic property of both clusters in solution and the solid state structure of each cluster revealed a distorted tetrahedral skeleton comprised of four Zr atoms and the presence of direct Zr-Zr bonds. The hydride-bridged Zr-Zr bond distances are in the range of 3.0516(6)-3.0585(6) Å in 1 and 3.0525(13)-3.0864(13) Å in 2. The chloride-bridged Zr-Zr distances in 1 are 3.5514(6) and 3.5643(6) Å. The existence of Zr-Zr bonds in both clusters was further confirmed by DFT calculations. 1 and 2 represent the first examples of Zr(4) tetrahedrons containing direct Zr-Zr bonds.
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