Transformation of Metal–Organic Framework Secondary Building Units into Hexanuclear Zr-Alkyl Catalysts for Ethylene Polymerization

Abstract

We report the stepwise and quantitative transformation of the Zr(μ-O)(μ-OH)(HCO) nodes in Zr-BTC (MOF-808) to the [Zr(μ-O)(μ-OH)Cl] nodes in ZrCl-BTC, and then to the organometallic [Zr(μ-O)(μ-OLi)R] nodes in ZrR-BTC (R = CHSiMe or Me). Activation of ZrCl-BTC with MMAO-12 generates ZrMe-BTC, which is an efficient catalyst for ethylene polymerization. ZrMe-BTC displays unusual electronic and steric properties compared to homogeneous Zr catalysts, possesses multimetallic active sites, and produces high-molecular-weight linear polyethylene. Metal-organic framework nodes can thus be directly transformed into novel single-site solid organometallic catalysts without homogeneous analogs for polymerization reactions.

Creation of Active Sites in MOF‐808(Zr) by a Facile Route for Oxidative Desulfurization of Model Diesel Oil

“…It is well known that generally zirconium‐based MOFs possess good structural stability . MOF‐808(Zr) as one member of them has received much attention due to its advantages such as high specific surface area (∼2000 m 2 /g), large pore opening, good stability and rich metal sites . These advantages make it a potential candidate in many applications such as gas storage and catalysis .…”

Stabilized Vanadium Catalyst for Olefin Polymerization by Site Isolation in a Metal–Organic Framework

“…[8] Them olecular-level structural control [9] and modularity [10] possible with MOFs allow molecule-like catalyst design in the solid state.A lthough essentially all components of aMOF may be modified for catalysis, the inorganic nodes have attracted increasing attention as as tructurally monodisperse and well-defined platform for transition-metal catalysis. Along these lines,our group [13] and others [14] have developed effective single-site heterogeneous catalysts for olefin polymerization by postsynthetic modification of MOF SBUs. Along these lines,our group [13] and others [14] have developed effective single-site heterogeneous catalysts for olefin polymerization by postsynthetic modification of MOF SBUs.…”

“…First, we evaluated the Al:V ratio using asample of 1 with aconstant vanadium loading (prepared by VCl 3 (THF) 3 exchange;s ee Figure S7.2), and found 300:1 to be optimal. [13,14] Consistent with heterogeneous catalysis,polyethylene was predominantly obtained as afree-flowing powder using 1 and 2,a sd esired for commercial applications.B yc ontrast, the combination of either TpVCl 3 or VCl 4 with MMAO-12 form homogeneous solutions in toluene,t hus polymerizing ethylene as as olid mass firmly attached to the reactor wall (see Section S7.13). Next we evaluated the effect of vanadium loading in 1,a tc onstant MMAO-12 concentration and ac onstant Al to Vr atio of 300:1.…”

“…[11] In particular, these clusters or secondary building units (SBUs) often undergo cation exchange with structural retention, [12] thus offering apredictable strategy to incorporate transition metals for catalysis. Along these lines,our group [13] and others [14] have developed effective single-site heterogeneous catalysts for olefin polymerization by postsynthetic modification of MOF SBUs.…”

“…Along these lines,t he combination of 1 and MMAO-12 shows an apparent first-order dependence of activity on ethylene pressure (see Figure S7.3), with am aximum turnover of 148 000 h À1 achieved at 50 bar.T his activity,p resumably underestimated because of the disproportional reactivity of surface-confined species,e xceeds the reported activity of prior MOF catalysts for olefin polymerization. [13,14] Consistent with heterogeneous catalysis,polyethylene was predominantly obtained as afree-flowing powder using 1 and 2,a sd esired for commercial applications.B yc ontrast, the combination of either TpVCl 3 or VCl 4 with MMAO-12 form homogeneous solutions in toluene,t hus polymerizing ethylene as as olid mass firmly attached to the reactor wall (see Section S7.13). Notably,b oth of these soluble catalysts are also less active than 1 under comparable conditions.T o confirm the heterogeneity of our MOF catalyst, asuspension containing 1 and MMAO-12 was stirred vigorously for 30 minutes and then separated under air-free conditions.…”