DACH-Bridged (DACH = trans-1,2-Diaminocyclohexane) Bis(iminophosphonamide) Derivatives of Groups 3 and 13 and Their Use in the Enantiomorphic Polymerization of Methyl Methacrylate
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- 作者：Shabana A. Ahmed ; Michael S. Hill ; Peter B. Hitchcock ; Stephen M. Mansell ; Oliver St John
- 刊名：Organometallics
- 出版年：2007
- 出版时间：January 29, 2007
- 年：2007
- 卷：26
- 期：3
- 页码：538 - 549
- 全文大小：250K
- 年卷期：v.26,no.3(January 29, 2007)
- ISSN：1520-6041
文摘
A straightforward and flexible one-pot synthesis of a series of racemic trans-1,2-diaminocyclohexyl(DACH)-linked N-aryl bis(iminophosphonamines) is reported. These compounds were readily metalatedwith either nBuLi or Et3Al. The five-coordinate asymmetric environments provided by the ligands in themonometallic species were readily apparent from the useful and diagnostic 31P{1H} NMR spectra andcorrelated with the observed solid-state configurations. Similar reactions with the sterically encumberedyttrium amide [Y{N(SiMe3)2}3] were only observed to produce the analogous N5-coordinated amide underforcing conditions, while reactions with the less sterically encumbered [M{N(SiHMe2)2}3(THF)n] (M =Sc (n = 2), Y (n = 3)) gave smooth conversion to the desired monometallic chelate complexes. All ofthe monometallic and bimetallic group 3 and group 13 compounds were assessed for the stereoselectivepolymerization of methyl methacrylate. Although the aluminum compounds were inactive as single-component initiators, activation with Gibson's three-component (L2AlR/MAD/Ni(acac)2) system yieldedactive catalysts. The isolated polymers revealed a definite syndiotactic (>80%) bias, albeit with broadpolydispersity indices (ca. 2) at ambient temperatures. In contrast, the yttrium complexes were found tofunction as efficient single-component polymerization initiators and yielded PMMA, which waspredominantly isotactic (>80%) and, in some cases, close to monodisperse. Comparison to controlexperiments in which [Y{N(SiMe3)2}3] was employed as initiator provided evidence that it was theasymmetric environment of the bis(iminophosphonamide) ligand, which was exerting a pronounced (i.e.enantiomorphic) effect upon polymer propagation.