A series of halogen-substituted 2,6-bis(imino)pyridyl ligands and their iron and cobalt complexes [{2,6-(2,6-X1X2C6H3NCCH3)2C5H3N}MCl2] (X1 = X2 = Br, M = Fe (1), Co (2); X1 = X2 = Cl, M = Fe (3), Co (4); X1 = Cl, X2 = H, M = Fe (5), Co (6); X1 = Br, X2 = H, M = Fe (7), Co (8); X1 = I, X2 = H, M = Fe (9), Co (10)) and [M{2,6-(2,6-X1X2C6H3NCCH3)2C5H3N}2]2+[MCl4]2- (X1 = F, X2 = H, M = Fe (11)) have been synthesized. The molecular structures of complexes 1, 8, 9, 10, and 11 were determined by X-ray diffraction. Crystallographic analyses indicate that 1, 8, 9, and 10 are five-coordinate complexes, while 11 is an ion-pair complex with one six-coordinate iron center and one four-coordinate iron center. These metal coordinative complexes, activated by modified methylaluminoxane (MMAO), lead to highly active ethylene polymerization and/or oligomerization catalysts. The catalyst productivity and product properties crucially depended on the metal center and the halogen substituents on the aryl rings. The catalyst productivities are in the range of (0−73.0) × 106 g/mol of cat·h. The species 11, having ion-pair structure, is inactive. In particular, the product molar masses were changed from high molar mass (M w of 377 000) to low molar mass oligomers by varying the halogen substituents. NMR and thermal analyses reveal the polymer is highly linear. The oligomer products follow a Schulz−Flory distribution with high selectivity for linear α-olefins. The effects of reaction condition on the polymerization and oligomerization have also been studied.

A general and practical procedure for the syntheses of 3 . 4 4 -hydmpyrimidiw-2(lH)-thiones by a one-pot coadensation of ak-lehyde, bketoester or fLdiketone and thiourea using La- Results and discussion IntroductionIn recent years, dihydropyrimidinethione derivatives have attracted considerable interest due to their promising activities as anticminogenic agents,' cdovascular agents2 and calcium channel blocke~s.~ In addition, some derivatives of dihydmpyrimidinethione were patented as agents for the protection of wool against moths. nus, the synthesis of this heterocyclic nucleus is of current importance. In 1893, Biginelli reported a simple and stmightforwad procedure starting from /3-dicarbonyl compounds, aldehyde and hourea under strong acidic conditions with low yields ( 20%--50% ) .' Recently, several improved procedures for the preparation of DHPMs ( BiginelLi compounds ) have been reported. However, all these methods gave low yields and the catalyst could not be recovered. Lanthanide triflates are unique Lewis acids that are currently of great research interest. In our previous work, it was found that Ln(OTf)3 is an efficient catalyst for two or In a typical general experimental procedure, a mixture of aldehyde, @dicarbonyl and thiourea was heated in a Schlenk tube at 100 F under stirring in the presence of a catalytic amount of La( o T f ) 3 (3 mol% ) for a certain period of time as required to complete the reaction. 'Ihen water was added into the reaction mixture, the solid p duct was filtered and r e c r y s W from ethanol.Several st~cturally varied kdicarbonyl compounds, aldehydes and thiourea are coupled together by this pmedure to p d u c e the corresponding dihydmpyrimidine-2( 1 H) -hiones. ?he results are listed in Table 1 . Both k keto ester and kdiketone can react with aldehyde and thiourea readily. A variety of s h t i t u t e d aromatic aldehydes have been subjected to this condensation efficiently.AU the lanthanide trifluommethanesdfonates examined showed good catalytic activities. However, La(oTf)3 was particularly effective for this reaction. 3 mol% of La-(OTf)3 was sufficient to provide the products in excellent *